AAS in Seattle: Tuesday, Jan. 6, 2015

comet-67p-s

A photo of Comet 67P/Churyumov-Gerasimenko taken from the Rosetta orbiter.

Note: I am writing this almost two years after the fact. Life has been busy and events carry one onward, but for the next week I hope to do some catching up on this blog. Fortunately, I took good notes and can remember most of what we did at the American Astronomical Society conference in Seattle in January, 2015.

paul-weissman

Dr. Paul Weissman, a scientist at JPL (now at the Planetary Science Institute) who worked the Rosetta mission.

On the second full day of the AAS conference in Seattle (Jan. 6, 2015), we had an incredibly busy and fulfilling day. This was the main day for educational posters and presentations, so I divided my time between a plenary session and presenting two posters. One I created on my own from my astronomy lesson plans that came out of my Research Experiences for Teachers (RET) program at Brigham Young University. The other one was a group poster created by the four educators involved in the NASA/IPAC Teacher Archive Research Program (NITARP) under Dr. Louisa Rebull.

rosetta_and_philae-s

An artist’s illustration of the Rosetta orbiter and Philae lander. The comet wound up being much more interesting that this illustration shows.

Before the beginning session, I called my students and none of them wanted to go with me to breakfast (they wanted the extra sleep), so I walked to a small convenience store nearby and bought some donuts and juice, which I ate back at the hotel room. I then walked to the convention center.

Plenary sessions are scheduled so that nothing else is going on and everyone can attend. The opening plenary session this day was by Paul Weissman, a scientist at JPL for the Rosetta-Philae mission to comet 67P/Churyumov-Gerasimenko. The European Space Agency built Rosetta, but management and data analysis tasks were shared between several agencies including JPL at NASA.

The large auditorium was full, and I sat toward the front to better see the slides. He had previously worked on the Galileo and Stardust missions. He worked on the Champollion lander/sample return mission, which was eventually scrapped, but much of the work and design was used in the more advanced Rosetta/Philae mission. It launched in March 2004 on an Arianne rocket and took a slow looping ride and several gravity assists (three of Earth and one of Mars) to catch up to the comet, arriving in July 2014 after encountering two asteroids.

comet_67p-s

Another view of the “rubber ducky” shape of comet 67P/Churyumov-Gerasimenko, taken from the Rosetta orbiter.

The Rosetta orbiter had 12 instruments and the Philae lander had nine. It was sent down very slowly toward the comet on Nov. 12, 2014 and was supposed to fire two harpoons that would stick it to the surface. The comet is small and lightweight compared to asteroids, so there isn’t much gravity and the idea was to prevent the lander from bouncing off. They picked a landing site that was the least objectionable to the scientists and had safe terrain.

philaes_sci_instruments

Diagram of the Philae lander. The MUPUS are two harpoons that were supposed to anchor the lander to the surface of the comet, but the lander bounced off and came to rest wedged on its side next to a cliff.

Unfortunately, the harpoons failed and the lander did bounce off. It took a slow arc up and eventually landed in the worst possible place, wedged up in a corner on its side next to a small cliff where sunlight can’t reach it very often. The lander had batteries for only about two days, and wasn’t able to use some of its instruments because of its awkward position. Yet it did return useful data while its batteries lasted and is considered a success.

An analysis of the images from the Rosetta orbiter show three holes where the lander feet tried to touch down – the two harpoons didn’t fire, possibly because the surface was softer than expected. Apparently the friable surface ice overlaid a much harder layer, which no one suspected was there. The resulting force of the landing poked the holes through the outer surface, but it hit the harder layer, rebounded, and launched the lander back into space.

philae_found-2-s

Final resting place of the Philae lander after it bounced off the surface of Comet 67P/Churyumov-Gerasimenko.

Every comet we’ve visited is unique. Some are fairly active, such as Halley or Wild 2. Others are older and aren’t outgassing much because their surfaces are covered with dark gunk – mostly carbon with a surface albedo of less than 5%. That makes them very hard to see – about the color of black printer toner powder. Comet 67P/Churyumov-Gerasimenko is one of these dark comets, covered with old outgassing basins. It looks as if two smaller comets collided and stuck together, with a thin neck between the two larger lobes that make it look something like a giant rubber ducky.

Dr. Weissman spoke of some of what we’ve learned from Rosetta-Philae. The comet rotates just over once per 12 hours (there is some variability due to outgasing) and is about 4 km in diameter. The dark outside layer insulates the remaining ice, and the neck area acts as a heat sink. The unusual shape creates stresses inside which can be seen as cracks in the surface. Analysis of its density (mass to size) and radio sounding of its interior show that it is made of some rubble (smaller boulders) and mostly dust. It contains more silicates and organic compounds than ices. It has a halo of smaller particles the size of hailstones orbiting around it. Its water ice has a different isotope ratio, with more deuterium than Earth water, which means Earth did not get its water from comets like 67P. It apparently formed in the very early solar system even before the Sun’s accretion disk was fully formed.

They have hopes that when the comet gets further in its orbit later in the year, sunlight might reach the lander and they will try to re-activate it. As of this writing (December 2016) they were able to successfully regain sporadic communication with the lander in June and July of 2015. At the end of the mission, the Rosetta orbiter was slowed down to gradually move in toward the surface and land as softly as possible on September 30, 2016.

david-black-poster

My personal poster at the AAS education poster session on Tuesday, Jan. 6, 2015. It explains several lesson plans I taught in my astronomy class that were developed from my work at the BYU-RET during the summer of 2014.

I had dropped off my poster prior to the plenary session, so I hurried from the session to the poster exhibit hall and tacking it up, then laid out copies of the lesson plans it describes. I’d had the poster printed at Kinko’s a few days before leaving for Seattle and carried it with me on the plane. For most of the remainder of the day, I attended to the poster and explained things to visitors. I had a good stream of people stop by, many of which were astronomy educators. Some were even from PhD programs in Science Education that I might someday apply to.

The lesson plans I presented included (1) using Adobe Photoshop to take WISE images from three wavelengths and combine them into the RGB channels as a representative color image, (2) charting Spectral Energy Distributions using data from SIMBAD and IPAC, and (3) calculating star distances using the distance-modulus formula. I’ve written up blog posts previously on each of these lessons, so you can scroll down to my other blog posts to find them.

dr-hintz-presenting-poster

Dr. Eric Hintz of Brigham Young University presenting his poster at the AAS educational session.

Dr. Eric Hintz, my mentor for the RET program at BYU, had his own poster near mine on using virtual reality glasses (Google Glass) to provide translation services in ASL for deaf visitors to the BYU planetarium. Before, when deaf people visited and ASL services were used, the planetarium couldn’t be darkened all the way so that the translator could be seen. Now, the translator can be in another room and videotaped, then projected into Google Glasses for the deaf visitors.

independent-nitarpers

Chelin Johnson (left with camera) and her students presenting their poster on an independent project at the AAS education poster session.

Chelin Johnson and her students had their own educational poster a few spaces down from mine. She has been a SOFIA Airborne Astronomy Ambassador like me, participated in NITARP, and has her students do independent WISE projects each year, which they present at this conference. It is a great example to me of what’s possible.

four-teachers-by-ed-poster

John Gibb, Elin Deeb, Estefania Larson, and David Black presenting their poster on the NITARP education program at the AAS conference in Seattle; Jan. 6, 2015.

We had divided up the times during the day for who would stay with our group NITARP educational poster, so I spent some time with it in the afternoon while also trying to see the other posters in the section. I was so busy all day trying to stay at two posters that I didn’t take time for lunch. When the day ended at 6:00, I was very ready for food. The EPO people at the SOFIA booth had arranged for a dinner at The Cheesecake Factory, and my students were invited. Elena and Kendall had other plans, but Rosie and Julie came with me. It was a good meal (I’d never eaten here before and hadn’t realized they have complete meals and not just cheesecake).

me-by-poster

David Black standing by his poster at the AAS education session; Jan. 6, 2015.

We had quite a group, and Ryan Lau was there (he was presenting a poster at the conference) and I asked him to explain his research to my students. He has now completed his PhD program at Cornell and explained what he’s been working on for his thesis. I wish I had brought along my cameras and could have recorded what he said. I had dropped them off in my room before supper, and didn’t have my notebook with me, either. My students were impressed and both became more interested in pursuing a career in astrophysics, hearing how Ryan’s work was so accessible. He talked about SOFIA’s instruments, how he has studied the galactic core and its accretion ring, and some of the huge Luminous Blue Variable stars near it.

me-presenting-my-poster

Presenting my poster at the AAS conference.

I was pretty exhausted after the dinner. I tried to get some work done back at my hotel room, but soon had to crash. It had been a great day of meeting people and sharing my astronomy lessons.

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2015 AAS in Seattle – Day 2: A Sampler of Sessions

JWST model

Functioning model of the James Webb Space Telescope. It demonstrates how the solar shields will unfurl and the primary mirror will unfold.

On the first full day of the American Astronomical Society Conference in Seattle, my students and I attended a variety of plenary sessions, poster sessions, parallel sessions, and a follow up meeting of all the NITARP groups. I also had the unexpected opportunity to meet one of my personal heroes and to meet someone who was about to become somewhat famous.

After getting up and getting ready, I called my students to see if they wanted to meet for breakfast. One thing I find irritating about nice hotels is that they don’t provide free breakfasts – I guess they figure that if you can afford a room at over $150 per night, you can afford your own breakfast. This is why I usually choose to stay at places like Comfort Inn or Days Inn – they provide free hot breakfasts and their rooms and beds are almost as nice – certainly nicer than what I have at home. And they cost less. But since the NITARP program was paying my way and providing a per diem for meals, I wasn’t complaining.

Julie and Rosie met me downstairs in the lobby and we ate next door at the restaurant associated with our hotel. The breakfast was good, but overpriced and not very filling. My other students opted out of breakfast so they could sleep in a bit.

Pickering_Van-Allen_von-Braun

William Pickering, James Van Allen, and Werner von Braun holding up a model of the Explorer 1 space probe after it successfully discovered the Van Allen Radiation Zones.

Van Allen’s Pants

The conference began officially with a plenary Kavli Foundation Lecture by Dan Baker on his work on Earth’s magnetosphere with the SAMPEX mission. It is expected that everyone attend the plenary sessions – nothing else is scheduled during these times. There was a large crowd attending and I sat toward the back. He told of how the Russians could have beat us to discovering the Van Allen Radiation Belts. There was an instrument package with Sputnik II (which contained the dog Laika). The probe reached apogee over Australia at a high enough altitude to be in the radiation belts, but the Australians refused to share the data with the Russians. So Explorer 1 with its Geiger counter onboard found out the belts were there, and Van Allen (who suggested putting the Geiger counter in the probe in the first place) made the cover of Time magazine. Van Allen was Dr. Baker’s mentor. When Van Allen was asked by a reporter what the belts were good for, he replied, “To hold up Van Allen’s pants!” Apparently, he hated the term “belts” and preferred to call them radiation “zones,” which is a more accurate description.

AAS 2015 posters 2

Posters and exhibits in the main hall of the Seattle convention center for the AAS 2015 conference.

The SAMPEX mission had an elliptical polar orbit, and as it dipped in and out of the zones, found out some interesting things. First, there are three, not two, radiation zones or layers. The newly discovered outer ring acts as a storage area for atmospheric ions. Second, radiation from the Sun has profound affects on the zones. Over time, the zones weaken, but whenever Coronal Mass Ejections (CMEs) are blasted off the surface of the Sun, they spiral out (because the Sun rotates) and as they interact with the Van Allen zones, they cause a stripping and decoupling of the ions in the zones, weakening them rapidly. But the CMEs also provide new particles that re-energize the zones, causing a reconnection within tens of minutes to hours. During these decoupling events, Earth’s energy and communication grids are vulnerable since high-energy electrons can penetrate through. Third, there are gaps or slots between the zones with fairly sharp edges.

AAS 2015 Monday posters 1

Posters at the Seattle AAS conference in Jan. 2015.

SOFIA booth at 2015 AAS

The SOFIA booth at AAS in Seattle; Jan. 2015

After his lecture, I walked to the main hall to look through the posters. I didn’t stay long – just got a quick overview and snapped a few pictures. I stopped by the SOFIA booth to talk to Coral Clark and see if we were getting together for dinner.

Exoplanet Atmospheres

I attended a parallel presentation session on exoplanet atmospheres, where graduate students give five-minute presentations on their work with two minutes for Q & A. I was intrigued by the title – it seems amazing that we can tease any information about atmospheres out of the exoplanet data from Kepler, where the signals for the planets themselves are so hard to ferret out of the noise. But you would be surprised, as I was, how much can be discovered from those slight dips in the light curve of a star.

Nick Cowan spoke on his study of Hot Jupiter atmospheres and the difficulty of inferring conclusions from such uncertain data. They did manage to get some good reads on the daytime temperatures of some planets. Joel Schwartz spoke further on how these temperature readings provide some clues as to the circulation, radiation, and albedos of the exoplanets.

Bjorn Benneke studied oxygen-rich Hot Jupiters to model where the planets formed and if they migrated inwards, which is a big question concerning Hot Jupiters. Our best models of planet formation say that a Jupiter-class planet with a thick gas atmosphere must form away from the star, or the star’s stellar wind would have stripped all the gases away. So conventional wisdom says they formed further out and migrated in. His analysis shows discrete cloud layers and compositions on some planets, others with hazy atmospheres and a top cloud deck.

Soon to Be Famous

Tabetha

Tabetha Boyajian, a post-doc student at Yale University and director of the Planet Hunters project.

The final presentation in this session was on the Planet Hunters project, where anyone can access Kepler data to look for planets. Ran like the other Zooniverse projects, each light curve is vetted by several citizen scientists. If one of them disagrees with the others, it is looked at by a moderator who makes the final decision. The presenter said that their search also looks for RR Lyrae and other variable stars. She gave her e-mail address at the end, but I was beginning to get sleepy in the warm room and my writing trailed off. In my notebook, it reads: “Tabetha.boy…..” before trailing off completely. Yes, it was Tabetha Boyajian, a postdoctoral student at Yale University who heads the Planet Hunters program.

Tabby Star map

Approximate location of KIC 8462852, also known as the Where’s the Flux Star and Tabby’s Star.

Little did I know (or she, for that matter) that within a year of making this presentation, she would become famous for Planet Hunters detecting the weirdest star yet spotted in the Kepler data – KIC 8462852, now called Tabby’s Star or the WTF (“Where’s the Flux?”) Star. It is a real space oddity, an F-type star in Cygnus about 1480 light years away. Instead of the regular, small dips in the light curve that indicate a nicely behaved exoplanet, this star has frequent, irregular dips of as much as 20% of the star’s light, as if it is orbited by large chunks of something much too big to be a planet. Tabetha’s analysis suggested it might be swarms of comets, as shown in the artist’s drawing. But recent further analysis shows that it would take 680,000 comets, each over 200 km across, to make that kind of dip in the star’s light. Not very plausible. There is no infrared excess, so there is no warm dust that one would expect from a collision scenario.

Tabby Star comets

The comet swarm hypothesis – a large number of cold comets are blocking the light of the star, possibly pulled out of their Oort cloud by a passing star (such as the red dwarf at about 830 AU from the primary).

So what is causing it? One suggestion is that an alien civilization is building some kind of megastructure around the star, perhaps a Ringworld or Dyson Swarm. But more recent detailed analysis of historical photographic plates shows that the star has gradually dimmed 20% over the last 100 years. It’s hard to think of any civilization having the wherewithal to cover 20% of their star in that short of a time period. There is none of the waste infrared energy that one would expect of an alien structure, and SETI searches during the fall of 2015 have found no evidence of signals. It just gets weirder and weirder. Several things are certain: Tabetha Boyajian’s presentation at the 2016 AAS will be very well attended! And it proves the importance of citizen science studies – no automated system would have discovered this. Many studies are underway as I write this to observe the star and determine if the dimming is caused by cold dust (from comets or Kuiper belt collisions) or if the obscuring objects are more solid. Stay tuned!

Megastructures

An artist’s concept of what a partially completed Dyson Sphere might look like, with pieces being moved into place and gradually obscuring the primary star.

Finding lunch was a bit problematic, but there was a small sandwich shop along the walk between the Hyatt and the Convention Center that I went to. Our NITARP group met together at some tables set up at the back of the main hall to eat lunch and plan our schedule for the next three days. Tuesday is the astronomy education day, with concurrent sessions and posters. I will have my individual poster to present all day, and we had our NITARP educational poster as well. We set up times for who would do what. The science poster would be presented on Wednesday, so we assigned groups of students to different times, with teachers to keep an eye on them.

Tabby Star light curves

Light curves from the Kepler Mission for KIC 8462852. Instead of nicely predictable periodic dips, this one has huge, irregular, asymmetrical dips in the light curve.

Meeting a Personal Hero

After lunch there was a plenary session on space exploration policy featuring Dr. John Logsdon of George Washington University and the Space Policy Institute. I wanted to attend to see what the future of NASA and space exploration was likely to be (or should be). I was sitting toward the back when two of John Gibb’s students, Ashwin and Matt, walked past and saw me. They said they were going to sit on the front row and invited me to join them. Now I knew that the front row is where the Big Wigs sit – NASA directors and AAS presidents and the like. I figured that the students would be able to get away with sitting there because no one would expect them to know the etiquette of these sessions, but I also decided to join them to make sure they didn’t commit any major faux pas.

Space policy lecture

Space Policy lecture by Dr. Jon Logsdon at the 2015 AAS conference in Seattle.

We sat down just to the side of the podium and I was crossing my fingers that no one would ask us to leave. It was several minutes before the session, and a photographer was taking photos of Dr. Logsdon at the podium in front of the big AAS sign. I was watching this when a man sat on my right, and I turned to discover it was Dr. Paul Hertz, Astrophysics Director for NASA, whom I had met at the reception at AAS in National Harbor last year. He was looking at notes, but I decided to be bold and introduce him to Matt and Ashwin. I re-introduced myself. He remembered me from last year and that I was part of NITARP and SOFIA. I introduced him to the students, and he said that this was a great opportunity for them because not many high school students ever get to come to professional astronomy meetings, let alone present. Then he said, “In fact, you really ought to meet my boss!” He tapped the shoulder of a man standing in front of us with his back turned. The man turned around, and it was John Grunsfeld, head of NASA’s Science Mission Directorate and a six-time astronaut. Three of those missions, he led the repairs/refurbishing of the Hubble Space Telescope and probably has more space walking time than anyone else on the planet.

John Grunsfeld as astronaut

John Grunsfeld on a spacewalk to service the Hubble Space Telescope.

Dr. Grunsfeld was very gracious, talking with us for several minutes. I mentioned I was here for NITARP but had also flown on SOFIA as an Airborne Astronomy Ambassador, and it was an amazing experience. He said that he and Dr. Hertz kept meaning to fly on SOFIA (since they are over it) but that getting his schedule to work out to take a trip to Palmdale, then sleep during the day, attend the briefing, and fly all night on SOFIA was hard to arrange. I encouraged them to try, and that it was worth the effort.

John_Grunsfeld

Astronaut John Grunsfeld, now Science Mission Director for NASA.

(Several months later, when looking through some press releases from SOFIA, I came across an article and photos showing John Grunsfeld on SOFIA, flying with Kathleen Freddette, a Cycle 0 AAA from Palmdale, in February 2015. That was only a month and a half after we had this conversation. I give myself credit for convincing him to do this!)

John Grunsfeld on SOFIA

John Grunsfeld and Kathleen Fredette on SOFIA in February 2015.

Drs. Grunsfeld and Hertz were pulled away by other matters as the session was about to start, so I turned to Ashwin and Matt and said, “Do you have any idea who that was? He’s the director of all science missions for NASA and a six-time astronaut!” I think they were duly impressed.

The Future of Space Policy

Dr. Logsdon asked what we should expect of a space program. We spend more on space than the rest of the world combined, and since 1971 the U.S. space program has been plagued by analysts who say we don’t have clear goals for what we want to accomplish in space. Pres. Kennedy’s challenge to go to the Moon was backed up by a 100% increase in funding for all aspects of space exploration – not just the Apollo program. It would be the equivalent of boosting NASA’s budget today to $40 billion. It’s true that much of this went to building the initial infrastructure we’re still using, but as Carl Sagan put it “A rising tide floats all boats.”

Pres. Nixon’s administration valued building capabilities over going on beyond the Moon. VP Spiro Agnew’s Blue Ribbon Panel recommended building the space shuttle to service a large space station, from which we could then go on to Mars. But Nixon saw it as too expensive and trimmed the ambitious plan. Nixon wanted space to take its place as just one of a rigorous system of national priorities.

Since the 1970s things are largely unchanged. Pres. Obama has not put the resources behind his rhetoric, and NASA’s real budget adjusted for inflation continues to slowly dwindle. Dr. Logsdon was on the Columbia accident review board in 2003 and part of their findings was that NASA was straining to do too much with too little, like trying to squeeze a 20 lb watermelon into a 2 lb bag.

But given its limited resources, NASA is doing OK. HEDS (the Human Exploration and Development of Space) gets the most public attention and faces the most uncertain budget. The President is also making direct decisions about HEDS instead of simply taking the recommendations of his scientists. Planetary Science, Robotics, and Astrophysics tend to have a more constant budget of $5-$6 billion per year without a lot of debate in Congress. The fact that they do decadal surveys and meet their goals speaks to the stability of these programs.

Grunsfeld repairing Hubble

John Grunsfeld repairing the Hubble Space Telescope. Say what you may about the Human Exploration and Development of Space (HEDS) mission of NASA, there are many things that simply can’t be done by robots or space probes. Finding life on Mars or elsewhere may well be something that only people with eyes and brains on the site can do.

As for HEDS, we continue to lack a strategic focus that everyone can get behind. He predicted the most likely outcome is that we will continue to muddle along with a weakly supported program, unable to make any truly bold explorations like going on to Mars. The only way this could change is if we get a president who truly supports space exploration or if we share the expense with other countries. As for civilian space programs such as SpaceX and the X-Prize, it takes a country to truly lead the way and show vision for such an undertaking. We’re not racing anywhere anymore, so it will take a coalition of countries with a compelling goal for us to move outward again.

None of what he said was new to me, and I’ve written about it in previous posts. I simply wish we had a compelling reason to explore Mars and beyond. The China Challenge simply isn’t getting anyone excited – so what if their stated goal is to return to the Moon and go beyond? I fear that in the next 50 years, China will surpass us in space simply because we lost the motivation. There’s no reason the first flag on Mars must be American. I guess I’m glad that I speak Chinese . . . because when we stop progressing, stop innovating, stop exploring, we will cede our spot as the leading country to whoever doesn’t stop. Perhaps those with vision will need to move to China.

Galactic Streams

After the plenary session I went to a parallel session on the galactic center, the Milky Way, and streams of stars. I was astonished again by how we are now able to determine which stars belong to which populations, and that there are streams of star formation that can be traced through space and time.

Lauren Campbell spoke of hypervelocity stars in the Sloan Digital Sky Survey. They have identified 18 O and B stars and 20 G and K in a 5 kiloparsec sphere, and are now looking for F stars. They’ve found over 15, and all are metal poor. These HVSs are moving at 600-1300 km/sec and are going too fast to stay bound to the Milky Way – they’re headed out into the intergalactic void. They hope to find a population of stars already ejected from the Milky Way. Their explanation is that these stars were once part of binary systems, possibly close to the galactic center, and were ejected by gravitational interactions.

Matthew Newby spoke on the Sagittarius Dwarf Galaxy Tidal Stream. As this dwarf galaxy on the opposite side of the Milky Way from us merges with us, at least two streams of stars are being pulled out. He had to look at the CCD and CMD turn-off points to eliminate any blue stragglers, and account for the Virgo overdensity (a bright stream probably not associated with the Sgr Dwarf). Actually, what amazed me the most about this presentation is that I actually understood all of it. I know what he means by turn-off points and blue stragglers.

Branimir Sesar looked at the Ophiucus Stream, a group of 12.7 Gigayear-old metal poor stars orbiting in a looping pattern about 9 kpc from the galactic center.

Heidi Newberg spoke of rings and radial waves in the galactic disk. By subtracting the north galactic disk from the south, they should cancel out but they don’t. It produces a corrugated wave pattern. These might be ripples caused by the infall of the Sagittarius Dwarf.

NITARP Meeting

NITARP group photo-Seattle 2015

The entire NITARP group at the 2015 AAS conference in Seattle. Most of the teachers and students were independent projects and found their own way here.

After supper, we had a meeting of all the NITARP groups, present and past (and teachers for the future) at 7:00. We asked what had been effective, what needed to be improved, with anonymous comments. I commented that I wished the students had had more to do with the final writing and analysis on the poster – it felt that the teachers took over for them, even though they will be presenting it. It was a large group, and we did some small group brainstorming on different questions.

I met Tim Spuck for the first time, and he told us about his new NSF funded program to take a group of astronomy educators to Chile to see the various telescope systems there, including the ALMA array. I decided I wanted to apply for this program, even though I would have to come up with my own $1800 airfare.

We took a large group picture, and by the time I got back to my room I was exhausted and brain dead. There is so much to see and do at these conferences, and this had been a very full day.

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Astronomy in Seattle: 2015 AAS Conference Day 1

 

HG-WELS Caltech-s

The entire HG-WELS (Hungry Giants-WISE Excess Lithium Study) group at Caltech: July, 2014.

From January 4th through 8th, 2015, I travelled with four of my students to Seattle to present posters at the American Astronomical Society Conference. Our experiences will be detailed in the next several posts.

Not many high school teachers or students get a chance to present at professional science conferences. We were able to do this through our participation in the NASA/IPAC Teacher Archive Research Program (NITARP) under the direction of Dr. Luisa Rebull of Caltech. We had travelled to Caltech the previous summer to learn how to use WISE, 2MASS, IRAS, and other infrared data housed at IPAC, the Infrared Processing and Analysis Center. We joined with students from two other schools: Millard South High School in Omaha, NE and Glencoe High School in Hillsboro, Oregon and with three teachers: Estefania Larsen, John Gibb, and Elin Deeb. Altogether ten students, four teachers, and Dr. Rebull were involved in our project. Another NITARP team under Dr. Varoujan Gorjian of JPL/Caltech also attended, as well as several teams with teachers who were alumni of NITARP. They continued to do their own research and created and submitted posters on their own, then found their own funding to get to Seattle.

Elena and Kendal with Luisa

Elena and Kendall with Dr. Luisa Rebull at Caltech, calculating flux densities for K-giant stars in our study using WISE and 2MASS data.

Preparation:

We decided our project at the previous AAS in National Harbor, Maryland in January 2014. Dr. Rebull proposed several ideas to the four of us, all using infrared data from IPAC, and we liked one idea best. It involved looking at K-giant stars that were noted for having a higher than normal abundance of lithium and faster than usual rotation. The most likely explanation for these star’s unusual properties was that as they ran out of hydrogen in their cores and started to expand into an orange giant star, they had consumed their own inner planets. These planets could have provided an extra angular momentum kick that caused the stars’ rotations to speed up, and the extra lithium could have come from the planets as well. Lithium is normally destroyed in the nuclear reactions of a star.

CCD K-22

Color-color diagram (CCD) for our K-giant stars, comparing 2MASS K – WISE 22 versus K. Diagram by John Gibb.

We proposed that if stars were ingesting planets, then we might see shrouds or disks of dust or gas surrounding these stars as further proof. Such a shroud or disk would show up as an infrared excess in the WISE, 2MASS, and other databases. We could determine this by looking at spectral energy distributions (SEDs) of these stars. Dr. Rebull built a database of likely candidate stars, which we analyzed during the spring and early summer of 2014. We looked up the stars in the IRSA finder chart, created representative color images, and put together a detailed spreadsheet on our notes. The stars came from several previous studies, especially done by de la Reza, et al, using older IRAS data, and a recent survey by Jolene Carlberg. Looking at the de la Reza stars with newer WISE and 2MASS data, we saw that many appeared to have source confusion (several stars in a cluster with the K-giant not at the central coordinates) or were not K-giant stars at all.

Source confusion RGB-s

An RGB combined image of one of our possible targets for NITARP. This image takes the 4.6 micron filter as blue, the 12 micron filter as green, and the 22 micron filter as red. It is an example of source confusion, since the K-giant (the large reddish star) is not at the center of the search coordinates (yellow circle).

I had three students interested in helping with this project during the spring of 2014: Elena, Kendall, and Rosie. I met with them once a week during the late spring and early summer to go over the list of stars and teach them how to use the IPAC data. We travelled to Caltech in late July to meet with the other teachers and their students. I’ve documented this trip in great detail in my previous posts, so you can read about what we did and how we analyzed the data and built SEDs there.

David Black AAS 2015 reg

My registration for the AAS conference in Seattle.

During the fall of 2014, we needed to put everything together into a nicely laid out poster, create an abstract, and submit it to the AAS portal by the deadline in late September. We (the four teachers and Dr. Rebull) communicated back and forth on a weekly basis by telecon. Students contributed many of the images we used, and helped proofread and edit the text. We had to decide which representative IR to RGB images to use, which SEDs, which Color-Color and Color-Magnitude Diagrams, and many other details. We used one large Powerpoint slide to lay this out, which is standard for astronomers. I’m used to using Adobe InDesign or other desktop publishing software, and had never tried to create an oversized slide before, but it worked out well. We went through several drafts as the fall progressed, finalizing the last details in mid December.

Elena with concept web

Elena working on her concept web during Fall 2014.

In addition to the science poster for the students to present, the four teachers worked up an education poster based on what students had learned from the summer training. We had the students create concept webs during the summer, and during the fall each teacher had the same students create follow up concept webs to see if they still retained most of what they had learned. The other teachers sent them to me for clean-up, and I added webs from my own students. Elin Deeb did the abstract, final write up, and lay out of this poster with our help. Dr. Rebull printed out this and our science poster and brought them with her.

HG-WELS abstract submission preview

Meanwhile, I had to get everyone registered for the AAS conference itself by the early bird deadline and get plane tickets worked out. We had a new student at Walden School who was very interested in joining us, named Julie. NITARP would pay for only myself and two students, so I had to find funds elsewhere for two more students. I applied for a grant to cover this from the newly created Utah STEM Action Center.

HG-WELS Ed Poster Abstract draft DEEB-with comments

Science poster draft

A draft of our science poster for AAS, nearing completion.

I also had to work up and submit an abstract and lay out my own educational poster based on my work the past summer at Brigham Young University. I figured as long as I was going to AAS, I might as well present my own work, too. My previous three posts explain the lesson plans I was presenting, but now I had to create a large Powerpoint slide, put in the text and images, and get it all printed out. I did most of this during winter break and took the poster to Kinkos for printing just the day before we left. I rolled it up in a plastic bag and packed it on the plane with me.

Rosie on the SeaTac light rail

Rosie on the light rail from SeaTac Airport to downtown Seattle; Jan. 4, 2015.

Travelling to Seattle:

On Sunday, Jan. 4, 2015 I met my four students at Walden School and we were driven to the Salt Lake airport by a shuttle van. We checked our bags and made it through Security with plenty of time to spare, and waited for our 10:40 flight. I handed out maps of Seattle to the students along with contact phone numbers. The flight itself was uneventful, and we landed at Seattle-Tacoma Airport and got out bags from the carousel. We had to hike for a ways through the covered parking lot and along a bridge way to the light rail terminal. I bought us all tickets, then we boarded and headed in to Seattle. It was drizzling a light rain (pretty normal for here) and I enjoyed the trip into the city. We passed through a tunnel and several neighborhoods, then got off at the main underground terminal at Westlake Station. We wheeled our bags through the light drizzle along Pine Street to the Grand Hyatt Hotel.

Seattle map-s

A map I created of the area around the Washington Convention Center, where the AAS conference was being held.

Seattle from hotel

Part of downtown Seattle as seen from the Grand Hyatt Hotel; Jan. 4, 2015.

We got checked in. My students had a room, and I shared a room with John Gibb. We were all starving by now, so Julie, Rosie, and I explored around and found a wonderful crepe and burger restaurant where Olive Street splits a few blocks from the hotel. We walked back to the hotel and picked up the others, then walked to our NITARP meeting at the Northwood Suites, across the bridge over the I-5 freeway at 3:00. They were just finishing up the orientation for the new teachers, and we all filed in and presented our posters to the entire group of about 40 teachers and students. We’ve certainly come a long ways in just one year – I actually feel as if I belong here now, that I really do know what it’s like to be an astronomer.

Lobby of the Grand Hyatt

Lobby of the Grand Hyatt Hotel in Seattle, WA.

We walked back across the bridge to the Convention Center. The registration desks were at the top of a long series of escalators, with the AAS sign at the top. We picked up our packets and nametags. We then went to the college reception (we’d signed up for this) at 5:30. I wanted my students to look around and see the various graduate programs in astronomy available out there, and perhaps make contacts. Julie is interested in astrophysics as a major, so she especially wanted to meet the program directors even though she is a sophomore in high school. Dr. Eric Hintz was there with the Brigham Young University program, along with several of the students I had worked with over the summer. Olivia Mulherrin, one of the two REU students I had worked closely with, was there to present a poster of her work. Angel wasn’t able to come. Dr. Hintz had some giveaway items, and I picked up a T-shirt and some BYU truffles. Yum! Dr. Meg Urey, President of AAS, welcomed everyone.

Crepe place

Julie and Rosie in front of the Saley (savory) crepe shop on Olive St. in Seattle; Jan. 4, 2015.

We then went to the Opening Reception at 7:00. We posed by the sign, and made arrangements for when to meet at the end. I didn’t want to stifle the students’ desire to explore and get to know people, but also knew this might be uncomfortable. I’m uncomfortable myself in such social situations. Kendall and Elena were independent enough and hung out with Meghan from Oregon, whom they had met the previous summer, but I made sure Julie and Rosie felt safe without hovering over them.

Eric Hintz at reception

Dr. Eric Hintz of Brigham Young University at the graduate program reception at the AAS conference in Seattle; Jan. 4, 2015.

I was nervous enough about my students that I didn’t really relax much myself, and the lines were long and the food not as good as last year, so I didn’t quite get enough to eat. I was glad for the burger I had eaten before. We met back together at 9:00 and headed back to the hotel. It had been a long day.

Kendall Julie Rosie Elena at AAS recept

Kendall, Julie, Rosie, and Elena at the American Astronomical Society conference in Seattle; Jan. 4, 2015.

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Making Spectral Energy Distributions

David Maxwell-HD 27524

A spectral energy distribution (SED) for HD 27524, an F5 dwarf star. The chart shows the flux densities of the star, measured in ergs per second per square centimeter at each wavelength in microns. F class stars are considered yellowish-white, and you can see that the flux peaks around the Johnson V (visible) wavelength, as expected. The final scales are logarithmic because the values are exponential, so a log scale makes the values easier to compare.

During our training at Caltech in the summer of 2014, my NITARP students and I learned how to create spectral energy distributions (SEDs) of our target K-giant stars. I wanted to develop a more general lesson plan for my astronomy students and include it on my poster for the American Astronomical Society conference. I decided to have students create SEDs of representative stars for each stellar class.

First, we had to determine which stars were representative. They had to be single stars, so we wouldn’t have source confusion. For each stellar class, there is a standard star. Vega used to be the standard for an A0 star, until astronomers realized that it was a young star with dust still surrounding it. Therefore the readings had too much reddening. Now, they speak of the representative for A0 as an “ideal” Vega. I did some research and came up with two stars for each of the main areas of stars in the Hertzsprung-Russell Diagram, including OBAFGKM and LTY main sequence stars, red giants, post AGB/Wolf-Rayet stars, and white dwarfs.

SIMBAD data on Ross 128

SIMBAD data on Ross 128, a nearby red dwarf star. It includes alternate names, coordinates, proper motion, radial velocity, parallax angle, spectral type, and fluxes (actually magnitudes) at various narrowband wavelengths.

Secondly, we had to look up the magnitudes of these stars at different wavelengths. I wanted to cover the standard Johnson filter wavelengths (UBVRI); the Sloan filters (ugriz) where available; the 2MASS J, H, and K filters; the WISE 1-4 wavelengths; and in some cases, the IRAS 12, 25, 60, and 100 micron data (although I know these are inaccurate from my work at Caltech). There is a repository of stellar data available online called SIMBAD (the Set of Identifications, Measurements, and Bibliography for Astronomical Data), which is ran by CDS out of Strasbourg, France. It contains data on over 8 million extrasolar objects from several catalogs with searchable bibliography.

To use it, one types in the object’s name. They are cross-referenced so that most objects can be found by several names. For example, I choose Ross 128 as my representative red dwarf M-class star. Typing that into the search engine provided the page shown here with all the basic information listed, including alternate names (like many red dwarfs, it is a flare star and so has a V* [variable star] designation), coordinates, proper motion, radial velocity, parallax, spectral type, and photometry fluxes (magnitudes) at various filter wavelengths, in this case the Johnson UBVRI and 2MASS J, H, and Ks. It also has a photograph from the DSS or 2MASS (not very remarkable – it is a red dwarf, after all). But it does have a bluish star close by, so that may interfere with the photometry.

VezieR SED of Ross 128

SED for Ross 128 automatically generated by VizieR. You can roll over the data points to get values, including the flux densities in ergs per second per square centimeter at each wavelength in microns. Here it is showing the IRAS 60 micron data.

There is also a tool called VizieR that will automatically generate an SED for the star and allow narrowing the field of view. In this case, I have zoomed in to 0.2 arcseconds as shown in the chart, and it has a fairly clear Wien’s Law curve that peaks in the red wavelengths (around Johnson R or I) and just to the left of the 2MASS J filter. However, you can see three flux measures at the top of the graph that represent the background blue star. One good thing about VizieR is that you can hover over the dots and it will give information on the mission (in this case IRAS), wavelength (61 microns), frequency (4.85e+3 GHz), electron volts, Janskys, watts per meter squared, and flux in ergs per second per centimeter squared per wavelength.

Mag to Flux Converter-s

Magnitude to Flux converter at the Spitzer Science Center website.

I wanted my students to do the calculations and chart themselves, and use VizieR as a backup and to check their results. This chart also doesn’t have the WISE magnitudes, so I wanted them to use IRSA to get those, then use SIMBAD to record the rest, and convert all of them from magnitudes to flux densities and create their own logarithmic SED charts. We did this, and worked through the MS Excel spreadsheet calculations as we had done at Caltech. I found an online calculator that can convert from magnitudes to flux densities automatically. It is at the Spitzer Science Center website, of all places, and we used it to double-check our answers. Comparing our “by hand” calculations with the automatic calculator produced some inconsistent results, as seen in the diagram of Ross 128 with SIMBAD and WISE data combined. I think this may be because I was using nanometers instead of microns, which would put the results off by a log value of three.

Beta CVn VizieR chart

SED for Beta CVn (Chara), a G0 star, from VezieR. It shows a nice Wien Curve peaking between the Johnson V and R wavelengths. A G star is slightly more yellowish compared with the F5 star above.

To give another example, I have worked through the process again with the G0 V star Beta Canum Venaticorum (Beta CVn), also known as Chara. This star is the “representative” star for the G0 class, and is about 26 light years from Earth. Our sun is a G2 V star, and so is slightly smaller and cooler than Chara. It is considered a top contender for having Earth-like planets with life due to its similarity to our sun, but so far no planets have been detected.

Beta CVn spreadsheet

My spreadsheet for Beta CVn. The flux densities were read from the individual data points in VezieR for this chart. The VezieR chart did not include WISE data.

I looked up the SIMBAD data, then created a VizieR chart. Instead of using the Spitzer converter, I read the flux densities directly from the chart by rolling over the data points, then filled in data from the SIMBAD chart for Johnson U and a few other filters. I went to IRSA and looked up the data in the SDSS, 2MASS, and WISE catalogs, but it did not have the magnitudes for WISE. Apparently the star is too bright to measure without saturating the detector on WISE.

Beta CVn SED-f

Final SED of Beta CVn (Chara) using VezieR data, converted into flux densities by wavelength. It peaks between the V and R filters as expected.

I put the flux densities from VizieR into a spreadsheet and added the formulas, then charted the data. In the case of my chart, it is the log of the wavelength on the horizontal axis and the log of the wavelength times the flux densities per wavelength on the vertical axis. The VizieR chart shows flux densities per frequency. My chart shows an “IRAS tail” in the 60 and 100 micron data, which was typical in our SEDs over the summer. We theorize that the IRAS detector, not having very good spatial resolution, was picking up background infrared flux as well. The Herschel and Spitzer MIPS data for the same wavelengths shows a much more consistent curve. The IRAS data also depends on whether you are using the Faint Source Catalog or the Point Source Catalog.

For the student charts, we had to do some cleanup to move the axes and include the units (log l vs. log (l •F l)). The end results worked well, showing the peak fluxes where expected for the various stellar classes.

Red Supergian SED -f

SED for a red supergiant, KY Cygni. The wavelengths of the Wien curve peak in the K band (deep red) and show a large infrared excess in the WISE bands. This chart was made using the “by hand” conversion method in an Excel spreadsheet.

As long as you use a consistent method of calculating throughout (such as using only VezieR fluxes, or only the Spitzer converter, or using only the “by hand” calculations), the results work out well. For the SED of KY Cygni, a red supergiant, I used only the “by hand” method. The Johnson V, 2MASS JHK, and WISE data all line up as they should with a large infrared excess (what one would expect of a red supergiant). I am attaching John Gibb’s worksheet for doing the conversions from magnitudes to flux densities by wavelength here. He created it for our summer workshop at Caltech.

Making SEDs starting with magnitudes using Excel

I am including some of the final charts created by my students. As previously noted here, a lot can be understood about a star from an SED, including whether it has an infrared excess from a shroud of dust or gas surrounding it (such as Vega), what type of star it is, etc. Because SEDs are used frequently by astronomers, I wanted my students to learn how to make them as well. We were getting close to the end of the semester and I didn’t get the full lesson plan worked up, but most of the students were successful in creating the charts.

WISE data -KY Cygni

WISE data for KY Cygni, a red supergiant, in the IRSA database at Caltech. The magnitudes for the WISE 1-4 images are listed in the green line below. You can see that the detector is saturated in the WISE 3 image.

I still hope to create lesson plans on doing photometry based on my BYU RET training over the summer of 2014. At the very least, however, I have shown to my satisfaction that high school students are capable of doing some fairly high-end astrophysics data analysis using readily available free and public sources. I gave the students some feedback forms for each of these three lesson plans, and the results and their test scores showed they had a good understanding of the concepts involved and what the data meant, even if they could have used more time on the exact procedures. I felt I had what I needed to finish my poster for the upcoming American Astronomical Society conference.

Brown Dwarf SED

An SED for a brown dwarf. Notice that the overall flux density values are very low, and that they are still going up beyond the 2MASS JHK data points at the right. Although we do not have WISE data here, the fluxes probably peak in the infrared. This star gives off very little visible light.

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The Distance Modulus Method

Fomalhaut

Fomalhaut, or Alpha Pisces Austrinis, as seen from Stellarium software.

One of the fundamental requirements for astronomy to work as a science is the need to accurately measure the distances to objects. Astronomers have developed a series of methods for measuring stellar and cosmic distances, which fit together and inform each other. Taken together, they’re referred to as the Distance Ladder, as each one provides the basis for the next step out in distance.

BLOSSOMS lesson plan

Website for our MIT BLOSSOMS video lesson plan on using the parallax method to find the distances to nearby stars.

For the first rung on the Distance Ladder, for objects closer than about 100 light years, we use the parallax method. I developed a lesson plan to teach this and my students and I made a video of this lesson for the MIT BLOSSOMS project. You can go to their website to see this video and download the lesson plan at:

https://blossoms.mit.edu/videos/lessons/parallax_activity_measuring_distances_nearby_stars 

I’ve also written a previous post about the parallax method here:

https://spacedoutclassroom.com/2012/12/07/the-parallax-method/.

As I developed lesson plans to use on my poster for the American Astronomical Society conference, I decided to revise my lesson that uses absolute and apparent magnitudes to determine the distances to stars. It would be a good way to introduce collecting and using astronomical data. My students were already familiar with the constellations, stellar classifications, and the Hertzsprung-Russell Diagram, they had been gathering data about the stars using Stellarium software, and had completed the parallax lesson, so they were ready to go. But this lesson requires some explanation:

Stellar Magnitudes:

Beyond 100 or so light years, we have to use a method called the Distance Modulus formula. To use it, one has to measure how bright a star appears (apparent magnitude, or m) with high accuracy. How bright a star appears is based on two things: how close it is and how much light the star actually emits. Astronomers eliminate differences in distance as a factor by pretending to move all stars to same distance: 32.6 light years or ten parsecs. Their brightness from this distance is called their absolute magnitude (M).

Separating out a spectrum of the star’s wavelengths provides a fingerprint that identifies the star’s classification, using the pattern of absorption lines and flux densities based on Wien’s Law. We’ve learned enough about each type and sub-type of star to know how much total light it gives off. This is called its luminosity, and is measured compared to our sun.

hipparchus

Hipparchus, who created the first accurate star catalog about 130 B.C. He provided magnitude numbers from 1 for the brightest stars to 6 for the dimmest that could be seen with the unaided eye.

Hipparchus, Herschel, and Newton:

To figure out the distance to a star is therefore to compare how bright a star really is (absolute magnitude) with how bright a star appears (apparent magnitude). Now this isn’t quite as straightforward as it seems. Sir Isaac Newton discovered that light follows an inverse square law – that the brightness of a light falls with the square of its distance. In other words, a light that is twice as far away will be one fourth as bright as before. It is an exponential curve.

Greek_Astronomers

Greek astronomers, as painted by Raphael in The School of Athens. Hipparchus is holding the celestial sphere.

Another problem is that the original magnitude scale was developed by the Greek astronomer Hipparchus in about 150 B.C. He created the first star catalog and assigned the stars numbers based on their perceived brightness, with the brightest star (Sirius) given the number 1 and the dimmest star visible the number 6. This inverted scale has stuck with us and can be a bit tricky to understand. The important thing is that the higher the magnitude number, the dimmer the star is. Lower numbers mean brighter stars.

98,Sir William Herschel,by Lemuel Francis Abbott

Sir William Herschel, who discovered that five differences in magnitude are about 100 times difference in brightness.

Once Newton put light on a mathematical basis, astronomers wanted to standardize the magnitude system so that mathematical formulas could be used. William Herschel, along with his sister Caroline, cataloging thousands of stars (and discovered Uranus along the way). They discovered that a magnitude 1 star was roughly 100 times brighter than a magnitude 6 star, or that five orders of magnitude produce a 100 fold change in brightness. Using this, the magnitude scale was adjusted to make it come out exactly 100 times, so some stars such as Sirius now have negative apparent magnitudes.

The Modulus Formula:

With the magnitude scale adjusted to fit a logarithmic curve, you can now say that one star is exactly so many times brighter than another. You can represent this relationship with the formula: (M – m – 5)/-5 = logD , where M is the absolute magnitude of the star, m is the apparent magnitude, and D is the distance in parsecs.

Let’s work this through for the star Fomalhaut. It has an apparent magnitude of 1.15, and an absolute magnitude of 1.72. So plugging in the numbers gives us: (1.72 – 1.15 – 5)/-5 = 0.886 = logD. Taking the antilog of 0.886 gives us 7.69 parsecs. Since there are 3.26 light years in a parsec, the distance to Fomalhaut is therefore 25.1 light years. Now, since this is also a nearby star, we can use the parallax method to double check the distance. The methods in the Distance Ladder back each other up.

Modulus page 1-s

Modulus Method Lesson Page 1

It gets harder when stars are so far away that you can’t accurately measure their apparent magnitude, or if they are in distant galaxies, etc. There are other methods in the Distance Ladder, such as Hubble’s Law, that can give a distance in an expanding universe based on the degree of a galaxy’s red shift. In between, there is a method first pioneered by Henrietta Leavitt based on the precise period-luminosity function of Cepheid variable stars. Hubble used her work to determine the distance to the Andromeda galaxy.

Mag--Lum function-s

The Magnitude – Luminosity Function. Since luminosity varies with the inverse of the distance squared, it is an exponential curve. In this case, if you know the ratio of luminosity between two stars, you can use the curve to determine the differences in magnitudes. The modulus formula uses logarithms to do the same calculations.

The Lesson Plan:

Now that I’ve explained all that, its time to try out the lesson plan. All three pages are attached here and can be downloaded. I had an older version of it in the form of often duplicated printouts, but no remaining digital copy, so I scanned the pages in and revised the explanation and data tables to make the process work better, then put student samples on my poster for AAS.

In addition to using the Modulus Formula directly, the lesson shows how to do the same using the inverse square light curve. With the curve, one can figure out the magnitude differences (between apparent and absolute or between two different stars, such as Fomalhaut and Alpha Centauri) and determine the difference in brightness. Or go the other direction – knowing the differences in brightness, one can determine the differences in magnitudes.

Modulus page 2-s

Modulus lesson plan Page 3

One trick is remembering whether a star has to be moved forward or back to get it to 32.6 light years. If forward, its absolute magnitude will be a lower number than its apparent magnitude. If the star is closer than 32.6 light years, then the apparent magnitude will be less that the absolute magnitude (it appears brighter because it is close to us – remember that it is a reversed scale).

After we did the parallax simulation activity together as a class, I had my students learn the Modulus method. I then taught them how to make the representative color images using WISE data presented in my last post. Most of them were able to grasp the concepts well, based on my feedback quizzes and assessment forms.

I’ve made a few more modifications for the purpose of posting the pages here, such as adding extra columns on the first page to facilitate doing more calculations. Eventually I need to make brand new digital versions that are easier to edit. Although effective, I’m still not quite satisfied with the flow or layout of the lesson.

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Turning Infrared Images into Representative Color Photos

 

M31-Infrared-s

A representative color RGB image of the Andromeda Galaxy (M31) with WISE 2 data in the blue channel, WISE 3 in the green channel, and WISE 4 in the red channel. The blue dots are probably field stars. The bright red areas indicate star-forming regions with lots of dust (heavy on the 22 micron wavelength) whereas the blue ares is heavy in the 4.6 micron wavelength.

 During fall semester, 2014, I taught the first half of a year-long astronomy course. This semester focused on constellations, cosmology, galaxies, and stars, whereas winter semester will focus on planetary science and the solar system.

M16-Lexi B-sharp-s

A representative infrared image of the Eagle Nebula, M16, by Lexi B. You can see the Eagle’s head and beak just to the lower left of the central red “finder” circle.

Because of my work at Brigham Young University for the Research Experiences for Teachers (RET) program during the previous summer, I wanted to incorporate what I had learned into my class by creating a series of new lesson plans. Ultimately, I wanted to experiment with these lessons, get student responses to them, and create a poster on their effectiveness to present at the American Astronomical Society conference in January. I would be going there anyway with the NITARP group, so why not present my own educational poster?

Helix Nebula-Wyatt-sharp-s

The Helix Nebula, a representative infrared image by Wyatt B. Notice the long infrared (22 micron) afterglow in the center of this planetary nebula and the shorter wavelength (3.4 and 12 micron) shock wave around it.

Altogether I worked up three lesson plans for this poster, including one on finding the distances to stars using the Distance Modulus formula (I have already published the precursor lesson about using the parallax method), another on using WISE infrared data to create representative RGB images, and a third on how to find data for stars and chart it into SEDs (Spectral Energy Distribution diagrams).

Here is a description of the second lesson. I am also attaching a finished PDF version here:

False Color RGB tutorial

Purpose: To teach high school astronomy students how to use the IRSA Finder Chart in the NASA/IPAC database to locate and download infrared data files from WISE and other missions, then use IR images of various wavelengths to create representative RGB images.

Part 1: Using IRSA to Locate and Download Infrared Images

IRSA is the NASA Infrared Science Archive located at IPAC, the Infrared Processing and Analysis Center at Caltech in Pasadena, CA. Infrared data and images from all United States and some other missions are archived at this location. The URL link is:

http://irsa.ipac.caltech.edu

Missions that have archived data here include WISE, Spitzer, IRAS, 2MASS, Herschel, Planck, Akari, and others. It is your one-stop shopping center for infrared data.

IRSA website

The main webpage for the NASA/IPAC Infrared Science Archive (IRSA). To download WISE or other data, click on the Finder Chart button.

To use IRSA, click on the “Finder Chart” icon/button from the homepage and it will get you to the search engine. You will need to type in the name of the object or its coordinates (right ascension and declination or galactic coordinates), then choose the area of the sky to look at, ranging from degrees down to arcseconds. Then choose the display size (usually you want “large”) and the datasets to retrieve, such as DSS, SDSS, 2MASS, WISE, or IRAS. Then click “Search.”

IRSA search entry

The Finder Chart search engine. Type in the name of the object (it may need to be a technical name, such as Messier 31, instead of the colloquial name) or you can type in the coordinates for the area you wish to view. You can specify which catalogs, such as WISE and 2MASS, and how large of an area of sky, down to 300 arcseconds.

For example, let’s say you want to look up the Horeshead Nebula. If you type that into Finder Chart, then it will tell you it can’t resolve the name. So you would want to find a more scientific name, possibly in Wikipedia. You would find it is also called Barnard 33 or emission nebula IC 434. Now the search engine is able to resolve the name (in other words, it found the data).

Horsey WISE and IRAS

The results for the Horsehead Nebula (IC —) in the IRSA finder chart search. This shows that WISE 1-4 wavelengths as well as the IRAS wavelengths (12, 25, 60, and 100 microns). The WISE mission had much greater resolution.

Using the default size of 300 arcseconds produces only a small part of the nebula, so you will need to increase the area covered by the image, let’s say to 20 arcminutes. We now get good images from DSS, nothing from SDSS, just small images from 2MASS, nicely detailed images from WISE, and very pixilated images from IRAS. You can tell from these that IRAS had much lower spatial resolution than the other space probes, with WISE and DSS having the best.

Horsey RGB-s

The Horsehead Nebula in infrared wavelengths. Notice the bright red star at the top of the horse’s head, which is invisible in the true color image below.

To download the images, click on the Save button (which looks like a floppy disk) in the upper left corner and choose the file type. For using these in Photoshop or Gimp, you will want to choose PNG for the format. If you will be using DS9, then choose FITS format. When the PNG file pops up in your Preview window, you will need to resave it under a better name, such as the name of the object and which mission/wavelength the image is, such as WISE 4 or 2MASS H band. Save them in a folder other than the Downloads folder for easier access.

Horsey true color

The Horsehead Nebula in true color. The dark nebula hides a hot, young protostar that shows up nicely in the WISE image above. The dark wall below in this image becomes a glowing cloud in infrared.

This lesson gives instructions using the menus and commands in Adobe Photoshop, but you can use GIMP instead, an open source program that is free for download. The instructions/commands are similar.

How Computers Handle Color – And What is Meant by a “Representative” Color Image:

Computer images are made up of three “channels,” which are images made of 256 shades of gray (in 8 bit color, which is 2^8 colors or 256). Each channel is an additive primary color: red, green, or blue. If you don’t know what I mean by an additive color, please do a Google search and look it up. All I want to say here is that color on a printed page is subtractive – as you add more pigments, the image gets darker as more light is subtracted. The primary colors are the colors of pigments: cyan, magenta, yellow, and black. But the image on a computer screen adds light to light, and so the primary colors are red, green, and blue. Red and green together make yellow. All three together make white.

Pasting in Green channel-s

The channels palette in Adobe Photoshop. By selecting and copying a narrowband image (say WISE 3 at 12 microns) and pasting it into only one channel (here the green one), three separate narrowband wavelengths can be built into one representative color RGB image.

The process here is to take three 256 grayscale infrared images at increasing wavelengths (such as WISE 1, 3 and 4) and use them to replace the blue, green, and red wavelengths respectively. The final image is not true color but represents the original invisible infrared wavelengths with colors our eyes can see.

Part 2: Combining Images in RGB

You will want to open Adobe Photoshop and choose “File-Open” and open three of the four WISE images or all three of the 2MASS bands. For WISE data, I recommend either the WISE 1 or 2 (3.4 or 4.6 microns) for the blue channel, WISE 3 (12 microns) for the green channel, and WISE 4 (22 microns) for the red channel.

Start with the WISE 1 or 2 image as your starting point. Choose “Image-Mode” and convert the photograph to RGB with 8 bits per channel. Then click on the WISE 3 image and select all of it (Command-A), then copy it (Command-C). Go back to the WISE 1 or 2 image and open the Channels window. Click on the green channel only, and paste in the WISE 3 image (Command –V). The WISE 3 image should now only appear as a grayscale image in the Green channel of the WISE 1 or 2 RGB document.

All channels in-negative

All three of the wavelengths are now combined as separate channels. However, since astronomical images are usually inverted (space is white and stars are black), we have to invert the image here.

Click on the WISE 4 image, select all of it and copy it, then go back to the WISE 1 or 2 image, go to Channels, select the red channel only, and paste in the WISE 4 data.

This will give an RGB image with the three wavelengths superimposed as the blue (WISE 1 or 2), green (WISE 3), and red (WISE 4) channels. This image will be inverted, so go to “Image – Invert Image” to have black as the background space color.

You may want to make some lighting adjustments (Image – Adjustments – Levels) and increase the resolution and dimensions of the image (Image – Image Size).

All channels postive

All the channels combined and the colors inverted so space is black. This is an image for one of our HG-WELS stars, where the IRAS data had source confusion (a grouping of stars “spoofed” the IRAS sensors). The actual target K-giant star is the one to the left of the red finder circle.

Save and rename the image so you know it is RGB. Then pat yourself on the back. You’ve done it. Or better yet, do another one.

m16eagle-Dave M-enhanced-s

Another view of the Eagle Nebula, M16, in representative infrared colors, this time with a larger view area. This was done by Dave M.

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BYU-RET Final Weeks

 

BYU grad luncheon

Graduation luncheon at the Eyring Science Center at Brigham Young University in August, 2014 for the College of Physical Sciences.

Upon completion of my trip to Caltech with my NITARP students, I resumed my studies at Brigham Young University for the remaining two weeks of my Research Experiences for Teachers (RET) program.

Combined N-W charts-labels-f

The same chart with regions labeled. Four open clusters are compared by H-alpha index and absolute magnitude. NGC 663 stars are magenta, NGC 659 stars are blue, NGC 752 stars are green, and M67 stars are red. Be stars are in the upper left, the main sequence is the orange curve peaking at A0 stars, the cool star red giant branch is the yellow area, the hot star red giant branch is the magenta area, blue stragglers are light blue, and field stars are light green.

Before the Caltech trip, as documented previously, I had charted four open clusters of various ages using a hydrogen alpha index. This color-magnitude diagram (CMD), once calibrated for distance, showed some interesting results. I was able to pick out the expected number of Be (B emission) stars in the younger clusters, see a well-defined turn-off point for three of the four clusters including blue stragglers, pick out the background field stars from the cluster stars, etc. It was the culmination of seven weeks of work involving learning how to use and chart data from IRAF, DAOPHOT, and DS9 software.

But my goals for this research were far from over. Now that I was back at BYU, I wanted to focus on learning other astronomy software such as AstroImageJ for doing other types of tasks. I wanted to learn how to chart the variability of stars, create Spectral Energy Distributions (SEDs), etc. I started with the SED because I had just learned how to do these at Caltech. I choose my old friend V*V831 Cas as a target star because I had good data for it over many nights from the BYU West Mountain 36 inch telescope.

SED for V831 Cas

Spectral Energy Distribution (SED) for V*V831 Cas. The peak is somewhere in the yellow-orange part of the spectrum (V stands for “Visible” or green, not violet). The hump in the WISE data probably indicates a ring or disk or dust surrounding this HMXB star. I don’t know what’s going on with the W4 reading – I might have a bad calculation or other anomaly there.

It was easy enough to look up the star’s magnitude information at the infrared wavelengths using 2MASS and WISE data, since I knew how to find it and feed it into the same spreadsheets I’d used last week. But I wanted a larger Wien curve, including the U, B, and V filters. This was a Be star, and I expected its flux densities to peak in the B or V part of the spectrum, so I needed those magnitudes as well. I looked them up in the SINBAD database, but had to find their zero points (compared to an A0 star) in order to convert them into flux densities. This took some research, and I’m still not sure I got the right values, but it did make a nice enough curve. It did not peak where expected, however. It peaked somewhere in the yellow-orange part of the spectrum.

According to the curve, V*V831 Cas also has a hump-shaped infrared excess between WISE 1 (3.4 microns) and WISE 2 (4.6 microns), which could indicate a ring of dust surrounding this star. As it is a High-Mass X-Ray Binary (HMXB) star, I would expect a ring or accretion disk of dust and gas as material is pulled off the B star onto the black hole or neutron star in this binary system.

V831 variability-Excel computed

Light curve for V*V831 Cas, To fit the data, Excel had to use a fifth order polynomial with a large difference in amplitudes. The average period is about 97.5 days.

Next, I read through the instructions for using AstroImageJ and used it to create a chart of V*V831 Cas’ variability. To do this, you read in the .fits files from each night of NGC 663 that I had data for. You then choose up to ten comparison stars (which should NOT be variable stars) around the target star on the first image, then run the images through making sure the comparison and target stars are all kept within the frame of the image, then track each star if there is movement from frame to frame. The comparison stars allow the software to adjust for differences in viewing from night to night. Once all the frames are entered, the results for the target star are placed in a spreadsheet with magnitude values versus Heliocentric Julian Dates. The data can be exported to an Excel spreadsheet, then charted into a curve such as the one shown here. For Excel to fit a curve to my data required a fifth-order polynomial.

V831 variable curve-estimated

My own attempt to fit the data to a curve. This has a more regular amplitude but the period calculated (84.5 days) appears too short compared with the AAVSO data.

I looked up the star in the American Association of Variable Star Observers database. The website has a function that can generate light curves using available data for a star. I used one and plotted what appeared to be the maximum points and estimated the period of its variability at about 105 days. Looking at the Excel generated chart gave me a period of 97.5 days, so pretty close for the minimal data I have available (only about two and a half periods and some of it sketchy during poor viewing months). But one thing about the Excel curve still bothered me – it seems to have too extreme of an amplitude change. I attempted to plot my own curve using the same magnitude points and came up with a curve that had a more consistent amplitude, but a period of only 81.2 days, which isn’t very close at all to the AAVSO data.

AAVSO chart of V831 Cas

Light curve generated automatically from the American Association of Variable Star Observers’ website. This showed available data for the last year and indicates a period of about 105 days (ignoring the missing data on the right). This corresponds better with the Excel calculated period than my own estimate.

One thing is certain: I need more data to see if my calculated period agrees with further AAVSO data. I suppose that is always the case. One always needs more data. To draw any real conclusions, I would need to observe V*V831 Cas for several years in order to get several periods. We tend to think of most scientific studies as being founded in deep sets of consistent long-term data but it isn’t often that way. You have to make do with what data you can get, and hope you did a good enough job gathering the data, calibrating your instruments, and using solid statistical tests. If all that is true, you can at least draw some tentative conclusions and hope further evidence supports your analysis.

V831 Cas-10 year variability

When I expand the AAVSO search to the last ten years, a more regular pattern emerges showing that V831 Cas has a period of about 143 days. However, my own calculations showing a 97.5 day variation might indicate there are patterns on top of patterns, which can occur in such a dynamic binary star system. Keep in mind that the black hole or neutron star and the visible Be star are orbiting each other in elliptical orbits while material is being pulled off the B star into an accretion disk around the black hole. The accretion disk itself has a period as do the co-orbiting stars.

During my final week at BYU, I had only three days to write up my final presentation and present it to the REU students and physics professors. They only provided 20 minutes per presentation, so I couldn’t say much and focused on my new work since returning from Caltech, and what conclusions I could draw from my efforts. I still have much I want to do, but I feel I’ve accomplished a lot for one summer. I am attaching a PDF copy of my final presentation here:

BYU final report-s

Now I must turn my attention back to my own astronomy class at Walden School this fall and how to integrate what I have learned. I hope to create several lesson plans and activities that I can present at the American Astronomical Society conference in January as an educational poster, since I will be there already with NITARP. I will have my astronomy students try these lesson plans out and make modifications. Dr. Hintz provided me with an entire hard drive full of images taken with the 36-inch telescope on West Mountain that have not been analyzed. I hope my astronomy students can make use of the data for science fair projects.

BYU REU students

Some of the REU students at BYU during the summer of 2014. Olivia Mulherrin is the lady smiling on the right side. This was the banquet on the last day of our program.

On our final day, which was also the summer term graduation exercises for BYU, we attended a nice reception luncheon put on by the Physics department for graduates and their families. Now the other REUs go back to their own universities to share what they’ve learned. I go back to school. Our contract days begin next week, and I’ve already begun to organize my room.

Since one of the three RET teachers didn’t complete his program, the available grant money will be split between the two of us remaining. I will get $1600, which I hope to spend on a new telescope. Hopefully I can use it for astrophotography, although a decent motorized equatorial mount and a CCD camera will be much more than $1600. At the very least, I can get a good Dobsonian mounted reflector. I look forward to finally having my own telescope.

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