On Wednesday, July 30, 2014, our second day at the NITARP workshop at Caltech, we accomplished three major things. First, we traveled to the Jet Propulsion Laboratory for a tour. Second, we began to wrap our brains around the calculations necessary to create the Spectral Energy Distributions (SEDs) for our target K-giant stars. Third, we visited Griffith Observatory.
I have been to JPL many times, and it is always a thrill to me. I consider it to be the coolest place in the world. Call me a nerd or a geek, but that’s how I feel. Certainly the IQ density of the planet peaks here and at other NASA facilities. When I visit here, I can’t help but be excited by the projects I know are being developed: space probes and mission instruments which will expand our knowledge of the universe and make fundamental new discoveries. But for the first time in all my work here, I am finally bringing students to share the experience with me. I wish I could bring a whole class down. Maybe some day. For today, I contented myself with experiencing this place through the eyes of my students. Kendall, Elena, and Rosie had heard some of my stories, but now they got to see what I had enthused about so much.
We drove past La Cañada High School to the front gate of JPL and showed our IDs, then parked in the main parking lot. It was early enough that we were able to find parking places in the shade (not an easy thing). We walked to the visitor office to get our badges and to wait for Varoujan Gorjian to arrive, who would be providing our tour. He is the leader of the other NITARP teacher group and works mostly at JPL.
We walked across the courtyard and main square to the Administration 180 building, where Dr. Gorjian showed us the scale model of Curiosity, the Mars Science Lab, in the lobby. I pointed out to my students that this was the place, in the conference room just around the corner, where I had gotten neodymium magnets stuck up my nose (long story – it was hilarious and rather painful at the same time). Last time I was here, in August 2012, this model was out in the courtyard under a tent along with models of the MER and Mars Pathfinder so that the press could take action shots during the Curiosity landing.
We walked down to the In-Situ Instruments Lab (ISIL) and climbed upstairs to the visitors’ gallery where we could look down on the tests. A test model of the new InSight mission, which will be launched to Mars in March 2016, as well as test beds for MER and Curiosity were in the sand box. InSight will contain a seismometer probe (seen in the photo as the gold Mylar covered object on the ground) and a heat transfer probe that will drill into the Martian surface will study the early geologic evolution of Mars and whether or not it still has a molten core. It will also carry two MarCO (Mars Cube One) relay satellites. During InSight’s two year mission at Elysium Planum, this test bed will allow commands to be tried out on the engineering model here before they’re sent to the real lander on Mars.
This mission looks a lot like the Phoenix mission because it reuses some of the same parts. And the Phoenix mission reused parts from the Mars Polar Lander that crashed in 1999 when its descent engines cut out too soon. Whenever a probe is created, each part is duplicated several times because many of them fail during the grueling tests that occur up at the Environmental Test Lab. I’ve been in this lab several times and it is often called “Shake and Bake” for good reason, because that is what they do to the probe parts to see if they can handle the stresses of launch and space travel. When more parts pass the tests than are needed, they are stored and often reused on subsequent missions with similar designs.
We walked to the Gift Shop, where I bought a nice dark navy blue polo shirt with the JPL logo on it. My old JPL shirts are wearing out. Then we walked to the Assembly 179 building to look down on the main clean room. A team of technicians was working on assembling and testing the Soil Moisture Active Passive (SMAP) probe, which will orbit Earth and measure the thaw and freeze cycles of water on Earth to better understand the water and carbon cycles, energy flows, and climate change. It will help to make flood and drought predictions and help us monitor the availability of water. Its most remarkable feature is a large radiometer dish the size of a big trampoline (and shaped like one) that will rotate at the end of a long arm. You can see the dish at the back of the clean room in the photos. It launched from Vandenberg Air Force Base in January 2015. As of this writing, it successfully reached orbit, deployed the dish, and the radar functioned until last month (Sept., 2015). Other mission science continues for two more years.
We walked to the Von Karman Auditorium and museum. I only had my iPad as a camera, since my good camera went on the fritz on our trip to Nevada in May. I tried to take some photos in the museum, but it is hard to get well-focused photos from an iPad with a swaying keypad attached. The photos shown here are mostly screen shots from my Flip HD cameras. We took some group photos in front of the IR camera in the museum. We also walked through the auditorium and saw the models of recent missions and one old friend: the Voyager model that has been there since I first visited JPL in 1978, although back then it was in the middle of the hall, not on the side.
My students enjoyed the tour, and it was fun for me to see this place with new eyes. We walked back to the cars and drove back to Caltech.
Our introduction yesterday taught us the infrared missions and the available data at IPAC, as well as the physics of K-giants. We hope to detect evidence that some of our target stars have ingested planets through looking for infrared excesses. These target stars have a high abundance of lithium, or A[Li], and faster than normal rotation. Planets have angular momentum as they orbit the star, and if they fall into the star as it expands to an orange giant, then that momentum will transfer to the star and kick up its rotation speed. As for the A[Li], stars going through their orange giant phase would tend to destroy what lithium they contain, unless the stars dredge up lithium from their cores. However, if the lithium were dredged up, the star would also see a higher than normal amount of carbon, which would be dredged up as well. The other possibility is that the high A[Li] came from outside, from a planet that was ingested and broken up into the star. If this happened, we hypothesize that the planet would pull stellar material toward it and would break up into a shroud or ring of dust around the star. This shroud or disk would produce an excess of infrared radiation from what one would normally expect of a K-giant.
The task, then, is to determine the flux densities at various wavelengths of normal K-giants and compare them to stars with high A[Li] and fast rotation to see if they also show a dust shell or disk. To do this, we will need to look at the target stars’ photometry (magnitudes) at various wavelengths from various missions and create Spectral Energy Distributions, or SEDs. This will require us to determine the photometry magnitudes in Janskys, then convert them into flux densities in terms of frequency with standard units (called cgs units, or ergs per second per centimeter squared per frequency), then finally into flux densities in terms of wavelength, or Fl (Flux sub lambda). We then plot the log of the wavelength (l) times the Fl as the vertical axis and the log of the wavelength (l) for the horizontal axis.
Why the logs, you should be asking? Because the wavelength scale spreads out so much between the visible and far infrared wavelengths that a logarithmic scale is much more useful. The end result, although difficult to arrive at, is very useful as it can tell you whether it is a Main Sequence star, a protostar, or a dying star. Our K-giants aren’t quite dead yet, but being on the red side of the blackbody curve (more on this later) we can tell a lot about them, especially at IR wavelengths, using these SEDs.
Dr. Rebull had already created preliminary SEDs for our target stars so that we could begin to identify likely candidates. Many of these had been identified from previous papers using only the data from the IRAS mission, which scanned all the sky at 12, 25, 60, and 100 microns. However, it was a 1980s mission and had low resolution, so we suspect that many of our stars from these studies might not be K-giants at all. There could be source confusion, or they might be protostars or post-Asymptotic Giant Branch (AGB) stars (in other words, very old red giants). To find a shroud of dust from a consumed planet, which would be a very temporary feature, we needed to find recently grown K-giants. Other more recent studies by Dr. Jolene Carlberg use the WISE data and are more reliable.
Dr. Rebull and the teachers, myself included, had gone through the list over the summer to get a beginning feel for the candidates. We created some RBG images using the WISE photographs, which skill I taught my students (and which I will report on this blog soon), in order to see if we had a good point source (a star) or something else. Now we divided up into teams and took about 50 stars each and looked at their SEDs to see if we could pick out any likely candidates. A good candidate for a dust shell or disk would have a raised right side to the blackbody curve of a normal star. In other words, the curve up through the Johnson filters (UBVR) would follow a normal star’s profile, but as we look in the infrared in the JHK, 2MASS, WISE, and IRAS wavelengths, we should see a raised arm or a bump indicating a higher than normal flux density in the infrared for a shell or a disk. This right side of the curve is called the Raleigh-Jean side (the left side is the Wien side, after the person who first developed the law that shows the relationship between peak light intensity (or flux) and wavelength for various types of stars). See the image for more information on Wien’s Displacement Law.
We reported back to the whole group. It doesn’t look like we have many candidates remaining from our 180+ stars just from eyeballing the SEDs, but more detailed analyses will be done tomorrow and Thursday as we learn how to make our own SEDs and compare wavelengths with each other to analyze if they truly have IR excesses.
We had decided tonight to also visit Griffith Observatory, which I had not seen since its renovation. My last time there was in 2001 or 2002. We looked up how to get there and made sure we had a navigator in each car, then drove on the 134 (Ventura Freeway) and exited to wind our way up to the top of Griffith Park. We finally found a place to park along West Canyon Drive and walked up to the observatory, following a stream of people as it started to get dark.
I stayed with Rosie as the rest scattered. We stopped at a public restroom, then on to the stairs up to the roof, where we took some photos of the Los Angeles skyline and the Hollywood sign. It was too much of a wait to look through the telescope, so we walked downstairs. Most of the main floor has remained the same, but they have excavated an entire new area under the front lawn containing scale models of the planets and the Leonard Nimoy Theater. It was not as crowded down there.
I can’t help but be reminded of all the movies filmed here, everything from “Rebel Without a Cause” to “The Rocketeer” and “Dragnet” to my personal favorite, “Bowfinger.” I wanted to run up on the roof and yell “Gotcha, Suckahs!”
We rendezvoused with the others and walked back to our cars, then drove back to Pasadena. We went to grocery stores and other places around the area of the Comfort Inn to find food for a late supper.