Luke Keller

Luke Keller

Dana Professor, Department of Physics and Astronomy

Specialty:Astrophysics, airborne astronomy, spectroscopy, optical instrumentation, natural science general education
Phone:(607) 274-3966
Office:264 Ctr for Natural Sciences
Ithaca, NY 14850


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Preparing for astronomy with NASA's newest airborne observatory

Posted by Luke Keller at 6:36PM   |  Add a comment
Martin Garay MacLean (IC Physics '14) working during the June 11th 2013 test flight (photo courtesy of NASA, Carla Thomas).

Martin Garay MacLean (IC Physics '14) arrived at LAX on June 9 and we made the short trip to Palmdale, CA, along Interstate 405 and then up to the Mojave Desert. He was pretty excited. Our SOFIA flight, scheduled for the night of June 11, would be his chance to see our data analysis software in action for the first time outside of our lab at Ithaca College. We met Kim Ennico Smith, a FORCAST grism team member who works at NASA, for a Mexican food dinner to discuss plans for the flight. We spent the next day getting our software and the latest data files loaded onto a laptop computer that will be our flight computer. Then we set off for the DAOF to get Martin his security badge and his first peek at SOFIA. It never gets old: walking into the huge hangar and seeing SOFIA towering over us is just an incredible experience. It was really fun for me to see each of my students experience that for the first time. That evening I joined Kim and Martin for their "egress training", a short safety course that prepares SOFIA flight participants for the unique safety issues possible on the aircraft. Since we wander the aircraft during flights, working at different stations, we need to carry emergency oxygen supplies with us in a small package the size of a small pack of tortilla chips. Next day was flight day!

Each flight begins at around 5:30 pm local time with a briefing that is required for all flight participants. We learn about the flight plan, weather reports along the way, and the flight manifest (who's flying and what their role is). This flight we had the privilege of hosting a great group of Airborne Ambassadors, middle and high school science teachers who fly and then collaborate with the researchers on the flight. They had lots of questions and it was fun to interact with them during the flight when we weren't busy with our test procedures. There was also a news crew from the CBS affiliate in Los Angeles. Takeoff was at 7:36 local time.

Martin and I set up at the Science Instrument rack, the FORCAST control center on SOFIA, during the flight legs testing our spectroscopic observing modes. Martin got to see data coming in real time and the software working well to reduce the data to spectral graphs we could use to verify that things were working well. We also kept a list of possible upgrades to the software that we'll work on as part of Martin's summer research internship. Ten hours after takeoff we landed on the same runway and taxied to the DAOF hangar. The sun was rising as we made our way to the hotel for a three hour's sleep before starting the journey home to Ithaca.

The past few weeks have been really fun for me. As an undergraduate student I was given an amazing opportunity to help develop an instrument for a new (at that time) large observatory. It's really gratifying, a dream come true really, to be able to provide that kind of opportunity for my students. All three got to see the culmination of their contributions to a big international science project in person. Really fun.

SOFIA has now started the first cycle of "General Observer" observations. That means observations conducted for new research projects by astronomers in the general professional community. Test flights are DONE for FORCAST; now comes the real fun!

Posted by Luke Keller at 6:02PM   |  Add a comment
Rob Lewis (IC Physics '13) and Luke Keller dwarfed by SOFIA

Quick SOFIA update: The telescope power problems are now fixed, but not in time for last night's flight. Rob Lewis got to see his software development work in action as we analyzed data from the previous flight, and he got to poke around SOFIA, but unfortunately he did not get to fly. The next flight is scheduled for Tuesday, June 11, but Rob is on his way to a new life and job in Seattle so he'll have to fly another time. Meanwhile IC physics major, Martin Garay MacLean, is preparing for the journey to Palmdale to participate on the June 11 flight. We're all working hard to get FORCAST tests finish since we are scheduled to begin the first cycle of general observer observations as soon as our tests are complete. That means flight activity will transition from mostly testing new equipment to mostly using that equipment for astronomy! It's what we've been working towards for over ten years!

Now back to grisms!

A grism is a combination of a diffraction grating (an optical filter with microscopic parallel lines on it that disperse light into it's constituent spectrum of colors) and a prism, which does the same thing with a wedge of optical material. Hence the name, GRating + prISM = GRISM. Grisms are very useful to us because they allow us to transform the FORCAST infrared camera into a spectrometer by simply replacing a filter with the grism. No other optical alterations are necessary. Since FORCAST has many options for filters, allowing us to record images in many different infrared "colors", we can put grisms in place of a few filters and significantly increase the utility of the instrument for many different astronomical observations. Images tell us what an object looks like, how its brightness changes with position on the sky, and where it is relative to other objects int he same region of sky. Combinations of images taken through different filters can allow astronomers to infer physical characteristics of objects, but splitting the light into a spectrum adds even more detail. The combination of images and spectral measurements allow us to learn about the temperature, density, and chemical composition of the objects we observe.

Posted by Luke Keller at 7:19AM   |  Add a comment

Sometimes the scientific process takes an unexpected turn and tonight was one of those times. Takeoff for our third commissioning flight on SOFIA was at 7:35 PM Pacific time. The flight manifest included NASA scientists and engineers, the Ithaca College and Cornell University FORCAST team members, journalists from an LA-area newspaper, and four public school science educators on board as part of the SOFIA Airborne Ambassador outreach program. Our flight plan took us on a tour of the american west and mid-west at an altitude of 39,000 feet and we were making good progress with tests of our camera when the telescope power system bagan to show low voltage levels. After only half of our flight, and just before our scheduled spectroscopic tests, the mission director made the decision to return to the SOFIA base in Palmdale since flying with the telescope underpowered could damage the system. Fortunately Casey Byrne got a little time at the controls of the data analysis computer to see the culmination of his work at IC over the past two years. He also spent some time with the Airborne Ambassadors, answering questions and explaining the work we were doing on the flight. 

IC student, Rob Lewis (Physics '13) arrived in time to watch SOFIA takeoff and will pick up where Casey left off on this Thursday's flight. We're optimistic that the power system will be back to 100% and Rob will complete the tests we had scheduled for tonight.

Next post: What's a GRISM?

Posted by Luke Keller at 2:46AM   |  Add a comment
Casey Byrne (IC Physics '13) on SOFIA
We've had a couple of years with relatively little flying while other instruments came on line and while improvements to the aircraft were under way, but FORCAST is now back in the stratosphere! We spent past two years making improvements to the camera and my Ithaca College students and I finished a new spectroscopic mode for FORCAST in collaboration with the "FORCAST Grism" team. We have added hardware and developed software to quickly record spectra with FORCAST. That allows us to disperse light entering the camera into the spectrum of infrared light; analogous to a prism dispersing visible light into a "rainbow" of colors. By comparing brightness of different colors of light from a source, astronomers can infer fundamental physical properties like chemical composition, temperature, density, and even motion.
FORCST is now in the final commissioning phase: the instrument is finished and we are conducting a series of tests over five flights that will demonstrate readiness to hand off the instrument and software to USRA as a facility instrument. We completed the first two commissioning flights on April 4th (SOFIA Flight 99) and May 30th (SOFIA flight 103) during which we recorded the first in-flight FORCAST spectra.
Recent Ithaca College alum Casey Byrne (Physics, 2013) will be on the third FORCAST commissioning flight to help test software he helped write as part of his physics senior thesis. IC alum Rob Lewis (Physics, 2013) and student Martin Garay MacLean will fly on the final two commissioning flights. On these flight the IC folks will be helping with data quality control to insure that we make the most of the 10-hour flights to gather the best data set possible.

Posted by Luke Keller at 11:48AM   |  Add a comment
FORCAST image of the central star forming region in the Orion nebula.

Seems it is time to change the subtitle of this blog from "Preparing for astronomy..." to "Doing astronomy with SOFIA." I am happy to report the transition of SOFIA from a flying telescope (amazing as that may be) to an observatory that can support a wide variety of astronomy and planetary science research projects. That was the goal of the Short Science series of flights that began in late November. It's called Short Science because the science team selected astronomical investigations and observations that required relatively short exposure times and would yield new research results that we could share with the public within weeks or months of the flights. It may sound like a long time to wait, but astronomical observations routinely require months of data processing and analysis.

After taking a break for the Thanksgiving holiday, we were back on the line with SOFIA on the night of Monday, November 30, rehearsing observing plans for SOFIA's initial science flight. This flight, the first of a three-flight series that ended in early December was the first were the primary goal was to conduct new astronomical observations that take advantage of the unique capabilities of SOFIA and contribute to new knowledge in the fields of astronomy and planetary science. The initial science flight (ISF) went very well and NASA held a press release just hours after we landed to announce the good news. Another goal of the ISF, and the subsequent two science flights, was to make infrared images that would demonstrate to the general public and the astronomical community that SOFIA is working well and producing interesting and useful data. The picture we chose for the first "science" image is a FORCAST view of the central massive star forming region in the Orion Nebula (M42). The two-color composite (false color image) uses red to indicate data taken through a 37 micron filter and green to indicate data taken through a 19 micron filter. Though ground-based telescopes are capable of imaging at 19 microns, such observations are highly dependent on excellent atmospheric conditions. Images like this will be routine on SOFIA. The 37 micron image is only possible from SOFIA since no existing or planned telescope anywhere (even in space) has instruments that operate in the 28 - 40 micron range of the infrared spectrum. 

It was exciting to fly on the three Short Science flights for many reasons, but one in particular for me was the fact that we gathered data for so many different astronomical studies. We now have images of a comet that was in the neighborhood late last year, the planet Jupiter (which we revisited in much more detail than we did for the First Light images), a "starburst galaxy", and several regions of star formation in our own Milky Way galaxy. The exciting thing about the images we got is that they have yielded very high quality data. The science team now has unique information for each of those objects and we are working very hard on data analysis over the next weeks and months to publish and share the results with the astronomical research community and the general public.

After we'd had a chance to work on data analysis for a few weeks, NASA and USRA released our new, larger and (I think) even more spectacular image of the Orion star forming region. I also made a short movie comparing visible light and infrared images of this region of space, which Terry Herter (FORCAST principle investigator) presented with the first scientific results from SOFIA this week at the meeting of the American Astronomical Society in Seattle, Washington. We're looking forward to sharing more images and results soon.

Stay tuned: The next SOFIA flight series begins later this spring with observations using the German Receiver for Astronomy at Terahertz Frequencies (GREAT, which is one of my favorite SOFIA acronyms). GREAT is an extremely high frequency radio receiver. After the Short Science flights with GREAT, we will bring FORCAST back into service for a second series of science flights proposed by many scientists from the general astronomical community.

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