Tuesday, December 4, 2018

First time at LCO

I’m Sunny Rhoades, a junior physics major at Pomona College. I was very fortunate to be invited to LCO by Gwen Rudie and Drew Newman, my mentors during the 2018 Carnegie summer undergraduate program. For several nights this November, I shadowed Gwen and Drew as they observed targets for an ongoing Lyman-alpha Tomography IMACS Survey (LATIS). 

Photo taken by Gwen Rudie. Notice the Magellanic Clouds in the background!

This past summer I worked on a bit of the data visualization for LATIS, which plans to spatially map the density field from z ~ 2 - 3. I worked exclusively with processed data to make 3D maps, so this trip allowed me to connect what I studied to observations. I hadn’t looked at a lot of spectra while working last summer, so was interested in familiarizing myself with the properties of LATIS spectra. The LATIS spectra taken using IMACS target the far-UV spectrum in the rest frame, and so are able to provide information (based on strong UV transitions) about the galaxies within our tomographically-reconstructed volume. IMACS was used for this project in part because it is a multi-object spectrograph, so works well where the density of interesting targets per field is large.

Most of my time at the Baade telescope was spent in the control room, learning about the interface and the procedures and strategies involved in observing. I learned about spectroscopic calibrations and was then able to take some on my own! The final product for spectroscopy of a source is the intensity as function of wavelength, so the data reduction requires you to determine the efficiency of the system as function of wavelength. Wavelength calibration for spectra—which is in part what I performed—is done using exposures of arc lamps, which emit light in many specific wavelength ranges. This calibration is to check if the line spectrum has emission lines that are distributed in a sufficient frequency over the whole wavelength range, no line blending, and no line saturation in the exposure. I also learned about taking twilight flats, which are required to determine the large-scale illumination of the CCD. They are especially useful for getting calibration frames in the UV. And once you have your final, reduced images, the goal is that the large-scale variations in the sky background across each CCD chip are smaller than the desired precision in your measurements of things you care about. 

I really enjoyed visiting LCO! I think I now have a much better understanding of how data for LATIS is taken, but I still have a lot to learn. Plus, I got to see some interesting animals (like the viscacha shown in the low-quality photo below).

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