We have built an Atmospheric Transmission Monitoring Camera (aTmCam), which consists of four telescopes and detectors each with a narrow-band filter that monitors the brightness of suitable standard stars. Each narrowband filter is selected to monito
r a different wavelength region of the atmospheric transmission, including regions dominated by the precipitable water vapor and aerosol optical depth. The colors of the stars are measured by this multi narrow-band imager system simultaneously. The measured colors, a model of the observed star, and the measured throughput of the system can be used to derive the atmospheric transmission of a site on sub-minute time scales. We deployed such a system to the Cerro Tololo Inter-American Observatory (CTIO) and executed two one-month-long observing campaigns in Oct-Nov 2012 and Sept-Oct 2013. We have determined the time and angular scales of variations in the atmospheric transmission above CTIO during these observing runs. We also compared our results with those from a GPS Water Vapor Monitoring System and find general agreement. The information for the atmospheric transmission can be used to improve photometric precision of large imaging surveys such as the Dark Energy Survey and the Large Synoptic Survey Telescope.
The Magellan Echellette (MagE) spectrograph is a single-object optical echellette spectrograph for the Magellan Clay telescope. MagE has been designed to have high throughput in the blue; the peak throughput is 22% at 5600 A including the telescope.
The wavelength coverage includes the entire optical window (3100 A - 1 micron). The spectral resolution for a 1 slit is R~4100. MagE is a very simple spectrograph with only four moving parts, prism cross-dispersion, and a vacuum Schmidt camera. The instrument saw first light in November 2007 and is now routinely taking science observations.
I develop a new technique to identify M-type extreme subdwarfs (esdMs) and demonstrate that it is substantially more efficient than previous methods. I begin by obtaining spectroscopy and improved photometry of a sample of 54 late-type halo candidate
s using the rNLTT reduced proper motion (RPM) diagram. From spectroscopy, I find that four of these are esdMs, three of which were previously unknown. From the improved photometry, I show that all four lie in a narrow RPM corridor that contains only 4 non-esdMs. Hence, with good photometry (i.e., without spectroscopy), it appears possible to select esdM candidates with a 50% esdM yield. This is more than an order of magnitude more efficient than previous methods.
