GeminiFocus April 2019 - Page 7

Galactic coordinates for the Gemini targets, color-coded by catalog. All of these spectra, interestingly, were gathered exclusively as part of the Poor Weather proposal cycle of- fered by the Gemini Observatory. Big Eyes and Cloudy Nights The targets selected from the RAVE and B&B catalogs were bright enough to be observed under poor, but usable, conditions, as part of the Poor Weather programs at Gemini. Such programs are executed only when noth- ing in the regular queue is observable and hence considered "weather loss" for time ac- counting purposes. The targets followed-up as part of this effort had no observing condi- tion constraints (CC = Any, IQ=Any, SB=Any/ Bright, and WV = Any), and spectra were taken using the Gemini Multi-Object Spec- trograph (GMOS; North and South) B600 gratings and 1-arcsecond slits. Figure 2 shows the total counts at 4000 ang- stroms in the observed spectra as a function of the visual magnitude of the stars. The size of the symbols is proportional to the exposure time for each object, in seconds. It is interesting to note the large spread in counts for stars with similar exposure times in a narrow range of magnitudes (e.g., blue filled circles at V ~13.5). Similarly, there are cases where it took up to four times longer to gather the same counts for stars with similar magnitudes (e.g., red filled squares at V ~12.5 and Counts ~1,000). These are telltale signs of the highly variable weather conditions (mostly image quality and cloud cover) in which these stars were observed. In total, seven GMOS Poor Weather programs were executed (three in the North and four in the South) spanning four semesters (from 2015A to 2016B). Those programs had 310 hours of allocated time. By adding all the exposure times, there were about 89 hours of on-target observations for the 666 stars, averaging about 8 minutes per exposure. Adding ~12 minutes for acquisition and cali- brations, these were 20-minute observing blocks, giving an average of three stars per hour. As a result, assuming 666 targets took 222 hours of observing time, the efficiency was around 72%, meaning that only 28% of Figure 2. Total counts at 4000 Å as a function of visual magnitude. The size of the symbols is proportional to the exposure time for each object, in seconds. April 2019 GeminiFocus 5