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
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