ARCSAT ID NUMBER: AS05

DESCRIPTIVE TITLE: Transients and Variables in Local Group Galaxies

PI: Guy Stringfellow

OBSERVER(S): Guy Stringfellow plus 2+ CU undergraduate students
Brandon Bell    CU APS undergraduate
Sara Grandone  CU APS undergraduate

UNCERTIFIED/UNTRAINED OBSERVERS: 

COLLABORATORS:
 
CONTACT INFORMATION: (PI/OBSERVER email, phone)
Guy Stringfellow    Guy.Stringfellow at colorado.edu     cell 303-506-3160

TIME REQUESTED: 
Run 1:   Oct 20-26 
Run 2:   Nov 17-23  
Run 3:   Dec 15-21 
Run 4:   Jan 19-25 (backup or if time is available)

INSTRUMENT:  SurveyCam 

FILTERS: 
Bessell BVRI, WC H-alpha

COMMENTS: 
Observing elsewhere Dec 23 - Jan 3.


BRIEF SCIENCE JUSTIFICATION:  

Luminous Blue Variable stars (LBVs)  represent an extremely rare class of stars that define an important 
and poorly understood phase in the evolution of the most massive and most luminous stars. The LBV 
phase lasts less than 10,000 years, and the evolutionary progression involving the LBV phase and the 
stars final subsequent outcome are not clear. For example, are all (or any) LBVs derived from a post red 
supergiant phase? Does the LBV phase invariably precede and lead to Wolf-Rayet stars?  Evidence now 
suggests that the LBV phase can be the final endpoint for some massive stars, leading directly to the 
explosion of Type II supernovae: SN 2011ht (Fraser et al. 2013, ApJ, 779, 8) and SN 2009ip (Pastorello 
et al. 2013, ApJ, 767, 1; Mauerhan et al. 2013, MNRAS, 430, 1801). But there is yet another fundamental 
problem associated with the post-main-sequence evolution of massive stars. It has become apparent that 
main-sequence mass loss rates for the most massive stars have previously been overestimated, with rates 
revised downwards by factors of 5 or more. With these revised rates, massive stars can not lose enough of 
their mass through winds during the main-sequence and early post-main-sequence evolution to reconcile 
observations. This indicates that much of the stellar mass needs to be lost in some other way. This places 
more importance on the major eruptive mass-loss events defining the LBV phase. The LBV phase may 
now be the critical phase where most of the star's mass-loss must now occur prior to stars becoming WR 
stars or exploding as supernovae. 

Only a few confirmed extragalactic LBVs (typically the brightest ones or those that have displayed 
dramatic variability, signaling interest) were previously known in the local group: for example, 4 LBVs 
are known to reside in M31, 5 in M33, and 3 in M101. Recent optical spectroscopy efforts have revealed 
an additional 20 new candidate LBVs in M31, and 35 in M33 (Massey et al. 2007, AJ, 134, 2474). These 
new candidate LBVs typically range from 20 < V < 16. To confirm these new extragalactic candidate LBVs 
as bona fide LBVs, they must be shown to undergo either spectroscopic or photometric variability. We 
intend to confirm  these as LBVs by demonstrating photometric variability through monitoring. LBV 
variability has been demonstrated to occur on time scales ranging from months to years, which is tractable 
with a monitoring program with cadence times of order a month. The proposed monitoring will yield other 
transient events, including novae, which are also being studied. 

Based on our previous ARCSAT observations, we now have an 11-tile grid covering M31.
It takes about 2-3 nights to cover this grid in 4 filters with 3x300s exposures in each filter for
each tile with an 8 hour observing window each night. As we are also interested in discovering 
and monitoring transient events, such as novae, we revisit tiles encompassing transients more 
frequently (once a night). In 3-4 night runs we will achieve both complete coverage of M31 in 
4 filters and revisit several tiles to monitor discovered transients. An example of the latter is 
given in AstroTel#6324 where we confirm M31 Nova 2014-07a and report pre-discovery 
photometry extending over a 5 day period. Our primary targets are M31 and M33, but we are also 
following (less frequently) M51, M81, M82, and M101 which compliment the visibility windows 
of the primary targets.  We need to establish a deep baseline for our grid during this time allocation, 
and hence require dark time. This was not possible during the summer when weather and seeing was 
generally poor. We have shown we can reach V~19 mag, and hope to extend a baseline down to 
V~20 mag, and corresponding limits in the other filters.

Our program would benefit from shorter and more frequent runs - 3-4 nights each month. If other programs 
would also benefit from shorter runs but more frequently scheduled, we could work out arrangements between 
ourselves - either before or after scheduling. Not knowing who else may propose prevents us from pursuing 
such amicable arrangements before submission.