ARCSAT ID NUMBER: AS07

DESCRIPTIVE TITLE: Census of Variable stars in the UMi dwarf
spheroidal galaxy.

PI: Karen Kinemuchi

OBSERVER(S): Karen Kinemuchi

UNCERTIFIED/UNTRAINED OBSERVERS: 

COLLABORATORS: Katie Grabowski (APO), Jim Nemec (Camosun College),
Charles Kuehn (Univ of Northern Colorado), Elizabeth Jeffrey (BYU)
 
CONTACT INFORMATION: Karen Kinemuchi:  (email): kinemuchi@apo.nmsu.edu
or kkinemuchi@gmail.com  (phone): 352-514-5013

TIME REQUESTED: 
March 14-20

INSTRUMENT: SurveyCam

FILTERS: Broadband Johnson BVRI (preferred) or Sloan gri

COMMENTS: 
March is the preferred time to observe the UMi dwarf galaxy as it is
above 2 airmasses for most of the night.  The week of the 14th is
ideal due to the moon distance to the field of view.  

BRIEF SCIENCE JUSTIFICATION:  

The classical dwarf spheroidal galaxy Ursa Minor contains a large
number of variable stars, particularly of the RR Lyrae and anomalous
Cepheid types.  I propose to do an updated census of variable stars of
the dwarf galaxy.  A previous census included data points from
photographic plates (22 epochs) and a number of CCD observations
(38 epochs) (Nemec et al. 1988).  The ARCSAT telescope and the
SurveyCam are ideally
suited for this project: the camera has a large enough field of view
to image most of the galaxy, and the telescope scheduling allows for
good
phase coverage for variable stars.  We expect the exposure times to be
on the order of 600-900 seconds in order to reach the horizontal
branch of UMi (V~19.5) (Bellazzini et al. 2002). 

The goal will be to produce an updated catalog of variable stars,
their (re)classification, new period determinations (or discovery of
period modulations), and a list of new ephermerides for the
pulsators.  We have previous ARCSAT observations of the galaxy, but we
have
found that the observational cadence produced period alias solutions
for almost all the detected variable stars.  A second set of
observations will minimize the alias solutions, and also provide more
phase coverage for light curve shape analyses (e.g. photometric [Fe/H]
metallicities).  The photometry will be done with DAOPHOT, much like
the
Nemec study, and the analysis of the RR Lyrae population will be
similar to the work done with the Draco dwarf spheroidal galaxy
(Kinemuchi et al. 2008).  We will determine
photometric metallicities using the Jurcsik & Kovacs (1996) method via
Fourier decomposition parameters.  We will provide an analysis of the
RR Lyrae variable star population, as well a discussion of other
variables discovered in this census.  We hope to also update the
number of anomalous Cepheids associated with this dwarf galaxy
(anomalous Cepheids are preferentially found in dwarf spheroidal
galaxies).  These Cepheids provide another independent method of
deriving distances to the galaxy, but are less understood than their
Pop I and II cousins.

Preliminary results have been presented at the RR Lyrae conference in
Visegrad, Hungary, and a conference proceeding will be published in
early 2016.  A full paper is expected later in 2016, which will
include data taken at the ARC 3.5m telescope and additional epochs
from the West Mountain 0.9m telescope of Brigham Young University.

REFERENCES:
Bellazzini, M., et al. 2001, AJ, 124, 3222
Jurcsik, J. & Kovacs, G., 1996, A&A 312, 111
Kinemuchi, K. et al. 2008, AJ 136, 1921 
Nemec, J., Wehlau, A., & Mendes de Oliveira, C., 1988, AJ, 96, 528