ARCSAT ID NUMBER: AS07

DESCRIPTIVE TITLE: Short Term Variability for Stars of Similar
Temperatures but Different Luminosities

PI: Tiffany Pewett (GSU)

OBSERVER(S): Tiffany Pewett (GSU), Michele Silverstein (GSU), Todd
Henry (GSU)

UNCERTIFIED/UNTRAINED OBSERVERS:

COLLABORATORS: Wei-Chun Jao (GSU)
 
CONTACT INFORMATION: Tiffany Pewett, pewett@astro.gsu.edu,
419-460-0072

TIME REQUESTED: 7 nights

1. APR 27-MAY 03
2. FEB 02-08
3. FEB 09-15

7 nights are requested to observe ~14 stars for photometric
variability.

Note: PI Pewett and CoI Silverstein (also requesting a week of ARCSAT
time) will coordinate observing to take advantage of weather
conditions in order to maximize the science.

INSTRUMENT: SurveyCam

FILTERS: Johnson Cousins VRI

COMMENTS: 

BRIEF SCIENCE JUSTIFICATION: The Main Sequence (MS) can span more than
three magnitudes in Mv for spectral types M0V to M5V, indicating that
stars of similar temperature differ by a factor of 16 in luminosity.
This implies that red dwarfs with identical V-K colors differ in
radius by a factor of four ... but why?

For her PhD thesis work, the PI is using various methods to uncover
the underlying causes of this widening of the MS.  Here we propose to
use the ARCSAT 0.5m to observe northern nearby (within 25pc) M dwarf
stars with accurate parallaxes and excellent photometry (hence, the MS
positions are not in question) to obtain short-term variability data
that can provide insight into the surface magnetic field activity of
these stars.  We will regularly observe a target for up to 5 hours
with the longest exposures being 300s, which will allow us to observe
two stars each night.  We do not require photometric conditions, nor a
completely dark sky as we are doing relative photometry.  So far we
have successfully observed 14 stars with ARCSAT and the initial
results for 8 full reduced stars indicate that we can routinely reach
a one standard deviation level in variability of ~4 mmags.  These data
will complement our spectroscopy efforts on the APO 3.5m to measure
metallicities, astrometric work to measure space velocities to probe
age characteristics, and programs at CTIO to sample southern stars.
Our goal is to obtain astrometric, photometric, and spectroscopic sets
of data on a minimum of 100 stars.  The ARCSAT monitoring is an
important piece of the thesis work that will allow us to understand
the role of magnetic activity in the width of the low mass MS.