SETI public: A Search for Variable Stars and Planetary Occultations in NGC 2301 II

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Paper: astro-ph/0509558
Date: Mon, 19 Sep 2005 18:46:04 GMT (368kb)

Title: A Search for Variable Stars and Planetary Occultations in NGC 2301
II:
Variability

Authors: Steve B. Howell, Cassandra VanOutryve, John L. Tonry, Mark E.
Everett, and Raelin Schneider

Categories: astro-ph

Comments: 25 pages, 21 figures Accepted to PASP
\\
We performed R-band time series observations of the young, metal rich open
cluster NGC 2301 for 12 nights in Feb. 2004. B images were also obtained and
color magnitude diagrams, having limits of R=19.5 and B=21.5, were produced.
Only asmall effort was made to determine cluster membership as our magnitude
limits are far deeper than previously published values. Our photometric
precision, for the brightest 5 magnitudes of sources, is 1-2 mmag. We
determine
that for the $\sim$4000 stars which have time-series data, 56% are variable
and
of these, approximately 13% are observed to exhibit periodic light curves
ranging from tens of minutes to days. We present some examples of the light
curves obtained and produce cuts in variability space based on parameters
such
as color and amplitude. The percentage of variability is approximately equal
across all colors with the majority of variables having amplitudes of 0.15
magnitudes or less. In general, redder stars show larger variability
amplitudes. We find a smooth decline in the number of periodic variables
toward
longer period. This decline is probably due to a transition from intrinsic
to
extrinsic variability and, in part, to our limited observing period of 12
nights. Essentially all the A and F main sequence stars in our sample are
variable ($\sim$2 mmag and larger) and most present complex light curves
containing multiple periods suggestive of their inclusion in the $\delta$Sct
and $\gamma$Dor classes. A variable non-cluster member giant and two
variable
white dwarf candidates are discussed. Our equational description of
variability
is shown to be an excellent predictive tool for determining the cumulative
fraction of variables that will be observed in a photometric survey. Our
entire
dataset is available electronically.

\\ ( http://arXiv.org/abs/astro-ph/0509558 , 368kb)

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