35 research outputs found
A Search for Variable Stars and Planetary Occultations in NGC 2301 II: Variability
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 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 (2 mmag and larger) and most present complex light curves
containing multiple periods suggestive of their inclusion in the Sct
and 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.Comment: 25 pages, 21 figures Accepted to PAS
WIYN Open Cluster Study. XIX. Main Sequence Fitting Distances to Open Clusters Using V-K Color-Magnitude Diagrams
We have combined existing optical magnitudes for stars in seven open clusters
and 54 field stars with the corresponding JHKs photometry from the Two Micron
All Sky Survey (2MASS). Combining optical with near-IR photometry broadens the
color baseline minimizing the influence of photometric errors and allows better
discrimination between cluster stars and contaminating foreground and
background populations. The open clusters in this study include NGC 2516, M35,
M34, NGC 3532, M37, M67, and NGC 188. The field stars we are using possess high
quality Hipparcos parallaxes and well-determined metal abundances allowing us
to empirically determine the dependence of (V-K) color on metal abundance in
the range -0.45<=[Fe/H]<=+0.35. Using this relation along with the parallaxes
of the field stars, we are able to construct an unevolved main sequence in the
[Mv,(V-K)o] diagram for a specific abundance. These diagrams are then used to
fit to the cluster main sequences in the [V,V-K] color-magnitude diagram in
order to estimate a distance for each open cluster. We find that the resultant
distances are within the range of distances found in the literature via the
main sequence fitting technique. It is hoped that this will spur an expansion
of the current (limited) database of star clusters with high quality (V-K)
photometry down to the unevolved main sequence.Comment: 17 pages, 7 figures, to appear in The Astronomical Journal - February
200