27,451 research outputs found
The Second Galex Ultraviolet Variability (GUVV-2) Catalog
We present the second Galaxy Evolution Explorer (GALEX) Ultraviolet
Variability (GUVV-2) Catalog that contains information on 410 newly discovered
time-variable sources gained through simultaneous near (NUV 1750-2750A) and far
(FUV 1350-1750A) ultraviolet photometric observations. Source variability was
determined by comparing the NUV and/or FUV fluxes derived from orbital
exposures recorded during a series of multiple observational visits to 169
GALEX fields on the sky. These sources, which were contained within a sky-area
of 161 square deg, varied on average by amplitudes of NUV = 0.6 mag and FUV =
0.9 mag during these observations. Of the 114 variable sources in the catalog
with previously known identifications, 67 can be categorized as being active
galaxies (QSO's, Seyfert 1 or BL Lac objects). The next largest groups of UV
variables are RR Lyrae stars, X-ray sources and novae.
By using a combination of UV and visible color-color plots we have been able
to tentatively identify 36 possible RR Lyrae and/or Delta Scuti type stars, as
well as 35 probable AGN's, many of which may be previously unidentified QSO's
or blazars. Finally, we show data for 3 particular variable objects: the
contact binary system of SDSS J141818.97+525006.7, the eclipsing dwarf nova
system of IY UMa and the highly variable unidentified source SDSS
J104325.06+563258.1.Comment: Astronomical Journal accepte
Photometric variability in the old open cluster M 67. II. General Survey
We use differential CCD photometry to search for variability in BVI among 990
stars projected in and around the old open cluster M 67. In a previous paper we
reported results for 22 cluster members that are optical counterparts to X-ray
sources; this study focuses on the other stars in our observations. A variety
of sampling rates were employed, allowing variability on time scales ranging
from \sim 0.3 hours to \sim 20 days to be studied. Among the brightest sources
studied, detection of variability as small as sigma approx 10 mmag is achieved
(with > 3 sigma confidence); for the typical star observed, sensitivity to
variability at levels sigma approx 20 mmag is achieved. The study is unbiased
for stars with 12.5 < B < 18.5, 12.5 < V < 18.5, and 12 < I < 18 within a
radius of about 10 arcmin from the cluster centre. In addition, stars with 10 <
BVI < 12.5 were monitored in a few small regions in the cluster. We present
photometry for all 990 sources studied, and report the variability
characteristics of those stars found to be variable at a statistically
significant level. Among the variables, we highlight several sources that merit
future study, including stars located on the cluster binary sequence, stars on
the giant branch, blue stragglers, and a newly discovered W UMa system.Comment: 12 pages, including 6 figures and 5 tables. Tables 1 and 3 only
available in electronic version of paper. Accepted by A&
Time-Series Photometry of M67: W UMa Systems, Blue Stragglers, and Related Systems
We present an analysis of over 2200 V images taken on 14 nights at the Mt.
Laguna 1 m telescope of the open cluster M67. Our observations overlap but
extend beyond the field analyzed by Gilliland et al. (1991), and complement
data recently published by van den Berg et al. (2002) and Stassun et al.
(2002). We show variability in the light curves of all 4 of the known W UMa
variables on timescales ranging from a day to decades (for AH Cnc). We have
modeled the light curve of AH Cnc, and the total eclipses allow us to determine
q = 0.16 +0.03/-0.02 and i = 86 +4/-8 degrees. The position of this system near
the turnoff of M67 makes it useful for constraining the turnoff mass for the
cluster. We have also detected two unusual features in the light curve of AH
Cnc that may be caused by prominences. We have also monitored cluster blue
stragglers for variability, and we present evidence hinting at low level
variations in the stragglers S752, S968, and S1263, and we place limits on the
variability of a number of other cluster blue stragglers. Finally, we provide
photometry of the sub-subgiant branch star S1063 showing variability on
timescales similar to the orbital period, while the ``red straggler'' S1040
shows evidence of an unexplained drop in brightness at phases corresponding to
the passage of the white dwarf in front of the giant.Comment: 44 pages, 16 figures, AASTeX, accepted for A
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