86 research outputs found
Long-term variability survey of the old open cluster NGC 6791
We present the results of a long-term variability survey of the old open
cluster NGC 6791. The BVI observations, collected over a time span of 6 years,
were analyzed using the ISIS image subtraction package. The main target of our
observations were two cataclysmic variables B7 and B8. We have identified
possible cycle lenghts of about 25 and 18 days for B7 and B8, respectively. We
tentatively classify B7 as a VY Scl type nova-like variable or a Z Cam type
dwarf nova. B8 is most likely an SS Cygni type dwarf nova. We have also
extracted the light curves of 42 other previously reported variable stars and
discovered seven new ones. The new variables show long-period or non-periodic
variability. The long baseline of our observations has also allowed us to
derive more precise periods for the variables, especially for the short period
eclipsing binaries.Comment: 13 pages LaTeX, including 8 PostScript figures and 4 tables. To
appear in June 2003 issue of The Astronomical Journa
The eclipsing massive X-ray binary M33 X-7: New X-ray observations and optical identification
The eclipsing X-ray binary M33 X-7 was in the field of view during several
observations of our XMM-Newton M33 survey and in the archival Chanfdra
observation 1730 which cover a large part of the 3.45 d orbital period. We
detect emission of M33 X-7 during eclipse and a soft X-ray spectrum of the
source out of eclipse that can best be described by bremsstrahlung or disk
blackbody models. No significant regular pulsations of the source in the range
0.25-1000 s were found. The average source luminosity out of eclipse is 5E37
erg/s (0.5-4.5 keV). In a special analysis of DIRECT observations we identify
as optical counterpart a B0I to O7I star of 18.89 mag in V which shows the
ellipsoidal heating light curve of a high mass X-ray binary with the M33 X-7
binary period. The location of the X-ray eclipse and the optical minima allow
us to determine an improved binary period and ephemeris of mid-eclipse as HJD
(2451760.61+-0.09)+- N * (3.45376+-0.00021). The mass of the compact object
derived from orbital parameters and the optical companion mass, the lack of
pulsations, and the X-ray spectrum of M33 X-7 may indicate that the compact
object in the system is a black hole. M33 X-7 would be the first detected
eclipsing high mass black hole X-ray binary.Comment: 9 pages including 6 figures, A&A accepte
The DIRECT project: Catalogs of stellar objects in nearby galaxies. II. Eastern arm and NGC 206 in M31
DIRECT is a project to directly obtain the distances to two important
galaxies in the cosmological distance ladder, M31 and M33, using detached
eclipsing binaries and Cepheids. As part of our search for these variables, we
have obtained photometry and positions for thousands of stellar objects within
the monitored fields, covering an area of 557.8 arcmin^2. In this research note
we present the equatorial coordinates and BVI photometry for 26712 stars in the
M31 galaxy, along the eastern arm and in the vicinity of the star forming
region NGC206.Comment: 2 LaTeX pages, 2 Postscript figures, submitted to Astronomy &
Astrophysic
DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. VIII. Additional Variables in the Field M33B Discovered with Image Subtraction
DIRECT is a project to obtain directly the distances to two Local Group
galaxies, M31 and M33, which occupy a crucial position near the bottom of the
cosmological distance ladder. As the first step of the DIRECT project we have
searched for detached eclipsing binaries (DEBs) and new Cepheids in the M31 and
M33 galaxies with 1m-class telescopes. In this eighth paper we present a
catalog of variable stars discovered in the data from the followup observations
of DEB system D33J013337.0+303032.8 in field M33B [(RA,Dec)= (23.48, 30.57),
J2000.0], collected with the Kitt Peak National Observatory 2.1m telescope. In
our search covering an area of 108 sq. arcmin. we have found 895 variable
stars: 96 eclipsing binaries, 349 Cepheids, and 450 other periodic, possible
long period or non-periodic variables. Of these variables 612 are newly
discovered. Their light curves were extracted using the ISIS image subtraction
package. For 77% of the variables we present light curves in standard V and B
magnitudes, with the remaining 23% expressed in units of differential flux. We
have discovered a population of first overtone Cepheid candidates and for six
of them we present strong arguments in favor of this interpretation. The
catalog of variables, as well as their photometry (about 9.2*10^4 BV
measurements) and finding charts, is available electronically via anonymous ftp
and the World Wide Web. The complete set of the CCD frames is available upon
request.Comment: 21 pages of text, 27 pages of tables, 14 figures; version with full
resolution figures available through ftp at
ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/papers/M33B2
DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. V. Variables in the Field M31F
We undertook a long term project, DIRECT, to obtain the direct distances to
two important galaxies in the cosmological distance ladder -- M31 and M33 --
using detached eclipsing binaries (DEBs) and Cepheids. While rare and difficult
to detect, DEBs provide us with the potential to determine these distances with
an accuracy better than 5%. The extensive photometry obtained in order to
detect DEBs provides us with good light curves for the Cepheid variables. These
are essential to the parallel project to derive direct Baade-Wesselink
distances to Cepheids in M31 and M33. For both Cepheids and eclipsing binaries,
the distance estimates will be free of any intermediate steps.
As a first step in the DIRECT project, between September 1996 and October
1997 we obtained 95 full/partial nights on the F. L. Whipple Observatory 1.2 m
telescope and 36 full nights on the Michigan-Dartmouth-MIT 1.3 m telescope to
search for DEBs and new Cepheids in the M31 and M33 galaxies. In this paper,
fifth in the series, we present the catalog of variable stars found in the
field M31F [(\alpha,\delta)= (10.\arcdeg10, 40.\arcdeg72), J2000.0]. We have
found 64 variable stars: 4 eclipsing binaries, 52 Cepheids and 8 other
periodic, possible long period or non-periodic variables. The catalog of
variables, as well as their photometry and finding charts, is available via
anonymous ftp and the World Wide Web. The complete set of the CCD frames is
available upon request.Comment: submitted to the Astronomical Journal, 31 pages, 18 figures; paper
and data available at ftp://cfa-ftp.harvard.edu/pub/kstanek/DIRECT/ and
through WWW at http://cfa-www.harvard.edu/~kstanek/DIRECT
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