664 research outputs found
The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Galactic Bulge Fields
We present OGLE-III Photometric Maps of the Galactic bulge fields observed
during the third phase of the OGLE project. This paper describes the last,
concluding set of maps based on OGLE-III data.
The maps contain precise, calibrated VI photometry of about 340 million stars
from 267 fields in the Galactic bulge observed during entire OGLE-III phase
(2002-2009), covering about 92 square degrees in the sky. Precise astrometry of
these objects is also provided.
We briefly discuss the photometry procedures and the quality of the data. We
also present sample data and color-magnitude diagrams of the observed fields.
All photometric data are available to the astronomical community from the
OGLE Internet archive.Comment: 15 pages, 12 figure
The Optical Gravitational Lensing Experiment. The Catalog of Stellar Proper Motions toward the Magellanic Clouds
We present a catalog of over 6.2 million stars with measured proper motions.
All these stars are observed in the direction of the Magellanic Clouds within
the brightness range 12 < I < 19 mag. Based on these proper motions about 440
000 Galactic foreground stars can be selected. Because the proper motions are
based on a few hundred epochs collected during eight years, their statistical
uncertainties are below 0.5 mas/yr for stars brighter than I = 18.5 mag. The
parallaxes are derived with uncertainties down to 1.6 mas. For above 13 000
objects parallaxes are derived with significance above 3\sigma, which allows
selecting around 270 white dwarfs (WDs). The search for common proper motion
binaries among stars presented was performed resulting in over 500 candidate
systems. The most interesting ones are candidate halo main sequence star-WD and
WD-WD systems. The application of the catalog to empirically bound the Cepheid
instability strip is also discussed
The Optical Gravitational Lensing Experiment. High Proper Motion Stars in the OGLE-III Data for Magellanic Clouds Fields
We present the results of a search for High Proper Motion (HPM) stars, i.e.
the ones with \mu > 100 mas/yr, in the direction to the Magellanic Clouds. This
sky area was not examined in detail as the high stellar density hampers efforts
in performing high-quality astrometry.
Altogether 549 HPM stars were found with median uncertainties of proper
motions per coordinate equal to 0.5 mas/yr. The fastest HPM star has the proper
motion of 722.19 +/- 0.74 mas/yr. For the majority of objects (70%) parallaxes
were also measured. The highest value found is \pi = 91.3 +/-1.6 mas. The
parallaxes were used to estimate absolute magnitudes which enriched with color
information show that 21 of HPM stars are white dwarfs. Other 23 candidate
white dwarfs were selected of HPM stars with no measurable parallaxes using
color-magnitude diagram. The search for common proper motion binaries revealed
27 such pairs in the catalog. The completeness of the catalog is estimated to
be > 80% and it is slightly higher than for previous catalogs in the direction
to the Magellanic Clouds
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. X. Enigmatic Class of Double Periodic Variables in the Large Magellanic Cloud
The tenth part of the OGLE-III Catalog of Variable Stars contains 125 Double
Periodic Variables (DPVs) from the Large Magellanic Cloud. DPVs are
semi-detached binaries which show additional variability with a period around
33 times longer than the orbital period. The cause of this long cycle is not
known and previous studies suggest it involves circumbinary matter. We discuss
the properties of the whole sample of the LMC DPVs and put more attention to
particularly interesting objects which may be crucial for verifying hypothesis
explaining long cycle variability. Secondary eclipses of one of the objects
disappear during some orbital cycles and primary eclipses are deeper during
long cycle minimum.Comment: 18 pages, 11 figure
The Optical Gravitational Lensing Experiment. Triple-Mode and 1O/3O Double-Mode Cepheids in the Large Magellanic Cloud
We report the discovery of three new triple-mode classical Cepheids in the
Large Magellanic Cloud, two of them with the fundamental, first overtone and
second overtone excited, and one pulsating simultaneously in the first three
overtones. Thus, the number of triple-mode Cepheids in the LMC is increased to
five. We also present two objects belonging probably to a new type of
double-mode Cepheids having the first and third overtones excited. We measure
the rates of period change in these stars and detect decrease of periods in two
of them, what is in conflict with theoretical predictions.Comment: 10 pages, 5 figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. V. R Coronae Borealis Stars in the Large Magellanic Cloud
The fifth part of the OGLE-III Catalog of Variable Stars presents 23 R CrB
(RCB) stars in the Large Magellanic Cloud (LMC). 17 of these objects have been
spectroscopically confirmed by previous studies, while 6 stars are new
candidates for RCB variables. We publish the VI multi-epoch OGLE photometry for
all objects.
We use the sample of carbon-rich long-period variables released in the
previous part of this catalog to select objects with severe drops in
luminosity, i.e. with the DY-Per-like light curves. DY Per stars are often
related to R CrB variables. We detect at least 600 candidates for DY Per stars,
mostly among dust enshrouded giants. We notice that our candidate DY Per stars
form a continuity with other carbon-rich long-period variables, so it seems
that DY Per stars do not constitute a separate group of variable stars.Comment: 13 pages, 5 color figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VII. Classical Cepheids in the Small Magellanic Cloud
The seventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS)
consists of 4630 classical Cepheids in the Small Magellanic Cloud (SMC). The
sample includes 2626 fundamental-mode (F), 1644 first-overtone (1O), 83
second-overtone (2O), 59 double-mode F/1O, 215 double-mode 1O/2O, and three
triple-mode classical Cepheids. For each object basic parameters, multi-epoch
VI photometry collected within 8 or 13 years of observations, and finding
charts are provided in the OGLE Internet archive. We present objects of
particular interest: exceptionally numerous sample of single-mode
second-overtone pulsators, five double Cepheids, two Cepheids with eclipsing
variations superimposed on the pulsation light curves. At least 139
first-overtone Cepheids exhibit low-amplitude secondary variations with periods
in the range 0.60-0.65 of the primary ones. These stars populate three distinct
sequences in the Petersen diagram. The origin of this secondary modulation is
still unknown. Contrary to the Large Magellanic Cloud (LMC) we found only a few
candidates for anomalous Cepheids in the SMC. This fact may be a clue for the
explanation of the origin of the anomalous Cepheids. The period and luminosity
distributions of Cepheids in both Magellanic Clouds suggest that there are two
or three populations of classical Cepheids in each of the galaxies. The main
difference between the LMC and SMC lays in different numbers of Cepheids in
each group. We fit the period-luminosity (PL) relations of SMC Cepheids and
compare them with the LMC PL laws.Comment: 23 pages, 11 (color) figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VI. Delta Scuti Stars in the Large Magellanic Cloud
The sixth part of the OGLE-III catalog of Variable Stars presents \delta Sct
pulsators in the Large Magellanic Cloud. Altogether 2786 variable stars were
found and amongst them 92 are multi-mode objects, including 67 stars pulsating
in the fundamental mode and the first overtone (F/1O), nine double-mode
pulsators with various combinations of the first three overtones excited
(1O/2O, 2O/3O and 1O/3O pulsators), and two triple mode (F/1O/2O) \delta Sct
stars. In total 1490 of stars are marked as uncertain, due to scattered
photometry and small amplitudes. For single-mode objects it was not possible to
unambiguously identify pulsation mode, however we suggest the most of the
single-mode variable stars pulsate in the first overtone.Comment: 16 pages, 7 figure
The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Large Magellanic Cloud
We present the OGLE-III Photometric Maps of the Large Magellanic Cloud. They
cover about 40 square degrees of the LMC and contain mean, calibrated VI
photometry and astrometry of about 35 million stars observed during seven
observing seasons of the third phase of the Optical Gravitational Lensing
Experiment - OGLE-III.
We discuss the quality of data and present color-magnitude diagrams of
selected fields. The OGLE-III Photometric Maps of the LMC are available to the
astronomical community from the OGLE Internet archive.Comment: 8 pages, 9 figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II. Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud
In the second part of the OGLE-III Catalog of Variable Stars (OIII-CVS) we
present 197 type II Cepheids and 83 anomalous Cepheids in the Large Magellanic
Cloud (LMC). The sample of type II Cepheids consists of 64 BL Her stars, 96 W
Vir stars and 37 RV Tau stars. Anomalous Cepheids are divided into 62
fundamental-mode and 21 first-overtone pulsators. These are the largest samples
of such types of variable stars detected anywhere outside the Galaxy.
We present the period-luminosity and color-magnitude diagrams of stars in the
sample. If the boundary period between BL Her and W Vir stars is adopted at 4
days, both groups differ significantly in (V-I) colors. We identify a group of
16 peculiar W Vir stars with different appearance of the light curves, brighter
and bluer than ordinary stars of that type. Four of these peculiar W Vir stars
show additional eclipsing modulation superimposed on the pulsation light
curves. Four other stars of that type show long-period secondary variations
which may be ellipsoidal modulations. It suggests that peculiar W Vir subgroup
may be related to binarity. In total, we identified seven type II Cepheids
simultaneously exhibiting eclipsing variations which is a very large fraction
compared to classical Cepheids in the LMC. We discuss diagrams showing Fourier
parameters of the light curve decomposition against periods. Three sharp
features interpreted as an effect of resonances between radial modes are
detectable in these diagrams for type II Cepheids.Comment: 20 pages, 9 figure
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