904 research outputs found
The Optical Gravitational Lensing Experiment. Additional Planetary and Low-Luminosity Object Transits from the OGLE 2001 and 2002 Observational Campaigns
The photometric data collected by OGLE-III during the 2001 and 2002
observational campaigns aiming at detection of planetary or low-luminosity
object transits were corrected for small scale systematic effects using the
data pipeline by Kruszewski and Semeniuk and searched again for low amplitude
transits. Sixteen new objects with small transiting companions, additional to
previously found samples, were discovered. Most of them are small amplitude
cases which remained undetected in the original data.
Several new objects seem to be very promising candidates for systems
containing substellar objects: extrasolar planets or brown dwarfs. Those
include OGLE-TR-122, OGLE-TR-125, OGLE-TR-130, OGLE-TR-131 and a few others.
Those objects are particularly worth spectroscopic follow-up observations for
radial velocity measurements and mass determination. With well known
photometric orbit only a few RV measurements should allow to confirm their
actual status.
All photometric data of presented objects are available to the astronomical
community from the OGLE Internet archive.Comment: 8 pages. Appendix in 'jpg' format. Minor changes. Full resolution
pages of Appendix and photometric data presented in the paper are available
from the OGLE Internet archive: See http://ogle.astrouw.edu.pl or its US
mirror, at http://bulge.princeton.edu/~ogl
The Optical Gravitational Lensing Experiment. Planetary and Low-Luminosity Object Transits in the Carina Fields of the Galactic Disk
We present results of the second planetary and low-luminosity object transit
campaign conducted by the OGLE-III survey. Three fields (35'x35' each) located
in the Carina regions of the Galactic disk (l~290) were monitored continuously
in February-May 2002. About 1150 epochs were collected for each field. The
search for low depth transits was conducted on about 103000 stars with
photometry better than 15 mmag. In total, we discovered 62 objects with shallow
depth (<0.08 mag) flat-bottomed transits. For each of these objects several
individual transits were detected and photometric elements were determined.
Also lower limits on radii of the primary and companion were calculated. The
2002 OGLE sample of stars with transiting companions contains considerably more
objects that may be Jupiter-sized (R<1.6 R_Jup) compared to our 2001 sample.
There is a group of planetary candidates with the orbital periods close to or
shorter than one day. If confirmed as planets, they would be the shortest
period extrasolar planetary systems. In general, the transiting objects may be
extrasolar planets, brown dwarfs, or M-type dwarfs. One should be, however,
aware that in some cases unresolved blends of regular eclipsing stars can mimic
transits. Future spectral analysis and eventual determination of the amplitude
of radial velocity should allow final classification. High resolution
spectroscopic follow-up observations are, therefore, strongly encouraged. All
photometric data are available from the OGLE Internet archive.
Note added for astro-ph version: One of the best planetary candidates from
the OGLE 2001 campaign, OGLE-TR-56, has recently been confirmed as a planetary
system by Konacki, Torres, Jha and Sasselov [astro-ph/0301052].Comment: 12 pages. Three pages of Appendix included ('jpg' format). Full
resolution pages of Appendix and photometric data presented in the paper are
available from the OGLE Internet archive: http://www.astrouw.edu.pl/~ogle or
its US mirror http://bulge.princeton.edu/~ogl
The Optical Gravitational Lensing Experiment. Variable Baseline Microlensing Events in the Galactic Bulge
We present the first systematic search for microlensing events with
variability in their baselines using data from the third phase of the Optical
Gravitational Lensing Experiment (OGLE-III). A total of 137 candidates (88 new)
was discovered toward the Galactic bulge. Among these, 21 have periodic
oscillations in their baselines, 111 are irregular variables and 5 are
potential long period detached eclipsing binaries. This is about 10% of the
total number of constant baseline events. They are hence quite common and can
be regarded as a new type of exotic events, which allow the determination of
extra parameters of the events. We show that microlensing of variable stars may
allow us to break the degeneracy between the blending parameter and
magnification. We note that in some cases variability hidden in the baseline
due to strong blending may be revealed in highly magnified events and resemble
other exotic microlensing behavior, including planetary deviation. A new system
(VEWS) for detecting ongoing variable baseline microlensing events is
presented.Comment: The paper with high quality figures is available from
http://www.astrouw.edu.pl/~wyrzykow/varbaseevents.ps.g
Mass Estimates for Some of the Binary Lenses in OGLE III Database
We model binary microlensing events OGLE 2003-BLG-170, 267, and 291. Source
angular sizes are measured for the events 267 and 291. Model fits to the light
curves give parallaxes for the events 267 and 291, and relative source sizes
for 170 and 267. Selfconsistency arguments provide extra limits on the models
of the event 291. As a result we obtain likelihood estimate of the lens mass
for the event 170, mass measurement based on angular size and parallax for 267,
and narrow limits on mass in the case of 291. Brown dwarfs are most likely
candidates for some of the lens components. The influence of the binary lens
rotation and the Earth parallax may be important but hard to distinguish when
modeling relatively short lasting binary lens events.Comment: 15 pages, 8 figure
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. Small Amplitude Variable Red Giants in the Magellanic Clouds
We present analysis of the large sample of variable red giants from the Large
and Small Magellanic Clouds detected during the second phase of the Optical
Gravitational Lensing Experiment (OGLE-II) and supplemented with OGLE-III
photometry. Comparing pulsation properties of detected objects we find that
they constitute two groups with clearly distinct features. In this paper we
analyze in detail small amplitude variable red giants (about 15400 and 3000
objects in the LMC and SMC, respectively). The vast majority of these objects
are multi-periodic. At least 30% of them exhibit two modes closely spaced in
the power spectrum, what likely indicates non-radial oscillations. About 50%
exhibit additional so called Long Secondary Period.
To distinguish between AGB and RGB red giants we compare PL diagrams of
multi-periodic red giants located above and below the tip of the Red Giant
Branch (TRGB). The giants above the TRGB form four parallel ridges in the PL
diagram. Among much more numerous sample of giants below the TRGB we find
objects located on the low luminosity extensions of these ridges, but most of
the stars are located on the ridges slightly shifted in logP. We interpret the
former as the second ascent AGB red giants and the latter as the first ascent
RGB objects. Thus, we empirically show that the pulsating red giants fainter
than the TRGB are a mixture of RGB and AGB giants.
Finally, we compare the Petersen diagrams of the LMC, SMC and Galactic bulge
variable red giants and find that they are basically identical indicating that
the variable red giants in all these different stellar environments share
similar pulsation properties.Comment: 23 pages, 13 figures included in GIF forma
The Optical Gravitational Lensing Experiment. Cepheids in the Galaxy IC1613: No Dependence of the Period--Luminosity Relation on Metallicity
We present results of the search for Cepheids in the galaxy IC1613 carried
out as a sub-project of the OGLE-II microlensing survey. 138 Cepheids were
found in the 14.2x14.2 arcmin region in the center of the galaxy. We present
light curves, VI photometry and basic data for all these objects, as well as
color-magnitude diagram of the observed field.
The Period--Luminosity (PL) diagrams for IC1613 fundamental mode Cepheids for
VI and interstellar extinction insensitive index W_I are constructed.
Comparison of PL relations in metal poor galaxy IC1613 ([Fe/H]~-1.0 dex) with
relations in metal richer Magellanic Clouds allows us to study dependence of
Cepheid PL relations on metallicity in the wide range of metallicities covered
by these three galaxies. The slopes of PL relations in IC1613 are identical as
in the Magellanic Clouds. The comparison of brightness of Cepheids with the
magnitudes of the tip of the red giant branch stars and RR Lyr stars in all
three objects provides information on the stability of zero points of PL
relations in the I and V-band, respectively. We find that the zero points of PL
relations are constant to better than mag over the entire range of
covered metallicities. Thus, the most important conclusion of the paper is that
the Cepheid PL relations do not depend on metallicity. Additionally we
determine the mean distance to IC1613, based on the common distance scale
resulting from four major stellar distance indicators: Cepheids, RR Lyr, TRGB
and red clump stars. The distance modulus to IC1613 is equal to
(m-M)_IC1613=24.20 mag with the standard deviation of +/-0.02 mag from six
measurements and systematic uncertainty of calibrations of +/-0.07 mag.Comment: 21 pages, Latex. Acta Astronomica submitted. Only one page of
Appendix A included. All pages of Appendix A and photometric data presented
in the paper are available from the OGLE Internet archive:
http://www.astrouw.edu.pl/~ogle or its US mirror
http://www.astro.princeton.edu/~ogl
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. 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
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