Searches for extrasolar planets have uncovered an astonishing diversity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search ...method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of ~0.71 and ~0.27 times the mass of Jupiter and orbital separations of ~2.3 and ~4.6 astronomical units orbiting a primary star of mass ~0.50 solar mass at a distance of ~1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
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The All Sky Automated Survey (ASAS) is a long-term project to monitor bright variable stars over the whole sky. It has discovered 50 099 variables brighter than V < 14 mag south of declination +28°, ...and among them 11 076 eclipsing binaries. We present a preliminary analysis of 5384 contact, 2949 semi-detached, and 2743 detached systems. The statistics of the distribution provides a qualitative confirmation of decades old idea of Flannery and Lucy that the W UMa-type binaries evolve through a series of relaxation oscillations: the ASAS finds comparable number of contact and semi-detached systems. The most surprising result is a very small number of detached eclipsing binaries with periods P < 1 d, the systems believed to be the progenitors of the W UMa stars. As many (perhaps all) contact binaries have companions, there is a possibility that some were formed in a Kozai cycle, as suggested by Eggleton and his associates.
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We present a measurement of the microlensing optical depth toward the Galactic bulge based on 4 years of the OGLE-II survey. We consider only bright sources in the extended red clump giant (RCG) ...region of the color-magnitude diagram, in 20 bulge fields covering 65 deg super(2) between 0 < l < 3 and -4 < b < -2 . Using a sample of 32 events we find t = 2.55 -0.46 +0.57 x 10 super(-6) at (l, b) = (1:16, - 2:75). Taking into account the measured gradient along the Galactic latitude b, t = (4.48 c 2.37) + (0.78 c 0.84) x b x 10 super(-) super(6), this value is consistent with previous measurements using RCG sources and recent theoretical predictions. We determine the microlensing parameters and select events using a model light curve that allows for flux blending. Photometric quality delivered by difference image analysis (DIA) combined with the 1."3 median seeing of the OGLE-II images are sufficient to constrain and reject the majority of strong blends. We find that 638% of the OGLE-II events that appear to have RCG sources are actually due to much fainter stars blended with a bright companion. We show explicitly that model fits without blending result in similar t estimates through partial cancellation of contributions from higher detection efficiency, underestimated timescales, and a larger number of selected events. The near cancellation of the optical depth bias and the fact that microlensing event selection based on models without blending discriminates against blends have been utilized by previous analyses based on RCG sources. The latter approach, however, leads to biased timescale distributions and event rates. Consequently, microlensing studies should carefully consider source confusion effects even for bright stars.
Gamma-ray bursts from quark stars Paczyński, B.; Haensel, P.
Monthly Notices of the Royal Astronomical Society Letters,
09/2005, Volume:
362, Issue:
1
Journal Article
Peer reviewed
Open access
Long gamma-ray bursts (GRBs) are believed to be related to the explosion of Type Ic supernovae, which have been stripped of their hydrogen and helium envelopes. There appear to be two types of these ...explosions: those that are approximately spherical (GRB 980425/SN 1998bw), and which are associated with weak bursts; and the classical GRBs which generate ultrarelativistic jets (GRB 030329/SN 2003dh). If this bimodality is real, Swift will provide clear evidence for it. We propose that classical powerful GRBs, which generate ultrarelativistic outflows, are a result of the formation of quark stars. Quark stars may provide additional energy for the explosion of Type Ic supernovae, but far more important is the creation of a surface which acts as a membrane that cannot be penetrated by baryons. A surface of a quark star allows only ultrarelativistic matter to escape: photons, neutrinos, electron–positron pairs and magnetic fields. The formation of a quark star follows several minutes after the initial core collapse. Possible evidence for this time delay is provided by BATSE precursors to GRBs, as analysed by Lazzati.
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Among over 200 000 Galactic bulge variable stars in the public domain Optical Gravitational Lensing Experiment (OGLE) catalogue, we found over 15 000 red giant variables following two well-defined ...period–amplitude relations. The periods are in the range 10 < P < 100 d, and amplitudes in the range 0.005 < A < 0.13 mag in the I band. The variables cover a broad range of reddening-corrected colours, 1 < (V−I)0 < 5, and a fairly narrow range of extinction-corrected apparent magnitudes, 10.5 < I0 < 13. A subset of variables (type A) has an rms scatter of only 0.44 mag. The average magnitudes for these stars are well correlated with the Galactic longitude, and vary from Ik,0= 11.82 for l=+ 8° to Ik,0= 12.07 for l=−5°, clearly indicating that they are located in the Galactic bar. Most variables have several oscillation periods.
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We report the discovery of a several-Jupiter-mass planetary companion to the primary lens star in microlensing event OGLE-2005-BLG-071. Precise ( 1%) photometry at the peak of the event yields an ...extremely high signal-to-noise ratio detection of a deviation from the light curve expected from an isolated lens. The planetary character of this deviation is easily and unambiguously discernible from the gross features of the light curve. Detailed modeling yields a tightly constrained planet-star mass ratio of q = p sub(p)/M = 0.0071 c 0.0003. This is the second robust detection of a planet with microlensing, demonstrating that the technique itself is viable and that planets are not rare in the systems probed by microlensing, which typically lie several kiloparsecs toward the Galactic center.
A model of AW UMa Paczyński, B.; Sienkiewicz, R.; Szczygieł, D. M.
Monthly Notices of the Royal Astronomical Society,
July 2007, Volume:
378, Issue:
3
Journal Article
Peer reviewed
Open access
The contact binary AW UMa has an extreme mass ratio, with the more-massive component (the current primary) close to the main sequence, while the low-mass star at q≈ 0.1 (the current secondary) has a ...much larger radius than a main-sequence star of a comparable mass. We propose that the current secondary has almost exhausted hydrogen in its centre and is much more advanced in its evolution, as suggested by Stȩpień. Presumably the current secondary lost most of its mass during its evolution with part of it transferred to the current primary. After losing a large fraction of its angular momentum, the binary may evolve into a system of FK Com type.
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