Paper: astro-ph/0508051
Date: Mon, 1 Aug 2005 20:48:14 GMT (373kb)

Title: Transit Photometry of the Core-Dominated Planet HD 149026b

Authors: David Charbonneau, Joshua N. Winn, David W. Latham, Gaspar Bakos,
Emilio E. Falco, Matthew J. Holman, Robert W. Noyes, Balazs Csak, Gilbert A.
Esquerdo, Mark E. Everett, and Francis T. O'Donovan

Comments: 18 pages, 4 figures, submitted to ApJ
\\
We report g, V, and r photometric time series of HD 149026 spanning predicted
times of transit of the Saturn-mass planetary companion, which was recently
discovered by Sato and collaborators. We present a joint analysis of our
observations and the previously reported photometry and radial velocities of
the central star. We refine the estimate of the transit ephemeris to Tc [HJD] =
2453527.87455^{+0.00085}_{-0.00091} + N * 2.87598^{+0.00012}_{-0.00017}.
Assuming that the star has a radius of 1.45 +/- 0.10 R_Sun and a mass of 1.30
+/- 0.10 M_Sun, we estimate the planet radius to be 0.726 +/- 0.064 R_Jup,
which implies a mean density of 1.07^{+0.42}_{-0.30} g/cm^3. This density is
significantly greater than that predicted for models which include the effects
of stellar insolation and for which the planet has only a small core of solid
material. Thus we confirm that this planet likely contains a large core, and
that the ratio of core mass to total planet mass is more akin to that of Uranus
and Neptune than that of either Jupiter or Saturn.

\\ ( http://arXiv.org/abs/astro-ph/0508051 , 373kb)

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Paper: astro-ph/0508052
Date: Mon, 1 Aug 2005 21:17:12 GMT (121kb)

Title: Observations of 51 Ophiuchi with MIDI at the VLTI

Authors: C. Gil, F. Malbet, M. Schoeller, O. Chesneau and Ch. Leinert

Comments: 5 pages, 3 figures, 2 tables, to be published in the proceedings of
"The Power of Optical / IR Interferometry: Recent Scientific Results and 2nd
Generation VLTI Instrumentation", Garching, April 4-8, 2005
\\
We present interferometric observations of the Be star 51 Ophiuchi. These
observations were obtained during the science demonstration phase of the MIDI
instrument at the Very Large Telescope Interferometer (VLTI). Using MIDI, a
Michelson 2 beam combiner that operates at the N band (8 to 13 microns), we
obtained for the first time observations of 51 Oph in the mid-infrared at
high-angular resolution. It is currently known that this object presents a
circumstellar dust and gas disk that shows a very different composition from
other Herbig Ae disks. The nature of the 51 Oph system is still a mystery to be
solved. Does it have a companion? Is it a protoplanetary system? We still don't
know. Observations with MIDI at the VLTI allowed us to reach high-angular
resolution (20 mas).We have several uv points that allowed us to constrain the
disk model. We have modeled 51 Oph visibilities and were able to constrain the
size and geometry of the 51 Oph circumstellar disk.

\\ ( http://arXiv.org/abs/astro-ph/0508052 , 121kb)

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Paper: astro-ph/0508081
Date: Tue, 2 Aug 2005 16:15:08 GMT (106kb)

Title: Testing the Rate of False Planetary Transits due to Binary Star Blending

Authors: G\'eza Kov\'acs & G\'asp\'ar Bakos

Comments: 5 pages with 4 figures. To appear in the Poster Proceedings of the
Symposium held in May 2-5, 2005 at the Space Telescope Science Institute,
Baltimore: "A Decade of Extrasolar Planets around Normal Stars", ed.: Mario
Livio
\\
We investigate the rate of false planetary transit detection due to blending
with eclipsing binaries. Our approach is purely empirical and is based on the
analysis of the artificially blended light curves of the eclipsing binary stars
in the Large Magellanic Cloud from the archive of the Optical Gravitational
Lensing Experiment (OGLE). Employing parameters that characterize the
significance of the transit and the amplitude of the variation out of the
transit, we can substantially limit the number of potential false positives.
Further constraint comes from the expected length of the transit by a possible
planetary companion. By the application of these criteria we are left only with
18 candidates from the full sample of 2495 stars. Visual inspection of these
remaining variables eliminates all of them for obvious reasons (e.g., for
visible fingerprints of orbital eccentricity). We draw the attention to the
short-period stars, where the false alarm rate is especially low.

\\ ( http://arXiv.org/abs/astro-ph/0508081 , 106kb)

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