Probing the Stellar Surface of HD 209458 from Multicolor Transit Observations

Multicolor photometric observations of a planetary transit in the system HD 209458 are analyzed. The observations, made in the Stromgren photometric system, allowed a recalculation of the basic physical properties of the star-planet system. This includes derivation of linear limb-darkening values of HD 209458, which is the first time that a limb-darkening sequence has observationally been determined for a star other than the Sun. As the derived physical properties depend on assumptions that are currently known with limited precision only, scaling relations between derived parameters and assumptions are given. The observed limb-darkening is in good agreement with theoretical predictions from evolutionary stellar models combined with ATLAS model atmospheres, verifying these models for the temperature (Teff ~ 6000K), surface gravity (log g ~ 4.3) and mass (~ 1.2 Msol) of HD 209458.Comment: 16 pages, 8 figures, uses elsart.cls, accepted for New Astronom

Planetary Transits Toward the Galactic Bulge

The primary difficulty with using transits to discover extrasolar planets is the low probability a planet has of transiting its parent star. One way of overcoming this difficulty is to search for transits in dense stellar fields, such as the Galactic bulge. Here I estimate the number of planets that might be detected from a monitoring campaign toward the bulge. A campaign lasting 10 nights on a 10 meter telescope (assuming 8 hours of observations per night and a 5'x5' field of view) would detect about 100 planets with radius \rp=1.5 \rjup, or about 30 planets with \rp=1.0 \rjup, if the frequency and distribution of planets in the bulge is similar to that in the solar neighborhood. Most of these planets will be discovered around stars just below the turn-off, i.e. slightly evolved G-dwarfs. Campaigns involving 1- or 4-m class telescopes are unlikely to discover any planets, unless there exists a substantial population of companions with \rp > 1.5 \rjup.Comment: 4 pages, 4 figures. Submitted to ApJ Letter

Non-grey dimming events of KIC 8462852 from GTC spectrophotometry

We report ground-based spectrophotometry of KIC 8462852, during its first dimming events since the end of the Kepler mission. The dimmings show a clear colour-signature, and are deeper in visual blue wavelengths than in red ones. The flux loss' wavelength dependency can be described with an \AA ngstr\"om absorption coefficient of $2.19\pm0.45$, which is compatible with absorption by optically thin dust with particle sizes on the order of 0.0015 to 0.15 $\mu$m. These particles would be smaller than is required to be resistant against blow-out by radiation pressure when close to the star. During occultation events, these particles must be replenished on time-scales of days. If dust is indeed the source of KIC 8462852's dimming events, deeper dimming events should show more neutral colours, as is expected from optically thick absorbers.Comment: 5 pages, accepted for A&A letter

Limits to the presence of transiting circumbinary planets in CoRoT data

The CoRoT mission during its flight-phase 2007-2012 delivered the light-curves for over 2000 eclipsing binaries. Data from the Kepler mission have proven the existence of several transiting circumbinary planets. Albeit light-curves from CoRoT have typically lower precision and shorter coverage, CoRoT's number of targets is similar to Kepler, and some of the known circumbinary planets could potentially be detected in CoRoT data as well. The aim of this work has been a revision of the entire CoRoT data-set for the presence of circumbinary planets, and the derivation of limits to the abundances of such planets. We developed a code which removes the light curve of the eclipsing binaries and searches for quasi-periodic transit-like features in a light curve after removal of binary eclipses and instrumental features. The code needs little information on the sample systems and can be used for other space missions as well, like Kepler, K2, TESS and PLATO. The code is broad in the requirements leading to detections, but was tuned to deliver an amount of detections that is manageable in a subsequent, mainly visual, revision about their nature. In the CoRoT sample we identified three planet candidates whose transits would have arisen from a single pass across the central binary. No candidates remained however with transit events from multiple planetary orbits. We calculated the upper limits for the number of Jupiter, Saturn and Neptune sized planets in co-planar orbits for different orbital period ranges. We found that there are much less giant planets in short-periodic orbits around close binary systems than around single stars.Comment: Accepted for publication in A&A, 11 pages, 4 figures and 4 tables. Updated to fix error in acknowledgemen