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An Upper Limit on the Albedo of HD 209458b: Direct Imaging Photometry with the MOST Satellite
We present space-based photometry of the transiting exoplanetary systemHD 209458 obtained with the Microvariablity and Oscillations of Stars(MOST) satellite, spanning 14 days and covering 4 transits and 4secondary eclipses. The HD 209458 photometry was obtained in MOST'slower precision direct imaging mode, which is used for targets in thebrightness range 6.5>=V>=13. We describe the photometric reductiontechniques for this mode of observing, in particular the corrections forstray earthshine. We do not detect the secondary eclipse in the MOSTdata, to a limit in depth of 0.053 mmag (1 σ). We set a 1 σupper limit on the planet-star flux ratio of 4.88×10-5corresponding to a geometric albedo upper limit in the MOST bandpass(400-700 nm) of 0.25. The corresponding numbers at the 3 σ levelare 1.34×10-4 and 0.68, respectively. HD 209458b ishalf as bright as Jupiter in the MOST bandpass. This low geometricalbedo value is an important constraint for theoretical models of the HD209458b atmosphere, in particular ruling out the presence of reflectiveclouds. A second MOST campaign on HD 209458 is expected to be sensitiveto an exoplanet albedo as low as 0.13 (1 σ), if the star does notbecome more intrinsically variable in the meantime.MOST is a Canadian Space Agency mission, operated jointly by Dynacon,Inc., and the Universities of Toronto and British Columbia, withassistance from the University of Vienna.
| Detection of Transits of Extrasolar Giant Planets with Inexpensive Telescopes and CCDs
A typical short-period giant planet occulting a parent star can producea ~1% dimming of the star's light for an interval of several hours. Thecombination of photometric and Doppler radial velocity (RV) measurementsof a transiting extrasolar planet can yield unambiguous measurements ofthe planet's mass, radius, density, and exact orbital parameters. Inthis article, we describe a low-cost observational and data-reductionpipeline which can be used to obtain 3 millimagnitude photometry with asmall-aperture telescope and a consumer-grade CCD detector. Thisprecision is sufficient to reliably detect the transit of a giantplanet. We discuss noise sources, and evaluate strategies for achievinga low overall noise floor. We describe the performance of our pipelinein a successful observation of an HD 209458 "b" transit, and in aphotometric survey of GJ 876 during an epoch in which we predicted thatGJ 876 "c" (P ~30d) could potentially be observed to transit. We alsobriefly describe the status of the ongoing www.transitsearch.orgproject, which coordinates a photometric search for planetary transitsamong known planet-bearing stars.
| Speckle Observations of Binary Stars with the WIYN Telescope. III. A Partial Survey of A, F, and G Dwarfs
Two hundred thirty nearby main-sequence stars with spectral types in therange of A to G have been observed by way of speckle interferometryusing the WIYN 3.5 m telescope at Kitt Peak, Arizona. The stars had noprevious mention of duplicity in the literature. Of those observed, 14showed clear evidence of a companion, and 63 were classified assuspected nonsingle based on a power spectrum analysis. The remainingstars discussed show no evidence of duplicity to the limit of thedetection system in high-quality observations. The WIYN Observatory is ajoint facility of the University of Wisconsin-Madison, IndianaUniversity, Yale University, and the National Optical AstronomyObservatory.
| Detection of Planetary Transits of the Star HD 209458 in the Hipparcos Data Set
A search of the Hipparcos satellite photometry data for the star HD209458 reveals evidence for a planetary transit signature consistentwith the planetary properties reported by Henry et al. and Charbonneauet al. and allows further refinement of the planet's orbital period. Thelong time baseline (about 2926 days or 830 periods) from the bestHipparcos transit-like event to the latest transit reported by Henry etal. for the night of 1999 November 15 (UT) allows for an orbital perioddetermination of 3.524736 days with an uncertainty of 0.000045 days (3.9s). The transit events observed by Charbonneau et al. fall at theinterim times expected to within the errors of this newly derivedperiod. A series of statistical tests was performed to assess thelikelihood of these events occurring by chance. This was crucial giventhe ill-conditioned problem presented by the sparse sampling of thelight curve and the non-Gaussian distribution of the points. Monte Carlosimulations using bootstrap methods with the actual Hipparcos HD 209458data set indicate that the transit-like signals of the depth observedwould only be produced by chance in 21 out of 1 million trials. Thetransit durations and depths obtained from the Hipparcos data are alsoconsistent with those determined by Charbonneau et al. and Henry et al.within the limitations of the sampling intervals and photometricprecision of the Hipparcos data.
| A new list of 617 radial velocities in four galactic fields
Four stellar fields in the -30 deg galactic latitude have been surveyedfor radial velocities, using a 62 cm objective prism. Exact positions,spectral types, and approximate magnitudes are provided for 617 stars infour different 4 x 4 deg fields. B to F4 stars were found which haveGaussian velocity distributions.
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| Takýmyýldýz: | Kanatli At |
| Sað Açýklýk: | 22h02m21.33s |
| Yükselim: | +18°49'59.2" |
| Görünürdeki Parlaklýk: | 8.332 |
| Uzaklýk: | 166.113 parsek |
| özdevim Sað Açýklýk: | 37.9 |
| özdevim Yükselim: | -4.2 |
| B-T magnitude: | 8.638 |
| V-T magnitude: | 8.358 |
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