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Direct imaging photometry with the MOST satellite
Canada's first space telescope, MOST (Microvariablity and Oscillationsof Stars) was successfully launched on June 30, 2003 with a primarymission to perform ultra-high-precision photometry to detect acousticoscillations in solar-like stars. MOST has the ability to observe singlefields for uninterrupted periods of up to two months and targets can beobserved either through Fabry lens imaging or Direct imaging. Thisreport reviews the Direct imaging capabilities of the MOST satellite andthe extraction of accurate stellar photometry.MOST is a Canadian Space Agency mission, operated jointly by Dynacon, Inc., and the Universities of Toronto and British Columbia, with assistance from the University of Vienna.
| 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.
| An Astrometric Study of Procyon
We report on the analysis of observations of Procyon obtained with theMultichannel Astrometric Photometer during the years 1986-2004. Whilethe results significantly increase the precision of the estimatedcharacteristics of the components of the system, they are generally ingood agreement with the most recent studies. The F5 IV primary is foundto have a mass of 1.43+/-0.034 Msolar, while the white dwarfcompanion's mass is 0.58+/-0.014 Msolar. The distance modulusis 2.277+/-0.005 mag, yielding an absolute visual magnitude for thecombined light of the system of 2.640+/-0.006 and an absolute visualmagnitude of the secondary of 13.20+/-0.05. The residuals of the fit ofthe positions of the photocenter to the excepted orbit support theparameters of that orbit, showing only a slight deviation in rightascension. The most significant improvements in our knowledge of thebinary system can be made with further measurements of the separation ofthe components. The masses found here tend to reaffirm the recent modelsof the nature of the primary and secondary stars.
| Estimation of a super-resolved PSF for the data reduction of undersampled stellar observations. Deriving an accurate model for fitting photometry with Corot space telescope
Context: .Fitting photometry algorithms can be very effective providedthat an accurate model of the instrumental point spread function (PSF)is available. When high-precision time-resolved photometry is required,however, the use of point-source star images as empirical PSF models canbe unsatisfactory, due to the limits in their spatial resolution.Theoretically-derived models, on the other hand, are limited by theunavoidable assumption of simplifying hypothesis, while the use ofanalytical approximations is restricted to regularly-shaped PSFs.Aims: .This work investigates an innovative technique for space-basedfitting photometry, based on the reconstruction of an empirical butproperly-resolved PSF. The aim is the exploitation of arbitrary starimages, including those produced under intentional defocus. The cases ofboth MOST and COROT, the first space telescopes dedicated totime-resolved stellar photometry, are considered in the evaluation ofthe effectiveness and performances of the proposed methodology.Methods: .PSF reconstruction is based on a set of star images,periodically acquired and presenting relative subpixel displacements dueto motion of the acquisition system, in this case the jitter of thesatellite attitude. Higher resolution is achieved through the solutionof the inverse problem. The approach can be regarded as a specialapplication of super-resolution techniques, though a specialisedprocedure is proposed to better meet the PSF determination problemspecificities. The application of such a model to fitting photometry isillustrated by numerical simulations for COROT and on a complete set ofobservations from MOST. Results: .We verify that, in bothscenarios, significantly better resolved PSFs can be estimated, leadingto corresponding improvements in photometric results. For COROT, indeed,subpixel reconstruction enabled the successful use of fitting algorithmsdespite its rather complex PSF profile, which could hardly be modeledotherwise. For MOST, whose direct-imaging PSF is closer to the ordinary,comparison to other models or photometry techniques were carried out andconfirmed the potential of PSF reconstruction in real observationalconditions.
| No stellar p-mode oscillations in space-based photometry of Procyon
Pressure-driven (p-mode) oscillations at the surface of the Sun,resulting from sound waves travelling through the solar interior, are apowerful probe of solar structure, just as seismology can reveal detailsabout the interior of the Earth. Astronomers have hoped to exploitp-mode asteroseismology in Sun-like stars to test detailed models ofstellar structure and evolution, but the observations are extremelydifficult. The bright star Procyon has been considered one of the bestcandidates for asteroseismology, on the basis of models and previousreports of p-modes detected in ground-based spectroscopy. Here wepresent a search for p-modes in 32 days of nearly continuous photometricsatellite-based observations of Procyon. If there are p-modes inProcyon, they must have lifetimes less than 2-3 days and/or peakamplitudes <15 parts per million, which defy expectations from theSun's oscillations and previous theoretical predictions. Targetselection for future planned asteroseismology space missions may need tobe reconsidered, as will the theory of stellar oscillations.
| A catalog of far-ultraviolet point sources detected with the fast FAUST Telescope on ATLAS-1
We list the photometric measurements of point sources made by the FarUltraviolet Space Telescope (FAUST) when it flew on the ATLAS-1 spaceshuttle mission. The list contains 4698 Galactic and extragalacticobjects detected in 22 wide-field images of the sky. At the locationssurveyed, this catalog reaches a limiting magnitude approximately afactor of 10 fainter than the previous UV all-sky survey, TDl. Thecatalog limit is approximately 1 x 10-14 ergs A sq cm/s,although it is not complete to this level. We list for each object theposition, FUV flux, the error in flux, and where possible anidentification from catalogs of nearby stars and galaxies. Thesecatalogs include the Michigan HD (MHD) and HD, SAO, the HIPPARCOS InputCatalog, the Position and Proper Motion Catalog, the TD1 Catalog, theMcCook and Sion Catalog of white dwarfs, and the RC3 Catalog ofGalaxies. We identify 2239 FAUST sources with objects in the stellarcatalogs and 172 with galaxies in the RC3 catalog. We estimate thenumber of sources with incorrect identifications to be less than 2%.
| Photometry of astrometric reference stars
UBVRI, DDO, and uvby, H-beta photometry of astrometric reference starsis presented. Spectral types and luminosity classifications made fromthe colors are used to determine their spectroscopic parallaxes. In thispaper, colors for 309 stars in 25 regions are given, and classificationsfor 210 stars have been made. These stars form reference frames in theAllegheny Observatory Multichannel Astrometric Photometer astrometricprogram, and in the Praesepe cluster reduced by Russell (1976). It isfound that the present photometric spectral types are reliable to within2.5 spectral subclasses.
| Spectroscopic parallaxes of MAP region stars from UBVRI, DDO, and uvbyH-beta photometry
This paper presents the results of spectral type and luminosityclassification of reference stars in the Allegheny Observatory MAPparallax program, using broadband and intermediate-band photometry. Inaddition to the use of UBVRI and DDO photometric systems, the uvbyH-betaphotometric system was included for classification of blue (B - V lessthan 0.6) reference stars. The stellar classifications made from thephotometry are used to determine spectroscopic parallaxes. Thespectroscopic parallaxes are used in turn to adjust the relativeparallaxes measured with the MAP to absolute parallaxes. A new methodfor dereddening stars using more than one photometric system ispresented. In the process of dereddening, visual extinctions, spectraltypes, and luminosity classes are determined, as well as a measure ofthe goodness of fit. The measure of goodness of fit quantifiesconfidence in the stellar classifications. It is found that the spectraltypes are reliable to within 2.5 spectral subclasses.
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Observation and Astrometry data
| Constellation: | Canis Minor |
| Right ascension: | 07h38m17.76s |
| Declination: | +04°56'34.6" |
| Apparent magnitude: | 7.965 |
| Proper motion RA: | -11.1 |
| Proper motion Dec: | 2.5 |
| B-T magnitude: | 8.243 |
| V-T magnitude: | 7.988 |
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