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Coronagraphic near-IR photometry of AB Doradus C
Context: Observations of low-mass companions for which the dynamicalmasses are well constrained help to improve the calibration ofevolutionary models. Such observations thereby provide more confidencein the estimation of the mass of a companion using the photometricmethods expected for the next generation of planet finder instruments.Aims: The commissioning of a new coronagraph at the Very LargeTelescope (VLT) was the occasion to test the performance of thistechnique on the well-known object AB Dor A and its 0.09 M_?companion AB Dor C. The purpose of this paper is to refine thephotometric analysis on this object and to provide an accuratephotometric error budget. Methods: In addition to coronagraphy,we calibrated the residual stellar halo with a reference star. We usedstandard techniques for photometric extraction. Results: Thecompanion AB Dor C is easily detected at 0.185'' from the primary star,and its magnitudes in H and Ks are in agreement with an M 5.5 object, asalready known from spectroscopic observations. However, these newmeasurements make the earlier J-band photometry less reliable. Finally,the comparison with evolutionary models supports an age of (75 ±25) Myr, contrary to previous analyses. These observations demonstratethat coronagraphic observations can be more efficient than directimaging, not only to improve contrast, but also to provide a betterphotometric estimation as long as a good calibration of the stellar halois achieved.
| Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. I. The Stellar Calibrator Sample and the 24 μm Calibration
We present the stellar calibrator sample and the conversion frominstrumental to physical units for the 24 μm channel of the MultibandImaging Photometer for Spitzer (MIPS). The primary calibrators are Astars, and the calibration factor based on those stars is4.54×10-2 MJy sr-1 (DNs-1)-1, with a nominal uncertainty of 2%. Wediscuss the data reduction procedures required to attain this accuracy;without these procedures, the calibration factor obtained using theautomated pipeline at the Spitzer Science Center is 1.6%+/-0.6% lower.We extend this work to predict 24 μm flux densities for a sample of238 stars that covers a larger range of flux densities and spectraltypes. We present a total of 348 measurements of 141 stars at 24 μm.This sample covers a factor of ~460 in 24 μm flux density, from 8.6mJy up to 4.0 Jy. We show that the calibration is linear over that rangewith respect to target flux and background level. The calibration isbased on observations made using 3 s exposures; a preliminary analysisshows that the calibration factor may be 1% and 2% lower for 10 and 30 sexposures, respectively. We also demonstrate that the calibration isvery stable: over the course of the mission, repeated measurements ofour routine calibrator, HD 159330, show a rms scatter of only 0.4%.Finally, we show that the point-spread function (PSF) is well measuredand allows us to calibrate extended sources accurately; InfraredAstronomy Satellite (IRAS) and MIPS measurements of a sample of nearbygalaxies are identical within the uncertainties.
| MSX, 2MASS, and the LARGE MAGELLANIC CLOUD: A Combined Near- and Mid-Infrared View
The Large Magellanic Cloud (LMC) has been observed by the MidcourseSpace Experiment (MSX) in the mid-infrared and the Two Micron All SkySurvey (2MASS) in the near-infrared. We have performed across-correlation of the 1806 MSX catalog sources and nearly 1.4 million2MASS cataloged point and extended sources and find 1664 matches. Usingthe available color information, we identify a number of stellarpopulations and nebulae, including main-sequence stars, giant stars, redsupergiants, carbon- and oxygen-rich asymptotic giant branch (AGB)stars, planetary nebulae, H II regions, and other dusty objects likelyassociated with early-type stars. A total of 731 of these sources haveno previous identification. We compile a listing of all objects, whichincludes photometry and astrometry. The 8.3 μm MSX sensitivity is thelimiting factor for object detection: only the brighter red objects,specifically the red supergiants, AGB stars, planetary nebulae, and H IIregions, are detected in the LMC. The remaining objects are likely inthe Galactic foreground. The spatial distribution of the infrared LMCsources may contribute to understanding stellar formation and evolutionand the overall galactic evolution. We demonstrate that a combined mid-and near-infrared photometric baseline provides a powerful means ofidentifying new objects in the LMC for future ground-based andspace-based follow-up observations.
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Besorolás csoportokba:
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Pozíciós és asztrometriai adatok
| Csillagkép: | Aranyhal |
| Rektaszcenzió: | 06h00m07.71s |
| Deklináció: | -64°18'36.0" |
| Vizuális fényesség: | 7.098 |
| Távolság: | 254.453 parszek |
| RA sajátmozgás: | -5.3 |
| Dec sajátmozgás: | 28.9 |
| B-T magnitude: | 8.381 |
| V-T magnitude: | 7.204 |
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