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מאמרים קשורים
Spectroscopic Confirmation of a z = 2.79 Multiply Imaged Luminous Infrared Galaxy Behind the Bullet Cluster
We report spectroscopic confirmation and high-resolution infraredimaging of a z = 2.79 triply imaged galaxy behind the Bullet Cluster.This source, a Spitzer-selected luminous infrared galaxy, is confirmedvia polycyclic aromatic hydrocarbon (PAH) features using the SpitzerInfrared Spectrograph (IRS) and resolved with Hubble Space TelescopeWide Field Camera 3 imaging. In this galaxy, which with a stellar mass M* ? 4 × 109 M sun is one ofthe two least massive ones studied with IRS at z>2, we also detectH2 S(4) and H2 S(5) pure rotational lines (at3.1? and 2.1?)—the first detection of these molecularhydrogen lines in a high-redshift galaxy. From the molecular hydrogenlines we infer an excitation temperature T = 377+68-84 K. The detection of these lines indicates that thewarm molecular gas mass is 6+36 -4% of thestellar mass and implies the likely existence of a substantial reservoirof cold molecular gas in the galaxy. Future spectral observations atlonger wavelengths with facilities such as the Herschel SpaceObservatory, the Large Millimeter Telescope, and the Atacama PathfinderExperiment thus hold the promise of precisely determining the totalmolecular gas mass. Given the redshift, and using refined astrometricpositions from the high-resolution imaging, we also update themagnification estimate and derived fundamental physical properties ofthis system. The previously published values for L IR, starformation rate, and dust temperature are confirmed modulo the revisedmagnification; however, we find that PAH emission is roughly a factor of5 stronger than would be predicted by the relations between LIR and L PAH reported for SMGs and starbursts inPope et al.
| Absolute Physical Calibration in the Infrared
We determine an absolute calibration for the Multiband ImagingPhotometer for Spitzer 24 μm band and recommend adjustments to thepublished calibrations for Two Micron All Sky Survey (2MASS), InfraredArray Camera (IRAC), and IRAS photometry to put them on the same scale.We show that consistent results are obtained by basing the calibrationon either an average A0V star spectral energy distribution (SED), or byusing the absolutely calibrated SED of the Sun in comparison withsolar-type stellar photometry (the solar analog method). After therejection of a small number of stars with anomalous SEDs (or badmeasurements), upper limits of ~1.5% root mean square (rms) are placedon the intrinsic infrared (IR) SED variations in both A-dwarf andsolar-type stars. These types of stars are therefore suitable asgeneral-purpose standard stars in the IR. We provide absolutelycalibrated SEDs for a standard zero magnitude A star and for the Sun toallow extending this work to any other IR photometric system. They allowthe recommended calibration to be applied from 1 to 25 μm with anaccuracy of ~2%, and with even higher accuracy at specific wavelengthssuch as 2.2, 10.6, and 24 μm, near which there are directmeasurements. However, we confirm earlier indications that Vega does notbehave as a typical A0V star between the visible and the IR, making itproblematic as the defining star for photometric systems. Theintegration of measurements of the Sun with those of solar-type starsalso provides an accurate estimate of the solar SED from 1 through 30μm, which we show agrees with theoretical models.
| 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.
| Debris Disk Evolution around A Stars
We report 24 and/or 70 μm measurements of ~160 A-type main-sequencestars using the Multiband Imaging Photometer for Spitzer (MIPS). Theirages range from 5 to 850 Myr, based on estimates from the literature(cluster or moving group associations) or from the H-R diagram andisochrones. The thermal infrared excess is identified by comparing thedeviation (~3% and ~15% at the 1 σ level at 24 and 70 μm,respectively) between the measurements and the synthetic Kuruczphotospheric predictions. Stars showing excess infrared emission due tostrong emission lines or extended nebulosity seen at 24 μm areexcluded from our sample; therefore, the remaining infrared excesses arelikely to arise from circumstellar debris disks. At the 3 σconfidence level, the excess rate at 24 and 70 μm is 32% and >=33%(with an uncertainty of 5%), considerably higher than what has beenfound for old solar analogs and M dwarfs. Our measurements placeconstraints on the fractional dust luminosities and temperatures in thedisks. We find that older stars tend to have lower fractional dustluminosity than younger ones. While the fractional luminosity from theexcess infrared emission follows a general 1/t relationship, the valuesat a given stellar age vary by at least 2 orders of magnitude. We alsofind that (1) older stars possess a narrow range of temperaturedistribution peaking at colder temperatures, and (2) the disk emissionat 70 μm persists longer than that at 24 μm. Both results suggestthat the debris disk clearing process is more effective in the innerregions.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Decay of Planetary Debris Disks
We report new Spitzer 24 μm photometry of 76 main-sequence A-typestars. We combine these results with previously reported Spitzer 24μm data and 24 and 25 μm photometry from the Infrared SpaceObservatory and the Infrared Astronomy Satellite. The result is a sampleof 266 stars with mass close to 2.5 Msolar, all detected toat least the ~7 σ level relative to their photospheric emission.We culled ages for the entire sample from the literature and/orestimated them using the H-R diagram and isochrones; they range from 5to 850 Myr. We identified excess thermal emission using an internallyderived K-24 (or 25) μm photospheric color and then compared allstars in the sample to that color. Because we have excluded stars withstrong emission lines or extended emission (associated with nearbyinterstellar gas), these excesses are likely to be generated by debrisdisks. Younger stars in the sample exhibit excess thermal emission morefrequently and with higher fractional excess than do the older stars.However, as many as 50% of the younger stars do not show excessemission. The decline in the magnitude of excess emission, for thosestars that show it, has a roughly t0/time dependence, witht0~150 Myr. If anything, stars in binary systems (includingAlgol-type stars) and λ Boo stars show less excess emission thanthe other members of the sample. Our results indicate that (1) there issubstantial variety among debris disks, including that a significantnumber of stars emerge from the protoplanetary stage of evolution withlittle remaining disk in the 10-60 AU region and (2) in addition, it islikely that much of the dust we detect is generated episodically bycollisions of large planetesimals during the planet accretion end game,and that individual events often dominate the radiometric properties ofa debris system. This latter behavior agrees generally with what we knowabout the evolution of the solar system, and also with theoreticalmodels of planetary system formation.
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דרקון |
| התרוממות ימנית: | 17h52m25.37s |
| סירוב: | +60°23'47.0" |
| גודל גלוי: | 6.856 |
| מרחק: | 196.464 פארסק |
| תנועה נכונה: | -2.3 |
| תנועה נכונה: | 42.4 |
| B-T magnitude: | 7.085 |
| V-T magnitude: | 6.875 |
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