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Imaging Young Giant Planets From Ground and Space
High-contrast imaging can find and characterize gas giant planets aroundnearby young stars and the closest M stars, complementing radialvelocity and astrometric searches by exploring orbital separationsinaccessible to indirect methods. Ground-based coronagraphs are alreadyprobing within 25 AU of nearby young stars to find objects as small as .This paper contrasts near-term and future ground-based capabilities withhigh-contrast imaging modes of the James Webb Space Telescope (JWST).Monte Carlo modeling reveals that JWST can detect planets with masses assmall as across a broad range of orbital separations. We present newcalculations for planet brightness as a function of mass and age forspecific JWST filters and extending to .
| 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.
| An Unbiased Survey of 500 Nearby Stars for Debris Disks: A JCMT Legacy Program
We present the scientific motivation and observing plan for an upcomingdetection survey for debris disks using the James Clerk MaxwellTelescope. The SCUBA-2 Unbiased Nearby Stars (SUNS) survey will observe500 nearby main-sequence and subgiant stars (100 of each of the A, F, G,K, and M spectral classes) to the 850 ?m extragalactic confusionlimit to search for evidence of submillimeter excess, an indication ofcircumstellar material. The survey distance boundaries are 8.6, 16.5,22, 25, and 45 pc for M, K, G, F, and A stars, respectively, and alltargets lie between the declinations of -40° to 80°. In thissurvey, no star will be rejected based on its inherent properties:binarity, presence of planetary companions, spectral type, or age. Thesurvey will commence in late 2007 and will be executed over 390 hr,reaching 90% completion within 2 years. This will be the first unbiasedsurvey for debris disks since the Infrared Astronomical Satellite. Weexpect to detect ~125 debris disks, including ~50 cold disks notdetectable in current shorter wavelength surveys. To fully exploit theorder of magnitude increase in debris disks detected in thesubmillimeter, a substantial amount of complementary data will berequired, especially at shorter wavelengths, to constrain thetemperatures and masses of discovered disks. High-resolution studieswill likely be required to resolve many of the disks. Therefore, thesesystems will be the focus of future observational studies using avariety of observatories, including Herschel, ALMA, and JWST, tocharacterize their physical properties. For nondetected systems, thissurvey will set constraints (upper limits) on the amount ofcircumstellar dust, of typically 200 times the Kuiper Belt mass, but aslow as 10 times the Kuiper Belt mass for the nearest stars in the sample(~2 pc).
| 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.
| 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.
| The Serendipitous Discovery of a Debris Disk around the A Dwarf HD 46190
The Infrared Spectrograph on the Spitzer Space Telescope has observedseveral A dwarfs as potential standards and cross-calibrators, and oneof these stars, HD 46190, shows the spectroscopic signature of a debrisdisk. The disk produces a spectral excess that can be fitted with a coolblackbody of ~81 K. If the emitting particles are spherical blackbodies,they would lie at a distance of ~82 AU from the central star. Thespectrum from the disk can also be fitted with a spectrum risingproportionally with wavelength, and this spectral behavior is consistentwith material falling into the inner disk as a result ofPoynting-Robertson drag.
| Rest-Frame Mid-Infrared Detection of an Extremely Luminous Lyman Break Galaxy with the Spitzer Infrared Spectrograph (IRS)
We present the first rest-frame ~4 ?m detection of a Lyman breakgalaxy. The data were obtained using the 16 ?m imaging capability ofthe Spitzer Infrared Spectrograph. The target object,J134026.44+634433.2, is an extremely luminous Lyman break galaxy atz=2.79, first identified in Sloan Digital Sky Survey (SDSS) spectra (asreported by Bentz et al.). The source is strongly detected with a fluxof 0.94+/-0.02 mJy. Combining Spitzer and SDSS photometry withsupporting ground-based J- and K-band data, we show that the spectralenergy distribution is consistent with an actively star-forming galaxy.We also detect other objects in the Spitzer field of view, including avery red mid-infrared source. We find no evidence of a strong lens amongthe mid-infrared sources.Based on observations obtained with the Spitzer Space Telescope, whichis operated by JPL, California Institute of Technology, for the NationalAeronautics and Space Administration.The IRS is a collaborative venture between Cornell University and BallAerospace Corporation that was funded by NASA through JPL.
| Hyades and Sirius supercluster members brighter than magnitude (V) 7.1. II - Right ascension six to twelve hours
The present star sample is contained in the Bright Star Catalogue andits Supplement, augmented with a further supplement of 788 stars foundduring various observing programs over the past 40 years. Accurate,four-color and H-beta, or (RI), photometry is available for most of thesupercluster members. The criteria for membership are the comparisons ofthe proper motion, radial velocity, and luminosity obtained from thesupercluster parameters with the observed motions and the luminosityderived from the photometric parameters. New proper motions, based onall available catalogs, have been derived for the additional 788 starsdiscussed here, as well as all supercluster members.
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| קבוצת-כוכבים: | צייר |
| התרוממות ימנית: | 06h27m48.62s |
| סירוב: | -62°08'59.7" |
| גודל גלוי: | 6.609 |
| מרחק: | 78.989 פארסק |
| תנועה נכונה: | 3 |
| תנועה נכונה: | 23.8 |
| B-T magnitude: | 6.709 |
| V-T magnitude: | 6.618 |
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