תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
MIPSGAL: A Survey of the Inner Galactic Plane at 24 and 70 μm
MIPSGAL is a 278 deg2 survey of the inner Galactic planeusing the Multiband Infrared Photometer for Spitzer aboard the SpitzerSpace Telescope. The survey field was imaged in two passbands, 24 and 70μm with resolutions of 6″ and 18″, respectively. Thesurvey was designed to provide a uniform, well-calibrated andwell-characterized data set for general inquiry of the inner Galacticplane and as a longer-wavelength complement to the shorter-wavelengthSpitzer survey of the Galactic plane: Galactic Plane Infrared MappingSurvey Extraordinaire. The primary science drivers of the current surveyare to identify all high-mass (M>5 Mȯ) protostars inthe inner Galactic disk and to probe the distribution, energetics, andproperties of interstellar dust in the Galactic disk. The observationswere planned to minimize data artifacts due to image latents at 24 μmand to provide full coverage at 70 μm. Observations at eclipticlatitudes within 15° of the ecliptic plane were taken at multipleepochs to help reject asteroids. The data for the survey were collectedin three epochs, 2005 September-October, 2006 April, and 2006 Octoberwith all of the data available to the public. The estimated point-sourcesensitivities of the survey are 2 and 75 mJy (3 σ) at 24 and 70μm, respectively. Additional data processing was needed to mitigateimage artifacts due to bright sources at 24 μm and detectorresponsivity variations at 70 μm due to the large dynamic range ofthe Galactic plane. Enhanced data products including artifact-mitigatedmosaics and point-source catalogs are being produced with the 24 μmmosaics already publicly available from the NASA/IPAC Infrared ScienceArchive. Some preliminary results using the enhanced data products aredescribed.
| Absolute Photometric Calibration of the Infrared Camera (IRC) aboard AKARI
The absolute photometric calibration of imaging observations with theInfrared Camera (IRC) aboard the AKARI satellite was performed bymonitoring the same stars regularly and by observing aset of standardstars. By our monitoring observations, we confirmed that all channels ofthe IRC were stable to within 4% and that their sensitivities wereconstant until the liquid helium was exhausted. Using the data of theserepeated observations, we evaluated the intrinsic errors as afunction ofthe brightnesses of objects and found that the errors increase rapidlytoward fainter objects. We also checked the consistency between shortand long exposure times, and confirmed that the data sampling had beenexecuted as designed. Finally, by comparing the estimated in-band fluxdensities and the observed data values of standard stars, we obtainedconversion factors to the absolute flux densities of all theband/exposure configurations. Their absolute uncertainties are estimatedto be less than 6%.
| NICMOS Spectrophotometry and Models for a Stars
Absolute flux distributions for eight stars are well measured from 0.8to 2.5 ?m with NICMOS grism spectrophotometry at a resolution of R ~100 and an accuracy of 1-2%. These spectral energy distributions (SEDs)are fitted with Castelli & Kurucz model atmospheres, and the resultsare compared with the Cohen-Walker-Witteborn (CWW) template models forthe same stars. In some cases, the T eff, log g, and log zparameters of the best-fitting model differ by up to 1000 K from theearlier CWW model. However, differences in the continua of the modeledinfrared flux distributions from 0.4 to 40 ?m are always less thanthe quoted CWW uncertainty of 5% because of compensating changes in themeasured extinction. At wavelengths longward of the 2.5 ?m NICMOSlimit, uncertainties still approach 5%, because A star models are notyet perfect. All of these A stars lie in the James Webb Space Telescope(JWST) continuous viewing zone and will be important absolute fluxstandards for the 0.8-30 ?m JWST wavelength range.
| Diameters and Albedos of Three Subkilometer Near-Earth Objects Derived from Spitzer Observations
Near-Earth objects (NEOs) are fragments of remnant primitive bodies thatdate from the era of solar system formation. At present, the physicalproperties and origins of NEOs are poorly understood. We have measuredthermal emission from three NEOs-(6037) 1988 EG, 1993 GD, and 2005GL-with Spitzer's IRAC instrument at 3.6, 4.5, 5.8, and 8.0 ?m (thelast object was detected only at 5.8 and 8.0 ?m). The diameters ofthese three objects are 400, 180, and 160 m, respectively, withuncertainties of around 20% (including both observational and systematicerrors). For all three the geometric albedos are around 0.30, inagreement with previous results that most NEOs are S-class asteroids.For the two objects detected at 3.6 and 4.5 ?m, diameters and albedosbased only on those data agree with the values based on modeling thedata in all four bands. This agreement, and the high sensitivity ofIRAC, shows the promise of the Spitzer Warm Mission for determining thephysical parameters for a large number of NEOs.
| 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.
| Steady State Evolution of Debris Disks around A Stars
This paper confronts a simple analytical model for the steady stateevolution of debris disks due to collisions with Spitzer observations ofdust around main-sequence A stars. It is assumed that every star has aplanetesimal belt, the initial mass and radius of which are drawn fromdistributions. In the model disk mass is constant until the largestplanetesimals reach collisional equilibrium, whereupon mass falls~t-1age. We find that the detection statistics andtrends seen at 24 and 70 μm can be fitted well by the model. Whilethere is no need to invoke stochastic evolution or delayed stirring toexplain the statistics, a moderate rate of stochastic events is notruled out. Potentially anomalous systems are identified by a high dustluminosity compared with the maximum permissible in the model (HD 3003,HD 38678, HD 115892, HD 172555); their planetesimals may have unusualproperties (high strength or low eccentricity), or this dust could betransient. The overall success of our model, which assumes planetesimalsin all belts have the same strength, eccentricity, and maximum size,suggests the outcome of planet formation is reasonably uniform. Thedistribution of planetesimal belt radii, once corrected for detectionbias, follows N(r)~r-0.8+/-0.3 for 3-120 AU. Since beltboundaries may be attributed to unseen planets, this provides a uniqueconstraint on A star planetary systems. It is also shown that P-R dragmay sculpt the inner edges of A star disks close to the Spitzerdetection threshold (HD 2262, HD 19356, HD 106591, HD 115892). Thismodel can be readily applied to the interpretation of future surveys,and predictions for the upcoming SCUBA-2 survey include that 17% of Astar disks should be detectable at 850 μm.
| 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
| Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
The Infrared Array Camera (IRAC) on the Spitzer Space Telescope isabsolutely calibrated by comparing photometry of a set of A stars nearthe north ecliptic pole to predictions based on ground-basedobservations and a stellar atmosphere model. The brightness of pointsources is calibrated to an accuracy of 3%, relative to models forA-star stellar atmospheres, for observations performed and analyzed inthe same manner as for the calibration stars. This includes correctionsfor the location of the star in the array and the location of thecentroid within the peak pixel. Long-term stability of the IRACphotometry was measured by monitoring the brightness of A dwarfs and Kgiants (near the north ecliptic pole) observed several times per month;the photometry is stable to 1.5% (rms) over a year.Intermediate-timescale stability of the IRAC photometry was measured bymonitoring at least one secondary calibrator (near the ecliptic plane)every 12 hr while IRAC was in nominal operations; the intermediate-termphotometry is stable, with a 1% dispersion (rms). One of the secondarycalibrators was found to have significantly time-variable (5%)mid-infrared emission, with a period (7.4 days) matching the opticallight curve; it is possibly a Cepheid variable.
| IRAC Observations of Taurus Pre-Main-Sequence Stars
We present infrared photometry obtained with the IRAC camera on theSpitzer Space Telescope of a sample of 82 pre-main-sequence stars andbrown dwarfs in the Taurus star-forming region. We find a clearseparation in some IRAC color-color diagrams between objects with andwithout disks. A few ``transition'' objects are noted, which correspondto systems in which the inner disk has been evacuated of small dust.Separating pure disk systems from objects with remnant protostellarenvelopes is more difficult at IRAC wavelengths, especially for objectswith infall at low rates and large angular momenta. Our resultsgenerally confirm the IRAC color classification scheme used in previouspapers by Allen et al. and Megeath et al. to distinguish betweenprotostars, T Tauri stars with disks, and young stars without (inner)disks. The observed IRAC colors are in good agreement with recentimproved disk models, and in general accord with models for protostellarenvelopes derived from analyzing a larger wavelength region. We alsocomment on a few Taurus objects of special interest. Our results shouldbe useful for interpreting IRAC results in other, less well studiedstar-forming regions.
| 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.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| Radial velocity measurements. I - Ground-based observations of the program stars for the HIPPARCOS satellite
The radial velocities of 272 stars brighter than m(pg) = 8.5 aredetermined by digital microphotometric measurement of plates obtainedwith dispersion 80 A/mm using the Marly slit spectrograph on the 120-cmtelescope of the Observatoire de Haute Provence. The objects wereselected as probable members of the input catalog for the ESA Hipparcosastrometric satellite. The measurement techniques and data-reductionprocedures are described in detail, and the results are presented inextensive tables and graphs and briefly characterized.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דרקון |
| התרוממות ימנית: | 18h02m30.74s |
| סירוב: | +58°37'38.2" |
| גודל גלוי: | 6.861 |
| מרחק: | 89.286 פארסק |
| תנועה נכונה: | -11.9 |
| תנועה נכונה: | 24.3 |
| B-T magnitude: | 7.02 |
| V-T magnitude: | 6.875 |
קטלוגים וכינוים:
|
