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Публикации по объекту
Investigating Disk Evolution: A High Spatial Resolution Mid-Infrared Survey of T Tauri Stars
We present a high spatial resolution, 10-20 μm survey of 65 T Tauribinary stars in Taurus, Ophiuchus, and Corona Australis using the Keck10 m telescopes. Designed to probe the inner ~1 AU region of thecircumstellar disks around the individual stellar components in thesebinary systems, this study increases the number of binaries withspatially resolved measurements at 10 μm by a factor of ~5. Combinedwith resolved near-infrared photometry and spectroscopic accretiondiagnostics, we find that ~10% of stars with a mid-infrared excess donot appear to be accreting. In contrast to an actively accreting disksystem, these passive disks have significantly lower near-infraredcolors that are, in most cases, consistent with photospheric emission,suggesting the presence of an inner disk hole. In addition, thereappears to be a spectral type/mass dependence associated with thepresence of a passive disk, with all passive disks occurring aroundM-type stars. The presence of a passive disk does not appear to berelated to the fact that these objects are in visual binary systems; thepassive disk systems span the entire range of binary separations presentin the sample, and a similar fraction of passive disks is observed in asample of single stars. The possibility that the passive disks arecaused by the presence of an as yet undetected companion at a smallseparation (0.3-3 AU) is possible for any individual system; however, itcannot account for the spectral type dependence of the passive disksample as a whole. We propose that these passive disks represent asubset of T Tauri stars that are undergoing significant disk evolution.The fraction of observed passive disks and the observed spectral typedependence can both be explained by models of disk evolution thatinclude disk photoevaporation from the central star.
| Mid-infrared images of the massive star forming region W75 N
An infrared study that includes ground-based mid-infrared images between8.7 and 18.7 μm and IRAC images at 3.6, 4.5, 5.8 and 8.0 μm of theW75 N massive star forming region is presented. The 12.5 μm imageshows the presence of four mid-infrared sources in the region W75 N(B),three of which have bright near-infrared counterparts, IRS 1, IRS 2 andIRS 3, all with significant excess emission at λ > 2.0 ~μm.IRS 2 has a steep energy distribution and the computed infraredluminosity is consistent with the presence of a young B3 star. Theobserved IRAC colors of IRS 3 indicate that this source is a Class IIintermediate mass young star, consistent with its infrared energydistribution and luminosity. The fourth, newly discovered, mid-infraredsource appears coincident with the ultracompact HII region VLA 3, and islocated within the millimeter core MM 1. We derived a luminosity of 750~L_ȯ and a visual extinction AV ≃ 90 forthis source. From the IRAC images, we detected 75 sources in an area of120'' × 120 '' centered in W75 N. At least 25 of these sources areassociated with the molecular cloud and form a young stellar cluster asshown in the IRAC two-color and the H-Ks versus K_s-[3.6]diagrams.
| Forty Years of Spectroscopic Stellar Astrophysics in Japan
The development of Japanese spectroscopic stellar astrophysics in therecent 40 years is reviewed from an observational point of view. In thisarticle, the research activities are provisionally divided into fourfields: hot stars, hot emission-line (Be) stars, cool stars, and otherstars. Historical developments of the observational facilities atOkayama Astrophysical Observatory (spectrographs and detectors) are alsosummarized in connection with the progress in scientific researchactivities.
| Investigating the Nature of the Dust Emission around Massive Protostar NGC 7538 IRS 1: Circumstellar Disk and Outflow?
We have obtained high-resolution mid-infrared images of the high-massprotostar NGC 7538 IRS 1 using Michelle on Gemini North and find thatthe circumstellar dust associated with this source is extended on bothlarge and small scales. The large-scale mid-infrared emission isasymmetric about the peak of IRS 1, being more extended to the northwestthan the southeast. The position angle of the mid-infrared emission issimilar to the position angle of the linearly distributed methanolmasers at this location that are thought to trace a circumstellar disk.However, this position angle is also very similar to that of the COoutflow in this region that appears to be centered on IRS 1. We suggestthat the large-scale extended mid-infrared emission is coming from dustheated on the walls of the outflow cavities near the source. IRS 1 isalso elongated in the mid-infrared on a smaller scale, and thiselongation is near perpendicular to the axis of the CO outflow (and thelinearly distributed methanol masers). Because of its orientation withrespect to the outflow and its estimated size (Rdisk~=450 AUat 11.7 μm), we propose that the small-scale elongation seen in themid-infrared is a circumstellar disk that may be collimating the outflowfrom IRS 1.
| The Effective Temperature Scale of FGK Stars. II. Teff:Color:[Fe/H] Calibrations
We present up-to-date metallicity-dependent temperature versus colorcalibrations for main-sequence and giant stars based on temperaturesderived with the infrared flux method (IRFM). Seventeen colors in thephotometric systems UBV, uvby, Vilnius, Geneva, RI(Cousins), DDO,Hipparcos-Tycho, and Two Micron All Sky Survey (2MASS) have beencalibrated. The spectral types covered by the calibrations range from F0to K5 (7000K>~Teff>~4000K) with some relationsextending below 4000 K or up to 8000 K. Most of the calibrations arevalid in the metallicity range -3.5>~[Fe/H]>~0.4, although some ofthem extend to as low as [Fe/H]~-4.0. All fits to the data have beenperformed with more than 100 stars; standard deviations range from 30 to120 K. Fits were carefully performed and corrected to eliminate thesmall systematic errors introduced by the calibration formulae. Tablesof colors as a function of Teff and [Fe/H] are provided. Thiswork is largely based on the study by A. Alonso and collaborators; thus,our relations do not significantly differ from theirs except for thevery metal-poor hot stars. From the calibrations, the temperatures of 44dwarf and giant stars with direct temperatures available are obtained.The comparison with direct temperatures confirms our finding in Paper Ithat the zero point of the IRFM temperature scale is in agreement, tothe 10 K level, with the absolute temperature scale (that based onstellar angular diameters) within the ranges of atmospheric parameterscovered by those 44 stars. The colors of the Sun are derived from thepresent IRFM Teff scale and they compare well with those offive solar analogs. It is shown that if the IRFM Teff scaleaccurately reproduces the temperatures of very metal-poor stars,systematic errors of the order of 200 K, introduced by the assumption of(V-K) being completely metallicity independent when studying verymetal-poor dwarf stars, are no longer acceptable. Comparisons with otherTeff scales, both empirical and theoretical, are also shownto be in reasonable agreement with our results, although it seems thatboth Kurucz and MARCS synthetic colors fail to predict the detailedmetallicity dependence, given that for [Fe/H]=-2.0, differences as highas approximately +/-200 K are found.
| Search for 17 μm H2 Pure Rotational Emission from Circumstellar Disks
We report the negative detection of the S(1) pure rotational lineemission of molecular hydrogen at 17.035 μm for four young stars, HD163296, MWC 863, CQ Tau, and LkCa 15, for which Infrared SpaceObservatory (ISO) observations detected the S(1) emission, with theCooled Mid-Infrared Camera and Spectrometer (COMICS) on the 8.2 m SubaruTelescope. We did not detect the line emission toward the central starnor within 15'' of the central star along the slit for any ofthe present targets. Upper limits of the present observations are muchsmaller than previous line flux estimates based on ISO Short WavelengthSpectrometer ( SWS) observations, irrespective of the intrinsic linewidth. The present results indicate that the emission detected by theISO SWS is not concentrated within the disk. Our detection limit of theH2 S(1) emission corresponds to upper limits of the diskmasses of (0.72-3.8)×10-4 Msolar within aradius of ~30-45 AU for the optically thin emission from the gas of 150K. The upper limits of the disk masses are significantly lower thanthose of the warm molecular hydrogen mass predicted by the model (Chiang& Goldreich 1997), suggesting that the optically thick emission fromdust dominates in the radiation from the disks in the mid-infraredwavelength. We point out that detectability of the H2emission in young stars depends on the evolution of the disks,particularly in the sedimentation and growth of dust grains in the disk.
| A library of high resolution synthetic stellar spectra from 300 nm to 1.8 μm with solar and α-enhanced composition
Libraries of stellar spectra are fundamental tools for the study ofstellar populations, and both empirical and synthetic libraries havebeen used for this purpose. In this paper, a new library of highresolution synthetic spectra is presented, ranging from thenear-ultraviolet (300 nm) to the near-infrared (1.8 μm). The libraryspans all the stellar types that are relevant to the integrated light ofold and intermediate-age stellar populations in the involved spectralregion (spectral types F through M and all luminosity classes). The gridwas computed for metallicities ranging from [Fe/H] = -2.5 to +0.5,including both solar and α-enhanced ([ α/Fe] = 0.4) chemicalcompositions. The synthetic spectra are a good match to observations ofstars throughout the stellar parameter space encompassed by the libraryand over the whole spectral region covered by the computations.
| Broad-band photometric colors and effective temperature calibrations for late-type giants. I. Z = 0.02
We present new synthetic broad-band photometric colors for late-typegiants based on synthetic spectra calculated with the PHOENIX modelatmosphere code. The grid covers effective temperatures T_eff=3000dots5000 K, gravities log g=-0.5dots{+3.5}, and metallicities[M/H]=+0.5dots{-4.0}. We show that individual broad-band photometriccolors are strongly affected by model parameters such as molecularopacities, gravity, microturbulent velocity, and stellar mass. Ourexploratory 3D modeling of a prototypical late-type giant shows thatconvection has a noticeable effect on the photometric colors too, as italters significantly both the vertical and horizontal thermal structuresin the outer atmosphere. The differences between colors calculated withfull 3D hydrodynamical and 1D model atmospheres are significant (e.g.,Δ(V-K)0.2 mag), translating into offsets in effectivetemperature of up to 70 K. For a sample of 74 late-type giants in theSolar neighborhood, with interferometric effective temperatures andbroad-band photometry available in the literature, we compare observedcolors with a new PHOENIX grid of synthetic photometric colors, as wellas with photometric colors calculated with the MARCS and ATLAS modelatmosphere codes. We find good agreement of the new synthetic colorswith observations and published T_eff-color and color-color relations,especially in the T_eff-(V-K), T_eff-(J-K) and (J-K)-(V-K) planes.Deviations from the observed trends in the T_eff-color planes aregenerally within ±100 K for T_eff=3500 to 4800 K. Syntheticcolors calculated with different stellar atmosphere models agree to±100 K, within a large range of effective temperatures andgravities. The comparison of the observed and synthetic spectra oflate-type giants shows that discrepancies result from the differencesboth in the strengths of various spectral lines/bands (especially thoseof molecular bands, such as TiO, H2O, CO) and the continuum level.Finally, we derive several new T_eff-log g-color relations for late-typegiants at solar-metallicity (valid for T_eff=3500 to 4800 K), based bothon the observed effective temperatures and colors of the nearby giants,and synthetic colors produced with PHOENIX, MARCS and ATLAS modelatmospheres.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Infrared Irradiance Calibration
Infrared astronomical measurements are calibrated against referencesources, usually primary standard stars that are, in turn, calibratedeither by direct or indirect means. A direct calibration compares thestar with a certified source, typically a blackbody. Indirect methodsextrapolate a direct measurement of the flux at one wavelength to theflux at another. Historically, α Lyr (Vega) has been used as theprimary standard as it is bright, easily accessible from the northernhemisphere, and is well calibrated in the visual. Until recently, thedirect absolute infrared calibrations of α Lyr and those derivedfrom the absolute solar flux scaled to the observed spectral energydistributions of solar type stars increasingly diverged with wavelengthfrom those obtained using a model atmosphere to extrapolate the absolutevisual flux of Vega into the infrared. The exception is the directcalibration by the 1996/97 Midcourse Space Experiment of the absolutefluxes for a number of the commonly used infrared standard stars,including Vega.
| Ca II K Emission-Line Asymmetries Among Red Giants
Measurements of the asymmetry of the K2 emission line of CaII have been made for a sample of bright field giants with B-V>1.15observed with the Cassegrain echelle spectrometer on the McDonaldObservatory 2.1 m telescope. The asymmetry of the Ca II K2line is quantified through measurement of a parameter V/R, which isdefined as the ratio between the maximum counts recorded in the violetand red components of the double-peaked emission profile. Red-maximumasymmetry (V/R<1.0) is found in our sample of 35 giants only amongstars with B-V>1.35, a trend that is still maintained (with oneexception) with the inclusion of an additional sample of giantspreviously observed by us with the same spectrograph. Althoughexceptional stars can be found in the literature, the data support anearlier finding by R. Stencel that among luminosity class III fieldgiants the occurrence of V/R<1.0 is generally restricted to effectivetemperatures cooler than 4320 K. This limit may coincide with the onsetof pulsation.
| High Spatial Resolution Mid-Infrared Observations of Five Seyfert Galaxies
High spatial resolution images at 12.5 μm of the nuclei of fivenearby Seyfert galaxies-I Zwicky 1, NGC 1320, NGC 2992, M81, and NGC7479-have been obtained with the 10 m Keck Telescope. The angular sizelimits indicate that under typical conditions the Keck Telescope showsan unresolved nucleus for these active galactic nuclei. In all cases,the lower limit to the infrared surface brightness is above3×1012 Lsolar kpc-2 this arguesthat nuclear starbursts do not contribute significantly to the infraredluminosities in these nuclei.
| The European Large Area ISO Survey - VIII. 90-μm final analysis and source counts
We present a re-analysis of the European Large Area Infrared SpaceObservatory (ISO) Survey (ELAIS) 90-μm observations carried out withISOPHOT, an instrument on board the ISO of the European Space Agency.With more than 12 deg2, the ELAIS survey is the largest areacovered by ISO in a single programme and is about one order of magnitudedeeper than the IRAS 100-μm survey. The data analysis is presentedand was mainly performed with the PHOT interactive analysis software butusing the pairwise method of Stickel et al. for signal processing fromedited raw data to signal per chopper plateau. The ELAIS 90-μmcatalogue contains 237 reliable sources with fluxes larger than 70 mJyand is available in the electronic version of this article. Numbercounts are presented and show an excess above the no-evolution modelprediction. This confirms the strong evolution detected at shorter (15μm) and longer (170 μm) wavelengths in other ISO surveys. TheELAIS counts are in agreement with previous works at 90 μm and inparticular with the deeper counts extracted from the Lockman holeobservations. Comparison with recent evolutionary models show that themodels of Franceschini et al. and Guiderdoni et al. (which includes aheavily extinguished population of galaxies) give the best fit to thedata. Deeper observations are nevertheless required to discriminatebetter between the model predictions in the far-infrared, and arescheduled with the Spitzer Space Telescope, which has already startedoperating, and will also be performed by ASTRO-F.
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Further Results of TiO-Band Observations of Starspots
We present measurements of starspot parameters (temperature and fillingfactor) on five highly active stars, using absorption bands of TiO, fromobservations made between 1998 March and 2001 December. We determinedstarspot parameters by fitting TiO bands using spectra of inactive G andK stars as proxies for the unspotted photospheres of the active starsand spectra of M stars as proxies for the spots. For three evolved RSCVn systems, we find spot filling factors between 0.28 and 0.42 for DMUMa, 0.22 and 0.40 for IN Vir, and 0.31 and 0.35 for XX Tri; thesevalues are similar to those found by other investigators usingphotometry and Doppler imaging. Among active dwarfs, we measured a lowerspot temperature (3350 K) for EQ Vir than found in a previous study ofTiO bands, and for EK Dra a lower spot temperature (~3800 K) than foundthrough photometry. For all active stars but XX Tri, we achieved goodphase coverage through a stellar rotational period. We also present ourfinal, extensive grid of spot and nonspot proxy stars.This paper includes data taken at McDonald Observatory of the Universityof Texas at Austin.
| Spectral Irradiance Calibration in the Infrared. XV. Absolute Calibration of Standard Stars by Experiments on the Midcourse Space Experiment
Calibration experiments were conducted with the SPIRIT III infraredinstrument on the Midcourse Space Experiment (MSX) against a number ofinfrared standard stars and five emissive reference spheres that wereejected at various times during the mission. The physical properties ofthe 2 cm diameter spheres, such as size and emissivity, were preciselymeasured in the laboratory. The energy balance equation between thetotal flux absorbed and that emitted by the sphere is solved to obtainthe time-dependent temperature of the sphere under the assumption thatthe sphere radiates as a blackbody with the measuredwavelength-dependent emissivity. The estimated uncertainties in themodeling of the sphere are about 1 K in the thermal component and 3% forthe geometric contribution. MSX also measured over 150 mean fluxes foreight standard infrared calibration stars during the 10 month mission.The measurements were scaled to the absolute fluxes that Cohen et al.adopt for α CMa (Sirius). The measured spectral energydistributions of the calibration stars relative to Sirius are within theuncertainties that Cohen et al. assign to the absolute fluxes from thesestars, with a few exceptions. However, the MSX measurement uncertaintiesare generally much smaller, and the mission-averaged fluxes revealstatistically significant deviations from the Cohen et al. values. Ofthe calibration stars, only β Peg was found to be variable. MSXalso measured excess fluxes for α Lyr (Vega) in the 12.1, 14.7,and 21.3 μm spectral bands; the excesses in the latter two bands areconsistent with the published thermal model for the dust ring aroundthis star. The absolute calibration of the fluxes of the stellarstandards based on the average of the measurements of the spheres overall MSX bands and the five experiments agrees with those predicted towithin the 1.4% MSX measurement uncertainties. The zero-magnitudeabsolute fluxes proposed by Cohen et al. are validated if the flux fromSirius is increased by 1%.
| MSX Observations of Standard Infrared Calibration Stars
The MSX program calibrated the SPIRIT III responsivity on orbit with sixcalibration experiments that tested the various operating modes or thesensor. On the average, two of these experiments were conducted eachweek over a nine month period before the end of the mission. Usually,each experiment observed two out of nine standard infrared calibrationstars and each observation nominally consisted of 20 to 80 individualmeasurements. A residual variation of SPIRIT III response with focalplane temperature was found and corrected. The corrections werenormalized to the absolute in-band fluxes from Sirius specified by Cohenet al., which scales the SPIRIT III calibration to this star. The MSXphotometry on the infrared calibration stars agrees well with thatpredicted from the absolute spectra of Cohen and his colleagues if theflux from Sirius is increased by about 1%. Discrepancies were observedfor β Peg, which MSX found to be variable, and α Lyr, forwhich MSX observed a flux excess at wavelengths longer than 14 μ mthat is consistent with emission from the circumstellar dust shell knownto surround this star. MSX validated the absolute flux for eight of theCohen et al. infrared standard stars with measurements errors of apercent or less and requires a statistically significant increase of 1%in the infrared flux of Sirius.
| On the analysis of band 3 of the ISO-SWS calibration sources
We analyse ISO-SWS 01 (R 1500) 12-27.5 μm (band 3) spectra ofthe 10 standard calibration stars with the highest flux using syntheticspectra generated from (MARCS) atmosphere models. The comparison betweenthe observed and synthetic spectra reveals the quality of (1) theatmospheric model construction and subsequent synthetic spectracomputation and of (2) the (OLP 10.1) calibration and data reduction ofthe spectrometer at these wavelengths.The models represent the general features of the observations, but thesynthetic spectrum computation is hampered by the lack of comprehensivemolecular and atomic line lists. We also suspect some problems with thetemperature distribution in the outer layers of the model andinaccuracies in the extrapolation of the collision-induced absorptioncoefficients of H2 pairs. We detect baseline ripples andfringes in the observed spectra, that survive the calibration anddetailed reduction process. Photometric calibration uncertainties areestimated by means of the scaling factors between the synthetic andobserved spectra.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.
| Oxygen isotopic ratios in first dredge-up red giant stars and nuclear reaction rate uncertainties revisited
We describe a general yet simple method to analyse the propagation ofnuclear reaction rate uncertainties in a stellar nucleosynthesis andmixing context. The method combines post-processing nucleosynthesis andmixing calculations with a Monte Carlo scheme. With this approach wereanalyse the dependence of theoretical oxygen isotopic ratiopredictions in first dredge-up red giant branch stars in a systematicway. Such predictions are important to the interpretation of pre-solarAl2O3 grains from meteorites. The reaction rateswith uncertainties were taken from the NACRE compilation of Angulo etal. We include seven reaction rates in our systematic analysis ofstellar models with initial masses from 1 to 3 Msolar. Wefind that the uncertainty of the 18O(p,α)15N reaction rate typically causes an error in thetheoretical 16O/18O ratio of ~= +20/ - 5 per cent.The error of the 16O/17O prediction is 10-40 percent depending on the stellar mass, and is persistently dominated by thecomparatively small uncertainty of the 16O(p,γ)17F reaction. With the new estimates on reaction rateuncertainties by the NACRE compilation, the p-capture reactions17O(p, α)14N and 17O(p,γ)18F have virtually no impact on theoreticalpredictions for stellar mass <=1.5 Msolar. However, theuncertainty in 17O(p, α)14N has an effectcomparable to or greater than that of 16O(p,γ)17F for masses >1.5 Msolar, where coremixing and subsequent envelope mixing interact. In these cases wherecore mixing complicates post-dredge-up surface abundances, uncertaintyin other reactions have a secondary but noticeable effect on surfaceabundances.
| Interactions between a Bright Young Stellar Object and the Midcourse Space Experiment Infrared-dark Cloud G79.3+0.3: An Early Stage of Triggered Star Formation?
Millimeter and mid-infrared observations have been made of the denseclumps of dust and gas and of young stellar objects (YSOs) associatedwith the bright, compact submillimeter source G79.3+0.3 P1 in therelatively nearby MSX infrared-dark cloud G79.3+0.3. The Geminimid-infrared observations reported here indicate the presence of threeYSOs within the cloud. BIMA 3 mm continuum observations show that thebrightest of the YSOs is likely to be a Herbig Ae/Be star. High angularresolution molecular line observations suggest that a wind from thisstar may be triggering collapse in the adjacent molecular cloud. Thesubmillimeter source G79.3+0.3 P1 itself does not contain infraredsources and may represent an earlier stage of star formation.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Angular Diameters of Stars from the Mark III Optical Interferometer
Observations of 85 stars were obtained at wavelengths between 451 and800 nm with the Mark III Stellar Interferometer on Mount Wilson, nearPasadena, California. Angular diameters were determined by fitting auniform-disk model to the visibility amplitude versus projected baselinelength. Half the angular diameters determined at 800 nm have formalerrors smaller than 1%. Limb-darkened angular diameters, effectivetemperatures, and surface brightnesses were determined for these stars,and relationships between these parameters are presented. Scatter inthese relationships is larger than would be expected from themeasurement uncertainties. We argue that this scatter is not due to anunderestimate of the angular diameter errors; whether it is due tophotometric errors or is intrinsic to the relationship is unresolved.The agreement with other observations of the same stars at the samewavelengths is good; the width of the difference distribution iscomparable to that estimated from the error bars, but the wings of thedistribution are larger than Gaussian. Comparison with infraredmeasurements is more problematic; in disagreement with models, coolerstars appear systematically smaller in the near-infrared than expected,warmer stars larger.
| The Albedo Distribution of Jovian Trojan Asteroids
We present radiometrically derived V-band geometric albedos andeffective radii for 32 Jovian Trojan asteroids, using near-simultaneousmid-infrared and visible observations. We sampled the large end of thegroup's size distribution, down to a radius of 25 km, using 14 objectsin the L4 swarm and 18 in the L5 swarm. We find that the albedodistribution is much narrower than previously derived from IRASmeasurements. The Trojans, for the most part, have very similar albedos.The actual mean and standard deviation of the distribution depend on theaverage Trojan beaming parameter η. The ``standard'' value of 0.756,which was used for the IRAS analysis, yields a mean albedo of0.056+/-0.003 and a standard deviation of 0.009. However, a value ofη=0.94, which we found represented our data better, yields0.041+/-0.002 and a standard deviation of just 0.007. The thermalbehavior of the Trojans seems to follow the ``slow rotator'' model, andthe thermal inertia itself can be no greater than about half the Moon'svalue. The Kolmogorov-Smirnov test was used to compare the Trojans'albedo distribution with that of cometary nuclei, dead-comet candidates,and outer solar system objects. We find that the Trojan distribution issimilar only to the cometary ones, and only if the Trojans' η~1.Observations of the binary (617) Patroclus reveal that its albedo israther typical among the distribution. We have also discovered that(4709) Ennomos has an extremely elevated albedo, about 0.15. This objectmay have a very unusual thermal behavior or have recently suffered alarge impact that excavated the surface down to a layer of highlyreflective, pristine ice.
| Infrared Colors and Variability of Evolved Stars from COBE DIRBE Data
For a complete 12 μm flux-limited sample of 207 IRAS sources(F12>=150 Jy, |b|>=5deg), the majority ofwhich are AGB stars (~87%), we have extracted light curves in seveninfrared bands between 1.25 and 60 μm using the database of theDiffuse Infrared Background Experiment (DIRBE) instrument on the CosmicBackground Explorer (COBE) satellite. Using previous infrared surveys,we filtered these light curves to remove data points affected by nearbycompanions and obtained time-averaged flux densities and infraredcolors, as well as estimates of their variability at each wavelength. Inthe time-averaged DIRBE color-color plots, we find clear segregation ofsemiregulars, Mira variables, carbon stars, OH/IR stars, and red giantswithout circumstellar dust (i.e., V-[12]<5) and with little or novisual variation (ΔV<0.1 mag). The DIRBE 1.25-25 μm colorsbecome progressively redder and the variability in the DIRBE databaseincreases along the oxygen-rich sequence nondusty slightly varying redgiants-->SRb/Lb-->SRa-->Mira-->OH/IR and the carbon-richSRb/Lb-->Mira sequence. This supports previous assertions that theseare evolutionary sequences involving the continued production andejection of dust. The carbon stars are redder than their oxygen-richcounterparts for the same variability type, except in theF12/F25 ratio, where they are bluer. Of the 28sources in the sample not previous noted to be variable, 18 are clearlyvariable in the DIRBE data, with amplitudes of variation of ~0.9 mag at4.9 μm and ~0.6 mag at 12 μm, consistent with them being verydusty Mira-like variables. We also present individual DIRBE light curvesof a few selected stars. The DIRBE light curves of the semiregularvariable L2 Pup are particularly remarkable. The maxima at1.25, 2.2, and 3.5 μm occur 10-20 days before those at 4.9 and 12μm, and, at 4.9 and 12 μm, another maximum is seen between the twonear-infrared maxima.
| High Spatial Resolution Mid-Infrared Observations of Three Seyfert Galaxies
Images at 12.5 μm of nuclei of three nearby Seyfert galaxies-NGC1275, NGC 4151, and NGC 7469-have been obtained with the 10 m KeckTelescope. NGC 7469 is resolved and deconvolution delineates a structure(<0.04")×0.08", or less than 13×26 pc at a position angleof 135°. From a comparison with structure seen at millimeterwavelengths, this structure is interpreted as a disk aligned with themolecular gas in the central few hundred parsecs of the galaxy. NGC 1275and NGC 4151 are not resolved; limits on the sizes of these nuclei are0.08" and 0.16", corresponding to physical spatial scales of 28 and 10pc. The lower limits to the brightness temperatures implied by thesesize limits and the measured flux densities are within ~50 K of the12-25 μm color temperatures of these systems, as inferred from IRASobservations. The angular size limits are within a factor of 2 of thesizes required to spatially resolve thermal emission from dust heated bya central luminosity source. These sizes preclude significantcontributions to the nuclear infrared emission from star-formingregions.
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. IV. Extending the cool MK stars sample
A library of high resolution spectra of MK standard and reference stars,observed in support to the GAIA mission, is presented. The aim of thispaper is to integrate the MK mapping of Paper I of this series as wellas to consider stars over a wider range of metallicities. Radialvelocities are measured for all the target stars.The spectra are available in electronic form (ASCII format) at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/406/995 and from the webpage http://ulisse.pd.astro.it/MoreMK/, where further bibliographicalinformation for the target stars is given.
| ISO-SWS calibration and the accurate modelling of cool-star atmospheres. IV. G9 to M2 stars
A detailed spectroscopic study of 11 giants with spectral type from G9to M2 is presented. The 2.38-4.08 mu m wavelength-range of band 1 ofISO-SWS (Short-Wavelength Spectrometers on board of the Infrared SpaceObservatory) in which many different molecules - with their owndependence on each of the stellar parameters - are absorbing, enables usto estimate the effective temperature, the gravity, the microturbulence,the metallicity, the CNO-abundances, the12C/13C-ratio and the angular diameter from theISO-SWS data. Using the Hipparcos' parallax, the radius, luminosity andgravity-inferred mass are derived. The stellar parameters obtained arein good agreement with other published values, though also somediscrepancies with values deduced by other authors are noted. For a fewstars (delta Dra, xi Dra, alpha Tuc, H Sco and alpha Cet) someparameters - e.g. the CNO-abundances - are derived for the first time.By examining the correspondence between different ISO-SWS observationsof the same object and between the ISO-SWS data and the correspondingsynthetic spectrum, it is shown that the relative accuracy of ISO-SWS inband 1 (2.38-4.08 mu m) is better than 2% for these high-flux sources.The high level of correspondence between observations and theoreticalpredictions, together with a confrontation of the estimatedTeff (ISO) value with Teff values derived fromcolours - which demonstrates the consistency between V-K,BCK, Teff and thetad derived fromoptical or IR data - proves that both the used MARCS models to derivethe stellar quantities and the flux calibration of the ISO-SWS detectorshave reached a high level of reliability.Based on observations with ISO, an ESA project with instruments fundedby ESA Member States (especially the PI countries France, Germany, TheNetherlands and the UK) and with the participation of ISAS and NASA.Appendices A-D are only available in electronic form athttp://www.edpsciences.org
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Наблюдательные данные и астрометрия
| Созвездие: | Пегас |
| Прямое восхождение: | 23h03m46.50s |
| Склонение: | +28°04'58.0" |
| Видимая звёздная величина: | 2.42 |
| Расстояние: | 61.087 парсек |
| Собственное движение RA: | 187.3 |
| Собственное движение Dec: | 136 |
| B-T magnitude: | 4.61 |
| V-T magnitude: | 2.654 |
Каталоги и обозначения:
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