Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The Reddening of Red Supergiants: When Smoke Gets in Your Eyes
Deriving the physical properties of red supergiants (RSGs) depends onaccurate corrections for reddening by dust. We use our recent modelingof the optical spectra of RSGs to address this topic. First, we findthat previous broadband studies have underestimated the correction forextinction in the visible, and hence the luminosities (if derived fromV); the shift in the effective wavelengths of the standard B and Vbandpasses necessitates using an effective value of the ratioR'V=4.2 to correct broadband photometry of RSGs ifRV=3.1 for early-type stars viewed through the same dust,where we have assumed the standard reddening law of Cardelli andcoauthors. Use of the Fitzpatrick reddening law would lead toR'V=3.8, as well as slightly lower values ofextinction derived from spectrophotometry, but results in slightlypoorer fits. Second, we find that a significant fraction of RSGs inGalactic OB associations and clusters show up to several magnitudes ofexcess visual extinction compared to OB stars in the same regions; weargue that this is likely due to circumstellar dust around the RSGs. Wealso show that the RSG dust production rate (as indicated by the 12μm excess) is well correlated with bolometric luminosity, contrary towhat has been found by earlier studies. The stars with the highestamount of extra visual extinction also show significant near-UV (NUV)excesses compared to the stellar models reddened by the standardreddening law. This NUV excess is likely due to scattering of the star'slight by the dust and/or a larger average grain size than that typicalof grains found in the diffuse interstellar medium. Similar excesseshave been attributed to circumstellar dust around R Coronae Borealisstars. Finally, we estimate that the RSGs contribute dust grains at therate of 3×10-8Msolar yr-1kpc-2 in the solar neighborhood, comparable to what weestimate for late-type WCs, 1×10-7Msolaryr-1 kpc-2. In the solar neighborhood thisrepresents only a few percent of the dust production (which is dominatedby low-mass AGBs), but we note that in low-metallicity starbursts, dustproduction by RSGs would likely dominate over other sources.
| The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCSstellar atmosphere models to determine the effective temperatures of 74Galactic red supergiants (RSGs). The stars are mostly members of OBassociations or clusters with known distances, allowing a criticalcomparison with modern stellar evolutionary tracks. We find we canachieve excellent matches between the observations and the reddenedmodel fluxes and molecular transitions, although the atomic lines Ca Iλ4226 and Ca II H and K are found to be unrealistically strong inthe models. Our new effective temperature scale is significantly warmerthan those in the literature, with the differences amounting to 400 Kfor the latest type M supergiants (i.e., M5 I). We show that the newlyderived temperatures and bolometric corrections give much betteragreement with stellar evolutionary tracks. This agreement provides acompletely independent verification of our new temperature scale. Thecombination of effective temperature and bolometric luminosities allowsus to calculate stellar radii; the coolest and most luminous stars (KWSgr, Case 75, KY Cyg, HD 206936=μ Cep) have radii of roughly 1500Rsolar (7 AU), in excellent accordance with the largeststellar radii predicted from current evolutionary theory, althoughsmaller than that found by others for the binary VV Cep and for thepeculiar star VY CMa. We find that similar results are obtained for theeffective temperatures and bolometric luminosities using only thedereddened V-K colors, providing a powerful demonstration of theself-consistency of the MARCS models.
| 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}
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are 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/399/1083
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| A catalog of rotational and radial velocities for evolved stars. II. Ib supergiant stars
Rotational velocity vsin i and mean radial velocity are presented for asample of 231 Ib supergiant stars covering the spectral region F, G andK. This work is the second part of the large survey carried out with theCORAVEL spectrometer to establish the behavior of the rotation for starsevolving off the main sequence (De Medeiros & Mayor 1999). Thesedata will add constraints to the study of the rotational behavior inevolved stars, as well as solid information concerning tidalinteractions in binary systems and on the link between rotation,chemical abundance and activity in stars of intermediate masses. Basedon observations collected at the Haute-Provence Observatory,Saint-Michel, France and at the European Southern Observatory, La Silla,Chile Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/395/97
| Structure and Mass of a Young Globular Cluster in NGC 6946
Using the Wide Field Planetary Camera 2 on board the Hubble SpaceTelescope, we have imaged a luminous young star cluster in the nearbyspiral galaxy NGC 6946. Within a radius of 65 pc, the cluster has anabsolute visual magnitude, MV=-13.2, comparable to the mostluminous young ``super star clusters'' in the Antennae merger galaxy.UBV colors indicate an age of about 15 Myr. The cluster has a compactcore (radius ~1.3 pc) surrounded by an extended envelope with apower-law luminosity profile. The outer parts of the cluster profilegradually merge with the general field, making it difficult to measure aprecise half-light radius Re, but we estimateRe~13 pc. Combined with population synthesis models, theluminosity and age of the cluster imply a mass of8.2×105 Msolar for a Salpeter initial massfunction (IMF) extending down to 0.1 Msolar. If the IMF islognormal below 0.4 Msolar, then the mass decreases to5.5×105 Msolar. Depending on modelassumptions, the central density of the cluster is between5.3×103 and 1.7×104 Msolarpc-3, comparable to other high-density star-forming regions.We also estimate a dynamical mass for the cluster using high-dispersionspectra from the HIRES spectrograph on the Keck I telescope. The HIRESdata indicate a velocity dispersion of 10.0+/-2.7 km s-1 andimply a total cluster mass within 65 pc of(1.7+/-0.9)×106 Msolar. Comparing thedynamical mass with the mass estimates based on the photometry andpopulation synthesis models, we find that the mass-to-light ratio is atleast as high as for a Salpeter IMF extending down to 0.1Msolar, although a turnover in the IMF at 0.4Msolar is still possible within the ~1 σ errors. Thecluster will presumably remain bound, evolving into a globularcluster-like object. Based on observations with the NASA/ESA HubbleSpace Telescope and with the W. M. Keck Telescope.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Radio emission from stars: A survey at 250 GHz
We have used the IRAM 30 m-telescope together with the Max PlanckInstitute for Radio Astronomy (MPIfR) bolometer to survey nearly 270stars of different types for 250 GHz continuum emission. We comparethese data with their low frequency (cm-range) properties. Early typestars show very often a deviation from the uniformly expanding windmodel which we tentatively attribute to temperature and/or densityfluctuations in their deeper atmospheric layers. For WR stars thisdeviation seems to depend on the effective temperature. Pre-mainsequence stars usually seem to be surrounded by a shell of warm dustmaking a substantial contribution to the 250 GHz flux density value. Wehave found especially for nearby giants and supergiants that a layer atthe transition from photosphere to chromosphere emits ample 250 GHzradiation. We show that the present data can still be explained by asimple uniformly illuminated disk model with the known stellar radius.Optically variable stars are not very strong emitters at 250 GHz. Wepreferentially detected the more exotic ones, a few Beta Lyr-type andsymbiotic stars. Comments on many individual objects are given in theappropriate sections.
| Groups of stars with common motion in the Galaxy - Groups of red supergiants of the luminosity classes I and II
Not Available
| Mass-losing M supergiants in the solar neighborhood
A list of the 21 mass-losing red supergiants (20 M type, one G type; Lgreater than 100,000 solar luminosities) within 2.5 kpc of the sun iscompiled. These supergiants are highly evolved descendants ofmain-sequence stars with initial masses larger than 20 solar masses. Thesurface density is between about 1 and 2/sq kpc. As found previously,these stars are much less concentrated toward the Galactic center thanW-R stars, which are also highly evolved massive stars. Although withconsiderable uncertainty, it is estimated that the mass return by the Msupergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpcyr. In the hemisphere facing the Galactic center there is much less massloss from M supergiants than from W-R stars, but, in the anticenterdirection, the M supergiants return more mass than do the W-R stars. Theduration of the M supergiant phase appears to be between 200,000 and400,000 yr. During this phase, a star of initially at least 20 solarmasses returns perhaps 3-10 solar masses into the interstellar medium.
| Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants
The metallicity gradient in the Galactic disk from in situ stars withvisual magnitude ranging from 6 to 10 is analyzed. Atmosphericparameters and detailed chemical abundances for 64 Population Isupergiants of spectral types F through M and luminosity classes Iathrough II have been determined. The derived Fe/H ratios ranging from-0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertaintyof + or - 0.2. A subset of 25 supergiants fainter than 7th magnitudelying in the direction of the Galactic center shows a Fe/H mean of +0.18+ or - 0.04, while a similar sample of 15 faint supergiants lying in thedirection of the Galactic anticenter shows a lower Fe/H mean of +0.07 +or - 0.06. For a sample of bright supergiants analyzed by Luck andLambert (1985), the mean abundance pattern for all 64 stars showed thefollowing: deficient C and O along with enhancement of N, indicatingmixing of CNO-cycled material to the stellar surfaces; an apparent Srenhancement attributed to departures from LTE; and an essentially solarpattern of other chemical elements.
| Infrared circumstellar shells - Origins, and clues to the evolution of massive stars
The infrared fluxes, spatial and spectral characteristics for a sampleof 111 supergiant stars of spectral types F0 through M5 are tabulated,and correlations examined with respect to the nature of theircircumstellar envelopes. One-fourth of these objects were spatialyresolved by IRAS at 60 microns and possess extended circumstellar shellmaterial, with implied expansion ages of about 10 to the 5th yr.Inferences about the production of dust, mass loss, and the relation ofthese characteristics of the evolution of massive stars, are discussed.
| Consequences of a chromospheric temperature rise on the formation of the H-alpha line in late-type supergiants
Computations of the H-alpha line profiles were performed in a non-LTEmoving chromosphere with temperature rise to simulate the observedH-alpha characteristics in G and K supergiants. The comoving frameradiative transfer code was modified to incorporate explicitly theeffects of hydrogen ionization. The sensitivity of H-alpha profiles to avariety of temperature structures, velocity gradients, and chromosphericextents and densities is examined and illustrated. Comparison of theobserved profiles to computed ones gives total hydrogen densities in therange between 10 to the 9th and 10 to the 11th/cu cm at the base of theline forming region. Integrated chromospheric optical depths in therange of 50-5000 and expansion velocities in the range of 0.25-2 timesthe maximum random (microturbent and thermal) velocity are found. Themass loss rate is inferred to be in the range between 10 to the -7th and10 to the -9th solar masses/year.
| Far-infrared circumstellar 'debris' shell of red supergiant stars
An examination of IRAS data of red supergiant stars in the field and ingalactic OB star associations indicates the presence of substantialamounts of 60-micron emitting material extending several arcminutesaround many such sources. The characteristics of these large shells arediscussed in terms of remnants of ongoing mass loss, and a simple modeldeveloped for the case of Alpha Orionis, in particular.
| IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
| Nineteen new spectroscopic binaries and the rate of binary stars among F-M supergiants
Nineteen spectroscopic binaries (SBs) have been discovered in radialvelocity measurements made with the CORAVEL spectrophotometer on 181northern F-M supergiants. The rate of detected SBs among northern F-Msupergiants is 21 percent, without any dependence on spectral orluminosity class. The study of the binary F-M supergiants with knownorbital elements indicates that all the systems with a period smallerthan the critical value P(circ) have a nearly circular orbit. The valueof P(circ) depends on the luminosity class, being 400-600 d for class Iband 2000-7000 d for class Ia. This circularization of the orbits may bedue to the transfer of angular momentum during the phase of binary massexchange.
| Supergiants and the galactic metallicity gradient. I - 27 late-type supergiants in the inner-arm regions
From an analysis of high-dispersion Kitt Peak echelle data, atmosphericparameters and chemical abundances have been derived for 27 supergiantsof spectral type F through M. Since the stars studied lie within about 1kpc of the sun, their abundances will form the local reference point forextensions of this study to larger distances. The derived Fe/H abundanceratios range from minus 0.6 to plus 0.1 dex, show a mean value of -0.15dex, and have an internal uncertainty of plus or minus 0.2 dex.
| Wavelength dependence of polarization. XXXIII - The Alpha Persei star cluster
This paper presents multicolor polarization observations of a largenumber of stars that are highly probable members of the Alpha Perseistar cluster and of certain surrounding stars in order to determine thewavelength dependence of polarization due to dust grains in andsurrounding the cluster. It is concluded that the grains in the clusterare no different from those in the general interstellar medium. The dataare combined with previously published work in order to determinepolarization-to-absorption ratios and to make better estimates of thedistance, size, and mass of the cluster and its associated gas and dustcloud. From these parameters it is concluded that a magnetic field ofabout 100 microgauss is necessary to produce the observed polarization.The role of the magnetic field in the cluster's evolution is discussed.
| Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...38..309H&db_key=AST
| Lithium abundance in stellar atmospheres
Data on the lithium abundance in the atmospheres of 491 stars arecompiled and reduced to a single system. The lithium abundances of thesestars are shown to differ by more than a factor of 1 million, and thedependence of lithium abundance on spectral type is determined forvarious groups of stars. It is found that cooler stars have lowerlithium abundances than hotter stars and that young stars have higherabundances than old stars. Data on the Li-6/Li-7 isotope ratio in theatmospheres of 30 stars are presented which indicate that Li-6 is notobserved in most cases and that the exceptions comprise magneticvariable stars with Li-6/Li-7 ratios of 0.10 to 2.00. It is concludedthat the observational results as a whole are satisfactorily explainedby the hypothesis that the same high lithium abundance characterized allstars at birth but then decreased in the course of evolution due tointermixing of matter.
| Lithium in K-supergiants.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.163..337W&db_key=AST
| Spectral properties of luminous late-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....16..329G&db_key=AST
| The space distribution and kinematics of supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..602H&db_key=AST
| Polarimetric Observations of Nearby Stars in the Directions of the Galactic Poles and the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...151..907A&db_key=AST
| UBV photometry of 550 F, G and K type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966MNRAS.133..475A&db_key=AST
| Hα Photometry of late-type stars I. F, G and K-type stars north of the equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964MNRAS.128..435P&db_key=AST
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Касиопеја |
| Ректацензија: | 02h56m24.80s |
| Deклинација: | +64°19'57.0" |
| Apparent магнитуда: | 6.24 |
| Даљина: | 392.157 parsecs |
| Proper motion RA: | -2.6 |
| Proper motion Dec: | -1.3 |
| B-T magnitude: | 8.886 |
| V-T magnitude: | 6.436 |
Каталог и designations:
|
