Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
Near-IR spectra of red supergiants and giants. I. Models with solar and with mixing-induced surface abundance ratios
Context: It remains difficult to interpret the near-IR emission of youngstellar populations. One main reason is our incomplete understanding ofthe spectra of luminous red stars. Aims: This work provides a grid oftheoretical spectra of red giant and supergiant stars, that extendsthrough optical and near-IR wavelengths. For the first time, models arealso provided with modified surface abundances of C, N and O, as a steptowards accounting for the changes that occur due to convectivedredge-up in red supergiants or may occur at earlier evolutionary stagesin the case of rotation. The aims are (i) to assess how well currentmodels reproduce observed spectra, in particular in the near-IR; (ii) toquantify the effects of the abundance changes on the spectra; and (iii)to determine how these changes affect estimates of fundamental stellarparameters. Methods: Spectra are computed with the model atmospherecode PHOENIX and compared with a homogeneous set of observations.Although the empirical spectra have a resolution of onlyλ/Δλ ˜ 1000, we emphasize that models must becalculated at high spectral resolution in order to reproduce the shapesof line blends and molecular bands. Results: Giant star spectra ofclass III can be fitted extremely well at solar metallicity down to~3400 K, where difficulties appear in the modelling of near-IR H2O andTiO absorption bands. Luminous giants of class II can be fitted welltoo, with modified surface abundances preferred in a minority of cases,possibly indicating mixing in excess of standard first dredge-up.Supergiant stars show a larger variety of near-IR spectra, and good fitsare currently obtained for about one third of the observations only.Modified surface abundances help reproducing strong CN bands, but do notsuffice to resolve the difficulties. The effect of the abundance changeson the estimated Teff depends on the wavelength range ofobservation and can amount several 100 K. Conclusions: Whiletheoretical spectra for giant stars are becoming very satisfactory, redsupergiants require further work. The model grid must be extended, inparticular to larger micro-turbulent velocities. Some observed spectramay call for models with even lower gravities than explored here (andtherefore probably stellar winds), and/or with more extreme abundancesthan predicted by standard non-rotating evolution models. Non-staticatmospheres models should also be envisaged.Selected theoretical spectra (see text) can be retrieved in FITS formatat CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/468/205
| An empirical formula for the mass-loss rates of dust-enshrouded red supergiants and oxygen-rich Asymptotic Giant Branch stars
We present an empirical determination of the mass-loss rate as afunction of stellar luminosity and effective temperature, foroxygen-rich dust-enshrouded Asymptotic Giant Branch stars and redsupergiants. To this aim we obtained optical spectra of a sample ofdust-enshrouded red giants in the Large Magellanic Cloud, which wecomplemented with spectroscopic and infrared photometric data from theliterature. Two of these turned out to be hot emission-line stars, ofwhich one is a definite B[e] star. The mass-loss rates were measuredthrough modelling of the spectral energy distributions. We thus obtainthe mass-loss rate formula log dot{M} = -5.65 + 1.05 log ( L / 10 000{L}_ȯ ) -6.3 log ( T_eff / 3500 K ), valid for dust-enshrouded redsupergiants and oxygen-rich AGB stars. Despite the low metallicity ofthe LMC, both AGB stars and red supergiants are found at late spectraltypes. A comparison with galactic AGB stars and red supergiants showsexcellent agreement between the mass-loss rate as predicted by ourformula and that derived from the 60 μm flux density fordust-enshrouded objects, but not for optically bright objects. Wediscuss the possible implications of this for the mass-loss mechanism.
| 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
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are 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/413/1037
| 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
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/386/492, and from theauthors on CD-Rom.
| Stellar and circumstellar evolution of long period variable stars
In a first paper, HIPPARCOS astrometric and kinematic data were used tocalibrate both infrared K and IRAS luminosities at the same time askinematic parameters of Long Period Variable stars (LPVs). Individualestimated absolute magnitudes and a probabilistic assignation togalactic populations were deduced from these calibrations for each LPVof our sample. Here we propose a scenario of simultaneous stellar andcircumstellar evolution according to the galactic populations. Thetransitory states of S and Tc stars allow us to confirm the location ofthe first dredge-up at Mbol=-3.5. There is also evidencesuggesting that a previous enrichment in s-elements from a more evolvedcompanion may accelerate the evolution along the AGB. The possibleevolution to OH LPVs is included in this scenario, and any of thesestars may have a mass at the limit of the capability for a C enrichmentup to C/O > 1. A list of bright massive LPVs with peculiar envelopeand luminosity properties is proposed as Hot Bottom Burning candidates.The He-shell flash star, R Cen, is found to be exceptionally bright andcould become, before leaving the AGB, a C-rich LPV brighter than theusual luminosity limit of carbon stars.
| Dust-enshrouded asymptotic giant branch stars in the solar neighbourhood
A study is made of a sample of 58 dust-enshrouded asymptotic giantbranch (AGB) stars (including two possible post-AGB stars), of which 27are carbon-rich and 31 are oxygen-rich. These objects were originallyidentified by Jura & Kleinmann as nearby (within about 1kpc of theSun) AGB stars with high mass-loss rates(Mȯ>10-6Msolaryr-1).Ground-based near-infrared photometry, data obtained by the IRASsatellite and kinematic data (radial and outflow velocities) from theliterature are combined to investigate the properties of these stars.The light amplitude in the near-infrared is found to be correlated withperiod, and this amplitude decreases with increasing wavelength.Statistical tests show that there is no reason to suspect any differencein the period distributions of the carbon- and oxygen-rich stars forperiods less than 1000d. There are no carbon-rich stars with periodslonger than 1000d in the sample. The colours are consistent with thoseof cool stars with evolved circumstellar dust shells. Luminosities anddistances are estimated using a period-luminosity relation. Mass-lossrates, estimated from the 60-μm fluxes, show a correlation withvarious infrared colours and pulsation period. The mass-loss rate istightly correlated with the K-[12] colour. The kinematics andscaleheight of the sample show that the sources with periods less than1000d must have low-mass main-sequence progenitors. It is argued thatthe three oxygen-rich stars with periods over 1000d probably hadintermediate-mass main-sequence progenitors. For the other stars anaverage progenitor mass of about 1.3Msolar is estimated witha final white dwarf mass of 0.6Msolar. The average lifetimeof stars in this high mass-loss AGB phase is estimated to be about4×104yr, which suggests that these stars will undergoat most one more thermal pulse before leaving the AGB, if currenttheoretical relations between thermal interpulse period and core massare correct.
| Long period variable stars: galactic populations and infrared luminosity calibrations
In this paper HIPPARCOS astrometric and kinematic data are used tocalibrate both infrared luminosities and kinematical parameters of LongPeriod Variable stars (LPVs). Individual absolute K and IRAS 12 and 25luminosities of 800 LPVs are determined and made available in electronicform. The estimated mean kinematics is analyzed in terms of galacticpopulations. LPVs are found to belong to galactic populations rangingfrom the thin disk to the extended disk. An age range and a lower limitof the initial mass is given for stars of each population. A differenceof 1.3 mag in K for the upper limit of the Asymptotic Giant Branch isfound between the disk and old disk galactic populations, confirming itsdependence on the mass in the main sequence. LPVs with a thin envelopeare distinguished using the estimated mean IRAS luminosities. The levelof attraction (in the classification sense) of each group for the usualclassifying parameters of LPVs (variability and spectral types) isexamined. Table 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/374/968 or via ASTRIDdatabase (http://astrid.graal.univ-montp2.fr).
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| A library of 0.5 to 2.5 mu m spectra of luminous cool stars
We present a library of 0.5-2.5 mu m digital spectra of cool, mostlyvariable, giant and supergiant stars which should be useful for spectralsynthesis applications, as well as for comparison with theoretical modelatmosphere calculations. The library includes carbon stars, GalacticBulge and Magellanic Cloud stars, and OH/IR stars. The stars observedcover a range of metallicities and masses. Most variable objects wereobserved several times, at different phases of their pulsation cycle. Wediscuss the effects of various fundamental parameters and of variabilityon the spectra. Based on period-luminosity relations and stellarevolutionary tracks, we tentatively assign initial masses to eachobject.
| Optical and near-infrared spectrophotometric properties of Long Period Variables and other luminous red stars
Based on a new and large sample of optical and near-infrared spectraobtained at the Mount Stromlo and Siding Spring Observatories(Lançon & Wood 1998; Lançon & Wood, inpreparation), spectrophotometric properties of cool oxygen- andcarbon-rich Long Period Variables and supergiants are presented.Temperatures of oxygen-rich stars are assigned by comparison withsynthetic spectra computed from up-to-date oxygen-rich model atmospheregrids. The existence of reliable optical and near-infrared temperatureindicators is investigated. A narrow relation between the bolometriccorrection BC_I and the broad-band colour I-J is obtained foroxygen-rich cool stars. The ability of specific near-infrared indices toseparate luminosity classes, atmospheric chemistry or variabilitysubtypes is discussed. Some comments are also given on extinctioneffects, water band strengths in Long Period Variables and theevaluation of \element[][12]{CO}/\element[][13]{CO} ratio in red giants.
| Oxygen-rich semiregular and irregular variables. A catalogue of circumstellar CO observations
Using the SEST, the Onsala 20 m telescope, the JCMT, and the IRAM 30 mtelescope we have carried out a survey of circumstellar CO(J=1-0, 2-1,3-2, and 4-3) emission on a large sample of oxygen-rich semiregular (SRaand SRb) and irregular variables (Lb). A total of 109 stars wereobserved in at least one CO line: 66 were shown to have circumstellar COline emission (7 SRa, 36 SRb, and 23 Lb variables), ~ 60% of thesemiregulars and all but one of the irregulars were detected for thefirst time. Most stars were observed in at least two transitions. Thereis a total of 138 detected CO lines. For twelve stars stronginterference from interstellar CO emission precluded detection. Wepresent here a catalogue of all observational data and the spectra ofall detections, as well as brief discussions on detection statistics(including its dependence on variability type, period, IRAS-colour, IRASLRS-class, and M-subclass), line profiles (including line shapeasymmetry, multi-component line shapes, and line intensity ratios), gasexpansion velocity distributions, and correlations between CO line andIR continuum fluxes (including implications for the mass-lossmechanism). Based on observations collected using at the EuropeanSouthern Observatory, La Silla, Chile, the Onsala Space Observatory,Chalmers Tekniska Högskola, Sweden, the James Clerk MaxwellTelescope, Hawaii and the IRAM 30~m telescope, Pico Veleta, Spain.
| The Infrared Spectral Classification of Oxygen-rich Dust Shells
This paper presents infrared spectral classifications for a flux-limitedsample of 635 optically identified oxygen-rich variables includingsupergiants and sources on the asymptotic giant branch (AGB). Severalclasses of spectra from oxygen-rich dust exist, and these can bearranged in a smoothly varying sequence of spectral shapes known as thesilicate dust sequence. Classification based on this sequence revealsseveral dependencies of the dust emission on the properties of thecentral star. Nearly all S stars show broad emission features fromalumina dust, while most of the supergiants exhibit classic featuresfrom amorphous silicate dust. Mira variables with symmetric light curvesgenerally show broad alumina emission, while those with more asymmetriclight curves show classic silicate emission. These differences may arisefrom differences in the photospheric C/O ratio.
| Infrared giants vs. supergiants. II. CO observations
We report systematic observations of millimeter CO emission from asample of 109 oxygen-rich evolved stars (AGB and supergiants),colour-selected from the IRAS Point Source Catalog (0.69 200). In most cases, the observed spread in the valuesof this ratio can be explained by a large range of luminosities. Thisleads to a new criterion to identify AGB stars: an object with {cal R}< 150 must have a low mass progenitor. Here we study the correlationsbetween {cal R} and various physical properties of the sources. Mostsources with high values of {cal R} also have low galactic latitudes,small IRAS variability indices, and early spectral types (typicallyM1-M5). Conversely, there is no dependence on the IRAS colours, nor onthe intensity of silicate 10;microns emission. However, a few AGB starsexhibit large {cal R}; other factors than luminosity are required toexplain these values. Different hypotheses, such as the possiblepresence of a chromosphere, a low (12) C abundance or a variablemass-loss rate, are examined. Considering the global high OH detectionrate ( ~ 67%), we studied the correlations with CO and OH emission. Thedetection of OH seems to be a useful discriminator of mechanisms thatenhance {cal R}.
| 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.
| Mainline OH detection rates from blue circumstellar shells.
We identified 240 accessible circumstellar shells with water and/or SiOmasers, and used the Arecibo and Nancay radio telescopes to search formainline OH emission from them. Our targets are often Mira variableswithout previously known mainline masers. This search results in 89detections, of which 77 are new. The probability of detecting a maser islarger once a water maser is known, and becomes progressively larger thethicker and redder the shell. Nevertheless, almost all of our examplesof solitary 1665MHz masers, rather than the joint occurrence of both1665 and 1667MHz masers, are in the bluest shells. The IRAS lowresolution spectral type is the strongest factor correlating with themainline detection rate. We find that 67% of objects with a silicateemission feature exhibit masers, whereas only 27% of objects with acomparatively featureless 1n type do. These rates are colourinsensitive. We ascribe this clearcut difference to differing UVextinction properties of the two grain types, which is likely to resultfrom differing grain-size distributions. The IR colour sensitivity ofthe overall mainline detection rate is thus almost entirely anincidental artifact of the changing proportion of the two grain typeswith colour. Inferentially, since 90% of the sample exhibit watermasers, and the proportion of blue sources with silicate features issubstantially larger than an unbiased selection from the IRAS PointSource Catalog would give, the incidence of water masers is similarlysensitive to spectral type.
| Spectral Classification of Cold IRAS Stars: Supergiants
We have observed 72 stars with low resolution optical spectra (85 A/mmwith 2.3 A/pixel) covering 6000 to 8800 A in an attempt to identify thespectral type and luminosity class of a number of dusty IRAS sources.These stars were chosen from region IIIa of the van der Veen &Habing color-color diagram, where infrared late-type stars are foundwith generally strong 10μm silicate emission and often OH maseremission. We present here initial classficiation results. These includethe probable identification of 19 new M0--4 supergiants and there-classification of 3 stars formerly categorized as S stars: IRC+70012(M8 III), NSV12260 (M8 III) and IRC+60374 (M4 I).\begin{tabular}{|l|c|c|c|l|} IRAS name & old type & new type& other name 03572+5509 & M4 & M4 I & AG Cam 05361+4644& M6 & M3 I & IRC+50149 17360-3140 & M6,K5 & M2 I& IRC-30309 17513-2313 & M5 & M4 I & V774 Sgr 18025-2113& M2 & M3-4 I & IRC-20427 18135-1740 & M3 & M2 I& IRC-20455 18522+0021 & M5 & M4 I & IRC+0039218539+0026 & M & M4 I & IRC+00396 19229+1708 & M4e &M3-4 I & 19307+1338 & & M0 I & 19325+2346 & K5,M0& M2-3 I & 20004+2955 & K8 & K2-4 I & V1027 Cyg20015+3019 & M4 & M4 I & V719 Cyg 22048+5914 & & M4I & RAFGL 4286 22480+6002 & & M0 I & IRC+6037022512+6100 & S & M4 I & IRC+60374 23000+5932 & M3 &M3 I & AS Cep 23252+6010 & & M4 I & 23278+6000 & M4& M4 I & IRC+60409
| Characterization and proportion of very cold C-rich circumstellar envelopes
The paper develops a method for identification of very cold C-richcircumstellar envelopes (CSEs) in IR regions colder than region VII(i.e., larger value of IRAS flux ratio S25/S12), by reviewing thedifferent criteria and by identifying C-rich CSEs in a sample of 228bright IRAS sources. By using the results of OH surveys and catalogstogether with the results of additional HCN/CO millimeter observationsperformed on critical classes of objects, a C/O classification isproposed for 94 percent of the sources with a good probability. It isshown that the low-resolution spectra by themselves are a reasonable andeasy way to identify C-rich late AGB CSEs. For post-AGB object with coldCSEs, HCN and OH observations or visible/near IR spectroscopy arenecessary.
| 1612 MHz OH survey of IRAS point sources. I - Observations made at Dwingeloo, Effelsberg and Parkes
The data from a large sky survey are presented including a northernpilot study and a detailed southern study in which detections are biasedtoward the most evolved sources and distant sources. Both areinvestigated at the 1612-MHz transition of OH to take advantage of thestrongest line for AGB stars with optically thick dust shells. The IRASsources are chosen by considering their IR colors related to fluxes at12, 25, and 60 microns. Observations are reported for 2703 IRAS pointsources at the 1612-MHz transition, and 738 OH/IR stars are detected.The survey identifies 597 of the sources as previously unidentified, and95 percent of the OH profiles observed have twin-peak masercharacteristics which are related to emission from expandingcircumstellar shells. The other 5 percent of the sources are concludedto be transition objects between OH/IR stars and planetary nebulae.
| IRAS low-resolution spectral observations of the 10 and 18 micron silicate emission feature
The IRAS LRS Atlas contains 8-23 micron spectra of 1816 stars withsilicate emission features. In order to study the shapes of the silicatedust features, the 117 stars whose emission features appear to beoptically thin and which have the best signal-to-noise ratio at thelongest wavelengths were analyzed. Simple spherical dust shell modelswere calculated in both the optically thin and the slightly opticalthick approximations. From the comparison of the predicted spectra ofthe dust and stellar continuum, the emissivity function Kappa(lambda)was derived. In the different stars, the shape of the 10-micron featureis either narrow or broad and it is peaked either at about 9.7 micronsor at 10 microns. Either particle size effects (particles above 0.75microns in radius) or optical depth effects (central optical depth about1) could broaden the 10-micron feature. Chemical composition differencesno doubt are also important, particularly as regards the position of thepeak of the 10-micron feature. The stars with the peak at 10 microns aremore closely confined to the Galactic plane than the stars with the peakat 9.7 microns. The shape of the 18-micron feature is essentially thesame in all stars, and can be used to extend the interstellar extinctioncurve past 13 to 22 microns.
| New SiO masers associated with bright southern IRAS sources
The discovery of 31 new SiO v = 1, J = 1 - 0 (43.122 GHz) masersassociated with southern IRAS sources is reported. The candidate listfor the search was produced systematically, and the high detectionsuccess rate (about 50 percent) led to the consideration of differencesbetween stars associated with masers and those showing maser emission. Aset of conditions is proposed which virtually guarantee the presence ofdetectable stellar SiO maser. One of the most important requirements islarge optical variability (2.5 mag or greater), a condition associatedwith high mass-loss rate. In addition, it is found that themaser-to-infrared flux ratio is approximately proportional to themass-loss rate. New polarization observations of the SiO maserassociated with R Aqr, one of the two symbiotic stars known to show anytype of maser emission, are also presented.
| Dust-enshrouded asymptotic giant branch stars in the solar neighborhood
Using available infrared catalogs, an inventory is taken of the AGB starlosing large amounts of mass within about 1 kpc of the sun. A surfacedensity of these stars is estimated of about 25/sq kpc projected ontothe plane of the Galaxy. Of these stars, about one-half are oxygen-richwhile the other half are carbon-rich. The total mass-loss rate from AGBstars into the interstellar medium is probably between 3 and 6 x 10 tothe -4th solar mass/sq kpc/yr. Within the uncertainties, this is inreasonable agreement with an estimated net loss rate of about 8 x 10 tothe -4th solar mass/sq kpc/yr for main-sequence stars with initialmasses between 1 and 5 solar masses as they evolve to white dwarfs.However, it is possible that there are important sources of mass losswhich have not yet been identified. In the solar neighborhood, aboutone-half of all about 1.2 solar mass main-sequence stars spend greaterthan 30,000 yr in a carbon-star phase where they lose 1-2 x 10 to the-5th solar mass/yr and then become white dwarfs with about 0.7 solarmass.
| Lunar occultations of IRAS point sources, 1991-2000
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989ApJS...69..651C&db_key=AST
| A Catalog of Stellar Angular Diameters Measured by Lunar Occultation
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987AJ.....94..751W&db_key=AST
| 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.
| Standard stars for the comparison of methods of diameter determination.
Not Available
| Stellar angular diameters and visual surface brightness. III - an improved definition of the relationship
The relation between visual surface brightness and (V-R)(0) is refinedby taking explicit account of the effects of limb darkening, by adding40 new stars to the previous calibration, introducing extensive new BVRIphotometry, and by incorporating additional angular-diametermeasurements. A tight correlation between the visual surface brightnessindex and (V-R)(0) was found to exist over the entire distribution;hence the conclusion is strengthened that (V-R)(0) can be used to infervisual surface brightness for all luminosity classes and spectral types,including S and C types.
| Angular diameters for 11 late-type stars by the lunar occultation technique
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..414R&db_key=AST
| Broad-band 20-mu photometry of 50 stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976AJ.....81..764S&db_key=AST
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Nyilas |
| Rektaszcenzió: | 17h54m26.14s |
| Deklináció: | -23°14'09.7" |
| Vizuális fényesség: | 9.689 |
| RA sajátmozgás: | 4.1 |
| Dec sajátmozgás: | 0.5 |
| B-T magnitude: | 13.12 |
| V-T magnitude: | 9.973 |
Katalógusok és elnevezések:
|
