Contents
Images
Upload your image
DSS Images Other Images
Related articles
UVBLUE: A New High-Resolution Theoretical Library of Ultraviolet Stellar Spectra
We present an extended ultraviolet-blue (850-4700 Å) library oftheoretical stellar spectral energy distributions computed at highresolution, λ/Δλ=50,000. The UVBLUE grid, as wenamed the library, is based on LTE calculations carried out with ATLAS9and SYNTHE codes developed by R. L. Kurucz and consists of nearly 1800entries that cover a large volume of the parameter space. It spans arange in Teff from 3000 to 50,000 K, the surface gravityranges from logg=0.0 to 5.0 with Δlogg=0.5 dex, while sevenchemical compositions are considered:[M/H]=-2.0,-1.5,-1.0,-0.5,+0.0,+0.3, and +0.5 dex. For its coverageacross the Hertzsprung-Russell diagram, this library is the mostcomprehensive one ever computed at high resolution in theshort-wavelength spectral range, and useful application can be foreseenfor both the study of single stars and in population synthesis models ofgalaxies and other stellar systems. We briefly discuss some relevantissues for a safe application of the theoretical output to ultravioletobservations, and a comparison of our LTE models with the non-LTE (NLTE)ones from the TLUSTY code is also carried out. NLTE spectra are found,on average, to be slightly ``redder'' compared to the LTE ones for thesame value of Teff, while a larger difference could bedetected for weak lines, which are nearly wiped out by the enhanced coreemission component in case of NLTE atmospheres. These effects seem to bemagnified at low metallicity (typically [M/H]<~-1). A match with aworking sample of 111 stars from the IUE atlas, with availableatmosphere parameters from the literature, shows that UVBLUE modelsprovide an accurate description of the main mid- and low-resolutionspectral features for stars along the whole sequence from the B to ~G5type. The comparison sensibly degrades for later spectral types, withsupergiant stars that are in general more poorly reproduced than dwarfs.As a possible explanation of this overall trend, we partly invoke theuncertainty in the input atmosphere parameters to compute thetheoretical spectra. In addition, one should also consider the importantcontamination of the IUE stellar sample, where the presence of binaryand variable stars certainly works in the sense of artificiallyworsening the match between theory and observations.
| HD 19993 and HD 29035: New bright A-type emission-line stars
We present the results of photometric and spectroscopic observations oftwo A-type stars (HD 19993 and HD 29035), optical counterparts of theIRAS sources (F03108+3729 and 04331+5211, respectively). Hα lineemission is found in the optical spectra of both objects for the firsttime. Our analysis of the spectral line profiles and the photometricinformation shows that HD 19993 is an A7/8 II star (Teff~7500+/-200 K, log g =2.7+/-0.2, v sin i =35+/-2 km s-1,M=4.8+/- 0.8 Msun ) with a mild metal deficit ([Fe/H] ~-0.3+/-0.1), while HD 29035 is a B9/A0 V star (Teff ~10 000K, log g ~ 4, vsin i ~ 150 km s-1). The presence of an IRexcess and the Hα emission in combination with a very differentlocation in the Hertzsprung-Russell diagram suggest the different natureand evolutionary stages of the objects. We conclude that HD 29035 is acandidate Herbig Ae type star, a possible member of a group of similarobjects. HD 19993 seems to be a post-main-sequence object.
| Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue 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/399/141
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. II. Basic Parameters of Program Stars and the Role of Microturbulence
Paper I of this series presented precise MK spectral types for 372 lateA-, F-, and early G-type stars with the aim of understanding the natureof luminosity classification on the MK spectral classification systemfor this range of spectral types. In this paper, a multidimensionaldownhill simplex technique is introduced to determine the basicparameters of the program stars from fits of synthetic spectra andfluxes with observed spectra and fluxes from Strömgren uvbyphotometry. This exercise yields useful calibrations of the MK spectralclassification system but, most importantly, gives insight into thephysical nature of luminosity classification on the MK spectralclassification system. In particular, we find that in this range ofspectral types, microturbulence appears to be at least as important asgravity in determining the MK luminosity type.
| The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. I. Precise Spectral Types for 372 Stars
This is the first in a series of two papers that address the problem ofthe physical nature of luminosity classification in the late A-, F-, andearly G-type stars. In this paper, we present precise spectralclassifications of 372 stars on the MK system. For those stars in theset with Strömgren uvbyβ photometry, we derive reddenings andpresent a calibration of MK temperature types in terms of the intrinsicStrömgren (b-y)0 index. We also examine the relationshipbetween the luminosity class and the Strömgren c1 index,which measures the Balmer jump. The second paper will address thederivation of the physical parameters of these stars, and therelationships between these physical parameters and the luminosityclass. Stars classified in this paper include one new λ Bootisstar and 10 of the F- and G-type dwarfs with recently discoveredplanets.
| The pre-main-sequence star IP Persei
We present the results of high- and low-resolution spectroscopic andbroadband multicolour photometric observations of the emission-lineA-type star IP Per. Significant variations of the Balmer line profilesand near-IR brightness are detected. Comparison with the spectra ofother stars and theoretical models allowed us to derive its fundamentalparameters as follows: T_eff =~ 8000 K, log g =~ 4.4, logLbol/Lsun =~ 1.0. They correspond to the MK typeA7 v. We also found that the metallicity of the object's atmosphere isnearly 40 per cent that of the Sun. Our result for the star's gravityimplies that it is located at the zero-age main-sequence. We concludethat IP Per is a pre-main-sequence Herbig Ae star, and belongs to thegroup of UX Ori-type stars showing irregular photometric minima. Arecent result by Kovalchuk & Pugach (\cite{kp97}), that IP Per is anevolved high-luminosity star, is not confirmed. The discrepancy in thelog g determination, which led to the difference in the luminosity,seems to be due to uncertainties in the échelle data reductionfor broad lines and a different estimate for the star's temperature.
| Helium and Carbon Abundances in Late-B and Early-A Supergiants
The abundances of carbon and helium were determined for representativelate-B and early-A supergiants based on the C I lines (9078, 9089, 9095,9112) in the near-IR, C II lines (4267, 6151), and the He I 6678 line,in an aim to investigate the nature of the envelope-mixing in theseevolved stars based on the anomaly (if any) of these elements combinedwith that of N and O published before. It turned out that N tends toincrease with a decrease in C, showing a tendency of conserving the sumof C+N nuclei, which suggests that the anomaly of C and N may bereasonably interpreted as being due to mixing of the CN-processedmaterial. However, this increase/decrease in N/C, indicative ofdredge-up of the H-burning product, is not accompanied by anyHe-enrichment. Even surprisingly, the observed tendency is just theopposite, i.e., [He/H] appears to decrease progressively in accordancewith a lowering of [C/H]. Instead of regarding this apparentcharacteristics as being real, we tentatively speculate that someactivity-related line-weakening mechanism (e.g., irradiance of X-rays)might act on the formation of He I lines, the extent of which isindirectly related to the efficiency of envelope mixing via stellarrotation.
| Understanding A-type supergiants. I. Ultraviolet and visible spectral atlas
This paper is the first of a series whose aim is to perform a systematicstudy of A-type supergiant atmospheres and winds. Here we present aspectral atlas of 41 A-supergiants observed by us in high and mediumresolution in the visible and ultraviolet. The atlas consists ofprofiles of the Hα , Hβ , Hγ , Hdelta , Hepsilon , CaII (H and K), Na I (D1 and D2), Mg II4481, Mg II [uv1] and FeII [uv1, uv2, uv3, uv62, uv63, uv161] lines for 41 stars with spectraltypes ranging from B9 to A9 and luminosity classes Ia, Iab and Ib, andprovides the basic data for a thoughtful study of these stars. Theoverall characteristics of the sample as well as the data reductionprocedures are described. We also present some examples of spectralvariability. Figures 1-3 are only available in electronic form at thehttp://www.edpsciences.com} of A-type supergiants\fnmsep\thanks{Based onobservations made with the INT and JKT telescopes operated on the islandof La Palma by the RGO in the Spanish Observatorio del Roque de LosMuchachos of the Instituto de Astrofisica de Canarias, with the 2.2~mtelescope at Calar Alto Observatory, Spain, with the Bernard Lyot 2~mtelescope at Pic Du Midi Observatory, France and observations collectedat the European Southern Observatory at La Silla, Chile.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Understanding A-type supergiants. II. Atmospheric parameters and rotational velocities of Galactic A-type supergiants
We present the second paper of a series whose aim is to perform a globalstudy of Galactic A-supergiants. Very little work has been carried outto determine the stellar parameters of these stars. This is illustratedwith a brief review of some previous works. In this paper we analyze thedetermination of absolute magnitudes, spectral types and atmosphericparameters using the most recent Kurucz LTE blanketed model atmospheresand we discuss the applicability of the calibrations, such as theSchmidt-Kaler's (\cite{Sch-K}) calibration. Rotation is also animportant parameter in A-supergiants but their rotational velocities arepoorly known. We have calculated projected rotational velocities fromthe Fourier analysis of the observed Mg II (4481 Ä) line. Based onobservations made with the INT and JKT telescopes operated on the islandof La Palma by the RGO in the Spanish Observatorio del Roque de LosMuchachos of the Instituto de Astrofisica de Canarias, with the 2.2mtelescope at Calar Alto Observatory, Spain, with the Bernard Lyot 2mtelescope at Pic Du Midi Observatory, France and observations collectedat the European Southern Observatory at La Silla, Chile
| Oxygen Abundances in Late-B through F Supergiants
A spectral-synthesis analysis was performed for twenty-six late-Bthrough F supergiants (including Cepheids) in order to determine theirphotospheric oxygen abundances from the O I 6156--8 feature, whiletaking into account the non-LTE effect, which is progressivelyT_eff-dependent from < 0.1 dex for F-type supergiants to ~ 0.4 dexfor late-B ones in terms of the non-LTE abundance correction. Theresulting oxygen abundances show a moderate underabundance relative tothe Sun ([O/H] ~ -0.3) along with a remarkably small scatter (within +/-0.1 dex) over this wide temperature range. Considering the recentevidence that the solar oxygen abundance is mildly enhanced by 0.2--0.3dex relative to that of the galactic gas which forms young stars, weconclude that the original O-composition in the atmosphere of thesesupergiants had suffered almost no appreciable alteration during theirpast evolutionary history, even though signs of significant mixing ofCN-cycle or NeNa-cycle products are evident. This excludes thepossibility of any global-mixing mechanism, such that producing asignificant reduction of oxygen due to a deep dredge-up of considerableON-processed material, whatever the details of the envelope-mixingprocess for these relatively massive stars may be.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| The yellow hypergiants
We list the main stellar data of known hypergiants and similarlyluminous stars, and then concentrate on a review of the yellowhypergiants. These stars are post-red supergiants evolving alongblueward loops in the Hertzsprung-Russell diagram. Their properties,their location in the Hertzsprung-Russell diagram and their occasionalmass ejections are related to a region of atmospheric instability in theH-R diagram, the Yellow Void. The `bouncing against the border of theVoid' of three objects: ρ Cas, HR8752 and IRC+10420, is described.The apparent atmospheric instability of yellow hypergiants is related tothe atmospheric pulsations. There are indications that the approach tothe Void is associated with an increased amplitude of the pulsation andwith enhanced mass loss. The observed small-scale motion field is onlyapparently strongly supersonic; the observed large stochastic velocitiesare the quasi-stochastically varying thermal motions in the many hotsheets that occur in the wakes of many small shocks, while the realhydrodynamic velocity component is small and subsonic. This shock-wavefield is also responsible for the observed rate of mass loss and foremission in the wings of Hα . Most yellow hypergiants haveenvelopes containing gas and dust, but a thick extended envelope,presumably dissipating and showing bipolar outflow, is only known aroundIRC+10420. At the interface of the bipolar wind and the interstellarmedium one or more stationary shocks may develop as is observed in thecase of IRC+10420 and suspected with ρ Cas.
| High resolution spectroscopy of symbiotic stars. IV. BX Monocerotis: orbital and stellar parameters
We investigate the orbit and the components of the symbiotic BX Monsystem with new high resolution spectroscopy, IUE spectra, publishedphotographic magnitudes, and brightness estimates from the RASNZ. Wereview the available photometry and deduce a new binary period of 1401days. We also find evidence in the IUE data that BX Mon is an eclipsingsystem. With our high resolution spectroscopy we determine the radialvelocity curve of the M giant from photospheric absorption features. BXMon is unusual for a symbiotic star in that its hot component is alsoobservable in the optical wavelength region. From correspondingabsorption features we are able to measure the hot component's radialvelocity. We determine semi-amplitudes for the cool and the hotcomponents of 4.3 km s(-1) and 29 km s(-1) , respectively. The massratio is thus ~ 7 which is among the highest yet found for symbioticsystems. The orbit of BX Mon is eccentric with an ellipticity of e=0.49.The binary mass function is 0.0076 M_sun. We determine the mass of thered giant as M_r=3.7 Msun and the mass of the hot componentas M_h=0.55 M_sun. This low M_h suggests that even relatively high masssymbiotics are unlikely to be supernova Type I progenitors. The distanceto BX Mon of 3 kpc is determined with the Na I lambda lambda5890 ,5896interstellar absorption lines and the interstellar extinction feature at2200 Angstroms. For the luminosity of the cool component we findL_r=3400 Lsun and a stellar radius R_r=160 Rsun.The red giant's radius remains within the inner Lagrangian point, evenat periastron. The hot component is unlikely to be a main sequence star.Based on observations obtained at the European Southern Observatory, LaSilla (Chile), visual brightness data from the RASNZ, and UV spectrafrom the IUE archive. ESO observations were granted for the programs47.7-081, 48.7-083, 49.7-041, 50.7-129, 51.7-093, 52.7-068, 53.7-083,54.E-061, 55.E-446, 56.E-526
| Temperatures for A0-K0 Supergiants from 13-Color Photometry
Observations on the 13-color photometric system are reported for 71A0-K0 supergiant stars brighter than V=6.0. Three independent methods todetermine the effective temperatures for A0-K0 supergiants from their13C photometry are discussed: 1) Calibrations between T$eff$and reddening-free indices are developed; temperatures were collectedfrom the literature for the calibration stars, and most of them werespectroscopically determined. 2) An empirical correlation betweenintrinsic colors in the 13C system and T$eff$ has beenderived. 3) The unreddened colors are compared with synthetic colorscalculated by Kurucz (1989); this leads to simultaneous estimates forT$eff$ and log $g$. The estimated uncertainties inT$eff$ by the three methods are comparable and areapproximately plus or minus 200-300K. (SECTION: Stars)
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| The Supergiant Binary BM CAS
Attracted by an earlier claim (Thiessen 1956) that BM Cas is aneclipsing binary with one component a classical Cepheid, we haveobtained new photometry and IUE ultraviolet spectra of the system. Whilewe verify that there is variability in addition to the eclipses, weconclude that there is no classical Cepheid present. The variability isirregular, and, since it is present in the uv spectra as well as in theV photometry, we believe it is associated with the hotter component. Wefind the latter to be a high-luminosity star of spectral type of A6, inclose agreement with the MK assignment of A7 Iab (Bidelman 1982), andthe secondary component most likely to be a late-K or early-M giant. Thelatter appears to fill or nearly fill it Roch lobe, while the primarystar is not far from doing so as well, implying a complex evolutionaryhistory for the syste. (SECTION: Stars)
| On the Variability of Early A-Type Supergiants
An examination of the Hipparcos photometry of 26 bright early A-typesupergiants shows that they are all variable.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Radiation driven wind models for A, F and G supergiants.
We investigate the effects of radiation pressure on the atmospheres ofA, F and G-supergiants by calculating hydrodynamical model atmospheresfor stars with 5500<=T_eff_<=9500K. In the subsonic part of thewind, the radiation pressure by continuum and lines from Kurucz (1992,ATLAS 6 program) is taken into account. In the supersonic part of thewind, the radiation pressure is expressed in terms of the forcemultiplier formalism (Castor et al. 1975ApJ...195..157C) with thecorrection for the finite disk taken into account. The temperaturestructure is from the T(τ) relation of blanketed model atmospheres.The predicted mass loss rates of the A-supergiants agrees excellentlywith the observed values. However the predicted terminal velocities areabout a factor 3 higher than observed. We discuss several possiblecauses for this discrepancy. The most likely one is a change in theforce multiplier parameter α of the line radiation force fromabout 0.5 in the lower parts of the wind to a much smaller value ofabout 0.1 throughout most of the wind. This might be the result of achange in the ionization of the wind with distance, or a decoupling ofthe line driven ions in the wind from the ambient gas. The predictedmass loss rate of the G-type supergiant 22Vul, which is the onlyG-supergiant with a reliable mass loss rate, is a factor 10^5^ smallerthan observed. This is probably due to the fact that G-supergiants havechromospheres, which were not taken into account in our model. Ourmodels for F-supergiants could not be compared with observations becausethere are no reliable empirical mass loss rates or terminal windvelocities for normal F-supergiants. The F-supergiants ρCas andHR8752 have highly variable mass loss rates which obviously cannot beexplained by our models. We conclude that mass loss from A-typesupergiants is most likely due to a line driven wind but that the massloss from G-supergiants is not. It is interesting to find the spectraltype between F0 and G3 where the radiation driven wind models break downand to compare that with the type where the chromospheres becomenoticeable. The high opacity in the hydrogen ionization zone produces anet outward force in those layers. This gives rise to a pressureinversion in the subsonic part of the atmosphere, but does not lead tohigh mass loss rates.
| On the Abundances of Nitrogen and Sulfur in Late-B through F Supergiants Atmospheres
An extensive non-LTE analysis of NI and SI lines at the spectral regionaround lambda ~ 8700Angstroms was performed for late-B through Fsupergiants in order to determine the photospheric abundances of N and Sin such massive evolved stars. It was revealed that the abundances ofnitrogen in these stars show a rather large diversity ( ~ +/- 0.4 dex)around the mean of [N/H] =~ 0.3 relative to the Sun, being roughlydivided into three groups: (i) markedly large overabundances amountingto 0.6--0.7 dex, (ii) mild N-excesses of 0.3--0.4 dex, and (iii)near-solar (or slightly subsolar) [N/H]-values. The abundances of sulfurfor F-supergiants were found to be nearly homogeneous and not muchdifferent from the solar composition ([S/H] ~ -0.2), while those for theA-type generally show a tendency of S-excess (up to +0.8 dex)systematically increasing with T_eff. There also appears a trend ofmass-dependence as well as a possibility of mutual correlation regardingthe values of [N/H] and [S/H] in those A-supergiants. It was confirmedthat the extent of the N-excess in A--F supergiants tends to depend onthat of sodium as [N/H] =~ [Na/H].
| Atmospheric Parameters and LTE Abundances for 22 Galactic, A-Type Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..659V&db_key=AST
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| Terminal Velocities and the Bistability of Stellar Winds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...455..269L&db_key=AST
| Sodium Enrichment in A--F Type Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...451..298E&db_key=AST
| CNO Abundances and the Evolutionary Status of Galactic, A-Type Supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...449..839V&db_key=AST
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
Catalogs and designations:
|
