Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
On the massive stellar population of the super star cluster Westerlund 1
We present new spectroscopic and photometric observations of the youngGalactic open cluster Westerlund 1 (Wd 1) that reveala unique population of massive evolved stars. We identify ~200 clustermembers and present spectroscopic classifications for ~25% of these. Wefind that all stars so classified are unambiguously post-Main Sequenceobjects, consistent with an apparent lack of an identifiable MainSequence in our photometric data to V 20. We are able to identifyrich populations of Wolf Rayet stars, OB supergiants and short livedtransitional objects. Of these, the latter group consists of both hot(Luminous Blue Variable and extreme B supergiant) and cool (YellowHypergiant and Red Supergiant) objects - we find that half the knownGalactic population of YHGs resides within Wd 1. We obtain a meanV-MV ~ 25 mag from the cluster Yellow Hypergiants, implying aMain Sequence turnoff at or below MV =-5 (O7 V or later).Based solely on the masses inferred for the 53 spectroscopicallyclassified stars, we determine an absolute minimum mass of ~1.5 ×10^3~Mȯ for Wd 1. However, considering the completephotometrically and spectroscopically selected cluster population andadopting a Kroupa IMF we infer a likely mass for Wd 1 of~10^5~Mȯ, noting that inevitable source confusion andincompleteness are likely to render this an underestimate. As such, Wd 1is the most massive compact young cluster yet identified in the LocalGroup, with a mass exceeding that of Galactic Centre clusters such asthe Arches and Quintuplet. Indeed, the luminosity, inferred mass andcompact nature of Wd 1 are comparable with those of Super Star Clusters- previously identified only in external galaxies - and is consistentwith expectations for a Globular Cluster progenitor.
| HD 183143: A Hypergiant
We present spectroscopic evidence that the luminosity of HD 183143 ishigher by one magnitude than thought previously. The star is yet anotherB6-8 Ia-0 white hypergiant of the Galaxy. Its absolute visual magnitudeis close to -8 mag, and its distance is close to 2 kpc. We describespectroscopic manifestations of the nonstationary behavior of itsatmosphere and wind.
| 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.
| Search for magnetic fields in A-type supergiants
We have searched for magnetic signatures in A-type supergiants. Theobtained magnetic values for seven of these stars are presented here.
| A Method for Simultaneous Determination of AV and R and Applications
A method for the simultaneous determination of the interstellarextinction (AV) and of the ratio of total to selectiveextinction (R), derived from the 1989 Cardelli, Clayton, & Mathisfitting of the interstellar extinction law, is presented and applied toa set of 1900 color excesses derived from observations of stars inUBVRIJHKL. The method is used to study the stability of AVand R within selected regions in Perseus, Scorpius, Monoceros, Orion,Sagittarius, Ophiuchus, Carina, and Serpens. Analysis shows that R isapproximately constant and peculiar to each sector, with mean valuesthat vary from 3.2 in Perseus to 5.6 in Ophiuchus. These results aresimilar to published values by Aiello et al., He et al., Vrba &Rydgren, O'Donnell, and Cardelli, Clayton, & Mathis.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only 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/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| 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
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
| An atlas of 2.4 to 4.1 mu m ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with theShort Wavelength Spectrometer (SWS) during the Post-Helium program ofthe Infrared Space Observatory (ISO). This program is aimed at extendingthe Morgan & Keenan classification scheme into the near-infrared.Later type stars will be discussed in a separate publication. Theobservations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 μm, supplemented with 10 spectra acquired during the nominal mission witha similar observational setting. For B-type stars, this sample providesample spectral coverage in terms of subtype and luminosity class. ForO-type stars, the ISO sample is coarse and therefore is complementedwith 8 UKIRT Larcmin -band observations. In terms of the presence ofdiagnostic lines, the Larcmin -band is likely the most promising of thenear-infrared atmospheric windows for the study of the physicalproperties of B stars. Specifically, this wavelength interval containsthe Bralpha , Pfgamma , and other Pfund lines which are probes ofspectral type, luminosity class and mass loss. Here, we present simpleempirical methods based on the lines present in the 2.4 to 4.1 mu minterval that allow the determination of i) the spectral type of Bdwarfs and giants to within two subtypes; ii) the luminosity class of Bstars to within two classes; iii) the mass-loss rate of O stars and Bsupergiants to within 0.25 dex. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA. The appendix is only available inelectronic form at the 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/384/473
| GMRT observations of interstellar clouds in the 21cm line of atomic hydrogen.
Nearby interstellar clouds with high (|v| >/= 10 km/s) randomvelocities although easily detected in NaI and CaII lines have hithertonot been detected (in emission or absorption) in the HI 21cm line. Wedescribe here deep Giant Metrewave Radio Telescope (GMRT) HI absorptionobservations toward radio sources with small angular separation frombright O and B stars whose spectra reveal the presence of interveninghigh random velocity CaII absorbing clouds. In 5 out of the 14directions searched we detect HI 21cm absorption features from theseclouds. The mean optical depth of these detections is ~ 0.09 and FWHM is~ 10 km/s, consistent with absorption arising from CNM clouds.
| 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
| 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.
| Spectral variability of luminous early type stars. I. Peculiar supergiant HD199478
We have obtained time-series of high-quality Hα spectra with highresolution in wavelength (R = lambda /delta lambda of 15000 to 22000)and time (Delta t =1d) of the late-type B supergiant HD199478. Thespectra were analysed in terms of line-profile variability (lpv) usingcontemporary techniques of time-series analysis, such as TemporalVariance Spectrum and the 2d- Discrete Fourier Transform. The Hαprofile is found to consist of a highly variable emission core (between-280 and +150 km s-1) superimposed on almost constant,extended (+/-1000 km s-1) emission wings. Due to the lack ofstrong line-emission, the latter is attributed to electron-scattering indeep atmospheric layers. The Hα variability manifests itself byvariations in velocity and intensity of blue- and red-shifted emissionpeaks, which result in drastic alterations in the shape of the profilefrom almost symmetric and unshifted emission, with respect to thestellar rest frame, through blue- or red-shifted asymmetric emission, todouble-peaked emission or a reverse P Cygni-type profile. Significantvariations in total emissivity (i.e. EW) of the line are also noted, butthese variations do not appear to be obviously linked to changes in theline-profile shape. The pattern of variability resembles that inBe-stars - though on a much shorter time scale - and suggestsinterpretation in terms of an axially symmetric and perturbed stellarwind. Since the time-scale of the V/R variations is found to be 3 to 5times longer than the radial fundamental pulsation period but consistentwith rotational period, rotational modulation as a possible cause forthis variability is considered. Besides variations in Hα ,continuous changes in velocity (typical dispersion of sigma ~ 5 kms-1) and strength, i.e. EW, (up to 13% of the mean) of asample of three absorption lines (CII lambda lambda6583 , 6578 and HeIlambda6678 ) were also observed. The phenomenon observed is more likelyconnected to changes in velocity and temperature structures of thestellar photosphere. Pulsation instability as a possible cause ofphotospheric variability is suggested.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Empirical calibration of the lambda 4000 Å break
Empirical fitting functions, describing the behaviour of the lambda 4000Ä break, D4000, in terms of effective temperature,metallicity and surface gravity, are presented. For this purpose, thebreak has been measured in 392 stars from the Lick/IDS Library. We havefollowed a very detailed error treatment in the reduction and fittingprocedures, allowing for a reliable estimation of the breakuncertainties. This calibration can be easily incorporated into stellarpopulation models to provide accurate predictions of the break amplitudefor, relatively old, composite systems. Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| On correlations between diffuse interstellar bands
One way to better apprehend the problem of diffuse interstellar bands(DIBs) is to search for correlations between the bands in a large sampleof spectra towards various lines of sight: a strict correlation mayimply that a common carrier is at the origin of the bands, whereas anon-correlation means that different species are involved. We proposethis observational test for 10 DIBs collected in up to 62 Galactic linesof sight. Strong DIBs do not strictly correlate, and sometimes thecorrelation is very poor. Only one example of a strict correlation hasbeen found in our sample between the DIBs at 6614 and 6196 Ä, thatcould signify a single carrier for those two bands. The general absenceof strict correlations is discussed in the context of molecular carriersfor the DIBs.
| Galactic B-supergiants: A non-LTE model atmosphere analysis to estimate atmospheric parameters and chemical compositions
A non-LTE model atmosphere analysis of moderate resolution (R ~ 5 000)spectra of 46 Galactic B-type supergiants is presented. Standardtechniques are adopted, viz. plane-parallel geometry and radiative andhydrostatic equilibrium. Spectroscopic atmospheric parameters (T_eff,log g & v_turb) and chemical abundances (He, C, N, O, Mg & Si)are estimated, both as a test of the validity of such an approach and inan attempt to provide consistent results for supergiants covering asignificant range of spectral types. The values of the estimatedatmospheric parameters and their dependence on the physics adopted inthe model atmospheres calculations are discussed. The absolute metalabundances are compared to those of main sequence B-type stars and, ingeneral, their chemical compositions appear to be similar. Theabundances for He, C, N & O are considered in some detail and arediscussed in the context of possible evolutionary histories for thisstellar sample. Specifically, it is found that the supergiant sample canbe subdivided into a number of evolutionarily distinct groups. The lowermass objects are predominantly chemically near-normal i.e. theirphotospheres show little or no evidence for chemical processing, whereasthe higher mass supergiants have CNO ratios which are indicative of CNand possibly NO-cycle burning. An attempt is made to quantify thedifference in nitrogen and carbon abundances between the high and lowmass targets but this is hampered by theoretical uncertainties. Thepossibilities that the most highly processed supergiants may have eitherlarger rotational velocities or have undergone mass transfer within abinary system are discussed.
| Suprathermal rotation of PAHs in the ISM II. Observational evidence for the rotational broadening of lambda 5797 DIB in reflection nebulae - implication for the carrier size
In a previous paper, we described a model which can explain thelambda5797 diffuse interstellar band (DIB) profile as seen in absorptionin the diffuse interstellar medium and in emission in the Red Rectangle(RR), as a rotational envelope of electronic transitions where themolecular carrier is a free PAH of size ~ 40 atoms. One of the strongestpredictions is the behaviour of the rotational temperature of PAH in thecase of regions rich in UV such as Reflection Nebulae: it must besuprathermal with respect to the gas temperature but clamped to ~ 100 Kfor any PAH size. The width of the DIB, in such regions, can then bebroader than in the classical ISM (T_rot ~ 30 K) if the values of themolecular transition are favorable. In order to test this prediction, wehave obtained high resolution spectra of 27 reddened early type stars,mostly in reflection nebulae, in order to compare their lambda 5797 DIBwidth to those of stars in classical diffuse interstellar medium. Thesespectra were made for several DIBs such as lambda 5797, lambda6379 andlambda6613 , with a spectral resolving power of about 60 000. Theanalysis of the results agrees with our predic tion since the width ofthe lambda 5797 DIB is broader in a majority of areas with strong UVradiation. Moreover, the broadening is not observed on DIBs lambda6379and lambda6613 , indicating that the molecular parameters of theelectronic transitions at the origin of the different DIBs are prettyvariable from one DIB to another and confirming that the measuredbroadening on lambda 5797 is not due to an instrumental bias. Thestatistical measurement of the lambda 5797 width in this medium permitsthe derivation of new constraints on the size of the carrier of thisDIB, a molecule that should have 30 to 45 carbon atoms if, as wepropose, it is indeed a PAH. Based on observations made at Observatoirede Haute Provence (CNRS), France.
| 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.
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - II.
Not Available
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - I.
Not Available
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| 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.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Photometric Monitoring of Bright Be Stars. III. 1988-89 and 1992-95
We report long-term photometric (BV) observations of 23 bright, activeBe stars made in 1988 and 1989 and 1992 and 1995 with the 0.4m telescopeat the University of Toronto. Cumulative light curves, includingobservations made earlier at the University of Toronto, and with theAutomatic Photometric Telescope Service in Arizona, are presented forseveral of the stars. Many of the stars show cyclic variations of up to0.2 in V and B on time scales of a few years, as well as variations ontime scales of about a day. (SECTION: Stars)
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| H gamma and H delta Absorption Features in Stars and Stellar Populations
The H gamma and H delta absorption features are measured in a sample of455 (out of an original 460) Lick/IDS stars with pseudo--equivalentwidth indices. For each Balmer feature, two definitions, involving anarrow (~20 Angstroms) and a wide (~40 Angstroms) central bandpass, aremeasured. These four new Balmer indices augment 21 indices previouslydetermined by Worthey et al., and polynomial fitting functions that giveindex strengths as a function of stellar temperature, gravity, and[Fe/H] are provided. The new indices are folded into models for theintegrated light of stellar populations, and predictions are given forsingle-burst stellar populations of a variety of ages and metallicities.Contrary to our initial hopes, the indices cannot break a degeneracybetween burst age and burst strength in post-starburst objects, but theyare successful mean-age indicators when used with sensitive metallicityindicators. An appendix gives data, advice, and examples of how totransform new spectra to the 25-index Lick/IDS system.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kugu |
| Sað Açýklýk: | 20h55m49.80s |
| Yükselim: | +47°25'04.0" |
| Görünürdeki Parlaklýk: | 5.67 |
| Uzaklýk: | 2857.143 parsek |
| özdevim Sað Açýklýk: | -1.9 |
| özdevim Yükselim: | -4.4 |
| B-T magnitude: | 6.178 |
| V-T magnitude: | 5.757 |
Kataloglar ve belirtme:
|
