Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Effects of gravitational darkening on the determination of fundamental parameters in fast-rotating B-type stars
In this paper we develop a calculation code to account for the effectscarried by fast rotation on the observed spectra of early-type stars.Stars are assumed to be in rigid rotation, and the grid ofplane-parallel model atmospheres used to represent the gravitationaldarkening are calculated by means of a non-LTE approach. Attention ispaid to the relation between the apparent and parent non-rotatingcounterpart stellar fundamental parameters and apparent, and true V sini parameters as a function of the rotation rate Ω/Ω_c,stellar mass, and inclination angle. It is shown that omitting ofgravitational darkening in the analysis of chemical abundances of CNOelements can produce systematic overestimation or underestimation,depending on the lines used, rotational rate, and inclination angle. Theproximity of Be stars to the critical rotation is revised whilecorrecting not only the V sin i of 130 Be stars, but also theireffective temperature and gravity to account for stellar rotationallyinduced geometrical distortion and for the concomitant gravitationaldarkening effect. We concluded that the V sin i increase is accompaniedby an even higher value for the stellar equatorial critical velocity, sothat the most probable average rate of the angular velocity of Be starsattains Ω/Ωc ≃ 0.88.
| Short-Period Variable Be Stars Discovered or Confirmed through Self-Correlation Analysis of Hipparcos Epoch Photometry
We have surveyed 277 bright Be stars for short-period (0.2-2 day)photometric variability using self-correlation analysis of Hipparcosepoch photometry. This extends the work of Percy et al.; the methods areas described there. We report the discovery, timescale, and amplitude ofshort-period variability in: HD 7636 (V764 Cas), HD 11606 (V777 Cas), HD13661 (V549 Per), HD 34921, HD 36408, HD 40978, HD 58343 (FW CMa), HD63460 (o Pup), HD 88195 (17 Sex), HD 89353 (AG Ant, HR 4049), HD 129954(CO Cir), HD 158220 (V862 Ara), HD 173219 (V947 Sct), and HD 187567(V1339 Aql). We report the confirmation of short-period variabilityusing an independent form of analysis in HD 52918 (19 Mon), HD 105382(V863 Cen), HD 137387 (κ-1 Aps), HD 157832 (V750 Ara), and HD163868 (V3984 Sgr). These include a β Cephei star (19 Mon), aVega-type star (17 Sex), and a post-asymptotic giant branch B star (HR4049). We find that short-period variability is more prevalent inearly-B stars than in late-B stars. We have found no β Cephei typevariables in our sample of Be stars, other than 19 Mon, which isapparently not a Be star.
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 are only available in electronic form at the CDS viaanonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/1083
| High and intermediate-resolution spectroscopy of Be stars 4481 lines
We present an atlas of Hγ , He i lambda 4471 and Mg ii lambda 4481line profiles obtained in a 10 year observation period of 116 Be stars,which enabled many of them to be observed at quite different emissionepochs. From the best fit of the observed He i lambda 4471 line profileswith non-LTE, uniform (Teff,log g) and full limb-darkenedmodel line profiles, we determined the V sin i of the program stars. Toaccount, to some degree, for the line formation peculiarities related tothe rapid rotation-induced non-uniform distributions of temperature andgravity on the stellar surface, the fit was achieved by considering(Teff,log g) as free parameters. This method produced V sin iestimations that correlate with the rotational velocities determined bySlettebak (1982) within a dispersion sigma <= 30 km s-1and without any systematic deviation. They can be considered as given inthe new Slettebak's et al. (1975) system. Only 13 program stars havediscrepant V sin i values. In some objects, this discrepancy could beattributed to binary effects. Using the newly determined V sin iparameters, we found that the ratio of true rotational velocitiesV/Vc of the program Be stars has a very low dispersion aroundthe mean value. Assuming then that all the stars are rigid rotators withthe same ratio V(/lineω)/Vc, we looked for the value of/line ω that better represents the distribution of V sini/Vc for randomly oriented rotational axes. We obtained/lineω = 0.795. This value enabled us to determine the probableinclination angle of the stellar rotation axis of the program stars. Inthe observed line profiles of Hγ , He i lambda 4471, Mg ii lambda4481 and Fe ii lambda 4351 we measured several parameters related to theabsorption and/or emission components, such as: equivalent width,residual emission and/or absorption intensity, FWHM, emission peakseparations, etc. The parameters related to the Hγ line emissionprofiles were used to investigate the structure of the nearbyenvironment of the central star. From the characteristics of thecorrelations between these quantities and the inferred inclinationangle, we concluded that in most of cases the Hγ line emissionforming regions may not be strongly flattened. Using a simplerepresentation of the radiation flux emitted by the star+envelopesystem, we derived first order estimates of physical parameterscharacterizing the Hγ line emission formation region. Thus, weobtained that the total extent of the Hγ region is Rf=~ 2.5 +/- 1.0 R* and that the density distribution in theselayers can be mimicked with a power law rho ~ R-alpha , wherealpha =2.5+2.2-0.6. The same approach enabled usto estimate the optical depth of the Hγ line emission formationregion. From its dependence with the aspect angle, we concluded thatthese regions are caracterized by a modest flattening and that the rho(equator)/rho (pole) density contrast of the circumstellar envelope nearthe star should be two orders of magnitude lower than predicted bymodels based on a priori disc-shaped circumstellar envelopes. We foundthat the separation between the emission peaks, Deltap, andthe full width at half maximum, Delta 1/2, of the Hγline emission are not only sensitive to kinematic effects, but to lineoptical depth as well. This finding agrees with previous theoreticalpredictions and confirms that Huang's (1972) relation overestimates theextent of the Hγ line emission formation region. Data obtained atCASLEO operated under agreement between the CONICET and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina, at ESOLa Silla, Chile and at OHP, France.}\fnmsep\thanks{Tables 2 to 7 andFigs. 1 and 2 are only available in full in electronic form at 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/378/861}} \subtitle{Anatlas of Hγ , He {\fontsize {10pt}{12pt}\selectfont I} 4471 and Mg{\fontsize {10pt}{12pt}\selectfont II
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| On the Variability of O4-B5 Luminosity Class III-V Stars
We investigate the Hipparcos Satellite photometry of O4-B5 luminosityclass III-V stars. Some for which further study is desirable areidentified. These stars in general are more variable than cooler stars
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| 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.
| Investigation of the variability of bright Be stars using HIPPARCOS photometry
The high accuracy and the homogeneity of Hipparcos data for bright starshave allowed us to quantify the degree of variability of Be stars. Thisdegree has been found to be highly dependent on the temperature of thestar. Rapid variability is the main feature of the 86% of early Be andless than 20% of late Be stars taking into account the limit ofdetection considered. In addition to Be stars reported in the Hipparcoscatalogue (ESA 1997) as short-period variables, we have been able toenlarge the number of detections as well as to confirm periodspreviously determined. Be stars that show larger amplitude rapidvariations are proposed as candidates for a search of multiperiodicityi.e. as non-radial pulsators. We have also searched for the presence ofoutbursts and fading events in the Hipparcos data. Outbursts have beenfrequently and preferentially detected in early Be stars with rather lowto moderate v sini while fading events seem to be more conspicuous instars with higher v sini. Mid-term and long-term variations have alsobeen investigated. Several stars have shown some evidence of temporaryquasi-periodic oscillations ranging between 10 and 200 days. Finallyinformation concerning long-term variations is reported. Cycles shorterthan or equal to the Hipparcos mission have mainly been detected instars earlier than B6. Long-term time scales of late Be stars areconfirmed to be longer by far. Tables 1 and 2 are only available inelectronic form at CDS via ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| On Space Velocities of Binary Stars in Which One Component Has Experienced a Supernova Explosion
When one component of an evolved binary loses a significant fraction ofits initial mass in a symmetric supernova explosion but remains bound toits companion, the remnant binary recoils with a velocity that can becomparable to the orbital velocity of the supernova precursor. Thisvelocity is enough to explain the observed peculiar space velocitiesand/or distances from the Galactic plane of most X-ray binaries andbinary OB runaway stars. Some exceptions certainly occur, butuncertainties in estimates of velocities and distances, as well asmechanisms other than a popular asymmetric kick, may be responsible formost of the exceptions.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| Spectral reclassification of some Be stars using Delta-Q method
The way in which the new defined value Delta-Q can play a role in thespectral reclassification of Be stars is shown by means of aninvestigation of 56 Be stars. A general survey carried out in order toobtain spectral subclasses or U, B, V values for these stars ispresented. The suggested Delta-Q method was found to be very helpful inchoosing the correct spectral subclass from among many subclassesassigned for the same star, and hence, the reclassification for thisstar.
| Distribution and motions of OB stars in the direction of H and KHI Perseus.
Not Available
| The binary frequency and origin of the OB runaway stars
A radial velocity survey of the bright northern OB runaway stars hasbeen undertaken to determine the frequency of binary stars in thishigh-velocity group. A total of 634 high-dispersion spectrograms of 36proposed runaway stars were obtained over a two year period.Approximately half of the stars are velocity-variable; these includeseven spectroscopic binaries, one possible beta-Cephei variable, and 10stars with emission lines in their spectra. The latter group containsseven of the eight Be stars observed and three luminous O stars, and itis argued that their variability is caused by nonradial pulsation.Fifteen of the program stars have a peculiar radial velocity greaterthan 30 km/s; five others are probable runaways on the basis of distancefrom the galactic plane and proper motion. Only two of the confirmed andprobable runaways, HD 3950 and HD 198846 (Y Cyg), are binaries, and bothare double-lines systems. New orbital elements are presented for HD 3950and the five new binary systems found among the low-velocity stars. Thestatisical methods used to assess velocity variability and periodicsignals are described in detail. The higher fractional abundance ofrunaways among more massive stars, their binary frequency, and theproperties of the runaway binaries suggest that they obtained their highvelocities through single-binary, binary-binary, or n-body closeencounters during the early dynamical evolution of associations.
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| A second catalog of the profile of the H-alpha line in 55 Be stars
A second catalog of the H-alpha line profile of 55 Be stars ispresented, thereby raising the total H-alpha line profiles for Be starsto 127 stars. The measurements were made with the echelle spectrographon the 152 cm telescope at the Haute Provence Observatory. Photosphericabsorption was dominant in 12 percent of the stars, and not visible atall in 64 percent of the objects, where H-alpha and H-beta radiationwere combined. A central absorption for the H-alpha emission wasdetected in 73 percent of the cases, and FWHM emission intensities werecorrelated with the rotational velocities of the stars. The group I Bestars displayed emission lines which were not detectable of stars ofother groupings.
| Four-color and H-beta photometry for O-A0 type stars in three regions near the galactic equator
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982A&AS...49..561W&db_key=AST
| A classification of Be stars
Based upon a sample of 140 stars observed over 20 years for which about5,000 spectrograms are available, a classification scheme of Be stars ispresented. This is the first attempt to subdivide the Be star group intophysically significant subgroups, from which typical objects can beselected for further study. The four groups proposed are based upon adiscussion of spectrum characteristics, multicolor photometry,polarization, rotational velocities, UV spectral types and timevariability. Starting with the group membership of a Be star,predictions can be made of the future behavior of it.
| Absolute ultraviolet spectrophotometry with the TD-1 satellite. XI - Spectrophotometric study of Be and shell stars with the S 2/68 experiment
Low resolution S 2/68 observations are used to show that Be stars ofspectral type B0-B5 have a deficiency of ultraviolet radiation (at 2100A) as compared to the visible with respect to normal stars of the samespectral type. The deficiency is statistically correlated with thestrength of visual emission lines, with the existence of an infraredexcess and with the presence of a shell. Comparison criteria for Be andB stars are discussed along with the relation between the interstellarcolor excess and the depth of the 2200 A absorption feature for normal Bstars. In addition, the origin of the flux deficiency is considered, andit is shown that the stars with a shell of hydrogen and metals (a strongshell) have a source of absorption different from that of the Be starswith strong emission.
| Wavelength dependence of interstellar polarization and ratio of total to selective extinction
A multichannel polarimeter-photometer which uses dichroic filters toseparate the (UBVR) spectral regions is described. The instrument wasused with a 24-inch rotatable tube telescope for polarimetricobservation of nearby stars. Polarization data for 364 nearby stars aretabulated, together with the wavelength dependence of linear andinterstellar polarization.
| Wavelength dependence of polarization. XXVI. The wavelength of maximum polarization as a characteristic parameter of interstellar grains.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974AJ.....79..581C&db_key=AST
| Etudes d'etoiles Be-decrements Balmer.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....11...57B&db_key=AST
| Wavelength dependence of polarization. XVII. Be-type stars.
Abstract image available at:http://adsabs.harvard.edu/abs/1969AJ.....74..528C
| Be stars and galactic rotation.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..338C&db_key=AST
| Spectral Classifications of 239 Early-Type Stars
Not Available
| Spiral arms
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967MNRAS.137..337D&db_key=AST
| Emissions-B-Sterne und Galaktische Struktur.
Not Available
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Cassiopeia |
| Ascensió Recta: | 01h55m42.85s |
| Declinació: | +59°16'24.4" |
| Magnitud Aparent: | 7.042 |
| Distancia: | 264.55 parsecs |
| Moviment propi RA: | 0.9 |
| Moviment propi Dec: | -0.3 |
| B-T magnitude: | 7.059 |
| V-T magnitude: | 7.044 |
Catàlegs i designacions:
|
