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Spectroscopic determination of the fundamental parameters of 66 B-type stars in the field-of-view of the CoRoT satellite
Aims: We determine the fundamental parameters of a sample of Bstars with apparent visual magnitudes brighter than 8 in thefield-of-view of the CoRoT space mission, from high-resolutionspectroscopy. Methods: We developed an automatic procedure forthe spectroscopic analysis of B-type stars with winds, based on anextensive grid of FASTWIND model atmospheres. We use the equivalentwidths and/or the line profile shapes of continuum normalized hydrogen,helium, and silicon line profiles to determine the fundamentalproperties of these stars in an automated way. Results: Afterthorough tests, on both synthetic datasets and very high-quality,high-resolution spectra of B stars for which we already had accuratevalues of physical properties from alternative analyses, we applied ourmethod to 66 B-type stars contained in the ground-based archive of theCoRoT space mission. We discuss the statistical properties of the sampleand compare them with those predicted by evolutionary models of B stars. Conclusions: Our spectroscopic results provide a valuablestarting point for any future seismic modelling of the stars, shouldthey be observed by CoRoT.
| Open clusters IC 4665 and Cr 359 and a probable birthplace of the pulsar PSR B1929+10
Based on the epicyclic approximation, we have simulated the motion ofthe young open star clusters IC 4665 and Collinder 359. The separationbetween the cluster centers is shown to have been minimal 7 Myr ago, 36pc. We have established a close evolutionary connection between IC 4665and the Scorpius-Centaurus association — the separation betweenthe centers of these structures was ?200 pc 15 Myr ago. In addition,the center of IC 4665 at this time was near two well-known regions ofcoronal gas: the Local Bubble and the North Polar Spur. The star HIP86768 is shown to be one of the candidates for a binary (in the past)with the pulsar PSR B1929+10. At the model radial velocity of the pulsarV r = 2 ± 50 km s?1, a closeencounter of this pair occurs in the vicinity of IC 4665 at a time of?1.1 Myr. At the same time, using currently available data for thepulsar B1929+10 at its model radial velocity V r = 200± 50 km s?1, we show that the hypothesis ofHoogerwerf et al. (2001) about the breakup of the ? Oph-B1929+10binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is moreplausible.
| Automated classification of ELODIE stellar spectral library using probabilistic artificial neural networks
A Probabilistic Neural Network model has been used for automatedclassification of ELODIE stellar spectral library consisting of about2000 spectra into 158 known spectro-luminosity classes. The full spectrawith 561 flux bins and a PCA reduced set of 57, 26 and 16 componentshave been used for the training and test sessions. The results show aspectral type classification accuracy of 3.2 sub-spectral type andluminosity class accuracy of 2.7 for the full spectra and an accuracy of3.1 and 2.6 respectively with the PCA set. This technique will be usefulfor future upcoming large databases and their rapid classification.
| Testing the accuracy of synthetic stellar libraries
One of the main ingredients of stellar population synthesis models is alibrary of stellar spectra. Both empirical and theoretical libraries areused for this purpose, and the question about which one is preferable isstill debated in the literature. Empirical and theoretical libraries arebeing improved significantly over the years, and many libraries havebecome available lately. However, it is not clear in the literature whatare the advantages of using each of these new libraries, and how farbehind models are compared to observations. Here we compare in detailsome of the major theoretical libraries available in the literature withobservations, aiming at detecting weaknesses and strengths from thestellar population modelling point of view. Our test is twofold: wecompared model predictions and observations for broad-band colours andfor high-resolution spectral features. Concerning the broad-bandcolours, we measured the stellar colour given by three recent sets ofmodel atmospheres and flux distributions, and compared them with arecent UBVRIJHK calibration which is mostly based on empirical data. Wefound that the models can reproduce with reasonable accuracy the stellarcolours for a fair interval in effective temperatures and gravities. Theexceptions are (1) the U - B colour, where the models are typicallyredder than the observations, and (2) the very cool stars in general (V- K >~ 3). Castelli & Kurucz is the set of models that bestreproduce the bluest colours (U - B, B - V) while Gustafsson et al. andBrott & Hauschildt more accurately predict the visual colours. Thethree sets of models perform in a similar way for the infrared colours.Concerning the high-resolution spectral features, we measured 35spectral indices defined in the literature on three high-resolutionsynthetic libraries, and compared them with the observed measurementsgiven by three empirical libraries. The measured indices cover thewavelength range from ~3500 to ~8700Å. We found that the directcomparison between models and observations is not a simple task, giventhe uncertainties in parameter determinations of empirical libraries.Taking that aside, we found that in general the three libraries presentsimilar behaviours and systematic deviations. For stars withTeff <= 7000K, the library by Coelho et al.is the one withbest average performance. We detect that lists of atomic and molecularline opacities still need improvement, specially in the blue region ofthe spectrum, and for the cool stars (Teff <~ 4500K).
| The Projected Rotational Velocity Distribution of a Sample of OB stars from a Calibration Based on Synthetic He I Lines
We derive projected rotational velocities (v sin i) for a sample of 156Galactic OB star members of 35 clusters, H II regions, and associations.The He I lines at 4026, 4388, and 4471 Å were analyzed in order todefine a calibration of the synthetic He I full widths at half-maximum(FWHMs) versus stellar v sin i. A grid of synthetic spectra of He I lineprofiles was calculated in non-LTE using an extensive helium model atomand updated atomic data. The v sin i values for all stars were derivedusing the He I FWHM calibrations, but also, for those target stars withrelatively sharp lines, v sin i values were obtained from best-fitsynthetic spectra of up to 40 lines of C II, N II, O II, Al III, Mg II,Si III, and S III. This calibration is a useful and efficient tool forestimating the projected rotational velocities of O9-B5 main-sequencestars. The distribution of v sin i for an unbiased sample of early Bstars in the unbound association Cep OB2 is consistent with thedistribution reported elsewhere for other unbound associations.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| An interesting nebular object in LDN 288
In this paper the results of multiwavelength investigation of an unusualnebular object SNO 85 are presented. In 2MASS images this object lookslike a star with a jet. In DSS2 R image the end of the jet is connectedwith an interesting symmetric structure, consisting of arcs and loops.Such a structure is seen also in the opposite direction from the centralstar; it favors the existence of two opposite jets, which repeat therotation and precession movements of the central star. The results of12CO observations of the dark nebula LDN 288, connected withSNO 85, are also given. From these observations the following resultswere obtained: SNO 85 is situated in a dense condensation and theneighbor B type star GSC 0625400181 is surrounded by a hollow cavity.The velocity of the dark cloud is ˜2.5 km/s and its distance isestimated as (380 990) pc. The object SNO 85 itself is associated withan IRAS point source IRAS 17547-1832, the infrared colors of this sourceare typical for a non-evolved source embedded in the dense dark cloud.This region is perhaps a star formation one because there is alsoanother star with a straight jet in the vicinity of B type star GSC0625400181.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Chemical Abundances for a Sample of Southern OB Stars
Chemical abundances are presented for carbon, nitrogen, oxygen,magnesium, aluminum, silicon, and sulfur in a sample of 25 OB stars thatare members of open clusters, OB associations, and H II regions havingGalactocentric distances that lie inside the solar Galactic orbit. Theelemental abundances are derived from fits of observed high-resolutionspectra to non-LTE synthetic line profiles. Our effective temperaturescale is based on calibrations of the Strömgren photometric indicescoupled to Hγ line profiles. For stars without Strömgrenindices, the reddening-free Q-parameter, defined from UBV photometry isused, with the Q-parameter calibrated against Teff for starsthat have Strömgren photometry. We also investigated othereffective temperature scales from the literature and conclude thatadoption of these other Teff scales, which typically resultin lower temperatures, produces dependences of the derived abundanceswith Teff. Our non-LTE abundances reveal dispersions that arevery similar to those expected from the analysis uncertainties. Thesolar abundances, some of which have been recently revised, fall withinthe abundance distributions defined by this sample of inner disk OBstars for all seven studied elements.Based on observations collected with the 1.52 m telescope at theEuropean Southern Observatory (La Silla, Chile) under agreement with theObservatório Nacional, Brazil.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| Atlas of Interstellar Extinction Curves of OB Stars Covering the Whole Available Wavelength Range
The paper presents a collection of 436 extinction curves covering thewhole available range of wavelengths from satellite UV to near-IR. Thedata were taken from the ANS photometric catalogue and from thecompilations of IR photometric measurements. The data curves have beenobtained with the aid of ``artificial standards": Papaj et al. (1993)and Wegner (1994, 1995). The visual magnitudes and spectralclassifications of O and B type stars with EB-V>= 0.05were taken from the SIMBAD database. The curves are given in the form ofplots and tables E{lambda - V} / EB-V versus1/λ. The observed variety of extinction laws among slightlyreddened stars is apparently due to the various physical parameters ofinterstellar clouds.
| On the origin of the O and B-type stars with high velocities. II. Runaway stars and pulsars ejected from the nearby young stellar groups
We use milli-arcsecond accuracy astrometry (proper motions andparallaxes) from Hipparcos and from radio observations to retrace theorbits of 56 runaway stars and nine compact objects with distances lessthan 700 pc, to identify the parent stellar group. It is possible todeduce the specific formation scenario with near certainty for twocases. (i) We find that the runaway star zeta Ophiuchi and the pulsarPSR J1932+1059 originated about 1 Myr ago in a supernova explosion in abinary in the Upper Scorpius subgroup of the Sco OB2 association. Thepulsar received a kick velocity of ~ 350 km s-1 in thisevent, which dissociated the binary, and gave zeta Oph its large spacevelocity. (ii) Blaauw & Morgan and Gies & Bolton alreadypostulated a common origin for the runaway-pair AE Aur and mu Col,possibly involving the massive highly-eccentric binary iota Ori, basedon their equal and opposite velocities. We demonstrate that these threeobjects indeed occupied a very small volume ~ 2.5 Myr ago, and show thatthey were ejected from the nascent Trapezium cluster. We identify theparent group for two more pulsars: both likely originate in the ~ 50 Myrold association Per OB3, which contains the open cluster alpha Persei.At least 21 of the 56 runaway stars in our sample can be linked to thenearby associations and young open clusters. These include the classicalrunaways 53 Arietis (Ori OB1), xi Persei (Per OB2), and lambda Cephei(Cep OB3), and fifteen new identifications, amongst which a pair ofstars running away in opposite directions from the region containing thelambda Ori cluster. Other currently nearby runaways and pulsarsoriginated beyond 700 pc, where our knowledge of the parent groups isvery incomplete.
| 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.
| Red and infrared colours of B stars and the reddening law in the Galaxy
The red and infrared intrinsic colours of B stars are derived fromphotometric observations through the UBV(RI)_CJHK and Hβ filters of257 early-type stars. Those stars for which the UBV and Hβmeasurements match the published spectral class, and which show no othersigns of peculiarity, are used to determine the intrinsic photometriccolours of B stars in the red and infrared. From these intrinsic coloursthe interstellar reddening relationships for the red and infraredcolours are evaluated, and the results are compared with previousestimates of these quantities. The values of R, E(B-V) and the distanceare then determined for the individual stars. R is confirmed to be closeto 3.1 in most cases, but was found to be much larger in somedirections. The relationship between R and the location of a star in theGalaxy is investigated. Usually the abnormally reddened stars seemed tobe associated with known regions of star formation. The paper alsoidentifies seven likely variable stars and a number of stars withpossible dust shells.
| A Search for Pulsar Companions to OB Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...461..357S&db_key=AST
| DO OB Runaway Stars Have Pulsar Companions?
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1220P&db_key=AST
| 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.
| Extinction law survey based on UV ANS photometry
The paper presents an extensive survey of interstellar extinction curvesderived from the ANS photometric measurements of early type starsbelonging to our Galaxy. This survey is more extensive and deeper thanany other one, based on spectral data. The UV color excesses aredetermined with the aid of 'artificial standards', a new techniqueproposed by the authors which allows the special check of Sp/L match ofa target and the selected standard. The results indicate that extinctionlaw changes from place to place.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Runaway stars from young star clusters containing initial binaries. II - A mass spectrum and a binary energy spectrum
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99..608L&db_key=AST
| The spectral energy distribution of early-type stars. II - The extinction law towards O-type stars
Photometric measurements through different pass-bands are used todetermine the color-excess E(B-V) for O-type stars in the UV and IRspectral regions. The results are used to examine the extinctioncharacter of the stars. It is found that, in the UV, each O-type starhas its own extinction character. In general, the visual and NIRextinction in the direction of O-type stars are normal.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
| Observations of the very broad-band structure by combined UVBY and UBV photometry
The features of the very broad-band structure (VBS) in the interstellarextinction curve were studied photometrically. It is shown that thecolor excess ratio E(b-y)/E(B-V) can be used as a measure of thestrength of the VBS. The color excess ratio was calibrated in terms ofthe central depth of the VBS; from the calibration stars and 13 reddenedyoung open clusters containing more than 10 B-type stars, a relationshipwas derived between the central depth of the VBS and the E(B-V)quantity.
| The spectral energy distribution of early type stars. I - A catalogue of photometric data of 259 stars from 0.15 to 4.8 microns
For the derivation of physical parameters (e.g., effective temperatureand radius) of early-type stars from their intrinsic spectral-energydistribution, and for the study of foreground interstellar and/orcircumstellar matter, a sample of 237 O, B, and A stars was chosen fromthe ANS catalog (Wesselius et al., 1982). The ANS ultraviolet and theJohnson UBV data (mostly from Nicolet's catalog, 1978) of these starswere supplemented with visual Walraven WULBV, red VRI, and near-infraredJHKLM measurements. All these data are given in the present catalog.Data for 22 stars of spectral type later than A are also included.
| 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.
| The variation of interstellar extinction in the ultraviolet
One hundred and fifty-four reddened stars that are apparently normal inthe visible were selected from the S2/68 Ultraviolet Sky Survey. Theultraviolet data for 92 of these cannot be explained in terms of a fixedinterstellar extinction law. Between 1400 and 2740 A, the extinctioncurve for each star can be well represented by two parts; astraight-line scattering component and a Lorentzian 2200 A absorptionfeature. Independent variations are found in both parts and these cannotbe explained by photometric or spectral classification errors. Bothparts vary smoothly, implying that there is no fixed extinction law, andone star in three is found to depart from the mean law by more than 1mag at either 1500 or 2200 A. The two variations allow not only all 154stars to be explained but also anomalous stars reported by otherauthors. These are not special but merely situated towards the limits ofthe variations. A variation in the relative proportions of graphite andsilicate grains goes some way towards explaining the observations. Theprofile of the 2200 A feature is determined, the symmetrical shape isconfirmed, and the profile fits a Lorentzian very closely.
| Observations of interstellar diffuse absorption band at 4430 A
Observations of the interstellar diffuse absorption band at 4430 A for800 O and B stars in Neckel's (1967) catalog are being carried out, and482 spectra obtained up to September 1983 have been reduced. It isconfirmed that the strength of the interstellar diffuse absorption bandat 4430 A does not simply relate to the abundance of interstellar grainson the line of sight. The relation between the color excess E(B-V) andthe equivalent width of the band to the direction of l = 130-140 deg andb = -5 to +5 deg shows that some parameter(s) other than E(B-V) is (are)needed to understand the cause of this band.
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| קבוצת-כוכבים: | מגן |
| התרוממות ימנית: | 18h40m48.05s |
| סירוב: | -08°43'07.7" |
| גודל גלוי: | 7.711 |
| מרחק: | 277.008 פארסק |
| תנועה נכונה: | -9.5 |
| תנועה נכונה: | -22.5 |
| B-T magnitude: | 8.248 |
| V-T magnitude: | 7.756 |
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