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Chemically peculiar stars and their temperature calibration
Aims. The determination of effective temperature for chemically peculiar(CP) stars by means of photometry is a sophisticated task due to theirabnormal colours. Standard calibrations for normal stars lead toerroneous results and, in most cases corrections are necessary. Methods: In order to specify appropriate corrections, direct temperaturedeterminations for 176 objects of the different subgroups were collectedfrom the literature. This much larger sample than in previous studiestherefore allows a more accurate investigation, mostly based on averagetemperatures. Results: For the three main photometric systems (UBV,Geneva, Strömgren {uvby}β), methods to determine effectivetemperature are presented together with a comparison with formerresults. Based on the compiled data we provide evidence that He (CP4)objects also need a considerable correction, not noticed in formerinvestigations due to their small number. Additionally, a new relationfor the bolometric correction and the capability of standardcalibrations to deduce interstellar reddening for magnetic CP stars areshown.Tables 4 to 8 are only available in electronic form at http://www.aanda.org
| Fundamental parameters of He-weak and He-strong stars
Context: He-weak and He-strong stars are chemically peculiar AB objectswhose He lines are anomalously weak or strong for their MK spectraltype. The determination of fundamental parameters for these stars isoften more complex than for normal stars due to their abundanceanomalies. Aims: We discuss the determination of fundamentalparameters: effective temperature, surface gravity, and visual andbolometric absolute magnitudes of He-weak and He-strong stars. Wecompare our values with those derived independently from methods basedon photometry and model fitting. Methods: We carried out low resolutionspectroscopic observations in the wavelength range 3400-4700 Å of20 He-weak and 8 He-strong stars to determine their fundamentalparameters by means of the Divan-Chalonge-Barbier (BCD)spectrophotometric system. This system is based on the measurement ofthe continuum energy distribution around the Balmer discontinuity (BD).For a few He-weak stars we also estimate the effective temperatures andthe angular diameters by integrating absolute fluxes observed over awide spectral range. Non-LTE model calculations are carried out to studythe influence of the He/H abundance ratio on the emergent radiation ofHe-strong stars and on their T_eff determination. Results: We find thatthe effective temperatures, surface gravities and bolometric absolutemagnitudes of He-weak stars estimated with the BCD system and theintegrated flux method are in good agreement between each other, andthey also agree with previous determinations based on several differentmethods. The mean discrepancy between the visual absolute magnitudesderived using the hipparcos parallaxes and the BCD values is on average±0.3 mag for He-weak stars, while it is ±0.5 mag forHe-strong stars. For He-strong stars, we note that the BCD calibration,based on stars in the solar environment, leads to overestimated valuesof T_eff. By means of model atmosphere calculations with enhanced He/Habundance ratios we show that larger He/H ratios produce smaller BDwhich naturally explains the T_eff overestimation. We take advantage ofthese calculations to introduce a method to estimate the He/H abundanceratio in He-strong stars. The BD of HD 37479 suggests that the T_eff ofthis star remains fairly constant as the star spectrum undergoes changesin the intensity of H and He absorption lines. Data for the He-strongstar HD 66765 are reported for the first time.Observations taken at CASLEO, operating under agreement of CONICET andthe Universities of La Plata, Córdoba and San Juan, Argentina.Tables [see full text]-[see full text] and Appendix A are only available in electronic form at http://www.aanda.org
| 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.
| 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
| 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.
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
| Properties of He-rich stars. II. CNO abundances and projected rotational velocities
We present an abundance analysis of light elements in the most massivechemically peculiar (CP) stars, He-rich stars. The analysis is based onboth low and high-resolution observations collected at ESO, La Silla,Chile in the optical region and includes 6 standard and 21 He-richstars. Light element abundances display a diverse pattern fromunder-solar up to above-solar values. Carbon is found underabundant inthe hottest He-rich stars and normal in the coolest ones, according tothe LTE model predictions. The distribution of projected rotationalvelocities shows a significant excess of slow rotators, no He-rich starshaving vsin i > 130 km s(-1) . Based on observations collected at theEuropean Southern Observatory, La Silla, Chile (programmes 7-043 and7-010 of periods 49 and 50 resp.)
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| New OB-Association in Pup - CMA
Not Available
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Light element abundances in He-rich stars
We present an abundance analysis of light elements in He-rich stars. Theanalysis is based on both low and high resolution observations collectedat ESO, La Silla, Chile in the optical region and includes 6 standardsand 21 He-rich stars. Light-element abundances display a diversepattern: they range from under-solar up to above-solar values.
| On the near infrared variability of chemically peculiar stars
Some CP stars have recently been discovered by Catalano et al. to bevariable also in the near infrared, although with smaller amplitudesthan in the visible. Hence an observational campaign was started inwhich the infrared light variability of a number of CP2 and CP4 starshas been investigated at the ESO-La Silla Observatory in the bands J, H,and K. As a general result, infrared variations show the same behaviorin all three filters but amplitudes are smaller than in the visible.
| 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 observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| Age variation of helium abundance in He-rich stars.
Not Available
| Magnesium abundance in main sequence B-type and magnetic chemically peculiar stars.
The abundance of magnesium for a sample of 19 main sequence B-type and41 magnetic chemically peculiar stars has been derived by spectrumsynthesis analysis of the MgII448.1nm line under the LTE assumption. Thelogarithm of the average Mg abundance for the main sequence stars is log(N(MgII)/N(Tot))=-4.28+/-0.19. Comparing magnetic chemically peculiar(Cp) and main sequence stars with equal effective temperature andgravity, one finds that the magnesium abundance tends to be lower inpeculiar stars with the exception of helium rich stars where thiselement can be overabundant. In Cp stars with effective temperature ofabout 14000K, the magnesium abundance does not depend on gravity,microturbulent velocity or rotational period. There appears to exist acorrelation between the magnesium abundance and the surface magneticfield, with the stars poorest in magnesium presenting the strongestmagnetic fields. In accord with the theory of magnetically controlleddiffusion - which predicts a non-homogeneous distribution of magnesiumover the stellar surface and stratification in the photosphere - somepeculiar stars show evidence of spectral variability with the rotationalphase; the respective magnesium abundances of the HgMn stars HD49606 andHD78316 depend on optical depth.
| Properties of He-rich stars. I. Their evolutionary state and helium abundance.
A determination of the surface gravity and an abundance analysis ofhelium in a sample of 17 He-rich and 5 normal, reference stars ispresented. These results are derived from low resolution CCD spectra,but each star was measured at least 6 times in order to obtain asignificant average spectrum for the spectroscopic variables. The heliumabundances derived from the models used are very close to 0.1 fornormal, reference stars and are larger for the others, clearlyindicating the He-rich phenomenon in them. NLTE effects, errors on themicroturbulence value or on the surface gravity do not influence theestimated helium abundances. Nevertheless, synthesized Geneva coloursare affected by the He-rich peculiarity, especially the [U-B] indexwhich systematically changes by -0.025 mag per 0.1 of He abundance forthe coolest stars in the sample. We cannot confirm the correlationbetween the evolutionary state and the helium abundance reportedpreviously (Zboril et al. 1994, International Conference on CP andMagnetic Stars.", Tatranska Lomnica, eds. J. Zverko and J. Ziznovsky, p.105), although we used a more reliable technique of log(g)determination. All He-rich objects lie within the main sequence: theirsurface gravities are all inside the range 4.1
| 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 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| A Search for Variability in Intermediate Helium Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269...33K&db_key=AST
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| The South African Astronomical Observatory.
Not Available
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Radio emission from chemically peculiar stars
In five VLA observing runs the initial survey of radio emission frommagnetic Bp-Ap stars by Drake et al. is extended to include a total of16 sources detected at 6 cm out of 61 observed, giving a detection rateof 26 percent. Of these stars, three are also detected at 2 cm, four at3.6 cm, and five at 20 cm. The 11 new stars detected as radio sourceshave spectral types B5-A0 and are He-weak and Si-strong. No classical(SrCrEu-type) Ap stars have yet been detected. The 16 detected sourcesshow a wide range of radio luminosities with the early-B He-S stars onaverage 20 times more radio luminous than the late-B He-W stars and 1000times more luminous than Theta Aurigae. Multifrequency observationsindicate flat spectra in all cases. Four stars have a detectable degreeof circular polarization at one or more frequencies. It is argued thatthe radio-emitting CP (chemically peculiar) stars form a distinct classof radio stars that differs from both the hot star wind sources and theactive late-type stars. The observed properties of radio emission fromthese stars may be understood in terms of optically thickgyrosynchrotron emission from a nonthermal distribution of electronsproduced in a current sheet far from the star. In this model theelectrons travel along magnetic fields to smaller radii and highermagnetic latitudes where they mirror and radiate microwave radiation.
| Mid-ultraviolet and optical photometry of helium stars
Mid-ultraviolet and optical photometric analysis of helium stars arepresented. A linear relation exists between the effective temperaturederived from model atmospheres and (1965-V)0 index. The effectivetemperatures derived from (1965-V)0 index are somewhat higher than thatof MK spectral type estimates especially for late B-type helium objects.
| Uvby-beta observations of 528 type B stars with V between the 8th and 9th magnitude
The paper presents uvby-beta measurements of 528 type B stars selectedfrom the SAO Catalog on the basis of two criteria: the spectral types inthe range B3-B5 and mV between the 8th and the 9th magnitude. Reddeningindependent (c1) values are estimated from the spectral classificationand compared to the observed values. No systematic trend with observed(b-y), H-beta, or spectral type appears to be present, but the range of(c1) residuals is surprisingly large. A rather large part of the starshas small beta values, smaller than for the BIa supergiants. Only twoare classified as O stars and most of them have the suffix e, ne, ornne. Most beta values for the O type stars are slightly above the upperlimit of 2.585 m.
| On dependence of helium abundance upon magnetic field in He-r stars.
Not Available
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