Herbig Ae/Be Stars in nearby OB Associations
We have carried out a study of the early-type stars in nearby OBassociations spanning an age range of ~3-16 Myr, with the aim ofdetermining the fraction of stars that belong to the Herbig Ae/Be class.We studied the B, A, and F stars in the nearby (<=500 pc) OBassociations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1,with membership determined from Hipparcos data. We also included in ourstudy the early-type stars in the Trumpler 37 cluster, part of the CepOB2 association. We obtained spectra for 440 Hipparcos stars in theseassociations, from which we determined accurate spectral types, visualextinctions, effective temperatures, luminosities and masses, usingHipparcos photometry. Using colors corrected for reddening, we find thatthe Herbig Ae/Be stars and the classical Be (CBe) stars occupy clearlydifferent regions in the JHK diagram. Thus, we use the location on theJHK diagram, as well as the presence of emission lines and of strong 12μm flux relative to the visual, to identify the Herbig Ae/Be stars inthe associations. We find that the Herbig Ae/Be stars constitute a smallfraction of the early-type stellar population even in the youngerassociations. Comparing the data from associations with different agesand assuming that the near-infrared excess in the Herbig Ae/Be starsarises from optically thick dusty inner disks, we determined theevolution of the inner disk frequency with age. We find that the innerdisk frequency in the age range 3-10 Myr in intermediate-mass stars islower than that in the low-mass stars (<1 Msolar) inparticular, it is a factor of ~10 lower at ~3 Myr. This indicates thatthe timescales for disk evolution are much shorter in theintermediate-mass stars, which could be a consequence of more efficientmechanisms of inner disk dispersal (viscous evolution, dust growth, andsettling toward the midplane).
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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.
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NaI and HI 3-D density distribution in the solar neighbourhood
A study of the local interstellar medium (LISM) using a robust inversionmethod, similar to current tomography techniques, is applied to compileddata on neutral interstellar absorbers and Hipparcos parallaxes. Wepresent here the 3-D distribution of two neutral species, NaI and HI.Our analysis enables us to obtain a reliable 3-D density distribution ofthe IS matter in the solar neighbourhood, providing a new basis for thediscussion of origin, present state and evolution of the LISM. We showthat neutral IS matter is distributed in compact clouds or in cloudcomplexes with cavities between them. It is now easy to distinguish theso-called Local Bubble and the Loop I cavities and also two tunnelslinking the Local Bubble to the outer regions of the galaxy, away fromthe galactic plane. Better accuracy is achieved for NaI, as to a largernumber of lines-of-sight and target stars than are available for HI. Arather detailed NaI 3-D density distribution is obtained with a 40 pcsmoothing length. The extended high-density regions in the NaI and HImaps are correlated which is not the case for the diffuse regions. Thedensity ratio rho_HI /rho_NaI is lower or equal to 9.1.108+/- 3.108 for extended high density clouds. Usingobservations from the ESA Hipparcos space astrometry mission.
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A spectroscopic study of some suspected chemically peculiar stars
Time-resolved spectra in the 410 - 700 nm range have been obtained toinvestigate 10 stars which are classified as suspected chemicallypeculiar stars in The General Catalogue of Ap and Am stars by Renson etal. (1991) or in the latest literature. Among the studied stars, HD20629presents metal abundances which are significantly different from mainsequence star values and it should be classified as Silicon star. Fromthe Hei587.6 nm line, we conclude that HD35575 is a helium weak star.Because of the found radial velocity variability and the derivedabundances, the periodic photometric variable HD38602 could be anellipsoidal variable.
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Photoelectric Photometry of Stars in the Orion Standard Region
Magnitudes and color indices in the Vilnius seven-color photometricsystem are given for 108 stars in the Orion standard region around theOrion Belt and the star lambda Orionis. New spectral and luminosityclasses, estimated from the photometric data, are given for some of thestars.
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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.
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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.
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Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
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Radio Emission from Magnetic Chemically Peculiar Stars - Results of the 1992 VLA Survey
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994A&A...283..908L&db_key=AST
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A new list of effective temperatures of chemically peculiar stars. II.
Not Available
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Far-ultraviolet stellar photometry: A field in Orion
Far-ultraviolet photometry for 625 objects in Orion is presented. Thesedata were extracted from electrographic camera images obtained duringsounding rocket flights in 1975 and 1982. The 1975 images were centeredclose to the belt of Orion while the 1982 images were centeredapproximately 9 deg further north. One hundred and fifty stars fell inthe overlapping region and were observed with both cameras. Sixty-eightpercent of the objects were tentatively identified with known starsusing the SIMBAD database while another 24% are blends of objects tooclose together to separate with our resolution. As in previous studies,the majority of the identified ultraviolet sources are early-type stars.However, there are a significant number for which no such identificationwas possible, and we suggest that these are interesting objects whichshould be further investigated. Seven stars were found which were brightin the ultraviolet but faint in the visible. We suggest that some ofthese are nearby white dwarfs.
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A high-resolution optical and radio study of Milky Way halo gas
Optical interstellar absorption lines of Ti II and Ca II and the 21 cmemission line of H I were observed at high-resolution (6 and 1 km/s,respectively) and high detection sensitivity along 25 lines of sight inthe Galactic halo. The sample includes 16 distant halo stars matchedwith one or more nearly aligned foreground stars as well as local starsalong five extragalactic sight lines. The data show substantialinterstellar material, at both low and intermediate velocities, between250 and 1000 pc beyond the Galactic plane. As much as one-third of thetotal gas observed in Ca II absorption may be beyond 1 kpc, and thegaseous Ti II may lie in an even thicker layer. The directly determinedgaseous Ti abundance above the Galactic plane exceeds that in the disk,on the average, by a factor of 4 to 6 and, for individual cloudcomponents, is further enhanced at higher LSR velocity. Thirty threediscrete high-latitude clouds are detected in Ca II absorption, and 17discrete clouds, including three high-velocity clouds, are identified inH I emission. The kinematics of the high-latitude gas observed in Ti IIand Ca II absorption is characterized by significant peculiar velocitieswith respect to a model corotating halo.
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Spectroscopic binaries in the Orion OB1 association
A radial velocity study of the brighter members of the Ori OB2association is reported. The radial velocity variables, new preliminaryorbital elements for six spectroscopic binaries, and the projected axialrotation in stars for which the orbital elements are lacking arereported. The correlation between the proportion of binaries and theaverage axial rotation for the subgroups of the association isdiscussed. It is found that the Orion main-sequence members rotate atalmost the same rate as field stars of the same types. The averageradial velocity for the whole association is 23 km/s. The percentage ofspectroscopic binaries with periods shorter than 100 days plus themagnetic Ap-Bp among the main-sequence members of the association is 32percent.
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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.
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Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
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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.
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Miscellaneous spectroscopic notes
Results of slit-spectrograph observations are reported for approximately260 stars. The data presented range from recognition of many new Ap, Am,and other unusual stars to H-alpha observations of early-typesupergiants and Be stars. The material discussed was obtained over thepast 40 years at a number of U.S. observatories and at the DominionAstrophysical Observatory in Victoria, B.C.
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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.
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On the Effective Temperatures of Chemically Peculiar Stars
Not Available
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A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
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Observational problems of investigation of stars with anomalous helium lines.
Not Available
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Absolute photometry of the southern Orion region in the vacuum ultraviolet (1300-2000 A)
Absolute photometry of the southern Orion region was carried out forfive passbands in the vacuum ultraviolet (1300-2000 A, Delta Lambda = 84A) with a rocket-borne spectrometer. More than 60 early-type stars andthe diffuse background radiation were observed within the raster-scannedfield of 8 x 8 deg centered at alpha = 5 h 30 m and delta = -4 deg.Stellar data suggest a revision of the current absolute scale by 10-30percent, which relatively suppresses the flux toward shorterwavelengths. The present data of the background radiation have thehighest spectral resolution among those published and indicate a steepsystematic increase of the flux toward shorter wavelengths. Directconsequences of the new calibration are briefly discussed.
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A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
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The interstellar 2200 A band - A catalogue of equivalent widths
Not Available
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Spectroscopic studies of stars in ORI OB1 /Belt/
MK spectral classifications are presented for 120 B- and A-type stars inthe Belt subgroup of the Ori OB1 association. Combined with otherpublished spectroscopic data, and the assumed absolute magnitudes givenby Schmidt-Kaler (1965) and Lesh (1979), a mean corrected distancemodulus of 8.56 + or - 0.11 is computed for the eastern region, whilefor the remainder of the Belt a modulus of 8.20 + or - 0.05 is derived.Several B9-A2 subgiants and A7-F0 main-sequence stars were observed inthe western and central regions of the Belt. The ages of these starsimply a spread in formation ages for these subgroups from about 1million yr to at least 10 million yr.
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H-beta photometry of southern early-type stars
H-beta photoelectric photometry is presented for 209 southern hemisphereearly-type stars from the HD catalog with galactic latitudes /b/ greaterthan 6 deg. Four-color photometry exists for all these stars and MKtypes for most of them. Absolute magnitudes have been estimated for allbut the emission-line stars and distances from the sun and the galacticplane determined.
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A Photoelectric Search for Ap-Stars in the Orion Association
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981A&A....94..134J&db_key=AST
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The fundamental physical parameters of main-sequence and near main-sequence B type stars as derived from uvby,beta photometry
From spectrophotometric measurements of hydrogen line intensities, uvbyphotometry and photoelectrically determined H-beta and H-gamma indicesof 75 B2-B6 main-sequence stars, effective temperature and surfacegravity are derived by using the model atmospheres computed by Kurucz(1974). Comparisons between the g values and the MK luminosityclassification show good agreement for the MK standard stars but ratherserious disagreement for the average stars in such a way that most ofthe stars classified in luminosity class V really belong to class IV.Using the evolutionary model sequences calculated by Hejlesen et al.(1972) the stellar mass, age and luminosity are determined from the uvbyand beta data through effective temperature and surface gravity. Thetheoretically derived luminosities are in excellent agreement with theluminosities derived by calibrations.
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A photometric study of the Orion OB 1 association. III - Subgroup analyses
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...36..497W&db_key=AST
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Four colour photometry of southern early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978MNRAS.182..629K&db_key=AST
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INHABITED SKY
