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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ROSAT PSPC observations of the Orion Trapezium area II. Source variability and revised source list
A deep ROSAT PSPC image centred on the Orion Trapezium has been reduceda second time using an improved version of the PSF to fit the data. Theouter rim of the field of view was also included. The new cataloguecontains 316 X-ray sources which are easily identified with pre-mainsequence stars of the Ori OB1 Ic and Id association. All 316 sourceswere tested for variability. No variations were found inside the singleexposures of about 45 minutes length each. Between the 4 exposuresspaced over 5 days about 1/3 of the sources show signs of activities ofvarious forms. As above 25% of these have somewhat regular lights curves(monotonically rising or falling or hill-shaped) we infer that at leastsome outbursts with time scales longer than a day are present and thatpast searches for X-ray flares of pre-main sequence stars were biasedtowards shorter time scales.
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The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
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A calibration of Geneva photometry for B to G stars in terms of Teff, log G and [M/H]
We have used recent Kurucz models and numerous standard stars to improvethe calibration of the Geneva photometric system proposed a few yearsago. A new photometric diagram for the classification of intermediatestars (8500 <= Teff <= 11000 K) is proposed and fills agap that the previous calibration had left open. Evidence is given for aclear inadequacy of the new Kurucz models in the region of the parameterspace where convection begins to take over radiation in the star'satmosphere. This problem makes the determination of the surface gravitydifficult, but leaves that of the other parameters apparentlyunaffected. The determination of metallicity is considerably improved,thanks to the homogeneous spectroscopic data published recently by\cite[Edvardsson et al. (1993)]{ref23}. Instead of showing thetraditional diagrams, we chose to publish the diagrams of the physicalparameters with the inverted grids inside, i.e. the lines of constantphotometric parameters.
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Proper motions of stars in the region of the Orion Nebula cluster (C 0532-054).
Relative proper motions and membership probabilities for 333 starswithin an area of 1.6deg by 1.8deg centred on the Orion Nebula M 42 aredetermined using plates taken over a period of 83 years with the doubleastrograph of Shanghai Observatory (scale of 30"/mm). The plates weremeasured with the ASTROSCAN automatic plate-measuring machine of LeidenObservatory. The average proper motion accuracy obtained for stars inthe photographic magnitude range 7 to 14 is 0.3mas/yr. Errors aresomewhat larger towards fainter and brighter magnitude, but the majoritylie well below 1mas/yr. 64% of the stars have been measured successfullyon at least 13 out of 18 plates. The number of stars with membershipprobabilities higher than 0.7 is 184. It is shown by a detaileddiscussion that the proper motions and membership probabilities of thestars determined in this paper are in good agreement with the resultspresented recently by other authors. Although there is a clearconcentration in the proper motion diagram, both the remainingdispersion of the internal motions and the distribution of "members" asprojected on the sky indicate that the stars in this region are notbound as one system, but do have a common origin. A similar conclusioncan be drawn from a comparison with spectroscopic and radial velocitydata.
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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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The complete Einstein Observatory X-ray survey of the Orion Nebula region.
We have analyzed archival Einstein Observatory images of a roughly 4.5square degree region centered on the Orion Nebula. In all, 245 distinctX-ray sources have been detected in six High Resolution Imager (HRI) and17 Imaging Proportional Counter (IPC) observations. An optical databaseof over 2700 stars has been assembled to search for candidatecounterparts to the X-ray sources. Roughly half the X-ray sources areidentified with a single Orion Nebula cluster member. The 10main-sequence O6-B5 cluster stars detected in Orion have X-ray activitylevels comparable to field O and B stars. X-ray emission has also beendetected in the direction of four main-sequence late-B and early-A typestars. Since the mechanisms producing X-rays in late-type coronae andearly-type winds cannot operate in the late-B and early-A typeatmospheres, we argue that the observed X-rays, with LXapproximately = 3 x 1030 ergs/s, are probably produced in thecoronae of unseen late-type binary companions. Over 100 X-ray sourceshave been associated with late-type pre-main sequence stars. The upperenvelope of X-ray activity rises sharply from mid-F to late-G, withLx/Lbol in the range 10-4 to 2 x10-3 for stars later than approximately G7. We have lookedfor variability of the late-type cluster members on timescales of a dayto a year and find that 1/4 of the stars show significantly variableX-ray emission. A handful of the late-type stars have publishedrotational periods and spectroscopic rotational velocities; however, wesee no correlation between X-ray activity and rotation. Thus, for thissample of pre-main-sequence stars, the large dispersion in X-rayactivity does not appear to be caused by the dispersion in rotation, incontrast with results obtained for low-mass main-sequence stars in thePleiades and pre-main-sequence stars in Taurus-Auriga.
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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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Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
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Machine-readable version of the Parenago catalogue of stars in the area of the Orion nebula
Not Available
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An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
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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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The type of variability of Herbig Ae/Be stars
The paper presents a list of 23 Herbig Ae/Be stars and Herbig Ae/Be starcandidates, compiled on the basis of 2 to 8 years of observations in theStromgren photometric system. Results of the study show that spectraltype A0 separates the stars showing large variations in their brightnessfrom stars showing small variations, with the later spectral type starsbeing the more variable. The behavior of the stars in thecolor-magnitude diagram could be divided into three classes: (1) classR, in which there is a monotonic dependence of the color index on visualbrightness, (2) class CR, in which this dependence is not monotonic, and(3) class RB, in which there is no dependence. It was also found thatthe behavior of a star in the color-magnitude diagram is dependent noton the spectral type but on the size of the variation in brightness.
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Long-term photometry of variables at ESO. I - The first data catalogue (1982-1986)
This paper presents the catalog of photometric data in the Stromgrensystem obtained during the first four years (October 1982 - September1986) of the Long-Term Photometry of Variables (LTPV) program at ESO.The data are available in computer-readable form.
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Absolute magnitudes of B emission line stars - Correlation between the luminosity excess and the effective temperature
A new determination of the visual absolute magnitude of Be stars iscarried out. For this, a new calibration of visual absolute magnitudesof B stars of luminosity classes, V, IV, and III is first obtained froma sample of 215 stars. The absolute luminosity excess in the visual isdetermined for a sample of 49 Be stars. It is found that this excess iscorrelated with the effective temperature of the underlying stars. Awell defined correlation between this excess and the emission in thefirst two Balmer lines is established. From these results, using asimple model of circumstellar envelope, it is inferred that the zones ofthe circumstellar envelope contributing to the emission in the continuumand in the lines have to be rather small. It is also deduced that theemission measure of the envelope is correlated with the temperature ofthe central star and that the irregular photometric variations of Bestars are an envelope-opacity phenomenon.
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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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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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A complex investigation of the star formation region in the Orion constellation
The proper motions of 54 young stars in the Ori OB1 cluster are refined.Cluster contraction with a characteristic time of 3 x 10 to the 6th yris found as well as cluster rotation with a period of 6 x 10 to the 6thyr. A cluster velocity of -10 km/s is determined from the spatialvelocities of 26 stars, indicating that about 1.4 x 10 to the 7th yrago, the cluster was situated in the Galactic symmetry plane; thiscoincides with the age of the oldest subcluster of the association.
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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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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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UBVRI photometry of stars useful for checking equipment orientation stability
Several sets of stars have been measured, equally spaced around the skyin right ascension, over a range in declination from -75 deg to +30 deg.The goal was to obtain a number of well-observed stars with qualityinternally consistent magnitudes and color indices. The stars wereneeded to check orientation effects of photometric equipment.
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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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Interstellar grain size. II - Infrared photometry and polarization in Orion
Infrared colors, polarization wavelength dependence and criteria forcluster membership are used to examine the interstellar extinction lawin the Orion region, in light of 0.36-0.82 micron linear polarimetry andinfrared photometry observations of stars within a degree of the OrionNebula. The stars inside the dust clouds are examined on a star-by-starbasis, and the different intracluster grain size indicators are found tobe in excellent agreement. Normal radius and maximum wavelength valuesof about 3.0 and 0.55 microns are observed in stars lying outside thetwo main regions of nebulosity, indicating normal grain sizes. For acarefully selected group of stars inside the nebulosity that ischaracterized by extinction by large interstellar grains, thecircumstellar emission does not significantly affect the values of Rderived from the V-K and V-L colors.
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A catalogue of stellar spectrophotometric data
A list of 378 sets of stellar energy distributions for 356 stars basedon photoelectric spectrophotometry is presented. Data from eight sourceshave been transformed to the Hayes-Latham calibration of Alpha Lyrae.The procedure follows that of Breger (1976) and the present list extendsprevious data, especially for stars of earliest and intermediatespectral types.
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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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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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Two sparse open clusters in the region of Collinder 132.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..803C&db_key=AST
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Spectral types in the ORI OB1 association.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..797A&db_key=AST
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A photometric study of the ORI OB1 association. II. Photometric analysis.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJS...34..207W&db_key=AST
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A photometric study of the Orion OB 1 association. I - Observational data.
A catalog of observational data is presented for stars in the region ofthe young stellar association Orion OB 1. Photoelectric observationsobtained in the uvby-beta and UBV systems are compiled along withprevious photoelectric and spectroscopic data for all these stars aswell as for several bright members of the association with availablephotometric indices. Mean weighted values are computed for thephotometric data and summarized in tables expected to be reasonablycomplete for association members earlier than spectral type A0.Membership criteria are derived, and qualitative membershipprobabilities summarized, for the 526 stars in the final program. Theanalytical procedures are discussed for association stars of B,intermediate, and AF types. Effects of the nebular environment andvarious calibrations of Balmer-line and four-color indices areconsidered for the determination of absolute magnitudes for the B-typestars.
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INHABITED SKY
