|Local interstellar medium kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds|
We present the results of a spectroscopic programme aiming toinvestigate the kinematics of the local interstellar medium componentstowards the Southern Coalsack and Chamaeleon-Musca dark clouds. Theanalysis is based upon high-resolution (R~ 60000) spectra of theinterstellar Na I D absorption lines towards 63 B-type stars (d<= 500pc) selected to cover these clouds and the connecting area defined bythe Galactic coordinates: 308°>=l>= 294° and-22°<=b<= 5°. The radial velocities, column densities,velocity dispersions, colour excess and photometric distances to thestars are used to understand the kinematics and distribution of theinterstellar cloud components. The analysis indicates that theinterstellar gas is distributed in two extended sheet-like structurespermeating the whole area, one at d<= 60 pc and another around120-150 pc from the Sun. The nearby feature is approaching the localstandard of rest with an average radial velocity of -7 kms-1, has low average column density logNNaI~ 11.2cm-2 and velocity dispersion b~ 5 km s-1. The moredistant feature has column densities between 12.3 <=logNNaI<= 13.2, average velocity dispersion b~ 2.5 kms-1 and seems associated with the dust sheet observed towardsthe Coalsack, Musca and Chamaeleon direction. Its velocity is centredaround 0 km s-1, but there is a trend for increasing from -3km s-1 near b= 1° to 3 km s-1 near b=-18°.The nearby low column density feature indicates a general outflow fromthe Sco-Cen association, in agreement with several independent lines ofdata in the general searched direction. The dust and gas feature around120-150 pc seem to be part of an extended large-scale feature of similarkinematic properties, supposedly identified with the interaction zone ofthe Local and Loop I Bubbles. Assuming that the interface and thering-like volume of dense neutral matter that would have been formedduring the collision of the two bubbles have similar properties, ourresults suggest that the interaction zone between the bubbles is twistedand folded.
|Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr|
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/913
|Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics|
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|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.
|Proper motions of faint ROSAT WTT stars in the Chamaeleon region|
We present proper motions of 59 stars of the ROSAT All-Sky Survey (RASS)located in direction of the Chamaeleon star forming region (SFR) in themagnitude range B=5.1 - 17 mag. Proper motions of the fainter stars werenewly derived utilizing survey Schmidt plates from the GSC II platearchive and from a set of special plates taken with the ESO Schmidttelescope. The vector point diagram (VPD) indicates that the certifiedWTT stars cluster away from the region occupied by the brighterpre-main-sequence stars (PMS) in Cha I. The distance to this newassociation is estimated at ~ 100 pc, sensibly smaller than the 150 pcgenerally assumed for the SFR. This yields an upper limit of 2 km s(-1)for the velocity dispersion of this new kinematic group. The de-reddenedCM diagram of the group members suggest the WTT stars are still PMSobjects, but older (3-30 Myr) and less massive than previousdeterminations. These revised age estimates, the newly derived grouppeculiar velocity, and current distance estimates to the Cha I/II/IIIcomplex would favour in-situ formation against that predicted by highvelocity cloud models. Finally, based on a redetermination of thepeculiar motions of stars and gas, we speculate that the whole SFRoriginated from the local Orion spur as a result of more classicalmechanisms like interactions with the spiral arms. Based on observationscollected at the European Southern Observatory (Chile) and on data fromthe Hipparcos astrometry satellite. Table~1 is available only inelectronic form at the CDS via anonymous ftp at 18.104.22.168.
|The ROSAT all-sky survey catalogue of optically bright OB-type stars.|
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
|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.
|A study of the Chamaeleon star forming region from the ROSAT all-sky survey. I. X-ray observations and optical identifications.|
We present the observations of the ROSAT all-sky survey (RASS) in thedirection of the Chamaeleon cloud complex, as well as the spectroscopicidentifications of the detected X-ray sources. The main purpose of thisidentification program was the search for low mass pre-main sequencestars. Sixteen previously known PMS stars were detected with highconfidence by ROSAT. Eight are classical T Tauri stars and eight areweak-line T Tauri stars, Seventy-seven new weak-line T Tauri stars wereidentified on the basis of the presence of strong Li λ 6707absorption, spectral type later than F0 and chromospheric emission. Wegive coordinates and count rates of the X-ray sources, and presentoptical spectra and finding charts for the sources identified opticallyas new pre-main sequence stars. Optical UBV(RI)_c_ and near-infraredJHKLM photometry for this sample of stars is also provided. In addition,6 new dKe-dMe candidates are found among the RASS sources.
|The distribution of interstellar dust in the solar neighborhood|
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
|The stellar temperature scale for stars of spectral types from O8 to F6 and the standard deviation of the MK spectral classification|
Empirical effective temperature of 211 early-type stars found in aprevious investigation (Kontizas and Theodossiou, 1980; Theodossiou,1985) are combined with the effective temperatures of 313 early-typestars from the literature. From these effective temperatures of a totalnumber of 524 early-type stars of spectral types from O8 to F6 a newstellar temperature scale is developed along with the standard deviationof the MK spectral classification.
|Effective temperature and gravity from c(0) and beta indices for B-type stars|
A sample of nonsupergiant B-type stars of solar chemical composition hasbeen analyzed for T(eff) and gravity differences due to the use of c(0)and beta indices from different photometric grids. The Moon andDworetsky (1985) grid, as well as an extension of the grid, are found toyield T(eff)s closer to those derived with other methods than the Lesteret al. (1986) grid; in addition, the former grid yields gravities thatare closer to values in the literature than the latter grid. A modifiedversion of the TEFFLOGG code of Moon (1985), which employs polynomialfunctions of the Stromgren indices, yields both T(eff) and gravity forthe present sample of B-type stars.
|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.
|Observed and computed spectral flux distribution of non-supergiant O9-G8 stars. III - Determination of T(eff) for the stars in the Breger Catalogue|
The effective temperatures and angular diameters of nonsupergiant O9-G8stars are determined from visible spectrophotometry. The results, whichrefer to 302 stars included in the Breger Catalogue, are derived fromthe comparison between the observed flux distributions and thepredictions of Kurucz's models (1979). The uncertainties to be expectedin individual results are discussed; their sizes are of the order of 5percent in effective temperature and 10 percent in angular diameter.
|The local system of early type stars - Spatial extent and kinematics|
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
|Observed and computed spectral distribution of early-type stars. II - Determination of T(e) for B5-A0 stars|
The automatic and fast procedure described in Malagnini et al (1982) hasbeen applied to a comparison of UV and visual spectral distributionswith Kurucz' (1979) models. The 48 stars of spectral types B-A0 andluminosity classes III-V that are included both in the UltravioletBright Star Spectrophotometric Catalog and in the Breger Catalog havebeen analyzed. The complete set of observations permits fairly accurateeffective temperature and angular diameter determinations. Comparisonswith other sources are also presented. The comparison between computedand observed fluxes shows that the residuals are always very small inthe visual region, while residuals in the region 1360-1500 A, at 1760 A,and at 2740 A, are fairly large and independent of spectral types.
|Starlight polarization in the direction of two H I complexes|
Upper limits to the gas/dust ratio in the direction of two complexes arederived based on 21-cm line observations and starlight polarizationmeasurements. Elongated H I structures parallel to the galactic magneticfield suggest that the gas and dust comprise a common cloud or cloudsystem. Dust producing the starlight polarization is mixed with the H Igas, aiding in estimating the distance for the two H I complexes.Distances of 100 pc for the filament at low velocities and of 200 pc foran intermediate-velocity cloud complex (IVC) are established frompolarimetric data, and possible origins for the filaments and IVC aresuggested.
|Empirical effective temperatures of B and early A stars|
Empirical effective temperatures of 112 B and early A type stars havebeen derived by comparing observed and computed fluxes in a wide andappropriate wavelength range. Space observations in the ultraviolet havebeen combined with ground-based observations, and the temperatures arederived by fitting computed fluxes to the observed fluxes in the visibleand ultraviolet spectral range. Effective temperatures found here are ingood agreement with those derived by previous workers.
|62nd Name-List of Variable Stars|
|Catalog of spectrophotometric scans of stars.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJS...32....7B&db_key=AST
|New kinematical data for bright southern OB-stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..129L&db_key=AST
|Four-color and H-beta photometry for bright B-type stars in the southern hemisphere.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..621C&db_key=AST
|MK Spectral Types for Bright Southern OB Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157..313H&db_key=AST
|A Photometric Investigation of the SCORPlO-CENTAURUS Association|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJS...15..459G&db_key=AST
|A Survey of Southern Be Stars|
|Radial velocities of 50 high velocity stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.126..381K&db_key=AST
|The Scorpio-Centaurus Association: II. Spectral types and luminosities of 220 O, B and a stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1961MNRAS.122..325M&db_key=AST
|New Bright Variable Stars|
|On the individual parallaxes of the brighter galactic helium stars in the southern hemisphere, together with considerations on the parallax of stars in general.|