Contents
Images
Upload your image
DSS Images Other Images
Related articles
A multiwavelength investigation of the temperature of the cold neutral medium
We present measurements of the HI spin temperatures (Ts) ofthe cold neutral medium (CNM) towards radio sources that are closelyaligned with stars for which published H2 ortho-paratemperatures (T01) are available from ultraviolet (UV)observations. Our sample consists of 18 radio sources close to 16 nearbystars. The transverse separation of the lines of sight of thecorresponding UV and radio observations varies from 0.1 to 12.0 pc atthe distance of the star. The UV measurements do not have velocityinformation, so we use the velocities of low ionization species (e.g.NaI/KI/CI) observed towards these same stars to make a plausibleidentification of the CNM corresponding to the H2 absorption.We then find that T01 and Ts match withinobservational uncertainties for lines of sight with H2 columndensity above 1015.8cm-2, but deviate from eachother below this threshold. This is consistent with the expectation thatin the CNM Ts tracks the kinetic temperature due tocollisions and that T01 is driven towards the kinetictemperature by proton exchange reactions.
| A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Adaptive Optics Photometry and Astrometry of Binary Stars
We present astrometric and photometric measurements of 39 binary starsmade with the adaptive optics system on the 3.6 m AdvancedElectro-Optical System (AEOS) telescope, taken from 2002 November to2003 March. The binaries have separations ranging from 0.08" to 5.11"and differential magnitudes ranging from 0.096 to 7.9. Also, we includea list of observations of 23 known binaries that we were unable toresolve. In the process of these measurements, we discovered three newcompanions to two previously known binary stars. We also discuss theeffects of scintillation and anisoplanatism on measurements of binarystar photometry in adaptive optics images. Suggestions on how tominimize these effects are then given.Based on observations made at the Maui Space Surveillance Systemoperated by Detachment 15 of the US Air Force Research Laboratory'sDirected Energy Directorate.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| 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.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| An ultra-high-resolution study of the interstellar medium towards Orion
We report ultra-high-resolution observations (R~9×105)of NaI, CaII, KI, CH and CH+ for interstellar sightlinestowards 12 bright stars in Orion. These data enable the detection ofmany more absorption components than previously recognized, providing amore accurate perspective on the absorbing medium. This is especially sofor the line of sight to the Orion nebula, a region not previouslystudied at very high resolution. Model fits have been constructed forthe absorption-line profiles, providing estimates for the columndensity, velocity dispersion and central velocity for each constituentvelocity component. A comparison between the absorption occurring insightlines with small angular separations has been used, along withcomparisons with other studies, to estimate the line-of-sight velocitystructures. Comparisons with earlier studies have also revealed temporalvariability in the absorption-line profile of ζ Ori, highlightingthe presence of small-scale spatial structure in the interstellar mediumon scales of ~10au. Where absorption from both Na0 andK0 is observed for a particular cloud, a comparison of thevelocity dispersions measured for each of these species providesrigorous limits on both the kinetic temperature and turbulent velocityprevailing in each cloud. Our results indicate the turbulent motions tobe subsonic in each case. Na0/Ca+ abundance ratiosare derived for individual clouds, providing an indication of theirphysical state.
| The Spatial Distribution of the λ Orionis Pre-Main-Sequence Population
The λ Ori star-forming region presents a snapshot of amoderate-mass giant molecular cloud 1-2 Myr after cloud disruption by OBstars, with the OB stars, the low-mass stellar population, remnantmolecular clouds, and the dispersed gas all still present. We have usedoptical photometry and multiobject spectroscopy for lithium absorptionto identify 266 pre-main-sequence stars in 8 deg2 of theregion. We also present new Strömgren photometry for the massivestars, from which we derive a distance of 450 pc and a turnoff age of6-7 Myr. Using these parameters and pre-main-sequence evolutionarymodels, we map the star formation history of the low-mass stars. We findthat low-mass star formation started throughout the region at about thesame time as the birth of the massive stars, and thereafter the birthrate accelerated. Within the last 1-2 Myr star formation ceased in thecenter of the star-forming region, near the concentration of OB stars,while it continues in dark clouds 20 pc away. We suggest that asupernova 1-2 Myr ago destroyed the molecular cloud core from which theOB stars formed, but it did not terminate star formation in more distantreaches of the giant molecular cloud. We find no secure evidence fortriggered or sequential star formation in the outer molecular clouds.The global star formation of the λ Ori region has generated thefield initial mass function, but local star formation in subregionsshows large deviations from the expected ratio of high- to low-massstars.
| 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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| On the origin of binaries with twin components
The existence of a statistically significant excess of dwarf binarieswith mass ratios from 0.95 to 1, as first noted by Lucy & Ricco (?),is confirmed by modern data. Excess of such binaries, called twins, isfound only for periods shorter than 40 days, and in the 2-30 days periodrange they constitute 10-20% of the total binary population. Twins musthave been formed by a special mechanism. It cannot be a mass transfer incontact pre-main-sequence binaries, fission is also unlikely. As shownby Bate (2000), accretion onto a close binary shifts mass ratio towards1, so twins may originate from binaries that became close while stillsurrounded by massive envelopes. Many twins are members ofhigher-multiplicity systems and/or clusters, which probably explains anearly formation of a close binary by stellar dynamics.
| A WIYN Lithium Survey for Young Stars in the λ Orionis Star-Forming Region
We have found 72 pre-main-sequence (PMS) stars near the center of theλ Orionis star-forming region by spectroscopically testing amagnitude-limited sample for the presence of lithium λ6708absorption, a diagnostic of youth. All of these stars show large lithiumequivalent widths and radial velocities consistent with Orionmembership, but only two were discovered previously via Hα orX-ray surveys. Comparison with PMS evolutionary tracks show that thelow-mass star formation did not begin prior to the initiation ofhigh-mass star formation 5-7 Myr ago. However, the subsequent detailedstar formation history is model dependent. Baraffe et al. isochronesimply that high- and low-mass stars began to form together 5-7 Myr ago,with the low-mass stellar formation ceasing abruptly 1 Myr ago. On theother hand, D'Antona & Mazzitelli isochrones indicate a narrowspread of PMS ages, which suggests a burst of low-mass star formation1-2 Myr ago. Furthermore, kinematic arguments require that the parentmolecular cloud gravitationally bound the stars together until recently,but at present the requisite gas mass is not visible. This leads us toconjecture that both the high- and low-mass stars were in a tightlybound cluster until a supernova blast about 1 Myr ago disrupted theparent cloud. This supernova also impacted on the PMS formation processby either (1) ceasing formation through removal of the gas supply or (2)triggering star births via cloud compression, depending on choice ofstellar evolution models. Finally, we find that despite their youth,only four of the 72 PMS stars have T Tauri-like Hα emission,suggesting the absence of accretion disks. We conjecture that this maybe the result of photoevaporation of the disks while the low-mass starswere in much closer proximity to the OB stars prior to becominggravitationally unbound.
| 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.
| On the normal spectral energy distribution of stars: Spectral types O9-B5
The normal energy distributions for fifteen spectral subtypes from O9 toB5 for luminosity classes V, IV, and III are derived. Threephotometrically uniform catalogs served as the source of thespectrophotometric data used. Synthetic color indices for all spectraltypes are calculated using the energy distribution curves obtained.Comparison of these indices with the expected normal color indicessuggests that the energy distributions derived are reliable.
| Spatially Resolved Hubble Space Telescope Spectra of the Chromosphere of alpha Orionis
Spatially resolved UV spectra of the supergiant alpha Orionis(Betelgeuse) obtained in 1995 March with the Goddard High ResolutionSpectrograph (GHRS) on board the Hubble Space Telescope (HST) show thatthe chromospheric emission in the Mg II h and k (around 280 nm) linesreaches a diameter of at least ~270 milliarcseconds, about twice thesize of ultraviolet continuum images obtained at the same time with theHST Faint Object Camera (FOC), and about 5 times the star's opticaldiameter. The signature of the unresolved bright spot observed in the1995 March FOC images occurs in the spectrum as an asymmetry in theintensity measured across the disk at constant wavelength. Because thespectra were obtained scanning across the stellar image, it is possibleto measure a differential line shift across the disk of the star thatcan be interpreted as being due to rotation. If this interpretation iscorrect, we can determine the axis of rotation of Betelgeuse andestimate its rotational speed to be 1.2 x 10^-8 rad s^-1, correspondingto a rotation period of 17 yr. In addition, it is plausible that the1995 March bright spot is congruent with the pole of the star,suggesting that star's angle of inclination is ~20 deg to the line ofsight. Considering the small number of bright spots that are present atany one time on the surface of Betelgeuse, and the signature of the 1995March spot in the Mg II resonance lines as observed with the GHRS, itappears that such spots are not the consequence of convective flows.Differences in the spatial distribution of the flux emerging fromdifferent layers of the atmosphere and the line asymmetries of the Mg IIh and k lines suggest that the spot is the signature of an outwardlypropagating shock wave in an atmosphere modified by rotation.
| Systematic Errors in the FK5 Catalog as Derived from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114..850S&db_key=AST
| The diffuse interstellar bands at 5797, 6379 and 6613 Angstroms. Ionization properties of the carriers
We present a study of the behaviour and ionization properties of threenarrow Diffuse Interstellar Bands (DIBs) at lambda lambda 5797, 6379 and6613 Angstroms. In all three DIBs substructures have recently beendetected, indicating large gaseous molecular carriers. Studying DIBs inregions with drastically different physical properties in terms of UVflux and density enables us to monitor the behaviour of the carriers andhence to constrain their nature. We observed these three DIBs along 40different lines-of-sight (35 program stars and 5 standard stars)consisting of HII regions, dark clouds, molecular clouds and reflectionnebulae. The DIB variations at low reddening are explained by a newmodel of photoionization equilibrium of the DIB carriers. This modeltakes into account the penetration depth of UV ionizing photonsthroughout the cloud. The slope of the variation of DIB strength as afunction of reddening thus allows us to estimate the effectiveionization potentials of the carriers. Following this new analysis, thecarriers of the lambda 5797 and lambda 6613 Angstroms DIBs would haveionization potentials above 10eV, reminiscent of large PAHs orfullerenes which have a single positive charge. The estimated ionizationpotential (7--9eV) of the lambda 6379 Angstroms DIB seems to indicate alarge neutral carrier. Based on observations with OHP 1.93m Telescopeand Elalie spectrograph.
| The effect of rotation on the absolute visual magnitudes of OB stars measured with Hipparcos.
We derive the absolute visual magnitudes of 14 OB-stars of luminosityclass III to V from the parallaxes measured by Hipparcos. The values ofM_V_ can differ by as much as 1.5mag from the M_V_-spectral typecalibration. Slowly rotating stars, vsini<100km/s, are significantlyfainter in M_V_ than stars with vsini>100km/s of the same spectraltype by about 1 magnitude. We discuss this effect and argue that it isdue to the influence of rotation on the assignment of spectral types andluminosity class. Slowly rotating stars are also fainter than thestandard M_V_-spectral type relation. This effect has importantconsequences on the distance determinations of stars and clusters fromM_v_ and V.
| The Pulkovo Spectrophotometric Catalog of Bright Stars in the Range from 320 TO 1080 NM
A spectrophotometric catalog is presented, combining results of numerousobservations made by Pulkovo astronomers at different observing sites.The catalog consists of three parts: the first contains the data for 602stars in the spectral range of 320--735 nm with a resolution of 5 nm,the second one contains 285 stars in the spectral range of 500--1080 nmwith a resolution of 10 nm and the third one contains 278 stars combinedfrom the preceding catalogs in the spectral range of 320--1080 nm with aresolution of 10 nm. The data are presented in absolute energy unitsW/m(2) m, with a step of 2.5 nm and with an accuracy not lower than1.5--2.0%.
| A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
| 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.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| The threshold for stellar winds in hot main-sequence stars
The profiles of ultraviolet resonance lines of C IV were surveyed in asample of 29 cluster and association members in the spectral type rangeO9-B2 III-V, together with a few field stars of interest. Thetemperatures and gravities of the stars were taken from the modelatmosphere analysis by Grigsby, Morrison, & Anderson (1992), and theluminosities were estimated on the basis of cluster and associationdistances from the recent literature. A parameter Pw wasdefined in order to describe the degree and assymetry of the C IVprofile. This parameter, together with total C IV equivalent width, wasfound to be well correlated with stellar luminosity and temperature. Afew anomalous stars were noted: tau Sco, HD 66665, HD 13621, and the ONstars HD12323 and HD 201345. The results suggest a sudden onset ofobservable mass loss at T(effective) = 27,500 +/- 500 K, log (L/solarluminosity) = 4.4 +/- 0.12, in agreement with the previous study byPrinja (1989). At T(effective) = 28,000 K and log g = 4, our non-LTEmodel atmospheres show an enhancement in the ground-state population ofC(+3) in their topmost layer, which could be responsible for initiationof the winds via radiation pressure on the C(+3) ions, or for the onsetof visibility of C(+3) ions in the wind because of an increase in theoptical depth in the C IV lines in the outermost layers.
| 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.
| The determination of T_eff_ of B, A and F main sequence stars from the continuum between 3200 A and 3600 A.
A method of determination of the effective temperature of B, A and Fmain sequence stars is proposed, using the slope of the continuumbetween 3200A and 3600A. The effective temperature calibration is basedon a sample of stars with energy distributions known from UV to the red.We have determined the Balmer jump and the effective temperatures for235 main sequence stars. The temperatures found have been compared withthose derived by Underhill et al. (1979), Kontizas & Theodossiou(1980), Theodossiou (1985), Morossi & Malagnini (1985). Thecomparison showed good agreement for most of the stars in common. On theother hand, the temperatures derived from the reddening-free colourfactor QUV, from the colour index (m1965-V) and from (B-V), given inGulati et al. (1989), are systematically lower than our temperatures,however the differences are within one-sigma error.
| An atlas of southern MK standards from 5800 to 10200 A
An atlas of stellar spectra covering the wavelength range from 5800 to10,200 A is presented of 126 southern MK standard stars, covering theluminosity classes I, III, and V. Some peculiar stars are included forcomparison purposes. The spectra were obtained at a resolution of 4.3 Aper pixel using a Cassegrain-mounted Boller and Chivens spectrographequipped with a Reticon detector. The quality and utility of the dataare discussed and examples of the spectra are presented. The atlas isavailable in digital format through the NSSDC.
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Ωρίων |
| Right ascension: | 05h34m49.20s |
| Declination: | +09°29'22.0" |
| Apparent magnitude: | 4.41 |
| Distance: | 302.115 parsecs |
| Proper motion RA: | 0 |
| Proper motion Dec: | -3 |
| B-T magnitude: | 4.181 |
| V-T magnitude: | 4.367 |
Catalogs and designations:
|
INHABITED SKY
