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Physical parameters and wind properties of galactic early B supergiants
We present optical studies of the physical and wind properties, plus CNOchemical abundances, of 25 O9.5-B3 Galactic supergiants. We employnon-LTE, line blanketed, extended model atmospheres, which provide amodest downward revision in the effective temperature scale of early Bsupergiants of up to 1-2 kK relative to previous non-blanketed results.The so-called "bistability jump" at B1 (Teff 21 kK)from Lamers et al. is rather a more gradual trend (with large scatter)from v&infy;/vesc3.4 for B0-0.5 supergiantsabove 24 kK to v&infy;/vesc 2.5 for B0.7-1supergiants with 20 kK ≤ Teff ≤ 24 kK, andv&infy;/vesc 1.9 for B1.5-3 supergiants below20 kK. This, in part, explains the break in observed UV spectralcharacteristics between B0.5 and B0.7 subtypes as discussed by Walbornet al. We compare derived (homogeneous) wind densities with recentresults for Magellanic Cloud B supergiants and generally confirmtheoretical expectations for stronger winds amongst Galacticsupergiants. However, winds are substantially weaker than predictionsfrom current radiatively driven wind theory, especially at mid-Bsubtypes, a problem which is exacerbated if winds are already clumped inthe Hα line forming region. In general, CNO elemental abundancesreveal strongly processed material at the surface of Galactic Bsupergiants, with mean N/C and N/O abundances 10 and 5 times higher thanthe Solar value, respectively, with HD 2905 (BC0.7 Ia) indicating thelowest degree of processing in our sample, and HD 152236 (B1.5Ia+) the highest.
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| Interstellar Ca II Line Intensities and the Distances of the OB stars
We show that the equivalent widths of the well-known interstellar Ca IIH and K lines can be used to determine the distances to OB stars in ourGalaxy. The equivalent widths, measured in the spectra of 147 early-typestars, are strongly related to the Hipparcos parallaxes of thoseobjects. The lines fitted to the parallax-equivalent width data aregiven by the formulae π=1/[2.78EW(K)+95] and π=1/[4.58EW(H)+102],where π is in arcseconds and EW is in milliangstroms. The form of theformulae, yielding a finite parallax even for zero absorption, showsthat space within ~100 pc of the Sun contains very little Ca II, whichis in agreement with the known dimensions of the Local Bubble. Using CaII lines for distance determination does not require the knowledge ofthe absolute magnitude of the object; it is thus well suited for targetsfor which the absolute calibration is either not precise (OBsupergiants) or not available at all (peculiar objects). We alsodemonstrate that neither the reddening E(B-V) nor the equivalent widthsof interstellar K I and CH lines are suitable candidates for distanceestimation, their relation with parallaxes being far less tight than forCa II.
| Correlations between diffuse interstellar bands and atomic lines
We present and discuss correlations between strengths of the well-known,strong interstellar atomic lines of KI and CaII, and four selected,strong unidentified diffuse interstellar bands (DIBs): 5780, 5797, 5850and 6614. In order to analyse a homogeneous sample of echellehigh-resolution spectra it has been chosen to use measurements fromTerskol Observatory in Northern Caucasus plus a selected number ofhigher resolution observations performed using other instruments. Wedemonstrate that the strength of certain DIBs correlate well withneutral potassium lines and to a much lower degree with ionized calciumlines. This fact suggests that the degree of irradiation of a cloud withUV photons, capable to ionize interstellar atoms, plays a crucial rolein the formation/maintenance of certain molecular species: possiblecarriers of DIBs.
| A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. VI. NGC 6910
We present results of variability search in the field of the young opencluster NGC 6910. We found four beta Cep-type stars in the cluster,which makes it rather exceptional among the northern clusters observedin our project. Two of these beta Cep stars show three modes withamplitudes above the detection level, in the remaining two we detectsingle modes. We discuss the possibility that the large number of betaCep stars in NGC 6910 is due to higher metallicity of the cluster. Inaddition, we found four other variables, one ellipsoidal or eclipsingbinary and three that show irregular variations. The latter three starshave H alpha in emission.We also provide VI_C photometry for 139 stars down to V=16.6 mag and Halpha photometry for 73 stars. Using this photometry we estimate thecluster age to be equal to 6+/-2 Myr, and the distance modulus,11.0+/-0.3 mag. The reddening is high and variable across the cluster.In terms of the E(V-I_C) color-excess it amounts to 1.25-1.7 mag,corresponding to E(B-V) between 1.0 mag and 1.4 mag. The averagereddening in the central field is E(V-I_ C=1.47+/-0.04 mag.
| The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons
We have obtained new Hubble Space Telescope/Space Telescope ImagingSpectrograph spectra to search for structure in the ultravioletinterstellar extinction curve, with particular emphasis on a search forabsorption features produced by polycyclic aromatic hydrocarbons (PAHs).The presence of these molecules in the interstellar medium has beenpostulated to explain the infrared emission features seen in the 3-13μm spectra of numerous sources. Ultraviolet (UV) spectra are uniquelycapable of identifying specific PAH molecules. We obtained highsignal-to-noise ratio UV spectra of stars that are significantly morereddened than those observed in previous studies. These data put limitson the role of small (30-50 carbon atoms) PAHs in UV extinction and callfor further observations to probe the role of larger PAHs. PAHs are ofimportance because of their ubiquity and high abundance inferred fromthe infrared data, and also because they may link the molecular and dustphases of the interstellar medium. A presence or absence of UVabsorption bands due to PAHs could be a definitive test of thishypothesis. We should be able to detect a 20 Å wide feature downto a 3 σ limit of ~0.02 AV. No such absorption featuresare seen other than the well-known 2175 Å bump.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555.
| 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.
| Observations of H3 in the Diffuse Interstellar Medium
Surprisingly large column densities of H+3 havebeen detected using infrared absorption spectroscopy in seven diffusecloud sight lines (Cygnus OB2 12, Cygnus OB2 5, HD 183143, HD 20041, WR104, WR 118, and WR 121), demonstrating that H+3is ubiquitous in the diffuse interstellar medium. Using the standardmodel of diffuse cloud chemistry, our H+3 columndensities imply unreasonably long path lengths (~1 kpc) and lowdensities (~3 cm-3). Complimentary millimeter-wave, infrared,and visible observations of related species suggest that the chemicalmodel is incorrect and that the number density ofH+3 must be increased by 1-2 orders of magnitude.Possible solutions include a reduced electron fraction, an enhanced rateof H2 ionization, and/or a smaller value of theH+3 dissociative recombination rate constant thanimplied by laboratory experiments.
| Chemical composition of B-type supergiants in the OB 8, OB 10, OB 48, OB 78 associations of M 31
Absolute and differential chemical abundances are presented for thelargest group of massive stars in M 31 studied to date. These resultswere derived from intermediate resolution spectra of seven B-typesupergiants, lying within four OB associations covering a galactocentricdistance of 5-12 kpc. The results are mainly based on an LTE analysis,and we additionally present a full non-LTE, unified model atmosphereanalysis of one star (OB 78-277) to demonstrate the reliability of thedifferential LTE technique. A comparison of the stellar oxygen abundancewith that of previous nebular results shows that there is an offset ofbetween ~ 0.15-0.4 dex between the two methods which is criticallydependent on the empirical calibration adopted for the R_23 parameterwith [O/H]. However within the typical errors of the stellar and nebularanalyses (and given the strength of dependence of the nebular results onthe calibration used) the oxygen abundances determined in each methodare fairly consistent. We determine the radial oxygen abundance gradientfrom these stars, and do not detect any systematic gradient across thisgalactocentric range. We find that the inner regions of M 31 are not, aspreviously thought, very ``metal rich''. Our abundances of C, N, O, Mg,Si, Al, S and Fe in the M 31 supergiants are very similar to those ofmassive stars in the solar neighbourhood.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
| An atlas of 2.4 to 4.1 mu m ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with theShort Wavelength Spectrometer (SWS) during the Post-Helium program ofthe Infrared Space Observatory (ISO). This program is aimed at extendingthe Morgan & Keenan classification scheme into the near-infrared.Later type stars will be discussed in a separate publication. Theobservations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 μm, supplemented with 10 spectra acquired during the nominal mission witha similar observational setting. For B-type stars, this sample providesample spectral coverage in terms of subtype and luminosity class. ForO-type stars, the ISO sample is coarse and therefore is complementedwith 8 UKIRT Larcmin -band observations. In terms of the presence ofdiagnostic lines, the Larcmin -band is likely the most promising of thenear-infrared atmospheric windows for the study of the physicalproperties of B stars. Specifically, this wavelength interval containsthe Bralpha , Pfgamma , and other Pfund lines which are probes ofspectral type, luminosity class and mass loss. Here, we present simpleempirical methods based on the lines present in the 2.4 to 4.1 mu minterval that allow the determination of i) the spectral type of Bdwarfs and giants to within two subtypes; ii) the luminosity class of Bstars to within two classes; iii) the mass-loss rate of O stars and Bsupergiants to within 0.25 dex. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA. The appendix is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin.qcat?J/A+A/384/473
| Narrow Diffuse Interstellar Bands: A Survey with Precise Wavelengths
We present an atlas of 271 diffuse interstellar bands (DIBs) between4460 and 8800 Å based on echelle spectra (R=45,000), of which morethan 100 are new DIBs discovered in this survey. The atlas is restrictedmostly to narrow features, and we describe the tests for an interstellarorigin. The rest wavelength of each DIB was determined in a high-qualitycomposite spectrum of the star HD 23180 using the interstellar Na I (D1and D2) lines to establish the radial velocity of the single interveningcloud. DIB wavelengths are quoted to 0.01 Å and are probablyaccurate to ~0.1 Å. Other, weak DIBs found in the spectra ofheavily reddened stars are included with a lower wavelength precision.
| On the identification of the C60+ interstellar features
The identity of the carriers of the diffuse interstellar bands (DIBs) isone of the most fascinating puzzles of modern spectroscopy. Over thelast few years the number of known DIBs has grown substantially. In thispaper we discuss the two recently discovered near-infrared weakinterstellar features which have already been proposed as fingerprintsof the buckminsterfullerene [formmu2] We present and discussmeasurements of the two related DIBs within a larger sample of reddenedtargets, observed with different spectrometers, telescopes and siteconditions. We provide additional arguments in favour of theinterstellar origin of the two bands. We find evidence around the9577-Å DIB of far-wing structures, which may affect broad-bandmeasurements. We estimate corrections and errors for telluric andstellar blends, and show that the cores of the two DIBs are wellcorrelated with a ratio near unity within 20per cent. Finally, wediscuss their relation to the laboratory spectra of [formmu3] and thesearch for two expected weaker [formmu4] transitions.
| Search for Pre-Main-Sequence Stars in the Young Galactic Cluster NGC 6910
Photometric CCD UBV measurements have been obtained in the field of theyoung Cygnus cluster NGC 6910. The observations reach down to magnitudeV~=18 for 206 stars measured in all three UBV bands, uncovering theregion of the color-magnitude diagram where pre-main-sequence (PMS)stars are expected. The transformation of our instrumental magnitudes tothe standard system is discussed on the basis of two different sets ofstandard stars: 22 stars from six fields in the Landolt catalogs and 48stars with published photoelectric photometry in common with ours in thefour clusters observed in this campaign. The latter set is preferred,since it enables the effect of systematic errors in the U-B colors to beminimized. The adopted cluster parameters are E(B-V)=1.02+/-0.13,V0-MV=11.2+/-0.2, and age=(6.5+/-3)x106yr. The search for PMS cluster members on the basis of the calculatedcolor excess and distance modulus results in the proposed membership for11 PMS stars of spectral types from A to G.
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Extragalactic Stellar Spectroscopy
The advent of large 8-10m telescopes heralds a new age in stellarastronomy. It is now possible to carry out detailed spectroscopicobservations at high resolution of the brightest stars of galaxies inthe Local Group, and it is envisaged that intermediate resolutionobservations will be extended to stars in the nearest galaxy clusterssuch as Virgo and Fornax. For some years the authors have been carryingout the groundwork involved in identifying young massive supergiantstars in nearby resolved galaxies, with a view to performing follow-updetailed studies of selected samples. In this article we summarize thecontribution that the William Herschel Telescope has made to thisproject, and further, show that even a 4.2m telescope with a bluesensitive, large format CCD at a good site with dependable sub-arcsecondseeing can make an important contribution to the detailed study of ournearest spiral neighbours M31 and M33.
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Polycyclic Aromatic Hydrocarbons and the Diffuse Interstellar Bands: A Survey
We discuss the proposal relating the origin of some of the diffuseinterstellar bands (DIBs) to neutral and ionized polycyclic aromatichydrocarbons (PAHs) present in interstellar clouds. Laboratory spectraof several PAHs, isolated at low temperature in inert gas matrices, arecompared with the spectra of five reddened early-type stars selectedfrom an extensive set of astronomical spectra. From this comparison, itis concluded that PAH ions are good candidates to explain some of theDIBs. Unambiguous assignments are difficult, however, because of theshift in wavelengths and the band broadening induced in the laboratoryspectra by the solid matrix. This situation is illustrated by acomparison with the gas-phase spectra made available recently for twoPAH ions. Definitive band assignments and, ultimately, the test of theproposal that PAH ions carry some of the DIBs must await theavailability of a larger set of gas-phase measurements in thelaboratory. The present assessment offers a guideline for futurelaboratory experiments by allowing the preselection of promising PAHmolecules to be studied in jet expansions.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| Galactic B-supergiants: A non-LTE model atmosphere analysis to estimate atmospheric parameters and chemical compositions
A non-LTE model atmosphere analysis of moderate resolution (R ~ 5 000)spectra of 46 Galactic B-type supergiants is presented. Standardtechniques are adopted, viz. plane-parallel geometry and radiative andhydrostatic equilibrium. Spectroscopic atmospheric parameters (T_eff,log g & v_turb) and chemical abundances (He, C, N, O, Mg & Si)are estimated, both as a test of the validity of such an approach and inan attempt to provide consistent results for supergiants covering asignificant range of spectral types. The values of the estimatedatmospheric parameters and their dependence on the physics adopted inthe model atmospheres calculations are discussed. The absolute metalabundances are compared to those of main sequence B-type stars and, ingeneral, their chemical compositions appear to be similar. Theabundances for He, C, N & O are considered in some detail and arediscussed in the context of possible evolutionary histories for thisstellar sample. Specifically, it is found that the supergiant sample canbe subdivided into a number of evolutionarily distinct groups. The lowermass objects are predominantly chemically near-normal i.e. theirphotospheres show little or no evidence for chemical processing, whereasthe higher mass supergiants have CNO ratios which are indicative of CNand possibly NO-cycle burning. An attempt is made to quantify thedifference in nitrogen and carbon abundances between the high and lowmass targets but this is hampered by theoretical uncertainties. Thepossibilities that the most highly processed supergiants may have eitherlarger rotational velocities or have undergone mass transfer within abinary system are discussed.
| On the relation between diffuse interstellar bands and simple molecular species
We present observations of the major diffuse interstellar bands (DIBs)at 5780 and 5797 Ä as well as literature data and our ownobservations of the violet lines of CH and CH(+) , in the lines of sighttoward some 70 stars representing various degrees of the interstellarreddening. The correlations are shown and discussed in the context ofindicators such as far-UV extinction parameters and neutral molecularabundances. The results show that the DIBs in question (lambda lambda5797 and 5780) both probably form in diffuse cloud interiors, in arelated regime where CH and H_2 form. The ratio of the two DIBscorrelates with CH abundance, confirming that the lambda 5797 carrier isfavoured in enhanced molecular gas regions over the lambda 5780 carrier.The ratio of the two DIBs correlates poorly with CH(+) abundance. Ourcompilation of observational data also suggests that the DIB ratio maybe equally useful as a cloud type indicator as is R_V, the ratio oftotal to selective extinction, and much more readily observed. Based onobservations obtained at the Russian Special Astrophysical Observatory(SAO), Terskol Observatory (TER), Canada France Hawaii Telescope (CFHT),European Southern Observatory (ESO), Observatoire de Haute-Provence(OHP)
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Near-Infrared H-Band Features in Late O and B Stars
We examine the spectral characteristics of normal OB stars withhigh-signal-to-noise ratio (>120) H-band (1.6 μm) spectra at aresolution of 2000. We find that several atomic lines vary smoothly withstellar temperature, as first shown by Blum et al. However, we find apreviously unreported, significant variation in the strength of some ofthese lines with stellar luminosity. B supergiant stars show stronger Hei and weaker Br 11 as compared with low-luminosity B dwarf stars of thesame spectral class. It is for this reason that luminosity class mustalso be determined to obtain an accurate spectral type for a given starusing H-band spectra. We suggest a method for estimating the spectraltype and luminosity of an OB star over the wavelength range from 1.66 to1.72 μm using hydrogen Br 11 at 1.681 mum, He i at 1.700 mum, and Heii at 1.693 mum. The use of the near-infrared spectral range forclassification has obvious advantages over optical classification whenapplied to heavily reddened stars, such as in star-forming regions ordeeply embedded lines of sight within the plane of the Galaxy, such asthe Galactic center. Furthermore, the H band is less likely to becontaminated by infrared excess emission, which is frequently seenaround massive young stellar objects beyond 2 mum.
| Radio observations of stellar winds from early type stars
Fifteen O and B supergiants have been observed with the Very Large Array(VLA) at 4.85, 8.45, and 14.95 GHz in order to make a detailedcomparative study of the mass loss rates evaluated from Hα andradio continuum observations and reveal and quantify possible departuresfrom standard wind conditions. We detected 12 sources, 7 of which forthe first time, thus increasing by 30% the total number of detections ofOB supergiants in the northern sky. Radio spectral slopes indicate thatthe radio emission is mainly of thermal origin in all objects with oneexception (HD 190603) out of the 12 detections. Our results demonstratethe value of using Hα for mass loss rate determinations,especially for stars that are too distant or too faint to be detectedwith radio techniques. The relationship dot {M} - L for supergiantsturns out to be appreciably flatter than commonly reported, i.e. log{dot {M}} =3D (1.25\pmm0.30) log {L}. Based on observations with theVery Large Array. The VLA is a facility of the National Radio AstronomyObservatory which is operated by the Associated Universities Inc. undercooperative agreement with the National Science Foundation.
| Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements
Proper motions measured by Hipparcos confirm the large anomalousvelocities of the OB associations located around the Cygnus Superbubble(Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organizedexpanding pattern in Canis Major OB1. At the distances of theseassociations, the organized velocity patterns imply LSR velocities of upto ~ 60 km s(-1) for the associations in Cygnus, and about ~ 15 km s(-1)in Canis Major OB1. The magnitude and spatial arrangement of theexpanding motions suggests that very energetic phenomena are responsiblefor the formation of the present OB associations. This is independentlysupported by observations of the associated interstellar medium carriedout in other wavelengths. The gravitational instability scenarioproposed by Comeron & Torra 1994 (ApJ 423, 652) to account for theformation of the stars in the Cygnus Superbubble region is reviewed inthe light of the new kinematic data. It is found that the energeticrequirements set by the highest velocities on the OB associationpowering the Superbubble, Cygnus OB2, are too large by orders ofmagnitude. However, the scenario can still account for the formation ofmost of the stars if, as can be reasonably expected, the stars with thehighest measured velocities are actually runaways from Cygnus OB2itself. As for Canis Major OB1, we consider their formation in asupernova remnant, as suggested by Herbst & Assousa 1977 (ApJ, 217,473). The detection of a new runaway star, HIC 35707 (=HD 57682), whosemotion is directed away from the derived center of expansion, supportsthis scenario and provides an independent age for the supernova remnant,assuming that the runaway star was the binary companion of thesupernova. Based on a number of arguments, however, we find it unlikelythat the stars are a direct consequence of instabilities in theexpanding shell. We propose instead that their formation was triggeredin preexisting clouds, accelerated and compressed by the supernovaexplosion.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| 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
| Near Infrared Spectroscopy of Highly Reddened Stars in the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112..235I&db_key=AST
| Evaluation of a 512X512-Element Platinum Silicide Schottky-Barrier Infrared Image Sensor and Pilot Observations of Cygnus X Region
We present evaluation of the performance of Mitsubishi's 512X512 elementplatinum silicide (PtSi) Schottky-Barrier infrared image sensor forapplication to astronomical observation. An infrared camera system,incorporating the PtSi array, was built and its performance wasevaluated both in the laboratory and in observations. Dark current, DCstability, noise, quantum efficiency (QE), linearity, and uniformitywere measured. Results of a series of measurements show that the arrayhas potential capability for astronomical use. Several problems such aslow QE and "splashes" are discussed. To demonstrate the effectiveness ofthe array by using this infrared camera, we have mapped an area of 8X9square degrees of the Cygnus X region with a small telescope consistingof a silicon singlet lens. More than 1000 stars brighter than 6.5 mag inH-band were detected in the region. (SECTION: AstronomicalInstrumentation)
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