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CN column densities and excitation temperatures
We analyse abundances and rotational temperatures of the interstellar CNmolecule. We have calculated the column densities and excitationtemperatures of the molecule along 73 lines of sight basing on ouroriginal measurements of the B 2?+ -X2?+ (0,0) vibrational band recorded in highsignal-to-noise ratio spectra and also for 88 directions based onmeasurements already available in literature. We compare the columndensities obtained from different bands of CN molecule available toground-based instruments. The obtained excitation temperatures in theanalysed directions show always an excess over the cosmic microwavebackground radiation (CMBR) temperature.
| A Preliminary Investigation of the Diffuse Interstellar Line at 8621 Å
We have obtained high-resolution spectra at the Dominion AstrophysicalObservatory, the Calar Alto Observatory, and the European SouthernObservatory of hot stars in the near-infrared region to study thediffuse interstellar band (DIB) at 8621 Å. Field stars as well asselected members of the Perseus spiral arm, the ρ Ophiuchi complex,and the Cygnus OB2 association were observed and the equivalent widthsof the band measured, as well as interstellar K I absorption at 7699Å. In total we measure the equivalent width of the 8621 band in 64stars. In a series of figures we show the correlations of the DIB withreddening, polarization, K I, and strengths of other DIBs at 5780, 5797,and 6613 Å. The quality of the correlations are discussed by meansof the Spearman rank correlation test. Good correlations are found withreddening and, among the other DIBs, 8621 correlates best with 5780. Byexamining the three special regions mentioned above we confirm theweakness of the 8621 DIB in the hot stars of the ρ Oph star-formingregion. In the Perseus spiral arm region we find that the DIBs areformed largely in foreground clouds but not in the gas that appears tohave been blown away from the young massive stars of the Perseus arm. InCyg OB2 we find that the equivalent widths of the 8621 line lie abovethe linear correlation of equivalent width with E(B-V) and theirstrength does not vary as strongly with reddening. The heavily reddenedCyg OB2 star 12 is the most extreme example of the relativeinsensitivity of the 8621 equivalent width to reddening in the CygnusOB2 region.
| Radial Velocities of Six OB Stars
We present new results from a radial velocity study of six bright OBstars with little or no prior measurements. One of these, HD 45314, maybe a long-period binary, but the velocity variations of this Be star maybe related to changes in its circumstellar disk. Significant velocityvariations were also found for HD 60848 (possibly related to nonradialpulsations) and HD 61827 (related to wind variations). The other threetargets, HD 46150, HD 54879, and HD 206183, are constant-velocityobjects, but we note that HD 54879 has Hα emission that mayoriginate from a binary companion. We illustrate the average redspectrum of each target.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| 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.
| A study of RV in Galactic O stars from the 2MASS catalogue
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 185 O stars, using J, H,Ks photometry from the 2MASS project. The results arecombined with data from the literature of 95 stars where RVhas been derived with the same technique, 22 of which in common with ourpresent sample from the 2MASS project catalogue. The averageRV from these 258 O stars is of 3.19 +/- 0.50. All objectswhose RV departs from this value by more than 2 sigma havebeen recognized. Ten objects have RV higher than this valueand two lower. It is found that anomalous RV can scarcely beassociated with anomalies in the general interstellar medium, e.g. withdifferent behaviour in different spiral arms. They are clearly linked tolocal cloud effect. In the Cygnus region RV values follow thebehaviour of the general interstellar medium, while in the Carina arm,in spite of the relatively larger distance, local cloud effects prevail.An explanation for this is suggested. The relatively few stars of oursample whose Hipparcos parallaxes are reliable, are found to havedistances systematically smaller than the distances derived by thespectroscopic parallaxes. We argue that this effect is consistent withthe recently claimed discovery of grey extinction towards OB stars.This publication makes use of data products from the Two Micron All SkySurvey (2MASS), which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center/CaliforniaInstitute of Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/905
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| 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.
| Interstellar CN toward CH+-forming regions
Measurements on interstellar CN absorption are presented for stars inthree southern OB associations, NGC 2439, Vela OB1, and Cen OB1. CN isdetected in 21 out of 31 stars observed. The doublet ratio for the R(1)and P(1) lines of the (0, 0) band of the B 2Sigma+-X 2Sigma + violet system and acomparison of violet system data with measurements of the (1, 0) and (2,0) bands of the A 2Pi -X 2Sigma + redsystem are used to derive Doppler parameters and total column densities.Inferred CN column densities vary by more than an order of magnitude forlines of sight with similar CH column densities. Observations of the (0,0) band of the CH B 2Sigma --X 2Pisystem are used to revise previously published CH column densitiestoward the lines of sight studied in CN. Together with earlier resultson CH, CH+, and C2, the CN data presented hereprovide a homogeneous set of column densities and radial velocities ofdiatomic molecules in three individual translucent clouds. We use thesedata to study CN production via chemical models. Gas densities areinferred from models based on production via CH and C2 incool gas. Most sightlines in our sample test densities typical fordiffuse molecular gas (a few hundred cm-3 ) when theultraviolet flux permeating the gas is between 1 and 5 times the averageinterstellar flux. A few lines of sight indicate that CN is producedunder dark cloud conditions because relatively large densities areobtained or because this simple chemical scheme is unable to reproducethe observed CN columns. Low densities are indicated for directions withupper limits on CN. We add an ad hoc component of a number oflow-velocity (<10 km s-1) criss-crossing MHD shocks toexplain observed column densities of interstellar CH+. Theseshocks also produce about 10 to 30% of the total CH column along theline of sight.
| Atlas of Interstellar Extinction Curves of OB Stars Covering the Whole Available Wavelength Range
The paper presents a collection of 436 extinction curves covering thewhole available range of wavelengths from satellite UV to near-IR. Thedata were taken from the ANS photometric catalogue and from thecompilations of IR photometric measurements. The data curves have beenobtained with the aid of ``artificial standards": Papaj et al. (1993)and Wegner (1994, 1995). The visual magnitudes and spectralclassifications of O and B type stars with EB-V>= 0.05were taken from the SIMBAD database. The curves are given in the form ofplots and tables E{lambda - V} / EB-V versus1/λ. The observed variety of extinction laws among slightlyreddened stars is apparently due to the various physical parameters ofinterstellar clouds.
| The distribution of bright OB stars in the Canis Major-Puppis-Vela region of the Milky Way
The picture of the young stellar groups in the Canis Major-Puppis-Vela(215 deg
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. I. Canis Major - Puppis - Vela
Strömgren and Hβ photometry of OB-stars generally brighterthan 9.5 mag in the Canis Major - Puppis - Vela region of Milky Way isreported. The observations are based on the Milky Way luminous-star (LS)identifications and are designed to create a complete, magnitude-limitedsample of LS for this field. We present new uvby photometry for 127 LSand Hβ photometry for 25 of them. These observations are part of anongoing effort to improve the completeness of the existing uvbybetadata-base for the bright OB-type stars in the Milky Way, with the aim toinvestigate the structure of selected star-forming regions. Based ondata from the Strömgren Automatic Telescope of the CopenhagenAstronomical Observatory, La Silla. Tables 3 and 4 are only available inelectronic form at the CDS via anonymous ftp to 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Interstellar C_2 absorption lines towards CH+ forming regions
Interstellar C_2 absorption line observations towards the southern OBassociations NGC 2439, Vela OB1, and Cen OB1 are used to infergaskinetic temperatures Tkin and densities nctowards lines of sight with previously determined large CH andCH+ column densities. Towards NGC 2439, the material ischaracterised by temperatures of Tkin = 75-85 K and densitiesexceeding nc > 1000 C_2m, and a fractional C_2 abundanceof about x(C_2) = 1.5 10-8. Temperatures and densitiesinferred towards two stars in Vela OB1 are Tkin = 65-85 K andnc >= 600 C_2m. C_2 fractional abundances in the cloudcomplex obscuring Vela OB1 are about half the value found in NGC 2439.For the lines of sight towards Cen OB1, values of Tkin =70-95 K and fractional abundances of x(C_2) ~ 5 10-9 arefound, and towards HD 114213, Tkin = 25 K and nc =400+/-100 C_2m. The observations demonstrate that C_2 resides in coolgas at temperature of Tkin < 100 K. The C_2 columndensities are correlated with those of CH, which is expected fromtheoretical models. This suggests that CH is efficiently formed in thecool material as well, together with C_2. This finding does not supportexpectations from recent MHD and vortex models of CH+formation, which stipulate that neutrals such as CH are abundantlyproduced in hot regions of many 100 K temperature.
| 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.
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
| Interstellar CH^+^ in southern OB associations.
Optical absorption line observations of interstellar CH^+^ and CH arepresented towards the southern OB associations CMa OB1, NGC 2439, VelaOB1, NGC 4755, and Cen OB1. A total of 5-11 stars per association wereobserved, with visual extinctions ranging from A_V_=0.5-4.5mag. Thederived CH^+^ and CH velocities agree within the measurement errors.Towards a particular association, the CH^+^ column density N(CH^+^) iscorrelated to the visual extinction of the background star. Thesefindings weaken the possibility that magnetic shocks are the generalmechanism that is required to produce interstellar CH^+^. It is foundthat N(CH^+^) is correlated to N(CH), which indicates that N(CH^+^) iscorrelated to the optical depth of a cloud. The correlations aredifficult to reconcile with scenarios where the sites of CH^+^ formationare constrained to the surface of molecular clouds. The observationssupport ideas which involve turbulence as a major CH^+^ productionmechanism. In particular, the results are in agreement with expectationsfrom a scenario where the CH^+^ formation proceeds in cool gas via afraction of fast, non-Maxwellian H_2_ or C^+^, created by thedissipation of interstellar turbulence.
| A spectroscopic database for Stephenson-Sanduleak Southern Luminous Stars
A database of published spectral classifications for objects in theStepenson-Sanduleak Luminous Stars in the Southern Milky Way catalog hasbeen compiled from the literature. A total of 6182 classifications for2562 stars from 139 sources are incorporated.
| The Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
| Tracing the Roots of Interstellar Mid Infrared Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...275..549J&db_key=AST
| Environment Dependence of Interstellar Extinction Curves
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...274..439J&db_key=AST
| UBV photometry of OB+ stars in the southern Milky Way
One thousand two hundred and twenty six new observations are combinedwith previously published results of the author to yield an internalyconsistent set of magnitudes and colors on the international UBV systemfor 666 stars classified as OB+ in the Stephenson-Sanduleak OB starsurvey. The U - B, B - V diagram indicates that these stars consistprimarily of O-type stars and early B-type supergiants, reddened by upto E(B - V) = 2.1 mag.
| The spectral energy distribution of early-type stars. II - The extinction law towards O-type stars
Photometric measurements through different pass-bands are used todetermine the color-excess E(B-V) for O-type stars in the UV and IRspectral regions. The results are used to examine the extinctioncharacter of the stars. It is found that, in the UV, each O-type starhas its own extinction character. In general, the visual and NIRextinction in the direction of O-type stars are normal.
| Atlas of the wavelength dependence of ultraviolet extinction in the Galaxy
The paper presents a collection of 115 extinction curves derived fromlow-dispersion IUE spectra. The spectra have been reduced with the useof techniques designed to reduce the effects of random noise and theinfluence of residual spectral features due to classification mismatch.The magnitudes of other instrumental and interpretational uncertaintiesare estimated. The extinction curves are presented with normalization toE(B-V) = 1 and the FUV portion (below 170 nm) is also shown for E(13-17)= 1. The atlas includes examples of extinction originating in thediffuse medium and several major nebulae and dense clouds.
| The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
| The spectral energy distribution of early type stars. I - A catalogue of photometric data of 259 stars from 0.15 to 4.8 microns
For the derivation of physical parameters (e.g., effective temperatureand radius) of early-type stars from their intrinsic spectral-energydistribution, and for the study of foreground interstellar and/orcircumstellar matter, a sample of 237 O, B, and A stars was chosen fromthe ANS catalog (Wesselius et al., 1982). The ANS ultraviolet and theJohnson UBV data (mostly from Nicolet's catalog, 1978) of these starswere supplemented with visual Walraven WULBV, red VRI, and near-infraredJHKLM measurements. All these data are given in the present catalog.Data for 22 stars of spectral type later than A are also included.
| 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.
| Early-type stars in OB associations in the infrared. I Extinction law and IR excesses
Observations have been made of 82 early-type stars of OB associations inthe infrared (JHKLM). The law of interstellar extinction isinvestigated. The empirical reddening curve (with R = 3.13) is found tobe in close agreement with van de Hulst's (1949) theoretical curve No.15. This law is generally valid for the OB associations considered. Themeasured infrared magnitudes were dereddened with this extinction law,and compared with the prediction of model atmospheres. Significantinfrared excesses due to circumstellar free-free radiation are found fora large number of stars. The strongest IR excess (about 0.5 mag in M) isfound for the Of-type stars HD 108, HD 151804, and HD 152408. In late Bsupergiants no significant excess radiation is detectable. However, thevery luminous hypergiants HD 168607 and HD 168625 do show excessradiation of about 0.2 mag in M.
| A study of B-type supergiants with the uvby,beta photometric system
The applicability of the uvby,beta photometric system to theclassification and study of B-type supergiants (BTS) is investigatedusing published data on 157 BTS and observations of 17 BTS made with the36-in. reflector at McDonald Observatory. The results are presented intabular form and analyzed to produce preliminary calibrations ofluminosity class vs. beta index and of absolute magnitude (Mv) vs. beta(or delta Mv vs. delta beta) for four associations of stars. Theeffectiveness of various color indices as temperature indicators isdiscussed. It is shown that there is good correspondence between MK anduvby,beta classifications of B-type main-sequence stars, giants, andBTS, confirming the usefulness of the uvby,beta system in furtherresearch on BTS.
| UBV photometry for southern OB stars
New UBV photometry of 1227 OB stars in the southern Milky Way ispresented. For 1113 of these stars, MK spectral types have been reportedpreviously in a comprehensive survey to B = 10.0 mag.
| Peculiar ultraviolet interstellar extinction
In connection with investigations of the physical characteristics ofinterstellar dust, a study of objects with peculiar extinction mightprovide new insights about the composition, size distribution,formation, and destruction of the particulate matter. Meyer and Savage(1981) have found that the dust toward many stars exhibits peculiar UVextinction. The present investigation is concerned with InternationalUltraviolet Explorer (IUE) spectrophotometric measurements for a sampleof stars judged by Meyer and Savage to have highly anomalous UVextinction as inferred from the broad-band Astronomical NetherlandsSatellite (ANS) data. The reported IUE measurements provide theopportunity to determine if the ANS photometry measurements of Meyer andSavage are anomalous because of peculiar extinction.
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