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To see or not to see a bow shock. Identifying bow shocks with Hα allsky surveys
OB-stars have the highest luminosities and strongest stellar winds ofall stars, which enables them to interact strongly with theirsurrounding ISM, thus creating bow shocks. These offer us an idealopportunity to learn more about the ISM. They were first detected andanalysed around runaway OB-stars using the IRAS allsky survey by vanBuren et al. (1995, AJ, 110, 2614). Using the geometry of such bowshocks information concerning the ISM density and its fluctuations canbe gained from such infrared observations. As to help to improve the bowshock models, additional observations at other wavelengths, e.g.Hα, are most welcome. However due to their low velocity these bowshocks have a size of 1°, and could only be observed as awhole with great difficulties. In the light of the new Hα allskysurveys (SHASSA/VTSS) this is no problem any more. We developeddifferent methods to detect bow shocks, e.g. the improved determinationof their symmetry axis with radial distance profiles. Using twoHα-allsky surveys (SHASSA/VTSS), we searched for bow shocks andcompared the different methods. From our sample we conclude, that thecorrelation between the direction of both proper motion and the symmetryaxis determined with radial distance profile is the most promisingdetection method. We found eight bow shocks around HD17505, HD 24430, HD48099, HD 57061, HD92206, HD 135240, HD149757, and HD 158186 from 37 candidatestaken from van Buren et al. (1995, AJ, 110, 2614). Additionally to thetraditional determination of ISM parameters using the standoff distanceof the bow shock, another approach was chosen, using the thickness ofthe bow-shock layer. Both methods lead to the same results, yieldingdensities ( 1 cm-3) and the maximal temperatures (104 K), that fit well to the up-to-date picture of the WarmIonised Medium.
| New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| New Runaway O-stars Based on Data from HIPPARCOS
12 new runaway O-stars are identified using an analysis of their propermotions based on data from HIPPARCOS. The peculiar tangential and totaltransverse velocities of these stars are determined. A list of theobserved runaway stars is given.
| 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
| Measurements of [O I] λ6300/Hα Line Intensity Ratios for Four O Star H II Regions
We have used the Wisconsin Hα Mapper facility to measure the [O I]λ6300/Hα line intensity ratios for four O star H IIregions: S27 (observation coordinates l=6.3d,b=+23.6d), S252(l=190.1d,b=+0.6d), S261 (l=194.1d,b=-1.9d), and S264(l=195.1d,b=-12.0d). We find that the ratios range from 0.0015 to0.0053. These results are roughly a factor of 10 lower than measured [OI]/Hα ratios in directions that sample the warm ionized componentof the interstellar medium. This difference implies a significantlylower hydrogen ionization ratio n(H+)/n(H0) orhigher electron temperature in the diffuse ionized gas compared withthat in the bright discrete O star H II regions.
| 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.
| Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
Reliable systemic radial velocities are almost impossible to secure forWolf-Rayet stars, difficult for O stars. Therefore, to study the motions- both systematic in the Galaxy and peculiar - of these two relatedtypes of hot, luminous star, we have examined the Hipparcos propermotions of some 70 stars of each type. We find that (a) both groupsfollow Galactic rotation in the same way, (b) both have a similarfraction of ``runaways'', (c) mean kinetic ages based on displacementand motion away from the Galactic plane tend to slightly favour thecluster ejection over the the binary supernova hypothesis for theirformation, and (d) those with significant peculiar supersonic motionrelative to the ambient ISM, tend to form bow shocks in the direction ofthe motion. Based on data from the ESA Hipparcos astrometry satellite.Table~1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Cross-correlation characteristics of OB stars from IUE spectroscopy
We present a catalogue of homogeneous measures of the linewidthparameter, v_esin i, for 373 O-type stars and early B supergiants(including the separate components of 25 binary and three triplesystems), produced by cross-correlating high-resolution,short-wavelength IUE spectra against a `template' spectrum of tauSco. Wealso tabulate terminal velocities. There are no O supergiants in oursample with v_esin i<65 km s^-1, and only one supergiant earlier thanB5 has v_esin i<50 km s^-1, confirming that an important linebroadening mechanism in addition to rotation must be present in theseobjects. A calibration of the area under the cross-correlation peakagainst spectral type is used to obtain estimates of continuum intensityratios of the components in 28 spectroscopically binary or multiplesystems. At least seven SB2 systems show evidence for the `Struve-Sahadeeffect', a systematic variation in relative line strength as a functionof orbital phase. The stellar wind profiles of the most rapid rotator inour sample, the O9III:n* star HD 191423 (v_esin i=436km s^-1), show itto have a `wind-compressed disc' similar to that of HD 93521; this starand other rapid rotators are good candidates for studies of non-radialpulsation.
| A Radial Velocity Database for Stephenson-Sanduleak Southern Luminous Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....113..823R&db_key=AST
| Bow Shocks Around Runaway Stars.III.The High Resolution Maps
In a recent survey for bow shock structures around OB runaway starsusing the ISSA/IRAS archival data and excess maps at 60 \mum, 58candidates were found. These objects are surrounded by extended infraredemission at 60 \mum, characteristic of warm dust heated by ultravioletphotons, a signature of wind bow shocks. High resolution IRAS (HiRes)images have been produced for these 58 objects and some of thosespatially resolved are presented in this study. The images were used todistinguish between multiple confused IR sources, possible artifacts andunambiguous bow shocks, as the sources of the extended 60 \mum emission.Six new bow shocks have been identified using this method, and threehave been rejected. Twenty two of the targets, however, remain spatiallyunresolved even at the nominal HiRes resolution of ~ 1arcmin . For thelarger and better defined bow shocks some internal substructure isdiscernible. The length of these features suggest that they arise as theresult of a subtle dynamical instability. It can not be ruled out,however, that some of the bow shock morphology could be imprinted by thesurrounding medium.
| 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.
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Extinction law survey based on UV ANS photometry
The paper presents an extensive survey of interstellar extinction curvesderived from the ANS photometric measurements of early type starsbelonging to our Galaxy. This survey is more extensive and deeper thanany other one, based on spectral data. The UV color excesses aredetermined with the aid of 'artificial standards', a new techniqueproposed by the authors which allows the special check of Sp/L match ofa target and the selected standard. The results indicate that extinctionlaw changes from place to place.
| Forbidden S II H-alpha intensity ratios in faint, extended H II regions and the origin of the interstellar emission-line background
The Wisconsin large-aperture Fabry-Perot spectrometer was used tomeasure forbidden S II 6716/H-alpha intensity ratios in very faint(emission measures as low as 5 cm to the -6th pc), extended (diametersas large as 260 pc) H II regions surrounding O and early B stars toinvestigate whether such regions can be the source of the interstellaremission-line background. H II regions with very dilute ionizingradiation fields were found to have higher forbidden S II/H-alphaintensity ratios than more compact regions. However, the forbidden SII/H-alpha ratios in the dilute H II regions are not as high as theratios found in the interstellar emission-line background. The datasugggest that, if the interstellar background is produced byphotoionized H II regions, then the regions have emission measures EMless than 1 cm to the -6th pc and are ionized by a Lyman continuum fluxF less than 6 x 10 to the 5th photons/cm s. This places importantconstraints on the origin and nature of the warm, ionized gas in thediffuse interstellar medium.
| 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.
| Eight-colour photometry of stars associated with selected Sharpless H II regions at L exp II of about 190 deg - S 252, S 254, S 255, S 257, and S 261
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&A...171..216C&db_key=AST
| Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
| 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.
| Internal Motions in HII Regions - Part Ten - are There Optical HII Regions Associated with the Origem Loop
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1982RMxAA...5..161P&db_key=AST
| The initial mass function for massive stars
A machine readable catalog of over 750 galactic O stars with publishedphotometry, spectral types, and luminosity classes has been compiled.The catalog is probably complete to a distance of about 2.5 kpc. Fromthis volume-limited data, the initial mass function (IMF) for stars moremassive than 20 solar masses has been derived. This IMF differs fromthat of Miller and Scalo (1979) and of Lequeux (1979), in havingproportionately more O type stars and not as steep a fall-off in numberof stars with increasing mass. Dividing the sample into stars inside andoutside the solar circle, a substantial difference in the IMF of themost massive stars is found. There are proportionally more toward thegalactic center. This gradient in the IMF may be related to the observedspace density of Wolf-Rayet stars, which are descendants of O typestars.
| A high-resolution search for small-scale structure in Sharpless H II regions at 4.995 GHz. II - General properties of the entire sample. III - Description of selected sources
A statistical study is presented of the properties of a sample of 75optically visible H II regions from the Sharpless Catalog observed at afrequency of 4.994 GHz by the Westerbork Synthesis Radio Telescope, andthe most interesting small-diameter H II components detected in thesurvey are discussed in detail. The optical and radio properties of theregions are compared, and results are presented of high-andlow-resolution observations. The nebulae are divided into five classesaccording to optical morphology and the presence of obscuration, whichclasses can be interpreted as representing subsequent evolutionarystages of a single H II region. It is also found that the change of theelectron density due to H II region expansion occurs at a higher ratefor H II regions ionized by stars of an earlier spectral type, and thatthe rate of change of the mean electron density for a given type isapproximately hyperbolic. Small-diameter, high-density components arefound preferentially in small, isolated nebulae with high mean electrondensities, while the ratio of the Lyman continuum flux contained in thesmall-diameter component to that contained in the entire H II regioncorrelates with the mean density of the region. Of the 22 objectsdiscussed individually, 12 can be classified as compact H II regionswith an internal source of excitation, and the remaining sources can beattributed to increases in the electron density at ionization frontslocated at the edges of dense molecular clouds. From an analysis ofradio, infrared and molecular line observations of several sources, itis concluded that a single early-type star embedded in the H II regionin the presence of dust can be the energy source of the observedemission.
| A comment on the nature of O-type runaway stars
The characteristics of O-type runaway stars are compared with those ofnormal, low-velocity O stars, in order to test the hypothesis that therunaway stars are members of the Old Disk Population. No evidence tosupport the hypothesis is found. The strong concentration to thegalactic plane shows that they are Extreme Population I stars.
| The nature of single-line population I Wolf-Rayet stars - Evidence for high space velocity
The paper examines the distribution of galactic Wolf-Rayet starsperpendicular to the plane which indicates that the single-line starsare on the average more distant from the plane than the binaries. Thisis observed independent of the choice of the cut-off in distance ormagnitude of the sample. From a limited sample, the mean absoluteseparation for the binaries is approximately 80 pc, like that for normalpopulation IOB-stars, while for the single-line stars it isapproximately 130 pc which is similar to the runaway OB-stars. Thisindicates that some single-line WR stars were accelerated out of theplane probably after the kick of a supernova explosion of the originalprimary in a binary system. While the binaries are generally moretightly and symmetrically distributed about the plane, the vast majorityof single-line stars beyond 80 pc are located at negative galacticlatitudes.
| Radio recombination lines from small H II regions
Hydrogen radio combination lines have been observed toward 35 small (fewarcmin) H II regions with the Arecibo 1000 foot (305 m) telescope.Twenty-two of these are first detections. A non-LTE analysis is employedby which physical parameters for the ionized clouds are derived. Ingeneral, the departure from LTE seems small for most H II regions.
| On the statistical parallax of O type runaway stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&A....65..279C&db_key=AST
| Spectroscopy and interferometry of four emission nebulae
Results are presented for spectrophotometric and interferometricobservations of four emission nebulae: (1) a bright compact nebula ofunknown nature identified with the nonthermal radio source G 6.4-0.5 inthe region W28, (2) RCW 171, identified with the radio source G23.1+0.6, (3) Simeiz 34 (Sharpless 261), and (4) the extended complex ofbright emission filaments in Cygnus that is partially projected on tothe possible supernova remnant W63. The electron densities andtemperatures are estimated, and the mean radial velocities aredetermined together with the parameters of internal motions within thenebulae. It is shown that the nebula in W28 is localized in the outerpart of a supernova remnant and that the filamentary complex in Cygnusmay be a superposition of a supernova remnant on an H II region.
| Spectral classification of early-type stars. Calibration using a TV-vidicon multichannel system.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976RMxAA...2...13B&db_key=AST
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| קבוצת-כוכבים: | אוריון |
| התרוממות ימנית: | 06h08m55.82s |
| סירוב: | +15°42'18.2" |
| גודל גלוי: | 8.473 |
| מרחק: | 909.091 פארסק |
| תנועה נכונה: | -3.2 |
| תנועה נכונה: | -11.3 |
| B-T magnitude: | 8.865 |
| V-T magnitude: | 8.506 |
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