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Cloud Fragmentation and Proplyd-like Features in H II Regions Imaged by the Hubble Space Telescope
We have analyzed Hubble Space Telescope ACS and WFPC2 new and archivalimages of eight H II regions to look for new protoplanetary disks(proplyds) similar to those found in the Orion Nebula. We find a wealthof features similar in size (although many are larger) to the brightcusps around the Orion Nebula proplyds. None of them, however, containsa definitive central star. From this, we deduce that the new cusps maynot be proplyds but instead fragments of molecular cloud material. Outof all the features found in the eight H II regions examined, only one,an apparent edge-on silhouette in M17, may have a central star. Thisfeature might join the small number of bona fide proplyds found outsidethe Orion Nebula, in M8, M20, and possibly M16. In line with the resultsfound recently by Smith et al., the paucity of proplyds outside theOrion Nebula can be explained by their transient nature, as well as bythe specific environmental conditions under which they can be observed.Several fragments are seen as dark silhouettes against a brightbackground. We have reanalyzed those found in IC 2944 by Reipurth et al.and found new, similar ones in M16. None of these fragments contains acentral star, and we exclude the possibility that they are disks.Reipurth et al. concluded that the IC 2944 silhouettes are not starforming. We argue here that their assumption of a constant optical depthfor these fragments is not physical and that it is more likely thatthese fragments are star forming, a condition that is supported,although not proved, by their shapes and distributions. The process ofcloud fragmentation and photoevaporation produces a large number ofsmall fragments, while the size hierarchy expected in a photoevaporativeenvironment would not favor small fragments. The size distributionsobserved will constrain any future theories of cloud fragmentation. Onebright microjet candidate is found in M17, protruding from a large,limb-brightened fragment. A second, larger, jetlike feature, similar inshape and size to a Herbig-Haro jet, is found in Pismis 24. No centralstar appears to be associated with either of these jet candidates.Based on observations made with the NASA/ESA Hubble Space Telescopeobtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy (AURA), Inc.,under NASA contract NAS5-26555.
| Radio continuum and molecular line observations of four bright-rimmed clouds
Aims.To search for evidence of triggered star formation within fourbright-rimmed clouds, SFO 58, SFO 68, SFO 75 and SFO 76. Methods:.We present the results of radio continuum and molecular lineobservations conducted using the Mopra millimetre-wave telescope andAustralia Telescope Compact Array. We use the J=1{-}0 transitions of12CO, 13CO and C18O to trace thedistribution of molecular material and to study its kinematics. Theradio continuum data is used to trace the distribution of the ionisedgas and to derive its parameters. Combining these observations witharchival data allows us to build up a comprehensive picture of thecurrent state of star formation within these clouds. Results:.These observations reveal the presence of a dense core(n{H_2}>104 cm-3) embedded withineach cloud, and the presence of a layer of hot ionised gas coincidedwith their bright-rims. The ionised gas has electron densitiessignificantly higher than the critical density (>25 cm-3)above which an ionised boundary layer can form and be maintained,strongly supporting the hypothesis that these clouds are beingphotoionised by the nearby OB star(s). Using a simple pressure-basedargument, photoionisation is shown to have a profound effect on thestability of these cores, leaving SFO 58 and SFO 68 on the edge ofgravitational stability, and is also likely to have rendered SFO 75 andSFO 76 unstable to gravitational collapse. From an evaluation of thepressure balance between the ionised and molecular gas, SFO 58 and SFO68 are identified as being in a post-pressure balance state, while SFO75 and SFO 76 are more likely to be in a pre-pressure balance state. Wefind secondary evidence for the presence of ongoing star formationwithin SFO 58 and SFO 68, such as molecular outflows, OH, H2O andmethanol masers, and identify a potential embedded UC HII region, butfind no evidence for any ongoing star formation within SFO 75 and SFO76. Conclusions: .Our results are consistent with the starformation within SFO 58 and SFO 68 having been triggered by theradiatively driven implosion of these clouds.
| 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.
| A Compact Array imaging survey of southern bright-rimmed clouds
We have carried out a radio-wavelength imaging survey of 45bright-rimmed clouds (BRCs), using the Australia Telescope Compact Arrayto characterise the physical properties in their ionised boundarylayers. We detected radio emission from a total of 25 clouds and using acombination of Digitised Sky Survey and mid-infrared MSX 8 \mum imagesclassified the emission into that associated with the ionised cloudrims, that associated with embedded possible massive YSOs and thatunlikely to be associated with the clouds at all. A total of 18 cloudsdisplay radio emission clearly associated with the cloud rim and wedetermine the ionising photon flux illuminating these clouds and theelectron density and pressure of their ionised boundary layers. Using aglobal estimate for the interior molecular pressure of these clouds weshow that the majority are likely to be in pressure equilibrium andhence are currently being shocked by photoionisation-induced shocks. Weidentify those clouds where the predicted ionising photon flux isinconsistent with that derived from the observations and show thateither the spectral types of the stars illuminating the BRCs are earlierthan previously thought or that there must be additional ionisingsources within the HII regions. Finally, we identify the radio sourcesembedded within the clouds with infrared stellar clusters and show thatthey contain late O and early B-type stars, demonstrating that a numberof BRCs are intimately involved with high to intermediate-mass starformation.Full Figs. \ref{fig:images} and \ref{fig:sfo86dss} are only available inelectronic form at http://www.edpsciences.org
| 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.
| Fragmentation of Globules in H II Regions: Hubble Space Telescope Images of Thackeray's Globules
We present Hubble Space Telescope WFPC2 images through an Hαfilter of Thackeray's globules in the southern H II region IC 2944. Theimages document the state of the globule complex during its currenthighly dynamical phase of breakup. A population of very small andshort-lived splinters suggests that continuous fragmentation must playan important role in increasing the surface-to-mass ratio of the neutralgas, thus accelerating the processes of photoevaporation andphotoablation. We are not able to single out which of varioustheoretical mechanisms for breakup is operating in the globule complex.
| The Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.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/cgi-bin/qcat?J/A+A/410/523
| Tomographic Separation of Composite Spectra. X. The Massive Close Binary HD 101131
We present the first orbital elements for the massive close binary HD101131, one of the brightest objects in the young open cluster IC 2944.This system is a double-lined spectroscopic binary in an ellipticalorbit with a period of 9.64659+/-0.00012 days. It is a young system ofunevolved stars (approximately 2 million yr old) that are well withintheir critical Roche surfaces. We use a Doppler tomography algorithm toreconstruct the individual component optical spectra, and we applywell-known criteria to arrive at classifications of O6.5 V((f)) and O8.5V for the primary and secondary, respectively. We compare thereconstructed spectra of the components to single-star spectrumstandards to determine a flux ratio off2/f1=0.55+/-0.08 in the V band. Both componentsare rotating faster than synchronously. We estimate the temperatures andluminosities of the components from the observed spectralclassifications, composite V magnitude, and cluster distance modulus.The lower limits on the masses derived from the orbital elements and thelack of eclipses are 25 and 14Msolar for the primary andsecondary, respectively. These limits are consistent with the somewhatlarger masses estimated from the positions of the stars in theHertzsprung-Russell diagram and evolutionary tracks for single stars.
| Mass loss rate determination of southern OB stars
A sample of OB stars (eleven Of, one O and one B supergiant) has beensurveyed with the Australia Telescope Compact Array at 4.8 and 8.64 GHzwith a resolution of ~ 2 arcsec-4 arcsec. Five stars were detected;three of them have negative spectral indices, consistent withnon-thermal emission, and two have positive indices. The thermalradiation from HD 150135 and HD 163181 can be explained as coming froman optically thick ionized stellar wind. The non-thermal radiation fromCD-47deg 4551, HD 124314 and HD 150136 possibly comes fromstrong shocks in the wind itself and/or in the wind colliding region ifthe stars have a massive early-type companion. The percentage ofnon-thermal emitters among detected O stars has increased up to ~ 50%.The Of star HD 124314 clearly shows flux density variations. Mass lossrates (or upper limits) were derived for all the observed stars and theresults compared with non-radio measurements and theoreticalpredictions.
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. III. Carina Spiral Feature
Strömgren and Hβ photometry of O and B type stars, generallybrighter than 9.5 mag is reported for the field of the Carina SpiralFeature. The observations are based on the PPM catalogue identificationsand are designed to improve the completeness of the existing uvbybetadata for the bright early-type stars in the field. We present new uvbyphotometry for 283 stars and Hβ photometry for 225 of them. Theseobservations are part of an ongoing effort to study the structure ofselected star-forming regions in the Milky Way by means of uvbybetaphotometry. A comparison of the new data to other uvbybeta data sets forthis field is presented. Based on data from the Strömgren AutomaticTelescope of the Copenhagen University Observatory, La Silla. Tables 1and 2 are only available in electronic form at the CDS via anonymous ftpto 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Deep Hα survey of the Milky Way. V. The l=289o to 295o area
An Hα study of the ionized hydrogen in the Galactic planedirection l = 290o has been undertaken. We describe anddiscuss the characteristics of the numerous filaments and emissionpatches observed. These appear linked to a major expanding HI bubble orshell over an area of several degrees. Thanks to morphological,kinematical and stellar distance considerations we have linked observedHII regions and molecular clouds into star-forming complexes whichmainly trace the Carina arm. We show particularly that the HII regionsGum35 (G289.8-1.3), Gum38b (G291.6-0.5, NGC 3603) and Hf 58 (G291.9-0.7)can be directly linked to the farthest complexes at a distance `d' of 8and 9 kpc, while HII regions Gum37 (G290.6+0.3), Gum38a (G291.3-0.7) andthe expanding shell can be linked to the closest complexes locatedbetween 2.6 and 2.9 kpc. Important internal motions have been identifiedin the Gum35, Gum37, Gum38a and Gum38b HII regions. The identificationand analysis of these motions are essential for a good systemic velocitydetermination. We have also identified and delineated that part of theGalactic plane exhibiting velocity departures of Delta Theta = 7 kms-1 (between 285o and 295o and d = 2.5and 3 kpc). Based on observations collected at the European SouthernObservatory.}
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Molecular Clouds and Star Formation in the Southern H II Regions
We have carried out extensive 13CO(J = 1-0) observationstoward 23 southern H II regions associated with bright-rimmed clouds. Intotal, 95 molecular clouds have been identified to be associated withthe H II regions. Among the 95, 57 clouds \ are found to be associatedwith 204 IRAS point sources which are candidates for young stellarobjects. There is a significant increase of star-formation efficiency onthe side facing to the H II regions; the luminosity-to-mass ratio,defined as the ratio of the stellar luminosity to the molecular cloudmass, is higher by an order of magnitude on the near side of the H II \regions than that on the far side. This indicates that molecular gasfacing to the H II regions is more actively forming massive s\ tarswhose luminosity is >~ 103 LO . In addition, the numberdensity of the IRAS point sources increases by a factor of 2 on the nearside of the H II regions compared with on the far side. These resultsstrongly suggest that the active formation of massive stars on the nearside of the H II regions is due to the effects of the H II regions, suchas the compression of molecular material by the ionization/shock fronts.For the whole Galaxy, we estimate that the present star-formation rateunder such effects is at least 0.2-0.4 MO yr-1, correspondingto a few 10% by mass.
| Five-colour photometry of OB-stars in the Southern Hemisphere
Observations of OB-stars, made in 1959 and 1960 at the Leiden SouthernStation near Hartebeespoortdam, South Africa, with the VBLUW photometerattached to the 90 cm light-collector, are given in this paper. They arecompared with photometry obtained by \cite[Graham (1968),]{gra68}\cite[Walraven & Walraven (1977),]{wal77} \cite[Lub & Pel(1977)]{lub77} and \cite[Van Genderen et al. (1984).]{gen84} Formulaefor the transformation of the present observations to those of\cite[Walraven & Walraven (1977)]{wal77} and \cite[Lub & Pel(1977)]{lub77} are given. Table 4 is only available in electronic format the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) orvia http://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| OB Stellar Associations in the Direction of Centaurus OB2
One hundred eighty-five mostly OB and some early A-type stars aredetected at 1640 Å with the ultraviolet telescope Glazar aboardthe Mir space station in an area of about 8 deg^2 in the directiontoward the stellar association Cen OB2. The limiting stellar magnitudem_1640 of the observations is about 8.5 mag. Stellar associations atdistances of 360, 850, 1500, 2300, 2700, 4000, and 6700 pc are detectedby the study of the space distribution of 111 of the observed stars withknown spectral types. It was shown that the cluster IC 2944 is locatedat a distance of 2200 pc. It is suggested that the extinction ofemission of stars in the content of the cluster is due to small dustclouds or even to circumstellar dust shells. It is shown also that thedust matter is practically absent in the space between stellarassociations and that the extinction of some stars within stellarassociations is caused by relatively small dust clouds, in which thestars are embedded. Two of the detected stars, HD 101316 and HD 101967,are of relatively late spectral types and therefore probably have hotdwarf or subdwarf companions.
| 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.
| 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
| Thackeray's globules in IC 2944
We have studied the complex of small globules discovered by A.D.Thackeray in the southern HII region IC 2944. They are located preciselyon the line-of-sight to the luminous OB stars in the region, and thusappear as shadows against the bright HII region. Thanks to thisgeometry, exceptionally fine details can be discerned on CCD images,which show that the globules are generally sharp-edged and highlystructured, and that the complex contains a multitude of fragments inall sizes down to the resolution element of about one arcsec (1800 AU).CO millimeter observations reveal that the largest globule consists oftwo kinematically separate entities, with masses of about 11 and 4M_sun. Very large velocity differences exist between the variousglobules, suggesting that the globules comprise a highly dynamic systemperhaps one million years old. We believe that the globules are theremnants of an elephant-trunk observed from behind, originating as aRayleigh-Taylor instability in an expanding neutral shell powered by thehot HII region. The globule complex is now in an advanced stage ofdisintegration. We have found no evidence for star formation in any ofthe globules. Based on observations collected at the European SouthernObservatory, La Silla, Chile
| Projected Rotational Velocities of O-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...463..737P&db_key=AST
| 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 72nd Name-List of Variable Stars
Not Available
| 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.
| Stromgren and H-Beta Photometry of Associations and Open Clusters - Part Three - CENTAURUS-OB1 and CRUX-OB1
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.269..289K&db_key=AST
| 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.
| Polarimetric study of the IC 2944 stellar aggregate
We present UBVRI polarimetric observations of 30 stars belonging to therich stellar aggregate IC 2944, which is embedded in an extensive H IIregion. Within the galaxy, it is located at the inner border of theCarina spiral feature. To analyze the characteristics of theinterstellar material associated with the aggregate, we have separatedthe frontside contribution of both color excesses and polarizations,leaving the intra-arm values of these quantities. We have found that theforeground polarization in the direction to IC 2944 is normal and has abar-lambdamax value of 0.550 +/- 0.025 microns. Its averagedirection in equatorial coordinates is 91.2 deg. About half of the starsnot considered to be frontside have some indication of intrinsicpolarization. Interpreting the polarization of the rest as intra-armpolarization, we find that Ardeberg & Maurice's Groups I, II, andIII cannot be separated in terms of polarization data and that theBright Rim Group and Group IV are significantly different from theothers. Finally, stars in Groups I, II, III, and IV show that theintra-arm (beyond 1.4 kpc) magnetic field is essentially contained inthe plane of the sky.
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