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X-Ray and IR Point Source Identification and Characteristics in the Embedded, Massive Star-Forming Region RCW 108
We report on the results of an approximately 90 ks Chandra observationof a complex region that hosts multiple sites of recent and active starformation in ARA OB1a. The field is centered on the embedded cluster RCW108-IR and includes a large portion of the open cluster NGC 6193. Wedetect over 420 X-ray sources in the field and combined these data withdeep near-IR, Spitzer/IRAC and Midcourse Space Experiment (MSX) mid-IRdata. We find about 360 of the X-ray sources have near-IR counterparts.We divide the region into five parts based on the X-ray point sourcecharacteristics and extended 8 μm emission. The most clearly definedregions are the central region, identified by embedded sources with highluminosities in the both the near-IR and X-ray as well as high X-raytemperatures (~3 keV), and the eastern region, identified by lowextinction and ~1 keV X-ray temperatures. Other regions, identified bytheir directional relationship to RCW 108-IR, are lessuniform—representing combinations of the first two regions,independent star formation epochs, or both. The cluster members range inX-ray luminosity from 1029 to 1033 ergs-1. Over 18% of the cluster members with over 100 countsexhibit flares. All sources with over 350 counts are variable. Overallabout 10% (16% in RCW 108-IR) appear to have optically thick disks asderived from their position in the (J - H), (H - K) diagram. The diskfraction becomes much higher when IRAC data are employed. The largestfraction of X-ray sources is best described as possessing some diskmaterial via a more detailed extinction fitting. We fit the bulk of theX-ray spectra as absorbed Raymond-Smith-type plasmas, and find that thecolumn to the RCW 108-IR members varies from 1021 to1023 cm-2. We find that the field contains 41candidate O or B stars, and estimate that the total number ofpre-main-sequence stars in the field is about 1600 ± 200.Approximately 800 are confined to the 3' (~1.1 pc) central region.
| H2O maser emission from bright rimmed clouds in the southern hemisphere
Context: Water maser emission is a powerful tracer of the presence ofembedded sources in dense clouds since it requires elevated temperatures(>100 K) and densities (>107 cm-3) that canbe found in circumstellar disks and/or jets/outflows associated withYoung Stellar Objects. Bright rimmed clouds compressed by ionizationfronts from nearby massive stars are considered good examples ofexternally triggered star formation, possibly resulting in the formationof massive stars. Aims: We aim to determine the water maser emissionfrequency and characteristics of 45 bright rimmed clouds in the southernhemisphere identified by Sugitani & Ogura (1994, ApJS, 92, 163). Methods: We have used the Tidbinbilla 70-m radiotelescope to perform ahigh sensitivity survey at 22.2 GHz of the maser emission from the616-523 rotational transition of H2O molecules. Results: We found 7 water maser sources out of 44 (16% detection rate),5 being new detections. With the exception of the maser associated withBRC 68, all the other maser are characterized by low integrated fluxesand luminosities. Conclusions: Most maser sources fall below thecorrelation between the H2O and far-infrared luminosity found in otherstudies towards a variety of star forming regions. These results aresimilar to those found in the companion survey of BRCs in the northernhemisphere by Valdettaro et al. (2005, A&A, 443, 535). The lowdetection frequency and the properties of water maser emission from BRCsindicate that low-mass star formation is the most natural outcome of theexternal compression induced by the ionization front from nearby massivestars.Based on observations obtained with the 70-m Tidbinbilla radiotelescope.
| Radio Detection of Colliding Wind Binaries
Four massive, early-type stars, three of which are confirmed binaries,have been observed with the Australia Telescope Compact Array at 1.4,2.4, 4.8, and 8.6 GHz. The earliest star cataloged so far, HD 93129A,was also observed at 17.8 and 24.5 GHz. Here we present an analysis ofthe spectra as well as the structure of the stellar systems. All fourspectra show clear evidence of non-thermal emission, indicative of abinary system with a colliding wind region. We discuss the magneticfield of the emitting region of HD 93129A and make predictions on theradiation at high energies. Archive X-ray observations towards thetarget sources are also investigated and interpreted in the light of thenon-thermal emission detected.
| Chandra X-ray observations of the young stellar cluster NGC 6193 in the Ara OB1 association
A 90-ks Chandra High Energy Transmission Grating observation of theyoung stellar cluster NGC 6193 in the southern Ara OB1 associationdetected 43 X-ray sources in a 2 × 2 arcmin2 coreregion centred on the massive O stars HD 150135 (O6.5V) and HD 150136(O3 + O6V). The cluster is dominated by exceptionally bright X-rayemission from the two O stars, which are separated by only 10 arcsec.The X-ray luminosity of HD 150136 is logLX= 33.39 (ergs-1), making it one of the most luminous O-star X-ray sourcesknown. All of the fainter X-ray sources in the core region havenear-infrared (near-IR) counterparts, but existing JHK photometryprovides little evidence for near-IR excesses. These core sources havetypical mean photon energies ~ 2 keV and about one-third arevariable. It is likely that some are young low-mass stars in thecluster, but cluster membership remains to be determined. Gratingspectra show that the X-ray properties of HD 150135 and HD 150136 aresimilar, but not identical. Both have moderately broadened unshiftedemission lines and their emission is dominated by cool plasma at kT~ 0.3keV, pointing to a wind-shock origin. However, the emission of HD 150136is slightly hotter and four times more luminous than its optical twin HD150135. We discuss the possibility that a radiative colliding wind shockcontributes to the prodigious X-ray output of the short-period (2.66 d)spectroscopic binary HD 150136. A surprising result is that the X-rayemission of HD 150136 is slowly variable on a time-scale of <1 d. Theorigin of the variability is not yet known but the observed behavioursuggests that it is an occultation effect.
| Star formation in RCW 108: Triggered or spontaneous?
We present visible, near infrared and mm-wave observations of RCW 108, amolecular cloud complex in the Ara OB1 association that is being erodedby the energetic radiation of two O-type stars in the nearby cluster NGC6193. The western part of the RCW108 molecular cloud, for which wederive a mass of ~8000 Mȯ, contains an embedded compactHII region, IRAS 16362-4845, ionized by an aggregate of early-type starsfor which we estimate a mass of 210 Mȯ. Thespectral type of the earliest star is O9, as confirmed by the visiblespectrum of the compact HII region. We notice a lack of stars later thanA0 in the aggregate, at least having the moderate reddenings that arecommon among its B-type stars, and we speculate that this might be aconsequence of the extreme youth of the aggregate. We also note theexistence of a dense ionized clump (n > 104cm-3) appearing near the main ionizing star of the compactHII region. We examine the distribution of stars displaying infraredexcesses projected across the molecular cloud. While many of them arelocated in the densest (n 104-5 cm-3) areaof the molecular cloud near the position of IRAS 16362-4845, we alsofind a group concentrating towards the edge of the cloud that faces NGC6193, as well as some other stars beyond the edge of the molecularcloud. The intense ionizing radiation field by the O stars in NGC 6193is a clear candidate trigger of star formation in the molecular cloud,and we suggest that the existence and arrangement of stars in thisregion of the molecular cloud supports a scenario in which theirformation may be a consequence of this. However, infrared excess starsare also present in some areas of the opposite side of the cloud, whereno obvious candidate external trigger is identified. The existence ofsuch tracers of recent star formation scattered across the more massivemolecular cloud associated with IRAS 16362-4845, and the low starformation efficiency that we derive, indicate that it is in a state tostill form stars. This is in contrast to the less massive cloud (660 Mȯ) close to NGC 6193, which seems to be moreevolved and mostly already recycled into stars, and whose internalkinematics show hints of having been perturbed by the presence of themassive stars formed out of it.
| 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.
| The nearest star of spectral type O3: a component of the multiple system HD 150136
From radial velocities determined in high signal-to-noise digitalspectra, we report the discovery that the brightest component of thebinary system HD 150136 is of spectral type O3. We also present thefirst double-lined orbital solution for this binary. Our radialvelocities confirm the previously published spectroscopic orbital periodof 2.6 d. HeII absorptions appear double at quadratures, but singlelines of NV and NIV visible in our spectra define a radial velocityorbit of higher semi-amplitude for the primary component than do theHeII lines. From our orbital analysis, we obtain minimum masses for thebinary components of 27 and 18 Msolar. The neutral Heabsorptions apparently do not follow the orbital motion of any of thebinary components, thus they most probably arise in a third star in thesystem.
| High-mass star formation within the bright-rimmed cloud SFO 79
We report Radio Recombination Line (RRL) and continuum observationstoward the IRAS point source 16362-4845, embedded within theBright-Rimmed Cloud (BRC) SFO 79, a small molecular cloud lying at theedge of the HII region RCW 108. High resolution observations of theH92α hydrogen recombination line and of the continuum emission(3.6 and 6 cm) confirm the presence of a resolved Ultra Compact (UC) HIIregion embedded within the molecular cloud. The integrated radio fluxessuggest the source of the ionisation to be an O9 Zero Age Main Sequence(ZAMS) star. Millimetre observations of 12CO, 13COand C18O (J=1-0) molecular lines reveal the presence of amolecular condensation offset 30 arcsec to the north of the IRASposition on the boundary of the UC HII region. Analysis of 2MASS datahas led to the identification of a small IR cluster of Young StellarObjects (YSOs) that are positionally coincident with the UC HII region,lying to the south east of the peak of the radio emission. Moreover, theUC HII region appears to be extended in the direction of the IR cluster,which suggests that the radio emission and the IR cluster are in someway related to each other. MSX 8.3 μm and 21.3 μm images have beenused to trace the large scale structure of the BRC, revealing thepresence of a Photo Dominated Region (PDR) and three embedded thermalsources within the molecular cloud. The PDR has a plane parallelmorphology which correlates extremely well with the morphology of theionised gas traced by the optical emission. The three thermal sources(labelled A, B, C) all lie at a similar projected distance from theinterface between the HII region and the molecular gas of the cloud.Thermal sources A and C are positionally coincident with the IRAS pointsources 16362-4845 and 16362-4841 respectively, both of which have IRAScolours consistent with the presence of UC HII regions. Given that UCHII regions are relatively short lived (105 yrs) it isreasonable to suggest that these two UC HII regions are of a similarage. The alignment of the three thermal sources along a line parallel tothe bright rim suggests that they could have been triggered by thepropagation of a plane parallel shock through the cloud.
| 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
| A 12CO (J = 1 -> 0) study towards the Ara OB1 region
Intermediate angular resolution (HPBW=8\farcm7 ) carbon monoxide(12CO J=1->0) line observations towards the OB associationAra OB1 are reported. The molecular line observations cover an area of2\fdg75 x 3\fdg00 , and disclose a rich and complex distribution of themolecular line emission. The molecular features likely to be associatedwith the OB-association Ara OB1 span the velocity range from -28 to -20km s-1. The most negative radial velocities are observedalong NGC 6188 (equiv Rim nebula). This nebula marks the interfacebetween the HII region RCW 108 and the highly absorbing molecularmaterial located westwards of the ionised region. The dominant COstructures, labeled E and F, have a radial velocity of about -23.5 and-21.8 km s-1, respectively. The former harbours a brightoptical knot, the infrared cluster RCW-108 and the strong IRAS source16362-4845. IRAS point sources are also seen in projection onto12CO concentrations F and H. This may indicate that the starforming process is a widespread phenomenon in this molecular complex.Extended continuum emission, having a high degree of spatial correlationwith both the infrared and molecular emission, is observed in theregion. We believe that this emission, thermal in nature, arises fromthe ionised surface layers of the molecular complex. The ionising agentsare the high mass stars of NGC 6193, the nucleus of Ara OB1. The totalamount of molecular gas related to Ara OB1 is about ~ 1.4x104 Msun.
| New infrared star clusters in the southern Milky Way with 2MASS
We carried out a 2MASS J, H and Ks survey of infrared starclusters in the Milky Way sector 230deg< l <350deg. This zone was the least studied in the literature,previously including only 12 infrared clusters or stellar groups with|b|< 10deg, according to the recent catalogue by Bica etal. (2003). We concentrated efforts on embedded clusters, which arethose expected in the areas of known radio and optical nebulae. Thepresent study provides 179 new infrared clusters and stellar groups,which are interesting targets for detailed future infrared studies. Thesample of catalogued infrared clusters and stellar groups in the Galaxyis now increased by 63%.
| The Molecular Gas Associated with ARA OB1
Not Available
| 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.
| High-mass binaries in the very young open cluster NGC 6231. Implication for cluster and star formation
New radial-velocity observations of 37 O- and B stars in the very youngopen cluster NGC 6231 confirm the high frequency of short-periodspectroscopic binaries on the upper main sequence. Among the 14 O-typestars, covering all luminosity classes from dwarfs to supergiants, 8 aredefinitively double-lined systems and all periods but one are shorterthan 7 days. Several additional binaries have been detected among theearly B-type stars. NGC 6231 is an exceptional cluster to constrain thescenarios of cluster- and binary-star formation over a large range ofstellar masses. We discuss the evidences, based on NGC 6231 and 21 otherclusters, with a total of 120 O-type stars, for a clear dichotomy in themultiplicity rate and structure of very young open clusters containingO-type stars in function of the number of massive stars. However, wecannot answer the question whether the observed characteristics resultfrom the formation processes or from the early dynamical evolution.
| 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
| 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.
| Binaries in the Praesepe and Coma Star Clusters and Their Implications for Binary Evolution
This completes a study of the evolution of binary systems in five openclusters of various ages. Among 21 stars observed in Praesepe, eight arefound or confirmed to be spectroscopic binaries and orbital elements arederived, while one more shows long-term binary motion. Among 18 starsobserved in the Coma Berenices cluster, five are found or confirmed tobe spectroscopic binaries and orbital elements are derived, while asixth has tentative elements. Among five clusters studied we searchedfor three expected evolutionary effects, namely an increase with age inthe mass ratios, a decrease with age of the binary periods, and anincrease in binary frequencies. We find that there is a progression (atthe 3 sigma level) from no binaries out of 10 with mass ratios greaterthan 0.5 in the youngest cluster (combined with the published resultsfor NGC 6193) to 25% such stars in the intermediate-age clusters to 43%such stars in these two oldest clusters. There is no evidence for anincrease in short-period binaries with age. And there is slight evidence(at the 1 sigma level) for an increase with age from 15% to 28% in thefraction of large-amplitude binaries. These results are mostlyconsistent with the idea that most binaries are formed or modified inthree-body interactions, and successive generations of formation anddisruptions tend to form binaries with larger mass ratios. However, partof the initial generation of binaries is probably primordial.
| 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.
| 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.
| Gamma-Ray Pulsars and Massive Stars in the Solar Neighborhood
We revisit the association of unidentified Galactic plane EGRET sourceswith tracers of recent massive star formation and death. Up-to-datecatalogs of OB associations, supernova remnants (SNRs), young pulsars, HII regions, and young open clusters were used in finding counterpartsfor a recent list of EGRET sources. It has been argued for some timethat EGRET source positions are correlated with SNRs and OB associationsas a class; we extend such analyses by finding additional counterpartsand assessing the probability of individual source identifications.Among the several scenarios relating EGRET sources to massive stars, wefocus on young neutron stars as the origin of the gamma -ray emission.The characteristics of the candidate identifications are compared to theknown gamma -ray pulsar sample and to detailed Galactic populationsyntheses using our outer gap pulsar model of gamma -ray emission. Boththe spatial distribution and luminosity function of the candidates arein good agreement with the model predictions; we infer that youngpulsars can account for essentially all of the excess low latitude EGRETsources. We show that with this identification, the gamma -ray pointsources provide an important new window into the history of recentmassive star death in the solar neighborhood.
| 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
| Deep Hα survey of the Milky Way. III. The l=338deg area.
The Galactic plane has been observed between l=337deg and l=342deg inthe frame of an Hα Survey of the Southern Milky Way. This area isknown to be rich in radio sources but poor in Hα emission. Theanalysis of high resolution profiles of the Hα emission observedin this direction nevertheless enabled to distinguish 6 differentvelocity components: 2 faint layers of diffuse ionized hydrogen at 0 and-12km/s (V_LSR_), 2 brighter layers at -28 and -39km/s includingindividual HII regions, a faint patch at -50km/s and two isolated brightHII regions at -61km/s. Combining these Hα observations withstellar and radio data we conclude about the most probable distances forthe different components.
| X-ray and γ-ray emission in open clusters.
We have studied a number of galactic open clusters that lie in the errorboxes of COS B sources. These clusters belong to complexes in whichsimilar star formation processes occur. They have similar ages, stellarpopulation and contain peculiar stars with very high-velocity stellarwinds. We propose that a system of shock fronts, set up at theinterfaces between the hypersonic wind of the peculiar stars and theother cluster members, generates acceleration of cosmic ray particles,whose interactions with the inter-cluster gas concentrations would beresponsible for the observed γ-ray emission. We find variousobservational evidences (including CGRO data, strongly supporting theassociation of the γ-ray source J 2021+37=2CG075+00 with Berk 87)for the presence of such shock fronts in some of these clusters. We showthat the diffuse hard X-ray emission from the clusters regions isconsistent with the geometric scenario inferred from the data and withthe assumed mechanism of cosmic ray acceleration.
| Young open clusters as gamma-ray emitters
Not Available
| 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.
| 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 interstellar medium in the ARA OB1 field
We report here the results of a detailed study of two surveys of H I, atlambda = 21 cm, in the field of the stellar association Ara OB1.Subtracting the background with a procedure developed here, we were ableto identify two H I shell-like features, at roughly the same positionbut at different velocities, whose parameters were determined. On thebasis of their kinematical distances, two concentrations of OB stars(one at 1400 pc, belonging to Ara OB1, and another at 2500 pc) might bethe progenitors of these shells. The nearest H I shell may havetriggered a process of star formation.
| Binary stars - Another effect contributing to the supposed abnormal extinction law in NGC 6193?
This paper reports UBVRI photoelectric photometry of stars lying in thefield of the open cluster NGC 6193. Attention is focused onto earlieranalysis, which had suggested that in this region both the E(U-B)/E(B-V)excess relation and the extinction law are not standard. But the newdata support that both E(U-B)/E(B-V) and the extinction law have valueswhich may be assumed to be the standard ones. It was found that thenear-infrared anomalies are related in some cases to binary stars.Single stars also showing near-infrared excess could be explained interms of circumstellar shell hypothesis. A similar feature is foundamong stars in the open cluster Tr 16. The cluster age is not greaterthan 3.1 x 10 exp 6 yr from isochrones computed for models with massloss and overshooting. The distance obtained is 1410 pc.
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Observation and Astrometry data
| Constellation: | Ara |
| Right ascension: | 16h41m19.45s |
| Declination: | -48°45'47.5" |
| Apparent magnitude: | 6.752 |
| Distance: | 458.716 parsecs |
| Proper motion RA: | 0 |
| Proper motion Dec: | 0 |
| B-T magnitude: | 6.889 |
| V-T magnitude: | 6.764 |
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INHABITED SKY
