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.
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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
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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%.
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Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is 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/399/141
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Modelling the CO emission in southern Bok globules
The analysis of the sample of southern globules investigated by Scappiniet al. in the CO (4-3) transition has been extended using a statisticalequilibrium-radiative transfer model and making use of the results ofBourke et al. and Henning & Launardt for those globules which are incommon among these samples. CO column densities and excitationtemperatures have been calculated and the results compared with achemical model representative of the chemistry of a spherical darkcloud. In a number of cases the gas kinetic temperatures have beenconstrained.
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Young Stars Associated with the Reflection Nebula NGC 2626
We have conducted a search for Hα emission-line stars within thefield containing the reflection nebula NGC 2626 and the associated darkcloud DC 259.9-0.0. Thirty-two Hα stars, most of them newlydiscovered, have been identified. Magnitudes and colors for these starsare listed. Some are found to be variable and are possible T Tauristars. Changes between 1991 and 1999 in the brightness and appearance ofa small reflection nebula in the region are shown. These are caused byan unevenly obscured young stellar object which is the probable sourceof IRAS 08337-4028 and the Herbig-Haro object HH 132. The overallmorphology of the small nebula is strikingly similar to that of thewell-studied HH 46-47 configuration, but the NGC 2626 region is at abouttwice the distance.
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Catalogue of J = 1-0 CO emission towards southern dark clouds
Using the 22-m 'Mopra' antenna (near Coonabarabran, NSW) of theAustralia Telescope National Facility (ATNF), we have observed emissionfrom the 115-GHz J = 1-0 transition of CO towards the centre of each ofthe 1101 clouds listed in the Catalogue of Southern Dark Clouds (SDC) ofHartley et al. (1986). The velocity range covered was -96 to +70 kmpersec, with a velocity resolution of 0.120 km per sec. CO was detected at1049 of the positions, with 367 spectra showing emission at more thanone radial velocity. Here we present the most comprehensive generalsurvey of the SDC catalogue, with the intensity, velocity and half-widthof the CO detection and a code describing the profile shape. Thepresence of blue- or red-shifted wings in many observations can providea starting point in searches for star-forming regions.
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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.
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Exploring southern nebulae.
Not Available
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Studies of star formation in isolated small dark clouds - II. A southern ammonia survey
A study of the set of small, southern molecular clouds (globules)compiled by Bourke, Hyland & Robinson has been undertaken, throughradio observations of ammonia using the Parkes 64-m telescope. The aimof the study is to determine the physical characteristics of theglobules, their role in the formation of low-mass stars, and thephysical mechanism that triggers the star formation process, orstabilizes the globules against collapse. With this general aim in mind,the (1,1) and (2,2) inversion transitions of ammonia have been surveyedin order to determine the densities, temperatures and masses of theglobules. Half of the globules have been detected in ammonia, but only 6per cent of the detections are `strong' (T*_a>=0.35K). Comparing theglobule properties with those of Benson & Myers for cores withincomplexes, we find that the globules are less opaque and less dense, andare less active sites of star formation. Other properties arecomparable. The Vela cometary globules are detected more readily inammonia than the more isolated globules, and are more active starformation sites. These results suggest that the dense core'senvironment, in particular the presence of either a large external massor a significant stellar wind, plays an important role in initiating thestar formation process.
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Studies of star formation in isolated small dark clouds - I. A catalogue of southern BOK globules: optical and IRAS properties
A comprehensive list of small southern molecular clouds (globules) hasbeen established from the survey of southern dark clouds of Hartley etal. Only the most opaque globules, and those with diameters less than 10arcmin, were included in the list. These are found to form an entirelycomplementary sample to that of Clemens & Barvainis in the northernsky. In this and the following paper, a detailed study of the clouds isundertaken through an examination of their optical and IRAS properties,and radio observations of ammonia. The aim of the study is to determinetheir physical characteristics, their role in the formation of low-massstars, and the physical mechanism that either triggers the starformation process or stabilizes the globules against collapse. Theglobules are predominantly elliptical. There is some evidence that theapparent galactic latitude distribution of our globules (as well as thatof the Clemens & Barvainis sample) is more highly concentratedtowards the galactic plane than that of the large molecular cloudcomplexes identified through CO surveys. This suggests that there arevery few high-latitude globules, or that selection effects play a majorrole in defining the apparent distribution. Of the 169 globules studied,76 are found to have IRAS sources lying towards them (totalling 83sources). The IRAS sample is dominated by cooler sources than is thesample found to be associated with molecular cloud cores by Beichman etal., and predominantly exhibits the colours of embedded sources.
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A study of the Orion cometary cloud L1616
With its cometary appearance and a reflection nebula near its edgefacing some bright Orion stars, Lynds' cloud L1616 shows ample evidenceof being affected by one or more of these massive stars. To estimate itsmass and star formation efficiency, as well as to determine if it isgravitationally bound, we mapped this cloud in J=1-->0 transitions of^12CO and ^13CO. It is found that the distribution of the emission inthe line wings shows clear evidence for substantial mass motions. Also,the `virial' mass of the cloud is found to be five times the actualcloud mass determined from the ^13CO column density map. It is arguedthat this cloud has abnormally high star formation efficiency and ispossibly disintegrating. The morphology and the location of the cloudindicate that it is being affected by the star epsilon Orionis, which isalso (possibly) responsible for the cloud's unusual star formationefficiency. Over a range of values of the relevant parameters, the staris found to satisfy quantitatively the requirements of being the causeof the observed characteristics of the cloud.
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Searches for Bright-Rimmed Clouds with IRAS Point Sources
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A catalog of bright-rimmed clouds with IRAS point sources: Candidates for star formation by radiation-driven implosion. 2: The southern hemisphere
Forty-five bright-rimmed clouds associated with Infrared AstronomicalSatellite (IRAS) point sources have been selected in the southernhemisphere from the ESO (R) Atlas in addition to the 44 objects of thenorthern work (Pape I). Again they are good candidates for the sites ofstar formation induced by radiation-driven implosion. Four of them areknown to be associated with HH objects, and three with molecularoutflows. Most of their sizes are approximately less than 1 pc, and theluminosities of the associated IRAS sources, approximately 20 to 3 x104 solar luminosity, are much larger than those of the IRASsources associated with Bok globules or dense cores in dark cloudcomplexes, both having a similar mass range. This suggests thatintermediate-mass stars or multiple-star systems are mainly formed inbright-rimmed clouds. IRAS luminosity to cloud mass ratios aresignificantly greater than those in Bok globules or dense cores. Theresults confirm most of the findings of Paper I.
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A Study of the Kinematics of the Local Dark Clouds
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Two Herbig-Haro objects discovered by narrow-band CCD imagery
Two new Herbig-Haro objects, HH 132 and HH 133, have been discovered byCCD imagery behind interference filters on and just off the forbidden SII lines in the red. They are located in Puppis R2 and in Vela R2.Possible locations of their exciting sources are discussed.
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The List of the Pairs of Stars with Different Light Absorptions in the Circumstellar Environments
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Monitoring OH/IR stars at the 1-m telescope
OH/IR star monitoring at the 1-m telescope is described with particularattention given to the following objects: OH/IR 285.05 + 0.07 and OH/IR286.50 + 0.06. With a period of about 550 days, OH/IR 286.50 + 0.06 isbelieved to be an extreme member of the Mira class at the top of theasymptotic giant branch. It is found that the light curve of OH/IR285.05 + 0.07 contains irregularities. Moreover, it exhibits a linearvariation for about 500 days followed by a plateau lasting at least 250days.
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A catalogue of southern dark clouds
A catalogue of 1101 dark clouds has been compiled from visual inspectionof ESO/SERC Southern J survey plates for declinations south of -33 deg.This catalogue complements that of Lynds (1962) which is based on thePalomar Sky Survey. Equatorial positions of accuracy 10 arcsec or betterare listed for each cloud along with size (major axis x minor axis),density class and ESO/SERC field number. Galactic coordinates, derivedfrom the equatorial positions, are used to define a name for each cloud.Complexes, consisting of several separately identifiable concentrations,are listed and identified by a trailing C on the name. The conclusionsof Lynds, that clouds are concentrated along the galactic equator andtoward the galactic centre, are reinforced. No clear connection withGould's Belt is evident in the distribution of southern clouds.
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A C-12O (J = 2 - 1) survey of southern hemisphere dark clouds, reflection nebulae and Herbig-Haro type objects
A search has been conducted for C-120(2 - 1) in 80 southern dark cloudswith and without associated nebulosities. It is noted that, in general,CO could be detected in about half of the clouds surveyed, and thatdetection statistics are dominated by beam dilution. Most of the darkclouds lacking visible nebulosity exhibit no sign of embedded energysources, and about 40 percent of clouds with associated nebulosity showlittle by way of dynamical interaction with a central energy sourcedespite the presence of nebulosities. Significantly enhanced,predominantly red 'wing' emission is seen in about 25 percent of thedetected cases. In the case of GGD 27/28, strong mass outflows from acentral object seem responsible for the observed line profiles.
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H2O masers in the direction of southern nebular objects
Thirteen Orion population stars and 4 H-H objects were searched forwater maser emission. Two variable water masers were detected toward RULupi and vBH 656, which represent the first southern water masersassociated with low luminosity stars. Both masers are very weak, andtheir accurate positions have not been determined, thus it is not knownwhether the masers originate in the dust envelopes surrounding the two TTauri stars.
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A study of stars in southern dust clouds with bright nebulosities
A study of a total of 24 regions with bright nebulosities in dust cloudssouth of declination -39 deg is presented. Forty-seven stars in theseregions were observed spectroscopically at a dispersion of 58 A/mm, andcoordinates were determined for most of the stars observed. In addition,the stars were classified on the MK system and the distance to eachregion was derived using existing and new photometric data. Attention isgiven to the regions in and around the Southern Coalsack, and eachregion is discussed separately. It is reported that the presentestimates of distances generally agree well with previous estimates.Finally, discrepant values lead to the conclusion that Cen R2 and Cir R2are not well defined groups and that Cen R3 should be removed from thelist of R associations.
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A catalogue of bright nebulosities in opaque dust clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1977A&AS...29...65B
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R associations. I - UBV photometry and MK spectroscopy of stars in southern reflection nebulae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..212H&db_key=AST
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Catalogue of southern stars embedded in nebulosity.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..208V&db_key=AST
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Studies of bright diffuse galactic nebulae with special regard to their spatial distribution.
Not Available
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New nebulæ shown on Franklin-Adams chart plates
Not Available
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