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The structure of the cometary globule CG 12: a high-latitude star-forming region
We have investigated the structure of the high galactic-latitudecometary globule 12 (CG 12) by means of radio molecular-lineobservations. Detailed, high signal-to-noise ratio maps inC18O (1-0), C18O (2-1) and molecules tracinghigh-density gas, CS (3-2), DCO+ (2-1), andH13CO+ (1-0), are presented. The C18Oline emission is distributed in a 10 arcmin long North-South elongatedlane with two strong maxima, CG 12-N(orth) and CG 12-S(outh). In CG 12-Sthe high-density tracers delineate a compact core, DCO+ core,which is offset by 15´´ from the C18O maximum.The observed strong C18O emission traces either the surfaceof the DCO+ core or a separate, adjacent cloud component. Thedriving source of the collimated molecular outflow detected in 1993 islocated in the DCO+ core. The C18O lines in CG12-S have low-intensity wings possibly caused by the outflow. Theemission in high-density tracers is weak in CG 12-N and especially theH13CO+}, DCO+, andN2H+ lines are +0.5 km s-1 offset invelocity with respect to the C18O lines. Evidence ispresented that the molecular gas is highly depleted. The observed strongC18O emission towards CG 12-N originates in the envelope ofthis depleted cloud component or in a separate entity seen in the sameline of sight. The C18O lines in CG 12 were analysed usingpositive matrix factorization, PMF. The shape and the spatialdistribution of the individual PMF factors fitted separately to theC18O (1-0) and (2-1) transitions were consistent with eachother. The results indicate a complex velocity and line excitationstructure in the cloud. Besides separate cloud velocity components theC18O line shapes and intensities are influenced by excitationtemperature variations caused by e.g., the molecular outflow or bymolecular depletion. Assuming a distance of 630 pc the size of the CG 12compact head, 1.1 pc by 1.8 pc, and the C18O mass larger than100 Mȯ are comparable to those of other nearbylow/intermediate mass star formation regions.Based on observations collected at the European Southern Observatory, LaSilla, Chile. Figures 11 and 12 and Appendix A are only available inelectronic form via http://www.aanda.org
| A VLT/NACO survey for triple and quadruple systems among visual pre-main sequence binaries
Aims.This paper describes a systematic search for high-ordermultiplicity among wide visual Pre-Main Sequence (PMS) binaries. Methods: .We conducted an Adaptive Optics survey of a sample of 58 PMSwide binaries from various star-forming regions, which include 52 TTauri systems with mostly K- and M-type primaries, with the NIRinstrument NACO at the VLT. Results: .Of these 52 systems, 7 arefound to be triple (2 new) and 7 quadruple (1 new). The new closecompanions are most likely physically bound based on their probabilityof chance projection and, for some of them, on their position on acolor-color diagram. The corresponding degree of multiplicity among widebinaries (number of triples and quadruples divided by the number ofsystems) is 26.9 ± 7.2% in the projected separation range ~0.07arcsec -12'', with the largest contribution from the Taurus-Aurigacloud. We also found that this degree of multiplicity is twice in Tauruscompared to Ophiuchus and Chamaeleon for which the same number ofsources are present in our sample. Considering a restricted samplecomposed of systems at distance 140-190 pc, the degree of multiplicityis 26.8 ± 8.1%, in the separation range 10/14 AU-1700/2300 AU (30binaries, 5 triples, 6 quadruples). The observed frequency agrees withresults from previous multiplicity surveys within the uncertainties,although a significant overabundance of quadruple systems compared totriple systems is apparent. Tentatively including the spectroscopicpairs in our restricted sample and comparing the multiplicity fractionsto those measured for solar-type main-sequence stars in the solarneighborhood leads to the conclusion that both the ratio of triples tobinaries and the ratio of quadruples to triples seems to be in excessamong young stars. Most of the current numerical simulations of multiplestar formation, and especially smoothed particles hydrodynamicssimulations, over-predict the fraction of high-order multiplicity whencompared to our results. The circumstellar properties around theindividual components of our high-order multiple systems tend to favormixed systems (i.e. systems including components of wTTS and cTTS type),which is in general agreement with previous studies of disks inbinaries, with the exception of Taurus, where we find a preponderance ofsimilar type of components among the multiples studied.
| C18O (3-2) observations of the Cometary Globule CG 12: a cold core and a C18O hot spot
The feasibility of observing the {C18O} (3-2) spectral linein cold clouds with the APEX telescope has been tested. As the line at329.330 GHz lies in the wing of a strong atmospheric H2O absorption itcan be observed only at high altitude observatories. Using the threelowest rotational levels instead of only two helps to narrow down thephysical properties of dark clouds and globules. The centres of two{C18O} maxima in the high latitude low mass star formingregion CG 12 were mapped in {C18O} (3-2)and the data were analyzed together with spectral line data from theSEST. The TMB (3-2)/TMB (2-1) ratio in thenorthern {C18O} maximum, CG 12-N, is 0.8, and in the southernmaximum, CG 12-S, 2. CG 12-N is modelled as a 120´´diameter (0.4 pc) cold core with a mass of 27 Mȯ. Asmall size maximum with a narrow, 0.8 {km s-1},{C18O} (3-2) spectral line with a peak temperature ofTMB ˜ 11 K was detected in CG 12-S. This maximum ismodelled as a 60´´-80´´ diameter ( 0.2 pc) hot(80 K ≲ Tex ≲ 200 K) 1.6 Mȯ clump.The source lies on the axis of a highly collimated bipolar molecularoutflow near its driving source. This is the first detection of such acompact, warm object in a low mass star forming region.
| Blue Luminescence and the Presence of Small Polycyclic Aromatic Hydrocarbons in the Interstellar Medium
Blue luminescence (BL) was first discovered in a proto-planetary nebula,the Red Rectangle (RR), surrounding the post-AGB star HD 44179. BL hasbeen attributed to fluorescence by small, 3-4 ringed neutral polycyclicaromatic hydrocarbon (PAH) molecules and was thought to be unique to theRR environment, where such small molecules are actively being producedand shielded from the harsh interstellar radiation by a densecircumstellar disk. In this paper we present the BL spectrum detected inseveral ordinary reflection nebulae illuminated by stars havingtemperatures between 10,000 and 23,000 K. All these nebulae are known toalso exhibit the infrared emission features called aromatic emissionfeatures (AEFs) attributed to large PAHs. We present the spatialdistribution of the BL in these nebulae. In the case of Ced 112, the BLis spatially correlated with mid-IR emission structures attributed toAEFs. These observations provide evidence for grain processing andpossibly for in situ formation of small grains and large molecules fromlarger aggregates. Most importantly, the detection of BL in theseordinary reflection nebulae suggests that the BL carrier is anubiquitous component of the interstellar medium and is not restricted tothe particular environment of the RR.
| Photometric and spectroscopic study of low mass embedded star clusters in reflection nebulae
An analysis of the candidate embedded stellar systems in the reflectionnebulae vdBH-RN 26, vdBH-RN} 38, vdBH-RN} 53a, GGD 20, ESO 95-RN 18 andNGC 6595 is presented. Optical spectroscopic data from CASLEO(Argentina) in conjunction with near infrared photometry from the 2MASSPoint Source Catalogue were employed. The analysis is based on sourcesurface density, colour-colour and colour-magnitude diagrams togetherwith theoretical pre-main sequence isochrones. We take into account thefield population affecting the analysis by carrying out a statisticalsubtraction. The fundamental parameters for the stellar systems werederived. The resulting ages are in the range 1-4 Myr and the objects aredominated by pre-main sequence stars. The observed masses locked in theclusters are less than 25 Mȯ. The studied systems haveno stars of spectral types earlier than B, indicating that star clustersdo not necessarily evolve through an HII region phase. The relativelysmall locked mass combined with the fact that they are not numerous incatalogues suggests that these low mass clusters are not importantdonors of stars to the field populations.Based on observations made at Complejo Astronómico El Leoncito,which is operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the National Universities of La Plata,Córdoba and San Juan, Argentina.
| Photometric distances to dark clouds: cometary globule CG 12
A method for determining distances to dark clouds and Bok globules basedon broad-band optical and near-infrared photometry is presented. In thismethod, intrinsic colour indices of stars projected towards thedirection of a cloud are computed by dereddening the observed colourindices using various trial values of extinction AV and astandard extinction law. The computed intrinsic colour indices for astar are then compared with the intrinsic colour indices of normalmain-sequence stars and a spectral type is assigned to the star forwhich the computed colour indices best match the standard intrinsiccolour indices. Distances (d) to the stars are determined using theAV and absolute magnitudes (MV) corresponding tothe spectral types thus obtained. A plot of AV against dundergoes a sharp rise at a distance corresponding to the distance tothe cloud. Using this method, we have determined a distance of 550 pc tothe cometary globule CG 12. The distance of 550 pc and a Galacticlatitude of b= 21° imply that CG 12 is at a height of ~200 pc abovethe galactic mid-plane. The star formation efficiency in this cloud isfound to be relatively high (>~16 per cent, to as large as ~33 percent). The existence of an HI shell centred at l= 315°, b= 30°with CG 12 near its boundary and its tail pointing away from the centreof the shell supports the suggestion of a supernova explosion, near thecentre of the HI shell, being responsible for the cometary morphologyand the triggering of star formation. Thus CG 12 is a rare example oftriggered high-mass star formation at relatively large galactic height.
| Magnetic fields in cometary globules - III. CG 12
We present results of optical linear polarization measurements of starsin the region of the relatively isolated cometary globule CG 12 inCentaurus at a galactic latitude b~= 21°. A polarization maprepresenting the geometry of the magnetic field in the cloud isproduced. In the lower-density outer parts of the cloud, the field ismore or less parallel to the cometary tail and other elongatedstructures like the bipolar molecular outflow from near the infraredsource IRAS 13547-3944 and the nebulosity around star 2 embedded in thecloud. Polaization vectors for the more highly reddened stars in thehead region of the globule are found to be more or less parallel to thelong axis of the elliptical, high-density C18O core of thecometary globule head.
| 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
| Intermediate galactic latitude starforming region-CG 12.
Not Available
| Search for Molecular Clouds toward Intermediate-to-High Latitude IRAS Sources in the Southern Sky
We have conducted a search for molecular clouds toward southern IRASpoint sources at intermediate-to-high galactic latitude (|b| >=10deg) in 12CO (J = 1-0) emission with the NANTENtelescope. The main purpose of the survey was to find a new sample ofstar-forming clouds unknown to date. Of the 29 targets, we detected COemission toward 5 IRAS sources, i.e., 04591-0856, 05044-0325,05050-0614, 06345-3023, and 13543-3941. Among 5 detections, themolecular cloud associated with 06345-3023 (G 239.2-16.3) was detectedfor the first time. If we assume the distance as being 1.5 kpc, this\source is ~ 430 pc away from the galactic plane. Three source is ~ 430pc away from the galactic plane. Three sources 04591-0856 (G208.3-28.4), 05044-0325 (G 203.5-24.7), and 05050-0614 (G 206.4-25.9)are located west to the Orion molecular clouds, and 13543-3941 (G316.4+21.2) is located in the cometary globule CG 12. Four of the 5clouds show a cometary shape with a ``head-tail'' distribution, andthree of them have the IRAS source located at the edge opposite to thetail. We find that all of the CO clouds are associated with the opticalnebulosities, which are likely to be reflection nebulae. A comparison ofthe present CO clouds with those in Ophiuchus, Taurus, Chamaeleon, and L1333 indicates that star-forming clouds tend to have a high columndensity, as well as a smaller ratio of the virial mass to the LTE mass.
| The Cometary Globules CG 30/31/38 in the GUM nebula. A radio line spectroscopic investigation
We present radio line observations from the SEST. On the basis of (13)CO (J=1-0) measurements we estimate the H_2 mass associated with theglobules CG 30/31A-C/38 to be ~ 43 M_ȯ. The gas kinetic temperatureof the globules is in the range 5 to 14 K. Line wings seen in the (12)CO spectra as well as higher dipole moment molecules towards CG 30,indicate that a dense molecular outflow is present. Especially the redwing reveals itself very clearly and is collimated, whereas the bluewing is weak and the emission is smeared out. The mass of the outflow is~ 0.3 M_ȯ and the dynamical time scale is 1.7x10(4) years. Themechanical luminosity is 0.11 L_ȯ for an assumed inclination of90(deg) . The (13) CO (J=1-0) data have revealed that CG 30 is apossible double globule, the small companion (here named CG 30B) havinga mass of ~ 25% of the larger globule, corresponding to ~ 2 M_ȯ.Based on observations collected at the European Southern Observatory, LaSilla, Chile.
| Protostellar candidates in southern molecular clouds.
In the course of an extensive 1300μm mapping survey of star formingregions in southern molecular clouds, we have identified five regionswhich contain new protostellar candidates. The objects are generallyseparated from nearby known IRAS sources. This, together with theirstrong 1300μm fluxes, points towards these objects being eitherprotostars or prestellar clumps, rather than pre-main sequence stars.Some of these protostellar candidates have several components,suggesting the possibility that they may represent simultaneousformation of multiple stars. Cha-MMS1 is located between the lobes of asmall compact, already known molecular outflow in the Ced 110 region ofthe Chamaeleon I molecular cloud, and is a likely candidate as thedriving source of the nearby HH 49/50 objects. Cha-MMS2 lies between thelobes of a major, already known molecular outflow in the northern partof the Chamaeleon I cloud complex. Cir-MMS1 is located in a massivecloud core between the lobes of a major, already known molecular outflowin a large cloud complex in Circinus. B59-MMS1 is found in thelittle-studied molecular cloud B59, and Sco-MMS1 is embedded in ananonymous Bok globule in Scorpius.
| FIR mapping of NGC 5367 a reflection nebula around young stars at high galactic altitudes.
Not Available
| 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.
| Low-mass star formation in CG1: a diffraction limited search for pre-main sequence stars next to NXPup.
Using adaptive optics at the ESO 3.6m telescope, we obtained diffractionlimited JHK-images of the region around the Herbig AeBe star NX Pup. Weclearly resolved the close companion (sep. 0.128") to NX Pup -originally discovered by HST - and measured its JHK magnitudes. A thirdobject at a separation of 7.0" from NX Pup was identified as a classicalT Tauri star so that NX Pup may in fact form a hierarchical triplesystem. We discuss the evolutionary status of these stars and deriveestimates for their spectral types, luminosities, masses and ages.
| A Co/ and IRAS Study of Cometary GLOBULE:12
Abstract image available at:http://adsabs.harvard.edu/abs/1993A&A...274L..33W
| Comet-like clouds at far-infrared and optical wavelengths - Mach cones and hydrodynamics?
Optical and far-IR studies have been conducted on 14 high Galacticlatitude clouds with comet-like or filamentary appearances. Theirphysical characteristics are deduced and found to be comparable to thoseof small, low-mass molecular clouds found in the solar neighborhood inrecent CO and H I surveys. The morphologies of five of the clouds arefound to be consistent with objects moving supersonically through theinterstellar medium. These clouds are also active in forming B-typestars in their nuclei where the dynamic pressures are expected to behighest. The filamentary clouds have shapes consistent with subsonic,low Reynolds number hydrodynamics, a feature they may share with theDraco molecular cloud. A simple qualitative scenario is also presented,describing a possible evolutionary link among these clouds as apopulation.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
| Cometary Globule 1
The age and distance of the variable F2 IIIe star illuminating the headof Cometary Globule 1, a dense dust cloud with a faint luminous tail, isexamined. Results show that the form of the globule is described well byWoodward's model of a spherical cloud through which an initially planeshock has passed. It is suggested that this appears to be the only meansto eject dense material downstream as has happened in the tail ofCometary Globule 1. If the illuminating star was formed by the implosionof the cloud and has since drifted to the front edge, comparison withthe models indicates that the implosion occurred 1.2 + or - 0.6 millionyears ago.
| The densities of the molecular clouds associated with Herbig Be/Ae and other young stars
The H2CO molecule has been studied toward 25 regions containingsignposts of recent star formation, either Herbig Be/Ae stars, LkH alphaemission-line stars, or stars with unusual circumstellar nebulosity. The2-cm and 2-mm lines of H2CO have been detected toward many of theseregions, allowing a determination of cloud density. Core densities from20,000 per cu cm to 150,000 per cu cm are found to be associated withmore than half of the regions studied. The cloud L 43 is unusual inbeing cold (kinetic temperature approximately 15 K) yet having a highdensity (150,000 per cm) more characteristic of the hotter regions ofstar formation. The H2CO abundances for these clouds with embedded youngstars are the same as the abundances of other clouds of similar densitythat do not have embedded stars.
| The present data situation for stars in open clusters. II
The present state of astrometric, spectroscopic, and photometric datafor stars in 63 open clusters nearer to the sun than 750 pc issummarized in tabular form. The limits of the available data arereported in terms of the apparent V magnitude. Information on theapparent V magnitude of the brightest main sequence star (Vbr) and onthe number of stars brighter than V equals 10 has been included. Thebluest spectral type on the main sequence has been used as an ageestimator.
| The young cluster NGC 5367 and A1353-40
The sparse young cluster embedded in and illuminating NGC 5367 in thehead of Cometary Globule 12 is shown to suffer about 1 magnitude ofvisual extinction in the cloud and to be about 630 pc away. Infraredphotometry and scanner spectroscopy of the two most luminous members,comprising the double h 4636, indicate that one component is surroundedby a circumstellar shell producing Balmer line emission and thermalreradiation by grains. The proposed identification of NGC 5367 with thetransient X-ray source A1353-40 is not favored. It is suggested that NGC5367 lies on an H I loop and that star formation in it was induced by asupernova explosion near galactic longitude 320 deg, latitude 30 deg,about 10 million years ago.
| A catalogue of bright nebulosities in opaque dust clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1977A&AS...29...65B
| Two short lived X-ray transients at high galactic latitude
Ariel V observations of two transient X-ray sources at high galacticlatitudes are reported. The characteristic time scales of these sources,A0000+28 and A0353-40, are of the order of hundreds of minutes. It isfound that the error box of the first source contains a Mira-typevariable and that the error box of the second source contains the brightreflection nebulosity NGC 5367. Noting that this nebulosity probably hasUV Ceti flare stars embedded within it, the possibility is consideredthat both sources are associated with flare stars.
| Observations of carbon monoxide emission in NGC 5367.
Abstract image available at:http://adsabs.harvard.edu/abs/1975ApJ...198..235V
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