A uniform CO survey of the molecular clouds in Orion and Monoceros
We report the results of a new large scale survey of the Orion-Monoceroscomplex of molecular clouds made in the J = 1 -> 0 line of12CO with the Harvard-Smithsonian 1.2 m millimetre-wavetelescope. The survey consists of 52 288 uniformly spaced spectra thatcover an area of 432 deg2 on the sky and represent the mostsensitive large-scale survey of the region to date. Distances to theconstituent molecular clouds of the complex, estimated from an analysisof foreground and background stars, have provided information on thethree dimensional structure of the entire complex.
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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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2MASS Observations of the Perseus, Orion A, Orion B, and Monoceros R2 Molecular Clouds
We use the 2MASS Second Incremental Release Point Source Catalog toinvestigate the spatial distribution of young stars in the Perseus,Orion A, Orion B, and MonR2 molecular clouds. After subtracting asemiempirical model of the field star contamination from the observedstar counts, stellar surface density maps are used to identify compactclusters and any stellar population found more uniformly distributedover the molecular cloud. Each cloud contains between two and sevenclusters, with at least half of the cluster population found in asingle, rich cluster. In addition, a distributed stellar population isinferred in the Orion A and MonR2 molecular clouds within theuncertainties of the field star subtraction with a surface densitybetween 0.013 and 0.083 arcmin-2. Sensitivity calculationssuggest, however, that the number of stars in the distributed populationmay be underestimated by a factor of 2 or more if stars have beenforming with a Miller-Scalo IMF at a constant star formation rate forlonger than 10 Myr. After considering the possible evolutionary statusof the distributed population, the global star formation efficiencyimplied by the sum of the distributed and cluster populations rangesbetween 1% and 9% among the four clouds. The fraction of the totalstellar population contained in clusters for the nominal extinctionmodel ranges from ~50% to 100% if the distributed population isrelatively young (<10 Myr), to ~25%-70% if it is relatively old (~100Myr). The relatively high fraction of stars contained in clustersregardless of the age of the distributed population, in conjunction withthe young ages generally inferred for embedded clusters in nearbymolecular clouds, indicates that a substantial fraction of the totalstellar population in these regions has formed within the past fewmillion years in dense clusters. This suggests that either the starformation rate in each these clouds has recently peaked if one assumesclouds have ages greater than 10 Myr or molecular clouds are youngerthan typically thought if one assumes that the star formation rate hasbeen approximately constant in time.
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A survey of the 6.7 GHz methanol maser emission from IRAS sources. I. Data
We report the first results of a search for 6.7 GHz methanol masers inthe direction of 1399 IRAS objects north of declination-20deg with the flux densities greater than 100 Jy at 60 mu mand the flux density ratio F60/F25>1.Observations were made with the sensitivity of 1.7 Jy and the velocityresolution of 0.04 km s-1 using the 32-m Toruń radiotelescope. Maser emission was found in 182 sources, including 70 newdetections. 32 new sources were identified with objects of radioemission associated with star-forming regions. Comparison of the presentdata set with other observations suggests that about 65% of methanolmasers exhibit moderate or strong variations on time-scales of about 4and 8 years. Table 2 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/Abstract.html
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The Medicina survey of methanol masers at 6.7 GHz
A survey of Class II methanol masers at 6.7 GHz was made in the Northernhemisphere with the 32-m Medicina radio telescope. 42 objects weredetected, 20 of them are new detections at 6.7 GHz. Our results showthat the detection rate of 6.7 GHz masers toward the inner part of theGalaxy is higher than in other directions. It is confirmed that most ofthe methanol masers are associated with faint compact HII regions. The6.7 GHz methanol masers show large velocity dispersion and largevelocity offset from the velocity of parent molecular clouds. Table 2 isonly available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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Studies of ultracompact HII regions - I. Methanol maser survey of IRAS-selected sources
A survey of ultracompact (UC) Hii regions has been carried out bysearching for 6.669-GHz methanol maser emission from a sample of 535IRAS-selected candidates. A total of 201 candidates exhibit methanolemission. These sources have been used, in conjunction with previouslyidentified UC Hii regions, to provide a base for further studies of suchregions. Estimates of distances have indicated that the identified UCHii regions tend to have some Galactic structure but it is not clearwhether they lie in or between the spiral arms of the Galaxy. Theregions are tightly constrained to the plane of the Galaxy. Comparisonof identified regions and IRAS sources selected by Wood & Churchwellindicates that there there is some degree of contamination, which couldbe due to an older phase in the life on an UC Hii region where methanolmaser emission is not apparent. Luminosities and spectral types havebeen derived for many of the regions. The maximum number of maser spotsobserved seems to increase with increasing peak maser luminosity, whichindicates that the maser emission is more dependent on the abundance ofmethanol than the availability of far-infrared radiation.
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Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
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Dusty Plasmas in Interstellar Clouds and Star Forming Regions
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IRAS-selected Galactic star-forming regions - II. Water maser detections in the extended sample
The results of the analysis of the occurrence of 22.2-GHz H_2O maseremission in a sample of 1409 IRAS sources north of declination -30 degassociated with star-forming regions are presented. Our sample containsall the IRAS sources that satisfy Emerson criteria for selectingmolecular cores associated with the earliest evolutionary stages of thestar-forming process. In a previous paper, we have reported the resultsof the observations of about one third of the sample. In the presentpaper the observations of the remaining IRAS sources are presented: 18of them are newly detected maser sources. The results show that 20 percent of all IRAS sources that satisfy the Wood & Churchwell criteriahave H_2O water masers. This is in agreement with the assumption thatthese criteria select objects that are connected with the early phasesof the evolution of high-mass star-forming regions. Moreover, about onethird of the whole sample selected according to Emerson criteriacontains IRAS sources that are not associated with massive star-formingprocesses, but probably with molecular cores in low-mass star-formingregions.
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The giant molecular cloud Monoceros R2. 1: Shell structure
We have obtained a 45 sec resolution, Nyquist-sampled map in CO J = 1-0covering approximately a 3 deg x 3 deg region of the giant molecularcloud Monoceros R2. The map consists of 167,000 spectra observed withthe 15 element focal-plane array system on the FCRAO 14 m telescope. Thedata reveal that the large-scale structure of Mon R2 is dominated by ais approximately 30 pc diameter largely hemispherical shell containingapproximately 4 x 104 solar mass of molecular material andexpanding at approximately 3-4 km s-1 with symmetric axisroughly along the line of sight. The dynamical timescale of the shell isestimated to be approximately 4 x 106 yr, which is consistentwith the age of main-sequence stars powering the clusters of reflectionnebulea in this region. There is no evidence for a redshifted shell onthe far side of the interior 'bubble,' which is largely devoid ofmolecular material. Distortions of the shell are obvious, suggestinginhomogeneity of the cloud and possible presence of a magnetic fieldprior to its formation. Dense clumps in Mon R2, including the main coreand the GGD 12-15 core, appear to be condensations located on the largeshell. The reflection nebulea with their illuminating stars as well asembedded IRAS sources suggest that triggered star formation has takenplace over a large part of the Mon R2 shell.
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A search for OH emission from IRAS sources at high galactic latitudes
A survey of high galactic latitude IRAS point sources with colourstypical for ultracompact HII regions was carried out in the main linesof OH. Amongst 70 IRAS sources surveyed, one new OH maser emitting onlyin the 1667 MHz main line was discovered and 6 weaker candidate maserswere found. It is proposed that the masers with dominant 1667 MHzemission are separate from the common main line Class I OH masersemitting mostly at 1665 MHz. The Class I masers could be divided intosubclasses Ia and Ib for 1665 and 1667 MHz emitting sourcesrespectively. A correlation between infrared and OH line emission fluxesis confirmed by a lower detection rate of the present survey as comparedto the survey of stronger IRAS sources. More than one half of thedetected sources show thermal OH emission and are probably associatedwith nearby dust clouds.
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Search for water vapor masers in the direction of IRAS sources associated with H II regions and molecular clouds
Results are reported from a search for water-vapor maser emission in thedirection of 187 selected IRAS sources. All these sources have colorindices typical of IR sources that were previously found to beassociated with water masers. Only eight new water masers were detectedabove the detection limit of 0.5 K (20 Jy). For three of theseassociated OH maser emission was found. No associated methanol maserswere found.
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IRAS catalogues and atlases - Atlas of low-resolution spectra
Plots of all 5425 spectra in the IRAS catalogue of low-resolutionspectra are presented. The catalogue contains the average spectra ofmost IRAS poiont sources with 12 micron flux densities above 10 Jy.
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The large system of molecular clouds in Orion and Monoceros
Emission is noted over about one-eighth of an 850-sq deg region centeredon Orion and Monoceros that has been surveyed in the J = 1 to 0 line ofCO; most of the emission arises from giant molecular clouds associatedwith Orion A and B, and Mon R2. A much smaller area was surveyed forC-13O emission. A comparison of cloud masses obtained by threeindependent methods indicates that CO luminosity is as accurate ameasure of cloud mass as other indicators. The possible relationshipsamong clouds in the survey are discussed, including the conjecture thatthe overall Orion complex of clouds is a much larger system thanpreviously considered, incorporating most of the clouds in the presentsurvey.
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Untersuchungen über Reflexionsnebel am Palomar Sky Survey I. Verzeichnis von Reflexionsnebeln
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Studies of bright diffuse galactic nebulae with special regard to their spatial distribution.
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TThe source of luminosity in galactic nebulae.
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The Region of H l 79 Ursae majoris
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