A 13CO and C18O Survey of the Molecular Gas Around Young Stellar Clusters within 1 Kiloparsec of the Sun
As the first step of a multiwavelength investigation into therelationship between young stellar clusters and their environment, wepresent fully sampled maps in the J=1-0 lines of 13CO andC18O and the J=2-1 line of C18O for a selectedgroup of 30 young stellar groups and clusters within 1 kpc of the Sun.This is the first systematic survey of these regions to date. Theclusters range in size from several stars to a few hundred stars. Thirtyfields ranging in size from 8'×8' to 30'×60' were mappedwith 47" resolution simultaneously in the two J=1-0 lines at the FiveCollege Radio Astronomy Observatory. Seventeen sources were mapped overfields ranging in size from 3'×3' to 13'×13' in the J=2-1line with 35" resolution at the Submillimeter Telescope Observatory. Wecompare the cloud properties derived from each of the three tracers inorder to better understand systematic uncertainties in determiningmasses and line widths. Cloud masses are determined independently usingthe 13CO and C18O transitions; these masses rangefrom 30 to 4000 Msolar. Finally, we present a simplemorphological classification scheme, which may serve as a roughindicator of cloud evolution.
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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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A Correlation between the Distributions of Pulsars and Emission Measures in the Galaxy
A correlation has been detected between the volume density of pulsarsand the density of interstellar ionized gas on scales of more than 500pc in Galactic longitude and 200 pc in Galactic latitude. On smallerscales, the correlation is present only for pulsars with ages less than60000 years, which are located predominantly near supernova remnants andH II regions. This all indicates that pulsars are born in regions withhigh concentrations of interstellar gas. The minimum emission measuresobserved in the directions toward pulsars are inversely proportional tothe pulsar ages. It is concluded that the ionized gas in the vicinitiesof a number of pulsars was formed during supernova explosions, andcorresponds to Strömgren zones. The ionization of the gas in thesezones requires a radiation energy on the order of 1050 1051 erg.
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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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Herbig Ae/Be stars with the IRAS low-resolution spectra.
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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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Regions of Low-Mass Star Formation
The fundamental question of the relationship between the properties ofthe star-forming material and the resulting stellar population isaddressed in general. Some detail is given on star formation in the ChaIII cloud, the status of the isolated T Tauri stars, and on globules asplaces of star-forming activity.
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SiO Maser Sources in the Outer Disk of the Galaxy
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..106..463J&db_key=AST
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Discovery of Three Radio Pulsars from an X-Ray--selected Sample
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...456..305Z
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Optical identification of IRAS Sources in the Outer Galaxy
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....111..231J
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Changes in the H-alpha emission line profile of the young star VY MON
H-alpha spectroscopy of the young star VY Mon is presented. Over the1986-1992 period, VY Mon exhibited three types of H-alpha profiles inits spectrum: a profile with short-wavelength P Cygni absorption (from-200 to -300 km/s), a profile with blue emission (-230 to -300 km/s),and a profile with a single emission feature (+140 km/s). The change ofprofile type appears to occur on a time scale of the order of one month,and a particular type persists no fewer than four months. All threeprofile types can be explained in terms of constrained models ofanisotropic stellar wind.
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Trapezium systems containing T tauri stars
The results of a spectroscopic investigation of four stars comprising aTrapezium system in the nebula Sh 155 are presented. The stars have anumber of emission lines typical of red emission stars and T Tau stars.This system is one of the 13 systems which we have found in the Palomaratlas. It is shown that all of these systems are members of OBassociations.
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Einstein X-ray observations of Herbig Ae/Be stars
We have investigated the X-ray emission from Herbig Ae/Be stars, usingthe full set of Einstein Imaging Proportional Counter (IPC)observations. Of a total of 31 observed Herbig stars, 11 are confidentlyidentified with X-ray sources, with four additonal dubiousidentifications. We have used maximum likelihood luminosity functions tostudy the distribution of X-ray luminosity, and we find that Be starsare significantly brighter in X-rays than Ae stars and that their X-rayluminosity is independent of projected rotational velocity v sin i. TheX-ray emission is instead correlated with stellar bolometric luminosityand with effective temperature, and also with the kinetic luminosity ofthe stellar wind. These results seem to exclude a solar-like origin forthe X-ray emission, a possibility suggested by the most recent models ofHerbig stars' structure, and suggest an analogy with the X-ray emissionof O (and early B) stars. We also observe correlations between X-rayluminosity and the emission at 2.2 microns (K band) and 25 microns,which strengthen the case for X-ray emission of Herbig stars originatingin their circumstellar envelopes.
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A new catalogue of members and candidate members of the Herbig Ae/Be (HAEBE) stellar group
A new up-to-date catalogue of Herbig Ae/Be (HAEBE) stars and relatedobjects is certainly needed, for both well-seasoned researchers and, inparticular, for new investigators starting to study the many interestingastrophysical properties of these very young objects. We present a briefdiscussion of the current observational characteristics that distinguishthis class from their main sequence counterparts. The HAEBE and relatedstars are listed in five tables, containing 287 objects. Table 1contains all Ae and Be stars which historically are recognized as trueHAEBE stars or potential candidate members. Table 2 gives the stars ofspectral type Fe, and emission line stars with very uncertain or unknownspectral type. In Table 3 are given all known Extreme Emission LineObjects (EELOs), of which most have not been identified to belong to anyspecific group. Table 4a and b list other Bep or B[e] stars with strongIR-excess and unknown spectral type. Table 5 contains the non-emissionline possible young objects. Furthermore, Table 6 contains 35 starsrejected from former published lists of HAEBE stars. In these tables weare including coordinates, spectral types, visual magnitudes, ranges inphotometric variability and references of several key publicationsrelated to each object. Relevant remarks, such as the presence of anebula in the vicinity of an object, are also given.
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IRAS sources beyond the solar circle. III - Observations of H2O, OH, CH3OH and CO
We have used the 100-m Effelsberg and 32-m Medicina radiotelescopes tosearch for H2O maser emission (22.235 GHz) towards 1143 IRAS sources,for OH (1665/67 MHz) towards 303 IRAS sources, and for CH3OH (12.179GHz) towards 19 IRAS sources. The IRAS sources have been selected tohave colors of premain sequence objects. To obtain an estimate of thekinematic distance, we observed (C-12)O (J = 2 to 1) and (C-12)O (J = 3to 2) with the KOSMA 3-m telescope towards 25 sources showing H2Oemission and not yet observed in CO. This paper presents theobservational results in form of tables with line parameters or upperlimits and spectra of detected sources.
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Infrared spectra and circumstellar emission of IRAS sources with ten-micron silicate absorption
Results are presented of near-infrared photometry carried out in the J,H, K, and L bands for 33 IRAS sources with a 10-micron silicateabsorption features. The observed sources were found to be mostlycomprised of two groups of stars which showed very different spectralcharacteristics from each other between 1 and 100 microns. These starswere either evolved OH/IR stars, which generally showed IR photometricspectra similar to black-body spectra; or they were young stellarobjects showing much broader spectral energy distributions thanblack-body spectra.
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A catalog of co-added IRAS fluxes of Orion population stars
A catalog of co-added IRAS fluxes for the pre-main-sequence objects inthe Herbig-Bell catalog (HBC) is presented. This catalog doubles thenumber of HBC stars with detected IRAS fluxes and provides improved fluxvalues for the previously known sources. Noise level are given for allHBC fields in each band, permitting upper limits to be estimated for allundetected sources.
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Emission from dust in visual reflection nebulae at infrared and submillimeter wavelengths
Far-IR and submillimeter images of five bright visual reflectionnebulae, IC 446, NGC2247, NGC 2245, NGC 7023, and CED 201 are presentedand used with composite IR spectra to derive parameters such as thefraction of nebulae emission attributed to molecule-sized grains, therange of nebulae grain albedos, gas densities, and gas cloud geometries.The results show that 30-45 percent of the nebulae emission lies atwavelengths of less than 30 microns. The variation in IR luminosity maybe related to variations in nebulae gas density and less than optimalgas cloud geometries rather than to anomalous grain albedos. Relativeextinction efficincies of roughly 1000-5000 are inferred for stellarphotospheres with effective wavelengths of roughly 0.25-0.5 micron. Theresultant mass-extinction coefficient is roughly 10-50 sq cm/g.
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A catalog of pre-main-sequence emission-line stars with IRAS source associations
To aid in finding premain-sequence (PMS) emission-line stars that mighthave dusty circumstellar environments, 361 PMS stars that are associatedwith 304 separate IRAS sources were identified. These stars include 200classical T Tauri stars, 25 weak-lined (naked) T Tauri stars, 56 HerbigAe/Be stars, six FU Orionis stars, and two SU Aurigae stars. All six ofthe FU Orionis stars surveyed by IRAS were detected. Of the PMS-IRASPoint Source Catalog (PSC) associations, 90 are new and are not noted inthe PSC. The other 271 entries include 104 that are correctly identifiedin the PSC but have not yet appeared in the literature, 56 more that canbe found in both the PSC and in the published and unpublished iterature,and 111 that are in the literature but not in the PSC. Spectral slopediagrams constructed from the 12-, 25-, and 60-micron flux densitiesreveal unique distributions for the different PMS subclasses; thesediagrams may help identify the best candidate PMS stars for observationsof circumstellar dust.
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VY Monocerotis and the IC 446 region - Far-infrared and submillimeter images of a massive young stellar object and its environment
The reflection nebulae IC 446 has been mapped in an 8 x 8-arcmin area at100, 160, and 370 microns using 32-channel bolometer-array detectors onthe 0.9-m telescope of the NASA Kuiper Airborne Observatory and the 3-mtelescope of the NASA Infrared Telescope Facility. These data have beencombined with IRAS profiles at 12, 25, 60, and 100 microns toinvestigate the morphology and energetics of the region. The FIR throughsubmm emission in the neighborhood of IC 446 is composed of threecomponents: a compact point source associated with the young stellarobject VY Mon, warm extended emission associated with dust in thereflection nebula IC 446, and cold extended emission associated with adark absorption nebula or globule.
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Emission From Dust in Visual Reflection Nebulae at Infrared and Submilimeter Wavelengths
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The structure of star formation regions. II - Studies of certain regions - RSF 3 MON
Photoelectric UBVR photometry and a spectral classification were carriedout for more than 100 stars associated with the nebulae NGC 2245-2247,IC 446, IC 2169, and the cluster Cr 95 in the western part of RSF 3 Mon.The stars associated with these nebulae, the cluster Cr 95, NGC 2264,and hot field stars represent a single star formation region. The age ofRSF 3 Mon exceeds 20 Myr.
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Catalog of emission line stars of the orion population : 3 : 1988
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Reflection Nebulae of Mon R1 in the Far-Infrared and Submillimeter
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CCD surface photometry of bright reflection nebulae
Surface brightness measurements in the B, V, R, and I photometric bandsare presented for 14 reflection nebulae. The analysis of nebula-starcolor differences leads to the conclusion that excess emission in the Iband beyond that expected from scattering is a common phenomenon amongreflection nebulae illuminated by B stars. An ultraviolet-poweredfluorescence mechanism is suggested. Both the absolute and the relativeV surface brightnesses of the nebulae in the sample are analyzed. Thedata can be explained, if the nebulae arise in moderately denseinterstellar clouds with illuminating stars embedded at an optical depthlevel of order unity and with dust of high albedo and with a stronglyforward-directed phase function. It is concluded that bright reflectionnebulae must arise under almost optimal scattering conditions, whichapparently are found when newly formed low-mass star clusters are stillembedded in the material from which they originated.
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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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Polarization of the light of the stars in the association MON R1
New observations of polarization of the light of the stars in thereflection nebula association Mon R1 are given. Of 17 stars investigatedin the B photometric system, nine are cores of reflection nebulas. Thestar VY Mon is found to have a large polarization. The manner in whichthe polarization of the stars and the structure of the nebulas arerelated to the magnetic field of the cloud in which they are situated isdiscussed.
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R associations. VI - The reddening law in dust clouds and the nature of early-type emission stars in nebulosity from a study of five associations
Positions, identification charts, UBVRIKLMN photometry and spectraltypes are given for stars, illuminating reflection nebulae that arevisible on the POSS prints, which have been identified in fiveassociations. With a ratio of total to selective extinction of 4.2, thereddening law applicable to the dust clouds in which the stars areembedded is steeper than normal. The five associations exhibit 18early-type stars with circumstellar shells, of which those with spectraltypes earlier than B5 characteristically have weak IR excesses, incontrast to the strong excesses indicative of circumstellar dust, oflater-type stars. Color-magnitude charts show a distribution lying abovethe ZAMS by up to about 2 mag for both the circumstellar shell stars andthose classified as rapid rotators. It is suggested that (1) rapidrotation accounts for the scatter in the color-magnitude diagram, and(2) many of the nebulous early-type emission-line stars are rapidrotators rather than pre-main sequence objects.
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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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NEWS@SKY (Science&Space News)
