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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 (22.214.171.124) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
|ISO spectroscopy of young intermediate-mass stars in the BD+40deg4124 group|
We present the results of ISO SWS and LWS grating scans towards thethree brightest members of the BD+40deg4124 group in theinfrared: BD+40deg4124 (B2Ve), LkHα 224 (A7e) and theembedded source LkHα 225. Emission from the pure rotational linesof H_2, from ro-vibrational transitions of CO, from PAHs, from H irecombination lines and from the infrared fine structure lines of [Feii], [Si ii], [S i], [O i], [O iii] and [C ii] was detected. Theseemission lines arise in the combination of a low-density (~102 cm-3) H ii region with a clumpy PDR in thecase of BD+40deg4124. The lower transitions of the infrared Hi lines observed in BD+40deg4124 are optically thick; mostlikely they arise in either a dense wind or a circumstellar disk. Thissame region is also responsible for the optical H i lines and the radiocontinuum emission. In the lines of sight towards LkHα 224 andLkHα 225, the observed emission lines arise in a non-dissociativeshock produced by a slow (~ 20 km s-1) outflow arising fromLkHα 225. Toward LkHα 225 we also observe a dissociativeshock, presumably located closer to the outflow source than thenon-dissociative shock. In the line of sight towards LkHα 225 weobserved absorption features due to solid water ice and amorphoussilicates, and due to gas-phase H_2O, CO and CO_2. No solid CO_2 wasdetected towards LkHα 225, making this the first line of sightwhere the bulk of the CO_2 is in the gas-phase. Based on observationswith ISO, an ESA project with instruments funded by ESA Member States(especially the PI countries: France, Germany, the Netherlands and theUnited Kingdom) and with the participation of ISAS and NASA.
|HIPPARCOS photometry of Herbig Ae/Be stars|
The photometric behaviour of a sample of 44 Herbig Ae/Be (HAeBe)candidate stars was studied using a uniform set of optical photometryobtained by the Hipparcos mission. Astrophysical parameters (distance,temperature, luminosity, mass, age) of this sample of stars were derivedas well by combining the astrometric data provided by Hipparcos withdata from literature. Our main conclusions can be summarized as follows:(1) More than 65% of all HAeBe stars show photometric variations with anamplitude larger than 0\fm05; (2) HAeBes with a spectral type earlierthan A0 only show moderate (amplitude < 0\fm5) variations, whereasthose of later spectral type can (but not necessarily have to) showvariations of more than 2\fm5. We explain this behaviour as being due tothe fact that stars with lower masses become optically visible, andhence recognizable as Herbig Ae stars, while still contracting towardsthe zero-age main sequence (ZAMS), whereas their more massivecounterparts only become optically visible after having reached theZAMS; (3) The Herbig stars with the smallest infrared excesses do notshow large photometric variations. This can be understood by identifyingthe stars with lower infrared excesses with the more evolved objects inour sample; (4) No correlation between the level of photometricvariability and the stellar v sin i could be found. If the largephotometric variations are due to variable amounts of extinction by dustclouds in the equatorial plane of the system, the evolutionary effectsprobably disturb the expected correlation between the two. Based on datafrom the Hipparcos astrometry satellite.
|Close binary systems in star-forming regions. V502 CYG in the association CYG T2.|
|The FU Orionis Variable Stars: Accretion in Action|
|Isolated star-forming regions containing Herbig Ae/Be stars. 1: The young stellar aggregate associated with BD +40deg 4124|
We use optical and infrared photometry in combination with red opticalspectra to study the star-forming region associated with the two HerbigAe/Be stars BD + 40 deg 4124 and V1686 Cyg. We identify a partiallyembedded, dense, isolated cluster of pre-main sequence starsconcentrated within 0.15 pc of the two young high-mass stars. Thecluster is isolated in that it is separated by approximately 0.7 pc froma surrounding H alpha-bright rim and lies at the center of a molecularcore with peak column density corresponding to 45 mag of visualextinction. The fraction of the stellar population with evidence forcircumsteller activity is 100% amongst the optically visible clustermembers and at least 50% amongst the embedded sources. This small regionis characterized by an apparent age spread of approximately 3 Myr withevidence for both high-and low-mass stars forming relativelysimultaneously (within several hundred thousand years). Comparison ofthe derived stellar mass distribution to that expected from Monte-Carlosampling of the solar neighborhood mass spectrum reveals that thisregion is producing an unusually large number of intermediate-andhigh-mass stars. Our result suggests that not all star formation sitesyield identical mass spectra, and that universal mass functions may beproduced only when integrating over large spatial areas and/or over manystar formation epochs. Futhermore, our data appear to exclude for the BD+40 deg 4124 region, the popular senario that low-mass star formationproceeds quietly and stochastically for several to ten Myr until thebirth of an early type star, and its subsequent dynamical interactionwith the cloud, ends all starformation processes in the core. Instead,we consider the hypothesis that star formation was induced in thisregion by the propagation of an external shock wave into the cloud core.This picture is similar to that invoked for other star-forming sitesdisplaying a bright-rim morphology on optical images and cometarymolecular structure, as we see in the vicinity of BD +40 deg 4124.
|Polycyclic aromatic hydrocarbons in interstellar chemistry|
Interstellar chemistry modifications resulting form the presence oflarge molecules such as polycyclic aromatic hydrocarbons (PAHs) areinvestigated. For abundances of PAH relative to hydrogen of greater than10 to the -8th, free electrons attach to PAH molecules to yield PAH(-)ions, and qualitative interstellar chemistry changes are shown to resultas atomic and molecular ions undergo nondestructive mutualneutralization reactions with these negative ions. An increase in thesteady state abundances of carbon-bearing molecules is also noted. For aPAH abundance ratio relative to hydrogen of 10 to the -7th, theequilibrium densities of C3H2 and neutral atomic C are found to beenhanced by two orders of magnitude.
|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.
|Deuterium fractionation mechanisms in interstellar clouds|
In the theory of the fractionation of deuterated molecules, it isassumed that almost all of the deuterium in dense clouds exists in theform of HD molecules and none in atomic form. In the presentinvestigation it is suggested that a significant fraction of thedeuterium is atomic and that the fractionation is assisted by reactionssuch as D + H3(+) yields H2D(+) + H and D + HCO(+) yields H + DCO(+).The theory is extended on the basis of the considered suggestions.Attention is given to the derivation of the upper and lower bounds tothe cosmic deuterium-hydrogen abundance ratio, the derivation of theupper limits for the fractional ionization, and the conditions for anumber of warm clouds and cold clouds.
|The evolution of star-bearing molecular clouds - The high-velocity HCO(+) flow in NGC 2071|
Observations of NGC 2071 in the J = 1-0 and J = 3-2 lines of HCO(+) andH(C-13)O(+) obtained with the 11-m NRAO antenna at Kitt Peak and the20-m mm-wave antenna at Onsala Space Observatory (J = 1-0) and with the4.9-m antenna at the Millimeter Wave Observatory (J = 3-2) during1980-1983 are reported and discussed in terms of the mass, momentum, andenergy distribution in the bidirectional molecular flow. The results arepresented in maps, profiles, diagrams, and tables. The velocity of thebidirectional flow emanating from a core of density 10 to the 6th/cu cmis found to decrease gradually from an initial value of about 35 km/sec,to consist mainly of dense clumps with radii less than 0.01 pc, and tohave had a constant momentum-injection rate over the last 10,000 yrs.Little enhancement of HCO(+) abundance or ionization level is detectedin the accelerated gas. The value of the higher-transition lines forprobing dense-core molecules is indicated, and the formulas used tocalculate the flow parameters are derived in an appendix.
|The Spectrum and Distance of Suspected Variable Star SVS2132|
|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.
|A catalogue of bright nebulosities in opaque dust clouds|
Abstract image available at:http://adsabs.harvard.edu/abs/1977A&AS...29...65B
|CO observations of galactic reflection nebulae|
Carbon monoxide emission has been observed toward about 35 galacticreflection nebulae. The peaking of CO temperatures near the hotter starsindicates substantial local heating of the gas and dust by the embeddedstars. Wide low-level emission wings are seen on several of the (C-12)Oline profiles; these are most plausibly interpreted as due to cloudmaterial accelerated by such processes as radiation pressure from thenewborn stars.
|A general study of diffuse galactic nebulae.|
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