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The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. VI. Perseus Observed with MIPS
We present observations of 10.6 deg2 of the Perseus molecularcloud at 24, 70, and 160 μm with Spitzer MIPS. The images showprominent, complex extended emission dominated by illuminating B starson the east side of the cloud and by cold filaments of 160 μmemission on the west side. Of 3950 point sources identified at 24 μm,1141 have 2MASS counterparts. A quarter of these populate regions of theKs versus Ks-[24] diagram that are distinct fromstellar photospheres and background galaxies and thus are likely to becloud members with infrared excess. Nearly half (46%) of these 24 μmexcess sources are distributed outside the IC 348 and NGC 1333 clusters.A significant number of IRAS PSC objects are not recovered by SpitzerMIPS, most often because the IRAS objects were confused by brightnebulosity. The intercluster region contains several tightly clumped(r~0.1 pc) young stellar aggregates whose members exhibit a wide varietyof infrared SEDs characteristic of different circumstellar environments.This could be explained by a significant age spread among the aggregatemembers, or if the members formed at the same time, a remarkably rapidcircumstellar evolution would be required to account for the associationof Class I and Class III sources at ages <~1 Myr. We highlightimportant results for the HH 211 flow, where the bow shocks are detectedat both 24 and 70 μm, and for the debris disk candidate BD +31 643,where the MIPS data show the linear nebulosity to be an unrelatedinterstellar feature. Our data, mosaics, and catalogs are available atthe Spitzer Science Archive for use by interested members of thecommunity.
| Herbig Ae/Be Stars in nearby OB Associations
We have carried out a study of the early-type stars in nearby OBassociations spanning an age range of ~3-16 Myr, with the aim ofdetermining the fraction of stars that belong to the Herbig Ae/Be class.We studied the B, A, and F stars in the nearby (<=500 pc) OBassociations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1,with membership determined from Hipparcos data. We also included in ourstudy the early-type stars in the Trumpler 37 cluster, part of the CepOB2 association. We obtained spectra for 440 Hipparcos stars in theseassociations, from which we determined accurate spectral types, visualextinctions, effective temperatures, luminosities and masses, usingHipparcos photometry. Using colors corrected for reddening, we find thatthe Herbig Ae/Be stars and the classical Be (CBe) stars occupy clearlydifferent regions in the JHK diagram. Thus, we use the location on theJHK diagram, as well as the presence of emission lines and of strong 12μm flux relative to the visual, to identify the Herbig Ae/Be stars inthe associations. We find that the Herbig Ae/Be stars constitute a smallfraction of the early-type stellar population even in the youngerassociations. Comparing the data from associations with different agesand assuming that the near-infrared excess in the Herbig Ae/Be starsarises from optically thick dusty inner disks, we determined theevolution of the inner disk frequency with age. We find that the innerdisk frequency in the age range 3-10 Myr in intermediate-mass stars islower than that in the low-mass stars (<1 Msolar) inparticular, it is a factor of ~10 lower at ~3 Myr. This indicates thatthe timescales for disk evolution are much shorter in theintermediate-mass stars, which could be a consequence of more efficientmechanisms of inner disk dispersal (viscous evolution, dust growth, andsettling toward the midplane).
| 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
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| 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.
| CH(+) in the interstellar medium
This paper describes observations of interstellar CH(+) along the linesof sight to O and B stars with E(B-V)s up to +1.13. Along some lines ofsight with strong detections of CH(+), we find distinct radial velocityshifts between the CH(+) lines and other neutral species, such as Ca Iand CH. The shifts are small but are predicted by shock models of CH(+)formation in which the shock is inclined with respect to the observer.We have also found no column densities exceeding approximately1013.8/sq cm. When these data are examined along with theother CH(+) data collected from the literature, the previously seentendency of CH(+) column density to increase with E(B-V) does notcontinue beyond reddenings of about +0.6. These findings offer supportto the shock model of CH(+) formation for at least some lines of sight.
| A Study of the Kinematics of the Local Dark Clouds
Not Available
| Interstellar extinction in the vicinity of the reflection nebula NGC 1333 in Perseus
The dependence of interstellar extinction on distance in the directionof a dark cloud around the reflection nebula NGC 1333 is determined onthe basis of photoelectric Vilnius photometry and photometricclassification of 78 stars. Two dust clouds are noted at distances 160and 220 pc. The first one, with mean extinction of 0.4 mag, is concludedto belong to the Taurus cloud complex and the second cloud, with meanextinction of 1.8 mag, belongs to the chain of dark clouds and otheryoung objects which is almost perpendicular to the spiral arm but liesabout 80 pc below the Galactic plane. The star BD +30 459 deg, whichilluminates the NGC 1333 nebula, is at a distance 212 pc from the sun.No extinction increase behind the Perseus cloud is detected.
| Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
| Molecular clouds associated with reflection nebulae. I - A survey of carbon monoxide emission
The paper presents 2.6 mm wavelength CO and (C-13)O observations of 130molecular clouds associated with reflection nebulae. Enhanced COemission was found in the vicinity of the illuminating star in abouthalf the objects studied. There is a tendency for the CO peak to beslightly displaced from the star. Many examples of peaks that appear toresult from heating of the cloud by the nearby star are found, whileothers appear to be associated with independent concentrations ofmaterial.
| On H-as a source of diffuse interstellar bands.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973ApJ...184..135S&db_key=AST
| Stars in reflection nebulae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..233R&db_key=AST
| A study of reflection nebulae.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966AJ.....71..990V&db_key=AST
| Studies of bright diffuse galactic nebulae with special regard to their spatial distribution.
Not Available
| A great nebulous region near omicron Persei.
Not Available
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