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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.
| The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. III. Perseus Observed with IRAC
We present observations of 3.86 deg2 of the Perseus molecularcloud complex with the Spitzer Space Telescope Infrared Array Camera(IRAC). The maps show strong extended emission arising from shockedH2 in outflows and from polycyclic aromatic hydrocarbonfeatures. More than 120,000 sources are extracted toward the cloud.Based on their IRAC colors and comparison to off-cloud and extragalacticfields, we identify 400 candidate young stellar objects. Abouttwo-thirds of these are associated with the young clusters IC 348 andNGC 1333, while the last third is distributed over the remaining cloud.The young stellar objects are classified according to the slope of theirspectral energy distributions. Significant differences are found betweenthe numbers of embedded Class I objects and more evolved Class IIobjects in IC 348, NGC 1333 and the remaining cloud, with the embeddedClass I and ``flat-spectrum'' YSOs constituting 14%, 36% and 47% of thetotal number of YSOs identified in each of these regions. The highnumber of Class I objects in the extended cloud (61% of the Class Iobjects in the entire cloud) suggests that a significant fraction of thecurrent star formation occurs outside the two main clusters. Finally, wediscuss a number of outflows and identify their driving sources,including the deeply embedded Class 0 sources outside the two mainclusters. The Class 0 objects are detected by Spitzer and have very red[3.6]-[4.5] colors, but they do not show similarly red [5.8]-[8.0]colors. The Class 0 objects are easily identifiable in color-colordiagrams but are problematic to extract automatically due to theextended emission from shocked gas or scattered light in cavitiesrelated to the associated outflows.
| The COMPLETE Nature of the Warm Dust Shell in Perseus
The Perseus molecular cloud complex is a >~30 pc long chain ofmolecular clouds most well known for the two star-forming clusters NGC1333 and IC 348 and the well-studied outflow source in B5. However, whenstudied at mid- to far-infrared wavelengths, the region is dominated bya ~10 pc diameter shell of warm dust, likely generated by an H II regioncaused by the early-B star HD 278942. Using a revised calibrationtechnique the COMPLETE team has produced high-sensitivity temperatureand column density maps of the Perseus region from IRAS Sky Survey Atlas(ISSA) 60 and 100 μm data. In this paper, we combine the ISSA-baseddust-emission maps with other observations collected as part of theCOMPLETE Survey, along with archival Hα and MSX observations.Molecular line observations from FCRAO and extinction maps constructedby applying the NICER method to the 2MASS catalog provide independentestimates of the ``true'' column density of the shell. Hα emissionin the region of the shell confirms that it is most likely an H IIregion located behind the cloud complex, and 8 μm data from MSXindicate that the shell may be interacting with the cloud. Finally, thetwo polarization components seen toward background stars in the regionby Goodman et al. can be explained by the association of the strongercomponent with the shell. If confirmed, this would be the firstobservation of a parsec-scale swept-up magnetic field.
| The COMPLETE Survey of Star-Forming Regions: Phase I Data
We present an overview of data available for the Ophiuchus and Perseusmolecular clouds from Phase I of the COMPLETE Survey of Star-FormingRegions. This survey provides a range of data complementary to theSpitzer Legacy Program ``From Molecular Cores to Planet Forming Disks.''Phase I includes the following: extinction maps derived from the TwoMicron All Sky Survey (2MASS) near-infrared data using the NICERalgorithm; extinction and temperature maps derived from IRAS 60 and 100μm emission; H I maps of atomic gas; 12CO and13CO maps of molecular gas; and submillimeter continuumimages of emission from dust in dense cores. Not unexpectedly, themorphology of the regions appears quite different depending on thecolumn density tracer that is used, with IRAS tracing mainly warmer dustand CO being biased by chemical, excitation, and optical depth effects.Histograms of column density distribution are presented, showing thatextinction as derived from 2MASS NICER gives the closest match to alognormal distribution, as is predicted by numerical simulations. Allthe data presented in this paper, and links to more detailedpublications on their implications, are publicly available at theCOMPLETE Web site.
| Detection of Anomalous Microwave Emission in the Perseus Molecular Cloud with the COSMOSOMAS Experiment
We present direct evidence for anomalous microwave emission in thePerseus molecular cloud, which shows a clear rising spectrum from 11 to17 GHz in the data from the COSMOSOMAS experiment. By extending thefrequency coverage using W ilkinson Microwave Anisotropy Probe mapsconvolved with the COSMOSOMAS scanning pattern, we reveal a peak fluxdensity of 42+/-4 Jy at 22 GHz integrated over an extended area of 1.65d×1.0d centered on R.A.=55.4d+/-0.1d and decl.=+31.8d+/-0.1d(J2000). The flux density that we measure at this frequency is nearly anorder of magnitude higher than can be explained in terms of normalGalactic emission processes (synchrotron, free-free, and thermal dust).An extended IRAS dust feature, G159.6-18.5, is found near this position,and no bright unresolved source that could be an ultracompact H IIregion or gigahertz-peaked source could be found. An adequate fit forthe spectral density distribution can be achieved from 10 to 50 GHz byincluding a very significant contribution from electric dipole emissionfrom small spinning dust grains.
| 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).
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
| Radial velocities of early-type stars in the Perseus OB2 association
We present radial velocities for 29 B- and A-type stars in the field ofthe nearby association Perseus OB2. The velocities are derived fromspectra obtained with AURELIE, via cross correlation with radialvelocity standards matched as closely as possible in spectral type. Theresulting accuracy is ~ 2-3 km s-1. We use thesemeasurements, together with published values for a few other early-typestars, to study membership of the association. The mean radial velocity(and measured velocity dispersion) of Per OB2 is 23.5 +/- 3.9 kms-1, and lies ~ 15 km s-1 away from the meanvelocity of the local disk field stars. We identify a number ofinterlopers in the list of possible late-B- and A-type members which wasbased on Hipparcos parallaxes and proper motions, and discuss thecolour-magnitude diagram of the association.Based on observations made at the Observatoire de Haute-Provence (CNRS),France.
| Interstellar Extinction in the Direction of the Barnard 1 Dark Cloud in Perseus
Spectral and luminosity classes, absolute magnitudes, color excesses,interstellar extinctions and distances are determined for 98 stars downto 13 mag in the Barnard 1 dark cloud belonging to the Per OB2association. The classification of stars is based on theirphotoelectric photometry in the Vilnius seven-color photometric system.The extinction vs. distance diagram exhibits the presence of two dustlayers at 150 and 230 pc distances. The distance of the first cloud,which gives an extinction A_V of 0.3 mag, coincides with the distance ofthe Taurus dark cloud complex. The second cloud with much largerextinction is about at the same distance as the clouds in the directionof the nearby objects: reflection nebula NGC 1333 and open cluster IC348.
| A Comparison of Photometric and Spectral Classification of Some Stars in Perseus
Photometric classification of 18 stars in the areas around thereflection nebula NGC 1333 and the open cluster IC 348 in Perseus, basedon the Vilnius seven-color photometric system, is compared with theclassification based on stellar spectra. In general, a goodcorrespondence of spectral classes is obtained. In some cases, theclassification differences may be the result of the unresolved binarityof stars. Three stars are confirmed to be emission-linepre-main-sequence objects. Interstellar reddening law in the directionof IC 348 is estimated.
| The Nature of the IRAS Ring G159.6-18.5 in Perseus and Its Exciting Star HD 278942
We discuss an extended feature in the Perseus molecular cloud complex,which is most prominent in the IRAS database as an almost complete ringof radius 0.75d but is also clearly seen in optical surveys and in radiocontinuum emission. While earlier identified as a supernova remnant, weargue that the feature is probably an H II region, based on newinterferometric radio continuum data at 408 and 1420 MHz, diffuseHα emission, and the identification of HD 278942 as an O9.5-B0 Vstar located at the geometric center of the IRAS ring. The spectralindex of the radio continuum emission is consistent with an opticallythin H II region. However, an origin of the radio continuum emission asat least partially caused by synchrotron emission from the interactionregion between the stellar wind and the remaining molecular cloud cannotbe ruled out. We present visual photometry, spectroscopy, andpolarimetry of the star HD 278942, which we believe to be the source ofthe excitation for the H II region and the stellar wind. Whilecoincident with an IRAS point source, no compact radio continuum sourceis seen at the location of the star. Null results for CO J=1-0 emissiondifferent from the ambient cloud are reported. The possibility that HD278942 is a main-sequence star with a circumstellar disk is suggested.
| 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.
| 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.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| Interstellar extinction in the direction of the open cluster IC 348 and the Per OB2 association
The relationship between interstellar extinction and distance in thedirection of dark clouds in the areas around the open cluster IC 348 andthe association Per OB2 is determined using the results of photoelectricphotometry of 189 stars in the Vilnius photometric system. Two absorbinglayers are found. The nearest layer, covering the whole area around IC348, shows the mean extinction A(V) of about 0.7 mag. It begins at thedistance of 160 pc and probably is an extension of the Taurus darkclouds to the northwest. The second absorbing layer has the form of achain of dark condensations named L1468, L1470, and L1471 and is at 260pc distance. This layer has a higher density, its mean extinction beingabout 2.0 mag. The cluster IC 348 is at about the same distance and isphysically related to the dark cloud L1470. The distance of the Per OB2association is found to be 340 pc and the mean extinction of its membersis 0.95 mag. A model of the spatial distribution of the Perseus andTaurus dark clouds based on photometric distance determinations in thisand previous papers is proposed. Six stars in the IC 348 area aresuspected to have emission in the H-alpha line.
| Precise positions in the FK4 system for 120 radio source reference stars
Positions are given in the FK4 system for 120 primary reference starsgrouped around the optical counterparts of 11 extragalactic radiosources. The observations were made in 1979 and 1980 with the 6-in.transit circle of the U.S. Naval Observatory. The results reported hererepresent the first step in a three-tiered process to determineastrometric positions of the optical counterparts referred to the systemof the FK4. One application of such positions is the determination of anearly inertial optical reference frame, which eventually may becompared to a reference frame at radio wavelengths.
| Meridian observations made in Brorfelde (Copenhagen University Observatory) 1975-76.
This catalogue presents positions for selected faint stars mainly fromAGK3 observed with the 7" transit circle at Brorfelde. The stars aredistributed in 43 selected areas around radio sources and are suitableas reference stars for measuring the optical counterparts to the radiosources. The obscr 'itioi cre carried out from 1975.16 to 1976.04, andevery star was observed at least two times giving a m.s.e. of "13 forthe catalogue positions given in the FK4 system. These positions usedtogether with AGK3 proper motions will in the period 1975 to 1980 have am.s.e. at the epoch ranging from `:13 to `:15, which is less than halfof what is expected when using AGK3 positions. Key words: transit circle- catalogue of positions
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