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Infrared Nebulae around Young Stellar Objects
We present a K-band atlas of 106 reflection nebulae, 41 of which are newdiscoveries. We observed these nebulae with the University of Hawaii 2.2m telescope in the course of an imaging survey of 197 objects that wereselected as nearby young Class I sources. K-band images andflux-calibrated surface brightness contour plots of each nebula arepresented. We found that the near-IR luminosities and physical sizes ofthe nebulae increase with the bolometric luminosity of the illuminatingsources. Only 22 nebulae, about 10% of these candidate Class I sources,have indications of shocked H2 emission. The great variety ofnebulae that we observed prevented us from classifying them based onmorphology. However, we note that as the spectral index decreases, thecentral star is more frequently visible at K band, and the flux from thecentral star tends to be dominant over the flux from the nebula. Forobjects that have a higher spectral index, most of the K-band flux isfrom the reflection nebula, and the central star is less frequentlyvisible. The nebula around IRAS 05450+0019 has a unique morphology, andwe speculate that it may be an example of a disk shadow being projectedinto the surrounding cloud. We present J-, H-, and K-band images of thisobject with surface brightness contours, as well as its spectral energydistribution from 1.2 to 100 μm.
| 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.
| 13CO (J = 1 -- 0) Survey of Molecular Clouds toward the Monoceros and Canis Major Region
rough a large-scale 13CO(J=1-0) survey toward a region inMonoceros and Canis Major, we present following results: (1) Weidentified in total 115 clouds. (2) GroupI (CMaOB1 and G220.8 ‑1.7) may physically connected with GroupII (Mon R2 and NGC2149). (3)496YSO candidates were chosen from IRAS point source catalog (IPC). (4)The mass spectrum of the Local clouds shows a power-law relation with anindex of ‑1.55 ± 0.09. (5) The number fraction ofstar-forming clouds increases as the cloud mass increases. Especially,massive clouds of Mcloud≥103.5Modot are all star-forming clouds. (6) Theline width-cloud radius relation is best fitted asΔVcomp ∝ rcloud0.47(correlation coefficient = 0.87). (7) The distribution of(Mvir / Mcloud) shows that star-forming cloudstend to be more virialized than no star-forming clouds. (8) Starformation in GroupI is more active than that in GroupII. (9) Unexpectedsmall number of low-mass clouds in GroupI may be due to strong UVradiation from O-type stars in the vicinity of the clouds. (10) Starformation in GroupII might occurred by self-gravitational, except forthe most massive cloud.
| Investigation of 131 Herbig Ae/Be Candidate Stars
We present a new catalog of 108 Herbig Ae/Be candidate stars identifiedin the Pico dos Dias Survey, together with 19 previously knowncandidates and four objects selected from the IRAS Faint Source Catalog.These 131 stars were observed with low- and/or medium-resolutionspectroscopy, and we complement these data with high-resolution spectraof 39 stars. The objects present a great variety of Hα lineprofiles and were separated according to them. Our study suggests thatmost of the time a Herbig Ae/Be star will present a double peak Hαline profile. Correlations among different physical parameters, such asspectral type and vsini with Hα line profiles were searched. Wefound no correlation among Hα line profiles and spectral type orvsini except for stars with P Cygni profiles, where there is acorrelation with vsini. We also use preliminary spectral energydistributions to seek for any influence of the circumstellar medium inthe Hα line profiles. The presence of [O I] and [S II] forbiddenlines is used together with the Hα line profiles and thesepreliminary spectral energy distributions to discuss the circumstellarenvironment of the Herbig Ae/Be candidates. The distribution of thedetected [O I] and [S II] forbidden lines among different spectral typespoints to a significantly higher occurrence of these lines among Bstars, whereas the distribution among different Hα profile typesindicates that forbidden lines are evenly distributed among eachHα line-profile type. Combining the distance estimates of theHerbig candidates with the knowledge of the interstellar mediumdistribution, we have found that 84 candidates can be associated withsome of the more conspicuous SFRs, being in the right direction and at acompatible distance. As a further means of checking the properties ofthe HAeBe candidates, as well as their present evolutionary status, thederived luminosities and effective temperatures of the stars withpossible association to the star-forming regions and/or Hipparcosdistances were plotted together with a set of pre-main-sequenceevolutionary tracks on an HR diagram. A set of 14 stars were found outof their expected positions in the HR diagram.Based on observations made at the Obsevatório do Pico dosDias/LNA (Brazil), ESO (Chile), and the Lick Observatory.
| New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS
We carried out a survey of infrared star clusters and stellar groups onthe 2MASS J, H and Ks all-sky release Atlas in the Northernand Equatorial Milky Way (350deg < l < 360deg, 0deg < l < 230 deg). Thesearch in this zone complements that in the Southern Milky Way (Dutra etal. \cite{Dutra03}a). The method concentrates efforts on the directionsof known optical and radio nebulae. The present study provides 167 newinfrared clusters, stellar groups and candidates. Combining the twostudies for the whole Milky Way, 346 infrared clusters, stellar groupsand candidates were discovered, whereas 315 objects were previouslyknown. They constitute an important new sample for future detailedstudies.
| 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
| Nature of OH maser and SiO thermal emission towards carbon star: IRAS 05373-0810 (V1187 Ori)
We present observational evidence that IRAS 05373-0810 is a genuinecarbon star with an ISO SWS spectrum closely resembling that of R Scl.Modelling of the spectral energy distribution of IRAS 05373-0810suggests that the star has luminosity of order of 8000 Lsunand loses mass at a rate of about 2-3*E-7 Msunyr-1. The detected OH maser emission at 1612, 1665 and 1667MHz and SiO thermal emission at 86.85 GHz towards IRAS 05373-0810 is notassociated with this source. The available observations imply that theselines, typical for O-rich sources, come from the molecular cloud L 1641in the Orion star forming region (OH) and, very likely, from the NGC2149 molecular complex (SiO). Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, the Netherlands and the United Kingdom) andwith participation of ISAS and NASA.
| Dynamical Effects on Winds and Radiation on the Structure of the Planetary Nebulae
Not Available
| Dusty Plasmas in Interstellar Clouds and Star Forming Regions
Not Available
| 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.
| 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.
| H2O masers from low and intermediate luminosity young stellar objects: H2O masers and YSOs
We have used the Medicina 32-m radiotelescope to search for H2O 22.2 GHzmaser emission from a sample of 68 red peculiar nebulosities associatedwith low luminosity (LIR less than 103 solarluminosity)) and intermediate luminosity (LIR approximately104 solar luminosity) Young Stellar Objects (YSOs). H2O maseremission was detected in 9 sources, with a new detection in IRAS18265+0028. Comparison with other samples indicates that YSOs have ahigher probability of hosting an H2O maser, when they are associatedwith red peculiar nebulosities. Seven of the detected sources areassociated with molecular outflows, which confirms that these twophenomena are strictly correlated. The maser sources associated with theClass I YSOs (IRAS 03225+3034, and IRAS 03245+3002, in the dark cloudsL1448 and L1455 respectively) appear overluminous with respect to theirIR luminosity. The maser emission shows a remarkable variability on timescales of months and years, which tends to be larger for lowerluminosity sources. This is indicative of unsaturated emission in lowluminosity sources.
| An OH survey of Orion South and GMC214 - 13
A low resolution large scale survey of OH main line emission ispresented that covers Orion South and GMC214 - 13, the giant molecularcloud associated with MonR2. OH emission is detected down to the lowestcontours in the (C-12)O survey of the Columbia group (Maddalena et al.,1986). An LTE approach gives a mass distribution in Orion South that issimilar to that derived from (C-13)O and H2CO observations and differsfrom that of W(C-12)O. Peaks in the (C-12)O emission,coinciding with reflection nebulae, are found at depressions and stronggradients in the LTE OH column density distribution. The total mass ofGMC214 - 13 is found to be (3 + or - 1) x 10 to the 5th and that ofOrion South (10 + or - 3) x 10 to the 4th solar masses. In GMC214 - 13there is no OB association nor is there a similar area of dense matteror a strong velocity gradient as observed in Orion South.
| Atomic hydrogen in the Orion star-forming region
A large-scale survey of atomic hydrogen in Orion reveals low-densitymaterial with a total mass comparable to that in dense molecular clouds.The atomic gas is sufficiently dense that it can shield the molecularmaterial from photodissociative radiation and provide a pressure link tothe low-density intercloud medium. An excess of H I emission comes fromphotodissociation fronts near the bright stars and from a giant shell inthe Orion Belt region. This shell may have caused the apparentbifurcation between the Orion A and B clouds, and the associatedpressures may have induced peculiar motions and star formation in NGC2023 and 2024.
| 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.
| A Search for Molecular Outflows Associated with Peculiar Nebulosities and Regions of Star Formation
Abstract image available at:http://adsabs.harvard.edu/abs/1983RMxAA...8..147T
| Red and nebulous objects in dark clouds - A survey
A search on the NGS-PO Sky Survey photographs has revealed 150interesting nebulous and/or red objects, mostly lying in dark clouds andnot previously catalogued. Spectral classifications are presented for 55objects. These indicate a small number of new members of the class ofHerbig-Haro objects, a significant number of new T Tauri stars, and afew emission-line hot stars. It is argued that hot, high-mass stars formpreferentially in the dense cores of dark clouds. The possible symbiosisof high and low mass stars is considered. A new morphology class isdefined for cometary nebulae, in which a star lies on the periphery of anebulous ring.
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