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|A survey of OH masers towards high mass protostellar objects|
Context: Masers are important tracers of the early evolution of younghigh mass stars, but the relationship between different types of maserand the evolutionary state of the exciting source remains unclear. Aims: To determine whether OH masers are common towards candidate highmass protostellar objects. Methods: We present a survey of OH maseremission towards a sample of high mass protostellar objects made usingthe Nançay and GBT telescopes. Results: OH maser emission wasdetected towards 63 objects with 36 new detections. There are 56star-forming regions and 7 OH/IR candidates. Nearly half of the detectedsources have OH flux densities ⪉1 Jy. There is no evidence thatsources with OH masers have a different range of luminosities from thenon-maser sources. The results of this survey are compared with previousH2O and class II CH3OH maser observations of the same objects. Some ofthe detected sources are only associated with OH masers and some sourcesare only associated with the 1720 MHz OH maser line. The velocity rangeof the maser emission suggests that the water maser sources may bedivided into two groups. The detection rates and velocity range of theOH and Class II CH3OH masers support the idea that there is a spatialassociation of the OH and Class II CH3OH masers. The sources span a widerange in R, the ratio of the methanol maser peak flux to OH 1665 MHzmaser peak flux, however there are only a few sources with intermediatevalues of R, 8
|The T Tauri Star Population of the Young Cluster NGC 2264|
An Hα emission survey of the young cluster NGC 2264 in the Mon OB1association resulted in the detection of 490 Hα emission stars ina 25'×40' field approximately centeredbetween the O7 V multiple star S Mon and the Cone Nebula. The survey wascarried out with the wide-field grism spectrograph (WFGS) on theUniversity of Hawaii 2.2 m telescope on Mauna Kea. X-ray observationsmade with the European Photon Imaging Camera on board the European SpaceAgency's XMM-Newton satellite observatory will be discussed in asubsequent paper. Optical (BVRCIC) photometry wasobtained for selected fields to supplement similar data from theliterature. Spectra covering the 6000-8000 Å region at aresolution of R~3000 (adequate for the determination of Li Iλ6708 line strengths) were obtained for 150 Hα and X-rayemission sources with the Gemini Multi-Object Spectrograph.Near-infrared spectra (1-2.5 μm) of a number of T Tauri stars (TTSs),X-ray sources, and LHα25 (W90) were also obtained using SpeX onthe Infrared Telescope Facility. Ages and masses for the Hαemitters were inferred from the isochrones and evolutionary tracks ofD'Antona & Mazzitelli. The median age for the TTS population isabout 1.1 Myr, but a considerable dispersion, from 0.1 to 5 Myr, existsfor individual objects. Several fields in the cluster were observed withthe WFGS on more than one occasion, permitting an examination ofHα variability over long baselines in time. About 90% of theclassical T Tauri stars (CTTSs) showed changes in W(Hα) of atleast 10%, while 57% varied at levels of 50% or more. No evidence wasfound for a significant pool of dormant Hα emitters. Summing themasses of the TTSs and the OB stellar population of NGC 2264, a lowerlimit for the total stellar mass content of the cluster is about 430Msolar. This is less than 1% of the total mass of the atomicand molecular gas believed to be associated with NGC 2264. Evidence forhierarchical structure within the cluster is suggested by the spatialdistribution of TTSs. Four concentrations of Hα emitters areevident: two near S Mon and two near the Cone Nebula. The median age ofthe TTSs in the immediate vicinity of S Mon was found to be greater thanthat of the TTSs near Allen's infrared source (IRS-1), but a significantdispersion is present. From the rotational data of Lamm et al. andMakidon et al., 241 of the TTSs are periodic variables, 150 weak-line TTauri stars (WTTSs) and 91 CTTSs, while 123 stars are irregularvariables (30 WTTSs and 93 CTTSs). A weak-to-moderate positivecorrelation is found between H-K color and Prot for theCTTSs, in the sense that stars having longer periods tend to have largerH-K colors. A similar positive correlation is found betweenLHα and Prot among the CTTSs. Nostatistically significant correlation is found between Protand theoretical age or between Prot and LX. Othertopics discussed include the fraction of Hα emitters that areWTTSs, f(WTTS)=N(WTTS)/N(TTS), for clusters of different ages; therelative detectability of Hα emission using WFGS and narrowbandfilter imaging techniques; and the correlation of W(Li I) withTe, age, H-K color, and W(Hα).
|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 (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
|Testing Models of Low-Excitation Photodissociation Regions with Far-Infrared Observations of Reflection Nebulae|
This paper presents Kuiper Airborne Observatory observations of thephotodissociation regions (PDRs) in nine reflection nebulae. Theseobservations include the far-infrared atomic fine-structure lines of [OI] 63 and 145 μm, [C II] 158 μm, and [Si II] 35 μm and theadjacent far-infrared continuum to these lines. Our analysis of thesefar-infrared observations provides estimates of the physical conditionsin each reflection nebula. In our sample of reflection nebulae, thestellar effective temperatures are 10,000-30,000 K, the gas densitiesare 4×102-2×104 cm-3, thegas temperatures are 200-690 K, and the incident far-ultravioletintensities are 300-8100 times the ambient interstellar radiation fieldstrength (1.2×10-4 ergs cm-2 s-1sr-1). Our observations are compared with current theory forlow-excitation PDRs. The [C II] 158 μm to [O I] 63 μm line ratiodecreases with increasing incident far-ultraviolet intensity. This trendis due in part to a positive correlation of gas density with incidentfar-ultraviolet intensity. We show that this correlation arises from abalance of pressure between the H II region and the surrounding PDR. The[O I] 145 to 63 μm line ratio is higher (greater than 0.1) thanpredicted and is insensitive to variations in incident far-ultravioletintensity and gas density. The stellar temperature has little effect onthe heating efficiency that primarily had the value3×10-3, within a factor of 2. This result agrees with amodel that modifies the photoelectric heating theory to account forcolor temperature effects and predicts that the heating efficiencieswould vary by less than a factor of 3 with the color temperature of theilluminating field. In addition to the single-pointing observations, an[O I] 63 μm scan was done across the molecular ridge of one of oursample reflection nebulae, NGC 1977. The result appears to supportprevious suggestions that the ionization front of this well-studied PDRis not purely edge-on.
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Herbig Ae/Be stars with the IRAS low-resolution spectra.|
|High-Resolution Far-Infrared Studies of Intermediate-Mass Pre-Main-Sequence Objects|
We have obtained high-resolution far-infrared maps of nine regions with10 Herbig Ae/Be stars (intermediate-mass pre-main-sequence stars).Similar maps were obtained for 10 embedded IRAS sources with S_nu(100μm) > S_nu(60 μm) and L ~ 200 L_ȯ, which are possibleevolutionary precursors of Herbig Ae/Be stars. Single far-infraredsources were found in most maps. The embedded sources have positions inagreement with those of the IRAS PSC, but some of the Herbig Ae/Be starsare offset significantly from the position of peak far-infraredemission. For all objects where it was possible to obtain 100 μm fluxdensities, they are consistent with those observed by IRAS, but derived50 μm flux densities are larger than expected. The far-infrared mapsreveal that objects in at least 17 of 19 emission regions aresignificantly extended at the 30"-40" resolution of the Kuiper AirborneObservatory at 100 mum. Only sources associated with AB Aur and possiblyIRAS 05338-0624 have unresolved far-infrared emission. Detailed analysesof the flux densities and positions from our maps suggest thefar-infrared emission in regions with Herbig Ae/Be stars may notimmediately surround these stars in all cases. Instead, far-infraredemission from these objects may originate from dust heated externally bythe Herbig stars, or from dust heated internally by other sources. Forother objects arguably surrounded by far-infrared emission, the Herbigstars or embedded IRAS objects have similar mean deconvolved sizes(i.e., 0.10-0.15 pc), but possibly have different mean deconvolvedshapes (i.e., aspect ratios). Thus, far-infrared emission here mayoriginate from flattened dust envelopes; the appearance of afar-infrared object as either a Herbig Ae/Be star or an embedded IRASsource may be merely a matter of viewing orientation.
|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.
|A new CO survey of the Monoceros OB1 region.|
A new, fully sampled, sensitive CO survey of 52.5 square degrees towardsthe Monoceros OB1 (Mon OB1) region has been completed using the CfA 1.2m millimeter-wave radio telescope. This survey extends from b=-1.5°to b=+3.5° and from l=196.0° to l=206.5° on a uniformlyspaced grid of 3.75' in l and b, and has substantially bettersensitivity than previous surveys of the region. CO is detected in 80%of the area, 60% of which is weak with integrated intensities less than5K.km/s. The large-scale kinematics are dominated by the Perseus andLocal spiral arms. Within the Local arm the molecular gas appears tohave been strongly influenced by supernova remnants and expanding HIIregions with the strongest emission at velocities ranging from -17 to+10km/s, and a total mass of 1.3x10^5^Msun_. Weak CO emissionfrom Perseus arm clouds shows that they have a mean kinematic distanceof 3.5kpc and are comparable in size and mass to local molecular clouds.The coincident positions of colour selected IRAS point sources indicatesthat these distant clouds are undergoing massive star formation.
|Spectroscopic observations of parsamian 21|
This work presents spectroscopic observations of Parsamian 21, which hasbeen shown recently by Staude and Neckel to be a fuor-type star. A listof identified absorption lines is given. The results are compared withprevious spectroscopic observations over the period 1966-1990. It isshown that the H line profile changed during this period; according tothe observations of 1986, the center of the H absorption line wasshifted by -140 km/sec from 0 and reached -600 km/sec at the line edge.It follows from the presented lightcurve that the star has undergonebrightness variations of nearly three magnitudes and most likely becamea fuor before 1902.
|A search for precursors of ultracompact HII regions in a sample of luminous IRAS sources. I. Association with ammonia cores.|
We present observations of NH_3_ (1,1) and (2,2) lines in twoflux-limited samples of IRAS sources selected according to colourcriteria which should result in a high fraction of Young StellarObjects. The first sample contains sources (named 'Low') whoseevolutionary status is essentially unknown, while the second samplecontains sources (named 'High') possibly associated with ultracompactHII regions, the distinction being based on the IRAS [25-12] colour.Indications from a previous study of H_2_O maser emission suggest thatthe sources in the first group may be in an evolutionary phase prior tothe appearance of an HII region, thus being among the youngest knownhigh-mass forming objects. Low sources were detected in ammonia with alower rate than High sources (45% and 80% respectively); the onlydifference between the two groups is in the linewidths: the (1,1) linesare generally narrower than (2,2) lines in High sources (FWHMs medianvalues are 1.81km/s and 2.00km/s respectively), while the opposite istrue in Low sources (FWHMs median values are 1.72km/s and 1.33km/s forthe (1,1) and (2,2) lines respectively). We propose that the Low groupconsists of two distinct populations of evolutionary different objects,based on the (non-) association with ammonia emission. The Low sourcesshowing ammonia emission are characterized by more quiescent envelopesthan those surrounding High sources, and the relationships betweenrelevant physical quantities derived from our observations and the IRAScolours suggest that High sources, contrary to Low, may harbour objectswhich dominate the physical and dynamical properties of the clump, thuspossibly implying the relative youth of this subgroup of the Lowsources.
|Discovery of Three Radio Pulsars from an X-Ray--selected Sample|
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...456..305Z
|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.
|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.
|Early-type emission-line stars with large infrared excesses|
A catalog is presented of early-type emission-line stars obtained bycross-identification between Wackerling's catalog and the IRAS catalogof point sources. A study of the distribution in space of the starsshows that these stars belong to the extreme Population I; thus thepresent compilation provides a rather complete sample for further studyof the evolution of pre- and post-main sequence stars of medium and highmasses.
|Water masers associated with dense molecular clouds and ultracompact H II regions|
Results are reported from a study surveying the occurrence of the H2O22GHz maser emission from bright IR sources in star-forming regions. Asample of 260 sources was selected from the IRAS Point Source Catalog,following the color selection criteria suggested by Richards et al.(1987), to identify dense molecular clouds where star formation might beat the earliest stages. Water vapor emission toward 32 sources wasdetected. Twelve new maser sources were found, all characterized byrather low integrated fluxes and narrow components. On the basis of FIRcolor indices and the maser detection rates, and from a comparison withother classes of objects, it is suggested that the sources included inthe sample not associated with ultracompact H II regions contain a highfraction of candidate molecular clouds with embedded high massprotostars still in the accretion phase.
|The young open clusters NGC 2244 and NGC 2264|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1991RMxAA..22...99P&db_key=AST
|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.
|Structure of molecular clouds around some pre-main sequence stars associated with cometary nebulae|
|Emission From Dust in Visual Reflection Nebulae at Infrared and Submilimeter Wavelengths|
|A survey of infrared features in H II regions, planetary nebulae and proto-planetary nebulae from the IRAS-LRS data base|
The paper reports systematic investigation of IR emission and absorptionfeatures in H II regions, planetary nebulae, and protoplanetary nebulaefrom the IRAS-Low Resolution Spectra data base. The resulting selectionconstitutes a new data base (containing 284 sources) which iscomplemented by all published lines in the range 2-20 microns.Information on atomic, molecular, and solid state material is provided.A preliminary analysis of the data set is presented, emphasizing the PAHemission features.
|IRAS sources beyond the solar circle. I - CO observations|
C-12O (J = 1-0) has been observed with the 15-m SEST and the 30-m IRAMtelescope in the direction of 1302 IRAS sources with colors of starforming regions located within 10 deg of the galactic plane in theinterval between 85 and 280 deg. Emission components with line profilesthat are non-Gaussian (showing, e.g., possible self-absorption or wings)are identified; this information may serve as a basis for selectingsources for future research. For all components, kinematic heliocentricand galactocentric distances, and distances from the galactic plane arederived. For those components which may be associated with the IRASsources, bolometric luminosities are derived. These data will beanalyzed and compared with HI data in subsequent papers.
|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.
|Observations of bipolar nebulae and associated stars|
The paper presents optical linear polarization maps of the nebulae NGC2245 and NGC 2247 and UBVRI and UBVRIJHK photometric measurements of thestars Lk H-alpha 215 and HDE 29431 which indicate the existence ofcircumstellar envelopes. The polarimetric variability of Lk H-alpha 215with a characteristic time of several days and of HDE 259431 on a timescale of several hours was observed. The possible nature of theseobjects is considered.
|Reflection Nebulae of Mon R1 in the Far-Infrared and Submillimeter|
|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.
|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.
|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.
|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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