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The Initial Mass Functions of Four Embedded Stellar Clusters
We present near-infrared J, H, and K images of four embedded stellarclusters in the Galaxy. We find a significant fraction ofpre-main-sequence stars present in at least one of the clusters. For theclusters dominated by main-sequence stars, we determine the initial massfunction (IMF) both by using the K luminosity function and a globalextinction correction and by deriving individual extinction correctionsfor each star based on their placement in the K versus H-Kcolor-magnitude diagram. Based on our IMFs we find a significantdiscrepancy between the mean IMF derived via the different methods,suggesting that taking individual extinctions into account is necessaryto correctly derive the IMF for an embedded cluster.
| Abundance Gradients in the Galaxy
Six H II regions at galactocentric distances of R=10-15 kpc have beenobserved in the far-IR emission lines of [O III] (52 μm, 88 μm),[N III] (57 μm), and [S III] (19 μm) using the Kuiper AirborneObservatory. These observations have been combined with Very Large Arrayradio continuum observations of these sources to determine theabundances of O++, N++, and S++relative to hydrogen. In addition, eight of the most recent sets ofmeasurements of ionic line strengths in H II regions have beenreanalyzed in order to attempt to reconcile differences in opticalversus far-IR abundance determinations. We have in total 168 sets ofobservations of 117 H II regions in our analysis. The new analysisincluded updating the atomic constants (transition probabilities andcollision cross sections), recalculation of some of the physicalconditions in the H II regions (ne and Te), andthe use of new photoionization models to determine stellar effectivetemperatures of the exciting stars. We also use the most recent dataavailable for the distances for these objects, although for most westill rely on kinematic distance determinations. Our analysis findslittle indication of differences between optical and infraredobservations of the nitrogen abundances, but some differences are seenin the oxygen and sulfur abundances. A very significant offset continuesto be seen between optical and infrared measurements of the N/Oabundance ratio.
| Detection of SiO Maser Emission in V838 Mon
We report on the detection of 43GHz SiO maser emission in V838 Mon, aprototype of a new class of eruptive variables, in which a redsupergiant was formed after a nova-like eruption in 2002. The detectionof SiO masers indicates that the star formed after the eruption isindeed a kind of cool mass-losing object with circumstellar masers. Themeasured radial velocity and the intensity of maser emission areconsistent with the object being located at a distance of about 7kpcfrom the sun. It also suggests that a considerable percentage of SiOmasing objects in the Galaxy are formed by the same mechanism as thatwhich created V838 Mon.
| On the progenitor of V838 Monocerotis
We summarize and analyze the available observational data on theprogenitor and the environment of V838 Mon. From the availablephotometric data for the progenitor of V838 Mon we exclude thepossibility that the object before eruption was an evolved red giantstar (AGB or RGB star). We find that most likely it was a main sequenceor pre-main sequence star of 5-10~ Mȯ. From thelight echo structure and evolution we conclude that the reflecting dustis of interstellar nature rather than blown by V838 Mon in the past. Wediscuss the IRAS and CO data for interstellar medium observed near theposition of V838 Mon. Several interstellar molecular regions have radialvelocities similar to that of V838 Mon, so dust seen in the light echomight be related to one of them.
| 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.
| Determination of temperature of the ionizing stars of H II regions
The determination of temperature (T_eff) of the ionizing stars of H Iiregions was considered. In this work we used photoionization models forH Ii regions ionized by a single star to show that the index R=log ([OIi]lambda lambda 3726+3729/[O Iii]lambda 5007) can be used to estimateT_eff. The relation R vs. T_eff proved to be rather independent of thechemical abundances, but strongly dependent on the ionization parameterof the nebula. In order to check the reliability of using R fortemperature determination, we compared the values of T_eff obtained viathe index R for a sample of H Ii regions with data available in theliterature with independent estimations.
| 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
| New infrared star clusters and candidates in the Galaxy detected with 2MASS
A sample of 42 new infrared star clusters, stellar groups and candidateswas found throughout the Galaxy in the 2MASS J, H and especiallyKS atlases. In the Cygnus X region 19 new clusters, stellargroups and candidates were found as compared to 6 such objects in theprevious literature. Colour-Magnitude Diagrams using the 2MASS PointSource Catalogue provided preliminary distance estimates in the range1.0 < dsun < 1.8 kpc for 7 Cygnus X clusters. Towardsthe central parts of the Galaxy 7 new IR clusters and candidates werefound as compared to 61 previous objects. A search for prominent darknebulae in KS was also carried out in the central bulge area.We report 5 dark nebulae, 2 of them are candidates for molecular cloudsable to generate massive star clusters near the Nucleus, such as theArches and Quintuplet clusters.
| An Empirical Test and Calibration of H II Region Diagnostics
We present spectrophotometry in the 3600-9700 Å region for asample of 39 H II regions in the Galaxy and Magellanic Clouds, for whichindependent information is available on the spectral types and effectivetemperatures of the ionizing stars. The spectra have been used toevaluate nebular diagnostics of stellar temperature, metal abundance,and ionization parameter, and to compare the observed behavior of theline indices with predictions of nebular photoionization models. Weobserve a strong degeneracy between forbidden-line sequences produced bychanges in stellar Teff and metal abundance, which severelycomplicates the application of many forbidden-line diagnostics toextragalactic H II regions. Our data confirm however that the Edmunds& Pagel [O II]+[O III] abundance index and the Vílchez &Pagel η' index provide more robust diagnostics of metalabundance and stellar effective temperature, respectively. A comparisonof the fractional helium ionization of the H II regions with stellartemperature confirms the reliability of the spectral type versusTeff calibration for the relevant temperature rangeTeff<=38,000 K. We use empirical relations between thenebular hardness indices and Teff to reinvestigate the casefor systematic variations in the stellar effective temperatures and theupper initial mass functions of massive stars in extragalactic H IIregions. The data are consistent with a significant softening of theionizing spectra (consistent with cooler stellar temperatures) withincreasing metal abundance, especially for Z<=Zsolar.However, unresolved degeneracies between Z and Teff stillcomplicate the interpretation of this result.
| Calibration of Nebular Emission-Line Diagnostics. I. Stellar Effective Temperatures
We present a detailed comparison of optical H II region spectra tophotoionization models based on modern stellar atmosphere models. Weexamine both spatially resolved and integrated emission-line spectra ofthe H II regions DEM L323, DEM L243, DEM L199, and DEM L301 in the LargeMagellanic Cloud. The published spectral classifications of the dominantstars range from O7 to WN3, and morphologies range from Strömgrensphere to shell structure. Two of the objects include SNR contamination.The overall agreement with the predictions is generally within 0.2 dexfor major diagnostic line ratios. An apparent pattern in the remainingdiscrepancies is that the predicted electron temperature is ~1000 Khotter than observed. [Ne III] intensities are also slightlyoverpredicted, which may or may not be related. We model the shockemission for the SNR-contaminated objects and find excellent agreementwith the observations for composite shock and photoionized spectra. DEML301's emission apparently results from both shocks and density-boundedphotoionization. The existence of contaminating shocks can be difficultto ascertain in the spatially integrated spectra. Our analysis of thecomplex DEM L199 allows a nebular emission-line test of unprecedenteddetail for WR atmospheres. Surprisingly, we find no nebular He IIλ4686 emission, despite the fact that both of the dominant WN3stars should be hot enough to fully ionize He I in their atmospheres.The nebular diagnostics are again in excellent agreement with the data,for stellar models not producing He+-ionizing photons. Theoptical diagnostics are furthermore quite insensitive to the ionizingenergy distribution for these early WR stars. We confirm that the η'emission-line parameter is not as useful as hoped for determining theionizing stellar effective temperature, T*. Both empiricallyand theoretically, we find that it is insensitive forT*>~40 kK and that it also varies spatially. Theshock-contaminated objects show that η' will also yield a spuriouslyhigh T* in the presence of shocks. It is furthermoresensitive to shell morphology. We suggest [Ne III]/Hβ as anadditional probe of T*. Although it is abundance dependent,[Ne III]/Hβ has higher sensitivity to T*, is independentof morphology, and is insensitive to shocks in our objects. Theseobservations should be useful data points for a first empiricalcalibration of nebular diagnostics of T*, which we attemptfor LMC metallicity.
| Internal variation of electron density in galactic Hbt II regions
A study on the internal variation of the electron density in galactic HIi regions has been conducted on a sample of 15 objects of differentsizes and evolutionary stages. The [S Ii] lambda 6716/lambda 6731 lineratio was adopted as electron density indicator. Long slitspectrophotometry of high signal-to-noise ratio with spectral dispersionof 0.75 Ä,pxl-1 and spatial scale of 0\farcs90pxl-1 were obtained at different slit positions andorientations. No systematic spatial variation of electron density wasdetected in nearly half of the objects studied (S255, S 257, S 271,S 285, S 301, S305, NGC 3372 and IC1275). They are in general the most diffuse and probablyevolved objects with low mean densities in the range Ne ~20-140 cm-3. The remaining objects (S 288,S 307, NGC 2579, NGC3503, Gum 62, Gum 64aand M 20) with mean densities Ne ~ 80-360cm-3, have shown a statistically significant electron densitydependence on position. In most of these cases, the spatial variation ofdensity may be interpreted as a radial gradient with the densitydecreasing from the centre to the edges. M 20 shows asystematic non-radial variation of electron density with maximum valuesoccurring at its prominent dark lanes. A mean filling factor of theorder of phi = 0.1 was found compatible with the data. Based on theirdensity profiles, NGC 2579, Gum62, Gum 64a and possibly NGC3503 were indicated as candidates of showing a `champagneflow'.
| Far-Infrared Abundance Measurements in the Outer Galaxy
Five H II regions at large distances from the center of the Galaxy (R =13-17 kpc) have been observed in the far-IR emission lines of [O III](52 and 88 mu m), [N III] (57 mu m), and [S III] (19 mu m) using theKuiper Airborne Observatory. These observations have been combined withVery Large Array radio continuum observations of these sources todetermine the abundances of O++, N++, and S++ relative to hydrogen. Asimple ionization correction scheme has been used to determine the totalabundances of nitrogen and sulfur relative to hydrogen, as well as therelative abundance N/O. For the two sources in common with previousoptical studies (S127 and S128), we find good agreement between thefar-infrared and optical determinations of N/H, S/H, and N/O. Ourresults from the outer Galaxy have been combined with previousfar-infrared results to determine the abundance gradient of theseelements in the Milky Way over a range of Galactocentric radii from R =0 to R = 17 kpc. Our results are consistent with a gradient of log N/H =-0.111 +/- 0.012 dex kpc-1 and a gradient of log S/H = -0.079 +/- 0.009dex kpc-1. Our method is not able to determine independently theabundances of both S and O, although other evidence suggests that theO/S ratio is approximately constant. While these results differ fromrecent optical studies, which suggest that these abundance gradientsflatten in the outer Galaxy, we do not yet have sufficient data to ruleout such a change in the gradient. The log N/O data are better fitted bya two-step function with a value of -0.50 +/- 0.02 for R < 6.2 kpcand -0.83 +/- 0.04 for R > 6.2 kpc. Both of these values areconsistent with secondary production of nitrogen. However, the outerGalaxy oxygen abundances are in the low abundance regime where nitrogenis expected to be produced by primary processes.
| Far Outer Galaxy H II Regions
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...458..653R
| The distance of the sun from the Galactic Center and the rotation curve from kinematic HI and HII data.
Not Available
| The Velocity Field of the Outer Galaxy
Abstract image available at:http://adsabs.harvard.edu/abs/1993A&A...275...67B
| A VLA survey of optically visible galactic H II regions
Radio continuum observations of 109 optically visible Galactic H IIregions were obtained with the Very Large Array. Contour plots of theimages of those that were well resolved and tables of radio continuumflux density for all detected objects are presented. The measured totalflux densities matched well with the results of single-dish surveys, andthus it is expected that the problem of missing 'zero-spacing flux' hasnot contributed greatly to the morphologies seen in the resultingimages. The relative numbers of objects of each morphological type werevery similar to the numbers seen in the survey of ultracompact H IIregions by Wood and Churchwell (1989) even though the objects in thisnew survey are on average 50 times larger (in radius) and thereforepresumably more evolved.
| Small Galactic H II regions. III - Images and spectrophotometry of the ionized gas
Narrow-band H-alpha and N II images and long-slit and aperturespectroscopy are presented for a sample of small Galactic H II regionslocated from 6 to 15 kpc from the Galactic center. Emission-line fluxesare measured from H-beta to S II 6717,31 for selected areas throughouteach nebula. Reddening is determined from the ratio of H-alpha to H-betaand density from the ratio of the S II lines. Abundances of S(+), N(+),and O(2+) relative to H(+) are determined for those regions for whichelectron temperatures exist in the literature. Variations of OIII/H-beta, N II/H-alpha, S II/H-alpha, and N II/S II within the nebulaeand from nebula to nebula as a function of distance from the enter ofthe Galaxy are examined. The status of the H II regions and theirrelationship to the molecular clouds are briefly discussed. These dataprovide a useful data base for studies of the interaction between H IIregions and their natal clouds, studies of the evolution of H IIregions, and studies of variations of elements and physical conditionswithin the Galaxy.
| VY Monocerotis and the IC 446 region - Far-infrared and submillimeter images of a massive young stellar object and its environment
The reflection nebulae IC 446 has been mapped in an 8 x 8-arcmin area at100, 160, and 370 microns using 32-channel bolometer-array detectors onthe 0.9-m telescope of the NASA Kuiper Airborne Observatory and the 3-mtelescope of the NASA Infrared Telescope Facility. These data have beencombined with IRAS profiles at 12, 25, 60, and 100 microns toinvestigate the morphology and energetics of the region. The FIR throughsubmm emission in the neighborhood of IC 446 is composed of threecomponents: a compact point source associated with the young stellarobject VY Mon, warm extended emission associated with dust in thereflection nebula IC 446, and cold extended emission associated with adark absorption nebula or globule.
| Small Galactic H II regions. I - Spectral classifications of massive stars
By studying the stellar content of star-forming regions with differentcharacteristics, such as gas cloud size, one can determine factors thataffect the star-formation process. This paper is part of a study of thestellar content and natal cloud characteristics of a sample ofrelatively small Galactic star-forming regions. Spectral classificationsbased on moderate dispersion spectra of the optically visible stars inthe regions are presented. The H-alpha, radio, and far-infraredluminosities of the nebulas are used as a check for additional embeddedor unidentitied hot stars. A histogram of the most massive star perstar-forming unit shows that there is a range in upper mass limits forthe sample and that one is statistically sampling a mass functionintermediate between that of Selpeter and that of Miller-Scalo.
| The rotation curve of the Milky Way to 2 R(0)
A unified analysis of the Galactic rotation curve is presented using H ICO, and spectrophotometric data obtained in the northern hemisphere areused to determine the rotation curve from R = 3-17 kpc. A number ofdifferent functional forms are examined to fit the data, and the errorsand uncertainties that go into its determination are discussed. Theresults are compared with nine recent studies of the rotation curve, andspecific recommendations are made on the choice of curves to use inkinematic studies and mass modeling.
| Kinematics of star forming regions
The cubic approximation of a general two-dimensional velocity field isused to study the radial velocities of 218 star forming regions up to 10kpc from the sun. It is found that departures from the Galactic circularflow are generally related to complexes of star forming regions 1-2 kpcin size. It is suggested that complexes are a consequence of clumpedstar formation and subsequent expansion of multisupernova remnants. Theresults imply that the negative departure from circular motion observedin complexes P(1)-P(4) may be due to the influence of the Perseus spiralarm.
| The galactic rotation outside the solar circle
New photometric and spectroscopic observations of the exciting stars ofgalactic HII regions are presented. Combining the derived distances withthe radial velocities of the regions gives evidence for a risingrotation curve beyond the solar circle.
| Optical H II regions in the outer galaxy
The results of the CO survey of optical H II regions of Blitz, Fich, andStark (1982) are used to obtain the distribution of H II regions andtheir associated molecular clouds beyond the solar circle. H II regionsare observed in the Milky Way to distances as large as R = 20 kpc, butthere are very few beyond this distance. This limiting distance does notappear to be the result of extinction and appears to be the approximateedge of the stellar disk of the Galaxy. The scale height of H II regionsat 10 kpc is about 100 pc as measured by the z distance dispersion, butthere is considerable variation in this quantity. The smallest scaleheights appear to be related to the major spiral arms. Beyond 12 kpc theH II regions follow the warp of the H I plane. H II regions are smalleron average at large R and few very large H II regions are observedbeyond 12 kpc.
| Exciting stars and the distances of the diffuse nebulae
Not Available
| Spectrophotometric Studies of Galactic Nebulae - Part Twenty-One - the Nebula SH:2-288 and its Ionizing Star
Not Available
| Catalog of CO radial velocities toward galactic H II regions
This is a catalog of 242 molecular cloud complexes which are associatedwith optical H II regions. CO observations were made toward all but fiveof the H II regions in the Sharpless catalog and toward 62 additionalsuspected H II regions, 33 of which are previously uncataloged. Radialvelocities are tabulated for each molecular cloud complex found to beassociated with an H II region. The CO antenna temperature and linewidth are given for the most intense CO line seen toward each source.The catalog also summarizes previous CO observations as well as theoptical distances to the stars exciting the H II regions. Radio-quiet HII regions (those with 1.4 GHz flux densities less than 100 mJy) arefound to be well correlated with objects having no associated CO. A listof kinematically distinct complexes is tabulated to facilitateinvestigations of the motions of the complexes.
| A High Resolution Search for Small-Scale Structure in Sharpless HII Regions at 4.995-GHZ - Part Three - Description of Selected Sources
Abstract image available at:http://adsabs.harvard.edu/abs/1981A&A...100...42F
| A high-resolution search for small-scale structure in Sharpless H II regions at 4.995 GHz. II - General properties of the entire sample. III - Description of selected sources
A statistical study is presented of the properties of a sample of 75optically visible H II regions from the Sharpless Catalog observed at afrequency of 4.994 GHz by the Westerbork Synthesis Radio Telescope, andthe most interesting small-diameter H II components detected in thesurvey are discussed in detail. The optical and radio properties of theregions are compared, and results are presented of high-andlow-resolution observations. The nebulae are divided into five classesaccording to optical morphology and the presence of obscuration, whichclasses can be interpreted as representing subsequent evolutionarystages of a single H II region. It is also found that the change of theelectron density due to H II region expansion occurs at a higher ratefor H II regions ionized by stars of an earlier spectral type, and thatthe rate of change of the mean electron density for a given type isapproximately hyperbolic. Small-diameter, high-density components arefound preferentially in small, isolated nebulae with high mean electrondensities, while the ratio of the Lyman continuum flux contained in thesmall-diameter component to that contained in the entire H II regioncorrelates with the mean density of the region. Of the 22 objectsdiscussed individually, 12 can be classified as compact H II regionswith an internal source of excitation, and the remaining sources can beattributed to increases in the electron density at ionization frontslocated at the edges of dense molecular clouds. From an analysis ofradio, infrared and molecular line observations of several sources, itis concluded that a single early-type star embedded in the H II regionin the presence of dust can be the energy source of the observedemission.
| The rotation and structure of the galaxy beyond the solar circle. I - Photometry and spectroscopy of 276 stars in 45 H II regions and other young stellar groups toward the galactic anticentre
Abstract image available at:http://adsabs.harvard.edu/abs/1979A&AS...38..197M
| Molecular observations of the Sharpless H II region S 228
Carbon monoxide and formaldehyde observations of the Sharpless H IIregion S 228 are presented. A cold (10 K) molecular cloud with H2density of about 350 per cu cm and a mass of about 2000 solar masses hasbeen mapped next to this H II region, which itself coincides with ahigher density and hotter region. A CO profile in the direction of S 288is also presented.
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