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3He in the Milky Way Interstellar Medium: Ionization Structure
The cosmic abundance of the 3He isotope has importantimplications for many fields of astrophysics. We are using the 8.665 GHzhyperfine transition of 3He+ to determine the3He/H abundance in Milky Way H II regions and planetarynebulae. This is one in a series of papers in which we discuss issuesinvolved in deriving accurate 3He/H abundance ratios from theavailable measurements. Here we describe the ionization correction weuse to convert the 3He+/H+ abundance,y+3, to the 3He/H abundance,y3. In principle the nebular ionization structure cansignificantly influence the y3 derived for individualsources. We find that in general there is insufficient informationavailable to make a detailed ionization correction. Here we make asimple correction and assess its validity. The correction is based onradio recombination line measurements of H+ and4He+, together with simple core-halo sourcemodels. We use these models to establish criteria that allow us toidentify sources that can be accurately corrected for ionization andthose that cannot. We argue that this effect cannot be very large formost of the sources in our observational sample. For a wide range ofmodels of nebular ionization structure we find that the ionizationcorrection factor varies from 1 to 1.8. Although larger corrections arepossible, there would have to be a conspiracy between the density andionization structure for us to underestimate the ionization correctionby a substantial amount.
| The Origin and Motion of PSR J0538+2817 in S147
We report on Very Long Baseline Array (VLBA) astrometry and Chandraimaging of PSR J0538+2817 in the supernova remnant S147. We measure aparallax distance of 1.47+0.42-0.27 kpc along witha high-precision proper motion, giving a transverse velocityV⊥=400+114-73 km s-1. Asmall extended wind nebula is detected around the pulsar; the symmetryaxis of this structure suggests that the spin axis lies12deg+/-4deg from the velocity vector(two-dimensional), but the emission is too faint for robustmodel-independent statements. The neutron star is hot, consistent withthe young ~40 kyr kinematic age. The pulsar progenitor is likely arunaway from a nearby cluster, with NGC 1960 (M36) a leading candidate.
| Anomalous H2CO Absorption toward the Galactic Anticenter: A Blind Search for Dense Molecular Clouds
We have carried out a blind search in the general direction of theGalactic anticenter for absorption of the cosmic microwave background(CMB) radiation near 4.83 GHz by molecular clouds containing gaseousortho-formaldehyde (H2CO). The observations were done usingthe 25 m radio telescope at Onsala in Sweden and covered strips inGalactic latitude -1deg<=b<=+1deg at severallongitudes in the region 170deg<=l<=190deg.Spectra were obtained in these strips with a grid spacing correspondingto the telescope resolution of 10'. We have detected H2CO CMBabsorption at ~10% of the survey pointings. This detection rate islikely to increase with further improvements in sensitivity and maybecome comparable to the detection rate expected from a blind CO surveywith a corresponding sensitivity limit. We have mapped some of thesedetections in more detail and compared the H2CO absorption toexisting maps of CO(1-0) emission in the same regions. There appears tobe a rough correlation between the velocity-integrated line strength ofthe CO(1-0) emission and that of the H2CO absorption.However, the scatter in this correlation is significantly larger thanthe measurement errors, indicating differences of detail at and belowthe linear resolution of our observations (~4-9 pc). Although these twotracers are expected to have similar excitation requirements on themicroscopic level characteristic of warm (TK>10 K) dense(103 cm-3
| New T Tauri Stars Associated with IRAS 05555-1405
We present for the first time medium resolution(Δλ/λ = 1320 Å) slit spectroscopy and MKclassifications for the brightest stars that comprise the stellartrapezium associated with IRAS point source IRAS 05555-1405, in thevdB64 reflection nebula. The five brightest members of the trapezium arefound through their LiI λ 6708 feature to be pre-main sequence(PMS) stars. Our data are compared with those of the near infrared (NIR)2 Micron All Sky Survey (2MASS) which confirms our results.
| Radio Recombination Lines in Galactic H II Regions
We report radio recombination line (RRL) and continuum observations of asample of 106 Galactic H II regions made with the NRAO 140 Foot (43 m)radio telescope in Green Bank, West Virginia. We believe this to be themost sensitive RRL survey ever made for a sample this large. Most of oursource integration times range between 6 and 90 hr, yielding typical rmsnoise levels of ~1.0-3.5 mK. Our data result from two differentexperiments performed, calibrated, and analyzed in similar ways. A C IIsurvey was made at the 3.5 cm wavelength to obtain accurate measurementsof carbon radio recombination lines. When combined with atomic (C I) andmolecular (CO) data, these measurements will constrain the composition,structure, kinematics, and physical properties of the photodissociationregions that lie on the edges of H II regions. A second survey was madeat the 3.5 cm wavelength to determine the abundance of 3He inthe interstellar medium of the Milky Way. Together with measurements ofthe 3He+ hyperfine line, we get high-precision RRLparameters for H, 4He, and C. Here we discuss significantimprovements in these data with both longer integrations and newlyobserved sources.
| Kinematics of the Open Cluster System in the Galaxy
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
| A multiwavelength study of the massive star-forming region IRAS 06055+2039 (RAFGL 5179)
Aims.We present a multiwavelength study of the massive star-formingregion associated with IRAS 06055+2039. Methods: .Narrow-bandnear-infrared (NIR) observations were carried out with UKIRT-UFTI inmolecular hydrogen and Brγ lines to trace the shocked and ionizedgases, respectively. We have used 2MASS {J H K}s data tostudy the nature of the embedded cluster associated with IRAS06055+2039. The radio emission from the ionized gas was mapped at 610and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India.Emission from warm dust and the unidentified infrared bands (UIBs) wasestimated using the mid-infrared (8-21 μm) data from the MSX survey.Submillimetre emission from the cold dust at 450 and 850 μm wasstudied using JCMT-SCUBA. Results: .For the infrared clusterassociated with IRAS 06055+2039, we obtain a power-law slope of0.43±0.09 for the K_s-band luminosity function (KLF), which is ingood agreement with other young embedded clusters. We estimate an age of2-3 Myr for this cluster. Apart from the diffuse emission, thehigh-resolution 1280 MHz map also shows the presence of several discretesources that possibly represent high-density clumps. The morphology ofshocked molecular hydrogen forms an arc towards the N-E of the centralIRAS point source and envelopes the radio emission. Submillimetreemission shows the presence of a dense cloud core that is probably at anearlier evolutionary stage compared to the ionized region with shockedmolecular gas lying between the two. The total mass of the cloud isestimated to be 7000-9000 Mȯ from the submillimetreemission at 450 and 850 μm. Conclusions: .The multiwavelengthstudy of this star-forming complex reveals an interesting scenario whereregions are at different stages in the evolution of star formation.
| A ``Missing'' Supernova Remnant Revealed by the 21 cm Line of Atomic Hydrogen
Although some 20,000-30,000 supernova remnants (SNRs) are expected toexist in the Milky Way, only about 230 are currently known. This impliesthat most SNRs are ``missing.'' Recently, we proposed that small(<~1°), faint, high-velocity features seen in large-scale 21 cmline surveys of atomic hydrogen (H I) in the Galactic plane could beexamples of such missing old SNRs. Here we report on high-resolution H Iobservations of one such candidate, FVW 190.2+1.1, which is revealed tobe a rapidly expanding (~80 km s-1) shell. The parameters ofthis shell seem only consistent with FVW 190.2+1.1 being the remnant ofa SN explosion that occurred in the outermost fringes of the Galaxy some~3×105 yr ago. This shell is not seen in any other waveband, suggesting that it represents the oldest type of SNR, that whichis essentially invisible except via its H I line emission. FVW 190.2+1.1is one of a hundred ``forbidden-velocity wings'' (FVWs) recentlyidentified in the Galactic plane, and our discovery suggests that manyof these are likely to be among the oldest SNRs. We discuss the possiblelink between FVWs and fast-moving atomic clouds in the Galaxy.
| Star formation associated with H II regions
Star formation associated with H II regions is briefly reviewed. Specialemphasis is laid on our series of observational studies on bright-rimmedclouds (BRCs), in which we found a phenomenon called "small-scalesequential star formation." In addition a new hypothesis is advocated onthe two modes of star formation associated with H II regions, i.e., thecluster and dispersed modes. The former gives birth to a rich clusterand in the associated H II region BRCs are formed only at a later stageof its evolution in the peripheries. In the latter mode no clusters oronly loose ones are formed, but BRCs can appear at earlier stages ininner part of the H II region. Presumably these modes depend on theinitial density distribution of the natal molecular cloud.
| 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.
| Proper motion determination of open clusters based on the UCAC2 catalogue
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
| O stars with weak winds: the Galactic case
We study the stellar and wind properties of a sample of Galactic Odwarfs to track the conditions under which weak winds (i.e. mass lossrates lower than 10-8 Mȯ yr-1)appear. The sample is composed of low and high luminosity dwarfsincluding Vz stars and stars known to display qualitatively weak winds.Atmosphere models including non-LTE treatment, spherical expansion andline blanketing are computed with the code CMFGEN (Hillier & Miller1998, ApJ, 496, 407). Both UV and Hα lines are used to derive windproperties while optical H and He lines give the stellar parameters. Wefind that the stars of our sample are usually 1 to 4 Myr old. Mass lossrates of all stars are found to be lower than expected from thehydrodynamical predictions of Vink et al. (2001, A&A, 369, 574). Forstars with log {L}/{Lȯ} 5.2, the reduction is byless than a factor 5 and is mainly due to the inclusion of clumping inthe models. For stars with log {L}/{Lȯ} 5.2 thereduction can be as high as a factor 100. The inclusion of X-rayemission (possibly due to magnetic mechanisms) in models with lowdensity is crucial to derive accurate mass loss rates from UV lines,while it is found to be unimportant for high density winds. The modifiedwind momentum - luminosity relation shows a significant change of slopearound this transition luminosity. Terminal velocities of low luminositystars are also found to be low. Both mass loss rates and terminalvelocities of low L stars are consistent with a reduced line forceparameter α. However, the physical reason for such a reduction isstill not clear although the finding of weak winds in Galactic starsexcludes the role of a reduced metallicity. There may be a link betweenan early evolutionary state and a weak wind, but this has to beconfirmed by further studies of Vz stars. X-rays, through the change inthe ionisation structure they imply, may be at the origin of a reductionof the radiative acceleration, leading to lower mass loss rates. Abetter understanding of the origin of X-rays is of crucial importancefor the study of the physics of weak winds.
| Low-Resolution Spectroscopy and uvby-β Photometry of Selected Stars in Haffner 18
We present MK spectral types of a sample of selected (bright) starsassociated with the galactic cluster Haffner 18 in Puppis. They wereobtained from low-resolution (λ / Δ λ = 1720)spectra by H α slit spectroscopy. Some of the selected stars werealso observed photoelectrically in the uvby- β system. Ourspectroscopic data show that over 1/4 of the estimated 50 star membersof the cluster are O and early B stars. We give MK spectral types anddiscuss the individual stars observed. Finally, based on thesespectroscopic results, on our photometry, and on published data webriefly reinspect the physical parameters of the cluster.
| Distribution of early type stars and dusty matter in the direction of the star cluster NGC 2175
The distribution of 120 O-B9-A2 stars and of the interstellar dust inthe direction of the star clusters NGC 2175 and NGC 2175s (the complexS252) is studied in terms of V, (B-V), and (U-B) data. Ten star groups(associations) are found at distances of 410, 720, 1000, 1500, 2200,3100, 4000, 5200, 7000, and 8100 pc. Three of these, at distances of410, 720, and 1000 pc, are type B associations. The remaining seven areOB associations. They are designated as Gem B 0.41, Gem B 0.72, Gem B1.0, Gem OB 1.5, Gem OB 2.2, Gem OB 3.1, Gem OB 4.0, Gem OB 5.2, Gem OB7.0, and Gem OB 8.1. The V absorption (AV) for stars No.2, 18, 20, 23,24, 26, 40, 41, 47, 69, 87, 88, 90, 95, 100 and 109 is estimated to be2m.78,4m.72, 2m.69, 3m.33, 2m.61, 2m.86, 4m.67, 6m.21, 3m.14, 3m.92,2m.69, 3m.04, 5m.95, 5m.95, 3m.20 and 5m.66, respectively. For most ofthese stars the absorption lies between 0m.5 and 2m.5. This largeabsorption may be caused by circumstellar absorption. The dust in theassociations Gem B 0.41 and Gem B 0.72 is distributed nonuniformly.There is no dust in the space between the associations. Essentiallythere is no dust inside those groups (associations) which lie atdistances greater than 1 kpc.
| Star-forming protoclusters associated with methanol masers
We present a multiwavelength study of five methanol maser sites whichare not directly associated with a strong (>100 mJy) radio continuumsource: G 31.28+0.06, G 59.78+0.06, G 173.49+2.42 (S231, S233IR), G188.95+0.89 (S252, AFGL5180) and G 192.60-0.05 (S255IR). Theseradio-quiet methanol maser sites are often interpreted as precursors ofultra-compact H II regions or massive protostar sites. In this work, theenvironment of methanol masers is probed from mid-IR to millimetrewavelengths at angular resolutions of 8''-34''. Spectral energydistribution (SED) diagrams for each site are presented, together withmass and luminosity estimates. Each radio-quiet maser site is alwaysassociated with a massive (>50 Mȯ), deeply embedded(Av>40 mag) and very luminous (>104Lȯ) molecular clump, with Ltotal∝Mgas0.75. These physical properties characterisemassive star-forming clumps in earlier evolutionary phases than H IIregions. In addition, colder gas clumps seen only at mm-wavelengths arealso found near the methanol maser sites. These colder clumps mayrepresent an even earlier phase of massive star formation. These resultssuggest an evolutionary sequence for massive star formation from a coldclump, seen only at mm wavelengths, evolving to a hot molecular corewith a two-component SED with peaks at far-IR and mid-IR wavelengths, toan (ultra-compact) H II region. Alternatively, the cold clumps might beclusters of low-mass YSOs, in formation near the massive star-formingclusters. Finally, the values of the dust grain emissivity index(β) range between 1.6 and 1.9.
| Long-term monitoring of 6.7-GHz methanol masers
A sample of 54 6.7-GHz methanol masers was monitored using theHartebeesthoek 26-m telescope during the period 1999 January - 2003March. The observations were taken at 1-2 week intervals, with dailyobservations when possible if a source was seen to be varying rapidly.It was found that the majority of the sources display a significantlevel of variability. The time-range of variations range from a few daysup to several years. The types of behaviour observed includednon-varying, monotonic increases or decreases, as well as aperiodic,quasi-periodic and periodic variations. Seven sources show clearevidence of periodicity, with periods ranging from 132 d up to 520 d.
| The relatively young and metal-poor Galactic open cluster NGC 2194
We present CCD VIKC photometry down to V~ 21 mag in the fieldof the rich open cluster NGC 2194, which is projected towards theGalactic anticentre direction. We measured V magnitudes and V-I coloursfor a total of 2515 stars in a field of 13.6 × 13.6arcmin2. These data are supplemented with CCD photometry inthe C, M and T1 filters of the Washington system andphotoelectric CMT1T2 photometry of 20 red giantcandidates. Based on the best fits of isochrones computed by the Genevaand Padova groups to the (V, V-I) colour-magnitude diagram, we derive acolour excess E(V-I) = 0.75, a cluster distance of 3.2 kpc and an age of400 Myr. Five independent Washington abundance indices yield a meancluster metallicity of [Fe/H]=-0.27 +/- 0.06, which is compatible withthe existence of both a radial and Z gradient in the Galactic disc. NGC2194 is a relatively young open cluster, whose deficiency in metalcontent can be accounted for by the fact that it was born not only farfrom the Galactic centre in the outer disc, but also at a relativelyhigh Z value.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| The Universality of Turbulence in the Molecular Interstellar Medium and Its Exploitation as a Distance Estimator
The turbulent energy spectrum of molecular clouds in a variety ofenvironments is measured via principal component analysis (PCA) ofspectral line imaging observations at millimeter wavelengths. Molecularclouds with known distances have been previously shown to accuratelyobey a universal scale dependence of turbulent velocity dispersion overspatial scales of 1-50 pc, via both standard object-based analysis and,more recently, PCA. The PCA-based spectrum is accurately obeyed suchthat it may be used as a distance estimator for molecular clouds with~30% accuracy, where the error budget is contributed to strongly byinput H II region distances used for the calibration. The use of13CO spectral line data for distance estimation is examinedand compared to the distance calibration established for 12COobservations. We show that distances estimated using 13CO arein good agreement with those obtained using 12CO, with apossible ~10% distance overestimation for 13CO relative tothe 12CO calibration. Several molecular clouds with knowndistances are subjected to PCA, and we demonstrate that the universalspectrum is closely respected by all clouds; PCA-based distancesestimated under the assumption of exact adherence to the universalspectrum are derived and are shown to be in excellent agreement withoptically estimated distances. We examine the possibility that the PCAdistance estimation method may be used to solve the kinematic distanceambiguity in the inner Galaxy. We establish how PCA may be used todiagnose severe blending of near/far emission and, in cases of little orno blending, to accurately establish the near or far distance. The innerGalaxy results provide initial support for the global validity of theuniversal PCA spectrum previously demonstrated for the outer Galaxyonly. In conjunction with the accurate velocity information provided bymillimeter wavelength spectral line data, PCA can provide usefulinformation for studies of Galactic structure and kinematics.
| Observations of Cyanoacetylene Sources
Thirty-four Galactic star-forming regions have been observed in theJ=4-3 line of cyanoacetylene (HC3N) at 36.4 GHz. Emission was detectedtoward 17 sources. The HC3N column density was determined in thedetected sources, and in eight of them (NGC 2264, L379, W51E1/E2, DR 21West, DR 21 (OH), DR 21, S140, and Cep A), the relative cyanoacetyleneabundance was estimated. The HC3N abundance in these objects is about 170×10-10.
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| Embedded Clusters in Molecular Clouds
Stellar clusters are born embedded within giant molecular clouds (GMCs)and during their formation and early evolution are often only visible atinfrared wavelengths, being heavily obscured by dust. Over the past 15years advances in infrared detection capabilities have enabled the firstsystematic studies of embedded clusters in galactic molecular clouds. Inthis article we review the current state of empirical knowledgeconcerning these extremely young protocluster systems. From a survey ofthe literature we compile the first extensive catalog of galacticembedded clusters. We use the catalog to construct the mass function andestimate the birthrate for embedded clusters within 2 kpc of the sun. Wefind that the embedded cluster birthrate exceeds that of visible openclusters by an order of magnitude or more indicating a high infantmortality rate for protocluster systems. Less than 4-7% of embeddedclusters survive emergence from molecular clouds to become boundclusters of Pleiades age. The vast majority (90%) of stars that form inembedded clusters form in rich clusters of 100 or more members withmasses in excess of 50 Mȯ. Moreover, observations ofnearby cloud complexes indicate that embedded clusters account for asignificant (70-90%) fraction of all stars formed in GMCs. We review therole of embedded clusters in investigating the nature of the initialmass function (IMF) that, in one nearby example, has been measured overthe entire range of stellar and substellar mass, from OB stars tosubstellar objects near the deuterium burning limit. We also review therole embedded clusters play in the investigation of circumstellar diskevolution and the important constraints they provide for understandingthe origin of planetary systems. Finally, we discuss current ideasconcerning the origin and dynamical evolution of embedded clusters andthe implications for the formation of bound open clusters.
| Measurements of [O I] λ6300/Hα Line Intensity Ratios for Four O Star H II Regions
We have used the Wisconsin Hα Mapper facility to measure the [O I]λ6300/Hα line intensity ratios for four O star H IIregions: S27 (observation coordinates l=6.3d,b=+23.6d), S252(l=190.1d,b=+0.6d), S261 (l=194.1d,b=-1.9d), and S264(l=195.1d,b=-12.0d). We find that the ratios range from 0.0015 to0.0053. These results are roughly a factor of 10 lower than measured [OI]/Hα ratios in directions that sample the warm ionized componentof the interstellar medium. This difference implies a significantlylower hydrogen ionization ratio n(H+)/n(H0) orhigher electron temperature in the diffuse ionized gas compared withthat in the bright discrete O star H II regions.
| Parameters of Warm Molecular Clouds from Methyl Acetylene Observations
The results of a survey of 63 Galactic star-forming regions in the 6K 5Kand 5 K 4K methyl acetylene lines at 102.5 and 85.5 GHz are presented.Fourty-three sources were detected at 102.5 GHz, and twenty-five at 85.5GHz. Emission was detected toward molecular clouds with kinetictemperatures of 20 60 K (so-called “warm clouds”). TheCH3CCH abundances in these clouds are about several ×10-9. Fivesources (NGC 2264, G30.8-0.1, G34.26+0.15, DR 21(OH), S140) were mappedusing the maximum-entropy method. The sizes of the mapped clouds fall inthe range 0.1 1.7 pc, and the clouds have virial masses of 90 6200 Mȯ and densities between 6×104 and 6×105 cm-3. TheCH3CCH sources coincide spatially with the CO and CS sources.Chemical-evolution simulations show that the typical methyl acetyleneabundances in the observed clouds correspond to ages of ≈6×104years.
| Torsionally excited methanol at 44.9 GHz
Using the Haystack Observatory 37-m radio telescope we have undertaken asearch for emission in the 20-31 E rotationaltransition of methanol in its first torsionally excited state(vt = 1) at 44.9 GHz. We examined seven galactic sources -six strong emitters of Class II methanol maser lines and OrionKL, the only source where this line had been previouslydetected. We confirm (at a level of 5sigma ) the previous detection andreport two new detections - a reliable (9sigma ) detection inW3(OH) and a marginal (3.5sigma ) detection inNGC 6334F. Upper limits for other sources arepresented. Although we did not see obvious signatures of maseramplification in this transition in any source, arguments in favor ofweak masing in W3(OH) are presented.
| BVRIJHK photometry of post-AGB candidates
BVRIJHK photometric observations are presented for 27 post-AGBcandidates. Almost all objects show a double peaked SED curve in theoptical to far-infrared wavelengths. Seventeen objects were classifiedas post-AGB stars on the basis of their spectral type, location in theIRAS color-color diagram and SED. The physical parameters of theobserved post-AGB stars, the inner radius of the detached shell, themass of the shell and the distance were derived using the simple dustshell model. We compared our observational sequence of post-AGB objectsto the theoretical evolutionary sequence (Schönberner\cite{schonberner1983}; Blöcker \cite{blocker}) in the stellartemperatures versus age diagram. We found that two post-AGB stars, IRAS05040+4820 and 08187-1905, have low stellar temperature with a largedynamical age of the dust shell. They appear to provide the firstobservational evidence that some low-mass stars bypass the planetarynebulae stage because of their slow increase in stellar temperature.Based on observations obtained at Kiso Observatory, Nagano, Japan.Table2 is also available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/385/884
| On the oxygen abundances in H II regions of the Galaxy
Oxygen abundances in H II regions of the Galaxy were derived with theclassical Te-method within the framework of the two-zone H IIregion model using published spectro-photometric data (69 spectra of 11H II regions in the range of galactocentric distances from 6.6 to 14.8kpc). The derived radial distribution of the oxygen abundance wascompared with that from Shaver et al. (1983), which is widely used inconstructing the model of the chemical evolution of the Galaxy. It wasfound that the oxygen abundances given by Shaver et al. areoverestimated by 0.2-0.3 dex.
| Thermal Emission of Methanol and Other Molecules at Millimeter Wavelengths
The paper reports the results of a survey of Galactic star-formingregions in the methanol lines 8-1 70 E at 229.8 GHz, 3-2 4-1 E at 230.0GHz, 00 1-1 E at 108.9 GHz, and a series of J 1 J 0 E lines near 165GHz. In addition to the methanol lines, lines of methyl cyanide (CH3CN),cyanoacetylene (HC3N), methyl formate (HCOOCH3), and sulphur dioxide(SO2) were detected. Analysis of the data indicates that the methanolemission arises in warm (30 50 K) gas.
| The cosmological density of baryons from observations of 3He+ in the Milky Way
Primordial nucleosynthesis after the Big Bang can be constrained by theabundances of the light elements and isotopes 2H,3He, 4He and 7Li (ref. 1). The standardtheory of stellar evolution predicts that 3He is alsoproduced by solar-type stars, so its abundance is of interest not onlyfor cosmology, but also for understanding stellar evolution and thechemical evolution of the Galaxy. The 3He abundance instar-forming (HII) regions agrees with the present value for the localinterstellar medium, but seems to be incompatible with the stellarproduction rates inferred from observations of planetary nebulae, whichprovide a direct test of stellar evolution theory. Here we develop ourearlier observations, which, when combined with recent theoreticaldevelopments in our understanding of light-element synthesis anddestruction in stars, allow us to determine an upper limit for theprimordial abundance of 3He relative to hydrogen:3He/H = (1.1 +/- 0.2) × 10-5. The primordialdensity of all baryons determined from the 3He data is inexcellent agreement with the densities calculated from othercosmological probes. The previous conflict is resolved because mostsolar-mass stars do not produce enough 3He to enrich theinterstellar medium significantly.
| A Near-Infrared Survey of Radio-selected Ultracompact H II Regions
A near-infrared (NIR) survey of 63 radio-selected, ultracompact (UC) HII regions representing 47 different star-forming sites has beencompleted. The survey was obtained using H-band imaging andmoderate-resolution, R=1200, K-band spectroscopy, centered on the radioemission peak of the UC H II regions. The goal of this survey was todetermine the fraction of radio-selected UC H II regions that can bestudied with NIR observations and analysis. Approximately 50% of the 63radio-selected UC H II regions appear to be detected at NIR wavelengthsin Brγ emission (107 ergs s-1cm-2 sr-1). Typical line-of-sight extinctiontoward the detected UC H II regions ranged from AV=30 to 50,though one source was measured to have AV=80. For a few ofthese UC H II regions, the central ionizing sources are detected throughhigh signal-to-noise ratio NIR spectra of photospheric transitions. Thispreliminary survey suggests that perhaps 5%-10% of UC H II regionsshowing NIR counterparts will have directly detectable central ionizingsources. Using the ratio of He I 2.11 to Brγ, the effectivetemperatures of the central ionizing stars in 25 UC H II regions havebeen estimated. While He I is not always detected in UC H II regions,when it was found or a meaningful upper limit determined, the spectraltype implied by the ratio of He I 2.11 to Brγ closely matchedsimilar estimates of spectral type derived from radio. Model predictionsbased on mid-infrared measurements appear to underestimate thetemperature of the central ionizing stars for which we have directlydetected spectral types. The line ratios of H2 2-1 S(1) and1-0 S(0) relative to the 1-0 S(1) line in our sample of UC H II regionsare generally indicative of dense photodissociation regions rather thanshocks, similar to what is seen in the Orion Bar. This was true even forUC H II regions showing very weak Brγ emission. While Brγwas generally found to be spatially correlated with the radio emission,H2 showed little correlation with the UC H II regions,typically lying >~10" from the central radio emission. A discussionof each UC H II region studied is included in an extensive appendix.
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