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Outflow and Infall in a Sample of Massive Star-forming Regions
We present single-pointing observations of SiO, HCO+, andH13CO+ from the James Clerk Maxwell Telescopetoward 23 massive star-forming regions previously known to containmolecular outflows and ultracompact H II regions. We detected SiO toward14 sources and suggest that the nondetections in the other nine sourcescould be due to those outflows being older and without ongoing shocks toreplenish the SiO. We serendipitously detected SO 2 toward 17sources in the same tuning as HCO+. We detectedHCO+ toward all sources, and suggest that it is tracinginfall in nine cases. For seven infall candidates, we estimate massinfall rates between 1×10-2 and 2×10-5Msolar yr-1. Seven sources show both SiOdetections (young outflows) and HCO+ infall signatures. Wealso find that the abundance of H13 CO+ tends toincrease along with the abundance of SiO in sources for which we coulddetermine abundances. We discuss these results with respect to currenttheories of massive star formation via accretion. From this survey, wesuggest that perhaps both models of ionized accretion and haltedaccretion may be important in describing the evolution of a massiveprotostar (or protostars) beyond the formation of an H II region.
| Position-Velocity Diagrams for the Maser Emission Coming from a Keplerian Ring
We have studied the maser emission from a thin, planar, gaseous ring inKeplerian rotation around a central mass observed edge-on. Theabsorption coefficient within the ring is assumed to follow a power-lawdependence on the distance from the central mass asκ=κ0r-q. We have calculatedposition-velocity diagrams for the most intense maser features, fordifferent values of the exponent q. We have found that, depending on thevalue of q, these diagrams can be qualitatively different. The mostintense maser emission at a given velocity can come mainly from eitherregions close to the inner or outer edges of the amplifying ring or theline perpendicular to the line of sight and passing through the centralmass (as is commonly assumed). Particularly, when q>1 theposition-velocity diagram is qualitatively similar to the one observedfor the water maser emission in the nucleus of the galaxy NGC 4258. Inthe context of this simple model, we conclude that in this object theabsorption coefficient depends on the radius of the amplifying ring as adecreasing function, in order to have significant emission coming fromthe inner edge of the ring.
| Evidence for a Massive Protocluster in S255N
S255N is a luminous far-infrared source that contains many indicationsof active star formation but lacks a prominent near-infrared stellarcluster. We present mid-infrared through radio observations aimed atexploring the evolutionary state of this region. Our observationsinclude 1.3 mm continuum and spectral line data from the SubmillimeterArray, Very Large Array 3.6 cm continuum and 1.3 cm water maser data,and multicolor IRAC images from the Spitzer Space Telescope. Thecometary morphology of the previously known UCH II region G192.584-0.041is clearly revealed in our sensitive, multiconfiguration 3.6 cm images.The 1.3 mm continuum emission has been resolved into three compactcores, all of which are dominated by dust emission and have radii<7000 AU. The mass estimates for these cores range from 6 to 35Msolar. The centroid of the brightest dust core (SMA1) isoffset by 1.1'' (2800 AU) from the peak of the cometary UCHII region and exhibits the strongest HC3N, CN, and DCN lineemission in the region. SMA1 also exhibits compact CH3OH,SiO, and H 2CO emission and likely contains a young hot core.We find spatial and kinematic evidence that SMA1 may contain furthermultiplicity, with one of the components coincident with a newlydetected H2O maser. There are no mid-infrared point-sourcecounterparts to any of the dust cores, further suggesting an earlyevolutionary phase for these objects. The dominant mid-infrared emissionis a diffuse, broadband component that traces the surface of thecometary UCH II region but is obscured by foreground material on itssouthern edge. An additional 4.5 μm linear feature emanating to thenortheast of SMA1 is aligned with a cluster of methanol masers andlikely traces a outflow from a protostar within SMA1. Our observationsprovide direct evidence that S255N is forming a cluster of intermediate-to high-mass stars.
| Investigation of the polarization observed in infrared absorption bands in the spectra of protostars
We investigate the linear polarization in the two deepest infraredabsorption bands observed in the spectra of protostars, the water-iceband with the center near 3.1 µm and the silicate band with thecenter near 9.7 µm, using a core-mantle confocal spheroid modelwith various axial ratios a/b and relative volumes of the core material.We consider the effect of the grain shape, structure, and type (oblate,prolate) as well as the type of grain orientation and its locationrelative to the incident ray of light and the magnetic field directionon the central wavelengths of the two bands and the polarizability inthe bands. We have found that the observed relationships between thepolarizability in the bands and the ratio of their optical depths at theband centers can be explained if we choose slightly oblate or prolateparticles (a/b ≲2 for the silicate band and 1.3 ≲ a/b ≲ 2for the ice band). For any type of orientation, the core-mantle confocalspheroid model requires different axial ratios for the ice and silicatebands to account for the observed polarization. We show thatpicket-fence-oriented particles can explain the observed polarization inthe ice band at angles α between the particle rotation axis andthe incident ray ≳30° and in the silicate band at any α.Perfectly Davis-Greenstein-oriented particles can explain the observedpolarization in the ice band at angles Ω between the line of sightand the magnetic field direction ≳60° and in the silicate bandat any Ω. The orientation parameter ζ (imperfectDavis-Greenstein orientation) must be no more than 0.5 (oblateparticles) and 0.1 (prolate particles) for the ice band and can bearbitrary for the silicate band.
| Luminosity functions of YSO clusters in Sh-2 255, W3 main and NGC 7538 star forming regions
We have conducted deep near-infrared surveys of the Sh-2 255, W3 Mainand NGC 7538 massive star forming regions using simultaneous observations of the JHKs -band with the near-infrared camera SIRIUS onthe UH 88-inch telescope. The near-infrared surveys cover a total areaof ~72 square arcmin of three regions with 10-sigma limiting magnitudesof ~19.5, 18.4 and 17.3 in J, H and Ks-band, respectively.Based on the colour-colour and colour- magnitude diagrams and theirclustering properties, the candidate young stellar objects areidentified and their luminosity functions are constructed in Sh-2 255,W3 Main and NGC 7538. A large number of previously unreported redsources (H - K > 2) have also been detected around these regions. Weargue that these red stars are most probably pre-main sequence starswith intrinsic colour excesses. The detected young stellar objects showa clear clustering pattern in each region: the Class I-like sources aremostly clustered in molecular cloud region, while the Class II-likesources in or around more evolved optical H II regions. We find thatthe slopes of the Ks -band luminosity functions of Sh-2 255, W3 Main andNGC 7538 are lower than the typical values reported for the youngembedded clusters and their stellar populations are primarily composedof low mass pre-main sequence stars. From the slopes of the Ks -bandluminosity functions, we infer that Sh-2 255, W3 Main and NGC 7538 starforming regions are rather young (age 1 Myr).
| 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.
| Tracing the base of protostellar wind(s) towards the high-mass star forming region AFGL 5142: VLA continuum and VLBA H2O maser observations
We have conducted phase-reference multi-epoch observations of the 22.2GHz water masers using the Very Long Baseline Array (VLBA) and amulti-frequency study of the continuum emission using the Very LargeArray (VLA) towards the high-mass star forming region (SFR) AFGL 5142.29 maser features were identified and most of them were persistent overthe four observing epochs, allowing absolute proper motions to bedetermined. The water maser emission comes from two elongated structures(indicated as Group I and Group II), with the measured proper motionsaligned along the structures' elongation axes. Each group consists oftwo (blue- and red-shifted) clusters of features separated by a fewhundreds and thousands of AU respectively for Group I and Group II. Themaser features of Group II have both positions and velocities alignedalong a direction close to the axis of the outflow traced byHCO+ and SiO emission on angular scales of tens of arcsec. Wepredict that the maser emission arises from dense, shocked molecularclumps displaced along the axis of the molecular outflow. The two maserclusters of Group I are oriented on the sky along a direction forming alarge angle (>≈60°) with the axis of the jet/outflow traced byGroup II maser features. We have detected a compact (8.4 and 22 GHz)continuum source (previously reported at 4.9 and 8.4 GHz) that fallsclose to the centroid of Group I masers, indicating that the sourceionizing the gas is also responsible for the excitation of the watermasers. The kinematic analysis indicates that the Group I masers traceoutflowing rather than rotating gas, discarding the Keplerian diskscenario proposed in a previous paper for Group I. Since the axisjoining the two maser clusters of Group II does not cross the positionof the continuum source, Group II masers might be excited by an(undetected) massive YSO, distinct from the one (pinpointed by the VLAcontinuum emission) responsible for the excitation of the Group Imasers. Our results give support to models of accretion and jet ejectionrelated to the formation of high-mass stars.
| Spectral observations of stars associated with nebulae. I. PP52, PP57, PP63, and PP89
Spectral observations of stars associated with nebulae, PP52, PP57,PP63, and PP89, are reported. The star PP52 is of spectral type A and isassociated with a reflecting nebula. PP57 is a nonstationary star. Aweak object (1079-0122733) immediately adjacent to PP57 is highlyvariable. It is shown that the nebulae PP63 and PP89 are cometary.
| A Millimeter Continuum Survey for Massive Protoclusters in the Outer Galaxy
Our search for the earliest stages of massive star formation turned up12 massive pre-protocluster candidates plus a few protoclusters. Forthis search, we selected 47 FIR-bright IRAS sources in the outer Galaxy.We mapped regions of several square arcminutes around the IRAS source inthe millimeter continuum in order to find massive cold cloud corespossibly being in a very early stage of massive star formation. Massesand densities are derived for the 128 molecular cloud cores found in theobtained maps. We present these maps together with near-infrared,mid-infrared, and radio data collected from the 2MASS, MSX, and NVSScatalogs. Further data from the literature on detections of high-densitytracers, outflows, and masers are added. The multiwavelength data setsare used to characterize each observed region. The massive cloud cores(M>100 Msolar) are placed in a tentative evolutionarysequence depending on their emission at the investigated wavelengths.Candidates for the youngest stages of massive star formation areidentified by the lack of detections in the above-mentionednear-infrared, mid-infrared, and radio surveys. Twelve massive coresprominent in the millimeter continuum fulfill this requirement. Sinceneither FIR nor radio emission have been detected from these cloudcores, massive protostars must be very deeply embedded in these cores.Some of these objects may actually be pre-protocluster cores: an up tonow rare object class, where the initial conditions of massive starformation can be studied.
| A search for shock-excited optical emission from the outflows of massive young stellar objects
We have searched for optical shock-excited emission lines in the outerparts of the bipolar outflows from massive young stellar objects wherethe flow terminates and the extinction is expected to be low. The TaurusTunable Filter (TTF) at the Anglo-Australian Telescope (AAT) was used toobtain narrow-band (12-15 Å) images of the Hα, [Nii] 6583,and [Sii] 6717/6731 lines around Mon R2 IRS3,S255 IRS1/3, GL 961 andGL 989. No clear examples of shocked emission werefound. A bow shock feature in the GL 989 region mayberelated with the molecular outflow NGC 2264 D. A weak optical bow-likefeature is seen in GL 961, but which of the stars inthe cluster is the driving source cannot be uniquely identified. Otheremission line features were found in Mon R2 and S255 that are consistentwith an Hii region origin. The observed fluxes and the upper limits werecompared with predictions from radiative shock models available in theliterature. Any head-on collisions of a jet with speeds of the order of500 km s-1 should have been detected if the extinctionAv < 10 mag. Estimates of the extinction in the outerparts of the molecular clouds are somewhat lower than this, although itis possible that it could be higher local to any interaction regions dueto swept up material. If the extinction is low, then the shocks musteither be slower (<150 km s-1) or very oblique(>75°), which would argue against the presence of highlycollimated jets from high mass young stellar objects.
| Precession of the Orbital Plane of Binary Pulsars and Significant Variabilities
There are two ways of expressing the precession of orbital plane of abinary pulsar system, given by Barker & O'Connell, Apostolatos etal. and Kidder, respectively. We point out that these two ways actuallycome from the same Lagrangian under different degrees of freedom. Damour& Schäfer and Wex & Kopeikin applied Barker &O'Connell's orbital precession velocity in pulsar timing measurement.This paper applies Apostolatos et al.'s and Kidder's orbital precessionvelocity. We show that Damour & Schäfer's treatment correspondsto negligible Spin-Orbit induced precession of periastron, while Wex& Kopeikin and this paper both found significant (but notequivalent) effects. The observational data of two typical binarypulsars, PSR J2051 0827 and PSR J1713+0747, apparently support asignificant Spin-Orbit coupling effect. Specific binary pulsars withorbital plane nearly edge on could discriminate between Wex &Kopeikin and this paper: if the orbital period derivative of thedouble-pulsar system PSRs J0737 3039 A and B, with orbital inclinationangle i = 87.7-29+17 deg, is much larger than thatof the gravitational radiation induced one, then the expression in thispaper is supported, otherwise Wex & Kopeikin's is supported.
| Structure of Solar-Wind Streams at the Maximum of Solar Cycle 23
We study the formation of solar-wind streams in the years of maximumsolar activity 2000 2002. We use observations of the scattering of radioemission by solar-wind streams at distances of ˜4 60R S from theSun, data on the magnetic field structure and strength in the sourceregion (R ˜ 2.5R S), and observations with the LASCO coronagraphonboard the SOHO spacecraft. Analysis of these data allowed us toinvestigate the changes in the structure of circumsolar plasma streamsduring the solar maximum. We constructed radio maps of the solar-windtransition, transonic region in which the heliolatitudinal streamstructure is compared with the structure of the white-light corona. Weshow that the heliolatitudinal structure of the white-light coronalargely determines the structure of the solar-wind transition region. Weanalyze the correlation between the location of the inner boundary ofthe transition region R in and the magnetic field strength on the sourcesurface |B R|. We discuss the peculiarities of the R in = F(|B R|)correlation diagrams that distinguish them from similar diagrams atprevious phases of the solar cycle.
| Near-Infrared Imaging of the Star Formation Region AFGL 5142
Near-infrared JHK' and H2 v=1-0 S(1) imaging observations ofthe star-forming region AFGL 5142 are presented. A cluster of youngstars is confirmed to be embedded in the dense molecular cloud core.Many point sources are newly detected. The cluster's K'-magnitudedistribution and [H-K'] color peak have brighter and reddermagnitudes than those outside the cluster. Many of the cluster sourcesexhibit infrared excesses typical of T Tauri stars, Herbig Ae/Be stars,and protostars. The observations also reveal new H2 lineemission around the cluster, exhibiting several jets, filaments, and afaint elliptical structure. The jets are associated with the CO outflowsin the region. The powering sources of the jets, the CO outflows, andthe small faint elliptical structure are identified and analyzedindividually. The strong H2 jets and faint diffuse emissionfurther confirm that the cluster is in an early stage of evolution.
| Analysis of Spatial Temperature Variations in Regions of Massive Star Formation
Using the 20-m Onsala Observatory telescope (Sweden), we performedobservations of the CH3C2H(6-5) line toward several regions of massivestar formation to estimate the kinetic temperature of the gas and studyits variations over the sources. Intense lines were detected in fiveobjects. For these, we estimated the kinetic temperature of the gas nearthe CS and N2H+ molecular emission peaks by the method of populationdiagrams. A significant temperature difference between these peaks isnoticeable only in W3 and, to a lesser degree, in DR 21. In theremaining cases, it is insignificant. This indicates that the chemicaldifferentiation of the molecules in these regions cannot be associatedwith temperature variations. The kinetic temperature determined frommethyl acetylene observations is usually slightly higher than thetemperature estimated from ammonia observations. This is probablybecause the methyl acetylene emission originates in denser, i.e., deeperand hotter layers of the cloud.
| A general catalogue of 6.7-GHz methanol masers. I. Data.
Methanol masers are often detected in regions of intense star formation.Several studies in the last decade indicate that they may even be theearliest signpost of a high-mass star-forming region. Their powerfulemission make them very good candidates for observations using bothsingle-dish telescopes and interferometers, the latter allows detailedstructural and dynamical studies of these objects. We have prepared acatalogue of all known 6.7-GHz methanol masers, discovered both bysurveys that targeted possible associated objects and unbiased surveyscovering a large fraction of galactic longitudes across the Galacticplane (-0.5 ° ≤ b ≤ 0.5 ° for most of the regions). Thecatalogue contains 519 sources which are listed with their kinematic(galactocentric and heliocentric) distances as well as possiblyassociated IR objects. We find that 6.7-GHz methanol masers clearlytrace the molecular ring of our Galaxy, where most of the OBassociations are located. The present list of masers also reportsdetections of other masing transitions of methanol as furtherinformation for the study of the maser phenomenon. In a furtherpublication we will address some statistical considerations.The complete catalogue (Table [see full text]) is available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/432/737 Figures 1 and 2are only available in electronic form at http://www.edpsciences.org
| Kinematics of H2O masers in high-mass star forming regions
We have conducted multi-epoch EVN observations of the 22.2 GHz watermasers towards four high-mass star forming regions (Sh 2-255 IR, IRAS23139+5939, WB89-234, and OMC2). The (three) observing epochs span 6months. In each region, the H2O maser emission likely originates close(within a few hundred AU) to a forming high-mass YSO. Several maserfeatures (~10) have been detected for each source and, for thosefeatures persistent over the three epochs, proper motions have beenderived. The amplitudes of the proper motions are found to be largerthan the range of variation of the line-of-sight velocities and in eachof the observed sources the proper motion orientation seems to indicateexpansion. The gas kinematics traced by the 22.2 GHz H2O masers iscompatible with the shock-excited nature of water maser emission. Threedifferent kinematic models (a spherical expanding shell, a Keplerianrotating disk and a conical outflow) were fitted to the 3-dimensionalvelocity field of the detected maser features. The results of thesefits, together with the comparison of the VLBI maps with thehighest-resolution images of the sources in several thermal tracers,suggest that the water maser features most likely trace the innerportion of the molecular outflows detected at much larger scales.
| Molecular Abundance Ratios as a Tracer of Accelerated Collapse in Regions of High-Mass Star Formation
Recent observations suggest that the behavior of tracer species such asN2H+ and CS is significantly different in regionsof high- and low-mass star formation. In the latter,N2H+ is a good tracer of mass, while CS is not.Observations show the reverse to be true in high-mass star formationregions. We use a computational chemical model to show that theabundances of these and other species may be significantly altered by aperiod of accelerated collapse in high-mass star-forming regions. Wesuggest that these results provide a potential explanation of theobservations, and make predictions for the behavior of other species.
| 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.
| An Update on the MIT Haystack Observatory Methanol Maser Study
Class I methanol masers have been detected in star forming regions, andmay be a critical link in detecting very early star formation. Class Imethanol masers are pumped by collisional excitation followed byspontaneous radiative decay and often occur in the outflows of youngstars. The Haystack 37m antenna has been used to conduct a search forClass I methanol masers at three transitions towards the knownstar-forming regions of S255, S235, OMC2, and W75N. The maser positionand the surrounding region were mapped at three transitions of Class Imethanol: 25 GHz, 36 GHz and 44 GHz. Methanol masers that are coincidentin position and velocity between 36 GHz and 44 GHz have been found, aswell as emission at 44 GHz with no corresponding emission at 36 or 25GHz. There have been no detections at 25 GHz. A comparison of linewidths is also presented. These data will facilitate modeling of thepumping mechanism of these masers and the surrounding physicalenvironment.
| A Catalog of CH3OH 70-61 A+ Maser Sources in Massive Star-forming Regions
We present a Very Large Array survey of 44 massive star-forming regionsin the 44 GHz 70-61 A+ methanoltransition; 37 fields showed maser emission. Thirty-one sources werealso observed in the 23 GHz 92-101 A+methanol line; two fields showed maser emission. Although the 44 GHzline is a class I maser, we find a large number of these masers inrelatively close association with H II regions and water masers. Severalsources show strong evidence for a correlation between 44 GHz masers andshocked molecular gas, supporting the interpretation that molecularoutflows may give rise to class I maser emission. We provide maserpositions with arcsecond accuracy that not only locate the masers withrespect to other star formation phenomena, but also provide, for thestronger masers, phase referencing sources that can be used to calibratefuture 7 mm (44 GHz) observations of these regions.
| Near-IR speckle imaging of massive young stellar objects
We present near-IR speckle images of 21 massive Young Stellar Objects(YSOs) associated with outflows. The aim of this study is to search forsub-arcsecond reflection nebulae associated with the outflow cavity. Wefind that 6 of the massive YSOs show a conical nebula which can beinterpreted in terms of reflected light from the dusty walls of theoutflow cavity. In all cases, the small scale structures seen in ourimages are compared with outflow indicators found in the literature. Noclear correlation is found between the presence of the reflectionnebulosity and any property such as degree of embeddedness. We also notethat 3 of the sources show close companions, one of them belonging alsoto the sample with conical nebula.Figures \ref{S140SpeckleFig}, \ref{S255SpeckleFig},\ref{Ha101Fig}-\ref{HGL490Fig} and\ref{GL2591SpeckleFig}-\ref{GL5180peckleFig} are only available inelectronic form at http://www.edpsciences.org
| A study of high velocity molecular outflows with an up-to-date sample
A statistical study of the properties of molecular outflows is performedbased on an up-to-date sample. 391 outflows were identified in publishedarticles or preprints before February 28, 2003. The parameters ofposition, morphology, mass, energy, outflow dynamics and central sourceluminosity are presented for each outflow source. Outflow lobe polarityis known for all the sources, and 84% are found to be bipolar. Thesources are divided into low mass and high mass groups according toeither the available bolometric luminosity of the central source or theoutflow mass. The pace of discovery of outflows over the past sevenyears has increased much more rapidly than in previous periods. Surveysfor outflows are still continuing. The number of high-mass outflowsdetected (139) has considerably increased, showing that they arecommonly associated with massive as well as low mass stars. Energeticmass ejection may be a common aspect of the formation of high mass aswell as low mass stars. Outflow masses are correlated strongly withbolometric luminosity of the center sources, which was obtained for thefirst time. There are also correlations between the central sourceluminosity and the parameters of mechanical luminosity and the thrust orforce necessary to drive the outflow. The results show that flow mass,momentum and energy depend on the nature of the central source. Despitetheir similarity, there are differences between the high mass and lowmass outflows. Low mass outflows are more collimated than high massoutflows. On average, the mass of high mass sources can be more than twoorders of magnitude larger than those of low mass outflows. The relationbetween flow mass and dynamical time appears to differ for the two typesof outflows. Low mass sources make up 90% of outflows associated with HHobjects while high mass outflows make up 61% of the sources associatedwith H_2O masers. Sources with characteristics of collapse or infallcomprise 12% of the entire outflow sample. The spatial distribution ofthe outflow sources in the Galaxy is presented and the local occurrencerate is compared with the stellar birth rate.Tables 1a and 1b are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/503
| Near-Infrared Observations of the Massive Star Forming Region IRAS 23151+5912
Near-infrared images and K-band spectroscopy of the massive star-formingregion IRAS 23151+5912 are presented. The JHK' images reveal anembedded infrared cluster associated with infrared nebula, and theH2 (2.12μm) narrow-band image provides for the first timeevidence of outflow activity associated with the cluster. That thecluster is young can be shown by the high percentage of infrared excesssources and the outflow activity. We suggest an age of the cluster of 106 yr. Eight young stars are found in the brightnebular core around IRAS 23151+5912. By the color-magnitude diagrams ofthe cluster, we found five high-mass YSOs and four intermediate-massYSOs in the cluster. Eight H2 emission features arediscovered in the region with a scattered and non-axisymmetricdistribution, indicating the existence of multiple outflows driven bythe cluster. Diffuse H2 emission detected to the north and tothe west of the cluster may result from UV leakage of the cluster. Brγ, H2, and CIV emission lines are found in the K-bandspectrum of the brightest source, NIRS 19, indicating the presence ofenvelope, stellar wind, and shock in the circumstellar environment. Wehave estimated an O7--O9 spectral type for the central massive YSO (20 30 Mȯ), with an age of less than 1 ×106 yr
| VLA observations of 6-cm excited OH
The Very Large Array (VLA) was used to determine precise positions for4765-MHz OH maser emission sources toward star-forming regions which hadbeen observed about seven months earlier with the Effelsberg 100-mtelescope. The observations were successful for K3-50, DR21EX, W75N andW49A. No line was detected toward S255: this line had decreased to lessthan 5 per cent of the flux density observed only seven months earlier.The time-variability of the observed features during the past 30 yr issummarized. In addition, to compare with the Effelsberg observations,the 4750- and 4660-MHz lines were observed in W49A. These lines werefound to originate primarily from an extended region which isdistinguished as an exceptional collection of compact continuumcomponents as well as by being the dynamical centre of the very powerfulH2O outflow.
| A CS J=5-->4 Mapping Survey Toward High-Mass Star-forming Cores Associated with Water Masers
We have mapped 63 regions forming high-mass stars in CS J=5-->4 usingthe CSO. The CS peak position was observed in C34S J=5-->4toward 57 cores and in 13CS J=5-->4 toward the ninebrightest cores. The sample is a subset of a sample originally selectedtoward water masers; the selection on maser sources should favor sourcesin an early stage of evolution. The cores are located in the first andsecond Galactic quadrants with an average distance of 5.3+/-3.7 kpc andwere well detected with a median peak signal-to-noise ratio in theintegrated intensity of 40. The integrated intensity of CS J=5-->4correlates very well with the dust continuum emission at 350 μm. For57 sufficiently isolated cores, a well-defined angular size (FWHM) wasdetermined. The core radius (RCS), aspect ratio[(a/b)obs], virial mass (Mvir), surface density(Σ), and the luminosity in the CS J=5-->4 line (L(CS54)) arecalculated. The distributions of size, virial mass, surface density, andluminosity are all peaked with a few cores skewed toward much largervalues than the mean. The median values, μ1/2, are asfollows: μ1/2 (RCS)=0.32 pc, μ1/2((a/b)obs)=1.20, μ1/2 (Mvir)=920Msolar, μ1/2 (Σ)=0.60 g cm-2,μ1/2 (L(CS54))=1.9×10-2Lsolar, and μ1/2(Lbol/Mvir)=165 (L/M)solar. We find aweak correlation between C34S line width and size, consistentwith Δv~R0.3. The line widths are much higher thanwould be predicted by the usual relations between line width and sizedetermined from regions of lower mass. These regions are very turbulent.The derived virial mass agrees within a factor of 2-3 with massestimates from dust emission at 350 μm after corrections for thedensity structure are accounted for. The resulting cumulative massspectrum of cores above 1000 Msolar can be approximated by apower law with a slope of about -0.9, steeper than that of cloudsmeasured with tracers of lower density gas and close to that for thetotal masses of stars in OB associations. The median turbulent pressuresare comparable to those in UCH II regions, and the pressures at smallradii are similar to those in hypercompact H II regions(P/k~1010 K cm-3). The filling factors for densegas are substantial, and the median abundance of CS is about10-9. The ratio of bolometric luminosity to virial mass ismuch higher than the value found for molecular clouds as a whole, andthe correlation of luminosity with mass is tighter.
| Slow Solar Wind: Sources and Components of the Stream Structure at the Solar Maximum
We study the sources and components of the solar-wind spatial streamstructure at the maximum of the solar cycle 23. In our analysis, we useseveral independent sets of experimental data: radio-astronomicalobservations of scattered radiation from compact sources with thedetermination of the distance from the Sun to the inner boundary of thetransonic-flow transition region (R_in); calculated data on themagnetic-field intensity and structure in the solar corona, in thesolar-wind source region, obtained from optical measurements of thephotospheric magnetic-field intensity at the Stanford Solar Observatory(USA); and observations of the white-light corona with the LASCOcoronograph onboard the SOHO spacecraft. We show that at the solarmaximum, low-speed streams with a transition region located far from theSun dominate in the solar-wind structure. A correlation analysis of thelocation of the inner boundary R_in and the source-surfacemagnetic-field intensity |B_R| on a sphere R = 2.5 R_solar is revealedthe previously unknown lowest-speed streams, which do not fit into theregular relationship between the parameters R_in and |B_R|. In thewhite-light corona, the sources of these streams are located near thedark strip, a coronal region with a greatly reduced density; thenonstandard parameters of the streams probably result from theinteraction of several discrete sources of different types.
| MODEST-2: a summary
This is a summary paper of MODEST-2, a workshop held at the AstronomicalInstitute `Anton Pannekoek' in Amsterdam, 16-17 December 2002. MODEST isa loose collaboration of people interested in MOdelling DEnse STellarsystems, particularly those interested in modelling these systems usingall the available physics (stellar dynamics, stellar evolution,hydrodynamics and the interplay between the three) by defininginterfaces between different codes. In this paper, we summarize: (1) themain advances in this endeavour since MODEST-1; (2) the main sciencegoals which can be and should be addressed by these types ofsimulations; and (3) the most pressing theoretical and modellingadvances that we identified.
| Indications of Inflow Motions in Regions Forming Massive Stars
Observational evidence of inflowing motions in massive star-formingregions has been extremely rare. We have made a spectroscopic survey ofa sample of 28 massive star-forming cores associated with water masers.An optically thick line of HCN (3-2) was used in combination withoptically thin lines [H13CN (3-2) or C34S (5-4),(3-2), and (2-1)] to identify ``blue'' line profiles that can indicateinflow. Comparing intensities for 18 double-peaked line profiles yields11 blue and three red profiles that are statistically significant. Inthe full sample of 28 sources, 12 show blue profiles, and six show redprofiles that are statistically significant based on the velocityoffsets of lines that are optically thick from those that are opticallythin. These results indicate that HCN (3-2) emission may trace inflow inregions forming high-mass stars.
| MSX mid-infrared imaging of massive star birth environments - I. Ultracompact HII regions
We present mid-infrared 21-μm images of a sample of radio-selectedultracompact HII (UCHII) regions, obtained with the Midcourse SpaceExperiment (MSX). With one possible exception, all are detected atmid-infrared wavelengths, sampling the warm dust emission of the cocoonsof the OB star central exciting sources. Many of the UCHII regions havenearby (up to ~ few pc distant) companion dust emission sources, whichrepresent other potential star birth sites. In some objects thecompanion dominates the IRAS point source catalogue entry for the UCHIIregion. We compare the mid- and far-infrared dust emission, measuringthe embedded hot star luminosity, with published UCHII radio emission,measuring the Lyman continuum (LyC) luminosity. We find a spectral typedependence, as predicted by the standard model of an ultracompactionized hydrogen region, surrounded by a natal dust shell, with somescatter, which can be understood by consideration of (1) dust absorptionof some fraction of the emitted Lyman continuum photons; (2) faintercompanion stars within the UCHII region; and (3) the structure of theUCHII regions differing from star to star. Overall, the higher spatialresolution offered by MSX alleviates difficulties often encountered bycomparison of IRAS far-infrared fluxes with radio-derived ionizingfluxes for UCHII regions.
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