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The magnetic field of the pre-main sequence Herbig Ae star HD 190073
Context: .The general context of this paper is the study of magneticfields in the pre-main sequence intermediate mass Herbig Ae/Be stars.Magnetic fields are likely to play an important role in pre-mainsequence evolution at these masses, in particular in controlling thegains and losses of stellar angular momentum. Aims: .Theparticular aim of this paper is to announce the detection of astructured magnetic field in the Herbig Ae star HD 190073, and todiscuss various scenarii for the geometry of the star, its environmentand its magnetic field. Methods: .We have used the ESPaDOnSspectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution,high signal-to-noise circular polarization spectra which demonstrateunambiguously the presence of a magnetic field in the photosphere ofthis star. Results: .Nine circular polarization spectra wereobtained, each one showing a clear Zeeman signature. This signature issuggestive of a magnetic field structured on large scales. Thesignature, which corresponds to a longitudinal magnetic field of74± 10 G, does not vary detectably on a one-year timeframe,indicating either an azimuthally symmetric field, a zero inclinationangle between the rotation axis and the line of sight, or a very longrotation period. The optical spectrum of HD 190073 exhibits a largenumber of emission lines. We discuss the formation of these emissionlines in the framework of a model involving a turbulent heated region atthe base of the stellar wind, possibly powered by magnetic accretion. Conclusions: .This magnetic detection contributes an important newobservational discovery which will aid our understanding of stellarmagnetism at intermediate masses.Based on observations obtained at the Canada-France-Hawaii Telescope(CFHT) which is operated by the National Research Council of Canada, theInstitut National des Sciences de l'Univers of the Centre National de laRecherche Scientifique of France, and the University of Hawaii.
| Large-Area Mapping at 850 μm. V. Analysis of the Clump Distribution in the Orion A South Molecular Cloud
We present results from a 2300 arcmin2 survey of the Orion Amolecular cloud at 450 and 850 μm using the Submillimeter Common-UserBolometer Array (SCUBA) on the James Clerk Maxwell Telescope. The regionmapped lies directly south of the OMC 1 cloud core and includes OMC 4,OMC 5, HH 1/2, HH 34, and L1641N. We identify 71 independent clumps inthe 850 μm map and compute size, flux, and degree of centralconcentration in each. Comparison with isothermal, pressure-confined,self-gravitating Bonnor-Ebert spheres implies that the clumps haveinternal temperatures Td~22+/-5 K and surface pressureslog(k-1 P cm-3 K)=6.0+/-0.2. The clump masses spanthe range 0.3-22 Msolar assuming a dust temperatureTd~20 K and a dust emissivity κ850=0.02cm2 g-1. The distribution of clump masses is wellcharacterized by a power law N(M)~M-α withα=2.0+/-0.5 for M>3.0 Msolar, indicating a clumpmass function steeper than the stellar initial mass function.Significant incompleteness makes determination of the slope at lowermasses difficult. A comparison of the submillimeter emission map with anH2 2.122 μm survey of the same region is performed.Several new Class 0 sources are revealed and a correlation is foundbetween both the column density and degree of concentration of thesubmillimeter sources and the likelihood of coincident H2shock emission.
| A catalogue of Galactic supernova remnants from the Canadian Galactic plane survey. I. Flux densities, spectra, and polarization characteristics
We present a new catalogue containing all known Galactic supernovaremnants observed in phase I and II of the Canadian Galactic PlaneSurvey (65° ≤ ℓ ≤ 175°, -5° ≤ b ≤+7°). Stokes I images at 1420 MHz of 34 SNRs and at 408 MHz of 36SNRs are displayed. From these 1 arcmin and 3 arcmin-resolution data(respectively) we determine accurate centre positions and angulardimensions. The flux densities at 1420 and 408 MHz are integrated andcombined with values from the literature to define more accurate radiospectra. The CGPS polarization data at 1420 MHz were examined andsignificant linear polarization from 18 SNRs is found, with a modestsignal from 6 others.
| On the origin of the X-ray emission from Herbig Ae/Be stars
Context: .Herbig Ae/Be stars are fully radiative and not expected tosupport dynamo action analogous to their convective lower-masscounterparts, the T Tauri stars. Alternative X-ray productionmechanisms, related to stellar winds or star-disk magnetospheres havebeen proposed, but their X-ray emission has remained a mystery. Aims: .A study of Herbig Ae/Be stars' global X-ray properties (such asdetection rate, luminosity, temperature, variability), helps toconstrain the emission mechanism by comparison to other types of stars,e.g. similar-age but lower-mass T Tauri stars, similar-mass but moreevolved main-sequence A- and B-type stars, and with respect to modelpredictions. Methods: .We performed a systematic search forChandra archival observations of Herbig Ae/Be stars. The superiorspatial resolution of this satellite with respect to previous X-rayinstrumentation has allowed us to also examine the possible role oflate-type companions in generating the observed X-rays. Results:.In the total sample of 17 Herbig Ae/Be stars, 8 are resolved from X-rayemitting faint companions or other unrelated X-ray bright objects within10''. The detection fraction of Herbig Ae/Be stars is 76%, but decreasesto 35% if all emission is attributed to further known and unresolvedcompanions. The spectral analysis confirms the high X-ray temperatures( 20 MK) and large range of fractional X-ray luminosities(log{L_x/L_*}) of this class derived from earlier studies of individualobjects. Conclusions: .Radiative winds are ruled out as anemission mechanism on the basis of the high temperatures. The X-rayproperties of Herbig Ae/Be stars are not vastly different from those oftheir late-type companion stars (if such are known), nor from otheryoung late-type stars used for comparison. Therefore, either a similarkind of process takes place in both classes of objects, or there must beas yet undiscovered companion stars.
| A survey for nanodiamond features in the 3 micron spectra of Herbig Ae/Be stars
Aims.We have carried out a survey of 60 Herbig Ae/Be stars in the 3micron wavelength region in search for the rare spectral features at3.43 and 3.53 micron. These features have been attributed to thepresence of large, hot, hydrogen-terminated nanodiamonds. Only twoHerbig Ae/Be stars, HD 97048 and Elias3-1 are known to display both these features. Methods:.We have obtained medium-resolution spectra (R 2500) with the ESOnear-IR instrument ISAAC in the 3.15-3.65 micron range. Results:.In our sample, no new examples of sources with prominent nanodiamondfeatures in their 3 micron spectra were discovered. Less than 4% of theHerbig targets show the prominent emission features at 3.43 and/or 3.53μm. Both features are detected in our spectrum of HD 97048. Weconfirm the detection of the 3.53 μm feature and the non-detection ofthe 3.43 μm feature in MWC 297. Furthermore, we report tentative 3.53μm detections in V921 Sco, HD 163296 and T CrA. The sources whichdisplay the nanodiamond features are not exceptional in the group ofHerbig stars with respect to disk properties, stellar characteristics,or disk and stellar activity. Moreover, the nanodiamond sources are verydifferent from each other in terms of these parameters. We do not findevidence for a recent supernova in the vicinity of any of thenanodiamond sources. We have analyzed the PAH 3.3 μm feature and thePfund δ hydrogen emission line, two other spectral features whichoccur in the 3 micron wavelength range. We reinforce the conclusion ofprevious authors that flared-disk systems display significantly more PAHemission than self-shadowed-disk sources. The Pf δ line detectionrate is higher in self-shadowed-disk sources than in the flared-disksystems. Conclusions: . We discuss the possible origin and paucityof the (nano)diamond features in Herbig stars. Different creationmechanisms have been proposed in the literature, amongst others in-situand supernova-induced formation. Our data set is inconclusive in provingor disproving either formation mechanism.
| Modeling of PMS Ae/Fe stars using UV spectra
Context: .Spectral classification of AeFe stars, based on visualobservations, may lead to ambiguous conclusions. Aims: . We aimto reduce these ambiguities by using UV spectra for the classificationof these stars, because the rise of the continuum in the UV is highlysensitive to the stellar spectral type of A/F-type stars. Methods: . We analyse the low-resolution UV spectra in terms of a3-component model, that consists of spectra of a central star, of anoptically-thick accretion disc, and of a boundary-layer between the discand star. The disc-component was calculated as a juxtaposition of Planckspectra, while the 2 other components were simulated by thelow-resolution UV spectra of well-classified standard stars (taken fromthe IUE spectral atlases). The hot boundary-layer shows strongsimilarities to the spectra of late-B type supergiants (see Appendix A). Results: . We modeled the low-resolution UV spectra of 37 AeFestars. Each spectral match provides 8 model parameters: spectral typeand luminosity-class of photosphere and boundary-layer, temperature andwidth of the boundary-layer, disc-inclination and circumstellarextinction. From the results of these analyses, combined with availabletheoretical PMS evolutionary tracks, we could estimate their masses andages and derive their mass-accretion rates. For a number of analysed PMSstars we calculated the corresponding SEDs and compared these with theobserved SEDs. Conclusions: . All stars (except βPic) showindications of accretion, that affect the resulting spectral type of thestellar photosphere. Formerly this led to ambiguities in classificatonof PMS stars as the boundary-layer was not taken into consideration. Wegive evidence for an increase of the mass-accretion rate with stellarmass and for a decreases of this rate with stellar age.
| On the binarity of Herbig Ae/Be stars
We present high-resolution spectro-astrometry of a sample of 28 HerbigAe/Be and three F-type pre-main-sequence stars. The spectro-astrometry,which is essentially the study of unresolved features in long-slitspectra, is shown from both empirical and simulated data to be capableof detecting binary companions that are fainter by up to 6mag atseparations larger than ~0.1arcsec. The nine targets that werepreviously known to be binary are all detected. In addition, we reportthe discovery of six new binaries and present five further possiblebinaries. The resulting binary fraction is 68 +/- 11 per cent. Thisoverall binary fraction is the largest reported for any observed sampleof Herbig Ae/Be stars, presumably because of the exquisite sensitivityof spectro-astrometry for detecting binary systems. The data hint thatthe binary frequency of the Herbig Be stars is larger than that of theHerbig Ae stars. The Appendix presents model simulations to assess thecapabilities of spectro-astrometry and reinforces the empiricalfindings. Most spectro-astrometric signatures in this sample of HerbigAe/Be stars can be explained by the presence of a binary system. Twoobjects, HD 87643 and Z CMa, display evidence for asymmetric outflows.Finally, the position angles of the binary systems have been comparedwith available orientations of the circumprimary disc and these appearto be coplanar. The alignment between the circumprimary discs and thebinary systems strongly suggests that the formation of binaries withintermediate-mass primaries is due to fragmentation as the alternative,stellar capture, does not naturally predict aligned discs. The alignmentextends to the most massive B-type stars in our sample. This leads us toconclude that formation mechanisms that do result in massive stars, butpredict random angles between the binaries and the circumprimary discs,such as stellar collisions, are also ruled out for the same reason.
| Near-Infrared and the Inner Regions of Protoplanetary Disks
We examine the ``puffed-up inner disk'' model proposed by Dullemond,Dominik, & Natta for explaining the near-IR excess radiation fromHerbig Ae/Be stars. Detailed model computations show that the observednear-IR excess requires more hot dust than is contained in the puffed-updisk rim. The rim can produce the observed near-IR excess only if itsdust has perfectly gray opacity, but such dust is in conflict with theobserved 10 μm spectral feature. We find that a compact (~10 AU),tenuous (τV<~0.4), dusty halo around the disk innerregions contains enough dust to readily explain the observations.Furthermore, this model also resolves the puzzling relationship noted byMonnier & Millan-Gabet between luminosity and the interferometricinner radii of disks.
| Discovery of the pre-main sequence progenitors of the magnetic Ap/Bp stars?
We report the discovery, using FORS1 at the ESO-VLT and ESPaDOnS at theCFHT, of magnetic fields in the young A-type stars HD 101412, V380 Oriand HD 72106A. Two of these stars (HD 101412 and V380 Ori) are pre-mainsequence Herbig Ae/Be (HAeBe) stars, while one (HD 72106A) is physicallyassociated with a HAeBe star. Remarkably, evidence of surface abundancespots is detected in the spectra of HD 72106A. The magnetic fields ofthese objects display intensities of order 1 kG at the photosphericlevel, are ordered on global scales, and appear in approximately 10% ofthe stars studied. Based on these properties, the detected stars maywell represent pre-main sequence progenitors of the magnetic Ap/Bpstars. The low masses inferred for these objects (2.6, 2.8 and 2.4M_ȯ) represent additional contradictions to the hypothesis ofHubrig et al. (2000, ApJ, 539, 352), who claim that magnetic fieldsappear in intermediate-mass stars only after 30% of their main sequenceevolution is complete. Finally, we fail to confirm claims by Hubrig etal. (2004, A&A, 428, L1) of magnetic fields in the Herbig Ae star HD139614.
| Pre-main sequence star Proper Motion Catalogue
We measured the proper motions of 1250 pre-main sequence (PMS) stars andof 104 PMS candidates spread over all-sky major star-forming regions.This work is the continuation of a previous effort where we obtainedproper motions for 213 PMS stars located in the major southernstar-forming regions. These stars are now included in this present workwith refined astrometry. The major upgrade presented here is theextension of proper motion measurements to other northern and southernstar-forming regions including the well-studied Orion and Taurus-Aurigaregions for objects as faint as V≤16.5. We improve the precision ofthe proper motions which benefited from the inclusion of newobservational material. In the PMS proper motion catalogue presentedhere, we provide for each star the mean position and proper motion aswell as important photometric information when available. We providealso the most common identifier. The rms of proper motions vary from 2to 5 mas/yr depending on the available sources of ancient positions anddepending also on the embedding and binarity of the source. With thiswork, we present the first all-sky catalogue of proper motions of PMSstars.
| Unusual Color Variability of Eruptive Stars
We substantiate the conclusion that the unusual color variability foundpreviously in some eruptive stars is typical of a broad class ofnonstationary objects, manifests itself over a wide temperature range(from B0 to K 3), and can be regarded as a new type of stellarvariability.
| A 10 μm spectroscopic survey of Herbig Ae star disks: Grain growth and crystallization
We present spectroscopic observations of a large sample of Herbig Aestars in the 10 μm spectral region. We perform compositional fits ofthe spectra based on properties of homogeneous as well as inhomogeneousspherical particles, and derive the mineralogy and typical grain sizesof the dust responsible for the 10 μm emission. Several trends arereported that can constrain theoretical models of dust processing inthese systems: i) none of the sources consists of fully pristine dustcomparable to that found in the interstellar medium; ii) all sourceswith a high fraction of crystalline silicates are dominated by largegrains; iii) the disks around more massive stars (M 2.5{M}ȯ, L 60 {L}ȯ) have a higherfraction of crystalline silicates than those around lower mass stars,iv) in the subset of lower mass stars (M 2.5 {M}ȯ)there is no correlation between stellar parameters and the derivedcrystallinity of the dust. The correlation between the shape andstrength of the 10 micron silicate feature reported by van Boekel et al.(2003) is reconfirmed with this larger sample. The evidence presented inthis paper is combined with that of other studies to present a likelyscenario of dust processing in Herbig Ae systems. We conclude that thepresent data favour a scenario in which the crystalline silicates areproduced in the innermost regions of the disk, close to the star, andtransported outward to the regions where they can be detected by meansof 10 micron spectroscopy. Additionally, we conclude that the finalcrystallinity of these disks is reached very soon after active accretionhas stopped.
| Upper limits on CO 4.7 μm emission from disks around five Herbig Ae/Be stars
We present the results of medium-resolution spectroscopy of five nearbyHerbig Ae/Be stars at 4.7 μm: UX Ori, HD 34282, HD 50138, V380 Ori,HK Ori. The goal was to search for CO fundamental ro-vibrationalemission. None of the targets show CO features, either in absorption norin emission. We derive a 5σ upper limit of <10-12cm-2 to the column density of hot CO (T ≈ 1500 K) in thesources. These upper limits are considerably lower than the values ofHerbig Ae/Be stars for which warm and hot CO emission has been reported.The non-detection of CO ν=1-0 emission in these five targets suggestthat Herbig Ae/Be stars are not a homogeneous group with respect to thestructure of the gaseous disk and/or the amount of CO in the inner 50 AUof their disks.
| Dust Morphology and Composition in FU Orionis Systems
FU Orionis stars are a small group of pre-main-sequence stars known forlarge-amplitude optical variability. These objects also exhibitmultiwavelength phenomena suggestive of active accretion from acircumstellar disk. We present high spatial resolution mid-IR imagingand spectroscopy, submillimeter photometry, and 3-4 μm photometry offour FU Ori-class objects, RNO 1B and C, Z CMa, and Par 21, and oneobject classified as a pre-FU Ori star, V380 Ori. We resolve multiple IRsources and extended emission in the RNO 1B/C system, and we discuss indetail their association with disk activity and the source of theInfrared Astronomical Satellite far-IR and radio maser emission in thisfield. We derive dust temperatures and masses for all sources anddiscuss how dust composition and morphology is related to theevolutionary stage of these objects.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Close binary companions of the HAeBe stars LkHα 198, Elias 1, HK Ori and V380 Ori
We present diffraction-limited bispectrum speckle interferometryobservations of four well-known Herbig Ae/Be (HAeBe) stars,LkHα 198, Elias 1,HK Ori and V380 Ori. For two ofthese, LkHα 198 and Elias 1, we present the first unambiguousdetection of close companions. The plane of the orbit of the newLkHα 198 companion appears to be significantly inclined to theplane of the circumprimary disk, as inferred from the orientation of theoutflow. We show that the Elias 1 companion may be a convective star,and suggest that it could therefore be the true origin of the X-rayemission from this object. In the cases of HK Ori and V380 Ori, wepresent new measurements of the relative positions of already-knowncompanions, indicating orbital motion. For HK Ori, photometricmeasurements of the brightness of the individual components in fourbands allowed us to decompose the system spectral energy distribution(SED) into the two separate component SEDs. The primary exhibits astrong infrared excess which suggests the presence of circumstellarmaterial, whereas the companion can be modelled as a naked photosphere.The infrared excess of HK Ori A was found to contribute around twothirds of the total emission from this component, suggesting thataccretion power contributes significantly to the flux. Submillimetreconstraints mean that the circumstellar disk cannot be particularlymassive, whilst the near-infrared data indicates a high accretion rate.Either the disk lifetime is very short, or the disk must be seen in anoutburst phase.Based on observations performed with the 6 m telescope of the SpecialAstrophysical Observatory, Russia, the 2.2 m ESO/MPG telescope at LaSilla, and with the NASA/ESA Hubble Space Telescope, obtained from thedata archive at the Space Telescope Institute. STScI is operated by theassociation of Universities for Research in Astronomy, Inc. under theNASA contract NAS 5-26555.
| Some implications of the introduction of scattered starlight in the spectrum of reddened stars
This paper presents new investigations on coherent scattering in theforward direction (orders of magnitude; conservation of energy;dependence of scattered light on geometry and wavelength), and on howscattered light contamination in the spectrum of reddened stars ispossibly related to as yet unexplained observations (the diminution ofthe 2200 Å bump when the obscuring material is close to the star,the difference between Hipparcos and photometric distances). This paperthen goes on to discuss the fit of the extinction curve, a possible roleof extinction by the gas in the far-UV, and the reasons of theinadequacy of the Fitzpatrick and Massa [ApJSS, 72 (1990) 163] fit.
| X-Ray Study of Herbig Ae/Be Stars
We present ASCA results of intermediate-mass pre-main-sequence (PMS)stars, or Herbig Ae/Be (HAeBe) stars. Among the 35 ASCA pointed sources,we detect 11 plausible X-ray counterparts. X-ray luminosities of thedetected sources in the 0.5-10 keV band are in the range oflogLX~30-32 ergs s-1, which is systematicallyhigher than those of low-mass PMS stars. This fact suggests that thecontribution of a possible low-mass companion is not large. Most of thebright sources show significant time variation; in particular, two HAeBestars-MWC 297 and TY CrA-exhibit flarelike events with long decaytimescales (e-folding time ~10-60 ks). These flare shapes are similar tothose of low-mass PMS stars. The X-ray spectra are successfullyreproduced by an absorbed one- or two-temperature thin-thermal plasmamodel. The temperatures are in the range of kT~1-5 keV, significantlyhigher than those of main-sequence OB stars (kT<1 keV). These X-rayproperties are not explained by wind-driven shocks, but are more likelydue to magnetic activity. On the other hand, the plasma temperaturerises as absorption column density increases or as HAeBe stars ascend toearlier phases. The X-ray luminosity reduces after stellar age of a fewtimes 106 yr. X-ray activity may be related to stellarevolution. The age of the activity decay is apparently near thetermination of jet or outflow activity. We thus hypothesize thatmagnetic activity originates from the interaction of the large-scalemagnetic fields coupled to the circumstellar disk. We also discussdifferences in X-ray properties between HAeBe stars and main-sequence OBstars.
| CO observations of Southern molecular clouds. Outflows from young stellar objects GRV 8 and GRV 16
12CO (1-0) observations of two Southern dark clouds (globules)associated with cometary nebulae GRV 8 (a biconical nebula) and GRV 16(a conelike nebula) are presented. GRV 8 shows an outflow from thecentral part of the nebula (where in 2MASS images a star is located,which is perhaps responsible for this outflow); however, both lobes ofthe outflow are redshifted with a velocity of +1.95 km/s with respect tothe molecular cloud. The two opposite redshifted lobes are a rather rarephenomenon that could be explained by the presence of a double starinstead of a single one as the engine responsible for the outflow. Thetwo lobes are almost parallel to the axis of symmetry of the biconicalnebula. In the case of the conelike nebula GRV 16 we observe a bipolaroutflow, where the eastern blueshifted lobe has a velocity of -4 km/swith respect to the molecular cloud, and the western redshifted one hasa velocity +2.5 km/s. The outflow has a direction almost coinciding withthe axis of symmetry of the conelike nebula. The star associated withthe conelike nebula is responsible for this outflow.
| PAHs in circumstellar disks around Herbig Ae/Be stars
We investigate the presence and properties of PAHs on the surface ofcircumstellar disks around Herbig Ae/Be stars by comparing thepredictions of disk models with observations. We present results of aradiation transfer code for disks heated by the central star, inhydrostatic equilibrium in the vertical direction (flared disks). Thedust is a mixture of large grains in thermal equilibrium, transientlyheated small grains and PAHs. Special attention is given to theinfluence of the stellar, disk and PAH properties on the strength of thePAH emission lines and their spatial distribution. The models predict aninfrared SED showing PAH features at 3.3, 6.2, 7.7, and 11.3 μmclearly visible above the continuum, and with some of them very strong.The PAH emission, spatially extended, comes mostly from the outer diskregion (R100 AU) while the continuum emission at similarwavelengths, mostly due to warm large grains, is confined to theinnermost disk regions (R few AU). We compare the model results toinfrared observations from ISO and ground-based telescopes of somethirty Herbig Ae/Be stars. Most of the observed PAH features in objectswith spectral type later than B9 are well described by our disk modelsand we discuss in some detail the PAH characteristics one can derivefrom the existing data. Objects with strong radiation field (generallyearlier than about B9) have the 3.3 μm feature (often the only oneobserved) much weaker than predicted, and we discuss possibleexplanations (dissipation of the disk, photoevaporation or modificationof the PAH properties).Appendix is only available in electronic form athttp://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
| On Rotation of an Isolated Globule
During CO observations of new Southern objects with the 15-m SEST mmtelescope (Cerro La Silla, Chile) we have found that the globuleconnected with the object CLN127-128 rotates with an angular velocity4.3 · 10-14 s-1, which corresponds to the velocity of extremelyfast rotating globules. The object CLN127-128 is a chain of three stars;two of them are connected with bright nebulae, and the third is asuspected Herbig Ae/Be star. All three stars are bright in near IR,which is specific for the existence of circumstellar shells (or disks)around them. The specific angular momentum of the globule confirms thatit is in virial equilibrium. Besides the finding of a rotating globule,CO observations suggest the presence of a blue-shifted outflow fromCLN127-128 with a velocity of -1.1 km/s (in the system connected withthe globule).
| Does the 3.3 Micron Polycyclic Aromatic Hydrocarbon Emission Feature Require Ultraviolet Excitation?
Unidentified infrared bands (UIBs) have been observed in virtually everydusty astrophysical environment investigated. The UIB carrier must beabundant and ubiquitous. Strong evidence points to polycyclic aromatichydrocarbons as likely candidates, but the identification is notcomplete. Additional diagnostics are needed to further constrain the UIBcarrier, such as probing excitation sources ranging from UV-strong toUV-weak to determine the ``band gap'' of the UIB carrier. Observationsand models suggest that the UIBs can be found in sources with weak UVfields. To that end, we present new results of observing the 3.3 μmspectral region in six stars embedded in reflection nebulae and in sixVega-like stars. These objects have effective temperatures ranging from3500 to 12,000 K. Their environments include dust that should berelatively unprocessed (reflection nebulae) and dust that has mostlikely undergone significant processing (Vega-like) by the embeddedillumination source. Together with data from the literature, we have asample of 27 sight lines. Our analysis suggests that neither thestrength of the UV field impinging on the dust nor the effectivetemperature of the star is the determining factor in whether the 3.3μm UIB emission is present in an object. We found three detections ofthe 3.3 μm emission band, one in a Vega-type object, one in a HerbigAe/Be object, and one in a reflection nebula, and all with disks. Therole of disk geometry is likely to be important in revealing orobscuring the photodissociation regions from which the UIB emissionarises.
| Optical Properties of the Circumstellar Dust around Stars with Aperiodic Fadings
Multicolor observations of 21 rapid, irregular variable stars withAlgol-like fadings and of R Coronae Borealis are used to derive theoptical extinction coefficients of the circumstellar dust associatedwith these objects, θ(λ). We used more than 3600 uniformmulti-color brightness measurements obtained in a rigorous U BV R systemat the Terskol High-altitude Observing Station. The mean extinctioncoefficient θ for the circumstellar dust for this sample of starscoincides almost exactly with the interstellar extinction coefficient,θis, but is somewhat higher in the ultraviolet. We suggest anexplanation for this difference.
| The stellar composition of the star formation region CMa R1 - III. A new outburst of the Be star component in Z CMa
We report on a recent event in which, after more than a decade of slowfading, the visual brightness of the massive young binary Z CMa suddenlystarted to rise by about 1 mag in 1999 December, followed by a rapiddecline to its previous brightness over the next six months. Thisbehaviour is similar to that exhibited by this system around itseruption in 1987 February. A comparison of the intrinsic luminosities ofthe system with recent evolutionary calculations shows that Z CMa mayconsist of a 16-Msolar B0 IIIe primary star and a~3-Msolar FUor secondary with a common age of ~3 ×105 yr. We also compare new high-resolution spectra obtainedin 2000 January and February, during the recent rise in brightness, witharchive data from 1991 and 1996. The spectra are rich in emission lines,which originate from the envelope of the early B-type primary star. Thestrength of these emission lines increased strongly with the brightnessof Z CMa. We interpret the collected spectral data in terms of anaccretion disc with atmosphere around the Herbig B0e component of Z CMa,which has expanded during the outbursts of 1987 and 2000. Ahigh-resolution profile of the 6300 Å[OI] emission line, obtainedby us in 2002 March, shows an increase in flux and a prominent blueshoulder to the feature extending to ~-700 km s-1, which wasmuch fainter in the pre-outburst spectra. We propose that this change inprofile is a result of a strong change in the collimation of a jet, as aresult of the outburst at the start of this century.
| Spectral Analysis and Classification of Herbig Ae/Be Stars
We present an analysis of the optical spectra of 75 early-typeemission-line stars, many of which have been classified previously asHerbig Ae/Be (HAeBe) stars. Accurate spectral types were derived for 58members of the sample; high continuum veiling, contamination bynonphotospheric absorption features, or a composite binary spectrumprevented accurate spectral typing for the rest. Approximately half ofour sample exhibited [O I] λ6300 forbidden-line emission down toour detection limit of 0.1 Å equivalent width; a third of thesample exhibited Fe II emission (multiplet 42). A subset of 11 of theHAeBe sample showed abnormally strong Fe II absorption; 75% of thissubset are confirmed UX Ori objects. Combining our spectral typingresults with photometry from the literature, we confirm previousfindings of high values of total-to-selective extinction(RV~5) in our larger sample, suggesting significant graingrowth in the environments of HAeBe stars. With this high value ofRV, the vast majority of HAeBe stars appear younger than withthe standard RV=3.1 extinction law and are more consistentwith being pre-main-sequence objects.
| The Herbig Ae/Be Star V586 Ori
Studies of the Herbig Ae/Be star V586 Ori based on photoelectricobservations in the Strömgren system are reported. It is found thatas the brightness decreases, the Balmer discontinuity index initiallyincreases and then begins to drop. As the star fades, the indexdecreases. We have previously found similar variations in the indicesand C for UX Ori, RR Tau, and V351 Ori. It is shown that V586 Ori hasthe characteristics of a shell-star.
| Cosmic Rays Acceleration in Wolf-Rayet Stellar Winds
Popescu et al (2004) gave a model for the observed cosmic rays between5×1015 and 3×1018 eV. Their source ispresumed to be the supernova of stars that explode in their winds. Theobserved cosmic rays abundance at the source are affected by spallationin the supernova shell, by the difference in ionization degree (beingone or two times ionized) at the injection in the supernova shock, thestars with initial masses 15MSun≤M≤30MSunhaving a different contribution to them than the stars with30MSun≤M≤50MSun, this being 2:1 for theelements with Z≥6. Still, the abundances after these corrections aredifferent by a factor Zi/ZHe, where Ziis the atomic number for the element i. This paper is dedicated to theexplanation of this factor and its physical meanings by consideringthat, prior to the shock injection, the wind particles are radiativeaccelerated.
| A Catalog of Young Stellar Groups and Clusters within 1 Kiloparsec of the Sun
We present a catalog of near-infrared surveys of young (<~ a few106 yr) stellar groups and clusters within 1 kpc from theSun, based on an extensive search of the literature from the past tenyears. We find 143 surveys from 69 published articles, covering 73different regions. The number distribution of stars in a region has amedian of 28 and a mean of 100. About 80% of the stars are in clusterswith at least 100 members. By a rough classification of the groups andclusters based on the number of their associated stars, we show thatmost of the stars form in large clusters. The spatial distribution ofcataloged regions in the Galactic plane shows a relative lack ofobserved stellar groups and clusters in the range270°
| Observations of Star-Forming Regions with the Midcourse Space Experiment
We have imaged seven nearby star-forming regions, the Rosette Nebula,the Orion Nebula, W3, the Pleiades, G300.2-16.8, S263, and G159.6-18.5,with the Spatial Infrared Imaging Telescope on the Midcourse SpaceExperiment (MSX) satellite at 18" resolution at 8.3, 12.1, 14.7, and21.3 μm. The large angular scale of the regions imaged (~7.2-50deg2) makes these data unique in terms of the combination ofsize and resolution. In addition to the star-forming regions, twocirrus-free fields (MSXBG 160 and MSXBG 161) and a field near the southGalactic pole (MSXBG 239) were also imaged. Point sources have beenextracted from each region, resulting in the identification over 500 newsources (i.e., no identified counterparts at other wavelengths), as wellas over 1300 with prior identifications. The extended emission from thestar-forming regions is described, and prominent structures areidentified, particularly in W3 and Orion. The Rosette Nebula isdiscussed in detail. The bulk of the mid-infrared emission is consistentwith that of photon-dominated regions, including the elephant trunkcomplex. The central clump, however, and a line of site toward thenorthern edge of the cavity show significantly redder colors than therest of the Rosette complex.
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Osservazione e dati astrometrici
| Costellazione: | Orione |
| Ascensione retta: | 05h36m25.43s |
| Declinazione: | -06°42'57.7" |
| Magnitudine apparente: | 10.871 |
| Moto proprio RA: | 7 |
| Moto proprio Dec: | -1.6 |
| B-T magnitude: | 11.676 |
| V-T magnitude: | 10.938 |
Cataloghi e designazioni:
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