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|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.
|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.
|Treasures of Orion.|
|The Intriguing Giant Bow Shocks near HH 131|
Using the High Dispersion Spectrograph (HDS) at the Subaru Telescope,echelle spectra of two giant arcs, i.e., nebulosities Cw and Lassociated with HH 131 in Orion are presented. Typical emission lines ofHerbig-Haro (HH) objects have been detected toward nebulosity Cw withthe broadband filter KV 408. With the low-dispersion spectrograph at theNational Astronomical Observatories (NAO) 2.16 m telescope, spectra ofnebulosities C, L, and K are obtained, which also show strong [S II]λ6717/λ6731, Hα, and [N II] λ6583 emissionlines. Position-velocity distributions of Cw and L are analyzed from thelong-slit spectra observed with the HDS Hα narrowband filter. Thefastest radial velocity of Cw is Vr~-18.0 km s-1.When the flow at L goes to the south, it slows down. The fastest radialvelocity of L has been observed at -45.0 km s-1, and theslowest value is about -18.3 km s-1 the radial velocitygradient is about 200 km s-1 pc-1. The similarityof the fastest radial velocity of Cw to the slowest value of L and theirpositional connection indicate that they are physically associated.There is a tendency for the entire flow to become less excited and lessionized when going further to the south (i.e., from nebulosities K to Land C), where the most extended (and presumably evolved) objects areseen. The electron densities of all the observed nebulosities are low(ne~102 cm-3). Double-peaked kinematicsignatures have been found in Cw from its [N II] λ6583 profiles,while the observed Hα profiles of Cw are almost symmetric. Bowshock models appear to agree with the observed position-velocitydiagrams of the [N II] spectra better than Hα spectra, and a bowshock with its wing, apex, and postshock has been possibly revealed nearCw from the [N II] emission. With the suggestion that these arcs are HHshocks possibly ejected out of the Orion A molecular cloud by anuncertain source, their spectra show low to intermediate excitation fromtheir diagnostic line ratios.Based in part on data collected at Subaru Telescope, which is operatedby the National Astronomical Observatory of Japan.
|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.
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/426/503
|Wide-Area Mapping of 155 Micron Continuum Emission from the Orion Molecular Cloud Complex|
We present the results of a wide-area mapping of the far-infraredcontinuum emission toward the Orion complex by using a Japaneseballoon-borne telescope. The 155-μm continuum emission was detectedover a region of 1.5 deg2 around the KL nebula with 3′resolution similar to that of the IRAS 100-μm map. Assuming asingle-temperature model of the thermal equilibrium dust, maps of thetemperature and the optical thickness were derived from the 155-μmintensity and the IRAS 100-μm intensity. The derived dust temperatureis 5-15K lower and the derived dust optical depth is 5-300 times largerthan those derived from the IRAS 60 and 100-μm intensities due to thesignificant contribution of the statistically heated very small grainsto the IRAS 60-μm intensity. The optical-thickness distribution showsa filamentary dust ridge that has a 1°.5 extent in the north-southdirection and well resembles the Integral-Shaped Filament (ISF)molecular gas distribution. The gas-to-dust ratio derived from the COmolecular gas distribution along the ISF is in the range 30-200, whichmay be interpreted as being an effect of CO depletion due to thephotodissociation and/or the freezing on dust grains.
|Merged catalogue of reflection nebulae|
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
|My researches at the infrared doors|
As a historical and biographical introduction to this Conference, I givehere a brief review about my studies in infrared astronomy. I begunmaking regular observations in this unexplored (at that time) fieldmoving from the wavelengths just beyond the visible, where I discovered,for example, the galaxies then named Maffei 1 and Maffei 2, located inthe Zone of Avoidance. The analysis of the material thus collected,mainly aimed at studies on long period variables (LPVs), produced aseries of new and hardly predicted results. Further importantdevelopments of my researches in infrared are now expected from theongoing development of an Antarctica telescope for the mid-infraredbands. These bands were an almost unexplored range of the spectrum onlya few years ago: now the researches discussed in this meeting show howmany new fields of study have become active in them.
|The Distribution of Atomic Carbon in the Orion Giant Molecular Cloud 1|
The large-scale distribution of the C I(3P1-3P0, 492 GHz) emissionline from Orion A and B giant molecular clouds has been imaged with theMount Fuji submillimeter-wave telescope. The total area observed isabout 15 deg2. The overall spatial and velocity structure ofthe C I line is found to be similar to that of the 13CO(J=1-0) line. The derived column density ratio N(C I)/N(CO) shows alarge variation ranging from 0.2 to 2.9 toward the cloud edges, whereasit is relatively constant between 0.1 and 0.2 toward the interior regionof the entire Orion clouds in both massive star-forming and dark cloudregions. This almost constant ratio suggests that C I can coexist withCO even in the deep inside of the molecular cloud.
|The Photophysics of the Carrier of Extended Red Emission|
Interstellar dust contains a component that reveals its presence byemitting a broad unstructured band of light in the 540-950 nm wavelengthrange, referred to as extended red emission (ERE). The presence ofinterstellar dust and ultraviolet photons are two necessary conditionsfor ERE to occur. This is the basis for suggestions that attribute EREto an interstellar dust component capable of photoluminescence. In thisstudy, we have collected all published ERE observations withabsolute-calibrated spectra for interstellar environments, where thedensity of ultraviolet photons can be estimated reliably. In each case,we determined the band-integrated ERE intensity, the wavelength of peakemission in the ERE band, and the efficiency with which absorbedultraviolet photons are contributing to the ERE. The data show thatradiation is not only driving the ERE, as expected for aphotoluminescence process, but is modifying the ERE carrier, asmanifested by a systematic increase in the ERE band's peak wavelengthand a general decrease in the photon conversion efficiency withincreasing densities of the prevailing exciting radiation. The overallspectral characteristics of the ERE and the observed high quantumefficiency of the ERE process are currently best matched by the recentlyproposed silicon nanoparticle (SNP) model. Using the experimentallyestablished fact that ionization of semiconductor nanoparticles quenchestheir photoluminescence, we proceeded to test the SNP model bydeveloping a quantitative model for the excitation and ionizationequilibrium of SNPs under interstellar conditions for a wide range ofradiation field densities. With a single adjustable parameter, the crosssection for photoionization, the model reproduces the observations ofERE intensity and ERE efficiency remarkably well. The assumption thatabout 50% of the ERE carriers are neutral under radiation conditionsencountered in the diffuse interstellar medium leads to a prediction ofthe single-photon ionization cross section of SNPs with average diameter3.5 nm of <=3.4×10-15 cm2. The shift ofthe ERE band's peak wavelength toward larger values with increasingradiation density requires a change of the size distribution of theactively luminescing ERE carriers through a gradual removal of thesmaller particles by size-dependent photofragmentation. We propose thatheat-assisted Coulomb decay of metastable, multiply charged SNPs is sucha process, which selectively removes the smaller components of anexisting SNP size distribution.
|Discovery of X-rays from the protostellar outflow object HH2|
Herbig-Haro (HH) objects have been known for 50 years to be luminouscondensations of gas in star-forming regions, but their underlyingphysical nature is still being elucidated. Previously suggested modelsencompass newborn stars, stellar winds clashing with nebular material,dense pockets of interstellar gas excited by shocks from outflows, andinterstellar `bullets' (ref. 6). Recent progress has been made with thejet-induced shock model, in which material streams out of young stellarobjects and collides with the surrounding interstellar medium. A clearprediction of this model is that the most energetic Herbig-Haro objectswill emit X-rays, although they have not hitherto been detected. Here wereport the discovery of X-ray emission from one of the brightest andclosest Herbig-Haro objects, HH2, at a level consistent with the modelpredictions. We conclude that this Herbig-Haro object containsshock-heated material located at or near its leading edge with atemperature of about 106K.
|Observations of a curving molecular outflow from V380Ori-NE: further support for prompt entrainment in protostellar outflows|
CO J=3-2 and 4-3 observations of V380Ori-NE reveal a highly collimatedbipolar molecular outflow associated with a jet traced here inH2 1-0 S(1) line emission. The source of the flow is alsodetected at 450 and 850μm with SCUBA. The combined CO and near-IRobservations offer compelling support for the prompt entrainment modelof jet-driven molecular outflows. Not only are the H2 shockfronts spatially coincident with peaks in the CO outflow lobes, but theslope of the mass-velocity distribution in the flow, measured here atintervals along both flow lobes, also clearly decreases just behind theadvancing shock fronts (and towards the ends of the flow lobes), as onewould expect if the high-to-low velocity mass fraction was enhanced bythe entraining shocks. We also find that both lobes of the CO outflowclearly deviate, by some 20°, from the H2 jet directionnear the source. Both lobes may be being deflected at the locations ofthe observed H2 shock fronts, where they impact dense,ambient material. Alternatively, the almost point-symmetric CO flowpattern could be caused by precession at the source. The submillimetre(submm) data reveal the source of the outflow, V380Ori-NE. The 450- and850-μm maps show an elongated peak superimposed on to an extensivepedestal of weaker emission. The major axis of the source is orientedparallel with the inner flow axis. Indeed, weak 850-μm emission isdetected along much of the bipolar outflow, particularly in the southernlobe and towards the southernmost CO intensity peak. The submm`continuum' data therefore probably trace warm dust and CO associatedwith the outflow. These data also confirm the status of V380Ori-NE as aClass I protostar. Overall, the orientation, simplicity and symmetry ofthis outflow, combined with the remarkable strength of the high-velocityline-wing emission in comparison to the ambient emission, make thissystem a perfect laboratory for future detailed studies of bipolarmolecular outflows and their association with collimated jets fromyoung, deeply embedded protostars.
|New Herbig-Haro objects and giant outflows in Orion|
We present the results of a photographic and CCD imaging survey forHerbig-Haro (HH) objects in the L1630 and L1641 giant molecular cloudsin Orion. The new HH flows were initially identified from a deepHα film from the recently commissioned AAO/UKST Hα Survey ofthe southern sky. Our scanned Hα and broad-band R images highlightboth the improved resolution of the Hα survey and the excellentcontrast of the Hα flux with respect to the broad-band R.Comparative IVN survey images allow us to distinguish between emissionand reflection nebulosity. Our CCD Hα, [Sii], continuum and I-bandimages confirm the presence of a parsec-scale HH flow associated withthe Ori I-2 cometary globule, and several parsec-scale strings of HHemission centred on the L1641-N infrared cluster. Several smalleroutflows display one-sided jets. Our results indicate that, fordeclinations south of -6 deg in L1641, parsec-scale flows appear to bethe major force in the large-scale movement of optical dust andmolecular gas.
|Revisiting Hipparcos data for pre-main sequence stars|
We cross-correlate the Herbig & Bell and Hipparcos Catalogues inorder to extract the results for young stellar objects (YSOs). Wecompare the distances of individual young stars and the distance oftheir presumably associated molecular clouds, taking into accountpost-Hipparcos distances to the relevant associations and usingHipparcos intermediate astrometric data to derive new parallaxes of thepre-main sequence stars based on their grouping. We confirm that YSOsare located in their associated clouds, as anticipated by a large bodyof work, and discuss reasons which make the individual parallaxes ofsome YSOs doubtful. We find in particular that the distance of TaurusYSOs as a group is entirely consistent with the molecular clouddistance, although Hipparcos distances of some faint Taurus-Auriga starsmust be viewed with caution. We then improve some of the solutions forthe binary and multiple pre-main sequence stars. In particular, weconfirm three new astrometric young binaries discovered by Hipparcos:RY Tau, UX Ori, and IXOph. Based on observations made with the ESA Hipparcosastrometry satellite
|The Cepheid distance to M96 and the Hubble constant|
HST WFPC2 observations of Cepheids in M96 (NGC 3368) are used to find adistance to that galaxy of 11.2+/-1.0Mpc. This estimate is based on acalibration of the Cepheid period-luminosity relation in the LargeMagellanic Cloud, and includes a correction for the difference inmetallicity between the two systems. There are good reasons forbelieving M96 is at the same distance as four E/S0 galaxies in the Leo-Igroup, and hence we calibrate secondary distance indicators based on theearly-type galaxies, namely the fundamental plane andsurface-brightness-fluctuation method. Also the Type Ia supernova 1998buoccurred in M96 itself and is used to calibrate the SN Ia distancescale. These methods reach to recession velocities of greater than5000kms-1 and can therefore allow us to evaluate the Hubbleconstant without reference to the peculiar velocity of M96 itself. Infact, these indicators agree well between themselves and hence we findH0=67+/-7kms-1Mpc-1 where the quotederror includes estimates of potential systematic effects.
|Survey of bipolar outflows and methanol masers in the C(32) S (2-1) and C(34) S (2-1) lines in the Northern sky|
A survey of 158 sources (bipolar outflows and methanol masers) wascarried out in the CS(2-1) and C(34) S(2-1) lines to measure and comparedensities in a large number of bipolar outflows and in Class I and ClassII methanol masers, both associated with and unrelated to bipolaroutflows. The statistical characteristics of the regions, forming ClassI methanol masers differ from those both in the centres of bipolaroutflows and in the regions forming Class II methanol masers. It ispossible that physical conditions in bipolar outflows are closer tophysical conditions of Class II methanol masers. Figures i and ii areonly available in electronic form at http://www.edpsciences.com
|Polarimetry and magnetic field structure of the Herbig-Haro objects HH1 and HH2 and their environment|
We present continuum and Hα imaging polarimetry of the Herbig-Haroobjects HH1 and HH2, the faint nebulosity which surrounds them, andnearby stars. We also discuss IRAS observations of the area. We findevidence for a strongly dichroic interstellar medium throughout thisregion, which polarizes local Hα emission and severely distortsthe underlying polarization pattern arising in light scattered from thecentral object VLA1. It also polarizes nearby stars. This dichroism canbe explained by alignment of dust in a magnetic field which, on largescales, is aligned at PA = 126 deg but, on smaller scales, is distortedwithin the HH1-HH2 system. Its geometry appears consistent with modelsof star formation in which a large-scale rotating disc drives an outflowvia twisted axial field lines. Both HH1 and HH2 are also associated withsmall-scale polarization patterns. These can best be understood asresulting from internal dichroic extinction arising in a concentrationof well-aligned dust grains lying within the shocked Hα-emittingregions of these objects. The polarization of HH1 exhibits spiralstructure, which may offer support to magnetized jet models, but thepolarization of HH2 is more disordered. Our results suggest that furtheremission-line polarimetry may offer new insights into the structure ofHH objects.
|V380 Ori--A Herbig Ae/Be star at an early stage of envelope formation: Hydrogen-line profiles|
We continue to analyze the spectrum of the Herbig Ae/Be star V380 Ori.The hydrogen-line profiles in the spectra of V380 Ori, BF Ori, and gammaCas shell stars (XX Oph and Pleione) are compared. We analyze thethree-component model that consists of optically thick and opticallythin (in continuum) envelopes around an A0 star with a luminosity closeto the ZAMS luminosity. The star manifests itself only in thehydrogen-line wings. The emission shell changes its luminosity andshape, which shows up in highly variable bright emission lines of gasesand metals. The optically thick envelope is more stable. The origin,luminosity, and instability of the envelopes are related tononstationary accretion from a cold protoplanetary disk. The chemicalcomposition of the envelopes lends support to this version.
|An X-Ray Survey of Very Young Stellar Objects|
Several recent studies with the ROSAT and ASCA satellites have reportedX-ray emission from Class I protostars. We present here an X-ray surveyof 156 protostellar sources using archived ROSAT PSPC pointedobservations. Targets are drawn from four samples: low-temperatureobjects in nearby star forming regions, Herbig-Haro outflow sources, COoutflow sources, and Class 0 embedded protostars. Over 90% are notdetected at the 3 sigma limit over the 1.0-2.4 keV band, with upperlimits of 0.1-40 counts ks^-1 corresponding to log L_X ~= 28-33 ergss^-1. Of the 11 detected objects, 10 are either Class II or III stars orpreviously detected Class I protostars. One new Class I source, Ced 110IRS 6 in the Chamaeleon I cloud, is found. The X-ray luminosity functionof protostars is calculated, but is quite uncertain. We conclude thatX-ray emission from protostars has a broad luminosity function and thatvery X-ray luminous (L_X >~ 10^31 ergs s^-1) protostars are rare.
|A Spatially Complete ^13CO J = 1-0 Survey of the Orion A Cloud|
We present the results of new ^13CO J = 1-0 observations of the Orion Amolecular cloud made with two 4 m telescopes at Nagoya University. Thearea observed, corresponding to l ~ 208 deg-215 deg and b ~ -20.5d to-18.0d, covers the full extent of this giant molecular cloud at a2.0′ grid spacing with a 2.7′ beam. The presentobservations provide the first complete coverage of the cloud in ^13COwith a reasonably high angular resolution relative to the cloud's size.In addition, the high velocity resolution of 0.1 km s^-1 allowed us toresolve velocity components of the ^13CO emission. The moleculardistribution is highly elongated along the Galactic plane and isfilamentary, as is consistent with previous molecular maps. The totalmolecular mass of the cloud is estimated to be ~5.4 x 10^4 M_ȯ. Byusing the velocity channel maps every 0.5 km s^-1, 39 individualfilamentary components have been identified, and their basic physicalquantities have been estimated. They typically are 4.8 pc in length, 1.4pc in width, and 660 M_ȯ in mass. We also find that thesefilamentary components are nearly in virial equilibrium.
|HIPPARCOS photometry of Herbig Ae/Be stars|
The photometric behaviour of a sample of 44 Herbig Ae/Be (HAeBe)candidate stars was studied using a uniform set of optical photometryobtained by the Hipparcos mission. Astrophysical parameters (distance,temperature, luminosity, mass, age) of this sample of stars were derivedas well by combining the astrometric data provided by Hipparcos withdata from literature. Our main conclusions can be summarized as follows:(1) More than 65% of all HAeBe stars show photometric variations with anamplitude larger than 0\fm05; (2) HAeBes with a spectral type earlierthan A0 only show moderate (amplitude < 0\fm5) variations, whereasthose of later spectral type can (but not necessarily have to) showvariations of more than 2\fm5. We explain this behaviour as being due tothe fact that stars with lower masses become optically visible, andhence recognizable as Herbig Ae stars, while still contracting towardsthe zero-age main sequence (ZAMS), whereas their more massivecounterparts only become optically visible after having reached theZAMS; (3) The Herbig stars with the smallest infrared excesses do notshow large photometric variations. This can be understood by identifyingthe stars with lower infrared excesses with the more evolved objects inour sample; (4) No correlation between the level of photometricvariability and the stellar v sin i could be found. If the largephotometric variations are due to variable amounts of extinction by dustclouds in the equatorial plane of the system, the evolutionary effectsprobably disturb the expected correlation between the two. Based on datafrom the Hipparcos astrometry satellite.
|Photodissociated H I in NGC 2023|
We report the detection of photodissociated H I toward the reflectionnebula NGC 2023. The Very Large Array observations reveal compact (~ 0.3pc) emission associated with the source. The observed spectrum has adouble-peaked profile that we believe is caused by absorbing foregroundneutral gas. We corrected the observed spectrum for the absorption, anddetermined with this absorption-corrected profile an H I column densityand mass of 1.7 ×1021 cm-2 and 1.2Modot, respectively. This column density agrees well withtheoretical model predictions. The H I 21 cm map shows a morphology verysimilar to that present in the images of [C II] at 158 μm, HIRES 60μm IRAS, and POSS optical.
|Extensive High-Resolution 12CO Imaging of L1641 in Orion|
We obtained extensive 12CO J = 1--0 images along the minor axis of theL1641 cloud in Orion with a 15" (0.03 pc) beam spaced by 34". Besidesbright ridgelike emission in the middle of the cloud, we detected COemission almost everywhere within the outermost boundary of the cloud.There are at least two distinct populations of molecular gas:well-defined "clumps" with high brightness temperature (~25 K) and smallline width (~=1.5 km s-1), and "extended components" with low brightnesstemperature (~2.5 K) and broad line width (~=2.5 km s-1). The 12CO J =1--0 emission shows clumpy features even in the periphery of the cloud.The clumps dominate the CO luminosity from the central ridge region andare severely overlapped, while they are isolated in the periphery of thecloud. The extended component is widely distributed, especially in theeastern side of the cloud, and seems to be connected to the atomic gaslayer in the Galactic plane. It lacks notable substructures at ourspatial resolution and exhibits a surface filling factor very close tounity. The extended component does not fill the interclump space, atleast in the velocity domain. The ridge component may be separating fromthe extended molecular material. To deduce physical conditions ofmolecular gas, we conducted simultaneous 12CO J = 2--1/J = 1--0strip-scan observations along the minor axis of the cloud with highersensitivity and denser sampling. Molecular gas density estimated fromexcitation analysis of the 12CO emission was >~3 x 103 cm-3 in theclumps and ~=2 x 102 cm-3 in the extended component. The peripheralregion of the cloud is fainter in CO brightness not because the surfacefilling factor of emitting gas is smaller, but because the emission isdominated by the tenuous extended component with low brightnesstemperature.
|50 Years of Herbig-Haro Research. From discovery to HST|
We review the events leading to the discovery of Herbig-Haro objectshalf a century ago, and the early efforts to understand the nature ofthese enigmatic objects. The recognition in the mid-seventies of theshocked nature of HH objects heralded a burst of observational andtheoretical efforts, and further impetus was soon after provided by thediscovery of high proper motions, and by detailed optical, infrared andultraviolet spectroscopic studies. The recognition in the early eightiesof HH jets was the starting point for the increasingly intense studiesduring the last 15 years which we discuss in this Symposium. In thesecond half of our review, we summarize the insights into the nature ofHH jets provided by analyzing high resolution images obtained with theHubble Space Telescope of two of the finest known HH jets, HH 47 and HH111.
|A Survey of Near-Infrared Emission in Visual Reflection Nebulae|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..102..369S&db_key=AST
|Herbig-Haro outflows in the V 380 Orionis region.|
We report the discovery of a remarkable emission line ``loop" to thewest of V 380 Ori. This ``loop", taken together with the known and somenewly found Herbig-Haro (HH) objects, appears to delineate a poorlycollimated optical outflow from this source. The optical outflowcomplements a redshifted molecular outflow to the east of V 380 Oriimplying an overall east-west outflow axis. Although V 380 Ori isclassified as a Herbig Ae/Be (HAEBE) star, it shows LiIλ6708 inabsorption suggesting the additional presence of a T-Tauri star. In thisregard, it is interesting that Leinert et al. (1994), usingnear-infrared speckle interferometry, have recently found V 380 Ori tobe a double. It seems unlikely, however, that the T-Tauri star isresponsible for the outflow. In the area around V 380 Ori, two otheroptical outflows were investigated, HH130 and the newly discoveredHH147. The bow-shaped HH130 was previously thought to be an isolatedobject but we show here that it is part of an extended (>0.7pc)outflow and demonstrate that it could be driven by a ``light" jet. HH147is particularly interesting in that its source, a T-Tauri star, is foundto exhibit a P-Cygni profile in Hα. HH147 itself appears tocontain both highly and poorly collimated outflow components.
|The spatial distribution of X-ray selected T-Tauri stars. I. Orion.|
We establish a criterion for selecting low-mass, pre-main sequence starcandidates from X-ray sources discovered in the ROSAT All-Sky Survey.X-ray properties and non-spectroscopic data (hardness ratios and X-rayto optical flux ratio) of 187 optically identified X-ray sources in theOrion star forming region are used as a training set for anon-parametric discrimination analysis. We show that high selectionreliabilities of weak-line T-Tauri stars (wTTS) can be obtained withthis method. We utilize the selection procedure to predict the largescale spatial distribution of TTS candidates in a 710deg^2^ field aroundthe Orion SFR. Five significant surface density enhancements areidentified, four of them are well matched with OB subgroup associations(OB1a, λ-Ori, OB1b, OB1c). A dispersion time of 2-10Myr can bederived from their spatial extent, consistent with the ages of thestellar component in these regions. We suspect a young stellar clusterin the vicinity of NGC 1788, where a high concentration of TTScandidates resides. The largest fraction of the predicted wTTSpopulation is distributed widely over an area many times greater thanthat of the molecular gas. If these sources really are wTTS, they mustbe either much older than usually assumed or have a high velocitydispersion.
|A K' imaging survey of molecular outflow sources|
A K'-band imaging survey with a approximately equals 8 min x 3 min fieldof view of all regions associated with CO molecular outflow from thelist of Fukui (1989) has been conducted. We present the individualimages and describe individual nebulous objects and star clusters. Thedata, including photometric calibration data, are being published asFITS files on a CD-ROM. The vast majority of all outflow sources areassociated with nebulosity detectable in K', so such nebulae can be usedas tracers for very young stars. We find a significant fraction(one-third) of molecular outflow sources to be associated with clustersof young stars. Most of the young embedded clusters show peaks in theirK' magnitude histograms that, if interpreted as an evolutionary effect,indicate average ages of the embedded star population of is less than 1x 106 yr.
|Herbig Ae/Be stars|
Herbig Ae/Be stars are the higher mass counterparts of the T Tauristars. In comparison with the latter, however, relatively little isknown about them. After a historical introduction, we briefly reviewtheir optical and ultraviolet (UV) spectroscopic properties. We considerthe evidence for and against disks around Herbig Ae/Be stars; theexistence of which remains highly controversial. We also examinein-depth their interaction with the surrounding medium as manifestedthrough optical outflows. It is shown that although there aresimilarities with analogous outflows from lower mass young stars, thosefrom Herbig Ae/Be stars may be more poorly collimated. Jets, however,are found in at least some cases.
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