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Post-outburst phase of McNeil's nebula (V1647 Orionis)
We present a detailed study of the post-outburst phase of McNeil'snebula (V1647 Orionis) using optical B, V, R, I and near-infrared (NIR)J, H, K photometric and low-resolution optical spectroscopicobservations. The observations were carried out with the Himalaya FaintObject Spectrograph Camera (HFOSC), NIR camera (NIRCAM), the TataInstitute of Fundamental Research (TIFR) Near-Infrared Camera (TIRCAM)and NICMOS cameras on the 2-m Himalayan Chandra Telescope (HCT) and1.2-m Physical Research Laboratory (PRL) telescopes during the period2004 February-2005 December. The optical and NIR observations show ageneral decline in the brightness of the exciting source of McNeil'snebula (V1647 Ori). Our recent optical images show that V1647 Ori hasfaded by more than 3 mag since February 2004. McNeil's nebula has alsofaded considerably. The optical/NIR photometric data also show asignificant variation in the magnitudes (ΔV= 0.78, ΔR= 0.44,ΔI= 0.21, ΔJ= 0.24 and ΔH= 0.20 mag) of V1647 Oriwithin a period of one month, which is possibly undergoing a phasesimilar to eruptive variables, like EXors or FUors. The optical spectrashow a few features such as strong Hα emission with blue-shiftedabsorption and the CaII IR triplet (8498, 8542 and 8662 Å) inemission. As compared to the period just after outburst, there is adecrease in the depth and extent of the blue-shifted absorptioncomponent, indicating a weakening in the powerful stellar wind. Thepresence of the CaII IR triplet in emission confirms that V1647 Ori is apre-main-sequence star. The long-term, post-outburst photometricobservations of V1647 Ori suggest an EXor rather than an FUor event. Anoptical/IR comparison of the region surrounding McNeil's nebula showsthat the optical nebula is more widely and predominantly extended to thenorth, whereas the IR nebula is relatively confined (diameter ~60arcsec), but definitely extended, to the south, too. The large colourgradient from north to south and the sudden absence of an optical nebulato the south are suggestive of a large-scale disc-like structure (orenvelope) surrounding the central source that hides the southern nebula.
| Star formation in the southern dark cloud DC 287.1+02.4
Aims.We report the discovery of a group of 12 new infrared sources seentoward IRAS 10501-5630 and the southern dark globule DC 287.1+02.4. Theglobule appears as a round patch of extinction in optical images with atypical diameter of 5 arcmin. Methods: .The sources are seen on Ksand L' band images taken using SOFI at the NTT and ISAAC at the VLT. Theglobule was mapped in millimeter molecular transitions (CO(1-0),C18O(1-0), C18O(2-1), CS(2-1), HCN(1-0)) using theSEST telescope. Results: .Millimeter-wave spectroscopy revealed asingle dense core seen in C18O, CS, and HCN, extending about2 arcmin. The infrared sources are likely to be embedded in the densecloud core. The reddest of the new infrared sources, named here DC287.1+02.4 IRS, is not detected shortward of 2 μm, and it exhibits avery red (Ks - L') colour. The location and colour of this sourcesuggest that this is the near-infrared counterpart of IRAS 10501-5630.Red nebular emission with an elongated shape is also seen in the H andKs band images and could be due to scattered light originating in theembedded objects.
| Decay of Planetary Debris Disks
We report new Spitzer 24 μm photometry of 76 main-sequence A-typestars. We combine these results with previously reported Spitzer 24μm data and 24 and 25 μm photometry from the Infrared SpaceObservatory and the Infrared Astronomy Satellite. The result is a sampleof 266 stars with mass close to 2.5 Msolar, all detected toat least the ~7 σ level relative to their photospheric emission.We culled ages for the entire sample from the literature and/orestimated them using the H-R diagram and isochrones; they range from 5to 850 Myr. We identified excess thermal emission using an internallyderived K-24 (or 25) μm photospheric color and then compared allstars in the sample to that color. Because we have excluded stars withstrong emission lines or extended emission (associated with nearbyinterstellar gas), these excesses are likely to be generated by debrisdisks. Younger stars in the sample exhibit excess thermal emission morefrequently and with higher fractional excess than do the older stars.However, as many as 50% of the younger stars do not show excessemission. The decline in the magnitude of excess emission, for thosestars that show it, has a roughly t0/time dependence, witht0~150 Myr. If anything, stars in binary systems (includingAlgol-type stars) and λ Boo stars show less excess emission thanthe other members of the sample. Our results indicate that (1) there issubstantial variety among debris disks, including that a significantnumber of stars emerge from the protoplanetary stage of evolution withlittle remaining disk in the 10-60 AU region and (2) in addition, it islikely that much of the dust we detect is generated episodically bycollisions of large planetesimals during the planet accretion end game,and that individual events often dominate the radiometric properties ofa debris system. This latter behavior agrees generally with what we knowabout the evolution of the solar system, and also with theoreticalmodels of planetary system formation.
| Disk Evolution in the Orion OB1 Association
We analyze multiband photometry of a subsample of low-mass stars in theassociations Ori OB1a and 1b discovered during the Centro deInvestigaciones de Astronomía (CIDA) Orion Variability Survey,which have ages of 7-10 and 3-5 Myr, respectively. We obtainedUBVRCIC photometry at Mount Hopkins for sixclassical T Tauri stars (CTTSs) and 26 weak T Tauri stars (WTTSs) in OriOB1a and for 21 CTTSs and two WTTSs in Ori OB1b. We also obtained L-bandphotometry for 14 CTTSs at Mount Hopkins and 10 and 18 μm photometrywith OSCIR at Gemini for six CTTSs; of these, all six were detected at10 μm, whereas only one was detected at 18 μm. We estimate massaccretion rates from the excess luminosity at U and find that they areconsistent with determinations for a number of other associations, withor without high-mass star formation. The observed decrease of massaccretion rate with age is qualitatively consistent with predictions ofviscous evolution of accretion disks, although other factors can alsoplay a role in slowing accretion rates. We compare the excesses overphotospheric fluxes in H-K, K-L, and K-N with the younger sample ofTaurus and find an overall decrease of disk emission from Taurus to OriOB1b to Ori OB1a. This decrease implies that significant grain growthand settling toward the midplane has taken place in the inner disks ofOri OB1. We compare the spectral energy distribution of the stardetected at both 10 and 18 μm with disk models for similar stellarand accretion parameters. We find that the low fluxes shortward of 18μm of this Ori OB1b star cannot be due to the smaller disk radiusexpected from viscous evolution in the presence of the far-ultravioletradiation fields from the OB stars in the association. Instead, we findthat the disk of this star is essentially a flat disk, with little ifany flaring, indicating a significant degree of dust settling toward themidplane, as expected from dust evolution in protoplanetary disks.
| 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.
| An L'-band survey for circumstellar discs around low-mass stars in the young σ Orionis cluster
We present new K- and L'-band imaging of a representative sample ofmembers of the young 3-5 Myr old σ Orionis cluster. We identifiedobjects with (K-L') excess by analysing colour-colour diagrams andcomparing the observations with empirical main-sequence colours. Thederived disc frequency depends on the method used: (54 +/- 15) per centif measured directly from the JHKL' colour-colour diagram, or (46 +/-14) per cent if excesses are computed with respect to predictedphotospheric colours (according to the object spectral types, 2σexcess detections). We compare the (K-L') excess with other indicatorsand show that this is a robust and reliable disc indicator. We alsocompare the derived disc frequency with similarly aged clusters anddiscuss possible implications for disc lifetimes. The computed age ofthe σ Ori cluster is very important; a cluster age of 3 Myr wouldsupport the overall disc lifetime of 6 Myr proposed in the literature,while an age >4 Myr would point to a slower disc destruction rate.
| L' and M' standard stars for the Mauna Kea Observatories Near-Infrared system
We present L' and M' photometry, obtained at the United Kingdom InfraredTelescope (UKIRT) using the Mauna Kea Observatories Near-Infrared(MKO-NIR) filter set, for 46 and 31 standard stars, respectively. The L'standards include 25 from the in-house `UKIRT Bright Standards' withmagnitudes deriving from Elias et al. and observations at the InfraredTelescope Facility in the early 1980s, and 21 fainter stars. The M'magnitudes derive from the results of Sinton and Tittemore. We estimatethe average external error to be 0.015 mag for the bright L' standardsand 0.025 mag for the fainter L' standards, and 0.026 mag for the M'standards. The new results provide a network of homogeneously observedstandards, and establish reference stars for the MKO system, in thesebands. They also extend the available standards to magnitudes whichshould be faint enough to be accessible for observations with moderndetectors on large and very large telescopes.
| Molecular Outflows in the Young Open Cluster IC 348
We present a wide-field survey of the young open cluster IC 348 formolecular H2 outflows. Outflow activity is only found at itssouthwestern limit, where a new subcluster of embedded sources is in anearly phase of its formation. If the IC 348 cluster had been built up bysuch subclusters forming at different times, this could explain thelarge age-spread that Herbig (1998) found for the IC 348 member stars.In addition to several compact groups of H2 knots, our surveyreveals a large north-south oriented outflow, and we identify the newlydiscovered far-infrared and millimeter object IC 348 MMS as its source.New deep images in the 1-0 S(1) line of molecular hydrogen trace the HH211 jet and counterjet as highly collimated chains of knots, resemblingthe interferometric CO and SiO jets. This jet system appears rotatedcounterclockwise by about 3° with respect to the prominentH2 bow shocks. Furthermore, we resolve HH 211-mm as a doublepointlike source in the millimeter continuum.Based on observations taken at the German-Spanish Astronomical Centre,Calar Alto, operated by the Max-Planck-Institute für Astronomie,Heidelberg, jointly with the Spanish National Commission for Astronomyand on observations with ISO, an ESA project with instruments funded byESA Member States (especially the PI countries: France, Germany, theNetherlands, and the United Kingdom) and with the participation of ISASand NASA.
| Near-Infrared Photometric Survey of Proto-planetary Nebula Candidates
We present JHK' photometric measurements of 78 objects mostly consistingof proto-planetary nebula candidates. Photometric magnitudes aredetermined by means of imaging and aperture photometry. Unlike theobservations with a photometer with a fixed-sized beam, the method ofimaging photometry permits accurate derivation of photometric values,because the target sources can be correctly identified and confusionwith neighboring sources can be easily avoided. Of the 78 sourcesobserved, we report nearly 10 cases in which the source seems to havebeen misidentified or confused by nearby bright sources. We also presentnearly two dozen cases in which the source seems to have indicated avariability that prompts a follow-up monitoring. There are also a fewsources that show previously unreported extendedness. In addition, wepresent H-band finding charts of the target sources.
| High angular resolution K-band spectroscopy of the nucleus of NGC 1068 with PUEO-GRIF (CFHT)
We provide new high angular resolution K-band spectroscopic observationsof the nucleus of NGC 1068 obtained with the new 3-Dspectrograph GriF coupled to PUEO, the CFHT adaptive optics system.Results match well with the general framework of the unified model ofactive galactic nuclei (AGN) and bring more precise evaluation of thesize and structure of the close AGN environment. The K-band emission isdominated by the thermal continuum of the compact central source (albeitresolved: FWHM ~ 0.12\arcsec) with a color temperature around 950 K(reddened sublimation temperature of the dust, corresponding to 1200 Kwhen deredenned), interpreted as the border of a sublimation cavitywithin the dust torus, surrounding the central core. Coronal emissionlines ([Si Vi], [Si Vii] and [Ca Viii]) are detected from a few tenthsof arcseconds around this compact source and a new [Si Vi] emission spotis found at 0.7\arcsec north of the central source. The Brackett gammaemission features a very broad component (FWHM=2500 km s-1)in the central 200 mas and we claim that it correponds to the broad lineregion seen through the dust. A narrower component (FWHM=1600 kms-1) is seen at larger angular distance and is likely thetrace of the narrow line region. Molecular hydrogen emission lines aredetected beyond 0.6\arcsec of the central source. We interpret the lackof emission in the center as a lack of excited molecular H_2 along theline of sight, because of the putitative dust torus shading gas from UVphotons. No evidence of stellar activity in a 1\arcsec radius around thecentral source can be found. We also compare these observations to theresults of a numerical model of a torus harboring an active galacticnucleus. The main characteristics of the observed spectra (slope, flux)match well with the unified scheme of AGN, in the case of a dense (tau_V=40) obscuring torus containing silicate grains with an inclinationangle of around 22° with regards to the line of sight.
| H II Emission from a Complete Spectroscopic Survey of Be Stars in h and χ Persei
We describe data for emission-line B stars observed in a spectroscopicsurvey of h and χ Persei. The survey is complete to V=12.5 andcovers an area of ~1100 arcmin2 roughly centered on the twoclusters. We detect 32 Be stars; some have low Hα emissionstrength. Seven of these are new identifications; seven others areconfirmations of Be stars previously identified using photometry. Fiveof the observed Be stars show significant Hα profile variationsfrom epoch to epoch. We show that spectral indices yield physicalcharacteristics of the H II emission region. This automatic method isrobust and easily applied to large spectroscopic samples. We inferHα:Hβ flux ratios of 2-5 and observe a linear relationshipbetween Hα emission and J-K color for these stars. We include aHertzsprung-Russell diagram for the B-type stars in the clusters.
| Near-Infrared Observations of S 255-2 : The Heart of a Massive YSO Cluster
High-resolution near-infrared (J H K L' M') images of a massivestar-forming region, S 255-2, were obtained with the Subaru Telescopeand an infrared camera, CIAO. These images clearly resolve two sets ofbipolar nebulae illuminated by two independent massive YSOs. A number ofcluster member YSOs have been detected, including 3 new sources. Sevenearly-B type stars have been identified within 10pc of S 255-2; threeare associated with extended optical H II regions. The variation in theappearance of these early-B type stars suggests an evolutionary sequenceof massive stars in the S 255 region.
| Mid-Infrared Spectral Energy Distribution of NGC 1068 with 0.1" Spatial Resolution
The central region of the Seyfert 2 galaxy NGC 1068 is imaged in themid-infrared (MIR) using the Mid-Infrared Test Observation System on the8.2 m Subaru Telescope. The oversampling pixel scale associated with theshift-and-add method shows 0.1" resolution images with a high dynamicrange after deconvolution. Along with an extended structure at aposition angle (P.A.) of -10° with higher surface brightness,another structure extends wider with lower surface brightness at a P.A.of 20°. The central peak elongates north-south with FWHM of0.3"×0.2". Spectral energy distribution (SED) of the central peakis fitted to have the silicate absorption feature ofτ9.7μm=0.9+/-0.3. This is half of the absorptionexpected from the near-infrared (NIR) feature of carbonaceous dust. Thissuggests a temperature gradient of the absorbing dust along the line ofsight. Another possibility, which is not distinguishable here, is thesize distribution of dust different from our Galaxy. Intrinsicluminosity of emission from the central peak is 3×1037W. The SED shows a hint of the polycyclic aromatic hydrocarbon (PAH)emission features. Although a high spatial resolution MIR spectrum isrequired, it suggests that the PAH carriers near the active galacticnuclei (AGNs) are sheltered from the high-energy emission from the AGNsand that the AGNs have nuclear starbursts. For the NIR disklikestructures, no counterparts are detected in the MIR. The nature of thestructures remains unclear. Based on data collected at Subaru Telescope,which is operated by the National Astronomical Observatory of Japan.
| Protoplanetary Disks in the Nearest Star-Forming Cloud: Mid-Infrared Imaging and Optical Spectroscopy of MBM 12 Members
The recent identification of several groups of young stars within 100 pcof the Sun has generated widespread interest. Given their proximity andpossible age differences, these systems are ideally suited for detailedstudies of star and planet formation. Here we report on the firstinvestigation of protoplanetary disks in one such group, thehigh-latitude cloud MBM 12 at a distance of ~65 pc. We presentmid-infrared observations of the eight candidate pre-main-sequence (PMS)members and the two main-sequence (MS) stars in the same line of sight,which may or may not be associated with the group. We have also derivedHα and Li line widths from medium-resolution optical spectra. Wereport the discovery of significant mid-infrared excess from six PMSstars-LkHα 262, LkHα 263, LkHα 264, E02553+2018, RXJ0258.3+1947, and S18-presumably due to optically thick circumstellardisks. Our flux measurements for the other two PMS stars and the two MSstars are consistent with photospheric emission, allowing us to rule outdusty inner disks. The disks we have found in MBM 12 represent thenearest known sample of very young protoplanetary systems and thus areprime targets for high-resolution imaging at infrared and millimeterwavelengths.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| A 10 Micron Search for Truncated Disks Among Pre-Main-Sequence Stars with Photometric Rotation Periods
We use mid-IR (primarily 10 μm) photometry as a diagnostic for thepresence of disks with inner cavities among 32 pre-main-sequence starsin Orion and in Taurus-Auriga for which rotation periods are known andfor which there is no evidence of inner disks at near-IR wavelengths.Disks with inner cavities are predicted by magnetic disk-locking modelsthat seek to explain the regulation of angular momentum in T Tauristars. Only three stars in our sample show evidence of excess mid-IRemission. Although these three stars may possess truncated disksconsistent with magnetic disk-locking models, the remaining 29 stars inour sample do not. Apparently, stars lacking near-IR excesses in generaldo not possess truncated disks to which they are magnetically coupled.We discuss the implications of this result for the hypothesis ofdisk-regulated angular momentum. Evidently, young stars can exist asslow rotators without the aid of present disk locking, and there existvery young stars already rotating at nearly breakup velocity whosesubsequent angular momentum evolution will not be regulated by disks.Moreover, we question whether disks, when present, truncate in themanner required by disk-locking scenarios. Finally, we discuss the needfor rotational evolution models to take full account of the largedispersion of rotation rates present at 1 Myr; doing so may allow themodels to explain the rotational evolution of low-mass pre-main-sequencestars in a way that does not depend on braking by disks.
| Infrared L-Band Observations of the Trapezium Cluster: A Census of Circumstellar Disks and Candidate Protostars
We report the results of a sensitive near-infrared JHKL imaging surveyof the Trapezium cluster in Orion. We use the JHKL colors to obtain acensus of infrared excess stars in the cluster. Of (391) stars brighterthan 12th magnitude in the K and L bands, 80%+/-7% are found to exhibitdetectable infrared excess on the J-H, K-L color-color diagram.Examination of a subsample of 285 of these stars with published spectraltypes yields a slightly higher infrared excess fraction of 85%. We findthat 97% of the optical proplyds in the cluster exhibit excess in theJHKL color-color diagram indicating that the most likely origin of theobserved infrared excesses is from circumstellar disks. We interpretthese results to indicate that the fraction of stars in the cluster withcircumstellar disks is between 80%-85%, confirming earlier publishedsuggestions of a high disk fraction for this young cluster. Moreover, wefind that the probability of finding an infrared excess around a star isindependent of stellar mass over essentially the entire range of thestellar mass function down to the hydrogen burning limit. Consequently,the vast majority of stars in the Trapezium cluster appear to have beenborn with circumstellar disks and the potential to subsequently formplanetary systems, despite formation within the environment of a richand dense stellar cluster. We identify 78 stars in our samplecharacterized by K-L colors suggestive of deeply embedded objects. Thespatial distribution of these objects differs from that of the rest ofthe cluster members and is similar to that of the dense molecular cloudridge behind the cluster. About half of these objects are detected inthe short wavelength (J and H) bands, and these are found to becharacterized by extreme infrared excess. This suggests that many ofthese sources could be protostellar in nature. If even a modest fraction(i.e., ~50%) of these objects are protostars, then star formation couldbe continuing in the molecular ridge at a rate comparable to that whichproduced the foreground Trapezium cluster.
| Revised Fluxes for Gliese 229B
We have used the coronagraphic instrument CoCo with the InfraredTelescope Facility's camera, NSFCAM, to obtain improved photometry atJHKL' of the giant planet/brown dwarf Gliese 229B. We have recalibratedthe published spectra for this object and recalculated its luminosity.Our L' value and our flux calibration of the spectra at JHK aresignificantly different from those previously published. Our resultsshow good agreement at all bands except H with evolutionary models byBurrows et al. which include grain condensation. The model comparisonimplies that Gliese 229B is likely to be a 0.5 Gyr old 25M_J object withT_eff~900 K.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The circumstellar environment of IRAS 05327+3404
We continue our study of the young stellar object associated with IRAS05327+3404. We have determined the spectral type of the central star tobe K2. We show that the star is most likely seen directly, not via areflection, and that the extinction is only A_V ~ 2.3 mag. The spectralenergy distribution shows the presence of large amounts of circumstellarmaterial. Near-IR and optical observations of the reflection nebula alsodemonstrate the presence of circumstellar material, and show thematerial to be arranged in a disk with a relatively wide central hole of~ 33 degr opening angle. The central hole and a CO outflow areco-aligned, and are roughly aligned with the ionized outflow. Severalsurprising aspects remain: Although the system has a strong ionizedoutflow, there is little or no evidence of active accretion in the formof UV excess, veiling, or strong high-Balmer line emission. Also, thespectral energy distribution is very wide, and suggests that theoriginal birth cloud had a large rotational velocity. We propose thatthe relative isolation of the system from other star formation activitymay explain the relatively large circumstellar disk for a system with awell-exposed central star.
| Young red supergiants and the near-infrared light appearance of disk galaxies
We have searched for spatial variations in the 2.3 m photometric COindex within the disks of three nearby galaxies. This index measures thestrength of the absorption bands of molecular CO in stellar atmospheresand is strong in cool, low surface gravity stars, reaching the largestvalues for red supergiants. We observe significant spatial CO indexvariations in two galaxies, indicating that the dominant stellarpopulation in the NIR is not everywhere the same. Central CO index peaksare present in two galaxies; these could be due to either metallicitygradients or to recent star formation activity. In addition, significantazimuthal CO index variations are observed in one. Because strongazimuthal metallicity gradients are physically implausible in diskgalaxies, these features are most naturally explained by the presence ofa young stellar population. The fraction of 2 m light due to youngstellar populations in star-forming regions can be calculated from ourdata. Overall, young stellar populations can contribute 3 percent of theNIR flux of a (normal) galaxy, which is consistent with other globalproperties. Locally, this fraction may rise to 33 percent. Thus, youngstars do not dominate the total NIR flux, but can be locally dominant instar-forming regions, and can bias estimates of spiral arm amplitude orother nonaxisymmetric structures in galaxies' mass distributions.
| The near-infrared extinction law and limits on the pre-main-sequence population of the Rho Ophiuchi dark cloud
We describe new techniques to measure the NIR extinction law and toplace limits on the premain-sequence stellar population of a dark cloud.We analyze JHK imaging data for the central 1 sq deg of the Rho Ophiuchicloud core and show that nearly all stars projected onto regions of lowCS intensity, ICS 10 K km/s, are background stars. Most sources atlarger CS intensities lie within cloud material. We use the backgroundstars to derive the slope of the NIR extinction law, E(J-H)/E(H-K) =1.57 +/- 0.03. This result is consistent with previous extinction lawsbut has a factor of two to three smaller uncertainty. The new Rho Ophextinction law yields strong constraints on the number of previouslyundiscovered premain-sequence stars in the cloud, 46 +/- 11, and thenumber of previously undiscovered young stars with near-IR excesses, 15+/- 4. Neither limit exceeds the number of known premain-sequence starsin the cloud about 100. Thus, current samples of premain-sequence starsare reasonably complete for K = 14 or less.
| Near-Infrared Imaging Polarimetry of Embedded Young Stars in the Taurus-Auriga Molecular Cloud
We describe near-infrared (JHK) imaging polarimetry of 21 embeddedprotostars in the Taurus-Auriga molecular cloud. These objects displayextended, highly polarized reflection nebulae with V-shaped, unipolar,and bipolar morphologies. Most sources have PK ~ 5%-20% in an 8"aperture; a few objects have PK <~ 5%. The polarization increasestoward shorter wavelengths and is generally aligned perpendicular to thelong axis of the reflection nebula. We develop an analytic scatteringmodel for the near-IR colors and polarizations of embedded protostars.Our Taurus data require visual extinctions, AV ~ 25-60 mag, comparableto those predicted for models of collapsing clouds. The ratio ofscattered flux to intrinsic source flux ranges from Fs/F0 ~ 0.001 at1.25 mu m to Fs/F0 ~ 0.015 at 3.5 mu m. These results indicate that theobserved ratio of scattered light to direct (extincted) light increasesfrom Fs/Fd ~ 0.1 at 3.5 mu m to Fs/Fd ~ 25 at 1.25 mu m. Our datafurther require intrinsic colors of 0.6 <~ J-H <~ 0.9, 0.3 <~H-K <~ 0.6, and 0.4 <~ K-L <~ 1.2 for the central sources ofTaurus protostars. We adopt the Terebey, Shu, & Cassen solution foran infalling, rotating protostellar cloud and use a two dimensionalMonte Carlo radiative transfer code to model the near-IR polarizationdata for this sample. Our results indicate envelope parameters inagreement with previous estimates from broadband spectral energydistributions and near-IR images. We estimate infall rates, M dot~(2-5)x10^{-6} Mȯ yr-1; centrifugal radii, Rc ~ 10-50 AU; andopening angles of the bipolar cavity, theta h ~ 10 deg-20 deg, for atypical object. Standard grain parameters can explain the near-IR colorsand polarizations of Taurus protostars. The polarization maps show thatTaurus grains have a high maximum polarization at K, Pmax,K >~ 80%.The large image sizes of this sample further imply a high K-band albedo,omega K ~ 0.3-0.4. Model polarization maps indicate that the size of the"polarization disk" increases with the size of the instrumentalpoint-spread function. Relating the morphology of polarization vectorsto disk or envelope properties thus requires some care and a goodunderstanding of the characteristics of the instrument.
| Near infrared surface photometry of late-type Virgo cluster galaxies
Near Infrared (K' band) surface photometry has been obtained for 102 (88late-type) Virgo cluster galaxies. A subset of 20 galaxies was alsoimaged in the H band. Magnitudes and diameters within the 21.5 and 22.0mag arcsec$^{-2}$ isophote, concentration indices and total H and K'magnitudes are derived. Basic statistical properties of a completesample of spiral galaxies spanning the range 6.3 < K'_T < 13.5 aregiven. Tables 3, 5 and 6 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html} Based on observations taken atthe Calar Alto Observatory, operated by the Max-Planck-Institut furAstronomie (Heidelberg) jointly with the Spanish National Commission forAstronomy.
| A molecular line and infrared study of NGC 2264 IRS 1.
We present a study of the region around the intermediate-mass youngstellar object NGC 2264 IRS1. This source is embedded in a dense cloudcore. Infrared images in the J, H, and K band show a jet-like structureconnected with IRS1 as well as a second very deeply embedded small starcluster to the southeastern side. IRS1 itself is surrounded by a numberof embedded low-mass stars. We mapped this area in various CStransitions, CO 3->2, some methanol lines and in C^18^O 2->1. Themapping results clearly show a second cloud clump centered at the smallstar cluster. Two molecular outflows were found in the observed region.One flow is oriented along our line of sight and associated with IRS1and the other flow is centered at the small star cluster. Severaladditional spectral line settings were taken at the IRS1 position to getmore accurate constraints on the gas temperature and density. Thesedata, as well as the maps, were analysed with statistical equilibriumexcitation calculations. The best fit results give an uniformtemperature of about 55K in a quite large inner cloud region (1'x1'),with even warmer gas (>70K) present close to IRS1 and the embeddedstar cluster. This warm cloud core is surrounded by extended material ata temperature of 20 to 30K. Radiative transfer models applied fordifferent molecules constrain the mean central density to 2x10^6^cm^-3^.We estimated the beam-averaged total H_2_ column densities at a numberof grid positions around IRS1 from the C^18^O measurements. Using themodeled CS excitation, we can constrain the beam-averaged CS abundancedistribution over the same area. The inferred CS abundance with respectto H_2_ of 1x10^-9^ is nearly constant over the whole region, and thereis no indication for a CS depletion on this scale. Observations of alarge number of other molecules have been obtained as well at the IRS1position. The resulting abundances are compared to those found in otherhigh- and low-mass young stellar objects. The abundances of the organicmolecules H_2_CO and CH_3_OH are somewhat enhanced, whereas those ofsulfur-bearing molecules are much lower. The most strikingcharacteristic of the NGC 2264 chemistry is its nitrogen chemistry,especially the very high abundances of N_2_H^+^ and N_2_. These resultssuggest that NGC 2264 is in a somewhat later evolutionary stage.
| Properties of Low-Mass Objects in NGC 2024
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...473..294C&db_key=AST
| The Cold, Massive Molecular Cloud G216-2.5. III. Infrared Properties
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...472..275L&db_key=AST
| An Infrared Study of the Star-forming Region IRAS 05380-0728
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...461..909C&db_key=AST
| Interacting System ARP 30
Arp 30 is a galaxy pair composed of a face-on spiral and an edge-on diskgalaxy. There have been very few observations of Arp 30, probablybecause of its great distance (160 Mpc for H_0_ of 50). We have obtainedCCD images of Arp 30 in the B, V, R, and I bands and a narrow filter atthe redshifted Hα wavelength, J, H, and K images from the KPNO'sSQIID, and optical-red spectra of each galaxy. These results combinedwith IRAS data show that Arp 30 is a moderate starburst system of abouttwice the luminosity of M82 and a total star formation rate of about 18M_sun_/yr. Star formation is occurring in both components of the pairand is most enhanced in the nucleus of the face-on galaxy. The galaxiesappear to be connected by a bridge containing clumpy Hα emission,a feature resembling young star clusters. The structure and starformation enhancement resemble simulations of disk galaxies in theirfirst close pass.
| 1.65 μm (H-band) surface photometry of disk galaxies. I. Observations of 158 galaxies with the Calar Alto 2.2 M telescope.
Near Infrared (H-band) surface photometry of 158 (mostly) disk galaxiesbelonging to the Coma Supercluster and to the A262 and Cancer clusterswas obtained using the 256^2^ NICMOS3 array MAGIC attached to the 2.2mCalar Alto telescope. Magnitudes and diameters within the21.5mag/arcsec^2^ isophote, concentration indices and total H magnitudesare derived.
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| Takýmyýldýz: | Avci |
| Sað Açýklýk: | 05h58m13.52s |
| Yükselim: | +01°51'23.0" |
| Görünürdeki Parlaklýk: | 6.916 |
| Uzaklýk: | 112.74 parsek |
| özdevim Sað Açýklýk: | 6.6 |
| özdevim Yükselim: | -7 |
| B-T magnitude: | 7.213 |
| V-T magnitude: | 6.941 |
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