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Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Near-Infrared Imaging of the Star Formation Region AFGL 5142
Near-infrared JHK' and H2 v=1-0 S(1) imaging observations ofthe star-forming region AFGL 5142 are presented. A cluster of youngstars is confirmed to be embedded in the dense molecular cloud core.Many point sources are newly detected. The cluster's K'-magnitudedistribution and [H-K'] color peak have brighter and reddermagnitudes than those outside the cluster. Many of the cluster sourcesexhibit infrared excesses typical of T Tauri stars, Herbig Ae/Be stars,and protostars. The observations also reveal new H2 lineemission around the cluster, exhibiting several jets, filaments, and afaint elliptical structure. The jets are associated with the CO outflowsin the region. The powering sources of the jets, the CO outflows, andthe small faint elliptical structure are identified and analyzedindividually. The strong H2 jets and faint diffuse emissionfurther confirm that the cluster is in an early stage of evolution.
| 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.
| A near-infrared study of the bow shocks within the L1634 protostellar outflow
The L1634 bright-rimmed globule contains an intriguing arrangement ofshock structures: two series of aligned molecular shock waves associatedwith the Herbig-Haro flows HH 240 and HH 241. We present near-infraredspectroscopy and narrow-band imaging in the (1, 0) S(1) and (2, 1) S(1)emission lines of molecular hydrogen. These observations yield thespatial distributions of both the molecular excitation and velocity,which demonstrate distinct properties for the individual bow shocks. Bowshock models are applied, varying the shock physics, geometry, speed,density and magnetic field properties to fit two prominent bow shocks.The models predict that both bows move at 60o to the plane ofthe sky. High magnetic fields and low molecular fractions are implied.The advancing compact bow HH 240C is interpreted as a J-type bow(frozen-in magnetic field) with the flanks in transition to C-type(field diffusion). It is a paraboloidal bow of speed 42 kms-1 entering a medium of quite high density (2 ×104 cm-3). The following bow HH 240A is fasterdespite a lower excitation, moving through a lower density medium. Wefind a C-type bow shock model to fit all the data for HH 240A. Thefavoured bow models are then tested comprehensively against publishedH2 emission line fluxes and CO spectroscopy. We concludethat, while the CO emission originates from cloud gas directly set inmotion, the H2 emission is generated from shocks sweepingthrough an outflow. Also considering optical data, we arrive at a globaloutflow model involving episodic slow-precessing twin jets.
| Hot H2O Emission and Evidence for Turbulence in the Disk of a Young Star
We report on the detection and analysis of hot rovibrationalH2O emission from SVS 13, a young stellar object previouslyknown to have strong CO overtone band head emission. Modeling of thehigh-resolution infrared spectrum shows that the H2O emissionis characterized by temperatures of ~1500 K, significantly lower thanthe temperatures that characterize the CO band head emission. The widthsof the H2O lines are also found to be smaller than those ofthe CO lines. We construct a disk model of the emission that reproducesthe CO and H2O spectrum. In this model, the H2Olines originate at somewhat larger disk radii (<=0.3 AU) than the COovertone lines (<=0.1 AU). We find that the H2O abundanceis about a factor of 10 lower than the calculated chemical equilibriumabundance. Large, approximately transonic, local line broadening isrequired to fit the profile of the CO band head. If this velocitydispersion is identified with turbulence, it is of significant interestregarding the transport of angular momentum in disks. Large localbroadening is also required in modeling CO overtone emission from otheryoung stellar objects, suggesting that large turbulent velocities may becharacteristic of the upper atmospheres of the inner disks of youngstars.
| 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.
| Infrared Space Observatory and Ground-Based Infrared Observations of the Classical Nova V723 Cassiopeiae
We present observations of the classical nova V723 Cassiopeiae (Nova Cas1995), obtained both with the Infrared Space Observatory (ISO) and fromthe ground. The infrared spectrum was dominated in the first year by Hand He recombination lines, and at later times by coronal lines. The Hrecombination lines imply a reddening of E(B-V)=0.78, an electrontemperature of 7000 K, and an electron density of 2×108cm-3 on day 250. We argue that the high-ionization species inthe infrared are most likely the result of collisional ionization ratherthan photoionization and are therefore truly ``coronal'' we estimate atemperature of 3.2×105 K in the coronal region andabundance ratios of S/Si~=2.1, Ca/Si~=1.6, and Al/Si~=1.5. The ejectedmass as determined from the Brα line was 2.6×10-5Msolar for a distance of 4 kpc; however, the mass deducedfrom the free-free emission, which we conclude arises primarily in thecoronal zone, is 4.3×10-4 Msolar. V723 Casdid not display the [O IV] 25.89 μm fine-structure line, which wastypically seen in the spectra of novae observed with ISO. There was noevidence of dust emission in V723 Cas.
| 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.
| JHK Standard Stars on the CIT Photometric System
We present a set of 58 stars with JHK standard values on the CIT systemand with a suitable magnitude range for use with array detectors onsmall- to moderate-size telescopes. Each final value is based on six to47 measures (with a mean of 17) obtained on separate nights with the USNaval Observatory (USNO) NICMOS3 (HgCdTe) camera. The objects include 20primary CIT standards from Elias et al. and 38 secondary sourcesselected from the SAAO and UKIRT standards lists, cover a K-magnituderange between 6.0 and 10.8, and lie north of declination -20°. Thestars were reduced to the CIT system as defined by Elias et al.,producing a USNO system that is identical to the near-infrared CITsystem. This work densifies the original CIT system by nearly a factorof 3 and extends its range by about 3 mag. The SAAO and UKIRT standardsare also compared with the CIT system.
| 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.
| 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.
| A Survey of Near Infrared Nebulosities around Luminous Young Stellar Objects: J, H, and K' Imaging
We present J, H, and K' images of 45 IRAS sources in the recent list byCampbell, Persson, & Matthews, which have been presumed to beluminous young stellar objects (YSOs) because of their infrared colorsand their large IRAS fluxes. These objects have been classified intofour groups according to two dust features in the 3 μm band-theH2O ice absorption and the unidentified infrared band (UIB)emission. Our near-infrared images reveal that most of them (42/45) havenebulosity in at least one of the three bands. By examining thenebulosities around these YSOs, we find that (1) nebulae around theobjects with the ice absorption can be explained by the scattered lightof the central stars, (2) nebulae around the objects with the UIBemission cannot be explained by the scattered light alone-additionalemission, most likely from very small grains, is necessary to explainthe nebular colors and the surface brightness, and (3) the objects withneither the ice absorption nor the UIB emission tend to have faint or nonebulosity. We interpret the variation of nebular brightness and thecolor as evolutionary phases of circumstellar matter of intermediate- tohigh-mass YSOs.
| Discovery of an Extremely Red Object in the Field of HD 155826
We have discovered an extremely red object, LSF 1, located 7" southwest(P.A. 217°) of the bright spectroscopic binary system HD 155826.Originally reported by IRAS as one source detected at 12-60 μm, andfound as a single 6-25 μm source of similar flux in the MidcourseSpace Experiment Galactic plane survey, two bright point sources werefound in arcsecond resolution infrared images obtained with the MIRLINcamera at the Infrared Telescope Facility and confirmed by the LongWavelength Spectrometer camera on Keck I. While HD 155826 itself waseasily detected in all the broadband and narrowband filters from 0.9 to12 μm that we used, the new counterpart, LSF 1, is only visible at 10μm. In Gunn z, J, H, and K', the upper limit to the new object'smagnitude is ~14. The detection of the new bright IR source explains theconfusing [K]-[N] IRAS colors that originally implied that HD 155826 wasa possible Vega-like system. The ``anomalous long-wavelength emission''is found to arise entirely from the new source. Without mid-IR extensionor excess long-wavelength emission, HD 155826 should no longer beclassified as a Vega-like system. We suspect LSF 1 to be either a highlyreddened carbon star or a Class II YSO, with no association with thehigh proper motion HD 155826 system.
| K'-Band Polarimetric Imaging of S187 IR and S233
K'-band polarimetric images of star-forming regions S187 IR and S233 arepresented. In S187 IR, a bipolar, near-infrared nebula is observedaround IRAS 01202+6133, with the southern part being bright and knotty,and the northern part being faint and filamentary. The polarizationpattern shows that the nebula is illuminated by a single near-infraredsource, which is associated with IRAS 01202+6133. A polarization disk isfound around this source with the disk plane roughly perpendicular tothe axis of the bipolar nebula. We conclude that this source is thedriving source of the outflow in the region. Two nebulae are detected inthe S233 region. Associated with a compact infrared cluster, S233 A isroughly round in shape and shows a weak polarization pattern. The S233 Bnebula shows roughly elongated geometry in the east-west direction. Thepolarization vectors divide it into three parts. Each part hasdistinctly different polarization from the others. The northeastern partof S233 B exhibits a centrosymmetric polarization pattern around acentroid, at which we locate a deeply embedded source (DES) undetectedin the K' band and shorter wavelengths. The DES is likely the excitingsource of water masers and outflows in the S233 B region. The westernpart of the nebula shows a parallel polarization pattern, but thesoutheastern part displays very little polarization. Comparison of themorphology and polarization of the nebulae in different star-formingregions suggests a close relationship between the evolutionary sequenceof the young stellar objects and the morphology of the associatednebulae.
| New results on the helium stars in the galactic center using BEAR spectro-imagery
Integral field spectroscopy of the central parsec of the Galactic Centerwas obtained at 2.06 mu m using BEAR, an imaging Fourier TransformSpectrometer, at a spectral resolution of 74 km s-1. Sixteenstars were confirmed as ``helium stars" by detecting the He I 2.058 mu mline in emission, providing a homogeneous set of fully resolved lineprofiles. These observations allow us to discard some of the earlierdetections of such stars in the central cluster and to add three newstars. The sources detected in the BEAR data were compared with adaptiveoptics images in the K band to determine whether the emission was due tosingle stars. Two sub-classes of almost equal number are clearlyidentified from the width of their line profiles, and from thebrightness of their continuum. The first class is characterized by verybroad line profiles (FWHM =~ 1000 km s-1) and by theirrelative faintness. The other, brighter in K by an average factor of ~9, has a much narrower emission component of width =~ 200 kms-1. Most of the emission lines show a P Cygni profile. Fromthese results, we propose that the latter group is formed of stars in ornear the LBV phase, and the other one of stars at the WR stage. Thedivision into two groups is also shown by their spatial distribution,with the narrow-line stars in a compact central cluster (IRS16) and the other group distributed at the periphery of thecentral cluster of hot stars. In the same data cube, streamers ofinterstellar helium gas are also detected. The helium emission tracesthe densest parts of the SgrA West Mini-Spiral. Several helium starshave a radial velocity comparable to the velocity of the interstellargas in which they are embedded. In the final discussion, all thesefindings are examined to present a possible scenario for the formationof very massive stars in the exceptional conditions of the vicinity ofthe central Black Hole.
| The Calar Alto Observatory - present and future instrumentation
The Calar Alto Observatory, located at 2168 m altitude in the Sierra delos Filabres in southern Spanish province of Andalucia, was founded inthe early 1970s in order to provide astronomers in Germany and in Spainwith modern observational facilities in the northern hemisphere. Thisrole is not going to change over the next decade as 2-4 m telescopes arestill essential and more efficient than 8 m telescopes, for wide-fieldand surface-brightness limited surveys, for support of surveys at otherwavelengths (X-ray, radio), for regular monitoring work, for pursuinginnovative ideas, for obtaining accurate astrometry and photometry ofreference objects and unknowns, etc. In order to pursue thesechallenges, state of the art instrumentation is required. In thefollowing, the existing facilities on Calar Alto are summarised, andfuture instrumentation projects are briefly discussed.
| 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.
| OASIS: A Multi-Purpose Near-Infrared Camera and Spectrograph
We have developed a near-infrared (1-2.5 mu m) camera and spectrograph,called OASIS (Okayama Astrophysical System for Infrared imaging andSpectroscopy). OASIS was designed for the 188 cm telescope at OkayamaAstrophysical Observatory, and developed as a common-use facilityinstrument. It has two observing capabilities: imaging with a field ofview of 4'times4 ' and long-slit spectroscopy with a resolving power of~ 1000 . This paper describes the design of OASIS and reports on thetotal system performance of the camera+telescope+atmosphere at theOkayama Observatory, together with the performance of an array detector,NICMOS 3, which OASIS utilizes.
| Unveiling Deeply Embedded Sources by Near-Infrared Polarimetric Imaging
Near-infrared polarimetric images are presented for six molecularoutflow sources: IRAS 20050+2720, IRAS 20126+4104, IRAS 20188+3928,S233, AFGL 5180, and AFGL 6366S. All the regions are found to exhibitreflection nebulae and to be associated with massive and clustered starformation. By inspecting polarimetric patterns in the nebulae, we haveidentified six deeply embedded sources (DESs) which illuminatecircumstellar nebulosity but are not detectable in wavelengths shorterthan 2 μm. While the DES in IRAS 20050 coincides with an infraredsource in a previous, longer wavelength observation and the one in IRAS20126 with a hot molecular core, the nature of the other newlydiscovered DESs is not known. From the compilation of the observationsof DESs over a large wavelength range, we suspect that the DESs possesscharacteristics similar to hot molecular cores and are likely to be inthe pre-ultracompact H II region phase of massive star formation.
| The hyperluminous infrared quasar 3C 318 and its implications for interpreting submm detections of high-redshift radio galaxies
We present near-infrared spectroscopy and imaging of the compactsteep-spectrum radio source 3C 318, which shows it to be a quasar atredshift z=1.574 (the z=0.752 value previously reported is incorrect).3C 318 is an IRAS, ISO and SCUBA source so its new redshift makes it themost intrinsically luminous far-infrared (FIR) source in the 3Ccatalogue (there is no evidence of strong gravitational lensingeffects). Its bolometric luminosity greatly exceeds the1013Lsolar level above which an object is said tobe hyperluminous. Its spectral energy distribution (SED) requires thatthe quasar heats the dust responsible for the FIR flux, as is believedto be the case in other hyperluminous galaxies, and contributes (at the>10per cent level) to the heating of the dust responsible for thesubmm emission. We cannot determine whether a starburst makes animportant contribution to the heating of the coolest dust, so evidencefor a high star formation rate is circumstantial, being based on thehigh dust, and hence gas, mass required by its submm detection. We showthat the current submm and FIR data available for the highest-redshiftradio galaxies are consistent with SEDs similar to that of 3C 318. Thisindicates that at least some of this population may be detected in thesubmm because of dust heated by the quasar nucleus, and thatinterpreting submm detection as evidence for very high(>~1000Msolaryr-1) star formation rates may notalways be valid. We show that the 3C 318 quasar is slightly reddened(AV~0.5), the most likely cause of which is SMC-type dust inthe host galaxy. If very distant radio galaxies are reddened in asimilar way then we show that only slightly greater amounts of dustcould obscure the quasars in these sources. We speculate that the lowfraction of quasars amongst the very high redshift (z>~3) objects inlow-frequency radio-selected samples is the result of such obscuration.The highest-z objects might be preferentially obscured because like 3C318 they are inevitably observed very shortly after the jet-triggeringevent, or because their host galaxies are richer in dust and gas atearlier cosmic epochs, or because of some combination of these twoeffects.
| 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
| Near-Infrared Imaging of the Star-forming Region AFGL 5157
We present near-infrared images of the star-forming region AFGL 5157 inthe JHK' broadband filters and H_2 v=1-0 S(1) narrowband filter. Theimages reveal a dense cluster of stars and infrared nebulositiesassociated with previously known infrared sources. Of 54 near-infraredsources detected in the nebula, NGC 1985, 12 exhibit infrared excessestypical of T Tauri stars, Herbig Ae/Be stars, and protostars. Themagnitude and color distribution of the cluster of stars in the nebulaare found to be different from those outside the nebular region. TheK'-magnitude distribution of the cluster is quite flat, while thenoncluster is peaked toward the low magnitude. The [H-K'] color of thecluster also displays 0.3 mag redder than that of the noncluster. Theinfrared nebula displays a bright nucleus with two spirals extended tothe north and south. In light of the color properties of the nebula, wepropose a shell model for the nebular structure that could be formed bystar-forming activity of the central cluster. Many sources with infraredexcesses are found to be embedded in the shell structure. Twelve shockedknots in H_2 emission are observed in the region. The nonaxisymmetricdistribution of the knots indicates the presence of multiple outflows inthe region. Although we failed to identify the powering sourcesresponsible for some of the HH-like objects, the relationship of the H_2emission with infrared sources shows that there must be severalspatially separated sources exciting the shocked H_2 emission as well asthe previously observed H_2O masers and molecular outflow. Diffuse H_2emission is also detected on the shell structure, which supports theshell model of the nebula. This diffuse emission could result fromfluorescence by relatively evolved stars in the cluster.
| Near infrared polarimetry of S255 IR complex.
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| A Near-Infrared Study of the NS 14 Bipolar Nebula
In this fifth paper of a series on high-mass star formation, we continueour study with the bipolar nebula NS 14. We have imaged this nebula at J(1.23 μm), H (1.65 μm), and K (2.23 μm) broadband near-infrared(NIR) wavelengths. We have also obtained 3.29 μm dust featureemission and Brgamma (n = 7 --> 4, 2.166 μm) hydrogenrecombination line emission images of this region. The broadbandreflection nebulosity, surrounding a central ``Trapezium'' of stars,forms a bipolar structure that is also seen in the 3.29 μm dustfeature emission. This dust feature emission exhibits limb brightening;therefore, small dust grains in the central regions of the bipolarstructure have been evacuated. The Brgamma line emission consists of acompact component <=2" in size and a more extended component ~5" x 7"or larger in size. A study of the stellar population of the cluster,centered on the nebular emission, has also been made.
| Near-Infrared Stellar Photometry of the M31 Spiral Arm around OB Association A24
Deep high-resolution JHK images of a 2' x 2' field around the OBassociation A24 near the 7 kpc spiral arm in M31 were measured to yieldphotometric data of more than 3000 stars with the faintest magnitudebeing J = 21.3, H = 20.5, and K = 19.6. The photometric data for the1037 stars that are brightest in the K band are presented. Judging fromthe color-magnitude and the two-color diagrams, we find that themajority of the observed stars are AGB stars including large-amplitudevariables. They are distributed smoothly over the observed field, and wefind no clear evidence of varying extinction over the field for thesered stars. The present sample includes bright AGB stars of M_K <= -8and about 30 young blue objects of (J-H) < 0.75 that are brighterthan M_J ~= -6.5.
| ^56Ni dredge-up in the type IIp supernova 1995V
We present contemporary infrared (IR) and optical spectra of the plateautype II SN 1995V in NGC 1087 covering four epochs, approximately 22 to84 d after shock break-out. The data show, for the first time, the IRspectroscopic evolution during the plateau phase of a typical type IIevent. In the optical region P Cygni lines of the Balmer series and ofmetals such as ScII, FeII, SrII, CaII and BaII lines were identified.The IR spectra were largely dominated by the continuum, but P CygniPaschen lines and Brackett gamma lines were also clearly seen. The otherprominent IR features are confined to wavelengths blueward of 11000Angstroms, and include SrII 10327, FeII 10547, CI 10695 and HeI 10830Angstroms. Helium has never before been unambiguously identified in atype IIp supernova spectrum during the plateau phase. We demonstrate thepresence of HeI 10830 Angstroms on days 69 and 85. The presence of thisline at such late times implies reionization. A likely reionizingmechanism is gamma-ray deposition following the radioactive decay of^56Ni. We examine this mechanism by constructing a spectral model forthe HeI 10830-Angstroms line based on explosion model s15s7b2f of Weaver& Woosley. We find that this does not generate the observed lineowing to the confinement of the ^56Ni to the central zones of theejecta. In order to reproduce the HeI line, it was necessary tointroduce additional upward mixing or `dredge-up' of the ^56Ni, with~10^-5 of the total nickel mass reaching above the helium photosphere.In addition, we argue that the HeI line formation region is likely tohave been in the form of pure helium clumps in the hydrogen envelope.The study of HeI 10830-Angstroms emission during the photospheric phaseof core-collapse supernovae provides a promising tool for the constraintof initial mixing conditions in explosion models.
| VIRIS: A Visual-Infrared Imaging System for the Lick Observatory 1 Meter Telescope
We describe a system in use at the Lick Observatory 1 m Nickel telescopefor near-simultaneous imaging at optical and near-infrared wavelengths.The combined availability of a CCD and a NICMOS3 camera makes the systemwell suited for photometric monitoring from 0.5 to 2.2 μm of avariety of astrophysical objects. Our science program thus far hasconcentrated on studying variability trends in young stellar objects.
| Near-IR imaging photometry of NGC 1333: a 3-μm imaging survey
We combine new near-infrared 3.42-μm imaging photometry with JHK datafrom Paper I to further probe the membership and physicalcharacteristics of the embedded pre-main-sequence (PMS) population inthe active star formation region NGC 1333-S. Our new data set coversapproximately 44 per cent of the 10x10 arcmin^2 area previouslysurveyed. In the current survey region we have detected 36 sources, 26being brighter than our 5sigma limiting magnitude of m_L=12.2. These 36objects represent 45 per cent of the 80 objects detected in the sameregion at K. From a near-IR J-K versus K-L colour-colour diagram weinfer the evolutionary state of the stars and compare the results withthose obtained from our JHK data. We additionally discuss the effect of3.08-μm ice absorption on photometry at 3.42mum for heavily embeddedobjects.
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Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Kahraman |
| Sað Açýklýk: | 03h03m31.94s |
| Yükselim: | +38°24'36.1" |
| Görünürdeki Parlaklýk: | 7.136 |
| Uzaklýk: | 408.163 parsek |
| özdevim Sað Açýklýk: | 3.8 |
| özdevim Yükselim: | -12.9 |
| B-T magnitude: | 7.117 |
| V-T magnitude: | 7.135 |
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