내용
사진
사진 업로드
DSS Images Other Images
관련 글
UBV(RI)C JHK observations of Hipparcos-selected nearby stars
We present homogeneous, standardized UBV(RI)C photometry forover 700 nearby stars selected on the basis of Hipparcos parallaxes.Additionally, we list JHK photometry for about half of these stars, aswell as L photometry for 86 of the brightest. A number of stars withpeculiar colours or anomalous locations in various colour-magnitudediagrams are discussed.
| An absolutely calibrated Teff scale from the infrared flux method. Dwarfs and subgiants
Various effective temperature scales have been proposed over the years.Despite much work and the high internal precision usually achieved,systematic differences of order 100 K (or more) among various scales arestill present. We present an investigation based on the infrared fluxmethod aimed at assessing the source of such discrepancies and pin downtheir origin. We break the impasse among different scales by using alarge set of solar twins, stars which are spectroscopically andphotometrically identical to the Sun, to set the absolute zero point ofthe effective temperature scale to within few degrees. Our newlycalibrated, accurate and precise temperature scale applies to dwarfs andsubgiants, from super-solar metallicities to the most metal-poor starscurrently known. At solar metallicities our results validatespectroscopic effective temperature scales, whereas for [Fe/H]? -2.5our temperatures are roughly 100 K hotter than those determined frommodel fits to the Balmer lines and 200 K hotter than those obtained fromthe excitation equilibrium of Fe lines. Empirical bolometric correctionsand useful relations linking photometric indices to effectivetemperatures and angular diameters have been derived. Our results takefull advantage of the high accuracy reached in absolute calibration inrecent years and are further validated by interferometric angulardiameters and space based spectrophotometry over a wide range ofeffective temperatures and metallicities.Table 8 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A54
| The main sequence from F to K stars of the solar neighbourhood in SDSS colours
For an understanding of Galactic stellar populations in the SDSS filtersystem well defined stellar samples are needed. The nearby stars providea complete stellar sample representative for the thin disc population.We compare the filter transformations of different authors applied tothe main sequence stars from F to K dwarfs to SDSS filter system anddiscuss the properties of the main sequence. The location of the meanmain sequence in colour-magnitude diagrams is very sensitive tosystematic differences in the filter transformation. A comparison withfiducial sequences of star clusters observed in g', r', and i' show goodagreement. Theoretical isochrones from Padua and from Dartmouth havestill some problems, especially in the (r-i) colours.
| Spectroscopic investigation of stars on the lower main sequence
Aims. The aim of this paper is to provide fundamental parameters andabundances with a high accuracy for a large sample of cool main sequencestars. This study is part of wider project, in which the metallicitydistribution of the local thin disc is investigated from a completesample of G and K dwarfs within 25 pc. Methods: The stars were observedat high resolution and a high signal-to-noise ratio with the ELODIEechelle spectrograph. The V sin i were obtained with a calibration ofthe cross-correlation function. Effective temperatures were estimated bythe line depth ratio method. Surface gravities (log g) were determinedby two methods: parallaxes and ionization balance of iron. The Mg and Naabundances were derived using a non-LTE approximation. Abundances ofother elements were obtained by measuring equivalent widths. Results:Rotational velocities, atmospheric parameters (T_eff, log g, [Fe/H],V_t), and Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, and Znabundances are provided for 131 stars. Among them, more than 30 starsare active stars with a fraction of BY Dra and RS CVn type stars forwhich spectral peculiarities were investigated. We find the meanabundances of the majority of elements in active and nonactive stars tobe similar, except for Li, and possibly for Zn and Co. The lithium isreliably detected in 54% of active stars but only in 20% of nonactivestars. No correlation is found between Li abundances and rotationalvelocities. A possible anticorrelation of log A(Li) with the index ofchromospheric activity GrandS is observed. Conclusions: Active andnonactive cool dwarfs show similar dependencies of most elemental ratiosvs. [Fe/H]. This allows us to use such abundance ratios to study thechemical and dynamical evolution of the Galaxy. Among active stars, noclear correlation has been found between different indicators ofactivity for our sample stars.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute Provence (France). Tables A.1-A3are only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/489/923
| Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants
We present the parameters of 891 stars, mostly clump giants, includingatmospheric parameters, distances, absolute magnitudes, spatialvelocities, galactic orbits and ages. One part of this sample consistsof local giants, within 100 pc, with atmospheric parameters eitherestimated from our spectroscopic observations at high resolution andhigh signal-to-noise ratio, or retrieved from the literature. The otherpart of the sample includes 523 distant stars, spanning distances up to1 kpc in the direction of the North Galactic Pole, for which we haveestimated atmospheric parameters from high resolution but lowsignal-to-noise Echelle spectra. This new sample is kinematicallyunbiased, with well-defined boundaries in magnitude and colours. Werevisit the basic properties of the Galactic thin disk as traced byclump giants. We find the metallicity distribution to be different fromthat of dwarfs, with fewer metal-rich stars. We find evidence for avertical metallicity gradient of -0.31 dex kpc-1 and for atransition at ~4-5 Gyr in both the metallicity and velocities. Theage-metallicity relation (AMR), which exhibits a very low dispersion,increases smoothly from 10 to 4 Gyr, with a steeper increase for youngerstars. The age-velocity relation (AVR) is characterized by thesaturation of the V and W dispersions at 5 Gyr, and continuous heatingin U.
| The effect of activity on stellar temperatures and radii
Context: Recent analyses of low-mass eclipsing binary stars haveunveiled a significant disagreement between the observations andpredictions of stellar structure models. Results show that theoreticalmodels underestimate the radii and overestimate the effectivetemperatures of low-mass stars but yield luminosities that accord withobservations. A hypothesis based upon the effects of stellar activitywas put forward to explain the discrepancies. Aims: In this paper westudy the existence of the same trend in single active stars and providea consistent scenario to explain systematic differences between activeand inactive stars in the H-R diagram reported earlier. Methods: Theanalysis is done using single field stars of spectral types late-K and Mand computing their bolometric magnitudes and temperatures throughinfrared colours and spectral indices. The properties of the stars insamples of active and inactive stars are compared statistically toreveal systematic differences. Results: After accounting for a numberof possible bias effects, active stars are shown to be cooler thaninactive stars of similar luminosity therefore implying a larger radiusas well, in proportions that are in excellent agreement with those foundfrom eclipsing binaries. Conclusions: The present results generalisethe existence of strong radius and temperature dependences on stellaractivity to the entire population of low-mass stars, regardless of theirmembership in close binary systems.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/478/507
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A Catalog of Northern Stars with Annual Proper Motions Larger than 0.15" (LSPM-NORTH Catalog)
The LSPM catalog is a comprehensive list of 61,977 stars north of theJ2000 celestial equator that have proper motions larger than 0.15"yr-1 (local-background-stars frame). The catalog has beengenerated primarily as a result of our systematic search for high propermotion stars in the Digitized Sky Surveys using our SUPERBLINK software.At brighter magnitudes, the catalog incorporates stars and data from theTycho-2 Catalogue and also, to a lesser extent, from the All-SkyCompiled Catalogue of 2.5 million stars. The LSPM catalog considerablyexpands over the old Luyten (Luyten Half-Second [LHS] and New LuytenTwo-Tenths [NLTT]) catalogs, superseding them for northern declinations.Positions are given with an accuracy of <~100 mas at the 2000.0epoch, and absolute proper motions are given with an accuracy of ~8 masyr-1. Corrections to the local-background-stars propermotions have been calculated, and absolute proper motions in theextragalactic frame are given. Whenever available, we also give opticalBT and VT magnitudes (from Tycho-2, ASCC-2.5),photographic BJ, RF, and IN magnitudes(from USNO-B1 catalog), and infrared J, H, and Ks magnitudes(from 2MASS). We also provide an estimated V magnitude and V-J color fornearly all catalog entries, useful for initial classification of thestars. The catalog is estimated to be over 99% complete at high Galacticlatitudes (|b|>15deg) and over 90% complete at lowGalactic latitudes (|b|>15deg), down to a magnitudeV=19.0, and has a limiting magnitude V=21.0. All the northern starslisted in the LHS and NLTT catalogs have been reidentified, and theirpositions, proper motions, and magnitudes reevaluated. The catalog alsolists a large number of completely new objects, which promise to expandvery significantly the census of red dwarfs, subdwarfs, and white dwarfsin the vicinity of the Sun.Based on data mining of the Digitized Sky Surveys (DSSs), developed andoperated by the Catalogs and Surveys Branch of the Space TelescopeScience Institute (STScI), Baltimore.Developed with support from the National Science Foundation (NSF), aspart of the NASA/NSF NStars program.
| 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.
| Diffraction-limited bispectrum speckle interferometry of the nuclear region of the Seyfert galaxy NGC 1068 in the H and K' bands
We present near-infrared bispectrum speckle interferometry studies ofthe nuclear region of the Seyfert 2 galaxy NGC 1068.A diffraction-limited K'-band image with 74 mas resolution and the firstH-band image with 57 mas resolution were reconstructed from speckleinterferograms obtained with the SAO 6 m telescope. The resolvedstructure consists of a compact core and an extended northern andsouth-eastern component. The compact core is resolved at all positionangles and has a north-western, tail-shaped extension as well as afainter, south-eastern extension. The K'-band FWHM diameter of thiscompact core is approximately 18 × 39 mas or 1.3 × 2.8 pc(FWHM of a single-component Gaussian fit; fit range 30-80&%slash; ofthe telescope cut-off frequency; the diameter errors are ±4 mas),and the position angle (PA) of the north-western extension is -16± 4 °. If 40% of the flux from the compact K' core isemission from a point source and 60% from a Gaussian intensitydistribution, then a slightly larger FWHM of approximately 26 × 58mas is obtained for the compact K' component. In the H band, the FWHMdiameter of the compact core is approximately 18 × 45 mas(±4 mas), and the PA is -18 ± 4 °. The extendednorthern component (PA 0 °) has an elongated structure with alength of about 400 mas or 29 pc. The extended south-eastern componentis fainter than the northern component. The K'- and H-band fluxes fromthe resolved compact core were measured to be 350 ± 90 mJy (i.e.,K' 8.2m) and 70 ± 20 mJy (H 10.4m), respectively. The PA of -16 ± 4 ° of thecompact 18 × 39 mas core is very similar to that of the westernwall (PA -15 °) of the bright region of the ionization cone.This suggests that the H- and K'-band emission from the compact core isboth thermal emission and scattered light from dust near the westernwall of a low-density, conical cavity or from the innermost region of aparsec-scale dusty torus that is heated by the central source (the dustsublimation radius of NGC 1068 is approximately 0.1-1pc). The northern extended 400 mas structure lies near the western wallof the ionization cone and coincides with the inner radio jet (PA 11 °). The large distance from the core suggests that the K'-bandemission of the northern extended component is scattered light from thewestern cavity region and the radio jet region.Based on observations made with the 6 m BTA telescope, which is operatedby the Special Astrophysical Observatory (SAO), Russia.
| High-resolution near-infrared speckle interferometry and radiative transfer modeling of the OH/IR star OH 104.9+2.4
We present near-infrared speckle interferometry of the OH/IR starOH 104.9+2.4 in the K' band obtained with the 6 mtelescope of the Special Astrophysical Observatory (SAO). At awavelength of λ = 2.12 μm the diffraction-limited resolutionof 74 mas was attained. The reconstructed visibility reveals aspherically symmetric, circumstellar dust shell (CDS) surrounding thecentral star. The visibility function shows that the stellarcontribution to the total flux at λ = 2.12 μm is less than50%, indicating a rather large optical depth of the CDS. Theazimuthally averaged 1-dimensional Gaussian visibility fit yields adiameter of 47 ± 3 mas (FHWM), which corresponds to 112 ±13 AU for an adopted distance of D = 2.38 ± 0.24 kpc. Todetermine the structure and the properties of the CDS of OH104.9+2.4, radiative transfer calculations using the codeDUSTY were performed to simultaneously model its visibility and thespectral energy distribution (SED). We found that both the ISO spectrumand the visibility of OH 104.9+2.4 can be wellreproduced by a radiative transfer model with an effective temperatureTeff = 2500 ± 500 K of the central source, a dusttemperature Tin = 1000 ± 200 K at the inner shellboundary Rin ≃ 9.1 R* = 25.4 AU, an opticaldepth τ2.2 μm = 6.5 ± 0.3, and dust g rainradii ranging from amin = 0.005 ± 0.003 μm toamax = 0.2 ± 0.02 μm with a power law n(a) ∝a-3.5. It was found that even minor changes inamax have a major impact on both the slope and the curvatureof the visibility function, while the SED shows only minor changes. Ourdetailed analysis demonstrates the potential of dust shell modelingconstrained by both the SED and visibilities.Based on data collected at the 6 m BTA telescope of the SpecialAstrophysical Observatory in Russia.
| The Pul-3 catalogue of 58483 stars in the Tycho-2 system
A catalogue of positions and proper motions of 58483 stars (Pul-3) hasbeen constructed at the Pulkovo observatory. The Pul-3 is based on theresults of measurements of photographic plates with galaxies (Deutsch'splan). All plates were taken using the Pulkovo Normal Astrograph (thefirst epoch is in the 1950s and the second epoch is in the 1970s).The Pul-3 catalogue contains stars of mainly 12 to 16.5 mag in 146fields with galaxies in the declination zone from -5o to+85o. The Tycho-2 has been used as a reference catalogue.The mean epoch of the Pul-3 is 1963.25. The internal positional accuracyof the Pul-3 catalogue at the mean epoch of observations is ±80mas. The accuracy of the proper motions is mostly within ±3mas/yr to ±12 mas/yr. Comparisons of the Pul-3 with Tycho-2 andARIHIP have been done at the mean epoch of the Pul-3. The Pul-3 externalpositional accuracy relative to Tycho-2 is ±150 mas.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/357
| 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.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
| 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.
| 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.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| High proper motion stars in Kapteyn Selected Area 94
We have applied the astrometric techniques devised by Murray foranalysis of 48-inch Schmidt photographic data to SuperCOSMOS scans of UKSchmidt plates centred on Kapteyn's Selected Area 94(α=2h 53m, δ=0°). In thispreliminary study, we combine astrometric data from four short-exposureV-band plates, taken in 1987 August (2 plates) and 1993 August (2plates), with BVRI photometry from sky-limited plate material, toidentify stars with proper motions exceeding 0.1arcsecyr-1.This paper discusses the completeness of the resulting sample andpresents spectroscopy of 30 stars with μ>0.2arcsecyr-1.Based on the latter observations and the distribution in the[HV, (V-I)] reduced proper-motion diagram, we have classifiedstars in the complete sample as candidate white dwarfs, main-sequencedwarfs and halo subdwarfs, and derived estimates of the disc and haloluminosity functions.
| Low-Mass Star Formation and the Initial Mass Function in IC 348
We have performed deep infrared and optical spectroscopy of virtuallythe entire stellar population within the 5' x 5' core of IC 348,measuring K (2.2 μm) band and optical spectral types that are in goodagreement. We have also identified several sources that may besubstellar depending on the choice of temperature scales andevolutionary tracks, with three particularly late-type objects (M7.5-M8)that are likely bonafide brown dwarfs. In conjunction with thetheoretical evolutionary tracks of D'Antona & Mazzitelli, the H-Rdiagram indicates a spread in ages from 0.5 to 10 Myr, with most of thecore star formation occurring in the last 3 Myr. Using K-band imaging toprovide a completeness correction to the spectroscopic sample, we arriveat an initial mass function (IMF) that matches that of Miller &Scalo from 0.25 to 3 M_ȯ. The IMF appears to fall slowly from 0.25M_ȯ to the hydrogen burning limit, slightly below the IMF of Miller& Scalo, which is flat in logarithmic units (as compared to slopesof ~1.35 and -2.6 for Salpeter and Scalo). Correction for unresolvedbinary systems could steepen the slope of the low-mass IMF by about 0.5,which implies a single-star IMF that is roughly flat below 0.25M_ȯ. The low-mass IMF in IC 348 is similar to that derived instudies of most other young clusters, implying that the IMF does notvary dramatically among clusters of differing environments; however, thederived IMF is dependent on the evolutionary tracks and the detailedshape of the IMF should be viewed with caution until these models aretested against observations, particularly at low masses (<0.3M_ȯ) and young ages (<10 Myr). Hα and Brgamma emissionstrengths are consistent with predictions of magnetospheric accretionmodels of Muzerolle, Calvet, & Hartmann for accretion rates of10^-9-10^-8 M_ȯ yr^-1. Combining our data with the Hαmeasurements of Herbig, we find that ~25% of stars within the core of IC348 and younger than 3 Myr exhibit signatures of disks in the form ofstrong Hα (>10 Å) or Brgamma (>1 Å) emission orK-band continuum veiling (r_K >= 0.5). Since no sources older than 3Myr show evidence for massive disks, disk lifetimes in the core of IC348 appear to be shorter than those observed in Taurus or in the outerregions of IC 348.
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
Not Available
| GPM1 - a catalog of absolute proper motions of stars with respect to galaxies
The description of the first version of the General Compiled Catalogueof Absolute Proper Motions (GPM1) for a sample of HIPPARCOS stars,derived with respect to galaxies within the plan called Catalogue ofFaint Stars (KSZ, Deutch 1952), is presented. The principal aim of theGPM1 construction was to provide absolute proper motions of stars todetermine the rotation of the HIPPARCOS system. The GPM1 cataloguecontains 977 HIPPARCOS Input Catalogue stars with V magnitudes $5^m -11^m in 180 fields north of -25 degrees of declination. The accuracy ofthe proper motions is 8 mas/yr (milliarcseconds per year). Comparison ofproper motions of GPM1 with those of the PPM and ACRS was performed andanalyzed with respect to systematic errors caused by spurious rotationof the FK5 system. The standard errors show that the rotation may bedetermined with an accuracy better than 1 mas/yr. Catalog is onlyavailable in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr or ftp 130.79.128.5.
| The Palomar/MSU Nearby Star Spectroscopic Survey.II.The Southern M Dwarfs and Investigation of Magnetic Activity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2799H&db_key=AST
| Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5).
We have applied the InfraRed Flux Method (IRFM) to a sample of 475dwarfs and subdwarfs in order to derive their effective temperatureswith a mean accuracy of about 1.5%. We have used the new homogeneousgrid of theoretical model atmosphere flux distributions developed byKurucz (1991, 1993) for the application of the IRFM. The atmosphericparameters of the stars cover, roughly, the ranges:3500K<=T_eff_<=8000K -3.5<=[Fe/H]<=+0.53.5<=log(g)<=5. The monocromatic infrared fluxes at the continuum,and the bolometric fluxes are derived using recent results, whichsatisfy the accuracy requeriments of the work. Photometric calibrationshave been revised and applied to estimate metallicities, although directspectroscopic determinations were preferred when available. The adoptedinfrared absolute flux calibration, based on direct optical measurementsof angular stellar diameters, sets the effective temperatures determinedusing the IRFM on the same scale than those obtained by direct methods.We derive three temperatures, T_J_, T_H_ and T_K_, for each star usingthe monochromatic fluxes at different infrared wavelengths in thephotometric bands J, H, and K. They show good consistency over 4000 K,and no trend with wavelength may be appreciated. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of the errors associated to the different inputs ofthe method, and their transmission into the final temperatures. We alsoprovide comparison with previous works.
| Optical and near-infrared spectropolarimetry of the infrared-luminous galaxy IRAS 23060+0505
We present optical and near-IR spectropolarimetry of the type 2infrared-luminous galaxy IRAS 23060+0505, which clearly shows both broadHα and Paalpha in polarized flux. The full widths at half maximum(FWHM) of these lines are consistent with that of Paalpha in total fluxas measured by Hines. From the ratio of the polarized and total broadHα fluxes, we calculate the intrinsic polarization to be ~25 percent, assuming that the scattering geometry is the same for both thecontinuum and broad-line radiation. We model the flux density andpolarization characteristics as a combination of scattered continuum anda dichroic view of the near-IR-emitting regions through the postulatedtorus, which obscures the type 1 nucleus from the line of sight. Theextinction along the path of the scattered radiation is A_V~2.9 mag,whilst that of the direct view to the near-IR emission region is 20 mag,and to the BLR is ~30 mag, substantially higher than previous estimates.The presence of high extinction along the scattering path may havestrong implications for the observability of scattered optical broadlines in other objects. The calculated broad Hα luminosity is(2.3+/-0.3)x10^44 erg s^-1, consistent with that of QSOs.
| Photometric survey near the main Galactic meridian: 2.1. Finding charts and photoelectric U,B,V,R stellar magnitudes in 25 fields
Finding charts and photoelectric U,B,V,R magnitudes of stars in 25fields in the Main Galactic Meridian (programme MEGA) are presented.This part of the photometric survey includes fields near the NorthGalactic pole and fields at southern Galactic latitudes. Together withthe finding charts of 2.5(deg) x2.5(deg) the equatorial coordinates ofthe stars are given for epoch and equinox 1950.
| Photometry of the intermediate-age open cluster NGC 2141
Optical V and I, and a selection of near-infrared J and H observationsare presented for the open cluster NGC 2141. The colour excess E(B-V)has been determined as 0.35+/-0.07 mag, based on the positions ofseveral giants and clump stars in a (V-I, J-H) diagram. The distancemodulus (m-M)_V is found to be 14.16+/-0.16 (4.2+/-0.4 kpc), based on acomparison between the magnitudes of the red giant clump stars in NGC2141 and M67. The age is estimated to be 2.5 Gyr, from a comparison ofthe colour-magnitude diagram with convective overshooting isochrones fora metallicity of Z=0.006.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| The Palomar/MSU Nearby-Star Spectroscopic Survey. I. The Northern M Dwarfs -Bandstrengths and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.1838R&db_key=AST
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
