Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The Disk and Environment of a Young Vega Analog: HD 169142
We trace the disk of HD 169142 (A8 Ve) from 0.57" to 1.4" (~80-200 AUprojected distance) in 1.1 μm scattered light with HST NICMOScoronagraphy. The azimuthally symmetric disk has a peak azimuthallymedianed surface brightness (SB) of ~5 mJy arcsec-2 at 0.57"from the star, and drops ~r-3. This radial SB profile isconsistent with the presence of spatially resolved PAH emission and aMeeus group I IR SED only if the inner disk is either substantiallyflatter than the outer disk or partially devoid of material. Analysis ofnew HST ACS FUV imagery in tandem with archival IUE data indicatesM˙acc<=10-9 Msolaryr-1. We estimate the age of HD 169142 to be6+6-3 Myr by identifying 2MASS 18242929-2946559,located 9.3" to the southwest, as a 130 mas separation weak-line T Tauribinary that is comoving with HD 169142 at the 4 σ confidencelevel. We find no evidence for any additional stellar companion ineither the ACS or Chandra ACIS-S data at r<=1''. HD169142 has previously been interpreted as a slowly rotating, chemicallypeculiar star. However, by combining the disk inclination and vsini fromthe literature, we find that the star has vequatorial~240 kms-1, making it a rapid rotator, similar to Altair or Vega.The UV data for HD 169142 are consistent with gravity darkening, whilethe X-ray luminosity and spectrum resembles early F stars at the age ofthe β Pictoris moving group, rather than mid-A stars. In thiscontext, spectral features previously interpreted as evidence forchemical peculiarity are more likely to reflect the presence of a strongphotospheric latitudinal temperature gradient. With such a gradient, HD169142 should closely resemble Vega at the epoch of central diskclearing.
| Experimental TiI oscillator strengths and their application to cool star analysis
We report experimental oscillator strengths for 88 TiI transitionscovering the wavelength range 465-3892 nm, 67 of which had no previousexperimental values. Radiative lifetimes for 13 energy levels, includingthe low energy levels 3d2(3F) 4s4p (3P)z 5D°j, have been measured using time-resolvedlaser-induced fluorescence. Intensity-calibrated TiI spectra have beenmeasured using Fourier transform spectroscopy to determine branchingfractions for the decay channels of these levels. The branchingfractions are combined with the radiative lifetimes to yield absolutetransition probabilities and oscillator strengths. Our measurementsinclude 50 transitions in the previously unobserved infrared regionλ > 1.0μm, a region of particular interest to the analysisof cool stars and brown dwarfs.
| Ca II H and K Chromospheric Emission Lines in Late-K and M Dwarfs
We have measured the profiles of the Ca II H and K chromosphericemission lines in 147 main-sequence stars of spectral type M5-K7 (masses0.30-0.55 Msolar) using multiple high-resolution spectraobtained during 6 years with the HIRES spectrometer on the Keck Itelescope. Remarkably, the average FWHM, equivalent widths, and lineluminosities of Ca II H and K increase by a factor of 3 with increasingstellar mass over this small range of stellar masses. We fit the Ca II Hand K lines with a double-Gaussian model to represent both thechromospheric emission and the non-LTE central absorption. Most of thesample stars display a central absorption that is typically redshiftedby ~0.1 km s-1 relative to the emission. This implies thatthe higher level, lower density chromospheric material has a smalleroutward velocity (or higher inward velocity) by 0.1 km s-1than the lower level material in the chromosphere, but the nature ofthis velocity gradient remains unknown. The FWHM of the Ca II H and Kemission lines increase with stellar luminosity, reminiscent of theWilson-Bappu effect in FGK-type stars. Both the equivalent widths andFWHM exhibit modest temporal variability in individual stars. At a givenvalue of MV, stars exhibit a spread in both the equivalentwidth and FWHM of Ca II H and K, due both to a spread in fundamentalstellar parameters, including rotation rate, age, and possiblymetallicity, and to the spread in stellar mass at a given MV.The K line is consistently wider than the H line, as expected, and itscentral absorption is more redshifted, indicating that the H and K linesform at slightly different heights in the chromosphere where thevelocities are slightly different. The equivalent width of Hαcorrelates with Ca II H and K only for stars having Ca II equivalentwidths above ~2 Å, suggesting the existence of a magneticthreshold above which the lower and upper chromospheres become thermallycoupled.Based on observations obtained at the W. M. Keck Observatory, which isoperated jointly by the University of California and the CaliforniaInstitute of Technology. Keck time has been granted by both NASA and theUniversity of California.
| The Radial Velocity Distribution of Class I and Flat-Spectrum Protostars
We analyze radial velocities for a sample of 31 Class I andflat-spectrum protostars in Taurus-Auriga, ρ Ophiuchi, and Serpensfor evidence of the global dynamical state of extremely young stellarpopulations buried within parental molecular clouds. Comparing theradial velocity of each protostar to that of the local CO gas, we areable to constrain the one-dimensional radial velocity dispersion ofClass I and flat-spectrum objects to ~2.5 km s-1 or below.This upper limit to the protostellar velocity dispersion is consistentwith the velocity dispersions of surrounding CO gas, which we measure tobe ~1.4 km s-1, suggesting that the motions of protostars andlocal CO gas are dynamically linked and are dominated by thegravitational potential of the molecular cloud. However, the upper limiton the protostellar velocity dispersion could still allow for slightlyinflated motions of protostars relative to the local molecular gas. Fourof the protostars analyzed appear to have velocities more than 3 σ(7.5 km s-1) away from the central local CO gas velocitywhile showing spectroscopic indicators of youth and accretion such asH2 emission, H I Brγ emission, or K-band continuumveiling. These radial velocity outliers may represent protostellarspectroscopic binaries or ejected cluster members.The data presented herein were obtained at the W. M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California, and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W. M. Keck Foundation.
| The Physical Natures of Class I and Flat-Spectrum Protostellar Photospheres: A Near-Infrared Spectroscopic Study
We present high-resolution (R~=18,000), high signal-to-noise ratio, 2μm spectra of 52 IR-selected Class I and flat-spectrum young stellarobjects in the Taurus-Auriga, ρ Ophiuchi, Serpens, Perseus, andCorona Australis dark clouds. We detect key absorption lines in 41objects and fit synthetic spectra generated from pre-main-sequencemodels to deduce the effective temperatures, surface gravities, near-IRveilings, rotation velocities, and radial velocities of each of these 41sources. We find these objects to span ranges in effective temperature,surface gravity, and stellar luminosity that appear similar to those oflate spectral type Class II sources and classical T Tauri stars.However, because of significant but uncertain corrections for scatteringand extinction, the derived luminosities for the embedded protostellarobjects must be regarded as being highly uncertain. We determine thatthe mean 2 μm veiling of Class I and flat-spectrum objects issignificantly higher than that of Class II objects in the same regionwhere both types of objects are extensively observed (ρ Oph). Wefind that a significant fraction of our protostellar sample alsoexhibits emission lines. Twenty-three objects show H2emission, which is usually indicative of the presence of energeticoutflows. Thirty-four sources show H I Brγ emission, and a numberof these exhibit profile asymmetries consistent with infall. Eightsources show significant Δv=2 CO emission suggestive of emissionfrom a circumstellar disk. Overall, these observations indicate thatClass I and flat-spectrum objects are self-embedded protostarsundergoing significant mass accretion, although the objects appear tospan a broad range of mass accretion activity.Data presented herein were obtained at the W. M. Keck Observatory fromtelescope time allocated to the National Aeronautics and SpaceAdministration through the agency's scientific partnership with theCalifornia Institute of Technology and the University of California. TheObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| 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.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| Roche tomography of cataclysmic variables - II. Images of the secondary stars in AM Her, QQ Vul, IP Peg and HU Aqr
We present a set of Roche tomography reconstructions of the secondarystars in the cataclysmic variables AM Her, QQ Vul, IP Peg and HU Aqr.The image reconstructions show distinct asymmetries in the irradiationpattern for all four systems that can be attributed to shielding of thesecondary star by the accretion stream/column in AM Her, QQ Vul and HUAqr, and increased irradiation by the bright-spot in IP Peg. We use theentropy landscape technique to derive accurate system parameters(M1, M2, i and γ) for the four binaries. Inprinciple, this technique should provide the most reliable massdeterminations available, since the intensity distribution across thesecondary star is known. We also find that the intensity distributioncan systematically affect the value of γ derived from circularorbit fits to radial velocity variations.
| 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
| Near-Infrared Spectroscopy of Very Low-Luminosity Young Stellar Objects in the Taurus Molecular Cloud
We carried out near-infrared spectroscopic observations of 23 verylow-luminosity young stellar object (YSO) candidates and 5 of theircompanions in Heiles Cloud 2, one of the densest parts of the Taurusmolecular cloud. Twelve objects were confirmed to be YSOs by theBγ feature. The effective temperatures of the YSOs and of thecompanions are estimated from the 2.26 - μm feature, the 2.21 - μmfeature, and the H2O band strengths. Detailed comparisons ofour photometric and spectroscopic observations with evolutionary trackson the HR diagram suggest some objects to be very low-mass YSOs.
| Radial Velocities for 889 Late-Type Stars
We report radial velocities for 844 FGKM-type main-sequence and subgiantstars and 45 K giants, most of which had either low-precision velocitymeasurements or none at all. These velocities differ from the standardstars of Udry et al. by 0.035 km s-1 (rms) for the 26 FGKstandard stars in common. The zero point of our velocities differs fromthat of Udry et al.: =+0.053km s-1. Thus, these new velocities agree with the best knownstandard stars both in precision and zero point, to well within 0.1 kms-1. Nonetheless, both these velocities and the standardssuffer from three sources of systematic error, namely, convectiveblueshift, gravitational redshift, and spectral type mismatch of thereference spectrum. These systematic errors are here forced to be zerofor G2 V stars by using the Sun as reference, with Vesta and day sky asproxies. But for spectral types departing from solar, the systematicerrors reach 0.3 km s-1 in the F and K stars and 0.4 kms-1 in M dwarfs. Multiple spectra were obtained for all 889stars during 4 years, and 782 of them exhibit velocity scatter less than0.1 km s-1. These stars may serve as radial velocitystandards if they remain constant in velocity. We found 11 newspectroscopic binaries and report orbital parameters for them. Based onobservations obtained at the W. M. Keck Observatory, which is operatedjointly by the University of California and the California Institute ofTechnology, and on observations obtained at the Lick Observatory, whichis operated by the University of California.
| Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog
We present refined coordinates and proper-motion data for the highproper-motion (HPM) stars in the Luyten Half-Second (LHS) catalog. Thepositional uncertainty in the original Luyten catalog is typicallygreater than 10" and is often greater than 30". We have used the digitalscans of the POSS I and POSS II plates to derive more accurate positionsand proper motions of the objects. Out of the 4470 candidates in the LHScatalog, 4323 objects were manually reidentified in the POSS I and POSSII scans. A small fraction of the stars were not found because of thelack of finder charts and digitized POSS II scans. The uncertainties inthe revised positions are typically ~2" but can be as high as ~8" in afew cases, which is a large improvement over the original data.Cross-correlation with the Tycho-2 and Hipparcos catalogs yielded 819candidates (with mR<~12). For these brighter sources, theposition and proper-motion data were replaced with the more accurateTycho-2/Hipparcos data. In total, we have revised proper-motionmeasurements and coordinates for 4040 stars and revised coordinates for4330 stars. The electronic version of the paper5 contains the updated information on all 4470stars in the LHS catalog.
| The Palomar/MSU Nearby Star Spectroscopic Survey. III. Chromospheric Activity, M Dwarf Ages, and the Local Star Formation History
We present high-resolution echelle spectroscopy of 676 nearby M dwarfs.Our measurements include radial velocities, equivalent widths ofimportant chromospheric emission lines, and rotational velocities forrapidly rotating stars. We identify several distinct groups by theirHα properties and investigate variations in chromospheric activityamong early (M0-M2.5) and mid (M3-M6) dwarfs. Using a volume-limitedsample together with a relationship between age and chromosphericactivity, we show that the rate of star formation in the immediate solarneighborhood has been relatively constant over the last 4 Gyr. Inparticular, our results are inconsistent with recent large bursts ofstar formation. We use the correlation between Hα activity and ageas a function of color to set constraints on the properties of L and Tdwarf secondary components in binary systems. We also identify a numberof interesting stars, including rapid rotators, radial velocityvariables, and spectroscopic binaries. Observations were made at the 60inch telescope at Palomar Mountain, which is jointly owned by theCalifornia Institute of Technology and the Carnegie Institution ofWashington.
| Late-type members of young stellar kinematic groups - I. Single stars
This is the first paper of a series aimed at studying the properties oflate-type members of young stellar kinematic groups. We concentrate ourstudy on classical young moving groups such as the Local Association(Pleiades moving group, 20-150Myr), IC 2391 supercluster (35Myr), UrsaMajor group (Sirius supercluster, 300Myr), and Hyades supercluster(600Myr), as well as on recently identified groups such as the Castormoving group (200Myr). In this paper we compile a preliminary list ofsingle late-type possible members of some of these young stellarkinematic groups. Stars are selected from previously established membersof stellar kinematic groups based on photometric and kinematicproperties as well as from candidates based on other criteria such astheir level of chromospheric activity, rotation rate and lithiumabundance. Precise measurements of proper motions and parallaxes takenfrom the Hipparcos Catalogue, as well as from the Tycho-2 Catalogue, andpublished radial velocity measurements are used to calculate theGalactic space motions (U, V, W) and to apply Eggen's kinematic criteriain order to determine the membership of the selected stars to thedifferent groups. Additional criteria using age-dating methods forlate-type stars will be applied in forthcoming papers of this series. Afurther study of the list of stars compiled here could lead to a betterunderstanding of the chromospheric activity and their age evolution, aswell as of the star formation history in the solar neighbourhood. Inaddition, these stars are also potential search targets for directimaging detection of substellar companions.
| Infrared spectroscopy of cataclysmic variables - III. Dwarf novae below the period gap and nova-like variables
We present K-band spectra of the short-period dwarf novae YZ Cnc, LYHya, BK Lyn, T Leo, SW UMa and WZ Sge, the nova-like variables DW UMa,V1315 Aql, RW Tri, VY Scl, UU Aqr and GP Com, and a series of fielddwarf stars with spectral types ranging from K2 to M6. The spectra ofthe dwarf novae are dominated by emission lines of Hi and Hei. The largevelocity and equivalent widths of these lines, in conjunction with thefact that the lines are double-peaked in the highest inclinationsystems, indicate an accretion disc origin. In the case of YZ Cnc and TLeo, for which we obtained time-resolved data covering a completeorbital cycle, the emission lines show modulations in their equivalentwidths that are most probably associated with the bright spot (theregion where the gas stream collides with the accretion disc). There areno clear detections of the secondary star in any of the dwarf novaebelow the period gap, yielding upper limits of 10-30per cent for thecontribution of the secondary star to the observed K-band flux. Inconjunction with the K-band magnitudes of the dwarf novae, we use thederived secondary star contributions to calculate lower limits to thedistances to these systems. The spectra of the nova-like variables aredominated by broad, single-peaked emission lines of Hi and Hei - eventhe eclipsing systems we observed do not show the double-peaked profilespredicted by standard accretion disc theory. With the exception of RWTri, which exhibits Nai, Cai and 12CO absorption featuresconsistent with a M0V secondary contributing 65per cent of the observedK-band flux, we find no evidence for the secondary star in any of thenova-like variables. The implications of this result are discussed.
| A mystery solved: the mass ratio of the dwarf nova EM Cygni
We have discovered that the spectrum of the well-known dwarf nova EM Cygis contaminated by light from a K2-5V star (in addition to the K-typemass donor star). The K2-5V star contributes approximately 16per cent ofthe light from the system and if not taken into account has aconsiderable effect upon radial velocity measurements of the mass donorstar. We obtain a new radial velocity amplitude for the mass donor starof K2=202+/-3kms-1, compared with the value ofK2=135+/-3kms-1 obtained in Stover, Robinson &Nather's classic study of EM Cyg. The revised value of the amplitude,combined with a measurement of rotational broadening of the mass donor,vsini=140+/-6kms-1, leads to a new mass ratio ofqM2M1=0.88+/-0.05. This solves a long-standingproblem with EM Cyg, because Stover et al.'s measurements indicated amass ratio q>1, a value that should have led to dynamically unstablemass transfer for the secondary mass deduced by Stover et al. Therevised value of the mass ratio, combined with the orbital inclinationi=67+/-2 deg, leads to masses of 0.99+/-0.12Msolar and1.12+/-0.08Msolar for the mass donor and white dwarfrespectively. The mass donor is evolved, because it has a later spectraltype (K3) than its mass would imply. We discuss whether the K star couldbe physically associated with EM Cyg or not, and present the results ofthe spectroscopic study.
| Photometric Measurements of the Fields of More than 700 Nearby Stars
In preparation for optical/IR interferometric searches for substellarcompanions of nearby stars, we undertook to characterize the fields ofall nearby stars visible from the Northern Hemisphere to determinesuitable companions for interferometric phase referencing. Because theKeck Interferometer in particular will be able to phase-reference oncompanions within the isoplanatic patch (30") to about 17th magnitude atK, we took images at V, r, and i that were deep enough to determine iffield stars were present to this magnitude around nearby stars using aspot-coated CCD. We report on 733 fields containing 10,629 measurementsin up to three filters (Gunn i, r and Johnson V) of nearby stars down toabout 13th magnitude at V.
| 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
| Photometry of Stars with Large Proper Motion
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.2300W&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.
| 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
| Optical spectroscopy of low-mass stars and brown dwarfs in the Pleiades
We present low-resolution spectra in the range 4600-9700 A of a sampleof low-mass stars and brown dwarf candidates in the Pleiades. We orderthe spectra into a temperature sequence, using a least-squaresminimization procedure, and assign spectral types. The effectiveness ofvarious proposed spectroscopic and photometric temperature indicatorsfor low-mass stars is investigated. We find that the most effectivespectroscopic temperature indicators are those based on molecular bands,especially TiO, rather than atomic transitions. We also find that thePleiades objects may have surface gravities slightly lower thanmain-sequence objects of the same temperature, supporting theiridentification as pre-main-sequence cluster members. We investigate theeffect of unresolved binarity on the temperature indicators, andconclude that ~46 per cent of low-mass sytems in the Pleiades aremultiple. Finally, we discuss how these results affect the status of ourbrown dwarf candidates, revising the number to 11 systems containingsuch candidates, of which three are single and the remainder binary.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Broad band JHK infrared photometry of an extended sample of late type dwarfs and subdwarfs.
The results of a long term programme of broad band JHK photometry, for asample of 360 late type stars, made at the Observatorio del Teide(Tenerife, Spain) are presented. Transformations between thesemagnitudes and those of several currently used systems (CIT (Elias etal. 1982 and Carney 1983), Johnson (Johnson 1966, and Lee 1970), and ESO(Bouchet et al. 1991)) are proposed. A comparison to the narrow-bandsystem of Selby et al. (1988) has been made, in order to check theaccuracy of the photometric system. A mean internal accuracy better than0.02mag in the three bands can be inferred from the comparison to thelarge number of stars in common with Carney (1983), and from thedispersion of the multiple measured stars. The list of standards, thefilter passbands and effective wavelengths, together with correlationsbetween the extinction coefficients, ultimately characterize thephotometric IR system of the Observatorio del Teide (TCS). Data ofcomparable quality previously published have been added in order tocomplete the sample. This way the final sample consists of 550 stars.From the analysis of optical and IR colour:colour diagrams, we maydeduce that the range F0-K0 is properly sampled for0.1>[Fe/H]>-3.0. In the range K0-M4, no reliable photometricestimates of metallicity can be assigned, and only a small number ofstars have spectroscopic determination of the metallicity. Nevertheless,after kinematical considerations, the stars in this spectral range arealso expected to sample the galactic populations of dwarfs. Themetallicity effects on the IR and optical colour:colour diagrams arebriefly discussed.
| Low mass companions to nearby stars: Spectral classification and its relation to the stellar/substellar break
The relationship between mass and spectral class for main-sequence starshas never been obtained for dwarfs cooler than M6; currently, the truenature of objects classified as M7, M8, M9, or later (be they stellar orsubstellar) is not known. In this paper, spectral types for thecomponents in five low mass binary systems are estimated based onpreviously published infrared speckle measurements, red/infraredphotometry, and parallax data, together with newly acquired highsignal-to-noise composite spectra of the systems and revised magnitudedifference relations for M dwarfs. For two of these binaries, thesecondary has a smaller mass (less than 0.09 solar mass) than any objecthaving a dynamically measured mass and a known spectral type, thusextending the spectral class/mass relation to lower masses than haspreviously been possible. Data from the higher mass components (0.09solar mass less than M less than 0.40 solar mass) are consistent withearlier results; the two lowest mass objects -- though having masserrors which could place them on either side of the M dwarf/brown dwarfdividing line (Mass is about 0.08 solar mass) -- are found to havespectral types no cooler than M6.5 V. An extrapolation of the updatedspectral class/mass relation to the hydrogen-burning limit suggests thatobjects of type M7 and later may be substellar. Direct confirmation ofthis awaits the discovery of a close, very late-type binary for whichdynamical masses can be measured.
| Far infrared properties of late type dwarfs. Infrared fluxes of K & M dwarfs
IRAS fluxes/upper limits are presented for a large sample of K and Mdwarfs. Good agreement is found between the 12 micrometer fluxes andthose derived from the photospheric models of Mould (1976).Relationships between the optical and infrared colors are derived. Theactive dMe/dKe stars appear systematically brighter in the infraredcompared with the less active dM/dK stars, which could be attributed tomore efficient nonradiative heating in their atmosphere. Any systematicdifferences found in our results when compared with those obtained fromprevious studies are attributed to the different analysis packages used.
| The importance of surface inhomogeneities for K and M dwarf chromospheric fluxes
We present published and archived spectroscopic and spectrophotometricdata of H-alpha, Ca II, Mg II, and X-rays for a large sample of K and Mdwarfs. The data set points to the importance that surfaceinhomogeneities have in the flux luminosity diagrams in these late-typedwarfs, irrespective of whether the Balmer lines are in emission orabsorption. Although supporting the fact that cooler stars exhibitincreasing levels of surface activity, evident through an increasingincidence of Balmer emission, surface inhomogeneities, or variations inthe local temperature and density structure, at the chromospheric level,dominate the total Ca II and Mg II fluxes. We show that the flux-fluxand luminosity-luminosity relations indicate differing extents ofinhomogeneity from the chromosphere through to the corona. A goodcorrelation between Ca II and Mg II fluxes indicates that they areformed in overlapping regions of the chromosphere, so that thecontribution of surface inhomogeneities is not evident from thisparticular flux-flux diagram. In the region of the upper chromospherethrough to the transition and corona, the correlation between Ly-alphaand X-ray fluxes indicates regions with similar levels of arealinhomogeneity. This appears to be uncorrelated with that at thechromospheric level.
| U.S. Naval Observatory photographic parallaxes - List IX
Trigonometric parallaxes, relative proper motions, and photometry arepresented for 122 stars in 111 systems. Of these stars, 70 are brighterthan V = 10.0.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Лабуд |
| Ректацензија: | 20h45m04.10s |
| Deклинација: | +44°29'56.5" |
| Apparent магнитуда: | 10.848 |
| Даљина: | 12.498 parsecs |
| Proper motion RA: | 433.6 |
| Proper motion Dec: | 268.6 |
| B-T magnitude: | 12.37 |
| V-T magnitude: | 10.974 |
Каталог и designations:
|
