Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The Brown Dwarf Kinematics Project. II. Details on Nine Wide Common Proper Motion Very Low Mass Companions to Nearby Stars
We report on nine wide common proper motion systems containing late-typeM, L, or T companions. We confirm six previously reported companions,and identify three new systems. The ages of these systems are determinedusing diagnostics for both stellar primaries and low-mass secondariesand masses for the secondaries are inferred using evolutionary models.Of our three new discoveries, the M3+T6.5 pair G 204-39 and SDSSJ1758+4633 has an age constrained to 0.5-1.5 Gyr making the secondary apotentially useful brown dwarf benchmark. The G5+L4 pair G 200-28 andSDSS J1416+5006 has a projected separation of ~25,000 AU making it oneof the widest and lowest binding energy systems known to date. Thesystem containing NLTT 2274 and SDSS J0041+1341 is an older M4+L0(>4.5 Gyr) pair which shows H? activity in the secondary butnot the primary making it a useful tracer of age/mass/activity trends.Two of the nine systems have discrepant component ages that emerge fromstellar or ultracool diagnostics indicating possible shortcomings in ourunderstanding of the age diagnostics of stars and brown dwarfs. We finda resolved binary frequency for widely separated (>100 AU) low-masscompanions (i.e., at least a triple system) which is at least twice thefrequency found for the field ultracool dwarf population. The ratio oftriples to binaries and quadruples to binaries is also high for thissample: 3:5 and 1:4, respectively, compared to 8 pc sample values of 1:4and 1:26. The additional components in these wide companion systemsindicates a formation mechanism that requires a third or fourthcomponent to maintain gravitational stability or facilitate the exchangeof angular momentum. The binding energies for the nine multiplesdiscussed in this text are among the lowest known for wide low-masssystems, suggesting that weakly bound, low-to-intermediate mass (0.2 Msun < M tot< 1.0 M sun) multiplescan form and survive to exist in the field (1-8 Gyr).This paper includes data gathered with the 6.5 meter Magellan Telescopeslocated at Las Campanas Observatory, Chile.This paper makes use of data obtained with the telescopes operated bythe SMARTS consortium.
| The minimum Jeans mass, brown dwarf companion IMF, and predictions for detection of Y-type dwarfs
Cool L- and T-type objects were discovered first as companions to starsin 1988 and 1995, respectively. A certain example of the even coolerY-type spectral class (T_eff ⪉ 500 K) has not been seen. Recentinfrared-imaging observations of stars and brown dwarfs indicate thatsubstellar companions with large semi-major axes and with masses lessthan the brown dwarf/giant planet dividing line ( 13.5{M}_J) are rare.Theoretical considerations of the Jeans mass fragmentation of molecularclouds are consistent with this minimum mass cutoff and also with thesemi-major axis (hundreds of AU) characteristic of the lowest massimaged companions. As a consequence, Y-class companions with largesemi-major axes should be scarce around stars <2 Gyr old, and alsoaround substellar primaries of all ages. By focusing on brown dwarfcompanions to young stellar primaries, it is possible to derive a firstestimate of the brown dwarf IMF over the entire range of brown dwarfmasses (13{M}J to 79{M}_J) - the number of companion browndwarfs is proportional to the mass to the -1.2±0.2 power.
| A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf ``Lithium Test'' at Early Ages
Using a large sample of optical spectra of late-type dwarfs, we identifya subset of late-M through L field dwarfs that, because of the presenceof low-gravity features in their spectra, are believed to be unusuallyyoung. From a combined sample of 303 field L dwarfs, we findobservationally that 7.6%+/-1.6% are younger than 100 Myr. Thispercentage is in agreement with theoretical predictions once observingbiases are taken into account. We find that these young L dwarfs tend tofall in the southern hemisphere (decl.<0deg) and may bepreviously unrecognized, low-mass members of nearby, young associationslike Tucana-Horologium, TW Hydrae, ? Pictoris, and AB Doradus. Weuse a homogeneously observed sample of ~150 optical spectra to examinelithium strength as a function of L/T spectral type and furthercorroborate the trends noted by Kirkpatrick and coworkers. We use ourlow-gravity spectra to investigate lithium strength as a function ofage. The data weakly suggest that for early- to mid-L dwarfs the linestrength reaches a maximum for a few×100 Myr, whereas for mucholder (few Gyr) and much younger (<100 Myr) L dwarfs the line isweaker or undetectable. We show that a weakening of lithium at lowergravities is predicted by model atmosphere calculations, an effectpartially corroborated by existing observational data. Larger samplescontaining L dwarfs of well-determined ages are needed to further testthis empirically. If verified, this result would reinforce the caveatfirst cited by Kirkpatrick and coworkers that the lithium test should beused with caution when attempting to confirm the substellar nature ofthe youngest brown dwarfs.Most of the spectroscopic data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership amongthe California Institute of Technology, the University of California,and the National Aeronautics and Space Administration. The Observatorywas made possible by the generous financial support of the W. M. KeckFoundation. Other spectroscopic data were collected at the SubaruTelescope, the twin telescopes of the Gemini Observatory, theMagellan-Clay Telescope, the Kitt Peak National Observatory MayallTelescope, and the Cerro Tololo Interamerican Observatory BlancoTelescope.
| 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
| Further observations of Hipparcos red stars and standards for UBV(RI)C photometry
We present homogeneous and standardized UBV(RI)C JHKphotometry for over 100 M stars selected from an earlier paper on thebasis of apparent photometric constancy. L photometry has been obtainedfor stars brighter than about L = 6. Most of the stars have asubstantial number of UBV(RI)C observations and, it is hoped,will prove useful as red supplementary standards. Additionally, we listJHK photometry for nearly 300 Hipparcos red stars not selected asstandards, as well as L photometry for the brightest stars.
| Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data
Context: .This paper is the last in a series devoted to the analysis ofthe binary content of the Hipparcos Catalogue. Aims: .Thecomparison of the proper motions constructed from positions spanning ashort (Hipparcos) or long time (Tycho-2) makes it possible to uncoverbinaries with periods of the order of or somewhat larger than the shorttime span (in this case, the 3 yr duration of the Hipparcos mission),since the unrecognised orbital motion will then add to the propermotion. Methods: .A list of candidate proper motion binaries isconstructed from a carefully designed χ2 test evaluatingthe statistical significance of the difference between the Tycho-2 andHipparcos proper motions for 103 134 stars in common between the twocatalogues (excluding components of visual systems). Since similar listsof proper-motion binaries have already been constructed, the presentpaper focuses on the evaluation of the detection efficiency ofproper-motion binaries, using different kinds of control data (mostlyradial velocities). The detection rate for entries from the NinthCatalogue of Spectroscopic Binary Orbits (S_B^9) is evaluated, as wellas for stars like barium stars, which are known to be all binaries, andfinally for spectroscopic binaries identified from radial velocity datain the Geneva-Copenhagen survey of F and G dwarfs in the solarneighbourhood. Results: .Proper motion binaries are efficientlydetected for systems with parallaxes in excess of ~20 mas, and periodsin the range 1000-30 000 d. The shortest periods in this range(1000-2000 d, i.e., once to twice the duration of the Hipparcos mission)may appear only as DMSA/G binaries (accelerated proper motion in theHipparcos Double and Multiple System Annex). Proper motion binariesdetected among S_B9 systems having periods shorter than about400 d hint at triple systems, the proper-motion binary involving acomponent with a longer orbital period. A list of 19 candidate triplesystems is provided. Binaries suspected of having low-mass(brown-dwarf-like) companions are listed as well. Among the 37 bariumstars with parallaxes larger than 5 mas, only 7 exhibit no evidence forduplicity whatsoever (be it spectroscopic or astrometric). Finally, thefraction of proper-motion binaries shows no significant variation amongthe various (regular) spectral classes, when due account is taken forthe detection biases.Full Table [see full textsee full text] is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/377
| Exploring the Frequency of Close-in Jovian Planets around M Dwarfs
We discuss our high-precision radial velocity results of a sample of 90M dwarfs observed with the Hobby-Eberly Telescope and the Harlan J.Smith 2.7 m Telescope at McDonald Observatory, as well as the ESO VLTand the Keck I telescopes, within the context of the overall frequencyof Jupiter-mass planetary companions to main-sequence stars. None of thestars in our sample show variability indicative of a giant planet in ashort-period orbit, with a<=1 AU. We estimate an upper limit of thefrequency f of close-in Jovian planets around M dwarfs as <1.27% (atthe 1 σ confidence level). Furthermore, we determine that theefficiency of our survey in noticing planets in circular orbits is 98%for companions with msini>3.8MJ and a<=0.7 AU. Foreccentric orbits (e=0.6) the survey completeness is 95% for all planetswith msini>3.5MJ and a<=0.7 AU. Our results pointtoward a generally lower frequency of close-in Jovian planets for Mdwarfs as compared to FGK-type stars. This is an important piece ofinformation for our understanding of the process of planet formation asa function of stellar mass.Based on data collected with the Hobby-Eberly Telescope, which isoperated by McDonald Observatory on behalf of the University of Texas atAustin, Pennsylvania State University, Stanford University,Ludwig-Maximilians-Universität München, andGeorg-August-Universität Göttingen. Also based on observationscollected at the European Southern Observatory, Chile (ESO programs65.L-0428, 66.C-0446, 267.C-5700, 68.C-0415, 69.C-0722, 70.C-0044,71.C-0498, 072.C-0495, 173.C-0606). Additional data were obtained at theW. M. Keck Observatory, which is operated as a scientific partnershipamong the California Institute of Technology, the University ofCalifornia, and the National Aeronautics and Space Administration(NASA), and with the McDonald Observatory Harlan J. Smith 2.7 mtelescope.
| Finding benchmark brown dwarfs to probe the substellar initial mass function as a function of time
Using a simulated disc brown dwarf (BD) population, we find that newlarge area infrared surveys are expected to identify enough BDs coveringwide enough mass-age ranges to potentially measure the present day massfunction down to ~0.03Msolar, and the BD formation historyout to 10Gyr, at a level that will be capable of establishing if BDformation follows star formation. We suggest these capabilities are bestrealized by spectroscopic calibration of BD properties (Teff,g and [M/H]) which when combined with a measured luminosity and anevolutionary model can give BD mass and age relatively independent of BDatmosphere models. Such calibration requires an empirical understandingof how BD spectra are affected by variations in these properties, andthus the identification and study of `benchmark BDs' whose age andcomposition can be established independently.We identify the best sources of benchmark BDs as young open clustermembers, moving group members, and wide (>1000au) BD companions toboth subgiant stars and high-mass white dwarfs (WDs). To accuratelyasses the likely number of wide companion BDs available, we haveconstrained the wide L dwarf companion fraction using the 2-Micron AllSky Survey (2MASS), and find a companion fraction of2.7+0.7-0.5percent for separations of~1000-5000au. This equates to a BD companion fraction of34+9-6percent if one assumes an α~ 1companion mass function. Using this BD companion fraction, we simulatepopulations of wide BD binaries, and estimate that80+21-14 subgiant-BD binaries, and50+13-10 benchmark WD-BD binaries could beidentified using current and new facilities. The WD-BD binaries shouldall be identifiable using the Large Area Survey component of the UnitedKingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey, combinedwith the Sloan Digital Sky Survey. Discovery of the subgiant-BD binarieswill require a near-infrared imaging campaign around a large (~900)sample of Hipparcos subgiants. If identified, spectral studies of thesebenchmark BD populations could reveal the spectral sensitivities acrossthe Teff, g and [M/H] space probed by new surveys.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| 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
| Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
Trigonometric parallax determinations are presented for 28 late-typedwarfs and brown dwarfs, including eight M dwarfs with spectral typesbetween M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8,and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz*)and/or near-IR wavelengths (JHK) is presented for these objects and for24 additional late-type dwarfs. Supplemented with astrometry andphotometry from the literature, including 10 L and two T dwarfs withparallaxes established by association with bright, usually Hipparcosprimaries, this material forms the basis for studying variouscolor-color and color-absolute magnitude relations. The I-J color is agood predictor of absolute magnitude for late M and L dwarfs.MJ becomes monotonically fainter with I-J color and withspectral type through late L dwarfs, then brightens for early T dwarfs.The combination of z*JK colors alone can be used to classify late M,early L, and T dwarfs accurately, as well as to predict their absolutemagnitudes, but is less effective at untangling the scatter among mid-and late L dwarfs. The mean tangential velocity of these objects isfound to be slightly less than that for dM stars in the solarneighborhood, consistent with a sample with a mean age of several Gyr.Using colors to estimate bolometric corrections and models to estimatestellar radii, effective temperatures are derived. The latest L dwarfsare found to have Teff~1360 K.
| UBV(RI)C photometry of Hipparcos red stars
We present homogeneous and standardized UBV(RI)C photometryfor nearly 550 M stars selected from the Hipparcos satellite data baseusing the following selection criteria: lack of obvious variability (noHipparcos variability flag); δ<+10°(V-I)>1.7 and Vmagnitude fainter than about 7.6. Comparisons are made between thecurrent photometry, other ground-based data sets and Hipparcosphotometry. We use linear discriminant analysis to determine aluminosity segregation criterion for late-type stars, and principalcomponent analysis to study the statistical structure of the colourindices and to calibrate absolute magnitude in terms of (V-I) for thedwarf stars. Various methods are used to determine the mean absolutemagnitude of the giant stars. We find 10 dwarf stars, apparentlypreviously unrecognized (prior to Hipparcos) as being within 25pc,including five within 20pc.
| Three Wide-Separation L Dwarf Companions from the Two Micron All Sky Survey: Gliese 337C, Gliese 618.1B, and HD 89744B
We present two confirmed wide-separation L dwarf common proper-motioncompanions to nearby stars and one candidate identified from the TwoMicron All Sky Survey. Spectral types from optical spectroscopy are L0V, L2.5 V, and L8 V. Near-infrared, low-resolution spectra of thecompanions are provided, as well as a grid of known objects spanning M6V-T dwarfs to support spectral type assignment for these and future Ldwarfs in the z'JHK bands. Using published measurements, weestimate ages of the companions from physical properties of theprimaries. These crude ages allow us to estimate companion masses usingtheoretical low-mass star and brown dwarf evolutionary models. The new Ldwarfs in this paper bring the number of known wide-binary(Δ>=100 AU) L dwarf companions of nearby stars to nine. One ofthe L dwarfs is a wide-separation companion to the F7 IV-V+extrasolarplanet system HD 89744Ab. Portions of the data presented here wereobtained at the W. M. Keck Observatory, which is operated as ascientific partnership among the California Institute of Technology, theUniversity of California, and the National Aeronautics and SpaceAdministration. The Observatory was made possible by the generousfinancial support of the W. M. Keck Foundation. Observations at thePalomar Observatory were made as part of a continuing collaborationbetween the California Institute of Technology and Cornell University.The 60 inch telescope at Palomar Mountain is jointly owned by theCalifornia Institute of Technology and the Carnegie Institution ofWashington.
| 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
| 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
| The general catalogue of trigonometric [stellar] paralaxes
Not Available
| 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.
| Infrared colors of low-mass stars
A total of 322 red dwarf stars are studied in a review of IR IJHKphotometry to discern chromospheric activity and kinematic dataregarding metallicity effects in the IR color:color diagrams. Themetallicity variations are employed to assess changes in the H(-)continuum opacity and water-vapor characterizations. The stars areclassified in terms of metal-richness with five categories includingyoung disk, old disk, and halo types with attention given to the inverserelationship between metallicity and water-band absorption strength. Theresults include IR photometric parallax relations for each metallicitygroup and absolute magnitudes for single stars as well as temperatures,intrinsic colors, and spectral types. The body of data is useful forconstraining models of the interiors and atmospheres of this class ofstars.
| Catalogue of Variable or Suspected Stars Nearby the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990A&AS...85..971P&db_key=AST
| BVRI photometry of the Gliese Catalogue stars
Photoelectri BVRI photometry on the Cousins (Kron-Cape) system has beenobtained for many of the southern faint stars in the Gliese Catalog(1969). This extends the work of Cousins (1980) and provides a uniformset of data for the nearby stars. Several red dwarfs are noted, whichwere used to define the red end of the Cousins system.
| The infrared luminosity function for low-mass stars
IR observational luminosity functions are presented for M dwarfs towardsthe South Galactic Pole and the Hyades cluster. A compilation of VRIJHKdata is given for 200 parallax stars. Two-color NIR/IR diagrams of thedata are used to demonstrate metallicity and gravity effects. It isshown that I-J is the purest temperature color index. The corrections tothe luminosity functions that are necessary to allow for magnitudeerrors (Malmquist effects) are discussed. It is found that there is arise in the luminosity function and the mass function for stars in thesolar neighborhood with masses close to the hydrogen-burning limit.
| U.S. Naval Observatory parallaxes of faint stars - List VIII
The paper presents trigonometric parallaxes, relative proper motions,and photoelectric photometry for 98 stars in 95 astrometric plateseries. These values were determined using plate material obtained withthe 1.55-m astrometric reflector. The results of perturbation analysesfor W922 are presented.
| Chromospheric activity, kinematics, and metallicities of nearby M dwarfs
Attention is given to the results of more than 1000 observations ofabout 200 Gliese (1969) catalog M dwarfs, whose BVRIJHK photometry isbelieved to be accurate to 0.015 mag in each bandpass. An analysis ofthese data indicates that the H-alpha equivalent widths are a usefulchromospheric indicator for M dwarfs; as the chromosphere increases instrength, the H-alpha absorption equivalent width first increases, thendecreases, and H-alpha finally goes into emission, as predicted by Gramand Mullan (1979) for M dwarf chromospheres. The present JHK photometryis used to identify stars with metallicities that are significantlydifferent from that of the sun. It is noted that dMe stars in thissample generally have young disk motions, are more luminous than dMstars of the same color, and have B-V colors that are too blue for theirV-I color.
| New subdwarfs. IV - UBV photometry of 1690 high-proper-motion stars
A photometric list of 1690 stars of known high proper motion is used tosearch for potential high-velocity stars of various metallicity valuesin order to find candidates for trigonometric programs on subdwarfs andto enlarge the sample with which to study the relation between stellarkinematics and metal abundance. A list of 113 stars with tangentialspace velocities of 300 km/s or greater is obtained, the highesttangential velocity relative to the sun being 630 km/s. By using thevariation of the tangential velocity with longitude and adopting thegalactic rotation at the solar circle to be 220 km/s, the rotation ofthe subdwarf system is estimated at 0 + or - 50 km/s from the transversevelocity alone, in agreement with determinations based on other methods.
| Parallaxes and proper motions from the McCormick Observatory List 45
Trigonometric parallaxes, relative proper motions, magnitudes, andcolors are presented for a selection of 21 stars in 17 fields, eight ofwhich have been taken from the Vyssotsky lists of dwarf M stars foundspectrophotometrically. No previous parallaxes have been reported for 11stars in this list; parallaxes for two Hyades stars and BY Dra areincluded.
| Predicted infrared brightness of stars within 25 parsecs of the sun
Procedures are given for transforming selected optical data intoinfrared flux densities or irradiances. The results provide R, T(eff)blackbody approximations for about 2000 of the stars in Woolley et al.'sCatalog of Stars (1970) within 25 pc of the sun, and additional whitedwarfs, with infrared flux densities predicted for them at ninewavelengths from 2.2 to 101 microns including the Infrared AstronomySatellite bands.
| Dwarf K and M stars in the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..486U&db_key=AST
| UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]
Not Available
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Змееносец |
| Прямое восхождение: | 16h20m24.78s |
| Склонение: | -04°16'02.3" |
| Видимая звёздная величина: | 10.722 |
| Расстояние: | 30.331 парсек |
| Собственное движение RA: | -432.9 |
| Собственное движение Dec: | -21.6 |
| B-T magnitude: | 12.274 |
| V-T magnitude: | 10.851 |
Каталоги и обозначения:
|
