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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.
| The Solar Neighborhood. XXI. Parallax Results from the CTIOPI 0.9 m Program: 20 New Members of the 25 Parsec White Dwarf Sample
We present accurate trigonometric parallaxes for 20 new members of the25 pc white dwarf (WD) sample as part of the Discovery and Evalution ofNearby Stellar Embers (DENSE) project.7 http://www.DenseProject.comPreviously, there were a total of 112 WD systems with trigonometricparallaxes placing them within 25 pc and of these, 99 have trigonometricparallaxes known to better than 10%. Thus, the 20 new members presentedin this work represent a 20% increase in the number of WDs accuratelyknown to be within 25 pc. In addition, we present updated parallaxes forseven known WDs within 10 pc that have been observed as part of theAstrometric Search for Planets Encircling Nearby Stars initiative tomonitor nearby southern red dwarfs and WDs for astrometric perturbationsfrom unseen companions. Including a few WD companions and WDs beyond 25pc, we present a total of 33 trigonometric parallaxes. We performatmospheric modeling for WDs to determine physical parameters (i.e., Teff, log g, mass, and WD age). Finally, a new ZZ Cetipulsating WD was identified and revised constraints are placed on twomixed H/He atmosphere cool WDs that display continuum absorption in thenear-infrared.
| a New Look at the Local White Dwarf Population
We have conducted a detailed new survey of the local population of whitedwarfs lying within 20 pc of the Sun. A new revised catalog of localwhite dwarfs containing 122 entries (126 individual degenerate stars) ispresented. This list contains 27 white dwarfs not included in a previouslist from 2002, as well as new and recently published trigonometricparallaxes. In several cases new members of the local white dwarfpopulation have come to light through accurate photometric distanceestimates. In addition, a suspected new double degenerate system (WD0423+120) has been identified. The 20 pc sample is currently estimatedto be 80% complete. Using a variety of recent spectroscopic,photometric, and trigonometric distance determinations, we re-compute aspace density of 4.8 ± 0.5 × 10 3 pc3 corresponding to a mass density of 3.2 ± 0.3 ×10 3 M sun pc 3 from the completeportion of the sample within 13 pc. We find an overall mean mass for thelocal white dwarfs of 0.665 M sun, a value larger than mostother non-volume-limited estimates. Although the sample is small, wefind no evidence of a correlation between mass and temperature in whichwhite dwarfs below 13,000 K are systematically more massive than thoseabove this temperature. Within 20 pc 25% of the white dwarfs are inbinary systems (including double degenerate systems). Approximately 6%are double degenerates and 6.5% are Sirius-like systems. The fraction ofmagnetic white dwarfs in the local population is found to be 13%.
| 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
| 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
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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).
| The spectroscopic characteristics of intermediate-aged pre-main-sequence stars: the η Chamaeleontis cluster
We present a study of calibrated low-resolution spectra of the 18 knownprimaries of the ~9-Myr-old η Chamaeleontis (η Cha)pre-main-sequence (PMS) star cluster. Using synthetic broad-band coloursand narrow-band continuum-sensitive, temperature-sensitive andgravity-sensitive indices derived from the spectra, we compare the ηCha stars to standard dwarfs. We find that the VRI colours of the PMSstars are indistinguishable from those of main-sequence stars, but thata B-band excess attaining ~0.2 mag for late-M cluster stars is present,which might be an indicator of gravity, metallicity and/or activitydifferences between the two samples of stars. The narrow-band spectralindices for the η Cha stars possibly indicate higher metallicity andstrongly indicate lower surface gravity than the dwarf indices,consistent with the elevated location of the cluster in theHertzsprung-Russell evolutionary diagram. Using the derived syntheticcolours and indices, we adopt spectral types for the late-type η Chastars. We then produce a table of absolute optical magnitudes andcolours representing the cluster isochrone for comparison with PMSevolutionary models. From our results we also conclude that the ηCha stars are unreddened, consistent with the group being a sample ofolder PMS stars distant from obscuring molecular clouds, except for theA1 member HD 75505 for which we confirm AV= 0.4 mag likelydue to the presence of circumstellar material.
| The component star masses in RW Tri
We use time-resolved spectra of the cataclysmic variable RW Tri in the Iand K bands to determine the orbital velocity of the secondary starusing skew-mapping and cross-correlation techniques respectively. Wefind radial velocity amplitudes of 250 +/- 47 km s-1 in the Iband, and 221 +/- 29 km s-1 in the K band. We also determinethe rotational velocity of the secondary star using the K-band data andfind a Vrot sin i of 120 +/- 20 km s-1. Acombination of these results coupled with an estimate of the effect ofheating on the secondary star suggests a mass ratioM2/M1 in the range 0.6-1.1 the mass ratio rangewith no correction for heating is 0.5-0.8. These lead to most likelyestimates of the primary and secondary star masses in the range 0.4-0.7and 0.3-0.4 Msolar respectively. Further refinement of thestellar masses is hampered by uncertain knowledge of the white dwarforbital velocity, and we discuss evidence that at least some estimatesof the white dwarf velocity are contaminated by non-orbital components.
| 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.
| 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.
| 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
| New proper motion determination of Luyten catalogue stars (LTT) with declination between -5(deg) and -30(deg) and right ascension between 0h and 13h 30m
Data are given for 353 LTT stars found on 42 areas, covering 25 squaredegrees each, with declination between -5(deg) and -30(deg) and rightascension between 0h and 13h 30m. Nineteen stars present differences inproper motion >= 0('') 10, twenty present differences in positionangle >= 20(deg) and six present those differences in both values.Table 2 only available in electronic foun at CDS viahttp://cdsweb.u-strasbg.fr/Abstract.html. Finding charts only availablein the electronic version.
| Astrometric positions of stars with high proper motions in the Southern Hemisphere
Several stars with large proper motions, cited by W.J. Luyten, wereincluded in the preliminary programme for the HIPPARCOS mission. Whenperforming preparatory measurements of plates, difficulties wereencountered in identifying certain of these stars when relying only onpublished coordinates. We have taken advantage of this work whichrelates to the southern sky in order to determine the astrometricposition of the greatest possible number of these objects, even forthose which were not included in the programme. Catalogue 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/Abstract.html
| 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.
| 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.
| Photometry of dwarf K and M stars
An observational program using UBVRI photometry is presented for 688stars from among the dwarf K and M stars already found spectroscopicallyby Vyssotsky (1958). Of these, 211 have not been observedphotometrically. These observations were obtained over a period ofseveral years at the Kitt Peak National Observatory using a GaAsphotomultiplier with an 0.9 m reflector. Based on night-to-nightvariations in the measures of individual stars, the internal errors maybe estimated to be roughly 0.01 mag for the colors and 0.015 for the Vmagnitudes. The photometric parallaxes reported for each star werecomputed in the manner discussed by Weis (1986).
| 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.
| Chromospheric diagnostics in late-type stars
Moderate and low resolution spectroscopic observations of late typedwarfs covering a broad range of activity are presented. The strength ofthe TiO band in 4762 A is used for spectral classification. Calibratedfluxes for the Balmer and the Ca II H and K lines are derived. H-alphaequivalent widths are given for those stars where the line is inabsorption as well as those in emission. It is confirmed that stars withno detectable or very weak H-alpha do exist. It is also shown that starswith very weak or no detectable emission in Ca II H and K also exist,this occurring preferentially in late M dwarfs. Although this can beexplained in terms of reduced nonradiative heating in the chromosphere,the results cannot be conclusive due to the limited resolution of thedata.
| The 8190-A Sodium Doublet in Cataclysmic Variables - Part Two - too Cool for Comfort
In this paper we present the results of time-resolved spectroscopy inthe near-infrared of five cataclysmic variables: U Gem, SS Aur, BDPav, DO Dra and CN Ori. The spectral region observed was chosen tocover the Na 1 doublet at ?8190 Å which is strong inlate-type dwarfs. Radial-velocity curves were measured for thesecondary stars and values for Kabs determined for eachobject. For DO Dra an improved orbital period of 3.969±0.003 hrwas derived.U Gem and SS Aur showed significant apparent eccentricities of0.027±0.012 and 0.17±0.07, respectively. This distortionof the radial-velocity curve is probably caused by line quenching dueto irradiation of the secondary, or contamination of the spectrum byemission from the disc, or a combination of the two. For U Gem theapparent eccentricity was used to correct the observed Kabsfor these effects. Mass ranges were derived for all the objects. For U Gem, which has themost closely constrained result, the secondary mass is larger thanpredicted using main-sequence mass-period relations. Spectral-typeestimates for U Gem and DO Dra are also later than expected if thesecondary obeys an empirical main-sequence mass-radius relation. It isconcluded that the assumption of main-sequence status for thesecondary star should be used with caution.
| Optical and infrared photometry of dwarf M and K stars
Absolute U, B, V, R, I, J, H, K, and L photometry are given for a groupof dwarf M and K stars. Using black-body fits to the data, bolometricluminosities and radii are derived. The derived bolometric luminositiesare good to + or - 10 percent and the effective temperatures to + or -100 K. A comparison is made with the values derived by other authors.The derived radii are 14 percent smaller than those derived from therevised Barnes et al. (1978) relation involving (V - R).
| 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.
| UBV (RI)c photometry of faint nearby stars.
Not Available
| The 8190 A sodium doublet in cataclysmic variables. I - The quest
The authors have carried out a near-infrared spectroscopic survey of 65cataclysmic variables aimed at detecting absorption features from thesecondary star, especially the Na I doublet at ??8183.3,8194.8 Å. They have positively identified these lines in 16cataclysmic variables of various types with periods from 3 to 9 hr. Manyof these objects show other features indicative of a late-type star. Theauthors have observed the ?7773 Å O I triplet in 28objects. This feature varies considerably from object to object and maybe a useful indicator of the state of the disc. The authors have alsodetected emission lines of He I (??7065, 7281 Å), HeII (?8236 Å), O I (?8446 Å), Ca II(?8498 Å) and a further emission feature to the red of?8200 Å that may be associated with the Paschen serieslimit.
| H-alpha photometry of dwarf K and M stars
Attention is given to the distribution of stars in the N-W, R-I planefor the case of 188 dM and dK stars for which H-alpha photometry hasbeen obtained. Most are found to lie along a single 'main sequence' ofabsorption which slopes up towards 0 EW with increasing R-I. Theabsorption EWs are noted to be large by comparison with photosphericmodel predictions, implying either that the models are in error or thatchromospheres are present in virtually all late-type dwarfs, and areresponsible for the H-alpha distribution feature in both absorption andemission.
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Observation and Astrometry data
| Constellation: | Ύδρα |
| Right ascension: | 10h12m08.15s |
| Declination: | -18°37'03.9" |
| Apparent magnitude: | 10.039 |
| Distance: | 17.068 parsecs |
| Proper motion RA: | -521.1 |
| Proper motion Dec: | -12.8 |
| B-T magnitude: | 11.911 |
| V-T magnitude: | 10.194 |
Catalogs and designations:
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