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The stellar population of the Rosat North Ecliptic Pole survey
Context: .X-ray surveys are a very efficient mean of detecting youngstars and therefore allow us to study the young stellar population inthe solar neighborhood and the local star formation history in the lastbillion of years. Aims: .We want to study the young stellarpopulation in the solar neighborhood, to constrain its spatial densityand scale height as well as the recent local star formation history. Methods: .We analyze the stellar content of the ROSAT North EclipticPole survey, and compare the observations with the predictions derivedfrom stellar galactic model. Since the ROSAT NEP survey is sensitive atintermediate fluxes is able to sample both the youngest stars and theintermediate age stars (younger than 109 years), linking theshallow and deep flux surveys already published in the literature. Results: .We confirm the existence of an excess of yellow stars inour neighborhood previously seen in shallow survey, which is likely dueto a young star population not accounted for in the model. However theexcellent agreement between observations and predictions of dM starscasts some doubt on the real nature of this active population.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.
We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site.
| 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.
| Multiplicity among solar-type stars. III. Statistical properties of the F7-K binaries with periods up to 10 years
Two CORAVEL radial velocity surveys - one among stars in the solarneighbourhood, the other in the Pleiades and in Praesepe - are merged toderive the statistical properties of main-sequence binaries withspectral types F7 to K and with periods up to 10 years. A sample of 89spectroscopic orbits was finally obtained. Among them, 52 relate to afree-of-bias selection of 405 stars (240 field stars and 165 clusterstars). The statistics corrected for selection effects yield thefollowing results: (1) No discrepancy is found between the binariesamong field stars and the binaries in open cluster. The distributions ofmass ratios, of periods, the period-eccentricity diagram and the binaryfrequencies are all within the same error intervals. (2) Thedistribution of mass ratios presents two maxima: a broad peak from q ~0.2 to q ~ 0.7, and a sharp peak for q > 0.8 (twins). Both arepresent among the early-type as well as among the late-type part of thesample, indicating a scale-free formation process. The peak for q >0.8 gradually decreases when long-period binaries are considered.Whatever their periods, the twins have eccentricities significantlylower than the other binaries, confirming a difference in the formationprocesses. Twins could be generated by in situ formation followed byaccretion from a gaseous envelope, whereas binaries with intermediatemass ratios could be formed at wide separations, but they are madecloser by migration led by interactions with a circumbinary disk. (3)The frequency of binaries with P<10 years is about 14%. (4) About0.3% of binaries are expected to appear as false positives in a planetsearch. Therefore, the frequency of planetary systems among stars ispresently 7+4-2%. The extension of thedistribution of mass ratios in the planetary range would result in avery sharp and very high peak, well separated from the binary stars withlow mass ratios. Based on photoelectric radial-velocity measurementscollected at Haute-Provence observatory and on observations made withthe ESA Hipparcos astrometry satellite.
| Variability of Southern T Tauri Stars (VASTT). III. The Continuum Flux Changes of the TW Hydrae Bright Spot
We have collected low-resolution spectrophotometric data of theclassical T Tauri star TW Hya in an effort to detect and to follow theexcess continuum emission (veiling) and the line changes atλ<5100 Å. The deveiled and calibrated flux distributionresembles that of a 30 Myr K7-M1 star of radius R=0.8Rsolar,mass M=0.7Msolar, and logg=4.5. The anticorrelation betweenthe veiling (in the B band) and the observed Balmer jump found byprevious authors, based on large samples of classical T Tauri stars, isconfirmed in TW Hya. The line emission luminosities of the H, Ca II, andHe I lines correlate with one another throughout the series, supportingthe claims that the bulk of the line emission is formed in a singleregion or that their growth is controlled by a common mechanism.Surprisingly, the line emission fluxes do not correlate with the veilingat 4250 Å (B band). The line luminosities are, in general, lessthan 1% of the continuum luminosities. The veiling time series presentsa cyclic behavior at 4.4+/-0.4 days. We collect all of the archivalphotometric data and analyze the B-band observations using differentalgorithms. We found solutions at either the 4.4 day timescale orone-half of this value. The data sets presenting the 2.2 day periodicityyield double-peaked light curves when folded at the 4.4 day timescale.We interpret the 4.4 day solution as the rotation period of the star.The veiling and the line emission measurements yield accretionluminosities for the series. We model the impacted area in thephotosphere by an isothermal gas of a given density, temperature, andsize (δ) whose parameters change as the star rotates. Estimates ofthe total spot area (δ), as a percentage of the stellar projectedarea, lie within the range 2.5<δ<6.0. The accretionluminosity of the impacted region does not remain constant throughoutthe series. The mass accretion rate (Macc) that governs theluminosity varies within1.0×10-9Msolaryr-1
| 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.
| The Halo Black Hole X-Ray Transient XTE J1118+480
Optical spectra were obtained of the optical counterpart of thehigh-latitude (b~=62deg) soft X-ray transient XTE J1118+480near its quiescent state (R~=18.3) with the new 6.5 m Multiple MirrorTelescope and the 4.2 m William Herschel Telescope. The spectrumexhibits broad, double-peaked emission lines of hydrogen (FWHM~=2400 kms-1) arising from an accretion disk superposed withabsorption lines of a late-type secondary star. Cross-correlation of the27 individual spectra with late-type stellar template spectra reveals asinusoidal variation in radial velocity with amplitude K=701+/-10 kms-1 and orbital period P=0.169930+/-0.000004 days. The massfunction, 6.1+/-0.3 Msolar, is a firm lower limit on the massof the compact object and strongly implies that it is a black hole. Weestimate the spectral type of the secondary to be K7 V-M0 V, and that itcontributes 28%+/-2% of the light in the 5800-6400 Å region on2000 November 20, increasing to 36%+/-2% by 2001 January 4 as the diskfaded. Photometric observations (R-band) with the Instituto deAstrofísica de Canarias 0.8 m telescope reveal ellipsoidal lightvariations of full amplitude 0.2 mag. Modeling of the light curve givesa large mass ratio (M1/M2~20) and a high orbitalinclination (i=81deg+/-2deg). Our combined fitsyield a mass of the black hole in the range M1=6.0-7.7Msolar (90% confidence) for plausible secondary star massesof M2=0.09-0.5 Msolar. The photometric periodmeasured during the outburst is 0.5% longer than our orbital period andprobably reflects superhump modulations, as observed in some other softX-ray transients. The estimated distance is d=1.9+/-0.4 kpc,corresponding to a height of 1.7+/-0.4 kpc above the Galactic plane. Thespectroscopic, photometric, and dynamical results indicate that XTEJ1118+480 is the first firmly identified black hole X-ray system in theGalactic halo. Based in part on observations obtained at the MMTObservatory, a joint facility of the University of Arizona and theSmithsonian Institution.
| 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
| The Fornax spectroscopic survey. I. Survey strategy and preliminary results on the redshift distribution of a complete sample of stars and galaxies
The Fornax Spectroscopic Survey will use the Two degree Fieldspectrograph (2dF) of the Anglo-Australian Telescope to obtain spectrafor a complete sample of all 14000 objects with 16.5 <= bj<= 19.7 in a 12 square degree area centred on the Fornax Cluster. Theaims of this project include the study of dwarf galaxies in the cluster(both known low surface brightness objects and putative normal surfacebrightness dwarfs) and a comparison sample of background field galaxies.We will also measure quasars and other active galaxies, any previouslyunrecognised compact galaxies and a large sample of Galactic stars. Byselecting all objects--both stars and galaxies--independent ofmorphology, we cover a much larger range of surface brightness and scalesize than previous surveys. In this paper we first describe the designof the survey. Our targets are selected from UK Schmidt Telescope skysurvey plates digitised by the Automated Plate Measuring (APM) facility.We then describe the photometric and astrometric calibration of thesedata and show that the APM astrometry is accurate enough for use withthe 2dF. We also describe a general approach to object identificationusing cross-correlations which allows us to identify and classify bothstellar and galaxy spectra. We present results from the first 2dF field.Redshift distributions and velocity structures are shown for allobserved objects in the direction of Fornax, including Galactic stars,galaxies in and around the Fornax Cluster, and for the background galaxypopulation. The velocity data for the stars show the contributions fromthe different Galactic components, plus a small tail to high velocities.We find no galaxies in the foreground to the cluster in our 2dF field.The Fornax Cluster is clearly defined kinematically. The mean velocityfrom the 26 cluster members having reliable redshifts is 1560 +/- 80\:km\:s-1. They show a velocity dispersion of 380 +/- 50\:km\:s-1. Large-scale structure can be traced behind thecluster to a redshift beyond z=0.3. Background compact galaxies and lowsurface brightness galaxies are found to follow the general galaxydistribution.
| 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.
| Measurements of magnetic field strength on T Tauri stars
We have investigated the magnetic field strength of one weak-line andfour classical T Tauri stars. The magnetic field strength is derivedfrom the differential change of the equivalent width of photospheric FeI lines in the presence of a magnetic field, calculated using a fullradiative transfer code. The method was successfully tested by applyingit to a non-magnetic solar-type star, and to VY Ariwhich is believed to have a strong magnetic field. For two of theclassical T Tauri stars, we find a product of magnetic field strengthand filling factor B * f = (2.35+/- 0.15) kG for TTau, and B * f = (1.1+/- 0.2) kG for LkCa15. For the classical T Tauri star UX Tau Aand the weak-line T Tauri star LkCa 16 the detectionis only marginal, indicating magnetic field strengths of the order of 1kG and possibly of more than 2 kG, respectively. No field could bedetected for the classical T Tauri star GW Ori. Forthe two classical T Tauri stars for which we have detected a field, wefind the filling factors to be larger than ~ 0.5, which indicates thatthe magnetic field covers most of the photosphere. We also show thatignoring a magnetic field can, depending on the lines used, result inerrors in effective temperature and underestimates of veiling. Based onobservations made with the William Herschel Telescope operated on theisland of La Palma by the Royal Greenwich Observatory in the SpanishObservatorio de los Roque de los Muchachos of the Instituto deAstrofisica de Canarias
| Surface inhomogeneities and line variability on DF Tau
We have mapped surface inhomogeneities on the classical T Tauri star DFTau, using the Lii doublet at 670.8 nm, the Cai lines at 612.2 nm and643.9 nm and a calcium and iron blend at 646.3 nm. We find compellingevidence that there are hotspots with temperatures of more than 5000 K.Two of the hotspots produce line-profile deformations that can be tracedas they move through the cross-correlated profiles. When one of thehotspots crosses the stellar disc, redshifted absorption componentsappear in the Na D lines. As these redshifted absorption features areusually tracers for mass-infall we interpret this hotspot as anaccretion shock close to the stellar surface. Parts of the surface of DFTau are covered with a hot chromosphere that is visible in the Caiiinfrared triplet lines and the narrow component of Hei. We find nocorrelation between the veiling and the lines that originate from thehot chromosphere, suggesting that the veiling and the chromosphericemission are produced in physically distinct regions.
| Library of high-resolution UES echelle spectra of F, G, K and M field dwarf stars
We present a library of Utrecht echelle spectrograph (UES) observationsof a sample of F, G, K and M field dwarf stars covering the spectralrange from 4800 \ Angstroms to 10600 \ Angstroms with a resolution of55000. These spectra include some of the spectral lines most widely usedas optical and near-infrared indicators of chromospheric activity suchas Hβ , Mg i b triplet, Na i D1, D2, He iD3, Hα , and Ca ii IRT lines, as well as a large numberof photospheric lines which can also be affected by chromosphericactivity. The spectra have been compiled with the aim of providing a setof standards observed at high-resolution to be used in the applicationof the spectral subtraction technique to obtain the active-chromospherecontribution to these lines in chromospherically active single andbinary stars. This library can also be used for spectral classificationpurposes. A digital version with all the spectra is available via ftpand the World Wide Web (WWW) in both ASCII and FITS formats. Based onobservations made with the William Herschel Telescope operated on theisland of La Palma by the Isaac Newton Group at the Spanish Observatoriodel Roque de Los Muchachos of the Instituto de Astrof\'{\i
| Quantitative spectral classification of galactic disc K-M stars from spectrophotometric measurements
New spectral observations for 47 southern galactic red supergiantsobtained with the new RUBIKON spectrophotometer (developed at theAstronomisches Institut der Ruhr-Universitat Bochum) at the Bochum 61-cmtelescope on La Silla are presented. The spectra range from 4800 to 7700A and their resolution is 10 A. The mean error of absolute fluxes is0.028 mag and that of relative fluxes 0.021 mag. The spectra will beavailable at the Strasbourg Stellar Database (CDS). Together with datataken from recently published spectral catalogues, the new observationshave been used to define spectral indices as measures of the strengthsof the following features: Fe i+TiOalpha_1, Mgb+TiOalpha_0,NaD+TiOgamma'_1, TiOgamma'_0 and TiOgamma_1 systems. The indices havebeen checked against errors introduced by reductions, interstellarreddening and different resolutions of different spectral catalogues,and have been found to be very insensitive to all these effects.Therefore, different catalogues may be combined without any loss ofaccuracy and homogeneity. The mean error of a single index has beenfound to be 0.011 mag. For stars from K4 to M7, a strong temperaturedependence is found for all indices. For the Fe i+TiO and especially theMgb+TiO features, a strong dependence on luminosity has also beenobserved. These indices therefore have been combined to form aluminosity index, while the others together form a spectral index. Thecombined indices have been calibrated in terms of MK data using thestepwise linear regression technique, and may be used for quantitativetwo- dimensional spectral classification of late K- and M-type stars.The mean error of the classification is 0.6 of spectral subtype and 0.8of luminosity class, which is much higher than would be expected fromthe uncertainty of the indices alone (which, e.g., for an M4 giantcorrespond to an uncertainty of 0.1 of spectral subtype and 0.3 ofluminosity class). This may be explained by the uncertainty of theoriginal MK classifications and the variability of some programme stars.
| 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
| 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
| V487 Cassiopeiae (HD 6474): a UU Herculis variable in the galactic plane?
New photoelectric photometry of V487 Cassiopeiae (HD 6474) made between1984 and 1992 is presented. The star has a rather complicated lightvariation: at least two periods (P1 = 160.3 days andP2 = 99.6 days) are present in the light curve, one of thempossibly with variable amplitude. The period ratio(P2/P1 = 0.62) and the nature of the lightvariation (i.e. the simultaneous presence of two modes, the amplitudechange) are both very similar to that of UU Herculis. This similarityindicates that V487 Cassiopeiae is a UU Her-type variable though it isin the galactic plane. A distinction between the UU Her-type and 89Her-type variables is suggested.
| 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).
| Selection of standard stars for photometric observations with the 91-cm reflector at Okayama
Not Available
| H-alpha photometry of dwarf K and M stars - Chromospheric activity
H-alpha photometry of 118 K and M dwarfs are presented, with H-alphaequivalent width measures accurate to about 0.05 A. The data arecombined with the spectroscopic surveys of Stauffer and Hartmann (1986)and Fleming et al. (1988) to study the main features of thechromospheric activity versus mass relation for low-mass stars. An upperbound to the H-alpha equivalent width is found to be a function of themass relation (R-I). H-alpha luminosities and surface fluxes arecalculated for active stars, showing that both quantities generallydecline with R-I. The upper bound to the fraction of a star's bolometricluminosity, however, is independent of R-I. The results suggest that thechromospheres of most dMe stars with R-I less than 1.1 are in anactivity-saturated state. Also, H-alpha variability, probably due toflares, is detected in several stars.
| Space motions of low-mass stars.
Radial-velocity measures are presented for 225 stars, most of which aredwarf K and M stars. The data were obtained with the CfA digitalspeedometer, whose uncertainty is less than 1 km/s. Calibrations ofthree earlier radial-velocity studies and comparisons with three othercontemporary ones lead to the evaluation of the standard error for anindividual star as determined in each investigation. The data from twomasks, matching solar type and M type stars, form a ratio that measuresstellar surface temperature quite closely and appear to be useful indetecting the presence of unseen companions. A few previouslyunrecognized binaries have been detected; those with most certaintyinclude stars nos. 366B, 453, and 46A of the McCormick lists of dwarfstars.
| 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.
| G. P. Kuiper's spectral classifications of proper-motion stars
Spectral classifications are listed for over 3200 stars, mainly of largeproper motion, observed and classified by Kuiper during the years1937-1944 at the Yerkes and McDonald Observatories. While Kuiper himselfpublished many of his types, and while improved classifications are nowavailable for many of these stars, much of value remains. For many ofthe objects, no other spectral data exist.
| Photometry of stars in the uvgr system
Photoelectric photometry is presented for over 400 stars using the uvgrsystem of Thuan and Gunn. Stars were selected to cover a wide range ofspectral type, luminosity class, and metallicity. A mean main sequenceis derived along with reddening curves and approximate transformationsto the UBVR system. The calibration of the standard-star sequence issignificantly improved.
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לינקים קשורים
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | קאסיופיאה |
| התרוממות ימנית: | 01h07m08.20s |
| סירוב: | +63°56'28.8" |
| גודל גלוי: | 9.026 |
| מרחק: | 15.047 פארסק |
| תנועה נכונה: | 1546.5 |
| תנועה נכונה: | 318 |
| B-T magnitude: | 10.655 |
| V-T magnitude: | 9.161 |
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INHABITED SKY
