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Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| Statistical properties of solar-type close binaries
Two Coravel radial velocity surveys dedicated to F7-K field dwarfs andto open clusters are merged in order to investigate the statisticalproperties of binaries with periods up to 10 years. Thanks to theaccurate trigonometric parallaxes provided by Hipparcos, an unbiasedsample of spectroscopic binaries (SB) is selected. After correction forthe uncertainties of the measurements, the following results areobtained: 1. The distribution of mass ratios exhibits a peak forequal-mass binaries (twins), which is higher for short-period binariesthan for long-period binaries. 2. Apart from the twins, the distributionof mass ratios exhibits a broad peak from 0.2 to 0.6. 3. The orbitaleccentricities of twins are slightly smaller than those of otherbinaries. 4. An excess of SB is observed with periods shorter than about50 days in comparison with the Duquennoy and Mayor log-normaldistribution of periods. These features suggest that close binary starsare generated by two different processes. A possible difference couldcome from the accretion onto the binary, for instance from a commonenvelope or from a circumbinary disk. Alternatively, twins could comefrom dynamic evolution of multiple systems. It is not clear whether theformation models are already sufficiently elaborated to reproduce ourstatistics.
| Chromospheric Ca II Emission in Nearby F, G, K, and M Stars
We present chromospheric Ca II H and K activity measurements, rotationperiods, and ages for ~1200 F, G, K, and M type main-sequence stars from~18,000 archival spectra taken at Keck and Lick Observatories as a partof the California and Carnegie Planet Search Project. We have calibratedour chromospheric S-values against the Mount Wilson chromosphericactivity data. From these measurements we have calculated medianactivity levels and derived R'HK, stellar ages,and rotation periods from general parameterizations for 1228 stars,~1000 of which have no previously published S-values. We also presentprecise time series of activity measurements for these stars.Based on observations obtained at Lick Observatory, which is operated bythe University of California, and on observations obtained at the W. M.Keck Observatory, which is operated jointly by the University ofCalifornia and the California Institute of Technology. The KeckObservatory was made possible by the generous financial support of theW. M. Keck Foundation.
| High-Precision Near-Infrared Photometry of a Large Sample of Bright Stars Visible from the Northern Hemisphere
We present the results of 8 yr of infrared photometric monitoring of alarge sample of stars visible from Teide Observatory (Tenerife, CanaryIslands). The final archive is made up of 10,949 photometric measuresthrough a standard InSb single-channel photometer system, principally inJHK, although some stars have measures in L'. The core of this list ofstars is the standard-star list developed for the Carlos SánchezTelescope. A total of 298 stars have been observed on at least twooccasions on a system carefully linked to the zero point defined byVega. We present high-precision photometry for these stars. The medianuncertainty in magnitude for stars with a minimum of four observationsand thus reliable statistics ranges from 0.0038 mag in J to 0.0033 magin K. Many of these stars are faint enough to be observable with arraydetectors (42 are K>8) and thus to permit a linkage of the bright andfaint infrared photometric systems. We also present photometry of anadditional 25 stars for which the original measures are no longeravailable, plus photometry in L' and/or M of 36 stars from the mainlist. We calculate the mean infrared colors of main-sequence stars fromA0 V to K5 V and show that the locus of the H-K color is linearlycorrelated with J-H. The rms dispersion in the correlation between J-Hand H-K is 0.0073 mag. We use the relationship to interpolate colors forall subclasses from A0 V to K5 V. We find that K and M main-sequence andgiant stars can be separated on the color-color diagram withhigh-precision near-infrared photometry and thus that photometry canallow us to identify potential mistakes in luminosity classclassification.
| 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.
| A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries
We report 25,563 radial velocity measurements for 1359 single-linedstars in the Carney-Latham sample of 1464 stars selected for high propermotion. For 171 of these, we present spectroscopic orbital solutions. Wefind no obvious difference between the binary characteristics in thehalo and the disk populations. The observed frequency is the same, andthe period distributions are consistent with the hypothesis that the twosets of binaries were drawn from the same parent population. Thissuggests that metallicity in general, and radiative opacities inparticular, have little influence over the fragmentation process thatleads to short-period binaries. All the binaries with periods shorterthan 10 days have nearly circular orbits, while the binaries withperiods longer than 20 days exhibit a wide range of eccentricities and amedian value of 0.37. For the metal-poor high-velocity halo binaries inour sample, the transition from circular to eccentric orbits appears tooccur at about 20 days, supporting the conclusion that tidalcircularization on the main sequence is important for the oldestbinaries in the Galaxy. Some of the results presented here usedobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| 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.
| Time-resolved spectroscopy and photometry of the dwarf nova FS Aurigae in quiescence
We present results of non-simultaneous time-resolved photometric andspectroscopic observations of the little-studied dwarf nova FS Aur inquiescence. The spectrum of FS Aur shows strong and broad emission linesof hydrogen and He I, and of weaker He II lambda4686 and C III/N IIIblend, similar to other quiescent dwarf novae. All emission lines aresingle-peaked, however their form varies with orbital phase. Absorptionlines from a late-type secondary are not detected. From the radialvelocity measurements of the hydrogen lines Hβ and Hγ wedetermined a most probable orbital period P=0.059 deg +/- 0.002 deg.This period agrees well with the 0.0595 deg +/- 0.0001 deg estimate byThorstensen et al. (1996). On the other hand, the period of photometricmodulations is longer than the spectroscopic period and can be estimatedas 3 hours. Longer time coverage during a single night is needed toresolve this problem. Using the semi-amplitude of the radial velocities,obtained from measurements of hydrogen and helium lines, and someempirical and theoretical relations we limited the basic parameters ofthe system: a mass ratio q >= 0.22, a primary massM1=0.34-0.46 Msun, a secondary mass M2<= 0.1 Msun, and an inclination anglei=51deg-65deg. Doppler tomography has shown atleast two bright regions in the accretion disk of FS Aur. The first,brighter spot is located at phase about 0.6. The second spot is locatedopposite the first one and occupies an extensive area at phases about0.85-1.15. Based on observations made at the Special AstrophysicalObservatory, Nizhnij Arkhyz, Russia.
| A comparison of DA white dwarf temperatures and gravities from Lyman and Balmer line studies
We present measurements of the effective temperatures and surfacegravities for a sample of hot DA white dwarfs, using the Lyman line dataavailable from the HUT, ORFEUS and FUSE FUV space missions. Comparingthe results with those from the standard Balmer line technique, we findthat there is a general good overall agreement between the two methods.However, significant differences are found for a number of stars, butnot always of a consistent nature in that sometimes the Balmertemperature exceeds that derived from the Lyman lines and in otherinstances it is lower. We conclude that, with the latest modelatmosphere calculations, these discrepancies probably do not arise froman inadequate theoretical treatment of the Lyman lines but rather fromsystematic effects in the observation and data reduction processes,which dominate the statistical errors in these spectra. If thesesystematic data reduction effects can be adequately controlled, theLyman line temperature and gravity measurements are consistent withthose obtained from the Balmer lines when allowance is made forreasonable observational uncertainties.
| Planetary nebula candidates in a southern region of M33
In a search for emission line objects made in a southern region of M 33using narrow band filters centered on [O III], Hα and adjacentcontinua, we detect some known and new objects that can be classified asplanetary nebulae candidates (PNc). This search, the deepest one made upto now in M 33, has allowed us to detect 48 PNc, from which 14 have aratio of [O III]-to-Hα fluxes greater than 1. We compare ourfindings with a previous search and present the list and finding chartsof these interesting objects. Figures 3 to 11 are only available inelectronic form at http://www.edpsciences.org
| The INES system. IV. The IUE absolute flux scale
This paper deals with the definition of the input fluxes used for thecalibration of the IUE Final Archive. The method adopted consists in thedetermination of the shape of the detector's sensitivity curves usingIUE low resolution observations with model fluxes of the DA white dwarfG191-B2B. A scale factor was then determined so that the IUEobservations of some bright OAO-2 standards match the originalmeasurements from Meade (\cite{meade}) in the spectral region 2100-2300Å. The ultraviolet fluxes of six standard stars used as input forthe Final Archive photometric calibration together with the model fluxesof G191-B2B normalized to the OAO-2 scale are given. A comparison withthe independent FOS calibration shows that the IUE flux scale for theUltraviolet is 7.2% lower. We consider this mainly to be caused by thedifferent normalization procedures. It is shown that the present fluxcalibration applies to spectra processed with the INES low resolutionextraction software.
| FUSE observations of hot white dwarfs
We have analyzed FUSE observations of six hot white dwarf stars: four DAwhite dwarfs with Teff >~ 45 000 K, the DAO Feige55 (Teff ~ 55 000 K), and the DA CD -38deg10980 (Teff ~ 24 000 K). Photospheric lines from SiIV, P V, and S VI can be observed in the majority of the five hotterobjects. Feige 55 shows also several other heavier elements. Themeasured abundances agree only partly with the predictions of theradiative levitation theory. We attribute this to current limitations ofthe models and the probable presence of mass loss. In the spectrum of CD-38deg 10980, we have observed the quasi-molecular satellitesof Lbeta . This confirms theoretical predictions about the visibilityrange for these features.
| 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
| 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 effective temperature scale of giant stars (F0-K5). I. The effective temperature determination by means of the IRFM
We have applied the InfraRed Flux Method (IRFM) to a sample ofapproximately 500 giant stars in order to derive their effectivetemperatures with an internal mean accuracy of about 1.5% and a maximumuncertainty in the zero point of the order of 0.9%. For the applicationof the IRFM, we have used a homogeneous grid of theoretical modelatmosphere flux distributions developed by \cite[Kurucz (1993)]{K93}.The atmospheric parameters of the stars roughly cover the ranges: 3500 K<= T_eff <= 8000 K; -3.0 <= [Fe/H] <= +0.5; 0.5 <= log(g) <= 3.5. The monochromatic infrared fluxes at the continuum arebased on recent photometry with errors that satisfy the accuracyrequirements of the work. We have derived the bolometric correction ofgiant stars by using a new calibration which takes the effect ofmetallicity into account. Direct spectroscopic determinations ofmetallicity have been adopted where available, although estimates basedon photometric calibrations have been considered for some stars lackingspectroscopic ones. The adopted infrared absolute flux calibration,based on direct optical measurements of stellar angular diameters, putsthe effective temperatures determined in this work in the same scale asthose obtained by direct methods. We have derived up to fourtemperatures, TJ, TH, TK and T_{L'},for each star using the monochromatic fluxes at different infraredwavelengths in the photometric bands J, H, K and L'. They show goodconsistency over 4000 K, and there is no appreciable trend withwavelength, metallicity and/or temperature. We provide a detaileddescription of the steps followed for the application of the IRFM, aswell as the sources of error and their effect on final temperatures. Wealso provide a comparison of the results with previous work.
| The emission-line pulse pattern in the intermediate polar RX J0558+53
We observed the intermediate polar RX J0558+53 with the 4.2-m WilliamHerschel Telescope (WHT) and find a `corkscrew' pattern in the pulsedemission lines, which indicates a two-pole white dwarf accretion. The`corkscrew' pattern consists of two emission-line pulses, separated byhalf the white dwarf spin period, and moving from red to bluevelocities. The detected emission-line pulsations have an amplitude of1.1-2.7 per cent in the He II and Balmer emission lines at the 545-sspin period of the white dwarf compared with 3.5-4.8 per cent for thecontinuum double-peak pulsations. We image the emission-line pulsepattern and it is shown to lag the continuum pulse by 0.12 spin cycles.We interpret the pattern by invoking an accretion curtain from thedisrupted, inner disc to the two poles of the magnetic white dwarf. Thesemi-amplitude of the He II pulse of 408 +/- 35 km s^-1 can be used toconstrain the size of the magnetosphere, R ~ 4.1 x 10^4 km, and themagnetic moment of the white dwarf (~ 2.4 x 10^32 G cm^3). Power spectrashow dominant frequencies at 2 omicron and 2(omicron - Ο) whichsuggest reprocessing of the illuminating beams of the white dwarf in theaccretion disc. Finally, the steady He II emission line shows a strongsinusoidal component moving from red to blue at binary phase 0.5, with awidth similar to that expected from irradiation of the secondary star.Imaging of the emission lines indicates illuminated locations at theinner side of the red star and the back side of the accretion disc.
| Towards a fundamental calibration of stellar parameters of A, F, G, K dwarfs and giants
I report on the implementation of the empirical surface brightnesstechnique using the near-infrared Johnson broadband { (V-K)} colour assuitable sampling observable aimed at providing accurate effectivetemperatures of 537 dwarfs and giants of A-F-G-K spectral-type selectedfor a flux calibration of the Infrared Space Observatory (ISO). Thesurface brightness-colour correlation is carefully calibrated using aset of high-precision angular diameters measured by moderninterferometry techniques. The stellar sizes predicted by thiscorrelation are then combined with the bolometric flux measurementsavailable for a subset of 327 ISO standard stars in order to determineone-dimensional { (T, V-K)} temperature scales of dwarfs and giants. Theresulting very tight relationships show an intrinsic scatter induced byobservational photometry and bolometric flux measurements well below thetarget accuracy of +/- 1 % required for temperature determinations ofthe ISO standards. Major improvements related to the actual directcalibration are the high-precision broadband { K} magnitudes obtainedfor this purpose and the use of Hipparcos parallaxes for dereddeningphotometric data. The temperature scale of F-G-K dwarfs shows thesmallest random errors closely consistent with those affecting theobservational photometry alone, indicating a negligible contributionfrom the component due to the bolometric flux measurements despite thewide range in metallicity for these stars. A more detailed analysisusing a subset of selected dwarfs with large metallicity gradientsstrongly supports the actual bolometric fluxes as being practicallyunaffected by the metallicity of field stars, in contrast with recentresults claiming somewhat significant effects. The temperature scale ofF-G-K giants is affected by random errors much larger than those ofdwarfs, indicating that most of the relevant component of the scattercomes from the bolometric flux measurements. Since the giants have smallmetallicities, only gravity effects become likely responsible for theincreased level of scatter. The empirical stellar temperatures withsmall model-dependent corrections are compared with the semiempiricaldata by the Infrared Flux Method (IRFM) using the large sample of 327comparison stars. One major achievement is that all empirical andsemiempirical temperature estimates of F-G-K giants and dwarfs are foundto be closely consistent between each other to within +/- 1 %. However,there is also evidence for somewhat significant differential effects.These include an average systematic shift of (2.33 +/- 0.13) % affectingthe A-type stars, the semiempirical estimates being too low by thisamount, and an additional component of scatter as significant as +/- 1 %affecting all the comparison stars. The systematic effect confirms theresults from other investigations and indicates that previousdiscrepancies in applying the IRFM to A-type stars are not yet removedby using new LTE line-blanketed model atmospheres along with the updatedabsolute flux calibration, whereas the additional random component isfound to disappear in a broadband version of the IRFM using an infraredreference flux derived from wide rather than narrow band photometricdata. Table 1 and 2 are only available in the electronic form of thispaper
| Broad-band JHK(L') photometry of a sample of giants with 0.5 > [Fe/H] > -3
We present the results of a three-year campaign of broad-band photometryin the near-infrared J, H, K and L' bands for a sample of approximately250 giant stars carried out at the Observatorio del Teide (Tenerife,Spain). Transformations of the Telescopio Carlos Sanchez systeminto/from several currently used infrared systems are extended to theredward part of the colour axis. The linearity of our photometric systemin the range -3 mag [Fe/H] >-3. Data of comparable quality previouslypublished have been added to the sample in order to increase thereliability of the relations to be obtained. We also provide mean IRcolours for giant stars according to spectral type.ables 1, 2 and 3 are only available in electronic form via the CDS(anonymous ftp 130.79.128.5 or http://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Combined Ultraviolet-Optical Spectropolarimetry of the Magnetic White Dwarf GD 229
Abstract image available at:http://adsabs.harvard.edu/abs/1996ApJ...463..320S
| The alpha Centauri Line of Sight: D/H Ratio, Physical Properties of Local Interstellar Gas, and Measurement of Heated Hydrogen (The 'Hydrogen Wall') Near the Heliopause
We analyze high-resolution spectra of the nearby (1.34 pc) stars alphaCen A (G2 V) and alpha Cen B (K1 V), which were obtained with theGoddard High Resolution Spectrograph on the Hubble Space Telescope. Theobservations consist of echelle spectra of the Mg II 2800 A and Fe II2599 A resonance lines and the Lyman-alpha lines of hydrogen anddeuterium. The interstellar gas has a velocity (v = - 18.0 +/- 0.2 km/s)consistent with the local flow vector proposed for this line of sight byLailement & Berlin (1992). The temperature and nonthermal velocityinferred from the Fe II, Mg II, and D I line profiles are T = 5400 +/-500 K and xi = 1.20 +/- 0.25 km/s, respectively. However,single-component fits to the H I Lyman-alpha lines yield a Dopplerparameter (bHI = 11.80 km/s) that implies a significantlywarmer temperature of 8350 K, and the velocity of the H I absorption (v= - 15.8 +/- 0.2 km/s) is redshifted by about 2.2 km/s with respect tothe Fe II, Mg II, and D I lines. The one-component model of theinterstellar gas suggests natural logarithm N base HI = 18.03 +/- 0.01and D/H = (5.7 +/- 0.2) x 10-6 . These parameters lead to agood fit to the observed spectra, but this model does not explain thehigher temperature and redshift of H I relative to the otherinterstellar lines. The most sensible way to resolve the discrepancybetween H(I) and the other lines is to add a second absorption componentto the H(I) lines. This second component is hotter (T approx. equals30,000 K), is redshifted relative to the primary component by 2-4 km/s,and has a column density too low to be detected in the Fe(II), Mg(II),and D(I) lines. We propose that the gas responsible for this componentis located near the heliopause, consisting of the heated H I gas fromthe interstellar medium that is compressed by the solar wind. Thisso-called 'hydrogen wall' is predicted by recent multifluid gasdynamicalmodels of the interstellar gas and solar wind interaction. Our dataprovide the first measurements of the temperature and column density ofH(I) in the hydrogen wall. After considering the effects that acorresponding hydrogen wall around alpha Cen would have on our analysis,our best estimates for the parameters of the solar hydrogen wall arenatural log N(2)(H(I)) = 14.74 +/- 0.24,b(2)(H(I)) = 21.9 +/- 1.7 km/s (corresponding to T = 29,000+/- 5000 K), and v(2)(H(I)) greater than -16km/s.Unfortunately, the existence of this heated H(I) reduces our ability tocompute the H(I) column density of the interstellar medium accuratelybecause, with slight alterations to our assumed stellar Lyman-alphaprofiles, we discovered that acceptable two-component fits also existwith natural log N(H(I))approx. 17.6. We, therefore, quote large errorbars for the H I column density along the alpha Cen line of sight,natural log N(H(I)) = 17.80 +/- 0.30. For this range in N(H(I)), n(H(I))= 0.15 /cu.cm (+/- a factor of 2) and D/H = (0.5-1.9) x 10-5.This is the first direct measurement of the H(I) density in a localcloud and allows us to predict the distance from the Sun to the edge ofthe local cloud along various lines of sight. This range in D/H isconsistent with the value D/H = 1.6 x 10-5 previously derivedfor the Capella and Procyon lines of sight. We cannot tell whether D/Hratio varies or is constant in the local interstellar medium, but we dofind that the D(I)/Mg(II) ratio for the alpha Cen line of sight is about4 times smaller than for the Capella and Procyon lines of sight.Therefore, either D/H or the Mg depletion varies significantly overdistance scales of only a few parsecs.
| 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.
| Improved Calculations of the Equilibrium Abundances of Heavy Elements Supported by Radiative Levitation in the Atmospheres of Hot DA White Dwarfs
Abstract image available at:http://adsabs.harvard.edu/abs/1995ApJ...454..429C
| Search for Coronal Emission Lines in Cooling Flow Clusters with the Keck 10 Meter Telescope
Abstract image available at:http://adsabs.harvard.edu/abs/1995ApJ...454...44Y
| An Improved Ephemeris for Z Camelopardalis
Not Available
| A survey of proper motion stars. 12: an expanded sample
We report new photometry and radial velocities for almost 500 stars fromthe Lowell Proper Motion Catalog. We combine these results with ourprior sample and rederive stellar temperatures based on the photometry,reddening, metallicities (using chi squared matching of our 22,500 lowSignal to Noise (S/N) high resolution echelle spectra with a grid ofsynthetic spectra), distances, space motions, and Galactic orbitalparameters for 1269 (kinematics) and 1261 (metallicity) of the 1464stars in the complete survey. The frequency of spectroscopic binariesfor the metal-poor ((m/H) less than or equal to -1.2) stars with periodsshorter than 3000 days is at least 15%. The spectroscopic binaryfrequency for metal-rich stars ((m/H) greater than -0.5) appears to belower, about 9%, but this may be a selection effect. We also discussspecial classes of stars, including treatment of the double-linedspectroscopic binaries, and identification of subgiants. Four possiblenew members of the class of field blue stragglers are noted. We pointout the detection of three possible new white dwarfs, six broad-lined(binary) systems, and discuss briefly the three already knownnitrogen-rich halo dwarfs. The primary result of this paper will beavailable on CD-ROM, in the form of a much larger table.
| Duplicity in the solar neighborhood. 7: Spectroscopic orbits of three K-dwarf stars
The spectroscopic orbits of single-lined binary dwarfs HD 23439B, HD237287 and HD 217580 are derived from the radial velocities measuredwith two correlation radial-velocity spectrometers, correlation radialvelocity (CORAVEL) and radial velocity meters (RVM). The mutualagreement of these two data sets is analyzed and found to be quite good.The estimated minimum mass of secondary component corresponds to that ofM-type dwarf for the first 2 systems and is equal to 0.06 solar mass forHD 217580.
| Spectroscopic detection of the spin pulse in GK Persei
I report the discovery of a coherent S-wave modulation with the 351-sspin period in the optical emission lines of the old nova system GKPersei. The pulsed fraction of the Balmer and He II line fluxes is 4 and8%, respectively. The spectroscopy presented in this work extends theorbital-phase coverage to the hitherto unobserved phase intervals duringwhich potential eclipses in the system might occur. From the absence ofeclipse signatures in the new data it is concluded that the orbitalinclination is 46 deg less than i less than 73 deg, implying a whitedwarf mass Ml greater than or approximately equal to 0.78solar mass. The spectral type of the secondary has been re-determined tobe K2-K3.
| 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.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Camelopardalis |
| Ascensió Recta: | 04h36m06.21s |
| Declinació: | +55°24'44.1" |
| Magnitud Aparent: | 8.333 |
| Distancia: | 29.214 parsecs |
| Moviment propi RA: | 546 |
| Moviment propi Dec: | -301.3 |
| B-T magnitude: | 9.466 |
| V-T magnitude: | 8.427 |
Catàlegs i designacions:
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