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Spectroscopic binaries among Hipparcos M giants^,. I. Data, orbits, and intrinsic variations
Context: This paper is a follow-up on the vast effort to collect radialvelocity data for stars belonging to the Hipparcos survey. Aims: We aimat extending the orbital data available for binaries with M giantprimaries. The data presented in this paper will be used in thecompanion papers of this series to (i) derive the binary frequency amongM giants and compare it to that of K giants (Paper II); and (ii) analysethe eccentricity - period diagram and the mass-function distribution(Paper III). Methods: Keplerian solutions are fitted to radial-velocitydata. However, for several stars, no satisfactory solution could befound, even though the radial-velocity standard deviation is greaterthan the instrumental error, because M giants suffer from intrinsicradial-velocity variations due to pulsations. We show that theseintrinsic radial-velocity variations can be linked with both the averagespectral-line width and the photometric variability. Results: Wepresent an extensive collection of spectroscopic orbits for M giantswith 12 new orbits, plus 17 from the literature. On top of these, 1preliminary orbit yielded an approximate value for the eccentricity andthe orbital period. Moreover, to illustrate how the largeradial-velocity jitter present in Mira and semi-regular variables mayeasily be confused with orbital variations, we also present examples ofpseudo-orbital variations (in S UMa, X Cnc, and possibly in HD 115 521,a former IAU radial-velocity standard). Because of this difficulty, Mgiants involving Mira variables were excluded from our monitored sample.We finally show that the majority of M giants detected as X-ray sourcesare actually binaries. Conclusions: The data presented in this paperconsiderably increase the orbital data set for M giants, and will allowus to conduct a detailed analysis of the eccentricity - period diagramin a companion paper (Paper III).Based on observations carried out at the Swiss telescope installed atthe Observatoire de Haute Provence (OHP, France), and at the 1.93-m OHPtelescope. Full Tables 2, 3, and Table 6 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/498/627
| The DA+dMe eclipsing binary EC13471-1258: its cup runneth over ... just
The optical spectrum and light curve of EC13471-1258 show that it is aneclipsing binary with an orbital period of 3h 37mcomprising a DA white dwarf and a dMe dwarf. Total eclipses of the whitedwarf are observed lasting 14 min, with the partial phases lasting 54 s.On one occasion, two pre-eclipse dips were seen. Timings of the eclipsesover 10 yr show jitter of up to 12 s. Flares from the M dwarf areregularly observed. The M dwarf also shows a large-amplitude ellipsoidalmodulation in the V-band light curve. The component stars emit almostequal amounts of light at 5500 Å.Hubble Space Telescope (HST) STIS spectra show strong Lyman-αabsorption with weak metal lines of C I,II and Si II superimposed. Modelatmosphere analysis yielded an effective temperature of 14 220 +/- 300 Kand logg of 8.34 +/- 0.20 for the white dwarf with these errors beingstrongly correlated. Its metal abundance is 1/30th solar with anuncertainty of 0.5 dex, and it is rapidly rotating with V1sin i= 400 +/- 100 km s-1. The white dwarf also shows radialvelocity variations with a semi-amplitude of 138 +/- 10 kms-1. The gravitational redshift of the white dwarf wasmeasured as 62 km s-1.From optical spectroscopy the spectral type of the M dwarf was found tobe M3.5-M4, its temperature 3100 +/- 75 K, its rotational velocity 140+/- 10 km s-1, its radial velocity semi-amplitude 266 +/- 5km s-1, its mean V-I colour 2.86 and its absolute V magnitude11.82. Intriguingly, its metal abundance is normal solar.The Hα emission line shows at least two distinct components, oneof which is uniformly distributed around the centre of mass of the Mdwarf and provided the estimate of the rotational velocity of the Mdwarf. The other arises from the other side of the binary centre ofmass, well within the white dwarf Roche lobe. This behaviour isconfirmed by Doppler tomography, which shows the presence of twodistinct velocity components within the primary Roche lobe. Theinterpretation of these features is uncertain. Variations in strength ofthe components with binary phase can be attributed to optical thicknessin the Balmer lines. Similar behaviour is seen in the observations ofthe other Balmer emission lines, although with a poorer signal-to-noiseratio. Flares in Hα were observed and are consistent with arisingfrom the vicinity of the M dwarf.Dynamical solutions for the binary are discussed and yield aninclination of 75.5°+/- 2.0o, a white dwarf mass andradius of 0.78 +/- 0.04 Msolar and 0.011 +/- 0.01Rsolar, and an M dwarf mass and radius of 0.43 +/- 0.04Msolar and 0.42 +/- 0.02 Rsolar. These parametersare consistent with the Wood mass-radius relation for white dwarfs andthe Clemens et al. mass-radius relation for M dwarfs; we argue that theM dwarf just fills its Roche lobe. The radius of the white dwarf and themodel fit imply a distance of 48 +/- 5 pc and an absolute V magnitude of11.74.The rapid rotation of the white dwarf strongly suggests that the systemhas undergone mass transfer in the past, and implies that it is ahibernating cataclysmic variable. The M dwarf shows the propertiesexpected of secondaries in cataclysmic variables: chromospheric activityand angular momentum loss.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
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Observation and Astrometry data
| Constellation: | Παρθένος |
| Right ascension: | 13h50m20.87s |
| Declination: | -13°06'36.9" |
| Apparent magnitude: | 7.53 |
| Distance: | 507.614 parsecs |
| Proper motion RA: | -20.9 |
| Proper motion Dec: | -5.2 |
| B-T magnitude: | 9.677 |
| V-T magnitude: | 7.708 |
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