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Accuracy of radial-velocity measurements for early-type stars. II. Investigations of spectrum mismatch from high-resolution observations
The accuracy with which radial velocities of early-type stars can bemeasured is limited in practice by the existence of asymmetricaldifferences between object and template spectrum, constituting``spectrum mismatch''. Our studies of the magnitude of spectrum-mismatcherrors, commenced in Paper I (Verschueren et al. \cite{VDG99}) on thebasis of synthetic spectra having different attributes of effectivetemperature (Teff and {log g}, are continued here in acomplementary approach that employs observed spectra. From over 60de-archived observations we derive accurate wavelength scales for thespectra of 16 dwarfs of spectral types B8-F7, and examine the results ofcross-correlating the spectra against different (observed) templatespectra. We also test the effects of (a) truncating the spectra atdifferent levels below the continuum, (b) adding rotational broadeningto enforce a visual match of line-width between object and template, (c)applying rotational broadening to exacerbate a rotational mismatch, and(d) neglecting the presence of faint companion spectra. We alsocross-correlate pairs of spectra such that the differences between theirTeff are minimal. We conclude that it will be possible tomeasure radial velocities to an accuracy considerably better than 1 kms-1 for slowly-rotating stars in the range of spectral typesexamined, and a careful discussion of the nature and sources of therandom and systematic errors that become significant in work of thisnature enables us to specify conditions that are important for achievingsuch accuracy routinely. We find that both rotational broadening, andthe star-to-star variations in line strengths that are so prevelantamong A-type spectra, can give rise to more deleterious mismatch shifts(RV errors) than do differences in Teff alone, even for DeltaTeff as great as 300-400 K. By intercomparing the resultsgiven by wide regions of spectrum ( ~ 800 Å) with those obtainedby isolating small groups of features in very narrow windows ( ~ 30Å), we have been able to designate a window near lambda 4570Åthat should be particularly reliable for high-accuracy results,and we propose further studies at very high S/N ratio in that specificwindow to complement and extend the results of the present paper.
| Contribution à l'étude des spectres composites. VIII. HD 174016-7, une étoile Ap associée à une géante G Contribution to the study of composite spectra VIII. HD 174016-7, an Ap star with a giant G
HD 174016-7, listed by \cite[Hynek (1938)]{Hynek} as a star having acomposite spectrum, was on our observing programmes of such objectscarried out both at the Cambridge Observatories and at the ObservatoireMidi-Pyrénées. Most of the observations were made with theCORAVEL spectrovelocimeter of the Swiss telescope at the Observatoire deHaute-Provence. We find that this star is a long-period spectroscopicbinary with two correlation dips; we obtain the following orbitalelements: P = 3097.9 days; T = JD 2450605.2; omega = 204fdg 8; e =0.600; K_1 = 12.95 km s-1; K_2 = 15.14 km s-1; V_0= -1.65 km s-1; a_1 sin i = 441.1 Gm; a_2 sin i = 516.0 Gm;M_1 sin 3i = 1.967 M_sun; M_2sin 3i = 1.681 M_sun.The primary is a giant star of spectral type near G6III, and the hotdwarf secondary is found to be a peculiar A star of type A0p Sr, Cr, Eu,Si; so HD 174016-7 is, to our knowledge, the second discoveredcomposite-spectrum binary with a Ap-type hot component. A confrontationwith Hipparcos data suggests Mv_1 = 0 and m_v = 0.6 mag. Onthe basis of very accurate masses of main sequence stars by\cite[Andersen (1991),]{Andersen} we estimate the mass, M_1 = 2.8 M_sun,of the giant primary, the orbital inclination, i = 63o, andthe mean linear separation of the components, a = 7.2 AU. Theevolutionary status of the system is discussed using \cite[Schaller etal. (1992)]{Schaller} M_bol / T_eff diagram for stars of solarmetallicity. Theoretical masses suggested by this diagram confirm theproposed model. Étude effectuée à partird'observations faites aux Observatoires de Haute-Provence et deCambridge.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| BVRI photometry of spectroscopic binaries
Not Available
| Spectroscopic binary orbits from photoelectric radial velocities. A synopsis of papers 1-100
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| Contribution to the study of composite spectra. IV - Orbital elements of the spectroscopic binaries AM HD 41724-5 and HD 177390-1
Observations of HD 41724-5 and HD 177390-1 made at the Observatoire deHaute-Provence show them to be detached Am spectroscopic binaries.Results for HD 41724-5 reveal a period of 2.887679 days and suggest thatthe secondary could be either an F or early G dwarf star. For HD177390-1, a period of 8.00802 days is found, and the MK spectral typesA2, A6, and F4 are obtained from the CaII K line, Balmer lines, andmetallic lines, respectively.
| Spectroscopic binary orbits from photoelectric radial velocities. Paper 81: HD 177390
Not Available
| Objective-prism discoveries in the northern sky - II.
Five tables list the observed characteristics of 244 northern hemispherestars recorded in 100 108 A/mm dispersion plates at H-gamma wavelengths.The 5 x 5 deg fields contained a number of suspected weak-metal objects.Listings are divided into peculiar A stars, metallic line and deltaDelphini stars, high luminosity objects, Ca II emission stars of the Gand K type, and composite spectra.
| A survey of stars with composite spectra.
Not Available
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