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Fourier-Doppler imaging of non-radial pulsations in gamma Doradus stars .
This paper deals with a class of non-radial pulsators along the mainsequence, namely the gamma Doradus stars for which much effort iscurrently made in order to constrain their pulsation characteristics.However, because of their relatively low amplitude (few tens of mmag inphotometry) and due to the long time scales of the variation (between0.3 and 3 days), the detection and identification of their pulsations israther difficult, using the photometric data only. Consequently, thespectroscopic studies of the stars having well-known photometricproperties are very valuable and we study in detail the line profilevariability (LPV) in gamma Doradus candidates observed at Observatoirede Haute-Provence during a two-year high-resolution spectroscopycampaign. The non-radial behavior of selected stars is revealed with theadvent of Doppler Mapping and two-dimensional Fourier-Doppler Imagingmethods for line-profile analysis, which allowed us to detect andidentify the pulsation modes described below.
| Non-radial pulsations in the γ Doradus star HD 195068
We present high resolution spectroscopic observations of the γDoradus star HD 195068. About 230 spectra werecollected over 2 years. Time series analysis performed on radialvelocity data shows a main peak at 1.61 d-1 , a frequency notyet detected in photometry. The Hipparcos photometric 1.25d-1 frequency is easily recovered as is 1.30 d-1while the third photometric frequency, 0.97 d-1 , is onlymarginally present. The good quality of our data, which includes 196spectra collected over seven consecutive nights, shows that both the1.61 d-1 and intermediate 1.27 d-1 (mixture of1.25 and 1.30 d-1 ) frequencies are present in the lineprofile variations. Using the Fourier-Doppler Imaging (FDI) method, thevariability associated with 1.61 d-1 can be successfullymodeled by a non-radial pulsation mode ℓ=5± 1, |m|=4±1. For the intermediate frequency 1.27 d-1 we deduceℓ=4± 1, |m|=3± 1. Evidence that the star is notpulsating in the radial mode (ℓ=0) rules out a previousclassification as an RR Lyrae type star. We investigate the timevariability of FDI power spectra concluding that the observed temporalvariability of modes can be explained by a beating phenomenon betweenclosely spaced frequencies of two non-radial modes. The distribution ofthe oscillation power within the line profile indicates that there is asignificant tangential velocity component of oscillations characteristicof high radial order gravity modes which are predicted to be observed inγ Doradus type stars.
| Time-dependent convection seismic study of five γ Doradus stars
We apply for the first time the time-dependent convection (TDC)treatment of Gabriel and Grigahcène et al. to the photometricmode identification in γ Doradus (γ Dor) stars. We considerthe influence of this treatment on the theoretical amplitude ratios andphase differences. Comparison with the observed amplitudes and phases ofthe stars γ Dor, 9 Aurigae, HD 207223 = HR 8330, HD 12901 and48501 is presented and enables us to identify the degree l of thepulsation modes for four of them. We also determine the mode stabilityfor different models of these stars. We show that our TDC models agreebetter with observations than with frozen convection models. Finally, wecompare the results obtained with different values of the mixing-lengthparameter α.
| 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
| A Theoretical γ Doradus Instability Strip
In this paper, we present the first theoretical γ Doradusinstability strip. We find that our model instability strip agrees verywell with the previously established, observationally based, instabilitystrip of Handler & Shobbrook. We stress, as do Guzik et al., thatthe convection zone depth plays the major role in the determination ofour instability strip. Once this depth becomes too deep or too shallow,the convection zone no longer allows for pulsational instability. Ourtheoretical γ Dor instability strip is bounded by ~6850 and 7360 Kat the red and blue edge, respectively, on the zero-age main sequenceand by ~6560 and 7000 K at the red and blue edge, respectively,approximately 2 mag more luminous. This theoretical strip, transformedto the observer's color-magnitude diagram, overlays the region wheremost of the 30 bona fide γ Dor stars are found.
| A Dozen New γ Doradus Stars
We use new high-dispersion spectroscopic and precise photometricobservations to identify 12 new γ Doradus stars. Two of the 12systems are double-lined binaries that show obvious velocityvariability. Five other stars have metallic lines with compositeprofiles characterized by a narrow feature near the center of each broadcomponent. Spectrograms of the Hα line indicate that all fivestars are binaries rather than shell stars. The remaining five stars inour sample are probably single. All 12 stars are photometricallyvariable with amplitudes between 6 and 87 mmag in Johnson B and periodsbetween 0.3 and 1.2 days. Four stars are monoperiodic; the rest havebetween two and five independent periods. The variability at all periodsapproximates a sinusoid. Although many of the stars lie within theδ Scuti instability strip, none exhibit the higher frequencyvariability seen in δ Scuti stars. We have increased the sample ofknown γ Doradus stars by 40% and revised the positions of a numberof variables in the H-R diagram by accounting for duplicity. Our list of42 confirmed γ Doradus variables gives some of their properties.All are dwarfs or subgiants and lie within a well-defined region of theH-R diagram that overlaps the cool edge of the δ Scuti instabilitystrip. We compare the observed location of the γ Doradus variableswith a recently published theoretical γ Doradus instability stripand find good agreement.
| The Orbit and Pulsation Periods of the γ Doradus Variable HR 6844 (V2502 Ophiuchi)
We obtained spectroscopic and photometric observations of the γDoradus variable HR 6844 (=V2502 Ophiuchi). Radial velocities show thatthis star is a single-lined binary with a period of 4.4852 days. Theprimary is an F1 V star, while the secondary is likely an M dwarf.Velocity residuals to a circular orbit have a period of 1.3071 days andan amplitude of ~3 km s-1. Three periods of light variationwere detected, 1.30702, 1.4350, and 0.62286 days. The first period isessentially identical to that found in the radial velocities and has thelargest amplitude, a peak-to-peak value of 0.067 mag in B. Thephotometric check star, 73 Oph (=HR 6795), has light variations with aperiod of 0.61439 in B. Although the star is a close visual binary, thelight variations are ascribed to the primary, making it most likely anewly discovered γ Doradus variable.
| Six New γ Doradus Stars
We present high-resolution spectroscopy and precision photometry of sixnew γ Doradus stars, one of which was independently discovered byanother group. This brings the total number of confirmed γ Doradusvariables to 30. All six of these variables fall in the spectral classrange F0-F2 all but one are subgiants. The six stars have between oneand five photometric periods in the range 0.3-1.2 days. We find noevidence for higher frequency δ Scuti pulsations in any of thesesix stars. Our spectroscopic observations reveal HD 108100 to be thefirst confirmed γ Doradus variable with composite broad and narrowline profiles suggesting the presence of a circumstellar shell or disk.HD 221866 has the most asymmetric absorption lines of the six stars inthis paper and also the largest photometric amplitude. Most of the 30confirmed γ Doradus variables lie in a fairly tight region of theH-R diagram on or just above the main sequence that partially overlapsthe cool edge of the δ Scuti instability strip. However, threestars, including two of the new variables in this paper, are subgiantsthat lie well within the δ Scuti strip. Among the 30 confirmedγ Doradus variables, we find no correlation between thephotometric periods and intrinsic color, absolute magnitude, orluminosity.
| Discovery and analysis of p-mode and g-mode oscillations in the A-type primary of the eccentric binary HD 209295*
We have discovered both intermediate-order gravity mode and low-orderpressure mode pulsation in the same star, HD 209295. It is thereforeboth a γ Doradus and a δ Scuti star, which makes it thefirst pulsating star to be a member of two classes. The analysis of our128h of multisite spectroscopic observations carried out over twoseasons reveals that the star is a single-lined spectroscopic binarywith an orbital period of 3.10575+/-0.00010d and an eccentricity of0.352+/-0.011. Only weak pulsational signals are found in both theradial velocity and line-profile variations, but we have succeeded inshowing that the two highest-amplitude γ Doradus pulsation modesare consistent with l=1 and |m|=1. These two modes dominated our 280h ofBVIC multisite photometry, also obtained over two seasons. Wedetected altogether ten frequencies in the light variations, one in theδ Scuti regime and nine in the γ Doradus domain. Five of theγ Doradus frequencies are exact integer multiples of the orbitalfrequency. This observation leads us to suspect they are tidallyexcited. Attempts to identify modes from the multicolour photometryfailed. We performed model calculations and a stability analysis of thepulsations. The frequency range in which δ Scuti modes are excitedagrees well with observations. However, our models do not showexcitation of γ Doradus pulsations, although the damping issmaller in the observed range. We also investigated tidal excitation ofγ Doradus modes. Some of the observed harmonics of the orbitalperiod were found to be unstable. The observed orbital harmonics whichare stable in the models can be understood as linear combinations of theunstable modes. We could not detect the secondary component of thesystem in infrared photometry, suggesting that it may not be amain-sequence star. Archival data of this star show that it has a strongultraviolet (UV) excess, the origin of which is not known. The orbit ofthe primary is consistent with a secondary mass ofM>1.04Msolar, which is indicative of a neutron star,although a white dwarf companion is not ruled out.
| On the relationship between the δ Scuti and γ Doradus pulsators
We searched for δ Scuti-type pulsations amongst known andcandidate γ Doradus stars. The motivations for such a project comefrom the need to understand the relationship of these two classes ofpulsator better, from the present poor knowledge of the hot border ofthe γ Doradus phenomenon, and from the exciting prospects forasteroseismology should stars be found which have both types ofpulsation excited. We acquired 270h of observations and monitored atotal of 26 stars. One target, HD 209295, turned out to be a member ofboth classes of pulsating star, but this object is peculiar in the sensethat it is a close binary. We classify six of our targets as new bonafide γ Doradus stars, whereas nine more are good γ Doraduscandidates, and three turned out to be ellipsoidal variables. One of ourprogramme stars was found to be a δ Scuti star, with no additionalγ Doradus variations. Furthermore, one star was already known tobe a bona fide γ Doradus star, and we could not find anunambiguous explanation for the variability of five more stars. Theanalysis of our data together with improved knowledge of stars from theliterature enabled us to revise the blue border of the γ Doradusphenomenon towards cooler temperatures. This new blue edge is muchbetter defined than the previous one and extends from a temperature ofabout 7550K on the ZAMS to 7400K one magnitude above it. Five bona fideγ Doradus stars we observed are located inside the δ Scutiinstability strip, but none of them exhibited observable δ Scutipulsations. We therefore suggest that γ Doradus stars are lesslikely to be δ Scuti pulsators compared with other normal stars inthe same region of the lower instability strip. In addition, we showthat there is a clear separation between the pulsation constants Q ofδ Scuti and γ Doradus stars. The γ Doradus stars knownto date all have Q>0.23d.
| Magnetic activity of six young solar analogues I. Starspot cycles from long-term photometry
A long-term photometric monitoring of a selected sample of solaranalogues has been carried out since early nineties as part of The Sunin time project, which is aimed at a multiwavelength study of stars withsolar-like global properties, but with different ages and thus atdifferent stages of their evolution. The extended time sequence ofground-based observations collected over more than a decade as part ofthis program has revealed the existence of starspot cycles. Also fromthese data it is possible to investigate surface differential rotationof the stars. In this paper we present the photometry collected to dateand report on cycles search for a selected subsample of five youngsingle G0-G5V stars with ages between =~ 130 Myr and 700 Myr:EK Dra, pi 1 UMa, HNPeg, k1 Cet and BE Cet.Also we include in this study the Pleiades-age ( =~ 130 Myr) K0V starDX Leo (HD 82443). All the cited stars show activitycycles whose period is, furthermore, the first determined fromphotometric data. They are compared to those activity cycles derivedfrom CaII H&K emission fluxes and differences are discussed. All thecycle periods, except for EK Dra, fit well the empirical relations withglobal stellar parameters derived from larger stellar samples. Thefollowing results are also inferred from the present study: i) thefastest rotating stars tend to have longer cycles; ii) the range in theobserved cycle lengths seems to converge with stellar age from a maximumdispersion around the Pleiades' age towards the solar cycle value at theSun's age; iii) the overall short- and long-term photometric variabilityincreases with inverse Rossby number with very high correlation degree,indicating that the level of magnetic activity at least in photosphereis still controlled by the stellar rotation even on the longest timescales; iiii) the increase with inverse Rossby number of the long-termoverall photometric variability seems to level off at the highestrotation rate, which may be interpreted as due to a saturation in thelevel of photospheric magnetic activity around the activity maximum.
| The multiperiodicity of the gamma Doradus stars HD 224945 and HD 224638 as detected from a multisite campaign
We discuss new photometric data collected on the gamma Dor variables HD224945 and HD 224638. Multiperiodicity was detected in both stars,thanks to the clear spectral window of a multisite campaign thatinvolved five observatories. HD 224945 shows the shortest period amongthe gamma Dor stars, i.e., 0.3330 d. The pulsation behaviour is verydifferent: HD 224945 displays a set of frequencies spread over aninterval much larger than that of HD 224638. We clearly found evidencefor amplitude variations in the excited modes by comparing data fromdifferent years. HD 224945 and HD 224638 are among the best examples ofgamma Dor stars that show multimode pulsations, which make them veryinteresting from an asteroseismological point of view. Based onobservations partially collected at ESO-La Silla (Proposals 54.E-018 and56.E-0308).
| The 76th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1406 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Pre-discovery Photometry of the gamma Doradus-type Pulsating Star HR 8330 (= HD 207223)
Not Available
| A Spectroscopic Analysis of the γ Doradus Star HD 207223 = HR 8330
We present a detailed analysis of 76 high-resolution, highsignal-to-noise spectra of the γ Doradus star HD 207223=HR 8330.Periodogram analysis of the moments of the line profiles reveals asingle period of 2.67+/-0.01 days, a result consistent with that foundin photometric studies. Mode identification was accomplished with boththe moment method and from direct line-profile fitting. Both methodsclearly point towards a sectoral mode of degree l>=2. The inclusionof rotational effects, by taking the Coriolis force into account,reveals a single consistent solution: an l=m=+2 retrograde sectoral modethat has a period of 1.4 days in the corotating frame. The star is seenat an inclination of 30°. From this, we derive a rotational periodof 4.9 days.
| 10 New γ Doradus and δ Scuti Stars
We present high-resolution spectroscopy and precision photometry of fivenew γ Doradus and five new δ Scuti variables. The five newγ Doradus variables substantially increase the number of confirmedstars of this class. All 10 stars fall in the spectral class rangeF0-F2, but they are cleanly separated into two groups by theirluminosity and photometric periods. However, the period gap between theγ Doradus and δ Scuti stars is becoming very narrow since weconfirm that HD 155154 is a γ Doradus star with the shortestperiods reported to date (the shortest of its four periods is ~0.312days). We do not find any evidence in our sample for stars exhibitingboth δ Scuti- and γ Doradus-type pulsations.
| Spots and plages on a young main-sequence solar-type star: HD 206860
The young solar type star HD 206860 is known to be aphotometric variable with emission in the core of Ca ii H & K lines,several times more intense than the Sun when observed as a star. Thephotometric and spectroscopic monitoring of HD 206860from near contemporaneous observations at Serra La Nave (Catania, Italy)and at the Observatoire de Haute Provence (OHP, France) shows thatchromospheric spectral-line flux and photometric variations follow thesame period (4.74 days). From Strömgren photometry and Ca ii andHα chromospheric emission clearly anti-correlated variations havebeen found. This result suggests that spots and plages in this singlesolar-type star are spatially associated, as frequently observed for thelargest sun-spot groups and for some very active RS CVn systems. Aspot/plage model applied to the observed flux curves allows a crudereconstruction of the 3D structure of the external atmosphere of thisstar. Based on observations collected at the Observatoire de HauteProvence (CNRS), France, and at the Osservatorio Astrofisico di Catania,Italy
| Search for gamma Doradus variable stars in the Pleiades cluster
Photometric observations in the uvbybeta system of A-F type stars in thePleiades cluster have been performed in order to detect pulsatingvariable stars of gamma Doradus type in the lower part of the Cepheidinstability strip. In order to obtain more information about thebehaviour of the studied objects and to be able to distinguish betweenlong period variable and non-variable stars, two statistical methodshave been developed. Several of these stars show some type ofvariability but only two of the observed objects, H1284 and S29, can besafely classified as gamma Dor stars. Furthermore, these observationshave provided us with Strömgren and Hβ photometry,non-existing up to now for some of them, which permitted us to perform aphotometric study of the Pleiades cluster.
| Gamma Doradus Stars: Defining a New Class of Pulsating Variables
In this paper we describe a new class of pulsating stars, the prototypeof which is the bright, early, F-type dwarf gamma Doradus. These starstypically have between 1 and 5 periods ranging from 0.4 to 3 days withphotometric amplitudes up to 0.1 mag in Johnson V. The mechanism forthese observed variations is high-order, low-degree, nonradial,gravity-mode pulsation.
| Simultaneous photometry and spectroscopy of the newly discovered γ Doradus variable HR 8330=HD 207223
We present BV photometry and simultaneous high-resolution, highsignal-to-noise ratio spectroscopy of the newly-discovered γDoradus variable HR 8330 taken during the 1997 and 1998 observingseasons. We calculate power spectra for the B- and V-band data sets andfor the time series defined throughout the observing season at eachpoint across the Feii λ4508.289 and the Tiii λ4501.278line profiles to search for periodic variability. Period analysisreveals a single, 2.6-d period in both the photometric and thespectroscopic data, with a 237 deg phase lag between them. Based on thelocation of HR 8330 in the HR diagram and the characteristics of itsphotometric and spectroscopic variations, we conclude that HR8330 is abona fide γ Doradus-type pulsating variable.
| HD 62454 and HD 68192: Two New γ Doradus Variables
We present multilongitude, multicolor photometry and simultaneoushigh-resolution, high signal-to-noise spectroscopy of the newlydiscovered γ Doradus variables HD 62454 and HD 68192. Fromcombined Johnson and Strömgren data, we are able to identify fiveindependent periods in HD 62454 and two stable periods in HD 68192. Thedata presented are sufficient to rule out all physically meaningfultypes of variations, with the one exception of the high-order,low-degree, nonradial gravity-mode pulsations that are believed to be atwork in γ Doradus stars. We also find that HD 62454 is adouble-lined spectroscopic binary and we present an orbital solution.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..551L&db_key=AST
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| U, V, W velocity components for the old disk using radial velocities of 1295 stars in the three cardinal Galactic directions
New radial velocities are presented for 1295 stars chosen at random nearthe three cardinal Galactic directions of l = 180 deg, b = 0; l = 90deg, b = 0 deg; and b = 90 deg, giving the distribution in U, V, and W,respectively, from the radial velocities alone. The measurements weremade with the coude spectrograph of the Mount Wilson 100 in. Hookerreflector. The purpose of the program is to set limits on the densitynormalization in the solar neighborhood of the old thin disk, the oldthick disk, and the halo. Many more high-velocity stars are present inthe unbiased sample than expected from previous estimates of thenormalization. The data suggest the density ratios in the solarneighborhood to be about 90 percent, 10 percent, and about 0.5 percentfor the thin disk, thick disk, and halo populations, respectively.
| ICCD speckle observations of binary stars. I - A survey for duplicity among the bright stars
A survey of a sample of 672 stars from the Yale Bright Star Catalog(Hoffleit, 1982) has been carried out using speckle interferometry onthe 3.6-cm Canada-France-Hawaii Telescope in order to establish thebinary star frequency within the sample. This effort was motivated bythe need for a more observationally determined basis for predicting thefrequency of failure of the Hubble Space Telescope (HST) fine-guidancesensors to achieve guide-star lock due to duplicity. This survey of 426dwarfs and 246 evolved stars yielded measurements of 52 newly discoveredbinaries and 60 previously known binary systems. It is shown that thefrequency of close visual binaries in the separation range 0.04-0.25arcsec is 11 percent, or nearly 3.5 times that previously known.
| The fourth meridian catalog of Besancon Observatory
The catalog presented gives differential meridian positions for 670F-type stars between plus 15 and plus 45 deg declination. The positionsare reduced to the equinox of 1950.0 without proper motions; 333 FK4stars were used as reference stars. A minimum of three and an average offive transits of each program star were observed photoelectrically usinga Gautier transit circle and a Hog grid. The internal accuracy ofindividual measurements is shown to range from 0.013 sec in rightascension and 0.30 arcsec in declination for brighter stars under betterobserving conditions to 0.020 sec in right ascension and 0.38 arcsec indeclination for fainter stars under worse conditions. The standarderrors were applied to compute weighted mean positions, mean epochs, andunweighted means for the program stars. Mean corrections for 283 FK4stars are also provided.
| Light Variations of the H and K Emission Star HD 206860
Not Available
| Absolute luminosity calibration of F stars
Luminosity calibrations are performed for a restricted sample of 706F-type field stars of all luminosity classes and a similarly restrictedsample of 251 main-sequence F stars. The samples are restricted withrespect to values of photometric and metallicity indices, propermotions, radial velocities, and apparent magnitudes. Both linear andsecond-order relations between absolute magnitude and the photometricindices beta, /c1/ or (b-y), /c1/ are considered.These relations are calibrated by the statistical parallax method basedon the principle of maximum likelihood. The possible effect ofinterstellar absorption on the calibration results is investigated alongwith an effect of a photometric correction to the absolute magnitudes.The results obtained are compared with those of Crawford (1975) as wellas with the trigonometric parallaxes. The coefficients of thecalibration relations are derived from the trigonometric parallaxes, andpoor agreement is indicated. It is concluded that the trigonometricparallaxes must be used very carefully and only for nearby stars.
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| Takýmyýldýz: | Kanatli At |
| Sað Açýklýk: | 21h47m04.70s |
| Yükselim: | +17°11'39.0" |
| Görünürdeki Parlaklýk: | 6.21 |
| Uzaklýk: | 50.251 parsek |
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