Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Computed Hβ indices from ATLAS9 model atmospheres
Aims.Grids of Hβ indices based on updated (new-ODF) ATLAS9 modelatmospheres were computed for solar and scaled solar metallicities[+0.5], [+0.2], [0.0], [ -0.5] , [ -1.0] , [ -1.5] , [ -2.0] , [ -2.5]and for α enhanced compositions [+0.5a], [0.0a], [ -0.5a] , [-1.0a] , [ -1.5a] , [ -2.0a] , [ -2.5a] , and [ -4.0a] . Methods:.Indices for T_eff > 5000 K were computed with the same methods asdescribed by Lester et al. (1986, LGK86) except for a differentnormalization of the computed natural system to the standard system.LGK86 used special ODFs to compute the fluxes. For T_eff ≤ 5000 K wecomputed the fluxes using the synthetic spectrum method. In order toassess the accuracy of the computed indices comparisons were made withthe indices computed by Smalley & Dworetsky (1995, A&A, 293,446, MD95) and with the empirical relations T_eff-Hβ given byAlonso et al. (1996, A&A, 313, 873) for several metallicities.Furthermore, for cool stars, temperatures inferred from the computedindices were compared with those of the fundamental stars listed byMD95. The same kind of comparison was made between gravities for B-typestars. Results: .The temperatures from the computed indices are ingood agreement, within the error limits, with the literature values for4750 K ≤ T_eff ≤ 8000 K, while the gravities agree for T_eff> 9000 K. The computed Hβ indices for the Sun and for Procyonare very close to the observed values. The comparison between theobserved and computed Hβ indices as function of the observedHβ has shown a very small trend which almost completely disappearswhen only stars hotter than 10 000 K are considered. The trend due tothe cool stars is probably related with the low accuracy of thefundamental T_eff which are affected by large errors for most of thestars.
| Automatic classification of eclipsing binaries light curves using neural networks
In this work we present a system for the automatic classification of thelight curves of eclipsing binaries. This system is based on aclassification scheme that aims to separate eclipsing binary systemsaccording to their geometrical configuration in a modified version ofthe traditional classification scheme. The classification is performedby a Bayesian ensemble of neural networks trained with Hipparcos data ofseven different categories including eccentric binary systems and twotypes of pulsating light curve morphologies.
| Observational Tests and Predictive Stellar Evolution. II. Nonstandard Models
We examine contributions of second-order physical processes to theresults of stellar evolution calculations that are amenable to directobservational testing. In the first paper in the series, we establishedbaseline results using only physics that were common to modern stellarevolution codes. In this paper we establish how much of the discrepancybetween observations and baseline models is due to particular elementsof new physics in the areas of mixing, diffusion, equations of state,and opacities. We then consider the impact of the observationaluncertainties on the maximum predictive accuracy achievable by a stellarevolution code. The Sun is an optimal case because of the precise andabundant observations and the relative simplicity of the underlyingstellar physics. The standard model is capable of matching the structureof the Sun as determined by helioseismology and gross surfaceobservables to better than a percent. Given an initial mass and surfacecomposition within the observational errors, and no current observablesas additional constraints for which the models can be optimized, it isnot possible to predict the Sun's current state to better than ~7%.Convectively induced mixing in radiative regions, terrestriallycalibrated by multidimensional numerical hydrodynamic simulations,dramatically improves the predictions for radii, luminosity, and apsidalmotions of eclipsing binaries while simultaneously maintainingconsistency with observed light element depletion and turnoff ages inyoung clusters. Systematic errors in core size for models of massivebinaries disappear with more complete mixing physics, and acceptablefits are achieved for all of the binaries without calibration of freeparameters. The lack of accurate abundance determinations for binariesis now the main obstacle to improving stellar models using this type oftest.
| First-Approximation, Semianalytical Solutions of Partial Eclipsing Binaries
In this paper a simple, semianalytical method is introduced for solvingpartial eclipsing binaries, using differential observations on twodifferent colors. A matrix formulation of the problem is introduced, andthe results are evaluated by comparing them against the synthetic lightcurves generated by Wilson and Devinney's light curve (LC) computerprogram. The surface temperatures of the components are also estimatedusing color curves. Although various proximity effects are neglected inthis analytical approach, the procedure may prove useful for a rapid,first-order solution of many detached partial or total eclipsingbinaries. These first-order solutions can be improved using detailednumerical calculations such as the LC and differential correctionalgorithms.
| An Apparent Descriptive Method for Judging the Synchronization of Rotation of Binary Stars
The problem of the synchronous rotation of binary stars is judged byusing a synchronous parameter Q introduced in an apparent descriptivemethod. The synchronous parameter Q is defined as the ratio of therotational period to the orbital period. The author suggests severalapparent phenomenal descriptive methods for judging the synchronizationof rotation of binary stars. The first method is applicable when theorbital inclination is well-known. The synchronous parameter is definedby using the orbital inclination i and the observable rotationalvelocity (V1,2 sin i)M. The method is mainly suitable for eclipsingbinary stars. Several others are suggested for the cases when theorbital inclination i is unknown. The synchronous parameters are definedby using a1,2 sin i,m1,2 sin3 i, the mass function f (m) andsemi-amplitudes of the velocity curve, K1,2 given in catalogue ofparameters of spectroscopic binary systems and (V1,2 sin i)M. Thesemethods are suitable for spectroscopic binary stars including those thatshow eclipses and visual binary stars concurrently. The synchronousparameters for fifty-five components in thirty binary systems arecalculated by using several methods. The numerical results are listed inTables 1 and 2. The statistical results are listed in Table 3. Inaddition, several apparent descriptive methods are discussed.
| An Assessment of Dynamical Mass Constraints on Pre-Main-Sequence Evolutionary Tracks
We have assembled a database of stars having both masses determined frommeasured orbital dynamics and sufficient spectral and photometricinformation for their placement on a theoretical H-R diagram. Our sampleconsists of 115 low-mass (M<2.0 Msolar) stars, 27pre-main-sequence and 88 main-sequence. We use a variety of availablepre-main-sequence evolutionary calculations to test the consistency ofpredicted stellar masses with dynamically determined masses. Despitesubstantial improvements in model physics over the past decade, largesystematic discrepancies still exist between empirical and theoreticallyderived masses. For main-sequence stars, all models considered predictmasses consistent with dynamical values above 1.2 Msolar andsome models predict consistent masses at solar or slightly lower masses,but no models predict consistent masses below 0.5 Msolar,with all models systematically underpredicting such low masses by5%-20%. The failure at low masses stems from the poor match of mostmodels to the empirical main sequence below temperatures of 3800 K, atwhich molecules become the dominant source of opacity and convection isthe dominant mode of energy transport. For the pre-main-sequence samplewe find similar trends. There is generally good agreement betweenpredicted and dynamical masses above 1.2 Msolar for allmodels. Below 1.2 Msolar and down to 0.3 Msolar(the lowest mass testable), most evolutionary models systematicallyunderpredict the dynamically determined masses by 10%-30%, on average,with the Lyon group models predicting marginally consistent masses inthe mean, although with large scatter. Over all mass ranges, theusefulness of dynamical mass constraints for pre-main-sequence stars isin many cases limited by the random errors caused by poorly determinedluminosities and especially temperatures of young stars. Adopting awarmer-than-dwarf temperature scale would help reconcile the systematicpre-main-sequence offset at the lowest masses, but the case for this isnot compelling, given the similar warm offset at older ages between mostsets of tracks and the empirical main sequence. Over all age ranges, thesystematic discrepancies between track-predicted and dynamicallydetermined masses appear to be dominated by inaccuracies in thetreatment of convection and in the adopted opacities.
| Apsidal motion in eccentric eclipsing binaries: V871 Aql, V345 Lac, V401 Lac and CR Sct
About thirty new times of minimum light recorded with photoelectric orCCD photometers were obtained for several little studied eccentric-orbiteclipsing binaries V871 Aql (P=3.0°, e=0.13), V345 Lac ( 7.5°,0.46), V401 Lac ( 2.0°, 0.16) and CR Sct ( 4.2°, 0.09). TheirO-C diagrams were analyzed using all reliable timings found in theliterature and in all cases an apsidal motion was either discovered orconfirmed. The new values for the elements of the apsidal motion werederived. We find periods of apsidal motion of about 255, 7000, 79.4 and4400 years for V871 Aql, V345 Lac, V401 Lac and CR Sct, respectively.Partly based on photoelectric observations secured at the HvarObservatory, Zagreb University, Croatia.
| 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
| Times of Minima of Eclipsing Binary Systems DO Cas, V1143 Cyg, GO Cyg, and VW Cep
11 photoelectric minima are presented from the observations of 4eclipsing binaries.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| Studies of Intermediate-Mass Stellar Models Using Eclipsing Binaries
Evolutionary computations for intermediate-mass stars are analyzed usingobserved parameters for eclipsing SB2 binaries and theoreticalparameters based on evolutionary tracks. Modern observations cannot beused to distinguish between models with and without convectiveovershooting for stars in the vicinity of the main sequence.Statistically significant discrepancies between the observed andcomputed stellar parameters are associated with systematic errors inphotometric effective temperatures. After taking into account systematiceffects, the theoretical computations fit the observational datauniformly well throughout the entire mass interval studied. Empiricaland semiempirical (i.e., reduced to the ZAMS and with solar elementalabundances) formulas for the mass-luminosity, mass-effectivetemperature, and mass-radius relations are proposed.
| The Third Body in the Eclipsing System RR Lyn
Based on 70 years of published photoelectric observations, we havedetected quasi-periodic cophased oscillations of the times of theprimary and secondary minima of RR Lyn, one of the brightest and nearesteclipsing binaries in the northern sky ( ; r=74 pc). Approximating theseoscillations using the light equation yields estimates of the orbitalparameters of the third body in the system and imposes constraints onits mass, M 3. In the most probable case when the orbits of theeclipsing and triple systems are coplanar, M 3=1.10±0.02M ȯ,and the semimajor axis of the orbit A 3=17.4±3.5 AU, with asubstantial eccentricity, e 3=0.96±0.02. We have carried out adetailed study of the apsidal rotation of this eclipsing and nowmultiple system, which was suggested by Koch as a test of generalrelativity as far back as 1973. Our high-precision W BV R photoelectricphotometry &$(sigma _{obs} ≅ 0mathop mlimits_. 0032)$; has removed some contradictions. At the same time, the proximity ofthe longitude of periastron ω 180°; the close correlationbetween the jointly estimated values of ω, e and thelimb-darkening coefficients for the component disks, u 1 and u 2; andmicrofluctuations in the brightnesses of the stars prevent determinationof the rate of rotation of the elliptical orbit in the system, evenusing the most accurate measurements.
| Determination of the Ages of Close Binary Stars on the Main Sequence from Evolutionary Model Stars of Claret and Gimenez
A grid of isochrones, covering a wide range of stellar ages from thezero-age main sequence to 10 billion years, is calculated in the presentwork on the basis of the model stars of Claret and Gimenez withallowance for convective overshoot and mass loss by the components. Theages of 88 eclipsing variables on the main sequence from Andersen'scatalog and 100 chromospherically active stars from Strassmeier'scatalog are calculated with a description of the method of optimuminterpolation. Comparisons with age determinations by other authors aregiven and good agreement is established.
| Apsidal Motion in Detached Binary Stars: Comparison of Theory and Observations
A list of 62 detached binaries having reliable data on the rotation ofthe line of apsides is considered. Theoretical estimates of the rate ofapsidal motion are obtained. These estimates are compared withobservational data. It is shown that cases in which the theoreticalestimate exceeds the observed value are several times more frequent thancases in which the theoretical value is lower than the observed one.This discrepancy increases when systems with more reliable observationaldata are considered.
| On the anomaly of Balmer line profiles of A-type stars. Fundamental binary systems
In previous work, Gardiner et al. (\cite{GKS99}) found evidence for adiscrepancy between the Teff obtained from Balmer lines withthat from photometry and fundamental values for A-type stars. Aninvestigation into this anomaly is presented using Balmer line profilesof stars in binary system with fundamental values of bothTeff and log g. A revision of the fundamental parameters forbinary systems given by Smalley & Dworetsky (\cite{SD95}) is alsopresented. The Teff obtained by fitting Hα and Hβline profiles is compared to the fundamental values and those obtainedfrom uvby photometry. We find that the discrepancy found by Gardiner etal. (\cite{GKS99}) for stars in the range 7000 K <~ Teff<~ 9000 K is no longer evident. Partly based on DENIS data obtainedat the European Southern Observatory.
| New results on the apsidal-motion test to stellar structure and evolution including the effects of dynamic tides
We revised the current status of the apsidal-motion test to stellarstructure and evolution. The observational sample was increased by about50% in comparison to previous studies. Classical and relativisticsystems were analyzed simultaneously and only systems with accurateabsolute dimensions were considered. New interior models incorporatingrecent opacity tables, stellar rotation, mass loss, and moderate coreovershooting were used as theoretical tools to compare the predictedwith the observed shifts of the position of the periastron. The stellarmodels were computed for the precise observed masses and the adoptedchemical compositions are consistent with the corresponding tables ofopacities to avoid the inherent problems of interpolation in mass and in(X, Z). The derived chemical composition for each individual system wasused to infer the primordial helium content as well as a law ofenrichment. The values found are in good agreement with those obtainedfrom various independent sources. For the first time, the effects ofdynamic tides are taken into account systematically to determine thecontribution of the tidal distortion to the predicted apsidal-motionrate. The deviations between the apsidal-motion rates resulting from theclassical formula and those determined by taking into account theeffects of dynamic tides are presented as a function of the level ofsynchronism. For systems close to synchronisation, dynamic tides causedeviations with respect to the classical apsidal-motion formula due tothe effects of the compressibility of the stellar fluid. For systemswith higher rotational angular velocities, additional deviations due toresonances arise when the forcing frequencies of the dynamic tides comeinto the range of the free oscillation modes of the component stars. Theresulting comparison shows a good agreement between the observed andtheoretical apsidal-motion rates. No systematic effects in the sensethat models are less mass concentrated than real stars and nocorrelations with the evolutionary status of the systems were detected.
| Times of Minima of Eclipsing Binaries DI Herculis and V1143 Cygni
Not Available
| Age and Metallicity Estimates for Moderate-Mass Stars in Eclipsing Binaries
We estimate the ages and metallicities for the components of 43 binarysystems using a compilation of accurate observational data on eclipsingbinaries for which lines of both components are visible in theirspectra, together with two independent modern sets of stellar evolutionmodels computed for a wide range of masses and chemical abundances. Theuncertainties of the resulting values are computed, and their stabilityis demonstrated. The ages and metallicity are compared with thosederived in other studies using different methods, as well as withindependent estimates from photometric observations and observations ofclusters. These comparisons con firm the reliability of our ageestimates. The resulting metallicities depend significantly on thechoice of theoretical model. Comparison with independent estimatesfavors the estimates based on the evolutionary tracks of the Genevagroup.
| Observational Tests and Predictive Stellar Evolution
We compare 18 binary systems with precisely determined radii and massesfrom 23 to 1.1 Msolar and stellar evolution models producedwith our newly revised code TYCHO. ``Overshooting'' and rotationalmixing were suppressed in order to establish a baseline for isolatingthese and other hydrodynamic effects. Acceptable coeval fits are foundfor 16 pairs without optimizing for heavy-element or helium abundance.The precision of these tests is limited by the accuracies of theobserved effective temperatures. High-dispersion spectra and detailedatmospheric modeling should give more accurate effective temperaturesand heavy-element abundances. PV Cas, a peculiar early A system, EK CepB, a known post-T Tauri star, and RS Cha, a member of a young OBassociation, are matched by pre-main-sequence models. Predicted massloss agrees with upper limits from IUE for CW Cep A and B. Relativelypoor fits are obtained for binaries having at least one component in themass range 1.7
| The post-Newtonian effects due to rotation of stars on the variation of orbital elements of the component in binary system
The author examined continuously the post-Newtonian effects due torotation of stars on the variation of the orbital elements for thecomponent in binary system in PPN formalism. The secular and periodicperturbation effects are both given. The results show that there existonly the periodic variations in semi-major axis and eccentricity, andexist the periodic and secular variations in longitude of periastron andmean anomaly of epoch. In addition, the author applied the obtainedresults to calculate the post-Newtonian effects of rotation to sixbinary stars (EK Cep?GT Cep?NY Cep?V448 Cyg?V1143 Cyg?V451 Oph)on thevariation of the Orbital elements of components and discussed. Thenumerical results are given in Tablel-3. It shows that thepost-Newtonian effect caused by the two rapid rotating massivecomponents is not negligible.
| 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
| Estimating the ages of eclipsing variable DM-stars on the basis of the evolutionary star models by Maeder and Meynet
A set of isochrones covering a wide range of star ages from5\cdot106 to 1010 yr was built on the basis of thestellar models by A. Maeder and G. Meynet with overshooting and massloss for Population I stars with abundances (X, Y, Z) = 0.70, 0.28,0.02. The isochrones were used to compute the ages of 88 eclipsingvariable stars from the catalog by Andersen which lie on the mainsequence. The influence of initial data errors on the rezultes wasinvestigated. The ages derived are in good agreement with the results ofother authors.
| Chemical composition of eclipsing binaries: a new approach to the helium-to-metal enrichment ratio
The chemical enrichment law Y(Z) is studied by using detacheddouble-lined eclipsing binaries with accurate absolute dimensions andeffective temperatures. A sample of 50 suitable systems was collectedfrom the literature, and their effective temperatures were carefullyre-determined. The chemical composition of each of the systems wasobtained by comparison with stellar evolutionary models, under theassumption that they should fit an isochrone to the observed propertiesof the components. Evolutionary models covering a wide grid in Z and Ywere adopted for our study. An algorithm was developed for searching thebest-fitting chemical composition (and the age) for the systems, basedon the minimization of a χ2 function. The errors (andbiases) of these parameters were estimated by means of Monte Carlosimulations, with special care put on the correlations existing betweenthe errors of both components. In order to check the physicalconsistency of the results, we compared our metallicity values withempirical determinations, obtaining excellent coherence. Theindependently derived Z and Y values yielded a determination of thechemical enrichment law via weighted linear least-squares fit. Our valueof the slope, ΔY/ΔZ=2.2+/-0.8, is in good agreement withrecent results, but it has a smaller formal error and it is free ofsystematic effects. Linear extrapolation of the enrichment law to zerometals leads to an estimation of the primordial helium abundance ofYp=0.225+/-0.013, possibly affected by systematics in theeffective temperature determination.
| On the Variability of F1-F9 Luminosity Class III-V Stars
Hipparcos Satellite photometry of F1-F9 luminosity class III-V starsindicates that most are not particularly variable. A few stars for whichfurther study is desirable are identified.
| Comparison of Parallaxes from Eclipsing Binaries Method with Hipparcos Parallaxes
The parallaxes determined by Lacy (1979) by means of eclipsing binariesmethod are compared with the Hipparcos parallaxes for 19 systems. Theresidual scatter of the distance moduli inferred from eclipsing binariesmethod - after allowing for known errors as given by Lacy and Hipparcos- is equal to 0.18 mag. It decreases to 0.08 mag when obviously notfitting semi-detached systems and systems with chromospheric activity ofcomponents are removed from the sample.
| Apsidal motion in southern eccentric eclipsing binaries: YY Sgr, V523 Sgr, V1647 Sgr, V2283 Sgr and V760 Sco
Several new times of minimum light recorded with photoelectric meanshave been gathered for the early-type eccentric eclipsing binaries YYSgr (P = 2fd 63, e = 0.16), V523 Sgr (2fd 32, 0.16), V1647 Sgr (3fd 28,0.41), V2283 Sgr (3fd 47, 0.49) and V760 Sco (1fd 73, 0.03). The O - Cdiagrams are analyzed using all reliable timings found in the literatureand improved values for the elements of the apsidal motion are computed.We find more precise periods of apsidal motion of about 290, 202, 531,528 and 38.5 years for YY Sgr, V523 Sgr V1647 Sgr, V2283 Sgr and V760Sco, respectively. The corresponding internal structure constants logk_2 are derived and compared to their theoretical values. Based onobservations collected at the South Africa Astronomical Observatory,Sutherland, South Africa
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| Testing convection theories using Balmer line profiles of A, F, and G stars
We consider the effects of convection on the Balmer line profiles({H_α} and {H_β}) of A, F, and G stars. The standardmixing-length theory (MLT) atlas9 models of Kurucz (1993), with andwithout overshooting, are compared to atlas9 models based on theturbulent convection theory proposed by Canuto & Mazzitelli (1991,1992) and implemented by Kupka (1996), and the improved version of thismodel proposed by Canuto et al. (1996) also implemented by Kupka. TheBalmer line profiles are a useful tool in investigating convectionbecause they are very sensitive to the parameters of convection used inthe stellar atmosphere codes. The {H_α} and {H_β} lines areformed at different depths in the atmosphere. The {H_α} line isformed just above the convection zone. The {H_β} line, however, ispartially formed inside the convection zone. We have calculated the{T_eff} of observed stars by fitting Balmer line profiles to syntheticspectra and compared this to: (i) the {T_eff} of the fundamental stars;(ii) the {T_eff} of stars determined by the Infra-Red Flux Method and(iii) the {T_eff} determined by Geneva photometry for the stars in theHyades cluster. We find that the results from the {H_α} and{H_β} lines are different, as expected, due to the differing levelsof formation. The tests are inconclusive between three of the fourmodels; MLT with no overshooting, CM and CGM models, which all giveresults in reasonable agreement with fundamental values. The resultsindicate that for the MLT theory with no overshooting it is necessary toset the mixing length parameter alpha equal to 0.5 for stars with {T_eff<= 6000} K or {T_eff >= 7000} K. However for stars with {6000}K{<= T_eff <= 7000} K the required value for the parameter is{alpha >= 1.25}. Models with overshooting are found to be clearlydiscrepant, consistent with the results with uvby photometry by Smalley& Kupka (1997). Based on observations made at the Observatorio delRoque de los Muchachos using the Richardson-Brealey Spectrograph on the1.0m Jacobs Kapteyn Telescope.
| HIPPARCOS Parallaxes of Eclipsing Binaries and the Radiative Flux Scale
Eclipsing binaries with Hipparcos parallaxes are found to define aradiative flux relation for main-sequence stars in the B6-F0 range aboutas well as stars with angular diameters and to extend the range to F8.The fluxes of components of binaries showing large intrinsic variationsfall well below the curve for other stars and its extension to lowertemperatures. Angular diameters of main-sequence stars obtained with thenew generation of stellar interferometers should improve and extend theflux calibration. Based on data from the ESA Hipparcos satellite.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Cigno |
| Ascensione retta: | 19h38m41.20s |
| Declinazione: | +54°58'26.0" |
| Magnitudine apparente: | 5.82 |
| Distanza: | 39.809 parsec |
| Moto proprio RA: | 34.9 |
| Moto proprio Dec: | 163.4 |
| B-T magnitude: | 6.432 |
| V-T magnitude: | 5.938 |
Cataloghi e designazioni:
|
INHABITED SKY
