Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
The Ca II infrared triplet as a stellar activity diagnostic. II. Test and calibration with high resolution observations
Aims.We report on our analysis of the high resolution spectra (R≈86000) of a sample of 42 late-type active stars (with measured{log{R'_HK}} spanning from ≈{ -}3 to ≈{ -}5) acquired with theItalian 3.6 m Telescopio Nazionale Galileo (TNG) using the SARGspectrometer in the 4960-10 110 Å range. The high quality of thespectra and the good activity-level coverage allow us to measure twodifferent chromospheric indicators that can be derived from the Ca iiinfrared triplet (Ca ii IRT) lines: the residual equivalent width (EQW)and the chromospheric indicator {R_IRT}. The aim of this work isdetermine and test the best way of deriving activity-level informationand errors from the Ca ii IRT lines, in preparation of the GAIACornerstone mission by ESA, by which the Ca ii IRT spectral range willbe spectroscopically observed for millions of stars. Methods: The{R_IRT} index is calculated for each observed star as the differencebetween the calculated NLTE photospheric central intensity and theobserved one. The residual EQW, {Δ W_IRT}, is calculated as thearea of the positive profile obtained as the difference between thecalculated NLTE photospheric and the observed profiles. We correlate{log{R'_HK}} with {R_IRT} and the {Δ W_IRT}. Results: Thisanalysis indicates that Ca ii IRT lines are good chromosphericdiagnostics. We find that both {Δ W_IRT} and the {R_IRT}quantities can be used as chromospheric indicators, although the formerexhibits a tighter correlation with the {log{R'_HK}} index. Furthermore,we find that the total chromospheric excess EQW in the Ca ii IRT isalmost linearly correlated with the excess in the Ca ii H & Kdoublet, as estimated through the {log{R'_HK}} index.Based on observations made with the Italian Telescopio Nazionale Galileo(TNG) operated on the island of La Palma by the Centro Galileo Galileiof the Consorzio Nazionale per l'Astronomia e l'Astrofisica at theSpanish Observatorio del Roque de los Muchachos of the Instituto deAstrofísica de Canarias. Table 4 is only available in electronicform at http://www.aanda.org
| Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars
Aims.We study the kinematic structure of peripheral areas of the UrsaMajoris stream (Sirius supercluster). Methods.We use diagrams ofindividual stellar apexes developed by us and the classical technique ofproper motion diagrams generalized to a star sample distributed over thesky. Results.Out of 128 cluster members we have identified threecorona (sub)structures comprised of 13, 13 and 8 stars. Thesubstructures have a spatial extension comparable to the size of thecorona. Kinematically, these groups are distinguished by their propermotions, radial velocities and by the directions of their spatialmotion. Coordinates of their apexes significantly differ from those ofthe apexes of the stream and its nucleus. Our analysis shows that thesesubstructures do not belong to known kinematic groups, such as Hyades orCastor. We find kinematic inhomogeneity of the corona of the UMa stream.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| 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
| Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group
Utilizing Hipparcos parallaxes, original radial velocities and recentliterature values, new Ca II H and K emission measurements,literature-based abundance estimates, and updated photometry (includingrecent resolved measurements of close doubles), we revisit the UrsaMajor moving group membership status of some 220 stars to produce afinal clean list of nearly 60 assured members, based on kinematic andphotometric criteria. Scatter in the velocity dispersions and H-Rdiagram is correlated with trial activity-based membership assignments,indicating the usefulness of criteria based on photometric andchromospheric emission to examine membership. Closer inspection,however, shows that activity is considerably more robust at excludingmembership, failing to do so only for <=15% of objects, perhapsconsiderably less. Our UMa members demonstrate nonzero vertex deviationin the Bottlinger diagram, behavior seen in older and recent studies ofnearby young disk stars and perhaps related to Galactic spiralstructure. Comparison of isochrones and our final UMa group membersindicates an age of 500+/-100 Myr, some 200 Myr older than thecanonically quoted UMa age. Our UMa kinematic/photometric members' meanchromospheric emission levels, rotational velocities, and scattertherein are indistinguishable from values in the Hyades and smaller thanthose evinced by members of the younger Pleiades and M34 clusters,suggesting these characteristics decline rapidly with age over 200-500Myr. None of our UMa members demonstrate inordinately low absolutevalues of chromospheric emission, but several may show residual fluxes afactor of >=2 below a Hyades-defined lower envelope. If one defines aMaunder-like minimum in a relative sense, then the UMa results maysuggest that solar-type stars spend 10% of their entire main-sequencelives in periods of precipitously low activity, which is consistent withestimates from older field stars. As related asides, we note six evolvedstars (among our UMa nonmembers) with distinctive kinematics that liealong a 2 Gyr isochrone and appear to be late-type counterparts to diskF stars defining intermediate-age star streams in previous studies,identify a small number of potentially very young but isolated fieldstars, note that active stars (whether UMa members or not) in our samplelie very close to the solar composition zero-age main sequence, unlikeHipparcos-based positions in the H-R diagram of Pleiades dwarfs, andargue that some extant transformations of activity indices are notadequate for cool dwarfs, for which Ca II infrared triplet emissionseems to be a better proxy than Hα-based values for Ca II H and Kindices.
| The Vienna-KPNO search for Doppler-imaging candidate stars. I. A catalog of stellar-activity indicators for 1058 late-type Hipparcos stars
We present the results from a spectroscopic Ca ii H&K survey of 1058late-type stars selected from a color-limited subsample of the Hipparcoscatalog. Out of these 1058 stars, 371 stars were found to showsignificant H&K emission, most of them previously unknown; 23% withstrong emission, 36% with moderate emission, and 41% with weak emission.These spectra are used to determine absolute H&K emission-linefluxes, radial velocities, and equivalent widths of theluminosity-sensitive Sr ii line at 4077 Ä. Red-wavelengthspectroscopic and Strömgren y photometric follow-up observations ofthe 371 stars with H&K emission are used to additionally determinethe absolute Hα -core flux, the lithium abundance from the Li i6708 Å equivalent width, the rotational velocity vsin i, theradial velocity, and the light variations and its periodicity. Thelatter is interpreted as the stellar rotation period due to aninhomogeneous surface brightness distribution. 156 stars were found withphotometric periods between 0.29 and 64 days, 11 additional systemsshowed quasi-periodic variations possibly in excess of ~50 days. Further54 stars had variations but no unique period was found, and four starswere essentially constant. Altogether, 170 new variable stars werediscovered. Additionally, we found 17 new SB1 (plus 16 new candidates)and 19 new SB2 systems, as well as one definite and two possible new SB3systems. Finally, we present a list of 21 stars that we think are mostsuitable candidates for a detailed study with the Doppler-imagingtechnique. Tables A1--A3 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Einstein Extended Medium-Sensitivity Survey Second Epoch: Results for the Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..701F&db_key=AST
| The space density of active binaries from X-ray surveys.
We review the currently available data on active binaries selected fromEinstein observatory based X-ray surveys, and compare the inferred spacedensity with the available estimates based on optically selectedsamples. It is shown that, in contrast to previous reports, nodisagreement is present between the optical and X-ray based estimates,and that the space density of active binaries is likely to be smallerthan previous estimates based on X-ray selected data. In particular, weshow that of the 18 systems in the δ>-20deg subsample of theEinstein Extended Medium Sensitivity Survey previously classified asactive binaries, 6 are not to be considered as such, while a further 5have a somewhat doubtful status. The total space density we derive is7.7x10^-5^pc^-3^ if the 5 doubtful systems are retained and3.7x10^-5^pc^-3^ if they are excluded. Both values are substantiallylower than the value of 4.5x10^-4^pc^-3^ originally derived from thesame subsample of Extended Medium Sensitivity Survey fields. Also, themedian X-ray luminosity of X-ray selected active binaries is found to behigher than previously reported, and again in contrast with previousreports, we find no disagreement between the X-ray luminosities of X-rayand optically selected samples. We briefly discuss the implication ofthe revised value of the space density on the contribution of activebinaries to the soft X-ray background.
| Chromospheric activity in G and K giants: the spectroscopic data base
I present high-resolution CCD spectra of CaII H and K emission lines of59 evolved stars of spectral type G and K and luminosity Class III,III-IV, and IV. This includes active stars like RS CVn binaries but alsoactive and inactive single stars. Most of the objects were observed forthe first time and several were discovered to be chromosphericallyactive. Spectra for ten stars of luminosity Class V are also given.
| Chromospheric activity in G and K giants and their rotation-activity relation
We obtained high-resolution CCD spectra of Ca II H and K emission linesof 59 evolved stars of spectral type G and K and luminosity class III,III-IV, and IV. Our sample includes active stars like RS CVn binariesbut also active and inactive single stars. Whenever possible wedetermine absolute emission line surface fluxes and use them,supplemented by previously published fluxes from high-resolutionspectra, to quantify the rotation-activity relation for evolved stars.We find that the Ca II surface fluxes from evolved stars scale linearlywith stellar rotational velocity and that the flux from the cooler starsdepends stronger upon rotation than the flux from the hotter stars, inagreement with previous findings for main-sequence stars. However, largescatter indicates that rotational velocity might not be the onlyrelevant parameter. We also present some evidence for the existence of a'basal' flux for evolved stars that scales approximately with the eightpower of the effective surface temperature.
| The ROSAT All-Sky Survey of active binary coronae. I - Quiescent fluxes for the RS Canum Venaticorum systems
One hundred and thirty-six RS CV(n) active binary systems were observedwith the ROSAT Position Sensitive Proportional Counter (PSPC) during theAll-Sky Survey component of the mission. The entire sky was surveyed,which represents the largest sample of RS CV(n) systems observed to dateat any wavelength, including X-rays. X-ray surface fluxes for the RSCV(n) systems are found to lie in the range 10 exp 4 to 10 exp 8 ergs/sqcm seconds. Surface flux as a function of (B - V) color is reported. Adecrease in surface flux with increasing rotation period for the entiresample is observed. The rotation period provides the best stellar ororbital parameter to predict the X-ray surface flux level. The absenceof correlation of F(x) or L(x) with Gamma is noted due to the fact thatthe coronal heating mechanism for these active stars must be magnetic incharacter, and the magnetic field depends on the interaction betweenconvection and differential rotation inside the star. X-ray propertiesof the RS CV(n) systems with 6 cm radio and C IV UV emission systems iscompared.
| The Einstein Observatory Extended Medium-Sensitivity Survey. II - The optical identifications
The optical identifications are presented of the Einstein ExtendedMedium-Sensitivity Survey (EMSS), including the methodology used tooptically identify the EMSS sources and the uncertainties involved withthat process. The optical properties of the classes of X-ray, optical,and radio data for each of the identified and, as yet, unidentifiedsources of the survey are described. A new class of X-ray emitters,cooling flow galaxies, is proposed. The criteria used to determinewhether the proposed optical counterpart to the X-ray source is aplausible identification are described. Plausibility is based on theoptical classification of the counterpart, e.g., AGN, cluster, G star,and the X-ray-to-optical flux ratios previously observed for theseclasses of X-ray emitters. Two independent schemes of opticalclassification of the counterparts are used to check the plausibility ofthese identifications; one is based on moderate-resolution opticalspectroscopy, and the other, on inferred X-ray luminosity and theoverall energy distribution.
| The Einstein Observatory Extended Medium-Sensitivity Survey. I - X-ray data and analysis
This paper presents the results of the analysis of the X-ray data andthe optical identification for the Einstein Observatory ExtendedMedium-Sensitivity Survey (EMSS). The survey consists of 835serendipitous sources detected at or above 4 times the rms level in 1435imaging proportional counter fields with centers located away from theGalactic plane. Their limiting sensitivities are about (5-300) x 10 tothe -14th ergs/sq cm sec in the 0.3-3.5-keV energy band. A total area of778 square deg of the high-Galactic-latitude sky has been covered. Thedata have been analyzed using the REV1 processing system, which takesinto account the nonuniformities of the detector. The resulting EMSScatalog of X-ray sources is a flux-limited and homogeneous sample ofastronomical objects that can be used for statistical studies.
| X-ray-selected candidates for the RS CVn and W UMa classes of binary stars
X-ray luminosity, spectral type, radial-velocity variation, rotationallybroadened line profile, and Ca II H and K line emission data are used toidentify 12 new candidates for the RS CVn class and seven new candidatesfor the W UMa class from spectroscopic binaries which are contained inthe Einstein Extended Medium Sensitivity Survey. Under the assumptionthat the candidates are genuine members of each class, local spacedensity estimates of 4.47 + or - 1.19 x 10 to the -4th/cu pc for RS CVnbinaries and 8.47 + or - 3.00 x 10 to the -5th/cu pc for W UMa binariesare found. Although the density estimate for the W UMa binaries is shownto be consistent with previous estimates obtained from opticallyselected samples, the estimate for the RS CVn binaries is more than anorder of magnitude greater than previously determined space densities.
| The relation between X-ray emission and rotation in late-type stars from the perspective of X-ray selection
An X-ray-selected sample of 128 late-type (F-M) stars analyzed. Thesestars were identified as optical counterparts to serendipitous X-raydetections made by the Einstein Observatory Extended Medium SensitivitySurvey. Once identified as X-ray sources, the sample was followed up byan extensive program of optical observations, including high-resolutionand low-resolution spectroscopy and photometry. Spectral types,luminosity classes, distances, X-ray luminosities, projected rotationrates (v sin i), radial velocities, and binary status have beendetermined for the sample.
| Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Волар |
| Ректацензија: | 14h42m00.71s |
| Deклинација: | +52°00'19.1" |
| Apparent магнитуда: | 7.549 |
| Даљина: | 68.074 parsecs |
| Proper motion RA: | 11.1 |
| Proper motion Dec: | 4.2 |
| B-T magnitude: | 8.008 |
| V-T magnitude: | 7.587 |
Каталог и designations:
|
