目录
图像
上传图像
DSS Images Other Images
相关文章
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
| Structure and evolution of FK Comae corona
FK Comae (HD 117555) is a rapidly rotating single G giant whosedistinctive characteristics include a quasisinusoidal optical lightcurve and high X-ray luminosity. FK Comae was observed twice at twoweeks interval in January 2001 by the XMM-Newton space observatory.Analysis results suggest a scenario where the corona of FK Comae isdominated by large magnetic structures similar in size tointerconnecting loops between solar active regions but significantlyhotter. The interaction of these structures themselves could explain thepermanent flaring activity on large scales that is responsible forheating FK Comae plasma to high temperatures. During our observations,these flares were not randomly distributed on the star surface but werepartly grouped within a large compact region of about 30 degree extentin longitude reminiscent of a large photospheric spot. We argue that thealpha -Omega dynamo driven activity on FK Comae will disappear in thefuture with the effect of suppressing large scale magnetic structures inits corona.
| Study of FK Comae Berenices. III. Photometry for the years 1993-2001
We present 8 years of previously unpublished photometric observations ofFK Com together with the determination of the stability of the primarycomparison star HD 117567. The observations have been carried outbetween 1993 and 2001 at four different observatories and they consistof 5157 data points in total: U(903), B(994), V(1643), R(166), I_c(573),b(461) and y(417). We also analyse this new data together with thepreviously published photometric observations. The V magnitude showsvariations with dominant periods of about 3, 6, 12, 14 and 31 years. Theshort-term light curve variations appear to be caused by rearrangementof approximately constant amount of cool spots. From the values fordifferent colours obtained during the brightest season observed,corresponding to the supposedly unspotted surface, the spectral type ofFK Com is determined to be G7 III. Based on the observations obtained atPhoenix 10, Arizona, USA; Wolfgang and Amadeus, Arizona, USA; MountMaidanak Observatory, Uzbekistan; La Palma KVA 0.6 m Cassegraintelescope, La Palma, Spain. Tables 2a-e are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http:/ /cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/374/1049
| 2000 BVR Photometry of FK Comae
Not Available
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Stars with ISM Polarization Observed with HPOL
Polarization data are given for stars whose polarizations are mostlyinterstellar which were observed for various programs with theUniversity of Wisconsin spectropolarimeter (HPOL) during 1989-1994.
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| ROSAT observations of FK comae berenices
We obtained ROSAT PSPC observations of FK Com over a period of 24.4 h,or 0.42 rotation. During the observations the x-ray flux increased by afactor of at least 5 before declining toward its previous level. Asingle temperature Raymond-Smith model is adequate to model the lowsignal-to-noise ratio spectrum from each observation interval. Initiallythe spectrum was that of a 8.5 x 106 K plasma, with L9subx)=0.66 x 1031 erg s-1. When the x-ray flux wasgreatest, the model plasma temperature rose to 2.5 x 107 K,and Lx=3.46 x 1031 ergs-1. During thepost-maximum decline in luminosity the plasma temperature wasapproximately 12 x 106 K. We conclude that the increase ofx-ray flux recorded by ROSAT was due to an x-ray flare with a 1.5 hdecline time scale.
| Collected photometry of FK Comae Berenices
New photometric observations of FK Comae Berenices are combined to thepreviously published photometry and a firm basis established for thelong--term phometric studies of this rapidly rotating late--type giant.The methods used to combine a quarter of a century of observations intoa homogeneous set of standard Johnson UBVRI photometry are presented.
| 1992 UBVRI Photometry of FK Comae
Not Available
| SPOT and flare activity of FK Comae Berenices: Long-term photometry
A quarter of a century of photometry of FK Comae Berenices is presentedand the photometric rotation period is improved to Pphot =2.4002466 d +/- 0.0000056 d. For a model with constant photometricrotation period, the concentrated part of the spot activity has remainedon two active longitudes 180 degrees apart, and a switch of the activity('flip-flop') between these two longitudes has occurred three timesduring 25 years. On the other hand, a model with varying photometricperiod gives an upper limit of 2.4% for the differential rotation. Thesetwo apparently contradictory models can be reconciled, if the source oftime dependence of the distribution of the spot activity of FK Comae isanalogous to the solar active longitudinal zones. The variation of themean brightness and the amplitude of the rotational modulation ofbrightness is not periodic, although some correlation with changes ofthe active longitudes may be present. The flaring activity seems toconcentrate on the same active longitudes, but originates predominantlyfrom the brighter hemisphere.
| UBV Photometry of FK Com during 1990
Not Available
| 1990 and 1991 UBVRI Photometry of FK Comae
Not Available
| 1988 and 1989 UBV Photometry of FK Comae
Not Available
| Kinematics and properties of F stars near the North Galactic Pole. II - The isothermal disc
Radial velocities are given for about 550 photometrically-identifieddisk-population F stars lying within 15 deg of the North Galactic Pole.The overall radial and z-velocity distributions are found to be closelyGaussian, with corrected rms and mean z velocities of 11.3 + or - 0.6and -9.5 + or - 0.5 km/s, respectively. The isothermal kinematics of thepopulation are reflected in the constant velocity dispersion to a zdistance of 400 pc. No systematic variation of either the velocitydispersion or the stellar age with the metallicity-sensitive Stromgrendelta m1 index is noted over a range of ages up to 5 Gyr.
| Radial velocity measurements. II - Ground-based observations of the program stars for the HIPPARCOS satellite
New radial velocities for 446 stars of magnitude 9.0 or brighter in 1616-sq-deg fields of the Northern Hemisphere are determined by automaticPDS measurement of 80-A/mm-dispersion spectra obtained at theObservatoire de Haute Provence using a 17-cm-diameter objective prism.The fields were selected to provide data for the input catalog of theESA Hipparcos astrometric satellite. The measurement techniques andprecision are discussed, and the results are presented in extensivetables and graphs.
| UBV photometry of stars whose positions are accurately known. IV
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..211O&db_key=AST
| Interstellar polarization from observations of A and F stars in high and intermediate galactic latitudes, and from stars in the Mathewson and Ford polarization catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986A&AS...64..487K&db_key=AST
| UBV photometry of FK Comae
UBV photometry of the peculiar star FK Comae, obtained during the periodJanuary-June 1983, is presented. The amplitude of the photometricvariation has raised with respect to the previous observations performedin 1981 and 1982, attaining about 0.18 mag in the V filter. Color curvesindicate that the star is redder at minimum light; this fact isconsistent with both the models presented to explain the properties ofFK Comae. A Fourier analysis of the light curves available in theliterature has been performed; the phases of minimum and maximum lightturn out to be noticeably stable in time. This fact is difficult to bereconciled with the hypothesis of dark spots that are observed tomigrate in other active stars. Rather, it could be explained by themodel of Walter and Basri (1982a, b), implying an extremely evolvedAlgol-type system accreting mass on its primary component.
| Photoelectric photometry of stars near the north Galactic pole. II
UBV photometric observations of about 700 stars near the north Galacticpole, obtained using single-channel photometers on the 40-cm and 60-cmCassegrain telescopes at Kvistaberg Observatory (during 1976-1983) andthe Spanish International Observatory (during 1984), respectively, aspart of a program including the stars to be observed by the Hipparcosspacecraft, are reported. The data are presented in a series of tablesand briefly characterized.
| Ultraviolet observations of circumstellar matter in Algol type binary systems
Properties of four components to the circumstellar matter in Algol typeinteracting binary systems which were investigated with the aid of timedhigh resolution IUE observations are discussed. The high temperatureaccretion region (HTAR), gas stream, restricted domains of materialoutflow, and the general wind are included. The geometrical distributionin the system, physical conditions, flow patterns, and stability arediscussed. The CX Dra serves as the illustrative example and a model forthe circumstellar matter in this system is presented.
| Light curve variations and H-alpha flaring of FK Comae
Multiband photoelectric observations reveal that the rapidly rotatinggiant FK Com's light curve is rapidly changing with respect toamplitude, shape, and light minimum phase. Analysis of the light curvesindicates that these variations are due to rotational modulation by twolarge, subluminous regions on the star's surface, which appear to beabout 800 + or - 150 K cooler than the star's photosphere. Flaringactivity in the H-alpha emission is also noted, but there is nomodulation of this emission with the 2.4-day photometric period or withany other period. This behavior is contrasted with the mechanismssuggested in the Walter and Basri (1982) model for the light variations.
| UBVRI and H-alpha photometry of FK COM
UBVRI and H-alpha photometry of FK Com during February 1983 has beenobtained. The distortion wave in the star's light curve is seen to haveincreased in amplitude and to have dramatically changed in shape sincethe previous observing season. In addition, a very energetic flare-likeevent was observed on the night of February 21/22, 1983. These data, andthe recent history of FK Com, are discussed in terms of the starspotphenomenology for stellar surface activity. In particular, modeling ofthe light curves yields a best-fit requiring two dark spots with atemperature difference between them and the surrounding photosphere of600 + or - 150 K, and a combined area of 0.26 + or - 0.06 of the stellarhemisphere.
| The photometric behavior of FK Comae Berenices
UBVRI light curves of FD Com obtained in February 1981 are presented.The light curves and two large flares on this star are investigated, andall published light curves of this object are Fourier analyzed anddiscussed in terms of the current models of this star. An improvedperiod of 2.39960 + or - 0.00015 days is also derived. It is pointed outthat both the star-spot model and the excretion-disk model are flexibleenough to account for the photometric variability. It is consideredintriguing that the mean magnitudes in all wavelengths have beendecreasing while the amplitude of variability is also decreasing. Theexpectation in a star-spot or disk model is that a decrease in theamount of variability would imply a decrease in the extent of thefeature and an increase in the magnitude of the star system.
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Four - a Catalogue of Uvbyr Photometry and Derived Quantities
Not Available
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
Not Available
| UBVRI photometry of FK Comae
The light curves in five Johnson photometry colors are given. The periodof photometric variability (2.400d) is confirmed, although somesystematic drifts of the light curves that are noticeable in less thanthree weeks also seem to be present. The flare activity is found toincrease the noise of the light curves, especially at shorterwavelengths. It is noted that the light variation of about 0.08 in V canbe explained by a longitudinally asymmetric region of dark spotscovering no less than 10% of the hemisphere; here, the temperaturedifference relative to the photosphere is of the order of 500-800 K. Thevariations of individual colors, however, are not consistent with aunique value of that difference. The V-R and R-I colors at maximumsuggest an effective temperature of about 4900 K, which agrees with thelow-temperature end in the range of existing spectral classifications.
| UVBY beta photometry of 210 B, A, and F stars in ten areas centered on extragalactic radio sources at high northern galactic latitudes
As part of a study of the reddening properties of the interstellarmedium at the South Galactic pole and particularly along the southernpart of the galactic plane, a catalog of ubvy beta photometry of 210 B,A, and F stars in 10 areas of equal size covering 160 sq deg atlatitudes higher than +30 deg is presented. Each of the observed areasis centered at radio sources that have emission or absorption in the21-cm line; and the main aim of the study is to obtain color excessesfor a comparison of neutral hydrogen column densities, tentativelyassociated with distinct clouds and with the occurrence of dust in theseclouds. V, (b-y), m1, c1, and beta are presented for the 210 stars.
| Visual multiples. VII - MK classifications
Classifications are given for 865 components of visual multiples; theyshow no systematic differences from the MK system, and the random errorsare one subclass in type and two-thirds of a luminosity class. It isfound that at least 1% of the F-type IV and V stars are weak-lined, 32%of the A4-F1 IV and V stars are Am, and 5% of the A0-A3 IV and V starsare early-type Am. Attention is called to the large fraction (55%) ofthe A3-A9 III-V stars that are of luminosity classes III or IV, unlikethe percentage (16%) at neighboring types.
| Magnitudes and colors for 833 Northern and Southern stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955AJ.....60...65E&db_key=AST
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
