Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 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/394/927
| Time series analysis of V511 Lyrae photometry
Our time series analysis of sixteen BV light curves of thechromospherically active binary V511 Lyr confirmed the 2fd7 rotationperiod uniquely. The seasonal periodicity changes of 3.8% indicated thepresence of detectable surface differential rotation. The significant2fd67455 periodicity in the light curve minimum epochs suggested thatthe strongest starspot formation in V511 Lyr was concentrated on onestable active longitude. Table 2 is only available in electronic form atthe CDS via anonymous ftp to cdarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A&A/383/197. Thephotometric data are also available athttp://schwab.tsuniv.edu/t3/v511lyr/v511lyr.html
| 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
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| Library of high and mid-resolution spectra in the CA II H & K, Hα, Hβ NA i D1, D2, and He i D3 line regions of F, G, K and M field stars
In this work we present spectroscopic observations centered in thespectral lines most widely used as optical indicators of chromosphericactivity (Hα, Hβ, Ca ii H & K, and He i D3) ina sample of F, G, K and M chromospherically inactive stars. The spectrahave been obtained with the aim of providing a library of high andmid-resolution spectra to be used in the application of the spectralsubtraction technique to obtain the active-chromosphere contribution tothese lines in chromospherically active single and binary stars. Thislibrary can also be used for spectral classification purposes. A digitalversion with all the spectra is available via ftp and the World Wide Web(WWW) in both ASCII and FITS formats. Based on observations made withthe Isaac Newton telescope and the William Herschel Telescope operatedon the island of La Palma by the Royal Greenwich Observatory at theSpanish Observatorio del Roque de Los Muchachos of the Instituto deAstrofisica de Canarias, and with the 2.2 m telescope of the CentroAstronomico Hispano-Aleman of Calar Alto (Almeria, Spain) operatedjointly by the Max Planck Institut fur Astronomie (Heidelberg) and theSpanish Comision Nacional de Astronomia. The spectra of the stars listedin Table \protect\ref{tab:par} are also available in electronic form atthe CDS via anonymous ftp to cdsarc.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.
| Narrow-band photometry of late-type stars. II
This paper presents extensive narrow-band photometry in the Uppsalasystem supplementing earlier published mesurements so that data now areavailable for all late-type stars brighter than V = 6.05 and a number ofgalactic cluster members. Numerous UBV and BV measurements are alsopublished. The data are used to determine relations for the predictionof UBV intrinsic colors for late-type stars from the narrow-bandmeasurements. The main purpose of the data is to constitute the basisfor the determination of solar-neighborhood space densities of late-typestars, mainly giants of different kinds; these space densities will becombined with narrow-band data for fainter stars in the north Galacticpole region to yield the decrease of space density with distance fromthe galactic plane for many kinds of late-type stars.
| Intercontinental simultaneous survey of the unique cepheid HR 7308 in photometry and radial velocity
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1986A&A...168..139B&db_key=AST
| Physical parameters and pulsational mode of short-period small-amplitude Cepheids
Nine galactic short-period (P less than 8 days) small-amplitude Cepheidshave been the subject of a study to determine their physical parametersand pulsational properties. UBVRI photometry and radial velocities wereobtained in the same observing seasons. The wings of H-alpha were usedto determine effective temperatures. Empirical radii, luminosities, andmasses were determined. The short-period stars lie inside and seem to beon the red side of the observational Cepheid instability strip. It wasfound that these stars are likely pulsating in the radial fundamentalmode except HR 8084 (DT Cyg) which is suspected to be a first overtonepulsator. As the small-amplitude Cepheids in the LMC are thought to befirst overtone pulsators, it is suggested that small-amplitudesinusoidal variations are not the consequence of pulsation in the firstovertone, but rather the response to a more general amplitude trendacross the instability strip in a particular galactic system.
| The intermediate and narrow band photoelectric studies of some delta Scuti stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983RMxAA...5..261I&db_key=AST
| UBVRI photometry of HR 7308
The star HR7308 (HD180583) is the shortest-period classical Cepheidknown. It is also unique (so far as it is currently known) in having avariable amplitude. A description is presented of UBVRI photometry (allon the Johnson system) of HR7308 obtained during the second half of1981. The data are used to derive interstellar reddening and, byapplication of the surface brightness technique of Barnes et al. (1977),to derive a distance, radius, and absolute magnitude for the star. Allobservations reported were obtained with a 0.5-m reflector equipped witha standard photon-counting photometer.
| Ultraviolet and optical studies of binaries with luminous cool primaries and hot companions. II - BVRI observations
Johnson system BVRI measurements are presented for 117 stars, most ofthem with no previous R and I photometry and many with no previous B andV. The prime objects for measurement are unresolved or nearly unresolvedbinaries containing a late-type giant or supergiant and an early-typecompanion. Other objects on the program include suspected binaries andother F-G giants and supergiants lacking at least R and I magnitudes.The variable F and G supergiants 1 Mon, 89 Her, HR 7308, HR 8157, HR8752, and rho-Cas and the eclipsing systems W Ser and ST Aqr wereobserved; HR 8752 showed significant dimming and cooling over 125 days.Several of Halliwell's (1979) candidates for nearby stars were measured.
| 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.
| I.A.U. Archives of Unpublished Observations of Variable Stars - 1979-1981 Data
Not Available
| The unusual Cepheid HR 7308 with a variable amplitude
HR 7308 is a classical Cepheid with the shortest known period.Photoelectric observations taken during 1966-1969 are presented andcombined with recent work. The primary period of oscillation is found tobe 1.49077 + or - 0.00001d, somewhat shorter than the previouslypublished period. The amplitude of HR 7308 varies by over a factor of 5with a period of about 1210d. An alternate period of 955d cannot beexcluded due to the 1970-1977 gap in observations. Except for thevariable amplitude, no secondary periods can be found in the data. The0.71 period ratio, commonly found in short-period Cepheids, is absent.Various models utilizing two close periods have been used (leading toamplitude variations and phase jitter of the primary oscillation) aswell as models of variable amplitudes superposed on a constantoscillation.
| HR 7308 - A unique Cepheid
Forty-four photometric observations and nine radial velocities of theF6I-IIb star HR7308 were obtained. The spectral type, the period, andthe relative range and phase of light, color, and velocity variationssuggest that the star is a small-amplitude Cepheid. The metal abundanceappears to be normal. However, the light amplitude decreased slowlyduring 1978 and increased slightly during 1979. Such behavior isunprecedented in a Population I Cepheid.
| 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.
| Rotation of evolving A and F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&A....18..428D&db_key=AST
| Short-Period Variability of b, a, and F Stars. III. a Survey of Delta Scuti Variable Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJS...19...79B&db_key=AST
| MK classifications for F and G-type stars. I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..916H&db_key=AST
| Short-period variability of B, A and F stars. II. Photometry of new delta Scuti stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..166B&db_key=AST
| UBV and narrow-band UVBY photometry of bright stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73...84B&db_key=AST
| Studies of Stellar Rotation. V. The Dependence of Rotation on Age among Solar-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...150..551K&db_key=AST
| Stellar Convection Zones, Chromospheres, and Rotation
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1966ApJ...144..695W&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Calgi |
| Sað Açýklýk: | 19h11m30.90s |
| Yükselim: | +26°44'09.0" |
| Görünürdeki Parlaklýk: | 6.36 |
| Uzaklýk: | 43.103 parsek |
| özdevim Sað Açýklýk: | 32.2 |
| özdevim Yükselim: | -32.2 |
| B-T magnitude: | 6.839 |
| V-T magnitude: | 6.386 |
Kataloglar ve belirtme:
|
INHABITED SKY
