Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
A new Böhm-Vitense gap in the temperature range 5560 to 5610 K in the main sequence hm-Vitense gap in the main sequence
Highly precise temperatures (σ = 10-15 K) have been determinedfrom line depth ratios for a set of 248 F-K field dwarfs of about solarmetallicity (-0.5 < [Fe/H] < +0.4), based on high resolution (R=42000), high S/N echelle spectra. A new gap has been discovered in thedistribution of stars on the Main Sequence in the temperature range 5560to 5610 K. This gap coincides with a jump in the microturbulent velocityVt and the well-known Li depression near 5600 K in fielddwarfs and open clusters. As the principal cause of the observeddiscontinuities in stellar properties we propose the penetration of theconvective zone into the inner layers of stars slightly less massivethan the Sun and related to it, a change in the temperature gradient.Based on spectra collected with the ELODIE spectrograph at the 1.93-mtelescope of the Observatoire de Haute-Provence (France).Full Table 1 is only available in electronic form athttp://www.edpsciences.org
| 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
| Near-Infrared Line Observations of Arp 299 as a Tracer of Activity in the Nuclei
We have obtained images of the molecular hydrogen (H2) andBrγ emission lines in the interacting galaxy system Arp 299. Inorder to investigate the nuclear activities, we also have obtained H-and K-band spectra for three of its 2 μm continuum peaks and alsoJ-band spectra for one of them. From the line ratios of Paγ,Paβ, Br10, and Brγ, and also those between [Fe II] 1.26 μmand [Fe II] 1.64 μm, we have successfully modeled the extinction forcomponent A as a combination of AK=2.6 mag region(s) andAK=0.3 mag region(s). The extinction corrected Brγluminosity requires 5x1054 s-1 of Lyman photons,which corresponds to 3x105 ``O6 stars.'' The mean stellardensity within its 100 pc core is comparable to those for the cores inblue compact dwarf galaxies even though the luminosity is almost 2orders of magnitude larger. The starbursts at the nucleus of component Aare probably the most dominant source for the far-infrared emission fromthis component. In this component, we have found large [Fe II]/H Iratios, which are at the higher end of starburst galaxies and aretypical for AGNs or AGN/starburst composites. The nucleus must be in astarburst phase that includes many supernova remnants. The spatialdistribution of the H2 emission for this interacting systemis similar to that of the 12CO 1-0 emission mapped by Aaltoet al. The H2 intensity, however, is not proportional to theCO intensity among components, because of the difference in theH2 excitation mechanism among them. We report the firstpossible detection of J-band H2 lines in infrared luminousgalaxies in component A, which suggests a significant contribution ofnonthermal excitation mechanisms.
| IRAS F10214+4724: the inner 100pc
We use new high-resolution near-infrared spectroscopy and our previouslypublished optical spectroscopy of the gravitationally lensed Seyfert 2galaxy F10214+4724 to study both the links between the starburst and AGNin this object and the properties of the line-emitting clouds in theinner narrow-line region. Close inspection of the rest frame UV spectrumreveals interstellar or stellar absorption features consistent with acompact, moderately reddened starburst providing about half the UVlight, and explaining the dilution of the UV continuum polarizationrelative to the broad emission lines. Spectroscopy of the Hα/[Nii]line blend has enabled us to assess the relative contributions of theemission from the narrow-line region of the Seyfert 2, and a moderatelyreddened emission-line region which we argue is associated with thestarburst activity. Estimates of the star formation rate from theunpolarized UV continuum flux and the Hα flux are consistent towithin their associated uncertainties. We find we can plausibly explainthe unusual emission-line properties of F10214+4724 in terms ofconventional models for nearby Seyfert 2 galaxies if lensing ispreferentially magnifying the side of the inner narrow-line regionbetween the AGN and the observer, and the other side is both lessmagnified and partially obscured by the torus. The hydrogen densities ofclouds in this region are high enough to make the Balmer lines opticallythick and to suppress forbidden emission lines with low criticaldensities. From the emission-line spectrum we have deduced the columndensity of both ionized and neutral gas in the narrow-line clouds, andthe density of the ionized gas. Using these we have been able toestimate the mass of the inner narrow-line clouds to be ~1M, and showthat the gas:dust ratio N_H/E(B-V) in these clouds must be~1.3x10^27m^-2mag^-1, significantly higher than the average value in theMilky Way, ~4.5x10^25m^-2mag^-1. The column density and low dust contentof a typical cloud are consistent with the properties of the warmabsorbers seen in the X-ray spectra of Seyfert 1 galaxies. Our resultsthus favour models in which the narrow-line clouds start life close tothe nucleus and flow out. An emission line from the lensing system hasallowed us to confirm its redshift as z~0.9.
| 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.
| Photometric surveys of suspected small-amplitude red variables. 3: an AAVSO photometric photometry survey
We have carried out a survey of the photometric (V) variability of 61'known' or suspected small-amplitude red variables, mostly M giants.Approximately two-thirds appear to be variable; several suspectedvariable comparison stars have also been identified. The incidence andaverage amplitude of variability increase rapidly from spectral type M0III to M6 III.
| ICCD speckle observations of binary stars. IV - Measurements during 1986-1988 from the Kitt Peak 4 M telescope
One thousand five hundred and fifty measurements of 1006 binary starsystems observed mostly during 1986 through mid-1988 by means of speckleinterferometry with the KPNO 4-m telescope are presented. Twenty-onesystems are directly resolved for the first time, including newcomponents to the cool supergiant Alpha Her A and the Pleiades shellstar Pleione. A continuing survey of The Bright Star Catalogue yieldedeight new binaries from 293 bright stars observed. Corrections tospeckle measures from the GSU/CHARA ICCD speckle camera previouslypublished are presented and discussed.
| MK spectral types for some F and G stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979PASP...91...83C&db_key=AST
| 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.
| Spectral classification of the bright F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88...95C&db_key=AST
| Lithium abundance in stellar atmospheres
Data on the lithium abundance in the atmospheres of 491 stars arecompiled and reduced to a single system. The lithium abundances of thesestars are shown to differ by more than a factor of 1 million, and thedependence of lithium abundance on spectral type is determined forvarious groups of stars. It is found that cooler stars have lowerlithium abundances than hotter stars and that young stars have higherabundances than old stars. Data on the Li-6/Li-7 isotope ratio in theatmospheres of 30 stars are presented which indicate that Li-6 is notobserved in most cases and that the exceptions comprise magneticvariable stars with Li-6/Li-7 ratios of 0.10 to 2.00. It is concludedthat the observational results as a whole are satisfactorily explainedby the hypothesis that the same high lithium abundance characterized allstars at birth but then decreased in the course of evolution due tointermixing of matter.
| Photoelectric UBV observations made on the Palomar 20-inch telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.164..133P&db_key=AST
| 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
| A catalogue of four-color photometry of late F-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969AJ.....74..705P&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
| The Strength of the li i Line in the Spectra of Main-Sequence f- and G-Type Stars.
Not Available
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Велики медвед |
| Ректацензија: | 10h20m14.80s |
| Deклинација: | +53°46'45.0" |
| Apparent магнитуда: | 6.45 |
| Даљина: | 30.581 parsecs |
| Proper motion RA: | -86.2 |
| Proper motion Dec: | 49.3 |
| B-T magnitude: | 7.145 |
| V-T magnitude: | 6.519 |
Каталог и designations:
|
