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מאמרים קשורים
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.
| Study of the optical variability of T Tau in the period 1962 2003
We present the results of our long-term U BV R observations of the starT Tauri performed at Mt. Maidanak Observatory from 1986 until 2003.These data, together with previous photoelectric observations of otherauthors, suggest that the long-term variations of the light curve arenot periodic, but have a cycle with a time scale of 6 9 yr. The lightcurve also exhibits slower variations with time scales of 30 40 yr.We confirm the existence of periodic brightness variations with a periodof over many years; this process is peculiar in that the phase and shapeof the phase curve change from season to season. We analyze the colorbehavior of the star. We found evidence of a strong flare occurred onOctober 5, 1999, when the brightness of the star reached . This is thestrongest flare recorded during its photoelectric observations.
| 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
| No Fossil Disk in the T Tauri Multiple System V773 Tauri
We present new multiepoch near-infrared (NIR) and optical high angularresolution images of the V773 Tau pre-main-sequence triple system, aweak-line T Tauri star (WTTS) system in which the presence of anevolved, ``fossil'' protoplanetary disk has been inferred on the basisof a significant IR excess. Our images reveal a fourth object bound tothe system, V773 Tau D. While it is much fainter than all othercomponents at 2 μm, it is the brightest source in the system at 4.7μm. We also present medium-resolution K-band adaptive opticsspectroscopy of this object, which is featureless with the exception ofa weak Brγ emission line. Based on this spectrum and on thespectral energy distribution (SED) of the system, we show that V773 TauD is another member of the small class of ``infrared companions'' (IRCs)to T Tauri stars (TTSs). It is the least luminous, and probably theleast massive, component of the system, as opposed to most other IRCs,which suggests that numerous low-luminosity IRCs such as V773 Tau D maystill remain to be discovered. Furthermore, it is the source of thestrong IR excess in the system. We therefore reject the interpretationof this excess as the signature of a fossil (or ``passive'') disk andfurther suggest that these systems may be much less frequent thanpreviously thought. We further show that V773 Tau C is a variableclassical TTS (CTTS) and that its motion provides a well-constrainedorbital model. We show that V773 Tau D can be dynamically stable withinthis quadruple system if its orbit is highly inclined. Finally, V773 Tauis the first multiple system to display such a variety of evolutionarystates (WTTS, CTTS, IRC), which may be the consequence of the strongstar-star interactions in this compact quadruple system.
| Adaptive Optics Imaging of the Circumbinary Disk around the T Tauri Binary UY Aurigae: Estimates of the Binary Mass and Circumbinary Dust Grain Size Distribution
We have obtained high-resolution (FWHM = 0."15) deep images of the UYAur binary at J, H, and K' with the University of Hawaii adaptive opticsinstrument. We clearly detect an R ~ 500 AU circumbinary disk discoveredwith millimeter interferometry, making UY Aur the second young binarywith a confirmed circumbinary disk. It appears that the disk is inclined~42 deg from face on. We find that the near side of the disk is brighterthan the far side by factors of 2.6, 2.7, and 6.5 times at K', H, and J,respectively. The original GG Tau circumbinary disk has been reexaminedand is found to have similar flux ratios of 1.5, 2.6, and 3.6 at K', H,and J, respectively. A realistic power-law distribution (p = 4.7) ofspherical dust aggregates (composed of silicates, amorphous carbon, andgraphite) that reproduces the observed ISM extinction curve alsopredicts these observed flux ratios from Mie scattering theory. We findthe observed preference of forward-scattering over back-scattering iswell fitted (global chi 2 minimization) by Mie scattering off particlesin the range amin = 0.03 mu m to amax = 0.5-0.6 mu m. The existence of asignificant population of grain radii larger than 0.6 mu m is notsupported by the scattering observations. Based on the observed diskinclination we derive an orbit for UY Aur where the mass for the binaryis 1.6^{+0.47}_{-0.67} Mȯ. Based on the observed K7 and M0 spectraltypes for UY Aur A and B, accretion disk models for the inner disksaround the central stars were constructed. The models suggest that small(lower limit R ~ 5-10 AU) inner disks exist around B and A. It appearsthat B is accreting ~5 times faster than A, and that both inner disksmay be exhausted in ~102-103 yr without replenishment from the outercircumbinary disk. Our images suggest that these inner disks may indeedbe resupplied with material through thin streamers of material thatpenetrate inside the circumbinary disk. Currently it appears that such astreamer may be a close to UY Aur B. Comparison of our IR images and themillimeter images of the gas clearly show that the dust seen in our IRimages traces the gas in the circumbinary disk, as was also the casewith GG Tau.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| The Hα environment of T Tauri resolved by speckle interferometry.
T Tauri, the prototype of a class of low-mass pre-main sequence stars,was observed with the 3.6m Canada-France-Hawaii telescope (CFHT) and theCP40 photon-counting camera in November 1989. The data have beenanalysed using techniques of Speckle Interferometry to obtaindiffraction-limited information on the spatial extent of T Tauri innarrow passbands centered on the Hα line and the nearby redcontinuum. The object appears unresolved in the continuum passband,while it is resolved in Hα. The Hα emission is fitted with amodel consisting of two strongly flattened two-dimensional gaussians. Inthis model ~80% of the flux lies in a component (A) which is onlymarginally resolved, and ~20% lies in a component (B) with a semi-majoraxis FWHM of ~0.09". After subtraction of continuum, 2/3 of the Hαemission is spatially unresolved and 1/3 is resolved. The position angleof component B is 192deg+/-5deg, which approximates the direction of theperpendicular to the jet known in the [OI] and [SII] lines; this jetextends 30" westwards up to the Herbig-Haro object HH1555. Thecorresponding linear size of the Hα emitting region B is ~6 by15AU FWHM assuming a distance of T Tauri of d=140pc. We argue that thisemission arises either from the interaction between a weakly collimatedwind with a circumstellar flaring disc, or from the basis of thewestward jet which is seen on a larger scale.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| A search for T Tauri's optical companion star
Speckle interferometric observations of the premain-sequence stellarsystem T Tauri at 650 and 800 nm, and at 1.6 (H) and 2.2 microns (K) inthe IR using the Palomar 200-in. telescope yield no evidence for atertiary optical companion star as reported in 1985. The presentobservations were of sufficient sensitivity to have detected the objectunambiguously if it had remained at its reported brightness and color.The IR results provide particularly stringent limits on the presence ofa third star in the system, since both the optical and southern IRcomponent are clearly resolved to the diffraction limit of the 200-in.telescope, including the H band where the southern component appearedabout 5 mag fainter than the optical primary. Possible resolutions tothe conflicting results concerning this object are discussed, and it isconcluded that if the star is bound to the T Tau system, it has dimmedby at least 1-3 mag at R, I, H, and K. The star is unlikely to be anormal M dwarf as reported, and the possibility that the star could be aHerbig-Haro object is discussed.
| Herbig-Haro phenomena associated with T Tauri - Evidence for a precessing jet?
The discovery of an additional HH nebulosity around T Tauri is reported.This, together with the forbidden S II emission-line image of the star,indicates the presence of morphological structure which may result froma precessing jet in the system.
| The color characteristics of the periodic component in brightness variations of Tauri
The results of photoelectric UBVR observations of T Tauri carried outduring October-November 1987 with the 1-m reflector of the SanglokObservatory are presented. The observations confirm the existence oflight variations with a period of 2.8 d. The amplitudes of thesinusoidal curves which agree best with the observations are 0.123,0.084, 0.070, and 0.057 m in the U, B, V, and R bands, respectively.These brightness and color variations may be explained by the rotationalmodulation due to dark or bright spots on the stellar surface.
| Rotation periods of four T Tauri stars
BVR photometry of nine T Tauri and related stars was obtained on 13nights in January 1988, in an attempt to confirm reported periodicitiesand discover new ones. Each star was observed an average of six timesper night. Rotation periods previously reported for T Tau by Herbst etal.(1986) and HM 4 (LHα 332-20) and HM 30 (LHα 332-21) byBouvier et al.(1986) were confirmed. A periodicity of 1.28 days wasdiscovered for TW Hya; it was also the only star to show significantvariations during the course of a single night. Analysis of a similardataset for TW Hya obtained by Rucinski and Krautter (1983) shows asimilar periodic variation, but with a 1.8 day cycle. SU Aur, RY Tau, BFOri, V380 Ori, and Fu Ori all exhibited variability, but withoutdetectable periodicity. This is in agreement with a previous suggestionthat periodicity is more easily found in the later-typepre-main-sequence stars (i.e., later than about KO).
| Photometric variations of Orion population stars. V - A search for periodicities
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987AJ.....94..137H&db_key=AST
| UBV photometry of stars whose positions are accurately known.
Photometric indices V, B-V, and U-B were measured for about 560 stars ofthe AGK3R and NPZT catalogs between BD declinations 11 deg and 23 deg,using the 40-cm Cassegrain telescope of the Kvistaberg Observatory fromApril 1986 to May 1987. The observation procedure and the reductiontechnique were the same as in the earlier papers of this series by Oja(1984, 1985, 1986, and 1987). The mean errors were calculated from theinternal consistency of the data. The accuracy was found to be the sameas for the earlier parts of the survey.
| Interstellar extinction in the Taurus dark clouds. II
The results of photoelectric photometry of 89 stars in the Vilniusseven-color system in the area of the Taurus dark clouds withcoordinates (1950) 4h16m-4h33m, +16 deg-+20 deg are presented.Photometric spectral types, absolute magnitudes, color excesses,interstellar extinctions and distances of the stars are determined. Thedistance of the dark nebula is found to be 140 pc and is in goodagreement with the distance determined by Straizys and Meistas (1980)for the dark nebula Khavtassi 286, 278. The average extinction in theinvestigated area is of the order of 1.4.
| Variability in the light and Hα emission of T Tau
Not Available
| The polarization of T and RY Tau.
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | שור |
| התרוממות ימנית: | 04h21m42.53s |
| סירוב: | +19°28'06.8" |
| גודל גלוי: | 8.379 |
| מרחק: | 83.612 פארסק |
| תנועה נכונה: | -36.3 |
| תנועה נכונה: | 4.4 |
| B-T magnitude: | 8.858 |
| V-T magnitude: | 8.419 |
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INHABITED SKY
