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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.
| Near-infrared adaptive optics dissection of the core of NGC 1068 with NAOS-CONICA
We present an update analysis of recent near-infrared adaptive opticsobservations of NGC 1068 obtained with NAOS-CONICA atVLT/UT4. Ks, L' and M' bands images were deconvolved using MISTRAL, aregularized algorithm based on a maximum a posteriori estimation of theobject. Two regularization methods, one including a new maximumlikelihood estimation of the object Power Spectral Density, and an edgepreserving one, have been tested and converge to consistent results. Thedeconvolved images show a coherent evolution of the IR emission from 2.2to 4.8 {μ m}. Deconvolution brings new elements: a) it strengthensthe very peculiar nature of the four parallel elongated nodulespreviously discovered along the jet, which appear unresolvedperpendicular to their long axis; b) it underlines the strongcorrelation between UV clouds and IR features, and c) it provides a moreaccurate multi-wavelength registration of the actual active nucleus. Theoverall aspect of the central 1 arcsec × 1 arcsec IR emissionseems to point to the jet as a major mechanism to shape the NLR. Foreach identified structure, we derive a color temperature now based onthree bands (M, L and K), before and after deconvolution, confirming theneed for clumps of dust at unexpectedly high and almost constanttemperature (about 500 K) up to 70 pc north of the nucleus. We exploreseveral mechanisms to explain the color temperature and show thatshocks, induced for instance by the interaction of the jet with a giantcloud, is unlikely to be the dominating mechanism to heat the dust. Wedetail our model of transient heating of Very Small Grains and show thatit can provide a consistent explanation of the K, L, M colors and theirlack of variation with distance when 0.6 nm diamond-like grains areheated by 4 to 8 eV UV photons. However, we do not exclude thepossibility that part of the excitation could come from shocks. At Ks,deconvolution reinforces the previous claim that the central core ispartially resolved along the N-S direction: the best fit to our data isan elliptical Gaussian extended along PA=-16 with a 2.1 pc FWHM alongthis direction. This result agrees with the predictions of the radiativetransfer model we previously developed to interpret the spectroscopicbehavior at K, and is consistent with VLTI/VINCI measurements. Severalquestions are raised by this study: a) is the jet dominant in shapingthe NLR of this AGN? b) what is the real state of the dust in theenvironment of the core; c) is the simple doughnut torus model able toexplain IR emission of the central source with a morphology that appearsincreasingly complex at small scale?
| Diffraction-limited bispectrum speckle interferometry of the nuclear region of the Seyfert galaxy NGC 1068 in the H and K' bands
We present near-infrared bispectrum speckle interferometry studies ofthe nuclear region of the Seyfert 2 galaxy NGC 1068.A diffraction-limited K'-band image with 74 mas resolution and the firstH-band image with 57 mas resolution were reconstructed from speckleinterferograms obtained with the SAO 6 m telescope. The resolvedstructure consists of a compact core and an extended northern andsouth-eastern component. The compact core is resolved at all positionangles and has a north-western, tail-shaped extension as well as afainter, south-eastern extension. The K'-band FWHM diameter of thiscompact core is approximately 18 × 39 mas or 1.3 × 2.8 pc(FWHM of a single-component Gaussian fit; fit range 30-80&%slash; ofthe telescope cut-off frequency; the diameter errors are ±4 mas),and the position angle (PA) of the north-western extension is -16± 4 °. If 40% of the flux from the compact K' core isemission from a point source and 60% from a Gaussian intensitydistribution, then a slightly larger FWHM of approximately 26 × 58mas is obtained for the compact K' component. In the H band, the FWHMdiameter of the compact core is approximately 18 × 45 mas(±4 mas), and the PA is -18 ± 4 °. The extendednorthern component (PA 0 °) has an elongated structure with alength of about 400 mas or 29 pc. The extended south-eastern componentis fainter than the northern component. The K'- and H-band fluxes fromthe resolved compact core were measured to be 350 ± 90 mJy (i.e.,K' 8.2m) and 70 ± 20 mJy (H 10.4m), respectively. The PA of -16 ± 4 ° of thecompact 18 × 39 mas core is very similar to that of the westernwall (PA -15 °) of the bright region of the ionization cone.This suggests that the H- and K'-band emission from the compact core isboth thermal emission and scattered light from dust near the westernwall of a low-density, conical cavity or from the innermost region of aparsec-scale dusty torus that is heated by the central source (the dustsublimation radius of NGC 1068 is approximately 0.1-1pc). The northern extended 400 mas structure lies near the western wallof the ionization cone and coincides with the inner radio jet (PA 11 °). The large distance from the core suggests that the K'-bandemission of the northern extended component is scattered light from thewestern cavity region and the radio jet region.Based on observations made with the 6 m BTA telescope, which is operatedby the Special Astrophysical Observatory (SAO), Russia.
| 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
| Diffraction-limited Imaging and Photometry of NGC 1068
The nearby Seyfert 2 galaxy NGC 1068 was observed with speckle imagingtechniques in the near-infrared H band (1.6 μm) with the 200-inchHale Telescope on Palomar Mountain and K band (2.2 μm) with the 10 mKeck I Telescope at the W. M. Keck Observatory. Images withdiffraction-limited or near-diffraction-limited resolutions of0.05"-0.1" were obtained and used to search for structure in the nuclearregion. Images of the nucleus of NGC 1068 reveal an extended region ofemission, accounting for nearly 50% of the nuclear flux in the K band.This region extends 10 pc on either side of an unresolved point-sourcenucleus that is at most 0.02" or 1.4 pc in size. Both the point sourceand the newly imaged extended emission are very red, with identical H-Kcolors corresponding to a color temperature of 800 K. While the pointsource is of a size to be consistent with grains in thermal equilibriumwith the nuclear source, the extended emission is not. It must consisteither of nuclear emission that has been reflected off an extended dustydisk or of small grains raised to transiently high temperatures byreflected UV photons.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
Not Available
| Photometric survey near the main Galactic meridian: 2.1. Finding charts and photoelectric U,B,V,R stellar magnitudes in 25 fields
Finding charts and photoelectric U,B,V,R magnitudes of stars in 25fields in the Main Galactic Meridian (programme MEGA) are presented.This part of the photometric survey includes fields near the NorthGalactic pole and fields at southern Galactic latitudes. Together withthe finding charts of 2.5(deg) x2.5(deg) the equatorial coordinates ofthe stars are given for epoch and equinox 1950.
| Photometric Survey Near the Main Galactic Meridian - Part One - Photoelectric Stellar Magnitudes and Colours in the UBVR System
Not Available
| 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
| Speckle imaging of NGC 1068 and NGC 4151 in the forbidden O III 5007 A line and nearby continuum
Images of NGC 1068 and NGC 4151 in the forbidden O III 5007 A emissionline and nearby continuum are presented with about 0.3 arcsecresolution. The images are reconstructed using recently developedspeckle imaging techniques. Each object shows a bipolar extendedstructure in the emission line with lobes extending about 0.4 arcsecfrom an apparently unresolved central source. The unresolved componentemits about half the flux and is smaller than single-densityphotoionization models predict.
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משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | לויתן |
| התרוממות ימנית: | 02h41m58.98s |
| סירוב: | +00°33'01.3" |
| גודל גלוי: | 7.59 |
| מרחק: | 125.156 פארסק |
| תנועה נכונה: | 10.2 |
| תנועה נכונה: | 10.7 |
| B-T magnitude: | 8.006 |
| V-T magnitude: | 7.625 |
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