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Resolving the asymmetric inner wind region of the yellow hypergiant IRC +10420 with VLTI/AMBER in low and high spectral resolution mode
Context: IRC +10420 is a massive evolved starbelonging to the group of yellow hypergiants. Currently, this star israpidly evolving through the Hertzprung-Russell diagram, crossing theso-called yellow void. IRC +10420 is suffering fromintensive mass loss which led to the formation of an extended dustshell. Moreover, the dense stellar wind of IRC +10420is subject to strong line emission. Aims: Our goal wasto probe the photosphere and the innermost circumstellar environment ofIRC +10420, to measure the size of its continuum- aswell as the Br? line-emitting region on milliarcsecond scales, andto search for evidence of an asymmetric distribution of IRC+10420's dense, circumstellar gas. Methods: We obtainednear-infrared long-baseline interferometry of IRC +10420 with the AMBER instrument of ESO's Very Large TelescopeInterferometer (VLTI). The measurements were carried out in May/June2007 and May 2008 in low-spectral resolution mode in the JHK bands usingthree auxillary telescopes (ATs) at projected baselines ranging from 30to 96 m, and in October 2008 in high-spectral resolution mode in the Kband around the Br? emission line using three unit telescopes(UTs) with projected baselines between 54 and 129 m. The high-spectralresolution mode observations were analyzed by means of radiativetransfer modeling using CMFGEN and the 2D Busche & Hillier codes.Results: For the first time, we have been able to absolutelycalibrate the H- and K-band data and, thus, to determine the angularsize of IRC+10420's continuum- and Br? line-emitting regions. Wefound that both the low resolution differential and closure phases arezero within the uncertainty limits across all three bands. In thehigh-spectral resolution observations, the visibilities show anoticeable drop across the Br? line on all three baselines. Wefound differential phases up to -25° in the redshifted part of theBr? line and a non-zero closure phase close to the line center.The calibrated visibilities were corrected for AMBER's limitedfield-of-view to appropriately account for the flux contribution ofIRC +10420's extended dust shell. From ourlow-spectral resolution AMBER data we derived FWHM Gaussian sizes of1.05±0.07 and 0.98±0.10 mas for IRC+10420's continuum-emitting region in the H and K bands,respectively. From the high-spectral resolution data, we obtained a FWHMGaussian size of 1.014±0.010 mas in the K-band continuum. TheBr? -emitting region can be fitted with a geometric ring modelwith a diameter of 4.18^+0.19-0.09 mas, which isapproximately 4 times the stellar size. The geometric model alsoprovides some evidence that the Br? line-emitting region iselongated towards a position angle of 36°, well aligned with thesymmetry axis of the outer reflection nebula. Assuming an unclumped windand a luminosity of 6×10^5{ {L}?}, the sphericalradiative transfer modeling with CMGFEN yields a current mass-loss rateof 1.5-2.0×10-5{ {M}? yr-1}based on the Br? equivalent width. However, the spherical CMFGENmodel poorly reproduces the observed line shape, blueshift, andextension, definitively showing that the IRC +10420outflow is asymmetric. Our 2D radiative transfer modelingshows that the blueshifted Br? emission and the shape of thevisibility across the emission line can be explained with an asymmetricbipolar outflow with a high density contrast from pole to equator(8-16), where the redshifted light is substantially diminished.The low-spectral resolution data have been obtained as part of theGuaranteed Time Programme for VLTI/AMBER (program ID: 079.D-0356(B)),while the high-spectral resolution data were obtained in the context ofscience verification observations (program ID: 60.A-9053(D)).
| The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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
| 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
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| Takýmyýldýz: | Saat |
| Sað Açýklýk: | 03h39m54.80s |
| Yükselim: | -51°41'13.0" |
| Görünürdeki Parlaklýk: | 8.498 |
| Uzaklýk: | 247.525 parsek |
| özdevim Sað Açýklýk: | 2.5 |
| özdevim Yükselim: | -21.8 |
| B-T magnitude: | 9.043 |
| V-T magnitude: | 8.543 |
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