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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
| Hot Debris Dust Around HD 106797
Photometry of the A0 V main-sequence star HD 106797 with AKARI andGemini/T-ReCS is used to detect excess emission over the expectedstellar photospheric emission between 10 and 20 ?m, which is bestattributed to hot circumstellar debris dust surrounding the star. Thetemperature of the debris dust is derived as T d ~ 190 K byassuming that the excess emission is approximated by a singletemperature blackbody. The derived temperature suggests that the innerradius of the debris disk is ~14 AU. The fractional luminosity of thedebris disk is 1000 times brighter than that of our own zodiacal cloud.The existence of such a large amount of hot dust around HD 106797 cannotbe accounted for by a simple model of the steady state evolution of adebris disk due to collisions, and it is likely that transient eventsplay a significant role. Our data also show a narrow spectral featurebetween 11 and 12 ?m attributable to crystalline silicates,suggesting that dust heating has occurred during the formation andevolution of the debris disk of HD 106797.
| The nature of mid-infrared excesses from hot dust around Sun-like stars
Aims. Studies of the debris disk phenomenon have shown that most systemsare analogous to the Edgeworth-Kuiper Belt (EKB). However a rare subsetof sun-like stars possess dust which lies, in contrast, in theterrestrial planet region. In this study we aim to determine how manysources with apparent mid-infrared excess are truly hosts of warm dust,and investigate where the dust in these systems must lie. Methods: Weobserved using ground-based mid-infrared imaging with TIMMI2, VISIR andMICHELLE a sample of FGK main sequence stars previously reported to havehot dust. A new modelling approach was developed to determine theconstraints that can be set on the radial extent of excess emission insuch observations by demonstrating how the detectability of a disk of agiven flux as a fraction of the total flux from the system(F{disk}/F{total}) depends primarily on the ratioof disk radius to PSF width and on the uncertainty on that PSF width. Results: We confirm the presence of warm dust around three of thecandidates; η Corvi, HD 145263 and HD 202406. For η Corvimodelling constrains the dust to lie in regions smaller than 3.5 AU.The modelling constrains the dust to regions smaller than 80-100 AU forHD 145263 and HD 202406, with SED fitting suggesting the dust lies at afew tens of AU. Of two alternative models for the η Corvi excessemission, we find that a model with one hot dust component at less than0.164 arcsec (<3 AU) (combined with the known submm dust populationat 150 AU) fits all the data better at the 2.6σ level than analternative model with two populations of dust emitting in themid-infrared: hot dust at less than 0.19 arcsec (<3.5 AU) and amid-temperature component at 0.66 arcsec (12 AU). We identify severalsystems which have a companion (HD 65277 and HD 79873) or backgroundobject (HD 53246, HD 123356 and HD 128400) responsible for theirmid-infrared excess, and for three other systems we were able to ruleout a point-like mid-infrared source near the star at the level ofexcess observed in lower resolution observations (HD 12039, HD 69830 andHD 191089). Conclusions: Hot dust sources are either young and possiblyprimordial or transitional in their emission, or have relatively smallradius steady-state planetesimal belts, or they are old and luminouswith transient emission. High resolution imaging can be used toconstrain the location of the disk and help to discriminate betweendifferent models of disk emission. For some small disks, interferometryis needed to resolve the disk location.
| 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
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| Stromgren and H-beta photometry of stars earlier than G0 in 5 areas containing high latitude molecular clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989A&AS...80..127F&db_key=AST
| Estimation of spectral classifications for bright southern stars with interesting Stromgren indices
This paper investigates the degree of success with which uvby photometrycan be applied to predict spectral classifications for 947 A, F, and Gstars brighter than an apparent magnitude of 8.3 and with four-colorindices indicating some kind of interesting, unusual, or peculiarspectrum. One or several possible spectral classifications are estimatedfor each star from photometry alone, double stars are distinguished, andthe estimates are compared with published classifications. The resultsshow that the framework provided by uvby photometry can be extended toinclude most G and K stars, reddened stars, peculiar stars, and certaintypes of double star.
| Spectral types of stars with unusual photometric indices
The Kitt Peak 2.1-m Cassegrain spectrograph was used to obtain spectraof 92 A5-G0 stars measured by Olsen in the Stromgren four-color systemand predicted to be abnormal in the sense of excessive reddening, highluminosity, or abnormal composition. Of the five stars predicted to bereddened B or A stars, four were indeed such while for the fifth Olsenobserved the blended components. Of twelve stars predicted to besupergiants, one is a supergiant, four are giants, two are subgiants,three are Ap stars, and two are Am stars. Thus photometrically predictedsupergiants are actually stars above main sequence in two out of threecases but mostly much less luminous than expected. Of ten predictedweak-lined stars, only two were found to be really so. Am stars werewell predicted, though detection is contaminated with Ap and luminousstars. It is concluded that four-color photometry is useful in selectinginteresting stars, but is often unable to tell the specific type ofabnormality present.
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