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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
| Chandra Observations of Expanding Shells in the Dwarf Starburst Galaxy NGC 3077
Deep Chandra observations (53 ks, ACIS-S3) of NGC 3077, a starburstdwarf galaxy in the M81 triplet, resolve the X-ray emission from severalsupershells. The emission is brightest in the cavities defined byexpanding shells detected previously in Hα emission. Thermalemission models fitted to the data imply temperatures ranging from ~1.3to 4.9×106 K and indicate that the strongest absorptionis coincident with the densest clouds traced by CO emission. The fittedemission measures give pressures ofP/k~(105-106)ξ-0.5f-0.5vK cm-3 (where ξ is the metallicity of the hot gas in solarunits and fv is the volume filling factor). Despite thesehigh pressures, the radial density profile of the hot gas is not assteep as that expected in a freely expanding wind (e.g., as seen in theneighboring starburst galaxy M82), implying that the hot gas is stillconfined by the Hα shells. The chaotic dynamical state of NGC 3077undermines reliable estimates of the escape velocity. The more relevantquantity for the ultimate fate of the outflow is probably the gasdensity in the rich intragroup medium. Based on the H I distribution ofNGC 3077 and a connected tidal tail we argue that the wind has thepotential to leave the gravitational well of NGC 3077 to the north butnot to the south. The total 0.3-6.0 keV X-ray luminosity is~(2-5)×1039 ergs s-1 (depending on theselected thermal plasma model). Most (~85%) of the X-ray luminosity inNGC 3077 comes from the hot interstellar gas; the remainder comes fromsix X-ray point sources. In spite of previous claims to the contrary, wedo not find X-ray emission originating from the prominent tidal tailnear NGC 3077.
| Mesures de vitesses radiales. VIII. Accompagnement AU sol DU programme d'observation DU satellite HIPPARCOS
We publish 1879 radial velocities of stars distributed in 105 fields of4^{\circ} \times 4^{\circ}. We continue the PPO series \cite[(Fehrenbachet al. 1987;]{Feh87} \cite[Duflot et al. 1990, 1992 and 1995),]{Du90}using the Fehrenbach objective prism method. Table 1 only available inelectronic form at CDS via to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Absolute stellar proper motions with reference to galaxies of the M81 group
We report on the measurement of absolute proper motions of stars ofmagnitude 7 to 14.5 in a 2 deg X 2 deg field in the region of the M81group of galaxies. This work is part of the Bonn program for theextragalactic link of Hipparcos. The proper motions were determined froma collection of photographic plates covering the time interval from 1894to 1994. The absolute reference system for the proper motions isrepresented by the galaxies M81, M81, and NGC3077, for which accurateoptical reference positions were obtained by means of an imagecross-correlation technique. For the majority of stars, the internalproper motion accuracy is better than 1 mas/a. The precision of therealization of the absolute system is found to be around 1 mas/a. Intotal, our measurements yield absolute proper motions for 24 Hipparcosstars and positions, proper motions and photometry for 330 additionalstars including a number of visual binaries and high proper motionstars. Among the latter one G-type sub-dwarf is identified. The resultsare relevant as a contribution to the Hipparcos link, but also as adatabase for kinematic investigations.
| GSC 4383-0870 - a distant companion to the visual binary ADS 7611.
Not Available
| Multicolor Photoelectric Photometry of SN 1993J
Not Available
| X-ray observations of NGC 3077
ROSAT X-ray observations show that the irregular starburst galaxy NGC3077 has an X-ray luminosity of 2.1 x 1038 erg/s centered onthe inner 1' nuclear region, which is consistent with that expected fromother well observed starbursts (e.g. M82). The X-ray emission can not beaccounted for by a point-like nucleus but can be modeled by a hotinterstellar medium (ISM) with kT = 0.65 +/- 0.51 keV and a centralhydrogen number density about 0.75/cu.cm. Alternative interpretationssuch as X-rays binaries would have to have a steep X-ray luminosityfunction to explain the non-detection of bright X-ray binaries, while atthe same time, young stars would have to contribute X-rays 7 times lessthan observed. If one assumes an ISM origin, the X-ray cooled mass 4.5 x107 solar mass and the cooling rate 0.091 solar mass/yr arecomparable to both the molecular mass 2 x 107 solar mass ofthe three giant molecular complexes detected in the same region and thestar formation rate 0.1 solar mass/yr determined from H alpha andinfrared observations. Both the high formation rates of molecular cloudsand stars in NGC 3077, as well as in M82 in the same M81 group, may bedue to tidal forces or ejection related to closer proximity to M81 about5 x 108 years ago. NGC 3077 and M82 are linked to the nearbyM81 by a neutral hydrogen bridge. We find that there is an excess ofnumber of X-ray sources over the X-ray background within the inner 10'region of the Position Sensitive Proportional Counter (PSPC) center thatis statistically significant at the 99.8% level Some sources aresituated close to the hydrogen bridge and thus may belong to the group.Possible origins of these sources are discussed.
| Double Star Measurements Made at Nice
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102..643M&db_key=AST
| A New Variable Star GSC 4383.0384
Not Available
| Supernova 1993J in NGC 3031
IAUC 5750 available at Central Bureau for Astronomical Telegrams.
| An unbiased survey of field star X-ray emission
To determine the X-ray luminosity function of normal stars, 1700 starsbrighter than 10th magnitude were surveyed by the imaging proportionalcounter aboard the Einstein Observatory. Seventy star positions werefound to contain excess X-ray counting rates. The number of stars persquare degree in a number of magnitude intervals was calculated as afunction of spectral type and luminosity class, and the total number ofstars for each spectral type brighter than magnitude 9.5 derived in thismanner was compared with the 1700-star sample. The agreement is good, asis that between the surface density of soft X-ray sources and the numberof stellar emitters predicted from the field star survey. It isconcluded that stars probably do not contribute significantly to thediffuse soft X-ray background. The findings are consistent with thenotion that stellar age and/or rotation velocity are importantdeterminants of stellar X-ray emission level.
| Relative motions of 17 visual double stars
The relative motions of 17 visual stars are studied; the data cited indeveloping the equations of relative motion are often from observationsmade 50 or more years ago. The results are compared with the data fromSAO, IDS and AGK catalogs.
| Mesures d'étoiles doubles faites à l'équatorial de 38 CM de l'Observatoire de Paris
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....6..147B&db_key=AST
| Mesures d'Etoiles Doubles faites à l'Observatoire de Paris (suite)
Not Available
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| Сазвежђа: | Велики медвед |
| Ректацензија: | 10h02m56.44s |
| Deклинација: | +68°47'09.2" |
| Apparent магнитуда: | 7.978 |
| Даљина: | 66.007 parsecs |
| Proper motion RA: | -26.8 |
| Proper motion Dec: | -19.4 |
| B-T magnitude: | 8.513 |
| V-T magnitude: | 8.023 |
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