תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
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
| A multiwavelength picture of the AFGL 5142 star-forming region.
We present molecular line, H_2_O maser, radio continuum and nearinfrared maps of the bipolar outflow source AFGL 5142. The highresolution of our molecular CO observations enables us to define themorphology of the large-scale bipolar outflow into a two lobe structureextending for ~2' on each side of the center. In the perpendiculardirection, we find consistent evidence for a second, more compact(<0.5') outflow in the form of a spatial velocity offset in the COmap and of an H_2_ jet-like structure derived from a near infrarednarrow band image. On a smaller scale size, the radio and infraredcontinuum observations reveal the engines of the molecular outflows. Themaser emission occurs near the position of the most embedded source ofthe cluster, IRS1. This is located at the center of the compact outflowand jets of shocked H_2_ and coincides with an ultra compact (UC) radiocontinuum source (most probably an ionized stellar wind). The H_2_Ocluster is composed of five spatial components: two are within 0.2-0.3"from the YSO (a few hundred AU) and three are at larger distance(1.5-2", a few thousand AU). A marginal detection of proper motion ofthe two more distant masers may suggest a high expansion velocity at adistance 4x10^3^AU from the YSO, similar to what is found in Orion KLand W49N. The brightest NIR source of the cluster (IRS2) is associatedwith an IRAS point source and lies along the axis of the large-scalebipolar outflow. We propose that the masers and the compact molecularoutflow are powered concurrently by the wind from the YSO associatedwith IRS1, while the large scale outflow could be the remnant from theformation of IRS2.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | אנדרומדה |
| התרוממות ימנית: | 01h58m24.31s |
| סירוב: | +40°54'49.2" |
| גודל גלוי: | 8.233 |
| מרחק: | 130.719 פארסק |
| תנועה נכונה: | 113.1 |
| תנועה נכונה: | -8.9 |
| B-T magnitude: | 9.274 |
| V-T magnitude: | 8.319 |
קטלוגים וכינוים:
|
