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Evolved GK stars near the Sun. 2: The young disk population
From a sample of nearly 2000 GK giants a group of young disk stars withwell determined space motions has been selected. The zero point of theluminosity calibrations, both from the ultraviolet flux (modifiedStroemgren system) and that in the region of 4200 to 4900 A (DDOsystem), show a discontinuity of about a half magnitude at the border ofthe young disk and old disk domains. The population separation is basedon the space velocity components, which are also an age discriminant,with the population interface near 2 x 109 yr, based onmodels with convective overshoot at the core. This age corresponds togiant masses near 1.7 solar mass, near the critical mass separating theyoung stars that do not burn helium in degenerate cores from older starsthat do. Ten percent of both populations show CN anomalies in that thederived value of P(Fe/H) from CN (Cm) and fromFe(M1) differ by more than 0.1 dex and the weak and strong CNstars occur equally in the old disk but the weak CN stars predominate inthe young disk. Peculiar stars, where flux distortions affect theluminosity calibrations, are of the CH+(Ba II) and CH-(weak G band)variety and represent less than 1% of the stars in both populations. Theyoung disk giants are restricted to ages greater than about109 yr, because younger stars are bright giants orsupergiants (luminosity class 2 or 1), and younger than about 2 x109 yr, because the old disk-young disk boundary occurs near1.7 solar mass. The distribution of heavy element abundances, P(Fe/H),for young disk giants is both more limited in range (+/- 0.4 dex) and isskewed toward higher abundances, compared with the nearly normaldistribution for old disk giants. The distribution of (U,V) velocityvectors gives (U,V,W) and their dispersions = (+17.6 +/- 18.4, -14.8 +/-8.4, -6.9 +/- 13.0) and (+3.6 +/- 38.4, -20.7 +/- 27.5, -6.7 +/-17.3)km/s for young and old disk giants, respectively.
| Large and kinematically unbiased samples of G- and K-type stars. V - Evolved stars in the selected areas at + 15-deg declination
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990PASP..102..242E&db_key=AST
| HD 39853 - A high velocity K 5 III star with an exceptionally large Li content
Observations obtained at wavelengths between 513.5 and 877.4 nm usingthe CES spectrograph with an 1870-diode reticon array on the CATtelescope at ESO between October 1982 and January 1986 are reported forHD 39853. The observational techniques and data-reduction procedures aredescribed; calibration curves are shown; and the results are presentedin extensive tables, graphs, and sample spectra. Characteristicsdiscussed include Fe/H = -0.5 + or - 0.1, log N(Li) = 2.8 + or - 0.2,O/Fe = +0.29 + or - 0.15, C/N = 8 + or - 2, (C-12)/(C-13) = 6.6 + or -1.2, and light-metal enhancement factor (with respect to Fe) = about2.5. Existing theoretical models are found to be insufficient to explainthese abundance features.
| Photoelectric radial velocities. IV. 528 7 to 10 mag stars in the +15degree selected areas.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971MNRAS.155....1G&db_key=AST
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דגים |
| התרוממות ימנית: | 01h19m14.03s |
| סירוב: | +13°53'30.3" |
| גודל גלוי: | 8.739 |
| תנועה נכונה: | 83 |
| תנועה נכונה: | -19 |
| B-T magnitude: | 10.111 |
| V-T magnitude: | 8.853 |
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