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Evolutionary Oddities in Old Disk Population Clusters
With a luminosity zero point fixed by the kinematics of old disksuperclusters (HR 1614, t = 6 Gyr, [Fe/H] = +0.1 dex) and groups(Arcturus, t = 14 Gyr, [Fe/H] = -0.65 dex), the luminosities and colorsof evolved old disk stars, especially red horizontal branch (RHB), earlyasymptotic branch [AGB(1)], thermally pulsing asymptotic giant branch[AGB(2)], and sdOB stars in old disk clusters (NGC 6791, 47 Tuc, M71,M67, Mel 66, NGC 2420, NGC 2204, and NGC 2443) are discussed. (1) TheRHB stars in the old disk all have M_V = +0.7 +/- 0.1 (M_K = -1.3 +/-0.1) mag. (2) Large-amplitude red variables (LARVs) with quasi-stableperiods and light curves are old disk stars on AGB(2). (3) AGB(1)objects include CH stars and semiregular (SRa) variables. (4) Thepopulous and overabundant cluster NGC 6791 may be the only disk clusterwith sdOB stars, populating the lower portion of the bifurcated extendedhorizontal branch that is usual in most ``blue tailed'' and high-densityhalo clusters. (5) Post-red giant branch (RGB) stars in old diskclusters show a B - V (b - y) defect when compared with RGB stars,possibly because of a change in the character of the atmospheres. (6) Ifthe bulk of the LARVs are pulsating in the fundamental mode, R Vir (P =145 days) is possibly a first-overtone pulsator. (7) The overabundantold disk clusters are within the solar circle, with Liller 1 being atthe Galactic center. (8) Several probable RHB stars at the southGalactic pole are identified. (9) The period-age relation, combined withthe known spatial distribution of Galactic LARVs, leads to a relationbetween age and scale height of distribution that monotonicallyincreases with age, leaving no obvious reason for a bifurcation of thepopulation.
| A catalog of K giants at the South Galactic Pole - Broadband and DDO photometry and radial velocities
We describe a sample of K giants at the South Galactic Pole, selected toexamine the chemical and kinematical properties of stars perpendicularto the galactic plane and to measure the local column density of thedisk. We report velocities, abundances, absolute magnitudes, andbroadband BV photometry for over 500 giants.
| Local dark matter from a carefully selected sample
The precise data obtained by Flynn and Freeman (1991) on K giants at thesouth Galactic pole are used to analyze the amount of local dark matterin which the systematic effects can be modeled easily and evaluatedaccurately. The method of Bahcall (1984) is employed to solve theself-consistent equations for the distribution of dark matter. TheK-giant survey is found to provide significant evidence for disk darkmatter. Taking into account all recognized sources of error using astatistical test devised by Gould (1989, 1990), a model with no darkmatter is inconsistent with the data at the 86-percent confidence level.The best-fit P-model (in which dark matter is distributed proportionallyto known matter) has 53 percent more dark matter than visible matter.
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Osservazione e dati astrometrici
| Costellazione: | Scultore |
| Ascensione retta: | 00h11m17.51s |
| Declinazione: | -29°38'25.9" |
| Magnitudine apparente: | 8.896 |
| Distanza: | 209.205 parsec |
| Moto proprio RA: | 32.9 |
| Moto proprio Dec: | -1.7 |
| B-T magnitude: | 10.365 |
| V-T magnitude: | 9.018 |
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