Giant star

Abstract: We present calibrations of the effective temperatures of giant stars versus [Fe/H] and colours , , , , , , , , , , and . These calibrations are based on a large sample of field and globular cluster stars which roughly cover spectral types from F0 to K5. Their effective temperatures, scaled to direct determinations via reliable angular diameter measurements, were derived by applying the infrared flux method. The empirical relations have been fitted to polynomials of the form by using the least squares method. The precision of the fits ranges from 40 K for to 170 K for . We tabulate intrinsic colours of giant stars in the ranges: 3500 K 8000 K; -3.0 . We also present the calibration of BC(V) as a function of log and metallicity. Finally, we compare the resulting scale of temperatures with previous works.

Abstract: We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy mapped by M giant star tracers detected in the complete Two Micron All-Sky Survey (2MASS) The main body is fit with a King profile of 30 deg limiting radius, but with a break in the density profile from stars in tidal tails We argue that much of the observed structure beyond the 224' core radius may be unbound as the satellite undergoes catastrophic disruption A striking, >150 deg trailing tidal tail extends from the Sgr center and arcs across the South Galactic Hemisphere A prominent leading debris arm extends from the Sgr center northward of the Galactic plane to an ~40 kpc apoGalacticon, loops towards the North Galactic Cap (NGC) and descends back towards the Galactic plane, foreshortened and covering the NGC The Sgr tails lie along a well-defined orbital plane that shows little precession, which supports the notion of a nearly spherical Galactic potential The Sun lies near the path of leading Sgr debris; thus, former Sgr stars may be near or in the solar neighborhood The number of M giants in the Sgr tails is >15% that within the King limiting radius of the Sgr center That several gigayear old M giants are so widespread along the Sgr tidal arms not only places limits on the dynamical age of these arms but poses a timing problem that bears on the recent binding energy of the Sgr core and that is naturally explained by recent and catastrophic mass loss Sgr appears to contribute >75% of the high latitude, halo M giants; no evidence for M giant tidal debris from the Magellanic Clouds is found Generally good correspondence is found between the M giant, all-sky map of the Sgr system and all previously published detections of potential Sgr debris with the exception of Sgr carbon stars -- which must be subluminous to resolve the discrepancy

Abstract: Population I stars of 15 M/sub sun/ and 25 M/sub sun/ have been evolved from the zero-age main sequence through iron core collapse utilizing a numerical model that incorporates both implicit hydro-dynamics and a detailed treatment of nuclear reactions. The stars end their presupernova evolution as red supergiants with photospheric radii of 3.9 x 10/sup 13/ cm and 6.7 x 10/sup 13/ cm, respectively, and density structures similar to those invoked to explain Type II supernova light curves on a strictly hydrodynamic basis. Both stars are found to form substantially neutronized ''iron'' cores of 1.56M/sub sun/ and 1.61 M/sub sun/, and central electron abundances of 0.427 and 0.439 moles g/sup -1/, respectively, during hydrostatic silicon burning. Just prior to collapse, the abundances of the elements in the 25 M/sub sun/ star (excluding the neutronized iron core) have ratios strikingly close to their solar system values over the mass range from oxygen to calcium, while the 15 M/sub sun/ star is characterized by large enhancements of Ne, Mg, and Si. It is pointed out on nucleo-synthetic grounds that the mass of the neutronized core must represent a lower limit to the mass of the neutron star or black hole remnant thatmore » stars in this mass range can normally produce.« less

Abstract: We have collected spectra of about 2000 red giant branch (RGB) stars in 19 Galactic globular clusters (GC) using FLAMES@VLT (about 100 stars with GIRAFFE and about 10 with UVES, respectively, in each GC). These observations provide an unprecedented, precise, and homogeneous data-set of Fe abundances in GCs. We use it to study the cosmic scatter of iron and find that, as far as Fe is concerned, most GCs can still be considered mono-metallic, since the upper limit to the scatter of iron is less than 0.05 dex, meaning that the degree of homogeneity is better than 12%. The scatter in Fe we find seems to have a dependence on luminosity, possibly due to the well-known inadequacies of stellar atmospheres for upper-RGB stars and/or to intrinsic variability. It also seems to be correlated with cluster properties, like the mass, indicating a larger scatter in more massive GCs which is likely a (small) true intrinsic scatter. The 19 GCs, covering the metallicity range of the bulk of Galactic GCs, define an accurate and updated metallicity scale. We provide transformation equations for a few existing scales. We also provide new values of [Fe/H], on our scale, for all GCs in the Harris catalogue.