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Red Giant (red + giant)

Distribution by Scientific Domains
Physics and Astronomy100%

Selected Abstracts

Stardust in Antarctic micrometeorites

METEORITICS & PLANETARY SCIENCE, Issue 8 2008
Toru YADA
The oxygen isotopic compositions of the eighteen presolar silicate (and one oxide) grains found are similar those observed previously in primitive meteorites and interplanetary dust particles, and indicate origins in oxygen-rich red giant or asymptotic giant branch stars, or in supernovae. Four grains with anomalous C isotopic compositions were also detected. 12C/13C as well as Si ratios are similar to those of mainstream SiC grains; the N isotopic composition of one grain is also consistent with a mainstream SiC classification. Presolar silicate grains were found in three of the seven AMMs studied, and are heterogeneously distributed within these micrometeorites. Fourteen of the 18 presolar silicate grains and 3 of the 4 C-anomalous grains were found within one AMM, T98G8. Presolar silicate-bearing micrometeorites contain crystalline silicates that give sharp X-ray diffractions and do not contain magnesiowüstite, which forms mainly through the decomposition of phyllosilicates and carbonates. The occurrence of this mineral in AMMs without presolar silicates suggests that secondary parent body processes probably determine the presence or absence of presolar silicates in Antarctic micrometeorites. [source]

Evolutionary models for two hyper-iron-poor low-mass stars

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
Gregory J. Harris
ABSTRACT The possible origin of two low-mass hyper-iron-poor (HIP) stars, HE0107-5240 and HE1327-2326 are investigated. The three scenarios tested are as follows. (i) The star forms metal free (Population III) and accretes metals throughout its lifetime. (ii) A Population III binary star system forms, and the lower mass star accretes metals from the higher mass star during its asymptotic giant branch phase. (iii) An HIP Population II star is formed and evolves with no further pollution. Using the ng-elms code, stellar evolution models of these three scenarios are computed and fitted to the observed colours. Models are computed at 0.8 and 0.7 M,, and for several metal accretion rates. It is not possible to unambiguously identify the origin, evolutionary stage or mass for either star with the present observational data. Our evolutionary models indicate that HE0107,5240 is either a red giant or a subgiant close to the base of the red giant branch. In line with the study of Aoki et al., HE1327,2326 is found to be either a main-sequence or a subgiant star. If HE1327,2326 is a main-sequence star the fits indicate that it must have a mass less than 0.8 M,; if the star is assumed to have an age of around 12.5 Gyr it will have a mass closer to 0.7 M,. Main-sequence low-mass model Population III stars which have been polluted with metals are found to closely resemble Population II stars. However, the case is different for subgiants. The polluted and unpolluted Population III subgiants have luminosity up to twice that of a comparable Population II model. If HE1327,2326 is a subgiant, its distance is measured and if its mass can be reasonably well constrained, it should be possible to determine if it is a Population II or III star. [source]

Prospects of stellar abundance studies from near-IR spectra observed with the E-ELT

ASTRONOMISCHE NACHRICHTEN, Issue 4 2010
N. Ryde
Abstract In 2006 ESO Council authorized a Phase B study of a European AO-telescope with a 42 m segmented primary with a 5-mirror design, the E-ELT. Several reports and working groups have already presented science cases for an E-ELT, specifically exploiting the new capabilities of such a large telescope. One of the aims of the design has been to find a balance in the performances between an E-ELT and the James Webb Space Telescope, JWST. Apart from the larger photon-collecting area, the strengths of the former is the higher attainable spatial and spectral resolutions. The E-ELT AO system will have an optimal performance in the near-IR, which makes it specially advantageous. High-resolution spectroscopy in the near-infrared has, however, not been discussed much. This paper aims at filling that gap, by specifically discussing spectroscopy of stellar (mainly red giant), photospheric abundances. Based on studies in the literature of stellar abundances, at the needed medium to high spectral resolutions in the near-infrared (0.8,2.4 ,m), I will try to extrapolate published results to the performance of the E-ELT and explore what could be done at the E-ELT in this field. A discussion on what instrument characteristics that would be needed for stellar abundance analyses in the near-IR will be given (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Orbital eccentricity of the symbiotic star MWC 560,

ASTRONOMISCHE NACHRICHTEN, Issue 3 2010
R.K. Zamanov
Abstract We present projected rotational velocity measurements of the red giant in the symbiotic star MWC 560, using the high-resolution spectroscopic observations with the FEROS spectrograph. We find that the projected rotational velocity of the red giant is v sin i = 8.2 ± 1.5 km s,1, and estimate its rotational period tobe Prot = 144,306 days. Using the theoretical predictions of tidal interaction and pseudosynchronization, we estimate the orbital eccentricity e = 0.68,0.82. We briefly discuss the connection of our results with the photometric variability of the object (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]