Перегляд за Автор "Spite, M."

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  • Ескіз
    Документ
    The CEMP star SDSSJ0222–0313: the first evidence of proton ingestion in very low-metallicity AGB stars?
    (2019) Caffau, E.; Monaco, L.; Bonifacio, P.; Korotin, S.; Andrievsky, Serhii M.; Cristallo, S.; Spite, M.; Spite, F.; Sbordone, L.; François, P.; Cescutti, G.; Salvadori, S.; Андрієвський, Сергій Михайлович; Андриевский, Сергей Михайлович
    Context. Carbon-enhanced metal-poor (CEMP) stars are common objects in the metal-poor regime. The lower the metallicity we look at, the larger the fraction of CEMP stars with respect to metal-poor stars with no enhancement in carbon. The chemical pattern of CEMP stars is diversified, strongly suggesting a different origin of the C enhancement in the different types of CEMP stars. Aims. We selected a CEMP star, SDSS J0222–0313, with a known high carbon abundance and, from a low-resolution analysis, a strong enhancement in neutron-capture elements of the first peak (Sr and Y) and of the second peak (Ba). The peculiarity of this object is a greater overabundance (with respect to iron) of the first s-process peak than the second s-process peak. Methods. We analysed a high-resolution spectrum obtained with the Mike spectrograph at the Clay Magellan 6.5m telescope in order to derive the detailed chemical composition of this star. Results. We confirmed the chemical pattern we expected; we derived abundances for a total of 18 elements and significant upper limits. Conclusions. We conclude that this star is a carbon-enhanced metal-poor star enriched in elements produced by s-process (CEMP-s), whose enhancement in heavy elements is due to mass transfer from the more evolved companion in its asymptotic giant branch (AGB) phase. The abundances imply that the evolved companion had a low main sequence mass and it suggests that it experienced a proton ingestion episode at the beginning of its AGB phase.
  • Ескіз
    Документ
    The Gaia RVS benchmark stars I. Chemical inventory of the first sample of evolved stars and its Rb NLTE investigation
    (2021) Caffau, E.; Bonifacio, P.; Korotin, S. A.; François, P.; Lallement, R; Matas Pinto, A. M.; Di Matteo, P.; Steffen, M.; Mucciarelli, A.; Katz, D.; Haywood, M.; Chemin, L.; Sartoretti, P.; Sbordone, L.; Andrievsky, Serhii M.; Андрієвський, Сергій Михайлович; Андриевский, Сергей Михайлович; Kovtyukh, V. V.; Spite, M.; Spite, F.; Panuzzo, P.; Royer, F.; Thévenin, F.; Ludwig, H.-G.; Marchal, O.; Plum, G.
    Context. The Radial Velocity Spectrometer (RVS) on board the Gaia satellite is not provided with a wavelength calibration lamp. It uses its observations of stars with known radial velocity to derive the dispersion relation. To derive an accurate radial velocity calibration, a precise knowledge of the line spread function (LSF) of the RVS is necessary. Good-quality ground-based observations in the wavelength range of the RVS are highly desired to determine the LSF. Aims. Several radial velocity standard stars are available to the Gaia community. The highest possible number of calibrators will surely allow us to improve the accuracy of the radial velocity. Because the LSF may vary across the focal plane of the RVS, a large number of high-quality spectra for the LSF calibration may allow us to better sample the properties of the focal plane. Methods. We selected a sample of stars to be observed with UVES at the Very Large Telescope, in a setting including the wavelength range of RVS, that are bright enough to allow obtaining high-quality spectra in a short time. We also selected stars that lack chemical investigation in order to increase the sample of bright, close by stars with a complete chemical inventory. Results. We here present the chemical analysis of the first sample of 80 evolved stars. The quality of the spectra is very good, therefore we were able to derive abundances for 20 elements. The metallicity range spanned by the sample is about 1 dex, from slightly metalpoor to solar metallicity.We derived the Rb abundance for all stars and investigated departures from local thermodynamical equilibrium (NLTE) in the formation of its lines. Conclusions. The sample of spectra is of good quality, which is useful for a Gaia radial velocity calibration. The Rb NLTE effects in this stellar parameters range are small but sometimes non-negligible, especially for spectra of this good quality.