Navegando por Autor "Recio-Blanco, A."

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An overview of the rotational bechavior of metal-poor stars
(Sociedade Astronômica Americana, 2009) Cortes, C.; Silva, J. R. P.; Recio-Blanco, A.; Catelan, M.; Nascimento Junior, Jose Dias do; Medeiros, José Renan de
This paper describes the behavior of the rotational velocity in metal-poor stars ([Fe/H] ≤ –0.5 dex) in different evolutionary stages, based on vsin i values from the literature. Our sample is comprised of stars in the field and some Galactic globular clusters, including stars on the main sequence, the red giant branch (RGB), and the horizontal branch (HB). The metal-poor stars are, mainly, slow rotators, and their vsin i distribution along the HR diagram is quite homogeneous. Nevertheless, a few moderate to high values of vsin i are found in stars located on the main sequence and the HB. We show that the overall distribution of vsin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating main sequence stars in our sample present rotation rates similar to their metal-rich counterparts, suggesting that some of them may actually be fairly young, in spite of their low metallicity, or else that at least some of them would be better classified as blue straggler stars. We do not find significant evidence of evolution in vsin i values as a function of position on the RGB; in particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue HB stars has been suggested to be due to angular momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms most likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and vsin i values. We present an extensive tabulation of all quantities discussed in this paper, including rotation velocities, temperatures, gravities, and metallicities [Fe/H], as well as broadband magnitudes and colors.
Lithium abundances for early F stars: new observational constraints for the Li dilution
(Astronomy & Astrophysics, 2006) Jasniewicz, G.; Recio-Blanco, A.; Laverny, P. de; Parthasarathy, M.; Medeiros, José Renan de
Aims. To investigate any correlation between Li abundances and rotational velocities among F–G evolved stars, we study a large sample of early F stars from the Bright Star Catalogue (BSC), most of them classified in the literature as giant stars. Methods. Physical parameters and Li abundances are estimated for each star, often for the first time, by comparing observed and synthetic spectra. We analyse the position of the stars in the H–R Diagram based on Hipparcos data using stellar evolutionary tracks and we discuss their Li abundances and projected rotational velocities. Results. Observed stars are mostly on the turnoff, with masses between 1.5 and 2.0 M. The stars with measured A(Li) abundance show high Li content, most of them with abundance near the cosmic value. The A(Li) versus V sin i diagram shows the same trend as reported in previous studies: fast rotators (V sin i > 30 km s−1) are also stars with high Li content, whereas slow rotators present a wide range of values of A(Li), ranging from no detected Li to the cosmic value.
Radial velocities of open stellar clusters: a new solid constraint favouring Tsallis maximum entropy theory
(Elsevier Inc., 2007-10-15) Carvalho, J.C.; Soares, B. B.; Martins, Bruno Leonardo Canto; Nascimento Júnior, José Dias do; Recio-Blanco, A.; Medeiros, José Renan de
In the present study we apply a Tsallis maximum entropy distribution law to the study of the stellar residual radial velocity in a sample of 13 stellar open clusters. From a comparison between results obtained from the analysis based on Tsallis law and on the one based on the Maxwellian law we show that the generalized Tsallis distribution fits more closely the observed distribution of the stellar residual radial velocities for these stellar clusters. We have found clear evidences that the q-parameter in the Tsallis generalized distribution depends on stellar cluster ages for clusters older than 10. There is also some indication that q increases with cluster galactocentric distance. The results obtained in this work represent an additional solid constraint in the stellar astrophysics favoring the Tsallis maximum entropy theory

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Navegando por Autor "Recio-Blanco, A."