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B. L. Canto Martins

Publications and source records attributed to B. L. Canto Martins.

40 records · Page 3Linked to original sources
arXiv2011

Lithium abundances and extra mixing processes in evolved stars of M67

Aims. We present a spectroscopic analysis of a sample of evolved stars in M67 (turn-off, subgiant and giant stars) in order to bring observational constraints to evolutionary models taking into account non-standard transport processes. Methods. We determined the stellar parameters (Teff, log g, [Fe/H]), microturbulent and rotational velocities and, Lithium abundances (ALi) for 27 evolved stars of M67 with the spectral synthesis method based on MARCS model atmospheres. We also computed non-standard stellar evolution models, taking into account atomic diffusion and rotation-induced transport of angular momentum and chemicals that were compared with this set of homogeneous data. Results. The lithium abundances that we derive for the 27 stars in our sample follow a clear evolutionary pattern ranging from the turn-off to the Red Giant Branch. Our abundance determination confirms the well known decrease of lithium content for evolved stars. For the first time, we provide a consistent interpretation of both the surface rotation velocity and of the lithium abundance patterns observed in an homogeneous sample of TO and evolved stars of M67. We show that the lithium evolution is determined by the evolution of the angular momentum through rotation-induced mixing in low-mass stars, in particular for those with initial masses larger than 1.30 M_\odot at solar metallicity.

astro-ph.SR↗
arXiv2010

Wavelet analysis of stellar rotation and other periodicities

The wavelet transform has been used for numerous studies in astrophysics, including signal--noise periodicity and decomposition as well as the signature of differential rotation in stellar light curves. In the present work, we apply the Morlet wavelet with an adjustable parameter $a$, which can be fine-tuned to produce optimal resolutions of time and frequency, and the Haar wavelet for decomposition at levels of light curves. We use the WaveLab--package (library of Matlab routines for wavelet analysis) for the decomposition and a modified version of Colorado--package for the wavelet maps of synthetic and observed light curve. From different applications, including Virgo/SoHO, NSO/Kitt Peak, Voyager 1 and Sunspot data and synthetic light curve produced by different simulators, we show that this technique is a solid procedure to extract the stellar rotation period and possible variations due to active regions evolution. In this paper we show the Morlet Wavelet Amplitude Maps, respectively corresponding to oscillations in the photospheric magnetic field of the Sun (NSO/Kitt Peak data), the daily averages of the magnetic field strength B versus time measured by Voyager 1 (V1) during 1978, and synthetic light curve produced by A. F. Lanza. We can also identify the noise level, as well as the contribution for the light curves produced by intensity, variability and mean lifetime of spots. Thus, we can identify clearly the temporal evolution of the rotation period in relation to other periodicity phenomena affecting stellar light curves. In this context, because the wavelet technique is a powerful tool to solve, in particular, not trivial cases of light curves, we are confident that such a procedure will play an important role on the CoRoT data analysis.

astro-ph.SR↗
arXiv2006

A catalog of rotational and radial velocities for evolved stars. IV. Metal-poor stars

The present paper describes the first results of an observational program intended to refine and extend the existing vsini measurements of metal-poor stars, with anemphasis on field evolved stars. The survey was carried out with the FEROS and CORALIE spectrometers. For the vsini measurements, obtained from spectral synthesis, we estimate an uncertainty of about 2.0 km/s. Precise rotational velocities vsini are presented for a large sample of 100 metal-poor stars, most of them evolving off the main-sequence. For the large majority of the stars composing the present sample, rotational velocities have been measured for the first time.

astro-ph↗