arXiv subjects

R. J. Garcia Lopez

Publications and source records attributed to R. J. Garcia Lopez.

22 records · Page 2Linked to original sources

arXiv1997

Fe I line shifts in the optical spectrum of the Sun

New improvements in the measurement of both the optical solar spectrum and laboratory wavelengths for lines of neutral iron are combined to extract central wavelength shifts for 1446 lines observed in the Sun. This provides the largest available database of accurate solar wavelengths useful as a reference for comparison with other solar-type stars. It is shown how the velocity shifts correlate with line strength, approaching a constant value, close to zero, for lines with equivalent widths larger than 200 mA.

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arXiv1997

The Age-Mass Relation for Chromospherically Active Binaries. II. Lithium Depletion in Dwarf Components

We present an extensive study of lithium abundances in dwarf components of chromospherically active binary stars (CABS). Since most of these binaries have known radii, masses and ages, this kind of data is especially useful for comparisons with theoretical models which try to explain the Li depletion phenomenon. We show that a significant part of these stars have clear Li overabundances. These excesses are evident when comparing our sample of CABS with binary and single stars belonging to open clusters of different ages, namely Pleiades, Hyades, NGC752, M67 and NGC188. The Li excesses are more conspicuous for masses in the range 0.75-0.95 Mo, indicating that the rate of Li depletion has been less pronounced in CABS than in single stars. This phenomenon is interpreted in the context of transport of angular momentum from the orbit to the stellar rotation due to tidal effects. Other explanations, however, can not be ruled out. This is the case of transport of material induced by internal gravity waves, which could be inhibited due to the presence of strong magnetic fields associated with the effective dynamo in CABS. The confirmed existence of a relation between Li and fluxes in CaII H&K lines can also be accommodated within both scenarios.

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arXiv1997

The Limited Influence of Pressure Gradients on Late-type Stellar Line Asymmetries

Line asymmetries and shifts are a powerful tool for studying velocity fields in the stellar photospheres. Other effects, however, could also generate asymmetries blurring the information of the velocity patterns. We have studied the shifts and asymmetries induced in the profiles of spectral lines by pressure effects. The best theoretical and experimental data on line broadening and shifts caused by collisions with atomic hydrogen were used to analyze the NaI D and three CaI lines. Line bisectors of synthetic spectra computed with accurate data for the NaI and CaI lines are compared with very high resolution high signal-to-noise ratio solar spectra and indicate that pressure broadening reproduces the wings of the observed lines, but pressure shifts introduce neither asymmetries nor shifts comparable to the observed ones.

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arXiv1995

Stars Approaching the Substellar Limit in the alpha Persei Open Cluster

We present intermediate dispersion optical spectroscopy for seven very low-mass stars in the alpha Per open cluster with spectral types between M3 and M6, including the brown dwarf candidate of Rebolo et al. (1992). Our radial velocity measurements are found to be generally consistent with the mean cluster velocity to within the measurement errors. Halpha equivalent widths have been measured and compared to previous published data for other known members of the cluster. A turnover in chromospheric activity around spectral type M3-M4 is observed. The brown dwarf candidate, located in the cool side of the turnover, is confirmed to exhibit a strong Halpha variability. It is the coolest alpha Per candidate member for which spectra are available and for which chromospheric activity has been measured. Using the LiI doublet at lambda 6707.8 angstroms, we derive upper limits to the atmospheric Li abundance in the sample and discuss them in the context of the most recent stellar evolutionary tracks. The non-detection of the LiI line in the spectrum of the brown dwarf candidate implies a mass greater than 0.08 solar masses, and therefore it is not a substellar object. However, its position in the HR diagram implies that this star is indeed very close to the substellar limit.

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