319 research outputs found

    The effect of continuum scattering processes on spectral line formation

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    The effect of scattering processes in the continuum on the formation of spectral lines in a static atmosphere with an arbitrary distribution of the internal energy sources is investigated using Ambartsumian's principle of invariance. Spectral line profiles are calculated to illustrate the effect the assumption of the complete redistribution on atoms and coherent scattering in continuum may have on the emergent intensity. The one-dimensional case is considered for simplicity.Comment: 11 pages (including 2 figures). Accepted for publication in Journ. of Quant. Spectr. and Rad. Transfe

    Abundances in Damped Ly-alpha Galaxies

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    Damped Ly_alpha galaxies provide a sample of young galaxies where chemical abundances can be derived throughout the whole universe with an accuracy comparable to that for the local universe. Despite a large spread in redshift, HI column density and metallicity, DLA galaxies show a remarkable uniformity in the elemental ratios rather suggestive of similar chemical evolution if not of an unique population. These galaxies are characterized by a moderate, if any, enhancement of alpha-elements over Fe-peak elemental abundance with [S/Zn] about 0 and [O/Zn] about 0.2, rather similarly to the dwarfs galaxies in the Local Group. Nitrogen shows a peculiar behaviour with a bimodal distribution and possibly two plateaux. In particular, the plateau at low N abundances ([N/H] < -3), is not observed in other atrophysical sites and might be evidence for primary N production by massive stars.Comment: To appear in the Proceedings of the ESO/Arcetri Workshop on "Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites", eds., L. Pasquini and S. Randich (Springer-Verlag Series, "ESO Astrophysics Symposia"

    Abundance ratios of volatile vs. refractory elements in planet-harbouring stars: hints of pollution?

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    We present the [X/H] trends as function of the elemental condensation temperature Tc in 88 planet host stars and in a volume-limited comparison sample of 33 dwarfs without detected planetary companions. We gathered homogeneous abundance results for many volatile and refractory elements spanning a wide range of Tc, from a few dozens to several hundreds kelvin. We investigate possible anomalous trends of planet hosts with respect to comparison sample stars in order to detect evidence of possible pollution events. No significant differences are found in the behaviour of stars with and without planets. This result is in agreement with a ``primordial'' origin of the metal excess in planet host stars. However, a subgroup of 5 planet host and 1 comparison sample stars stands out for having particularly high [X/H] vs. Tc slopes.Comment: 10 pages, 7 figures, accepted for publication in A&A. Figures with higher resolution are available at www.iac.es/proyect/abuntes

    ARES v2 - new features and improved performance

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    Aims: We present a new upgraded version of ARES. The new version includes a series of interesting new features such as automatic radial velocity correction, a fully automatic continuum determination, and an estimation of the errors for the equivalent widths. Methods: The automatic correction of the radial velocity is achieved with a simple cross-correlation function, and the automatic continuum determination, as well as the estimation of the errors, relies on a new approach to evaluating the spectral noise at the continuum level. Results: ARES v2 is totally compatible with its predecessor. We show that the fully automatic continuum determination is consistent with the previous methods applied for this task. It also presents a significant improvement on its performance thanks to the implementation of a parallel computation using the OpenMP library.Comment: 4 pages, 2 Figures; accepted in A&A; ARES Webpage: www.astro.up.pt/~sousasag/are

    On the functional form of the metallicity-giant planet correlation

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    It is generally accepted that the presence of a giant planet is strongly dependent on the stellar metallicity. A stellar mass dependence has also been investigated, but this dependence does not seem as strong as the metallicity dependence. Even for metallicity, however, the exact form of the correlation has not been established. In this paper, we test several scenarios for describing the frequency of giant planets as a function of its host parameters. We perform this test on two volume-limited samples (from CORALIE and HARPS). By using a Bayesian analysis, we quantitatively compared the different scenarios. We confirm that giant planet frequency is indeed a function of metallicity. However, there is no statistical difference between a constant or an exponential function for stars with subsolar metallicities contrary to what has been previously stated in the literature. The dependence on stellar mass could neither be confirmed nor be discarded.Comment: 5 pages, 2 figures, accepted in A&

    Higher depletion of lithium in planet host stars: no age and mass effect

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    Recent observational work by Israelian et al. has shown that sun-like planet host stars in the temperature range 5700K < Teff < 5850K have lithium abundances that are significantly lower than those observed for "single" field stars. In this letter we use stellar evolutionary models to show that differences in stellar mass and age are not responsible for the observed correlation. This result, along with the finding of Israelian et al., strongly suggest that the observed lithium difference is likely linked to some process related to the formation and evolution of planetary systems.Comment: 4 pages, 4 figures, letter accepted for publication in Astronomy & Astrophysic

    The Black Hole Binary Nova Scorpii 1994 (GRO J1655-40): An improved chemical analysis

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    The chemical analysis of secondary stars of low mass X-ray binaries provides an opportunity to study the formation processes of compact objects, either black holes or neutron stars. Following the discovery of overabundances of α\alpha-elements in the HIRES/Keck spectrum of the secondary star of Nova Scorpii 1994 (Israelian et al. 1999), we obtained UVES/VLT high-resolution spectroscopy with the aim of performing a detailed abundance analysis of this secondary star. Using a χ2\chi2-minimization procedure and a grid of synthetic spectra, we derive the stellar parameters and atmospheric abundances of O, Mg, Al, Ca, Ti, Fe and Ni, using a new UVES spectrum and the HIRES spectrum.The abundances of Al, Ca, Ti, Fe and Ni seem to be consistent with solar values, whereas Na, and especially O, Mg, Si and S are significantly enhanced in comparison with Galactic trends of these elements. A comparison with spherically and non-spherically symmetric supernova explosion models may provide stringent constraints to the model parameters as mass-cut and the explosion energy, in particular from the relative abundances of Si, S, Ca, Ti, Fe and Ni. Most probably the black hole in this system formed in a hypernova explosion of a 30--35 \Msun progenitor star with a mass-cut in the range 2--3.5 \Msun. However, these models produce abundances of Al and Na almost ten times higher than the observed values.Comment: New Accepted version for publication in Astronomy and Astrophysics Table 2: Correcte
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