Gustavo Mello - Academia.edu (original) (raw)
Papers by Gustavo Mello
The files table2.dat and table3.dat contain the [Mn/H] and [Co/H] abundance ratios, respectively,... more The files table2.dat and table3.dat contain the [Mn/H] and [Co/H] abundance ratios, respectively, for all measured lines, sample stars and sources of hyperfine splitting structure. Some lines have not been effectively used in some stars; these have abundance ratios equal to +9.99 in the files. (3 data files).
A search for line profile variations correlated with stellar radial velocities (RVs) is presented... more A search for line profile variations correlated with stellar radial velocities (RVs) is presented. The goal is to develop a correction method of RVs for activity effects enabling the search for planets orbiting active, i.e., young stars. The Coude Echelle Spectrometer (CES) at the ESO 3.6m telescope with its high spectral resolution (R=220,000) has been used to monitor some active stars for changes in their RVs and absorption line profiles. In the case of HD 166435 it is demonstrated that a correction of the measured RVs for line profile variations is feasible and improves the RVs scatter down to the measurement precision.
Table 2 contains the lines, atomic constants, equivalent widths, and abundance results for the el... more Table 2 contains the lines, atomic constants, equivalent widths, and abundance results for the elements other than iron, and Table 3 contains the average for the abundances and their uncertainties. (4 data files).
The Astrophysical Journal, 1997
The detailed analysis of the optical spectrum and evolutionary state of the G2 Va star HR 6060 sh... more The detailed analysis of the optical spectrum and evolutionary state of the G2 Va star HR 6060 shows this object to have atmospheric parameters, mass, chromospheric activity, and UBV colors indistinguishable from the solar ones within the observational uncertainties. Only its luminosity and age are slightly higher than solar. Its abundance pattern is solar, with the exception of a slight excess of Sc, V, and the elements heavier than Sr. HR 6060 surpasses all previously claimed solar twins in likeness to the Sun, and we recommend that it be considered for strong priority in the ongoing planet-searching programs as well as in SETI surveys.
The Astrophysical Journal, 1997
The young solar-type star HR 6094 is found to be a barium dwarf, overabundant in the s-process el... more The young solar-type star HR 6094 is found to be a barium dwarf, overabundant in the s-process elements as well as deficient in C. It is a member of the solar-metallicity, 0.3 Gyr old Ursa Major kinematical group. Measurements of radial velocity and ultraviolet flux do not support the attribution of such abundance anomalies to an unseen degenerate companion. A common proper motion, V ϭ 10, DA white dwarf (WD), located 5360 AU away, however, strongly supports the explanation of the origin of this barium star by the process of mass transfer in a binary system, in which the secondary component accreted matter from the primary one (now the WD) when it was an asymptotic giant branch (AGB) star self-enriched in the s-process elements. The membership in the UMa group of another s-process-rich and C-deficient star, HR 2047, suggests that these stars could have formed a multiple system in the past, which was disrupted by the mass-loss episode of the former AGB star. Their [C͞Fe] deficiency could be explained by the action of the hot-bottomed envelope burning process in the late AGB, thereby reconverting it from a C-rich to an O-rich star, depleting C while enriching its envelope with Li and neutron capture elements. This is the first identification of the barium phenomenon in a near-zero-age star, besides being the first barium system in which the remnant of the late AGB star responsible for the heavy-element enrichment may have been directly spotted.
The Astronomical Journal, 1991
A detailed analysis of the F8 V star Phi(2) Pav is reported. The following atmospheric parameters... more A detailed analysis of the F8 V star Phi(2) Pav is reported. The following atmospheric parameters were found: theta(eff) = 0.84, log g = 3.70, Fe/H = -0.37, and xi = 1.5 km/s. The spectroscopically determined surface gravity is in conflict with that determined from M(bol), though hardly by more than the error limits. The influence of this disagreement on
The Astronomical Journal, 1997
ABSTRACT We report the detailed spectroscopic analysis of the high-resolution optical spectra of ... more ABSTRACT We report the detailed spectroscopic analysis of the high-resolution optical spectra of the cool component of the symbiotic star BD-21° 3873. Its atmospheric and kinematic parameters identify it as a typical halo giant star, with the exception of a 0.45 dex excess of the heavy neutron-capture elements. Its luminosity is insufficient for an AGB star which could have commenced shell helium burning and become self-enriched in the neutron-capture elements. Its heavy element excess is thus ascribed to the barium phenomenon, in which the secondary component accreted matter from the primary one (now the white dwarf) when it was a TP-AGB star self-enriched in the s-process elements. This object therefore provides yet another link between the symbiotic systems and the barium stars. We have obtained as a novel result a deficiency of Cu in the photosphere of BD-21° 3873, which could be related to the depletion of this element by the operation of the neutron-capture synthesis during the TP-AGB phase of the former primary component.
![Research paper thumbnail of M dwarf spectral indices at moderate resolution: accurate Teff and [Fe/H] for 178 southern stars](https://attachments.academia-assets.com/92983467/thumbnails/1.jpg)
](Monthly Notices of the Royal Astronomical Society, 2021
We present a spectroscopic and photometric calibration to derive effective temperatures Teff and ... more We present a spectroscopic and photometric calibration to derive effective temperatures Teff and metallicities [Fe/H] for M dwarfs, based on a principal component analysis (PCA) of 147 spectral indices measured off moderate resolution (R∼11 000), high S/N (>100) spectra in the λλ 8390–8834 region, plus the J−H colour. Internal uncertainties, estimated by the residuals, are 81 K and 0.12 dex, respectively, for Teff and [Fe/H], the calibrations being valid for 3050 K < T$_\text{eff}\, \lt $ 4100 K and −0.45 < [Fe/H] lt,+\lt \, +lt,+0.50 dex. The PCA calibration is a competitive model-independent method to derive Teff and [Fe/H] for large samples of M dwarfs, well suited to the available database of far-red spectra. The median uncertainties are 105 K and 0.23 dex for Teff and [Fe/H], respectively, estimated by Monte Carlo simulations. We compare our values to other works based on photometric and spectroscopic techniques and find median differences 75 ± 273 K and 0.02 ± 0.31 dex for ...
Proceedings of the International Astronomical Union, 2017
In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to... more In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to migration, and the metallicity of the host star, based on the core accretion model, and radial profiles of dust surface density and gas temperature. At that time, less than 200 extrasolar planets were known, limiting the scope of our analysis. Here, we take into account the expanded statistics allowed by new discoveries, in order to check the validity of some premises. We compare predictions with the present available data and results for different stellar mass ranges. We find that the zero age planetary orbit (ZAPO) hypothesis continues to hold after a two order of magnitude increase in discovered planets, as well as the prediction that planets around metal poor stars would have shorter orbits.
Astronomy & Astrophysics, 2019
Context. The flux distribution of solar analogues is required for calculating the spectral albedo... more Context. The flux distribution of solar analogues is required for calculating the spectral albedo of solar system bodies such as asteroids and trans-Neptunian objects. Ideally a solar analogue should be comparatively faint as the target of interest, but very few analogues fainter than V = 9 mag have been identified so far. Only atmospheric parameters equal to solar guarantee a flux distribution equal to solar as well, while only photometric colours equal to solar do not. Reddening is also a factor to consider when selecting faint analogue candidates. Aims. Our aim is to implement the methodology for identifying faint analogues at the limit of precision allowed by the current spectroscopic surveys. We quantify the precision attainable for the atmospheric parameters of effective temperature (Teff), metallicity ([Fe/H]), and surface gravity (log g) when derived from moderately low-resolution (R = 8000) spectra with S∕N ~ 100. We estimate the significance of reddening at 100–300 pc from...
Astronomy & Astrophysics, 2019
Context. The determination of stellar effective temperature (Teff) in F, G, and K stars using Hα ... more Context. The determination of stellar effective temperature (Teff) in F, G, and K stars using Hα profile fitting is a quite remarkable and powerful tool because it does not depend on reddening and is only slightly sensitive to other atmospheric parameters. Nevertheless, this technique is not frequently used because of the complex procedure needed to recover the profile of broad lines in echelle spectra. As a consequence, tests performed on different models have sometimes provided ambiguous results. Aims. The main aim of this work is to test the ability of the Hα profile fitting technique to derive Teff. We also aim to improve the applicability of this technique to echelle spectra and to test how well 1D + LTE models perform on a variety of F–K stars. We also apply the technique to HARPS spectra and test the reliability and the stability of the HARPS response over several years using the Sun. Methods. We have developed a normalization method for recovering undistorted Hα profiles and...
Monthly Notices of the Royal Astronomical Society, 2018
Combining stellar atmospheric parameters, such as effective temperature, surface gravity, and met... more Combining stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity, with barycentric radial velocity data provides insight into the chemo-dynamics of the Milky Way and our local Galactic environment. We analyse 3075 stars with spectroscopic data from the Sloan Digital Sky Survey III MARVELS radial velocity survey and present atmospheric parameters for 2343 dwarf stars using the spectral indices method, a modified version of the equivalent width method. We present barycentric radial velocities for a sample of 2610 stars with a median uncertainty of 0.3 km s −1. We determine stellar ages using two independent methods and calculate ages for 2335 stars with a maximum-likelihood isochronal age-dating method and for 2194 stars with a Bayesian age-dating method. Using previously published parallax data, we compute Galactic orbits and space velocities for 2504 stars to explore stellar populations based on kinematic and age parameters. This study combines good ages and exquisite velocities to explore local chemo-kinematics of the Milky Way, which complements many of the recent studies of giant stars with the APOGEE survey, and we find our results to be in agreement with current chemo-dynamical models of the Milky Way. Particularly, we find from our metallicity distributions and velocity-age relations of a kinematically defined thin disc that the metal-rich end has stars of all ages, even after we clean the sample of highly eccentric stars, suggesting that radial migration plays a key role in the metallicity scatter of the thin disc. All stellar parameters and kinematic data derived in this work are catalogued and published online in machine-readable form.
Proceedings of the International Astronomical Union, 2016
We derive T eff and [Fe/H] for a sample of 72 nearby M-dwarfs with Hipparcos parallaxes and δ <... more We derive T eff and [Fe/H] for a sample of 72 nearby M-dwarfs with Hipparcos parallaxes and δ < +30. Spectra, acquired at the Observatório do Pico dos Dias, Brazil, have R = 10,000 and S/N ≳ 100 for nearly all targets in the λλ8380-8880 range. Atmospheric parameters were derived from VJHK colors and a system of spectral line indices calibrated against sample stars with interferometric T eff and [Fe/H] from detailed analysis of FGK binary companions. A PCA method of calibration yields internal errors within 70 K and 0.1 dex for T eff and [Fe/H]. For 18 stars we present the first T eff or [Fe/H] derivation in the literature. We compute the star's luminosities, calculate the position of their habitable zones and estimate that, were all of they to harbour rocky planets inside their HZ, 15–20 of these would be detectable by the E-ELT Planetary Camera and Spectrograph.
Monthly Notices of the Royal Astronomical Society, 2017
Planet searches using the radial velocity technique show a paucity of companions to solar-type st... more Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ∼5 au in the mass range of ∼10-80 M Jup. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help assess the reality of the desert and provide insight to the formation and evolution of these objects. Here, we present 10 new brown dwarf and 2 low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III. These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from ∼13 to 76 M Jup and have orbital radii of less than 1 au. The two stellar companions have minimum masses of ∼98 and 100 M Jup. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 ± 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than ∼300 d to be ∼0.56 per cent.
Symposium - International Astronomical Union, 2000
We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. Th... more We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. The unevolved stars in this sample present high (> 2.00) Li abundances. We found a few cases of subgiant stars which present high Li content. The Sun seems to be part of a population of nearly unevolved stars which have depleted their Li to a high degree: all other metal-normal, near ZAMS stars in our sample show higher than solar Li content. There seems to be no correlation of the degree of Li depletion with mass, atmospheric parameters or state of evolution: as an example we found a star (HR1532) almost identical to the Sun in its state of evolution and atmospheric parameters, but with over ten times the solar Li abundance. We propose that different histories of angular momentum distribution at star birth, and/or post-birth angular momentum evolution, may account for these differences.
Astronomy & Astrophysics, 2016
Fine structure of the age-chromospheric activity relation in solar-type stars I. The Ca II infrar... more Fine structure of the age-chromospheric activity relation in solar-type stars I. The Ca II infrared triplet: Absolute flux calibration ,
The files table2.dat and table3.dat contain the [Mn/H] and [Co/H] abundance ratios, respectively,... more The files table2.dat and table3.dat contain the [Mn/H] and [Co/H] abundance ratios, respectively, for all measured lines, sample stars and sources of hyperfine splitting structure. Some lines have not been effectively used in some stars; these have abundance ratios equal to +9.99 in the files. (3 data files).
A search for line profile variations correlated with stellar radial velocities (RVs) is presented... more A search for line profile variations correlated with stellar radial velocities (RVs) is presented. The goal is to develop a correction method of RVs for activity effects enabling the search for planets orbiting active, i.e., young stars. The Coude Echelle Spectrometer (CES) at the ESO 3.6m telescope with its high spectral resolution (R=220,000) has been used to monitor some active stars for changes in their RVs and absorption line profiles. In the case of HD 166435 it is demonstrated that a correction of the measured RVs for line profile variations is feasible and improves the RVs scatter down to the measurement precision.
Table 2 contains the lines, atomic constants, equivalent widths, and abundance results for the el... more Table 2 contains the lines, atomic constants, equivalent widths, and abundance results for the elements other than iron, and Table 3 contains the average for the abundances and their uncertainties. (4 data files).
The Astrophysical Journal, 1997
The detailed analysis of the optical spectrum and evolutionary state of the G2 Va star HR 6060 sh... more The detailed analysis of the optical spectrum and evolutionary state of the G2 Va star HR 6060 shows this object to have atmospheric parameters, mass, chromospheric activity, and UBV colors indistinguishable from the solar ones within the observational uncertainties. Only its luminosity and age are slightly higher than solar. Its abundance pattern is solar, with the exception of a slight excess of Sc, V, and the elements heavier than Sr. HR 6060 surpasses all previously claimed solar twins in likeness to the Sun, and we recommend that it be considered for strong priority in the ongoing planet-searching programs as well as in SETI surveys.
The Astrophysical Journal, 1997
The young solar-type star HR 6094 is found to be a barium dwarf, overabundant in the s-process el... more The young solar-type star HR 6094 is found to be a barium dwarf, overabundant in the s-process elements as well as deficient in C. It is a member of the solar-metallicity, 0.3 Gyr old Ursa Major kinematical group. Measurements of radial velocity and ultraviolet flux do not support the attribution of such abundance anomalies to an unseen degenerate companion. A common proper motion, V ϭ 10, DA white dwarf (WD), located 5360 AU away, however, strongly supports the explanation of the origin of this barium star by the process of mass transfer in a binary system, in which the secondary component accreted matter from the primary one (now the WD) when it was an asymptotic giant branch (AGB) star self-enriched in the s-process elements. The membership in the UMa group of another s-process-rich and C-deficient star, HR 2047, suggests that these stars could have formed a multiple system in the past, which was disrupted by the mass-loss episode of the former AGB star. Their [C͞Fe] deficiency could be explained by the action of the hot-bottomed envelope burning process in the late AGB, thereby reconverting it from a C-rich to an O-rich star, depleting C while enriching its envelope with Li and neutron capture elements. This is the first identification of the barium phenomenon in a near-zero-age star, besides being the first barium system in which the remnant of the late AGB star responsible for the heavy-element enrichment may have been directly spotted.
The Astronomical Journal, 1991
A detailed analysis of the F8 V star Phi(2) Pav is reported. The following atmospheric parameters... more A detailed analysis of the F8 V star Phi(2) Pav is reported. The following atmospheric parameters were found: theta(eff) = 0.84, log g = 3.70, Fe/H = -0.37, and xi = 1.5 km/s. The spectroscopically determined surface gravity is in conflict with that determined from M(bol), though hardly by more than the error limits. The influence of this disagreement on
The Astronomical Journal, 1997
ABSTRACT We report the detailed spectroscopic analysis of the high-resolution optical spectra of ... more ABSTRACT We report the detailed spectroscopic analysis of the high-resolution optical spectra of the cool component of the symbiotic star BD-21° 3873. Its atmospheric and kinematic parameters identify it as a typical halo giant star, with the exception of a 0.45 dex excess of the heavy neutron-capture elements. Its luminosity is insufficient for an AGB star which could have commenced shell helium burning and become self-enriched in the neutron-capture elements. Its heavy element excess is thus ascribed to the barium phenomenon, in which the secondary component accreted matter from the primary one (now the white dwarf) when it was a TP-AGB star self-enriched in the s-process elements. This object therefore provides yet another link between the symbiotic systems and the barium stars. We have obtained as a novel result a deficiency of Cu in the photosphere of BD-21° 3873, which could be related to the depletion of this element by the operation of the neutron-capture synthesis during the TP-AGB phase of the former primary component.
Monthly Notices of the Royal Astronomical Society, 2021
We present a spectroscopic and photometric calibration to derive effective temperatures Teff and ... more We present a spectroscopic and photometric calibration to derive effective temperatures Teff and metallicities [Fe/H] for M dwarfs, based on a principal component analysis (PCA) of 147 spectral indices measured off moderate resolution (R∼11 000), high S/N (>100) spectra in the λλ 8390–8834 region, plus the J−H colour. Internal uncertainties, estimated by the residuals, are 81 K and 0.12 dex, respectively, for Teff and [Fe/H], the calibrations being valid for 3050 K < T$_\text{eff}\, \lt $ 4100 K and −0.45 < [Fe/H] lt,+\lt \, +lt,+0.50 dex. The PCA calibration is a competitive model-independent method to derive Teff and [Fe/H] for large samples of M dwarfs, well suited to the available database of far-red spectra. The median uncertainties are 105 K and 0.23 dex for Teff and [Fe/H], respectively, estimated by Monte Carlo simulations. We compare our values to other works based on photometric and spectroscopic techniques and find median differences 75 ± 273 K and 0.02 ± 0.31 dex for ...
Proceedings of the International Astronomical Union, 2017
In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to... more In 2005 we suggested a relation between the optimal locus of gas giant planet formation, prior to migration, and the metallicity of the host star, based on the core accretion model, and radial profiles of dust surface density and gas temperature. At that time, less than 200 extrasolar planets were known, limiting the scope of our analysis. Here, we take into account the expanded statistics allowed by new discoveries, in order to check the validity of some premises. We compare predictions with the present available data and results for different stellar mass ranges. We find that the zero age planetary orbit (ZAPO) hypothesis continues to hold after a two order of magnitude increase in discovered planets, as well as the prediction that planets around metal poor stars would have shorter orbits.
Astronomy & Astrophysics, 2019
Context. The flux distribution of solar analogues is required for calculating the spectral albedo... more Context. The flux distribution of solar analogues is required for calculating the spectral albedo of solar system bodies such as asteroids and trans-Neptunian objects. Ideally a solar analogue should be comparatively faint as the target of interest, but very few analogues fainter than V = 9 mag have been identified so far. Only atmospheric parameters equal to solar guarantee a flux distribution equal to solar as well, while only photometric colours equal to solar do not. Reddening is also a factor to consider when selecting faint analogue candidates. Aims. Our aim is to implement the methodology for identifying faint analogues at the limit of precision allowed by the current spectroscopic surveys. We quantify the precision attainable for the atmospheric parameters of effective temperature (Teff), metallicity ([Fe/H]), and surface gravity (log g) when derived from moderately low-resolution (R = 8000) spectra with S∕N ~ 100. We estimate the significance of reddening at 100–300 pc from...
Astronomy & Astrophysics, 2019
Context. The determination of stellar effective temperature (Teff) in F, G, and K stars using Hα ... more Context. The determination of stellar effective temperature (Teff) in F, G, and K stars using Hα profile fitting is a quite remarkable and powerful tool because it does not depend on reddening and is only slightly sensitive to other atmospheric parameters. Nevertheless, this technique is not frequently used because of the complex procedure needed to recover the profile of broad lines in echelle spectra. As a consequence, tests performed on different models have sometimes provided ambiguous results. Aims. The main aim of this work is to test the ability of the Hα profile fitting technique to derive Teff. We also aim to improve the applicability of this technique to echelle spectra and to test how well 1D + LTE models perform on a variety of F–K stars. We also apply the technique to HARPS spectra and test the reliability and the stability of the HARPS response over several years using the Sun. Methods. We have developed a normalization method for recovering undistorted Hα profiles and...
Monthly Notices of the Royal Astronomical Society, 2018
Combining stellar atmospheric parameters, such as effective temperature, surface gravity, and met... more Combining stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity, with barycentric radial velocity data provides insight into the chemo-dynamics of the Milky Way and our local Galactic environment. We analyse 3075 stars with spectroscopic data from the Sloan Digital Sky Survey III MARVELS radial velocity survey and present atmospheric parameters for 2343 dwarf stars using the spectral indices method, a modified version of the equivalent width method. We present barycentric radial velocities for a sample of 2610 stars with a median uncertainty of 0.3 km s −1. We determine stellar ages using two independent methods and calculate ages for 2335 stars with a maximum-likelihood isochronal age-dating method and for 2194 stars with a Bayesian age-dating method. Using previously published parallax data, we compute Galactic orbits and space velocities for 2504 stars to explore stellar populations based on kinematic and age parameters. This study combines good ages and exquisite velocities to explore local chemo-kinematics of the Milky Way, which complements many of the recent studies of giant stars with the APOGEE survey, and we find our results to be in agreement with current chemo-dynamical models of the Milky Way. Particularly, we find from our metallicity distributions and velocity-age relations of a kinematically defined thin disc that the metal-rich end has stars of all ages, even after we clean the sample of highly eccentric stars, suggesting that radial migration plays a key role in the metallicity scatter of the thin disc. All stellar parameters and kinematic data derived in this work are catalogued and published online in machine-readable form.
Proceedings of the International Astronomical Union, 2016
We derive T eff and [Fe/H] for a sample of 72 nearby M-dwarfs with Hipparcos parallaxes and δ <... more We derive T eff and [Fe/H] for a sample of 72 nearby M-dwarfs with Hipparcos parallaxes and δ < +30. Spectra, acquired at the Observatório do Pico dos Dias, Brazil, have R = 10,000 and S/N ≳ 100 for nearly all targets in the λλ8380-8880 range. Atmospheric parameters were derived from VJHK colors and a system of spectral line indices calibrated against sample stars with interferometric T eff and [Fe/H] from detailed analysis of FGK binary companions. A PCA method of calibration yields internal errors within 70 K and 0.1 dex for T eff and [Fe/H]. For 18 stars we present the first T eff or [Fe/H] derivation in the literature. We compute the star's luminosities, calculate the position of their habitable zones and estimate that, were all of they to harbour rocky planets inside their HZ, 15–20 of these would be detectable by the E-ELT Planetary Camera and Spectrograph.
Monthly Notices of the Royal Astronomical Society, 2017
Planet searches using the radial velocity technique show a paucity of companions to solar-type st... more Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ∼5 au in the mass range of ∼10-80 M Jup. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help assess the reality of the desert and provide insight to the formation and evolution of these objects. Here, we present 10 new brown dwarf and 2 low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III. These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from ∼13 to 76 M Jup and have orbital radii of less than 1 au. The two stellar companions have minimum masses of ∼98 and 100 M Jup. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 ± 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than ∼300 d to be ∼0.56 per cent.
Symposium - International Astronomical Union, 2000
We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. Th... more We report Li abundances from the λ6707 line for 19 nearby dwarf and subgiant solar-type stars. The unevolved stars in this sample present high (> 2.00) Li abundances. We found a few cases of subgiant stars which present high Li content. The Sun seems to be part of a population of nearly unevolved stars which have depleted their Li to a high degree: all other metal-normal, near ZAMS stars in our sample show higher than solar Li content. There seems to be no correlation of the degree of Li depletion with mass, atmospheric parameters or state of evolution: as an example we found a star (HR1532) almost identical to the Sun in its state of evolution and atmospheric parameters, but with over ten times the solar Li abundance. We propose that different histories of angular momentum distribution at star birth, and/or post-birth angular momentum evolution, may account for these differences.
Astronomy & Astrophysics, 2016
Fine structure of the age-chromospheric activity relation in solar-type stars I. The Ca II infrar... more Fine structure of the age-chromospheric activity relation in solar-type stars I. The Ca II infrared triplet: Absolute flux calibration ,