Rio Setiawan - Academia.edu (original) (raw)

Papers by Rio Setiawan

G and K giants are a class of radial velocity (RV) variables. One reason for this variability are... more G and K giants are a class of radial velocity (RV) variables. One reason for this variability are planetary companions which are indicated in time series of stellar spectra. Since 2004 these spectra in the visual range were obtained with the high resolution coudé échelle spectrograph mounted on the 2m telescope of the Thüringer Landessternwarte Tautenburg (TLS) for a northern sample of 62 very bright K giants. In the South around 300 G and K giants were observed with HARPS mounted on the 3.6m telescope on La Silla. The TLS sample contains at least 11 stars (18 %) which show low-amplitude, long-period RV variations most likely due to planets. This percentage of planet frequency is confirmed by preliminary results of the HARPS study. Moreover the TLS survey seems to indicate that giant planets do not favour metal-rich stars, are more massive, and have longer periods than those found around solar-type host stars.

Asteroseismology is an indispensable tool that uses the properties of stellar oscillations to pro... more Asteroseismology is an indispensable tool that uses the properties of stellar oscillations to probe the internal structure of stars. This can provide a direct test of stellar structure and evolution theory. Precise stellar radial velocity (RV) measurements made in recent years have not only discovered the first extra-solar planets, but have also uncovered new classes of low-amplitude variable stars. One such is represented by the K giant stars which exhibit RV variations with amplitudes in the range of 50-300 m/s (Walker et al. 1989, Hatzes & Cochran 1993,1994 ab). This variability is multi-periodic and occurring on two time- scales: less than 10 days and several hundreds of days.

We present oxygen abundances derived from the forbidden oxygen line for G and K giants with preci... more We present oxygen abundances derived from the forbidden oxygen line for G and K giants with precise radial velocity (RV) measurements. Our goal is determine the evolutionary stage for 75 G and K giant stars using CNO abundances. The abundance analysis was done in standard Local Thermodynamic Equilibrium (LTE) with appropriate NLTE corrections and high precision spectra obtained with the FEROS (Setiawan et al. 2003) spectrograph. The fundamental parameters T eff, log g and [Fe/H] were determined from a detailed analysis to obtain the position of stars on the HR diagram as precise as possible. The abundances were derived from a synthetic analysis using plane-parallel, line-blanketed atmospheric models (Kurucz et al. 1993) and an updated version of the spectral analysis code MOOG (Sneden 1973). These abundances offer a unique possibility to establish the evolutionary stage of the objects, specially for those stars presenting a misclassification from the evolutionary tracks. Our stars sample presents three giants with extra solar planets detection HD 47536, HD 122430 and HD 11977 (Figure 1). In addition, derived CNO abundances permit to study the behavior of these elements in low mass (M ≤ 1 - 3.0 M⊙) evolved stars.

Astronomy & Astrophysics, 2006

We present the detailed spectroscopic analysis of 72 evolved stars, which were previously studied... more We present the detailed spectroscopic analysis of 72 evolved stars, which were previously studied for accurate radial velocity variations. Using one Hyades giant and another well studied star as the reference abundance, we determine the [Fe/H] for the whole sample. These metallicities, together with the T eff values and the absolute V-band magnitude derived from Hipparcos parallaxes, are used to estimate basic stellar parameters (ages, masses, radii, (B−V) 0 and log g) using theoretical isochrones and a Bayesian estimation method. The (B−V) 0 values so estimated turn out to be in excellent agreement (to within ∼ 0.05 mag) with the observed (B−V), confirming the reliability of the T eff -(B−V) 0 relation used in the isochrones. On the other hand, the estimated log g values are typically 0.2 dex lower than those derived from spectroscopy; this effect has a negligible impact on [Fe/H] determinations. The estimated diameters θ have been compared with limb darkening-corrected ones measured with independent methods, finding an agreement better than 0.3 mas within the 1 < θ < 10 mas interval (or, alternatively, finding mean differences of just 6 %). We derive the age-metallicity relation for the solar neighborhood; for the first time to our knowledge, such a relation has been derived from observations of field giants rather than from open clusters and field dwarfs and subdwarfs. The age-metallicity relation is characterized by close-to-solar metallicities for stars younger than ∼ 4 Gyr, and by a large [Fe/H] spread with a trend towards lower metallicities for higher ages. In disagreement with other studies, we find that the [Fe/H] dispersion of young stars (less than 1 Gyr) is comparable to the observational errors, indicating that stars in the solar neighbourhood are formed from interstellar matter of quite homogeneous chemical composition. The three giants of our sample which have been proposed to host planets are not metal rich; this result is at odds with those for main sequence stars. However, two of these stars have masses much larger than a solar mass so we may be sampling a different stellar population from most radial velocity searches for extrasolar planets. We also confirm the previous indication that the radial velocity variability tends to increase along the RGB, and in particular with the stellar radius. 2 L. da Silva et al.: Basic physical parameters of Giant stars

We present oxygen abundances derived from the forbidden oxygen line for G and K giants with preci... more We present oxygen abundances derived from the forbidden oxygen line for G and K giants with precise radial velocity (RV) measurements. Our goal is determine the evolutionary stage for 75 G and K giant stars using CNO abundances. The abundance analysis was done in standard Local Thermodynamic Equilibrium (LTE) with appropriate NLTE corrections and high precision spectra obtained with the FEROS (Setiawan et al. 2003) spectrograph. The fundamental parameters T eff, log g and [Fe/H] were determined from a detailed analysis to obtain the position of stars on the HR diagram as precise as possible. The abundances were derived from a synthetic analysis using plane-parallel, line-blanketed atmospheric models (Kurucz et al. 1993) and an updated version of the spectral analysis code MOOG (Sneden 1973). These abundances offer a unique possibility to establish the evolutionary stage of the objects, specially for those stars presenting a misclassification from the evolutionary tracks. Our stars sample presents three giants with extra solar planets detection HD 47536, HD 122430 and HD 11977 (Figure 1). In addition, derived CNO abundances permit to study the behavior of these elements in low mass (M ≤ 1 − 3.0 M⊙) evolved stars.

Astronomy & Astrophysics, 2009

Context: We found evidence for a sub-stellar companion around the K giant star HD 110014. This co... more Context: We found evidence for a sub-stellar companion around the K giant star HD 110014. This cool evolved star, with a spectral type K2III and an estimated mass between 1.9 and 2.4 M&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;sun;, is slightly metal rich with [Fe/H] = 0.19 and a rotational velocity V sin i = 2.0 km s-1. Aims: To search for extrasolar planets around intermediate-mass

Recently we have published the detailed spectroscopic analysis of 72 evolved stars, previously st... more Recently we have published the detailed spectroscopic analysis of 72 evolved stars, previously studied for accurate radial velocity variations (da Silva et al. 2006). The spectroscopic observations were performed with the FEROS spectrograph (RP ∼ 50000) at the 1.5m ESO telescope at La Silla (Chile). The stellar atmosphere parameters (Teff, log g,[Fe/H]) and the micro-turbulence velocities were determined spectroscopically, using a LTE code and the MARCS models. These metallicities, together with the Teff values and the absolute V-band magnitude derived from Hipparcos parallaxes, were used to estimate basic stellar parameters (ages, masses, radii, (B-V)o and log g) using theoretical isochrones and a modified version of (2005) method. The (B-V)o values so estimated turn out to be in excellent agreement with the observed ones, confirming the reliability of the (Teff,(B-V)o) relation used in the isochrones. The estimated stellar diameters also are in good agreement, with the ones measured by independent methods, better than 0.3 mas.

Proceedings of The International Astronomical Union, 2008

Planet searches around evolved giant stars are bringing new insights to planet formation theories... more Planet searches around evolved giant stars are bringing new insights to planet formation theories by virtue of the broader stellar mass range of the host stars compared to the solar-type stars that have been the subject of most current planet searches programs. These searches among giant stars are producing extremely interesting results. Contrary to main sequence stars planet-hosting giants do not show a tendency of being more metal rich. Even if limited, the statistics also suggest a higher frequency of giant planets (at least 10 % ) that are more massive compared to solar-type main sequence stars.

G and K giants are a class of radial velocity (RV) variables. One reason for this variability are... more G and K giants are a class of radial velocity (RV) variables. One reason for this variability are planetary companions which are indicated in time series of stellar spectra. Since 2004 these spectra in the visual range were obtained with the high resolution coudé échelle spectrograph mounted on the 2m telescope of the Thüringer Landessternwarte Tautenburg (TLS) for a northern sample of 62 very bright K giants. In the South around 300 G and K giants were observed with HARPS mounted on the 3.6m telescope on La Silla. The TLS sample contains at least 11 stars (18 %) which show low-amplitude, long-period RV variations most likely due to planets. This percentage of planet frequency is confirmed by preliminary results of the HARPS study. Moreover the TLS survey seems to indicate that giant planets do not favour metal-rich stars, are more massive, and have longer periods than those found around solar-type host stars.

Asteroseismology is an indispensable tool that uses the properties of stellar oscillations to pro... more Asteroseismology is an indispensable tool that uses the properties of stellar oscillations to probe the internal structure of stars. This can provide a direct test of stellar structure and evolution theory. Precise stellar radial velocity (RV) measurements made in recent years have not only discovered the first extra-solar planets, but have also uncovered new classes of low-amplitude variable stars. One such is represented by the K giant stars which exhibit RV variations with amplitudes in the range of 50-300 m/s (Walker et al. 1989, Hatzes & Cochran 1993,1994 ab). This variability is multi-periodic and occurring on two time- scales: less than 10 days and several hundreds of days.

We present oxygen abundances derived from the forbidden oxygen line for G and K giants with preci... more We present oxygen abundances derived from the forbidden oxygen line for G and K giants with precise radial velocity (RV) measurements. Our goal is determine the evolutionary stage for 75 G and K giant stars using CNO abundances. The abundance analysis was done in standard Local Thermodynamic Equilibrium (LTE) with appropriate NLTE corrections and high precision spectra obtained with the FEROS (Setiawan et al. 2003) spectrograph. The fundamental parameters T eff, log g and [Fe/H] were determined from a detailed analysis to obtain the position of stars on the HR diagram as precise as possible. The abundances were derived from a synthetic analysis using plane-parallel, line-blanketed atmospheric models (Kurucz et al. 1993) and an updated version of the spectral analysis code MOOG (Sneden 1973). These abundances offer a unique possibility to establish the evolutionary stage of the objects, specially for those stars presenting a misclassification from the evolutionary tracks. Our stars sample presents three giants with extra solar planets detection HD 47536, HD 122430 and HD 11977 (Figure 1). In addition, derived CNO abundances permit to study the behavior of these elements in low mass (M ≤ 1 - 3.0 M⊙) evolved stars.

Astronomy & Astrophysics, 2006

We present the detailed spectroscopic analysis of 72 evolved stars, which were previously studied... more We present the detailed spectroscopic analysis of 72 evolved stars, which were previously studied for accurate radial velocity variations. Using one Hyades giant and another well studied star as the reference abundance, we determine the [Fe/H] for the whole sample. These metallicities, together with the T eff values and the absolute V-band magnitude derived from Hipparcos parallaxes, are used to estimate basic stellar parameters (ages, masses, radii, (B−V) 0 and log g) using theoretical isochrones and a Bayesian estimation method. The (B−V) 0 values so estimated turn out to be in excellent agreement (to within ∼ 0.05 mag) with the observed (B−V), confirming the reliability of the T eff -(B−V) 0 relation used in the isochrones. On the other hand, the estimated log g values are typically 0.2 dex lower than those derived from spectroscopy; this effect has a negligible impact on [Fe/H] determinations. The estimated diameters θ have been compared with limb darkening-corrected ones measured with independent methods, finding an agreement better than 0.3 mas within the 1 < θ < 10 mas interval (or, alternatively, finding mean differences of just 6 %). We derive the age-metallicity relation for the solar neighborhood; for the first time to our knowledge, such a relation has been derived from observations of field giants rather than from open clusters and field dwarfs and subdwarfs. The age-metallicity relation is characterized by close-to-solar metallicities for stars younger than ∼ 4 Gyr, and by a large [Fe/H] spread with a trend towards lower metallicities for higher ages. In disagreement with other studies, we find that the [Fe/H] dispersion of young stars (less than 1 Gyr) is comparable to the observational errors, indicating that stars in the solar neighbourhood are formed from interstellar matter of quite homogeneous chemical composition. The three giants of our sample which have been proposed to host planets are not metal rich; this result is at odds with those for main sequence stars. However, two of these stars have masses much larger than a solar mass so we may be sampling a different stellar population from most radial velocity searches for extrasolar planets. We also confirm the previous indication that the radial velocity variability tends to increase along the RGB, and in particular with the stellar radius. 2 L. da Silva et al.: Basic physical parameters of Giant stars

We present oxygen abundances derived from the forbidden oxygen line for G and K giants with preci... more We present oxygen abundances derived from the forbidden oxygen line for G and K giants with precise radial velocity (RV) measurements. Our goal is determine the evolutionary stage for 75 G and K giant stars using CNO abundances. The abundance analysis was done in standard Local Thermodynamic Equilibrium (LTE) with appropriate NLTE corrections and high precision spectra obtained with the FEROS (Setiawan et al. 2003) spectrograph. The fundamental parameters T eff, log g and [Fe/H] were determined from a detailed analysis to obtain the position of stars on the HR diagram as precise as possible. The abundances were derived from a synthetic analysis using plane-parallel, line-blanketed atmospheric models (Kurucz et al. 1993) and an updated version of the spectral analysis code MOOG (Sneden 1973). These abundances offer a unique possibility to establish the evolutionary stage of the objects, specially for those stars presenting a misclassification from the evolutionary tracks. Our stars sample presents three giants with extra solar planets detection HD 47536, HD 122430 and HD 11977 (Figure 1). In addition, derived CNO abundances permit to study the behavior of these elements in low mass (M ≤ 1 − 3.0 M⊙) evolved stars.

Astronomy & Astrophysics, 2009

Context: We found evidence for a sub-stellar companion around the K giant star HD 110014. This co... more Context: We found evidence for a sub-stellar companion around the K giant star HD 110014. This cool evolved star, with a spectral type K2III and an estimated mass between 1.9 and 2.4 M&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;sun;, is slightly metal rich with [Fe/H] = 0.19 and a rotational velocity V sin i = 2.0 km s-1. Aims: To search for extrasolar planets around intermediate-mass

Recently we have published the detailed spectroscopic analysis of 72 evolved stars, previously st... more Recently we have published the detailed spectroscopic analysis of 72 evolved stars, previously studied for accurate radial velocity variations (da Silva et al. 2006). The spectroscopic observations were performed with the FEROS spectrograph (RP ∼ 50000) at the 1.5m ESO telescope at La Silla (Chile). The stellar atmosphere parameters (Teff, log g,[Fe/H]) and the micro-turbulence velocities were determined spectroscopically, using a LTE code and the MARCS models. These metallicities, together with the Teff values and the absolute V-band magnitude derived from Hipparcos parallaxes, were used to estimate basic stellar parameters (ages, masses, radii, (B-V)o and log g) using theoretical isochrones and a modified version of (2005) method. The (B-V)o values so estimated turn out to be in excellent agreement with the observed ones, confirming the reliability of the (Teff,(B-V)o) relation used in the isochrones. The estimated stellar diameters also are in good agreement, with the ones measured by independent methods, better than 0.3 mas.

Proceedings of The International Astronomical Union, 2008

Planet searches around evolved giant stars are bringing new insights to planet formation theories... more Planet searches around evolved giant stars are bringing new insights to planet formation theories by virtue of the broader stellar mass range of the host stars compared to the solar-type stars that have been the subject of most current planet searches programs. These searches among giant stars are producing extremely interesting results. Contrary to main sequence stars planet-hosting giants do not show a tendency of being more metal rich. Even if limited, the statistics also suggest a higher frequency of giant planets (at least 10 % ) that are more massive compared to solar-type main sequence stars.