Michel Grenon

Detailed Analysis of Nearby Bulgelike Dwarf Stars. III. α-Element and Heavy-Element Abundances

The present sample of nearby bulgelike dwarf stars has kinematics and metallicities characteristic of a probable inner disk or bulge origin. Ages derived by using isochrones give 10-11 Gyr for these stars, and metallicities are in the range -0.80 ≤ [Fe/H] ≤ +0.40. We calculate stellar parameters from spectroscopic data, and chemical abundances of Mg, Si, Ca, Ti, La, Ba, Y, Zr, and Eu are derived by using spectrum synthesis. We found that [α-elements/Fe] show different patterns, depending on the element. Si/Fe, Ca/Fe, and Ti/Fe ratios decline smoothly for increasing metallicities and essentially follow the disk pattern. O and Mg, products of massive supernovae, and also the r-process element Eu are overabundant relative to disk stars, showing a steeper decline for metallicities [Fe/H] > -0.3 dex, and [s-elements/Fe] roughly track the solar values, with no apparent trend with metallicity for [Fe/H] < 0, showing subsolar values for the metal rich stars. Both kinematical and chemical properties of the bulgelike stars indicate a distinct identity of this population when compared with disk stars.

Detailed Analysis of Nearby Bulgelike Dwarf Stars. I. Stellar Parameters, Kinematics, and Oxygen Abundances*

High-resolution echelle spectra were obtained with the Fiber-fed Extended Range Optical Spectrograph at the 1.5 m ESO telescope for 35 nearby bulgelike stars with metallicities in the range -0.8 ≤ [Fe/H] ≤ +0.4. Geneva photometry, astrometric data from Hipparcos, and radial velocities from CORAVEL are available for these stars. From Hipparcos data, it appears that the turnoff of this population indicates an age of 10-11 Gyr (as stated by Grenon in 1999). Detailed analysis of the sample stars is carried out, and atmospheric parameters derived from spectroscopic and photometric determinations are presented. Oxygen abundances are derived based on the forbidden [O I] 6300.3 A line. The results show an oxygen overabundance pattern for most of the sample stars when compared to their disk counterparts.

Fundamental Stellar Parameters of γ[TSUP]2[/TSUP] Velorum from [ITAL]HIPPARCOS[/ITAL] Data

We report parallax measurements by the HIPPARCOS satellite of zeta Puppis and gamma^2 Velorum. The distance of zeta Pup is d=429 (+120/ -77) pc, in agreement with the commonly adopted value to Vela OB2. However, a significantly smaller distance is found for the gamma^2 Vel system: d=258 (+41/-31) pc. The total mass of gamma^2 Vel derived from its parallax, the angular size of the semi-major axis as measured with intensity interferometry, and the period is M(WR+O)=29.5 (+/-15.9) Msun. This result favors the orbital solution of Pike et al. (1983) over that of Moffat et al. (1986). The stellar parameters for the O star companion derived from line blanketed non-LTE atmosphere models are: Teff=34000 (+/-1500) K, log L/Lsun=5.3 (+/-0.15) from which an evolutionary mass of M=29 (+/-4) Msun and an age of 4.0 (+0.8/-0.5) Myr is obtained from single star evolutionary models. With non-LTE model calculations including He and C we derive a luminosity log L/Lsun~4.7 (+/-0.2) for the WR star. The mass-luminosity relation of hydrogen-free WR stars implies a mass of M(WR)~5 (+/-1.5) Msun. From our data we favor an age of ~10 Myr for the bulk of the Vela OB2 stars. Evolutionary scenarios for zeta Pup and gamma^2 Vel are discussed in the light of our results.

Detailed Analysis of Nearby Bulgelike Dwarf Stars. II. Lithium Abundances

Li abundances are derived for a sample of bulgelike stars with isochronal ages of 10-11 Gyr. These stars have orbits with pericentric distances, Rp, as small as 2-3 kpc and Zmax < 1 kpc. The sample comprises G and K dwarf stars in the metallicity range -0.80 ≤ [Fe/H] ≤ +0.40. Few data on Li abundances in old turnoff stars (≥4.5 Gyr) within the present metallicity range are available. M67 (4.7 Gyr) and NGC 188 (6 Gyr) are the oldest studied metal-rich open clusters with late-type stars. Li abundances have also been studied for a few samples of old metal-rich field stars. In the present work, a high dispersion in Li abundances is found for bulgelike stars with all metallicity ranges, comparable with values in M67. The role of metallicity and age on a Li depletion pattern is discussed. The possible connection between Li depletion and oxygen abundance due to atmospheric opacity effects is investigated.

Fundamental Stellar Parameters of γ2 Velorum from HIPPARCOS Data

We report parallax measurements by the HIPPARCOS satellite of zeta Puppis and gamma^2 Velorum. The distance of zeta Pup is d=429 (+120/ -77) pc, in agreement with the commonly adopted value to Vela OB2. However, a significantly smaller distance is found for the gamma^2 Vel system: d=258 (+41/-31) pc. The total mass of gamma^2 Vel derived from its parallax, the angular size of the semi-major axis as measured with intensity interferometry, and the period is M(WR+O)=29.5 (+/-15.9) Msun. This result favors the orbital solution of Pike et al. (1983) over that of Moffat et al. (1986). The stellar parameters for the O star companion derived from line blanketed non-LTE atmosphere models are: Teff=34000 (+/-1500) K, log L/Lsun=5.3 (+/-0.15) from which an evolutionary mass of M=29 (+/-4) Msun and an age of 4.0 (+0.8/-0.5) Myr is obtained from single star evolutionary models. With non-LTE model calculations including He and C we derive a luminosity log L/Lsun~4.7 (+/-0.2) for the WR star. The mass-luminosity relation of hydrogen-free WR stars implies a mass of M(WR)~5 (+/-1.5) Msun. From our data we favor an age of ~10 Myr for the bulk of the Vela OB2 stars. Evolutionary scenarios for zeta Pup and gamma^2 Vel are discussed in the light of our results.

Lithium abundances in Bulge-like SMR stars

We analyze a sample of 21 super-metal-rich (SMR) stars, using high-resolution échelle spectra obtained with the FEROS Spectrograph at the 1.5m ESO telescope. The metallicities are in the range 0.15 < [Fe/H] < 0.5, 3 of them in common with Pompéia et al. (2002). Geneva photometry, astrometric data from Hipparcos, and radial velocities from CORAVEL are available for these stars. The peculiar kinematics suggests the thin disk close to the bulge as the probable birthplace of these stars (Grenon 1999). From Hipparcos data, it appears that the turnoff of this population indicates an age of 10-11 Gyr (Grenon 1999). Detailed analysis of the sample stars is carried out. Lithium abundances of these stars were derived, and their behaviour with effective temperature is shown.

FEROS Abundance Analysis of 21 Bulgelike SMR Stars

We analyze a sample of 21 super-metal-rich (SMR) stars, using high-resolution echelle spectra obtained with the Fiber-fed Extended Range Optical Spectrograph at the 1.5m ESO telescope. The metallicities are in the range 0.07 ≤ [ Fe / H ] ≤ 0.45, 3 of them in common with Pompeia et al . (2009). Geneva photometry, astrometric data from Hipparcos , and radial velocities from CORAVEL are available for these stars. The peculiar kinematics suggests the thin disk close to the bulge as the probable birthplace of these stars (Grenon 1999). From Hipparcos data, it appears that the turnoff of this population indicates an age of 10-11 Gyr (Grenon 1999). Detailed analysis of the sample stars is carried out, and atmospheric parameters are derived from spectroscopic and photometric determinations. Oxygen abundances of these stars are derived, and [ O / Fe ] overabundances up to +0.35 are found.

The Variability of R, N, and C Stars from HIPPARCOS and AAVSO Data

Accurate photometry was obtained for all programme stars during the 3.3-year HIPPARCOS mission. The final observing programme included several hundred Mirae (M), semiregular (SR) long-period and irregular (L) variables. A detailed calibration of the aging of the optics allowed the evaluation of very precise magnitudes over the whole range of star colours. Since the time coverage of the satellite observations was not sufficient to describe the behaviour of M, SR, or L type variables, smooth curves were fitted statistically to the dense AAVSO observations. These curves were then transformed to the HIPPARCOS system in order to complement the HIPPARCOS photometry and thus produce precise light curves with fuller time coverage, for a set of several hundred late-type variables, including most Carbon stars brighter than V = 12.4 at minimum luminosity. A preliminary discussion of the behaviour of C stars, as observed from the space in the broad Hp band, is given.

Fundamental stellar parameters of zeta Pup and gamma^2 Vel from HIPPARCOS data

We report parallax measurements by the HIPPARCOS satellite of zeta Puppis and gamma^2 Velorum. The distance of zeta Pup is d=429 (+120/ -77) pc, in agreement with the commonly adopted value to Vela OB2. However, a significantly smaller distance is found for the gamma^2 Vel system: d=258 (+41/-31) pc. The total mass of gamma^2 Vel derived from its parallax, the angular size of the semi-major axis as measured with intensity interferometry, and the period is M(WR+O)=29.5 (+/-15.9) Msun. This result favors the orbital solution of Pike et al. (1983) over that of Moffat et al. (1986). The stellar parameters for the O star companion derived from line blanketed non-LTE atmosphere models are: Teff=34000 (+/-1500) K, log L/Lsun=5.3 (+/-0.15) from which an evolutionary mass of M=29 (+/-4) Msun and an age of 4.0 (+0.8/-0.5) Myr is obtained from single star evolutionary models. With non-LTE model calculations including He and C we derive a luminosity log L/Lsun~4.7 (+/-0.2) for the WR star. The mass-luminosity relation of hydrogen-free WR stars implies a mass of M(WR)~5 (+/-1.5) Msun. From our data we favor an age of ~10 Myr for the bulk of the Vela OB2 stars. Evolutionary scenarios for zeta Pup and gamma^2 Vel are discussed in the light of our results.