Based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan telescopes, we present detailed elemental abundances for 20 red giant stars in the outer Galactic disk, located at ...Galactocentric distances between 9 and 13 kpc. The outer disk sample is complemented with samples of red giants from the inner Galactic disk and the solar neighborhood, analyzed using identical methods. For Galactocentric distances beyond 10 kpc, we only find chemical patterns associated with the local thin disk, even for stars far above the Galactic plane. Our results show that the relative densities of the thick and thin disks are dramatically different from the solar neighborhood, and we therefore suggest that the radial scale length of the thick disk is much shorter than that of the thin disk. We make a first estimate of the thick disk scale length of L thick = 2.0 kpc, assuming L thin = 3.8 kpc for the thin disk. We suggest that radial migration may explain the lack of radial age, metallicity, and abundance gradients in the thick disk, possibly also explaining the link between the thick disk and the metal-poor bulge.
Context. The formation and evolution of the Galactic bulge and its relationship with the other Galactic populations is still poorly understood. Aims. To establish the chemical differences and ...similarities between the bulge and other stellar populations, we performed an elemental abundance analysis of α- (O, Mg, Si, Ca, and Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge as well as of local thin disk, thick disk and halo giants. Methods. We use high-resolution optical spectra of 25 bulge giants in Baade's window and 55 comparison giants (4 halo, 29 thin disk and 22 thick disk giants) in the solar neighborhood. All stars have similar stellar parameters but cover a broad range in metallicity (-1.5 < Fe/H < +0.5). A standard 1D local thermodynamic equilibrium analysis using both Kurucz and MARCS models yielded the abundances of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential analysis of the Galactic stellar populations ensured that systematic errors were minimized. Results. We confirm the well-established differences for α/Fe at a given metallicity between the local thin and thick disks. For all the elements investigated, we find no chemical distinction between the bulge and the local thick disk, in agreement with our previous study of C, N and O but in contrast to other groups relying on literature values for nearby disk dwarf stars. For -1.5 < Fe/H < -0.3 exactly the same trend is followed by both the bulge and thick disk stars, with a star-to-star scatter of only 0.03 dex. Furthermore, both populations share the location of the knee in the α/Fe vs. Fe/H diagram. It still remains to be confirmed that the local thick disk extends to super-solar metallicities as is the case for the bulge. These are the most stringent constraints to date on the chemical similarity of these stellar populations. Conclusions. Our findings suggest that the bulge and local thick disk stars experienced similar formation timescales, star formation rates and initial mass functions, confirming thus the main outcomes of our previous homogeneous analysis of O/Fe from infrared spectra for nearly the same sample. The identical α-enhancements of thick disk and bulge stars may reflect a rapid chemical evolution taking place before the bulge and thick disk structures we see today were formed, or it may reflect Galactic orbital migration of inner disk/bulge stars resulting in stars in the solar neighborhood with thick-disk kinematics.
The Solar Twin Planet Search Ramirez, I; Melendez, J; Bean, J ...
Astronomy and astrophysics (Berlin),
12/2014, Volume:
572
Journal Article
Peer reviewed
We are carrying out a search for planets around a sample of solar twin stars using the HARPS spectrograph. The goal of this project is to exploit the advantage offered by solar twins to obtain ...chemical abundances of unmatched precision. This survey will enable new studies of the stellar composition -- planet connection. We determine the fundamental parameters of the 88 solar twin stars that have been chosen as targets for our experiment. We present the largest sample of solar twins analyzed homogeneously using high quality spectra. The fundamental parameters derived from this work will be employed in subsequent work that aims to explore the connections between planet formation and stellar chemical composition.
ABSTRACT
The kinematics, mean α-elements, and ages of the stars reveal two distinct disc populations observed in the Solar neighbourhood. Although several studies have been carried out to ...characterize abundances of chemical elements and kinematic identifications in these populations, there are few studies that dealt with the analysis of stellar rotation and characteristics of populations focused on low-mass stars of the F and G types. In this work, we propose a new approach to classify stellar populations from the thin and thick disc for F and G dwarf stars by relating chemical abundance and rotation (v sin i) of these stars in the rotational–chemical–plane (v sin i–α/Fe–Fe/H plot). Our results show that the two rotational-chemical sequences disentangled, high- and low-α/Fe components, present properties (α-enhanced, ages, kinematics, space velocity gradients, local density ratio) closely linked to the stars of the chemically and kinematically defined as thin and thick disc components. This study has an impact on calibrations that relate ages to rotation (gyro-chronology) as well as age to chemical abundances (chemochronology), as well as sheds light on the understanding of the processes of Galactic disc formation.
ABSTRACT
This work aims to examine in detail the depletion of lithium in solar twins to better constrain stellar evolution models and investigate its possible connection with exoplanets. We employ ...spectral synthesis in the region of the asymmetric 6707.75 Å Li I line for a sample of 77 stars plus the Sun. As in previous works based on a smaller sample of solar twins, we find a strong correlation between Li depletion and stellar age. In addition, for the first time we show that the Sun has the lowest Li abundance in comparison with solar twins at similar age (4.6 ± 0.5 Gyr). We compare the lithium content with the condensation temperature slope for a subsample of the best solar twins and determine that the most lithium-depleted stars also have fewer refractory elements. We speculate whether the low lithium content in the Sun might be related to the particular configuration of our Solar system.
Aims. Globular clusters are tracers of the history of star formation and chemical enrichment in the early Galaxy. Their abundance pattern can help understanding their chemical enrichment processes. ...In particular, the iron-peak elements have been relatively little studied so far in the Galactic bulge. Methods. The main aim of this work is to verify the strength of abundances of iron-peak elements for chemical tagging in view of identifying different stellar populations. Besides, the nucleosynthesis processes that build these elements are complex, therefore observational data can help constraining theoretical models, as well as give suggestions as to the kinds of supernovae that enriched the gas before these stars formed. Results. The abundances of iron-peak elements are derived for the sample clusters, and compared with bulge field, and thick disk stars. We derived abundances of the iron-peak elements Sc, V, Mn, Cu, and Zn in individual stars of five bulge globular clusters (NGC 6528, NGC 6553, NGC 6522, NGC 6558, HP 1), and of the reference thick disk/or inner halo cluster 47 Tucanae (NGC 104). High resolution spectra were obtained with the UVES spectrograph at the Very Large Telescope over the years. Conclusions. The sample globular clusters studied span metallicities in the range –1.2 ≲ Fe/H ≲ 0.0. V and Sc appear to vary in lockstep with Fe, indicating that they are produced in the same supernovae as Fe. We find that Mn is deficient in metal-poor stars, confirming that it is underproduced in massive stars; Mn-over-Fe steadily increases at the higher metallicities due to a metallicity-dependent enrichment by supernovae of type Ia. Cu behaves as a secondary element, indicating its production in a weak-s process in massive stars. Zn has an alpha-like behaviour at low metallicities, which can be explained in terms of nucleosynthesis in hypernovae. At the metal-rich end, Zn decreases with increasing metallicity, similarly to the alpha-elements.
Pulsation in TESS Objects of Interest Gomes, R. L.; Martins, B. L. Canto; Fontinele, D. O. ...
Astrophysical journal/The Astrophysical journal,
01/2024, Volume:
961, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract
We report the discovery of three Transiting Exoplanet Survey Satellite Objects of Interest (TOI) with signatures of pulsation, observed in more than one sector. Our main goal is to explore ...how large is the variety of classical pulsators such as
δ
Sct,
γ
Dor, RR Lyrae and Cepheid among TOI pulsators. The analysis reveals two stars with signatures of
δ
Sct and one of
γ
Dor, out of a sample of 3901 TOIs with available light curves (LCs). To date, there is a very scarce number of known pulsating stars hosting planets. The present finding also emerges as an exciting laboratory for studying different astrophysical phenomena, including the effects of star–planet interaction on pulsation and timing detection of planetary companions. We have also identified 16 TOI stars with periodicities and LCs morphology compatible with different classical pulsating classes, but for most of them, the dominant frequency signals originate from contaminating sources.
We study the relationship between age, metallicity, and α-enhancement of FGK stars in the Galactic disk. The results are based upon the analysis of high-resolution UVES spectra from the Gaia-ESO ...large stellar survey. We explore the limitations of the observed dataset, i.e. the accuracy of stellar parameters and the selection effects that are caused by the photometric target preselection. We find that the colour and magnitude cuts in the survey suppress old metal-rich stars and young metal-poor stars. This suppression may be as high as 97% in some regions of the age-metallicity relationship. The dataset consists of 144 stars with a wide range of ages from 0.5 Gyr to 13.5 Gyr, Galactocentric distances from 6 kpcto 9.5 kpc, and vertical distances from the plane 0 < |Z| < 1.5 kpc. On this basis, we find that i) the observed age-metallicity relation is nearly flat in the range of ages between 0 Gyr and 8 Gyr; ii) at ages older than 9 Gyr, we see a decrease in Fe/H and a clear absence of metal-rich stars; this cannot be explained by the survey selection functions; iii) there is a significant scatter of Fe/H at any age; and iv) Mg/Fe increases with age, but the dispersion of Mg/Fe at ages >9 Gyr is not as small as advocated by some other studies. In agreement with earlier work, we find that radial abundance gradients change as a function of vertical distance from the plane. The Mg/Fe gradient steepens and becomes negative. In addition, we show that the inner disk is not only more α-rich compared to the outer disk, but also older, as traced independently by the ages and Mg abundances of stars.
ABSTRACT
Abundances of light elements in dwarf stars of different ages are important constraints for stellar yields, Galactic chemical evolution and exoplanet chemical composition studies. We have ...measured C and N abundances and 12C/13C ratios for a sample of 63 solar twins spanning a wide range in age, based on spectral synthesis of a comprehensive list of CH A-X and CN B-X features using HARPS spectra. The analysis of 55 thin disc solar twins confirms the dependences of C/Fe and N/Fe on Fe/H. N/Fe is investigated as a function of Fe/H and age for the first time for these stars. Our derived correlation C/Fe–age agrees with works for solar-type stars and solar twins, but the N/Fe–age correlation does not. The relations C,N/Fe–Fe/H and C,N/Fe–age for the solar twins lay under solar. 12C/13C is found correlated with Fe/H and seems to have decreased along the evolution of the local thin disc. Predictions from chemical evolution models for the solar vicinity corroborate the relations C,N/Fe–Fe/H, 12C/13C–age, and N/O–O/H, but do not for the 12C/13C–Fe/H and C/O–O/H relations. The N/O ratio in the Sun is placed at the high end of the homogeneous distribution of solar twins, which suggests uniformity in the N–O budget for the formation of icy planetesimals, watery superearths, and giant planets. C and N had different nucleosynthetic origins along the thin disc evolution, as shown by the relations of C/N, C/O, and N/O against O/H and age. C/N and C/O are particularly observed increasing in time for solar twins younger than the Sun.
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