High-precision abundances of elements in solar-type stars

Aims. Previous high-precision studies of abundances of elements in solar twin stars are extended to a wider metallicity range to see how the trends of element ratios with stellar age depend on [Fe/H]. Methods. HARPS spectra with signal-to-noise ratios S/N ≳ 600 at λ ∼ 6000 Å were analysed with MARCS model atmospheres to obtain 1D LTE abundances of C, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Sr, and Y for 72 nearby solar-type stars with metallicities in the range of −0.3 ≲ [Fe/H] ≲ +0.3 and ASTEC stellar models were used to determine stellar ages from effective temperatures, luminosities obtained via Gaia DR2 parallaxes, and heavy element abundances. Results. The age-metallicity distribution appears to consist of the following two distinct populations: a sequence of old stars with a steep rise of [Fe/H] to ∼ + 0.3 dex at an age of ∼7 Gyr and a younger sequence with [Fe/H] increasing from about −0.3 dex to ∼ + 0.2 dex over the last 6 Gyr. Furthermore, the trends of several abundance ratios, [O/Fe], [Na/Fe], [Ca/Fe], and [Ni/Fe], as a function of stellar age, split into two corresponding sequences. The [Y/Mg]-age relation, on the other hand, shows no offset between the two age sequences and has no significant dependence on [Fe/H], but the components of a visual binary star, ζ Reticuli, have a large and puzzling deviation. Conclusions. The split of the age-metallicity distribution into two sequences may be interpreted as evidence of two episodes of accretion of gas onto the Galactic disk with a quenching of star formation in between. Some of the [X/Fe]-age relations support this scenario but other relations are not so easy to explain, which calls for a deeper study of systematic errors in the derived abundances as a function of [Fe/H], in particular 3D non-LTE effects.

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Spatial variations in the Milky Way disc metallicity–age relation

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2221 ◽

2019 ◽

Vol 489 (2) ◽

pp. 1742-1752 ◽

Cited By ~ 9

Author(s):

Diane K Feuillet ◽

Neige Frankel ◽

Karin Lind ◽

Peter M Frinchaboy ◽

D A García-Hernández ◽

...

Keyword(s):

Milky Way ◽

Star Formation History ◽

Chemical Abundance ◽

Crucial Component ◽

Stellar Ages ◽

Formation History ◽

History Of ◽

Age Relation ◽

Age Relations ◽

Spatial Locations

ABSTRACT Stellar ages are a crucial component to studying the evolution of the Milky Way. Using Gaia DR2 distance estimates, it is now possible to estimate stellar ages for a larger volume of evolved stars through isochrone matching. This work presents [M/H]–age and [α/M]–age relations derived for different spatial locations in the Milky Way disc. These relations are derived by hierarchically modelling the star formation history of stars within a given chemical abundance bin. For the first time, we directly observe that significant variation is apparent in the [M/H]–age relation as a function of both Galactocentric radius and distance from the disc mid-plane. The [M/H]–age relations support claims that radial migration has a significant effect in the plane of the disc. Using the [M/H] bin with the youngest mean age at each radial zone in the plane of the disc, the present-day metallicity gradient is measured to be −0.059 ± 0.010 dex kpc−1, in agreement with Cepheids and young field stars. We find a vertically flared distribution of young stars in the outer disc, confirming predictions of models and previous observations. The mean age of the [M/H]–[α/M] distribution of the solar neighbourhood suggests that the high-[M/H] stars are not an evolutionary extension of the low-α sequence. Our observational results are important constraints to Galactic simulations and models of chemical evolution.

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Stellar noise and planet detection. I. Oscillations, granulation and sun-like spots

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311021089 ◽

2010 ◽

Vol 6 (S276) ◽

pp. 527-529

Author(s):

Xavier Dumusque ◽

Nuno C. Santos ◽

Stéphane Udry ◽

Cristophe Lovis ◽

Xavier Bonfils

Keyword(s):

Radial Velocity ◽

Time Scales ◽

High Precision ◽

Habitable Zone ◽

Planet Detection ◽

Solar Type ◽

Physical Phenomena ◽

Instrumental Precision ◽

Observational Strategy ◽

Different Time Scales

AbstractSpectrographs like HARPS can now reach a sub-ms−1 precision in radial-velocity (RV) (Pepe & Lovis 2008). At this level of accuracy, we start to be confronted with stellar noise produced by 3 different physical phenomena: oscillations, granulation phenomena (granulation, meso- and super-granulation) and activity. On solar type stars, these 3 types of perturbation can induce ms−1 RV variation, but on different time scales: 3 to 15 minutes for oscillations, 15 minutes to 1.5 days for granulation phenomena and 10 to 50 days for activity. The high precision observational strategy used on HARPS, 1 measure per night of 15 minutes, on 10 consecutive days each month, is optimized, due to a long exposure time, to average out the noise coming from oscillations (Dumusque et al. 2011a) but not to reduce the noise coming from granulation and activity (Dumusque et al. 2011a and Dumusque et al. 2011b). The smallest planets found with this strategy (Mayor et al. 2009) seems to be at the limit of the actual observational strategy and not at the limit of the instrumental precision. To be able to find Earth mass planets in the habitable zone of solar-type stars (200 days for a K0 dwarf), new observational strategies, averaging out simultaneously all type of stellar noise, are required.

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Using non-solar-scaled opacities to derive stellar parameters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833753 ◽

2018 ◽

Vol 620 ◽

pp. A54 ◽

Cited By ~ 4

Author(s):

C. Saffe ◽

M. Flores ◽

P. Miquelarena ◽

F. M. López ◽

M. Jaque Arancibia ◽

...

Keyword(s):

High Precision ◽

Chemical Species ◽

Model Atmosphere ◽

Condensation Temperature ◽

Spectroscopic Methods ◽

Fundamental Parameters ◽

Evolved Stars ◽

Solar Type ◽

Scaled Models ◽

Previous Step

Aims. In an effort to improve spectroscopic methods of stellar parameters determination, we implemented non-solar-scaled opacities in a simultaneous derivation of fundamental parameters and abundances. We wanted to compare the results with the usual solar-scaled method using a sample of solar-type and evolved stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying non-solar-scaled opacities and model atmospheres. Our sample is composed of 20 stars, including main sequence and evolved objects. The stellar parameters were determined by imposing ionization and excitation equilibrium of Fe lines, with an updated version of the FUNDPAR program, together with plane-parallel ATLAS12 model atmospheres and the MOOG code. Opacities for an arbitrary composition and vmicro were calculated through the opacity sampling (OS) method. We used solar-scaled models in the first step, and then continued the process, but scaled to the abundance values found in the previous step (i.e. non-solar-scaled). The process finishes when the stellar parameters of one step are the same as in the previous step, i.e. we use a doubly iterated method. Results. We obtained a small difference in stellar parameters derived with non-solar-scaled opacities compared to classical solar-scaled models. The differences in Teff, log g, and [Fe/H] amount to 26 K, 0.05 dex, and 0.020 dex for the stars in our sample. These differences can be considered the first estimation of the error due to the use of classical solar-scaled opacities to derive stellar parameters with solar-type and evolved stars. We note that some chemical species could also show an individual variation greater than those of the [Fe/H] (up to ~0.03 dex) and varying from one species to another, obtaining a chemical pattern difference between the two methods. This means that condensation temperature Tc trends could also present a variation. We include an example showing that using non-solar-scaled opacities, the solution found with the classical solar-scaled method indeed cannot always verify the excitation and ionization balance conditions required for a model atmosphere. We discuss in the text the significance of the differences obtained when using solar-scaled versus non-solar-scaled methods. Conclusions. We consider that the use of the non-solar-scaled opacities is not mandatory in every statistical study with large samples of stars. However, for those high-precision works whose results depend on the mutual comparison of different chemical species (such as the analysis of condensation temperature Tc trends), we consider its application to be worthwhile. To date, this is probably one of the most precise spectroscopic methods for stellar parameter derivation.

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The Bologna Open Cluster Chemical Evolution project: a large, homogeneous sample of Galactic open clusters

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309031809 ◽

2008 ◽

Vol 4 (S258) ◽

pp. 153-160

Author(s):

Angela Bragaglia

Keyword(s):

Chemical Evolution ◽

Galactic Disk ◽

Open Cluster ◽

Open Clusters ◽

Photometric Data ◽

Homogeneous Sample ◽

Metallicity Distribution

AbstractThe Bologna Open Cluster Chemical Evolution (BOCCE) project is a photometric and spectroscopic survey of open clusters, to be used as tracers of the Galactic disk properties and evolution. The clusters parameters (age, distance, reddening, metallicity, and detailed abundances) are derived in a precise and homogeneous way. This will contribute to a solid, reliable description of the disk: the clusters parameters will be used, for instance, to determine the metallicity distribution in the Galactic disk and how it has evolved with time. We have concentrated on old open clusters and we have presently in our hands data for about 40 open clusters; we have fully analyzed the photometric data for about one half of them and the spectra for one quarter of them.

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High Precision Effective Temperatures and New Abundances for a Large Sample of Disk Stars

Chemical Abundances and Mixing in Stars in the Milky Way and its Satellites - ESO ASTROPHYSICS SYMPOSIA ◽

10.1007/978-3-540-34136-9_32 ◽

2006 ◽

pp. 80-81

Author(s):

T.V. Mishenina ◽

C. Soubiran ◽

O. Bienaymé ◽

V.V. Kovtyukh ◽

S.A. Korotin ◽

...

Keyword(s):

High Precision ◽

Large Sample ◽

Effective Temperatures

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IUE Observations of the Chromospheric Activity-Age Relation in Young Solar-Type Stars

Symposium - International Astronomical Union ◽

10.1017/s007418090002982x ◽

1983 ◽

Vol 102 ◽

pp. 161-164

Author(s):

Theodore Simon ◽

Ann Merchant Boesgaard

Keyword(s):

Magnetic Fields ◽

Flare Activity ◽

The Sun ◽

Late Type ◽

Cool Star ◽

Opportune Time ◽

Solar Type ◽

Age Relation ◽

Relationship Of ◽

The Relationship

The difficulties of measuring magnetic fields in late-type stars other than the sun are well known, as one is reminded by other contributions to these Proceedings. This Symposium nevertheless comes at a very opportune time, as we are now at the point where we can begin to explore the relationship of stellar magnetism to flare activity and quiescent cool star chromospheres, transition regions (TRs), and coronae.

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Statistical Modeling and Analysis of Wide Binary Star Systems

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307006230 ◽

2006 ◽

Vol 2 (S240) ◽

pp. 686-689

Author(s):

K.B. Johnston ◽

T.D. Oswalt ◽

D. Valls-Gabaud

Keyword(s):

Mass Loss ◽

Main Sequence ◽

Galactic Disk ◽

Binary Star ◽

Wide Binary ◽

Robust Test ◽

Modeling And Analysis ◽

Tidal Interactions ◽

Wide Pairs ◽

Binary Separations

AbstractPost-main-sequence (MS) mass loss causes orbital separation amplification in fragile (i.e. common proper motion) binary star systems. Components typically have separations around ∼1000 AU. Such wide pairs experience negligible tidal interactions and mass transfer between companions; thus they evolve as two separate but coeval stars. In this paper we compute the rate of mass loss during the components' lifetimes and attempt to model how it will statistically distort a frequency distribution of fragile binary separations. Understanding this process provides a robust test of current theories of stellar evolution and sets constraints on the dynamics of the Galactic disk.

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