Context. New space missions, such as NASA TESS or ESA PLATO, will focus on bright stars, which have been largely ignored by modern large surveys, especially in the northern sky. Spectroscopic ...information is of paramount importance in characterising the stars and analysing planets possibly orbiting them, and in studying the Galactic disc evolution. Aims. The aim of this work was to analyse all bright (V < 8 mag) F, G, and K dwarf stars using high-resolution spectra in the selected sky fields near the northern celestial pole. Methods. The observations were carried out with the 1.65 m diameter telescope at the Molėtai Astronomical Observatory and a fibre-fed high-resolution spectrograph covering a full visible wavelength range (4000–8500 Å). The atmospheric parameters were derived using the classical equivalent width approach while the individual chemical element abundances were determined from spectral synthesis. For both tasks the one-dimensional plane-parallel LTE MARCS stellar model atmospheres were applied. The NLTE effects for the majority of elemental abundances in our sample were negligible; however, we did calculate the NLTE corrections for the potassium abundances, as they were determined from the large 7698.9 Å line. For manganese and copper we have accounted for a hyperfine splitting. Results. We determined the main atmospheric parameters, kinematic properties, orbital parameters, and stellar ages for 109 newly observed stars and chemical abundances of Na I, Mg I, Al I, Si I, Si II, S I, K I, Ca I, Ca II, Sc I, Sc II, Ti I, Ti II, V I, Cr I, Cr II, Mn I, Fe I, Fe II, Co I, Ni I, Cu I, and Zn I for 249 F, G, and K dwarf stars observed in the present study and in our previous study. The Mg I/Fe I ratio was adopted to define the thin-disc (α-poor) and thick-disc (α-rich) stars in our sample. We explored the behaviour of 21 chemical species in the El/Fe I versus Fe I/H and El/Fe I versus age planes, and compared the results with the latest Galactic chemical evolution models. We also explored El/Fe I gradients according to the mean Galactocentric distances and maximum height above the Galactic plane. Conclusions. We found that in the Galactic thin-disc El/Fe I ratios of α-elements and aluminium have a positive trend with respect to age while the trend of Mn is clearly negative. Abundances of other species do not display significant trends. While the current theoretical models are able to reproduce the generic trends of the elements, they often seem to overestimate or underestimate the observational abundances. We found that the α-element and zinc abundances have slightly positive or flat radial and vertical gradients, while gradients for the odd-Z element Na, K, V, and Mn abundances are negative.
Context.
The derivation of accurate and precise masses and radii is possible for eclipsing binary stars, allowing for insights into their evolution. When residing in star clusters, they provide ...measurements of even greater precision, along with additional information on their properties. Asteroseismic investigations of solar-like oscillations offers similar possibilities for single stars.
Aims.
We wish to improve the previously established properties of the Hyades eclipsing binary HD 27130 and re-assess the asteroseismic properties of the giant star
ϵ
Tau. The physical properties of these members of the Hyades can be used to constrain the helium content and age of the cluster.
Methods.
New multi-colour light curves were combined with multi-epoch radial velocities to yield masses and radii of HD 27130. Measurements of
T
eff
were derived from spectroscopy and photometry, and verified using the
Gaia
parallax. We estimated the cluster age from re-evaluated asteroseismic properties of
ϵ
Tau while using HD 27130 to constrain the helium content.
Results.
The masses, radii, and
T
eff
of HD 27130 were found to be
M
= 1.0245 ± 0.0024
M
⊙
,
R
= 0.9226 ± 0.015
R
⊙
,
T
eff
= 5650 ± 50 K for the primary, and
M
= 0.7426 ± 0.0016
M
⊙
,
R
= 0.7388 ± 0.026
R
⊙
,
T
eff
= 4300 ± 100 K for the secondary component. Our re-evaluation of
ϵ
Tau suggests that the previous literature estimates are trustworthy and that the
HIPPARCOS
parallax is more reliable than the
Gaia
DR2 parallax.
Conclusions.
The helium content of HD 27130 and, thus, of the Hyades is found to be
Y
= 0.27 but with a significant model dependency. Correlations with the adopted metallicity result in a robust helium enrichment law, with Δ
Y
/Δ
Z
close to 1.2 We estimate the age of the Hyades to be 0.9 ± 0.1 (stat) ±0.1 (sys) Gyr, which is in slight tension with recent age estimates based on the cluster white dwarfs. The precision of the age estimate can be much improved via asteroseismic investigations of the other Hyades giants and by future improvements to the
Gaia
parallax for bright stars.
Milky Way open clusters are very diverse in terms of age, chemical composition, and kinematic properties. Intermediate-age and old open clusters are less common, and it is even harder to find them ...inside the solar Galactocentric radius, due to the high mortality rate and strong extinction inside this region. NGC 6802 is one of the inner disk open clusters (IOCs) observed by the Gaia-ESO survey (GES). This cluster is an important target for calibrating the abundances derived in the survey due to the kinematic and chemical homogeneity of the members in open clusters. Using the measurements from Gaia-ESO internal data release 4 (iDR4), we identify 95 main-sequence dwarfs as cluster members from the GIRAFFE target list, and eight giants as cluster members from the UVES target list. The dwarf cluster members have a median radial velocity of 13.6 ± 1.9 km s-1, while the giant cluster members have a median radial velocity of 12.0 ± 0.9 km s-1 and a median Fe/H of 0.10 ± 0.02 dex. The color–magnitude diagram of these cluster members suggests an age of 0.9 ± 0.1 Gyr, with (m−M)0 = 11.4 and E(B−V) = 0.86. We perform the first detailed chemical abundance analysis of NGC 6802, including 27 elemental species. To gain a more general picture about IOCs, the measurements of NGC 6802 are compared with those of other IOCs previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs. These elements are compared with nucleosynthetic models as a function of cluster turn-off mass. The α, iron-peak, and neutron-capture elements are also explored in a self-consistent way.
Correction to: Astrophys Space Sci
https://doi.org/10.1007/s10509-019-3522-3
We would like to add the following sentence into the acknowledgement:
Students of Horten Upper Secondary School (Horten ...Videregående Skole) B. Berg, Å. Hansli, V.H. Hatlo, M.B. Hjelmervik, C.T. Lavre, V. Moskvil, and V. Skui are acknowledged for taking part in observing eclipsing binary candidate TYC 2764-1997-1 star on the Nordic Optical Telescope.
As extensive ground-based observations and characterisation of different variable stars are of the utmost importance in preparing optimal input catalogues for space missions, our aim was to search ...for new variable stars in selected fields of the northern sky. We obtained 24 470 CCD images and analysed photometric time series of stars using the DAOPHOT based package Muniwin as the first step, and the Period04 package was used to further analyse the suspected new variable stars. The light curves and other observational results are presented for 3598 stars online. We found 81 new variable stars, among them is an eclipsing binary with a variable component and possibly eccentric orbits TYC4038-693-1 which we also observed spectroscopically, four
δ
Scuti candidates, six other variable stars with periods falling into the interval of 35 minutes to 20 days. Furthermore, we identified 70 slowly varying stars with so far undefined periodicity. Additional photometric and spectral observations were carried out for TYC2764-1997-1, and its previous candidacy for eclipsing binaries was approved.
Context. Determination and calibration of the ages of stars, which heavily rely on stellar evolutionary models, are very challenging, while representing a crucial aspect in many astrophysical areas. ...Aims. We describe the methodologies that, taking advantage of Gaia-DR1 and the Gaia-ESO Survey data, enable the comparison of observed open star cluster sequences with stellar evolutionary models. The final, long-term goal is the exploitation of open clusters as age calibrators. Methods. We perform a homogeneous analysis of eight open clusters using the Gaia-DR1 TGAS catalogue for bright members and information from the Gaia-ESO Survey for fainter stars. Cluster membership probabilities for the Gaia-ESO Survey targets are derived based on several spectroscopic tracers. The Gaia-ESO Survey also provides the cluster chemical composition. We obtain cluster parallaxes using two methods. The first one relies on the astrometric selection of a sample of bona fide members, while the other one fits the parallax distribution of a larger sample of TGAS sources. Ages and reddening values are recovered through a Bayesian analysis using the 2MASS magnitudes and three sets of standard models. Lithium depletion boundary (LDB) ages are also determined using literature observations and the same models employed for the Bayesian analysis. Results. For all but one cluster, parallaxes derived by us agree with those presented in Gaia Collaboration (2017, A&A, 601, A19), while a discrepancy is found for NGC 2516; we provide evidence supporting our own determination. Inferred cluster ages are robust against models and are generally consistent with literature values. Conclusions. The systematic parallax errors inherent in the Gaia DR1 data presently limit the precision of our results. Nevertheless, we have been able to place these eight clusters onto the same age scale for the first time, with good agreement between isochronal and LDB ages where there is overlap. Our approach appears promising and demonstrates the potential of combining Gaia and ground-based spectroscopic datasets.
Stars and planets form from the same material, thus some of their properties are expected to be inter-connected. In order to characterise exoplanets, we need to investigate the planet-hosting stars. ...Carbon and oxygen are quite abundant and play an important role in stellar interiors by generating energy in thermonuclear reactions. Abundances of C and O may influence water availability on exoplanets. The C/O ratio also controls an amount of carbides and silicates that can be formed. Thus, we are performing a uniform study of C/O ratios in bright stars ( V < mag) located towards the northern ecliptic pole which will be targeted by the TESS and JWST space missions. The first results for a sample of 140 stars analysed are presented.
High-resolution spectra for all bright ( mag) and cooler than F5 spectral class dwarf stars were observed in two fields with radii of 20 degrees (centered at (2000) = 161.03º and (2000) = 86.60º and ...at (2000) = 265.08º and (2000) = 39.58º) towards the northern ecliptic pole. They coincide with two of the preliminary ESA PLATO fields which also will be targeted by the NASA TESS mission. We use high-resolution spectra obtained with the VUES spectrograph mounted on the 1.65 m telescope at the Moletai Astronomical Observatory of the Institute of Theoretical Physics and Astronomy, Vilnius University. In total we observed 405 stars. Spectroscopic atmospheric parameters and abundances of 23 neutral and ionised atomic species were determined for 261 slowly rotating stars (up to 15 kms-1). 73% of stars were analysed spectroscopically for the first time. We also derived stellar ages and orbital parameters to draw a chemical picture of the Solar vicinity.
Context. Despite a rich observational background, few spectroscopic studies have dealt with the measurement of the carbon isotopic ratio in giant stars. However, it is a key element in understanding ...the mixing mechanisms that occur in the interiors of giant stars. Aims. We present the CNO and 12 C/ 13 C abundances derived for 71 giant field stars. Then, using this new catalogue and complementary data from the Kepler and Gaia satellites, we study the efficiency of mixing occurring in the giant branch as a function of the stellar properties of the stars (e.g. mass, age, metallicity). Methods. We determined the abundances of CNO and more specifically the carbon isotopic ratio using the high-resolution FIbre-fed Echelle Spectrograph on the Nordic Optical Telescope, for 71 giant field stars. In addition, asteroseismology from the Kepler satellite is available for all stars, providing the stellar masses, ages, and evolutionary states. Finally, astrometry from the Gaia data is also available for most of the sample. We compare these new determinations with stellar evolution models taking into account the effects of transport processes. To exploit the complete potential of our extensive catalogue, and considering both the Milky Way evolution and the impact of stellar evolution, we built mock catalogues using the Besançon Galaxy model in which stellar evolution models taking into account the effects of thermohaline instability are included. Results. We confirm that the carbon isotopic ratio at the surface of core He-burning stars is lower than that of first-ascent RGB stars. The carbon isotopic ratio measured at the surface of the core He-burning stars increases with Fe/H and stellar mass, while it decreases with stellar age. These trends are all nicely explained by the thermohaline mixing that occurs in red giants. We show that our models can explain the behaviour of 12 C/ 13 C versus N/O, although the observations seem to show a lower N/O than the models. We also note that more constraints on the thick disc core He-burning stars are needed to understand this difference. Conclusions. Overall, the current model including thermohaline mixing is able to reproduce very well the 12 C/ 13 C with the stellar metallicity and with the stellar mass and age.
Context.
In the last 15 years different ground-based spectroscopic surveys have been started (and completed) with the general aim of delivering stellar parameters and elemental abundances for large ...samples of Galactic stars, complementing
Gaia
astrometry. Among those surveys, the
Gaia
-ESO Public Spectroscopic Survey, the only one performed on a 8m class telescope, was designed to target 100 000 stars using FLAMES on the ESO VLT (both Giraffe and UVES spectrographs), covering all the Milky Way populations, with a special focus on open star clusters.
Aims.
This article provides an overview of the survey implementation (observations, data quality, analysis and its success, data products, and releases), of the open cluster survey, of the science results and potential, and of the survey legacy. A companion article reviews the overall survey motivation, strategy, Giraffe pipeline data reduction, organisation, and workflow.
Methods.
We made use of the information recorded and archived in the observing blocks; during the observing runs; in a number of relevant documents; in the spectra and master catalogue of spectra; in the parameters delivered by the analysis nodes and the working groups; in the final catalogue; and in the science papers. Based on these sources, we critically analyse and discuss the output and products of the Survey, including science highlights. We also determined the average metallicities of the open clusters observed as science targets and of a sample of clusters whose spectra were retrieved from the ESO archive.
Results.
The Gaia-ESO Survey has determined homogeneous good-quality radial velocities and stellar parameters for a large fraction of its more than 110 000 unique target stars. Elemental abundances were derived for up to 31 elements for targets observed with UVES. Lithium abundances are delivered for about 1/3 of the sample. The analysis and homogenisation strategies have proven to be successful; several science topics have been addressed by the
Gaia
-ESO consortium and the community, with many highlight results achieved.
Conclusions.
The final catalogue will be released through the ESO archive in the first half of 2022, including the complete set of advanced data products. In addition to these results, the
Gaia
-ESO Survey will leave a very important legacy, for several aspects and for many years to come.
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