The aim of this work is to determine abundances of neutron-capture elements for thin- and thick-disc F, G, and K stars in several sky fields near the north ecliptic pole and to compare the results with the Galactic chemical evolution models, to explore elemental gradients according to stellar ages, mean galactocentric distances, and maximum heights above the Galactic plane. The observational data were obtained with the 1.65m telescope at the Moletai Astronomical Observatory and a fibre-fed high-resolution spectrograph. Elemental abundances were determined using a differential spectrum synthesis with the MARCS stellar model atmospheres and accounting for the hyperfine-structure effects. We determined abundances of Sr, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, and Eu for 424 thin- and 82 thick-disc stars. The sample of thick-disc stars shows a clearly visible decrease in [Eu/Mg] with increasing [Fe/H] compared to the thin-disc stars, bringing more evidence of a different chemical evolution in these two Galactic components. Abundance correlation with age slopes for the investigated thin-disc stars are slightly negative for the majority of s-process dominated elements, while r-process dominated elements have positive correlations. Our sample of thin-disc stars with ages spanning from 0.1 to 9 Gyrs give the [Y/Mg]=0.022 ($\pm$0.015)-0.027 ($\pm$0.003)*age [Gyr] relation. For the thick-disc stars, when we also took data from other studies into account, we found that [Y/Mg] cannot serve as an age indicator. The radial [El/Fe] gradients in the thin disc are negligible for the s-process dominated elements and become positive for the r-process dominated elements. The vertical gradients are negative for the light s-process dominated elements and become positive for the r-process dominated elements. In the thick disc, the radial [El/Fe] slopes are negligible, and the vertical slopes are predominantly negative.
The Galactic orbital parameters of 159 cataclysmic variables in the Solar neighbourhood are calculated, for the first time, to determine their population types using published kinematical parameters. Population analysis shows that about 6 per cent of cataclysmic variables in the sample are members of the thick disc component of the Galaxy. This value is consistent with the fraction obtained from star count analysis. The rest of the systems in the sample are found to be in the thin disc component of the Galaxy. Our analysis revealed no halo CVs in the Solar vicinity. About 60 per cent of the th…
Using 17 chemical elements as a proxy for stellar DNA, we present a full phylogenetic study of stars in the solar neighbourhood. This entails applying a clustering technique that is widely used in molecular biology to construct an evolutionary tree from which three branches emerge. These are interpreted as stellar populations which separate in age and kinematics and can be thus attributed to the thin disk, the thick disk, and an intermediate population of probable distinct origin. We further find six lone stars of intermediate age that could not be assigned to any population with enough statis…
The aim of this paper is to characterise the abundance patterns of five iron-peak elements (Mn, Fe, Ni, Cu, and Zn) for which the stellar origin and chemical evolution are still debated. We automatically derived iron peak (Mn, Fe, Ni, Cu, and Zn) and alpha element (Mg) chemical abundances for 4666 stars. We used the bimodal distribution of [Mg/Fe] to chemically classify sample stars into different Galactic substructures: thin disc, metal-poor and high-alpha metal rich, high-alpha and low-alpha metal-poor populations. High-alpha and low-alpha metal-poor populations are fully distinct in Mg, Cu,…
Galactic Archeology is a powerful tool for investigating the formation and evolution of the Milky Way. We use this technique to study kinematic groups of F- and G-stars in the solar neighbourhood. From correlations between orbital parameters, three new coherent groups of stars were recently identified and suggested to correspond to remnants of disrupted satellites. We determine detailed elemental abundances in stars belonging to one of these groups and compare their chemical composition with Galactic disc stars. The aim is to look for possible chemical signatures that might give information ab…
A sample of mostly old metal-rich dwarf and turn-off stars with high eccentricity and low maximum height above the Galactic plane has been identified. From their kinematics, it was suggested that the inner disk is their most probable birthplace. Their chemical imprints may therefore reveal important information about the formation and evolution of the still poorly understood inner disk. To probe the formation history of these stellar populations, a detailed analysis of a sample of very metal-rich stars is carried out. We derive the metallicities, abundances of α elements, ages, and Galactic or…
From correlations between orbital parameters, several new coherent groups of stars were recently identified in the Galactic disc and suggested to correspond to remnants of disrupted satellites. To reconstruct their origin at least three main observational parameters - kinematics, chemical composition and age - must be known. We determine detailed elemental abundances in stars belonging to the so-called Group 2 of the Geneva-Copenhagen Survey and compare the chemical composition with Galactic thin- and thick-disc stars, as well as with the Arcturus and AF06 streams. The aim is to search for che…
We explored a method to reconstruct the distribution function of the Galactic thick disc within the action space where nearby thick-disc stars are distributed. By applying this method to 127 chemically-selected thick-disc stars in the Solar neighbourhood, we found that the vertical velocity dispersion that corresponds to the reconstructed distribution function declines approximately as $\exp (-R/R_s)$ at 4.5 kpc < R < 9.5 kpc, with $R_s$ = 8.3 $\pm$ 1.1 (rand.) $\pm$ 1.6 (sys.) kpc. Also, we found that the vertical velocity dispersion $σ_z$ of our local thick-disc stars shows only weak depende…
The evolution of chemical elements in a galaxy is linked to its star formation history. Variations in star formation history are imprinted in the relative abundances of chemical elements produced in different supernova events and asymptotic giant branch stars. We determine detailed elemental abundances of s- and r-process elements in stars belonging to Group3 of the Geneva-Copenhagen survey and compare their chemical composition with Galactic disc stars. The aim is to look for possible chemical signatures that might give information about the formation history of this kinematic group of stars,…
Isotope ratios have opened a new window into the study of the details of stellar evolution, supernovae, and galactic chemical evolution. We present the evolution of the isotope ratios of elemental abundances (from C to Zn) in the solar neighbourhood, bulge, halo, and thick disk, using chemical evolution models with updated yields of Asymptotic Giant Branch (AGB) stars and core-collapse supernovae. The evolutionary history of each element is different owing to the effects of the initial progenitor mass and metallicity on element production. In the bulge and thick disk the star formation timesca…
We determine detailed elemental abundances in stars belonging to the so-called Group 1 of the Geneva-Copenhagen survey (GCS) and compare the chemical composition with the Galactic thin- and thick-disc stars, with the GCS Group 2 and Group 3 stars, as well as with several kinematic streams of similar metallicities. The aim is to search for chemical signatures that might give information about the formation history of this kinematic group of stars. High-resolution spectra were obtained with the Fibre-fed Echelle Spectrograph (FIES) spectrograph at the Nordic Optical Telescope, La Palma, and were…
We present a re-analysis of the Geneva-Copenhagen survey, which benefits from the infrared flux method to improve the accuracy of the derived stellar effective temperatures and uses the latter to build a consistent and improved metallicity scale. Metallicities are calibrated on high-resolution spectroscopy and checked against four open clusters and a moving group, showing excellent consistency. The new temperature and metallicity scales provide a better match to theoretical isochrones, which are used for a Bayesian analysis of stellar ages. With respect to previous analyses, our stars are on a…
A period of quenching between the formation of the thick and thin disks of the Milky Way has been recently proposed to explain the observed age-[α/Fe] distribution of stars in the solar neighbourhood. However, robust constraints on stellar ages are currently available for only a limited number of stars. The all-sky survey TESS (Transiting Exoplanet Survey Satellite) will observe the brightest stars in the sky and thus can be used to investigate the age distributions of stars in these components of the Galaxy via asteroseismology, where previously this has been difficult using other techniques.…
We present a kinematical study of 314 RR~Lyrae stars in the solar neighbourhood using the publicly available photometric, spectroscopic, and {\it Gaia} DR2 astrometric data to explore their distribution in the Milky Way. We report an overdensity of 22 RR~Lyrae stars in the solar neighbourhood at a pericenter distance of between 5--9\,kpc from the Galactic center. Their orbital parameters and their chemistry indicate that these 22 variables share the kinematics and the [Fe/H] values of the Galactic disc, with an average metallicity and tangential velocity of [Fe/H]=$-0.60$\,dex and $v_θ = 241$\…
We find that the combined LF of N- and SC-type stars are consistent with a Gaussian distribution peaking at M_bol~ -5.2 mag. The resulting LF however shows two tails at lower and higher luminosities more extended than those previously found, indicating that AGB carbon stars with Solar metallicity may reach M_bol~-6.0 mag. We find that J-type stars are about half a magnitude fainter on average than N- and SC-type stars, while R-hot stars are half a magnitude brighter than previously found. The Galactic spatial distribution and velocity components of the N-, SC- and J-type stars are very similar…
We cross-match the Alma catalog of OB stars with Gaia DR2 astrometry and photometry as a first step towards producing a clean sample of massive stars in the solar neighbourhood with a high degree of completeness. We analyze the resulting colour-absolute magnitude diagram to divide our sample into categories and compare extinction estimates from two sources, finding problems with both of them. The distances obtained with three different priors are found to have few differences among them, indicating that Gaia DR2 distances are robust. An analysis of the 3-D distribution of massive stars in the …
I use a sample of more than 120,000 stars in the solar neighbourhood with parallaxes, magnitudes and colours estimated with unprecedented accuracy by the second data release of the Gaia mission to derive the initial mass function of the Galactic disc. A full-forward technique is used to take into account for the population of unresolved binaries, the metallicity distribution, the star formation history and their variation across the Galactic disk as well as all the observational effects. The shape of the initial mass function is well represented by a segmented power-law with two breaks at char…
Exploring the Milky Way stellar disk. Carbon, nitrogen, oxygen, sulphur, potassium, and copper abundances for 714 F- and G-type dwarf stars in the solar neighbourhood
The age-metallicity relation (AMR) is a fundamental observational constraint for understanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR for the solar neighbourhood, primarily due to the difficulty in obtaining accurate stellar ages for individual field stars. We have started an observational campaign for providing the much needed observational input by using wide white dwarf-main sequence (WDMS) binaries. White dwarfs are natural clocks and can be used to derive accurate ages. Metallicities ca…
The termination in the white dwarf luminosity function is a standard diagnostic tool for measuring the total age of nearby stellar populations. In this paper, an algorithm is presented for inverting the full white dwarf luminosity function to obtain a maximum likelihood estimate of the time varying star formation rate of the host stellar population. Tests with synthetic data demonstrate that the algorithm converges over a wide class of underlying star formation rate forms. The algorithm successfully estimates the moving average star formation rate as a function of lookback time in the presence…
Setting the timeline of the events which shaped the Milky Way disc through its 13 billion year old history is one of the major challenges in the theory of galaxy formation. Achieving this goal is possible using late-type stars, which in virtue of their long lifetimes can be regarded as fossil remnants from various epochs of the formation of the Galaxy. There are two main paths to reliably age-date late-type stars: astrometric distances for stars in the turn-off and subgiant region, or oscillation frequencies along the red giant branch. So far, these methods have been applied to large samples o…
The age-metallicity relation is a fundamental tool for constraining the chemical evolution of the Galactic disc. In this work we analyse the observational properties of this relation using binary stars that have not interacted consisting of a white dwarf - from which we can derive the total age of the system - and a main sequence star - from which we can derive the metallicity as traced by the [Fe/H] abundances. Our sample consists of 46 widely separated, but unresolved spectroscopic binaries identified within the Sloan Digital Sky Survey, and 189 white dwarf plus main sequence common proper m…
In the last three decades several hundred nearby members of young stellar moving groups (MGs) have been identified, but there has been less systematic effort to quantify or characterise young stars that do not belong to previously identified MGs. Using a kinematically unbiased sample of 225 lithium-rich stars within 100 pc, we find that only $50 \pm 10$ per cent of young ($\lesssim 125$ Myr), low-mass ($0.5<M/M_{\odot}<1.0$) stars, are kinematically associated with known MGs. Whilst we find some evidence that six of the non-MG stars may be connected with the Lower Centaurus-Crux association, t…
Debris discs - analogous to the Asteroid and Kuiper-Edgeworth belts in the Solar system - have so far mostly been identified and studied in thermal emission shortward of 100 um. The Herschel space observatory and the SCUBA-2 camera on the James Clerk Maxwell Telescope will allow efficient photometric surveying at 70 to 850 um, which allow for the detection of cooler discs not yet discovered, and the measurement of disc masses and temperatures when combined with shorter wavelength photometry. The SCUBA-2 Unbiased Nearby Stars (SUNS) survey and the DEBRIS Herschel Open Time Key Project are compl…
For the first time, we present an extensive study of stars with individual non-local thermodynamic equilibrium (NLTE) abundances for 17 chemical elements from Li to Eu in a sample of stars uniformly distributed over the $-2.62 \le$ [Fe/H] $\le +0.24$ metallicity range that is suitable for the Galactic chemical evolution research. The star sample has been kinematically selected to trace the Galactic thin and thick disks and halo. We find new and improve earlier results as follows. (i) The element-to-iron ratios for Mg, Si, Ca, and Ti form a MP plateau at a similar height of 0.3~dex, and the kne…
Atmospheric parameters and chemical compositions for ten stars with metallicities in the region of -2.2< [Fe/H] <-0.6 were precisely determined using high resolution, high signal to noise, spectra. For each star the abundances, for 14 to 27 elements, were derived using both LTE and NLTE approaches. In particular, differences by assuming LTE or NLTE are about 0.10 dex; depending on [Fe/H], Teff, gravity and element lines used in the analysis. We find that the O abundance has the largest error, ranging from 0.10 and 0.2 dex. The best measured elements are Cr, Fe, and Mn; with errors etween 0.03 …
We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool ($T_{\rm eff}$ < 4000 K) white dwarfs (WDs) in the solar neighbourhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21 pc to >100 pc, and include five stars within 30 pc. Contrary to expectations, all but two of them have tangential velocities smaller than 150 km s$^{-1}$ thus suggesting Galactic disc membership. The oldest WDs in this sample have WD cooling ages of 10 Gyr, pro…
The majority of Milky Way extrasolar planets likely reside within a few kpc of the Galactic centre. The Galactic tidal forces acting on planets scale inversely with radius in the Galaxy and so are much greater in the inner Galaxy than in the Solar neighbourhood. Within a range of 3.5 to 10 kpc, the vertical tide from the Galactic disc is predominant. Interior to 3.5 kpc, the effects of the Galactic bulge cannot be neglected and the in-plane tidal components are as important as the vertical ones. Here, we quantify the orbital changes induced by these tides. We find that the greatest perturbatio…
We present a global study of low mass, young stellar object (YSO) surface densities in nearby (< 500 pc) star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys. We show that the distribution of YSO surface densities in the solar neighbourhood is a smooth distribution, being adequately described by a lognormal function from a few to 10^3 YSOs per pc^2, with a peak at 22 stars/pc^2 and a dispersion of 0.85. We do not find evidence for multiple discrete modes of star-formation (e.g. clustered and distributed). Comparing the observed surface density distributio…
We have, for the first time, compiled a nearly complete census of planetary nebulae (PNe) centred on the Sun. Our goal is the generation of an unbiased volume-limited sample, in order to answer some long-standing statistical questions regarding the overall population of Galactic disk PNe and their central stars. Much improved discrimination of classical PNe from their mimics is now possible based on the wide variety of high-quality multiwavelength data sets that are now available. However, we note that evidence is increasing that PNe are heterogeneous, and probably derived from multiple evolut…
In preparation for the HERMES chemical tagging survey of about a million Galactic FGK stars, we estimate the number of independent dimensions of the space defined by the stellar chemical element abundances [X/Fe]. [...] We explore abundances in several environments, including solar neighbourhood thin/thick disk stars, halo metal-poor stars, globular clusters, open clusters, the Large Magellanic Cloud and the Fornax dwarf spheroidal galaxy. [...] We find that, especially at low metallicity, the production of r-process elements is likely to be associated with the production of alpha-elements. Th…
We analyse the results of a 5.5-yr photometric campaign that monitored 247 southern, semi-regular variables with relatively precise Hipparcos parallaxes to demonstrate an unambiguous detection of Red Giant Branch (RGB) pulsations in the solar neighbourhood. We show that Sequence A' contains a mixture of AGB and RGB stars, as indicated by a temperature related shift at the TRGB. Large Magellanic Cloud (LMC) and Galactic sequences are compared in several ways to show that the P-L sequence zero-points have a negligible metallicity dependence. We describe a new method to determine absolute magnitu…
We present a self-consistent, absolute isochronal age scale for young (< 200 Myr), nearby (< 100 pc) moving groups, which is consistent with recent lithium depletion boundary ages for both the Beta Pic and Tucana-Horologium moving groups. This age scale was derived using a set of semi-empirical pre-main-sequence model isochrones that incorporate an empirical colour-Teff relation and bolometric corrections based on the observed colours of Pleiades members, with theoretical corrections for the dependence on log g. Absolute ages for young, nearby groups are vital as these regions play a crucial r…
We present a global study of low mass, young stellar object (YSO) surface densities (Sigma) in nearby (< 500 pc) star forming regions based on a comprehensive collection of Spitzer Space Telescope surveys. We show that the distribution of YSO surface densities is a smooth distribution, being adequately described by a lognormal function from a few to 10^3 YSOs per pc^2, with a peak at ~22 stars pc^-2. The observed lognormal Sigma is consistent with predictions of hierarchically structured star-formation at scales below 10 pc, arising from the molecular cloud structures. We do not find evidence …
Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. The aim of this paper is to provide robust numbers for the incidence of debris discs around FGK stars in the solar neighbourhood. The full sample of 177 FGK stars with d<20 pc proposed for the DUNES survey is presented. Herschel/PACS observations at 100 and 160 micron complemented with data at 70 micron, and at 250, 350 and 500 micron SPIRE photometry, were obtained. The 123 objects observed by the…
We present the first results of a ground-based programme conducted on 1-4m class telescopes. Our sample consists of 1097 active and presumably young stars, all of them being optical counterparts of RASS X-ray sources in the northern hemisphere. We concentrate on the 704 optically brightest (V_Ticho<=9.5 mag) candidates. We acquired high-res spectroscopy in the Halpha/Li spectral regions for 426 of such stars without relevant literature data. We describe the sample and the observations and we start to discuss its physical properties. We used a cross-correlation technique and other tools to deri…
