Abundances and possible diffusion of elements in M67 stars

We present a spectroscopic study at high resolution, R~50,000, of 14 stars located on the main sequence, at the turn-off point and on the early subgiant branch in the cluster M67 in order to investigate its detailed chemical composition, for comparison with the Sun and solar twins in the solar neighbourhood, and to explore selective atomic diffusion of chemical elements as predicted by stellar-structure theory. We have obtained VLT/FLAMES-UVES spectra and analysed these strictly differentially in order to explore chemical-abundance similarities and differences between the M67 stars and the Sun, and among the M67 stars themselves. Individual abundances of 19 different chemical elements are obtained for the stars. They are found to agree very well with solar abundances, with abundance ratios closer to solar than those of most solar twins in the solar neighbourhood. An exception is Li which shows a considerable scatter among the cluster stars. There is a tendency for the cluster-star abundances to be depleted relative to the abundances in the field stars in correlation with the condensation temperature of the elements, a tendency earlier found also for the Sun. The results support the hypothesis that the gas of the proto-cluster was depleted by formation and cleansing of dust before the stars formed. They also add support to the proposal that the Sun was once formed in a dense stellar environment. Moreover, the observed minor reductions of heavy elements in the atmospheres of the dwarfs and turn-off point stars relative to our standard star M67-1194 and the subgiants seem to suggest that diffusion processes are at work in these stars, although the evidence is not compelling. Based on theoretical models the diffusion-corrected initial metallicity of M67 is estimated to be [Fe/H]=+0.06.Comment: 14 pages, 9 figures, 5 tables. Accepted for publication in section 8. Stellar atmospheres of Astronomy and Astrophysics. Minor language corrections and an update of section 4.1 as compared to previous publicatio

Broadband UBVR_CI_C Photometry of Horizontal-Branch and Metal-poor Candidates from the HK and Hamburg/ESO Surveys. I.

We report broadband UBV and/or BVR_CI_C CCD photometry for a total of 1857 stars in the thick-disk and halo populations of the Galaxy. The majority of our targets were selected as candidate field horizontal-branch or other A-type stars (FHB/A, N = 576), or candidate low-metallicity stars (N = 1221), from the HK and Hamburg/ESO objective-prism surveys. Similar data for a small number of additional stars from other samples are also reported. These data are being used for several purposes. In the case of the FHB/A candidates they are used to accurately separate the lower gravity FHB stars from various higher gravity A-type stars, a subsample that includes the so-called blue metal poor stars, halo and thick-disk blue stragglers, main-sequence A-type dwarfs, and Am and Ap stars. These data are also being used to derive photometric distance estimates to high-velocity hydrogen clouds in the Galaxy and for improved measurements of the mass of the Galaxy. Photometric data for the metal-poor candidates are being used to refine estimates of stellar metallicity for objects with available medium-resolution spectroscopy, to obtain distance estimates for kinematic analyses, and to establish initial estimates of effective temperature for analysis of high-resolution spectroscopy of the stars for which this information now exists

Solar Type Stars as Calibrators : A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars

Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. Their surface layers are well mixed and just little affected by the interior nuclear processes. They may therefore be used as samples of the gas from which the stars were once formed. Models of stellar atmospheres are used to derive fundamental stellar quantities such as chemical composition, effective temperature, surface gravity, age and rotation. It is therefore also important to investigate the progress and shortcomings of the atmospheric models and the reliability of calibrations based upon these. In this thesis we explore the potential of synthetic uvbyHβ colours for deriving atmospheric parameters. The theoretical colours are derived using high-resolution synthetic spectra based on 1D atmosphere models of late-type stars. Furthermore, possible applications of the established synthetic colours on globular stellar clusters are tested. Observations of solar-type stars have demonstrated the existence of stars very similar to the Sun, so-called solar twins. A detailed chemical analysis of these stars, however, shows that most solar-twins are systematically richer, as compared with the Sun, in refractory elements such as Fe, Ni and Al, relative to volatile elements like C, N and O. This chemical abundance pattern has been suggested to be related to the formation of planets or the birth environment of the respective star. In this thesis we present a high-accuracy study on a solar-twin star in the old open cluster M67. We find that the star is very similar to the Sun when comparing their atmospheric parameters, effective temperature, surface gravity and metallicity. Remarkably enough, unlike most solar twins observed in the solar vicinity, the cluster twin shows the same refractory to volatile pattern as the Sun.The reason for this similarity is still unknown but further observations of the cluster will help to clarify the matter. M dwarfs constitute a large fraction of the detectable baryonic matter. In spite of this, detailed knowledge on the numerous neighbouring low-mass stars is still not available. The presence of strong molecular features in the spectra, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for detailed spectroscopic abundance analysis. In this thesis we present a high resolution spectroscopic study of early-type M dwarfs in the infrared. The lack of prominent molecular bands in parts of the infrared J-band (1100--1400 nm) allows a precise continuum placement. Furthermore, we verify the adequacy of using the model atmospheres for abundance determination by observing a set of binary systems with a solar-type primary and an M dwarf companion. We present a reliable zero-point for the metallicity scale of early-type M dwarfs and verify the reliability of spectroscopic abundance analyses in the infrared

Solar Type Stars as Calibrators : A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars

Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. Their surface layers are well mixed and just little affected by the interior nuclear processes. They may therefore be used as samples of the gas from which the stars were once formed. Models of stellar atmospheres are used to derive fundamental stellar quantities such as chemical composition, effective temperature, surface gravity, age and rotation. It is therefore also important to investigate the progress and shortcomings of the atmospheric models and the reliability of calibrations based upon these. In this thesis we explore the potential of synthetic uvbyHβ colours for deriving atmospheric parameters. The theoretical colours are derived using high-resolution synthetic spectra based on 1D atmosphere models of late-type stars. Furthermore, possible applications of the established synthetic colours on globular stellar clusters are tested. Observations of solar-type stars have demonstrated the existence of stars very similar to the Sun, so-called solar twins. A detailed chemical analysis of these stars, however, shows that most solar-twins are systematically richer, as compared with the Sun, in refractory elements such as Fe, Ni and Al, relative to volatile elements like C, N and O. This chemical abundance pattern has been suggested to be related to the formation of planets or the birth environment of the respective star. In this thesis we present a high-accuracy study on a solar-twin star in the old open cluster M67. We find that the star is very similar to the Sun when comparing their atmospheric parameters, effective temperature, surface gravity and metallicity. Remarkably enough, unlike most solar twins observed in the solar vicinity, the cluster twin shows the same refractory to volatile pattern as the Sun.The reason for this similarity is still unknown but further observations of the cluster will help to clarify the matter. M dwarfs constitute a large fraction of the detectable baryonic matter. In spite of this, detailed knowledge on the numerous neighbouring low-mass stars is still not available. The presence of strong molecular features in the spectra, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for detailed spectroscopic abundance analysis. In this thesis we present a high resolution spectroscopic study of early-type M dwarfs in the infrared. The lack of prominent molecular bands in parts of the infrared J-band (1100--1400 nm) allows a precise continuum placement. Furthermore, we verify the adequacy of using the model atmospheres for abundance determination by observing a set of binary systems with a solar-type primary and an M dwarf companion. We present a reliable zero-point for the metallicity scale of early-type M dwarfs and verify the reliability of spectroscopic abundance analyses in the infrared

Solar Type Stars as Calibrators : A Photometric and Spectroscopic Study on the Atmospheric Properties of Late-type Stars

Detailed knowledge of solar-type stars is essential in the understanding of the evolutionary past, presence and future of the Sun as well as the formation of its planetary system. Moreover, solar-type stars are of key significance for the study of the evolution of the Galaxy. The ages of solar-type stars map the full galactic evolution. Their surface layers are well mixed and just little affected by the interior nuclear processes. They may therefore be used as samples of the gas from which the stars were once formed. Models of stellar atmospheres are used to derive fundamental stellar quantities such as chemical composition, effective temperature, surface gravity, age and rotation. It is therefore also important to investigate the progress and shortcomings of the atmospheric models and the reliability of calibrations based upon these. In this thesis we explore the potential of synthetic uvbyHβ colours for deriving atmospheric parameters. The theoretical colours are derived using high-resolution synthetic spectra based on 1D atmosphere models of late-type stars. Furthermore, possible applications of the established synthetic colours on globular stellar clusters are tested. Observations of solar-type stars have demonstrated the existence of stars very similar to the Sun, so-called solar twins. A detailed chemical analysis of these stars, however, shows that most solar-twins are systematically richer, as compared with the Sun, in refractory elements such as Fe, Ni and Al, relative to volatile elements like C, N and O. This chemical abundance pattern has been suggested to be related to the formation of planets or the birth environment of the respective star. In this thesis we present a high-accuracy study on a solar-twin star in the old open cluster M67. We find that the star is very similar to the Sun when comparing their atmospheric parameters, effective temperature, surface gravity and metallicity. Remarkably enough, unlike most solar twins observed in the solar vicinity, the cluster twin shows the same refractory to volatile pattern as the Sun.The reason for this similarity is still unknown but further observations of the cluster will help to clarify the matter. M dwarfs constitute a large fraction of the detectable baryonic matter. In spite of this, detailed knowledge on the numerous neighbouring low-mass stars is still not available. The presence of strong molecular features in the spectra, and incomplete line lists for the corresponding molecules have made metallicity determinations of M dwarfs difficult. Furthermore, the faint M dwarfs require long exposure times for a signal-to-noise ratio sufficient for detailed spectroscopic abundance analysis. In this thesis we present a high resolution spectroscopic study of early-type M dwarfs in the infrared. The lack of prominent molecular bands in parts of the infrared J-band (1100--1400 nm) allows a precise continuum placement. Furthermore, we verify the adequacy of using the model atmospheres for abundance determination by observing a set of binary systems with a solar-type primary and an M dwarf companion. We present a reliable zero-point for the metallicity scale of early-type M dwarfs and verify the reliability of spectroscopic abundance analyses in the infrared

Bland alla dessa stjärnor finns en som lyser precis som solen

Hur hittar man en exakt kopia av solen bland alla stjärnor på natthimlen? Och vad berättar sådana ”soltvillingar” för oss? Två forskare vid Uppsala universitet håller för närvarande på att analysera en nyupptäckt soltvilling

Bland alla dessa stjärnor finns en som lyser precis som solen

Hur hittar man en exakt kopia av solen bland alla stjärnor på natthimlen? Och vad berättar sådana ”soltvillingar” för oss? Två forskare vid Uppsala universitet håller för närvarande på att analysera en nyupptäckt soltvilling

Bland alla dessa stjärnor finns en som lyser precis som solen

Hur hittar man en exakt kopia av solen bland alla stjärnor på natthimlen? Och vad berättar sådana ”soltvillingar” för oss? Två forskare vid Uppsala universitet håller för närvarande på att analysera en nyupptäckt soltvilling