Thomas Bensby - Lund Observatory, Department of Astronomy and Theoretical Physics, Lund, Sweden

Thomas Bensby
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Thomas Bensby
Lund Observatory, Department of Astronomy and Theoretical Physics, Lund, Sweden

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Astrophysics of Galaxies (9)
Solar and Stellar Astrophysics (7)
Astrophysics (1)
High Energy Astrophysical Phenomena (1)

Publications Authored By Thomas Bensby

It has recently been discovered that some, if not all, classical novae emit GeV gamma-rays during outburst, but the mechanics of this gamma-ray emission are still not well understood. We present here a comprehensive, multi-wavelength dataset---from radio to X-rays---for the most gamma-ray luminous classical nova to-date, V1324 Sco. Using this dataset, we show that V1324 Sco is a canonical dusty Fe-II type nova, with a bulk ejecta velocity of $1150 \pm 40~\rm km~s^{-1}$ and an ejecta mass of $2. Read More

Knowledge of abundance ratios as functions of metallicity can lead to insights on the origin and evolution of our Galaxy and its stellar populations. We aim to trace the chemical evolution of the neutron-capture elements Sr, Zr, La, Ce, Nd, Sm, and Eu in the Milky Way stellar disk to constrain the formation sites of these elements as well as to probe the evolution of the Galactic thin and thick disks. Using spectra of high resolution and high signal-to-noise we determine Sr, Zr, La, Ce, Nd, Sm, and Eu abundances for a sample of 593 F and G dwarf stars in the Solar neighbourhood. Read More

Affiliations: 1Lund Observatory, Department of Astronomy and Theoretical Physics, Lund, Sweden, 2Lund Observatory, Department of Astronomy and Theoretical Physics, Lund, Sweden

AIMS: The aim of this study is to investigate the origin and evolution of Sc, V, Mn, and Co for a homogeneous and statistically significant sample of stars probing the different populations of the Milky Way, in particular the thin and thick disks. METHODS: Using high-resolution spectra obtained with MIKE, FEROS, SOFIN, FIES, UVES and HARPS spectrographs, we determine Sc, V, Mn, and Co abundances for a large sample of F and G dwarfs in Solar neighbourhood. The method is based on spectral synthesis and using one-dimensional (1-D), plane-parallel, LTE model stellar atmospheres calculated with the MARCS 2012 code. Read More

Affiliations: 1Lund Observatory, Sweden, 2University of Surrey, UK, 3Lund Observatory, Sweden, 4ETH Zurich, Switzerland, 5Lund Observatory, Sweden

The Milky Way is expected to host an accreted disc of stars and dark matter. This forms as massive >1:10 mergers are preferentially dragged towards the disc plane by dynamical friction and then tidally shredded. The accreted disc likely contributes only a tiny fraction of the Milky Way's thin and thick stellar disc. Read More

This is a brief overview of the elemental abundance patterns that have been observed in the different Galactic stellar populations. Main focus is on studies that are based on high-resolution spectra of dwarf and subgiant stars, and in some cases red giant stars. Of particular interest is the thin-thick disk dichotomy, the variation of abundances and stellar ages with galactocentric radius, multiple stellar populations in the Galactic bulge region, and how some of these may be connected with other Galactic populations. Read More

Thick disks appear to be common in external large spiral galaxies and our own Milky Way also hosts one. The existence of a thick disk is possibly directly linked to the formation history of the host galaxy and if its properties is known it can constrain models of galaxy formation and help us to better understand galaxy formation and evolution. This brief review attempts to highlight some of the characteristics of the Galactic thick disk and how it relates to other stellar populations such as the thin disk and the Galactic bulge. Read More

Elemental abundance patterns can provide vital clues to the formation and enrichment history of a stellar population. Here we present an investigation of the Galactic bulge, where we apply principal component abundance analysis (PCAA)---a principal component decomposition of relative abundances [X/Fe]---to a sample of 35 microlensed bulge dwarf and subgiant stars, characterizing their distribution in the 12-dimensional space defined by their measured elemental abundances. The first principal component PC1, which suffices to describe the abundance patterns of most stars in the sample, shows a strong contribution from alpha-elements, reflecting the relative contributions of Type II and Type Ia supernovae. Read More

Galactic bulges are central to understanding galaxy formation and evolution. Here we report on recent studies using micro-lensing events to obtain spectra of high resolution and moderately high signal-to-noise ratios of dwarf stars in the Galactic bulge. Normally this is not feasible for the faint turn-off stars in the Galactic bulge, but micro-lensing offers this possibility. Read More

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. Read More

Nova Scorpii 2008 was the target of our Directory Discretionary Time proposal at VLT+UVES in order to study the evolution, origin and abundances of the heavy-element absorption system recently discovered in 80% of classical novae in outburst. The early decline of Nova Scorpii 2008 was monitored with high resolution echelle spectroscopy at 5 different epochs. The analysis of the absorption and the emission lines show many unusual characteristics. Read More

We study a sample of 16 microlensed Galactic bulge main sequence turnoff region stars for which high dispersion spectra have been obtained with detailed abundance analyses. We demonstrate that there is a very strong and highly statistically significant correlation between the maximum magnification of the microlensed bulge star and the value of the [Fe/H] deduced from the high resolution spectrum of each object. Physics demands that this correlation, assuming it to be real, be the result of some sample bias. Read More

A widely supported formation scenario for the Galactic disc is that it formed inside-out from material accumulated via accretion events. The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is the best example of a such accretion, and its ongoing disruption has resulted in that its stars are being deposited in the Milky Way halo and outer disc. It is therefore appealing to search for possible signatures of the Sgr dSph contribution to the build-up of the Galactic disc. Read More

Affiliations: 1European Southern Observatory, Vitacura, Santiago, Chile, 2Lund Observatory, Lund, Sweden
Category: Astrophysics

[ABRIDGED] We have determined carbon abundances for 51 dwarf stars and manganese abundances for 95 dwarf stars in two distinct and well defined stellar populations - the Galactic thin and thick disks. As these two populations have different chemical histories we have been able to, through a differential abundance analysis using high-resolution spectra, constrain the formation sites for carbon and manganese in the Galactic disk(s). The analysis of carbon is based on the forbidden [C I] line at 872. Read More