Papers by Birgitta Nordström
Proceedings of the International Astronomical Union, 2007
Division VII provides a forum for astronomers studying our home galaxy, the Milky Way, which offe... more Division VII provides a forum for astronomers studying our home galaxy, the Milky Way, which offers a unique laboratory for exploring the detailed structure of the stellar and gaseous components of galaxies and the process by which they form and evolve.
A short report on some of the Research on the structure and dynamics of the Galactic System durin... more A short report on some of the Research on the structure and dynamics of the Galactic System during 2012-2015
Astronomy and Astrophysics
Proceedings of the International Astronomical Union, 2008
ABSTRACT The term “heating” is used loosely to refer to a range of processes that result in an in... more ABSTRACT The term “heating” is used loosely to refer to a range of processes that result in an increase in velocity dispersion with age for subgroups of disk stars. We briefly summarise the observational basis for studies of disk heating and show that qualitative differences exist between the evolution of the in-plane and vertical motions. Ways to discriminate between various heating scenarios are discussed; the most recent galaxy merger simulations may in fact suggest that discrimination on purely kinematic grounds might be unfeasible, even with large samples of stars with excellent ages.
Romanian Astronomical Journal
The Evolution of Galaxies, 2003
ABSTRACT
ESO ASTROPHYSICS SYMPOSIA, 2000
We have carried out a new analysis of two of the most extreme CH/CN very metal poor giants (origi... more We have carried out a new analysis of two of the most extreme CH/CN very metal poor giants (originally discovered as part of the ongoing Beers Preston & Shectman HK survey [2]) with high resolution spectroscopy to determine the precise chemical composition of these objects, paying special attention to the heavy s and r neutron-capture elements. The results of this study are presented and discussed in terms of the possible origins for these objects: mass-transfer from a binary companion or intrinsic evolutionary stage of evolved Pop III stars?
Astronomy and Astrophysics, 2002
A&A 382, 368-377 (2002) DOI: 10.1051/0004-6361:20011597. Experimental oscillator strength... more A&A 382, 368-377 (2002) DOI: 10.1051/0004-6361:20011597. Experimental oscillator strengths in Th II. H. Nilsson 1 - ZG Zhang 2 - H. Lundberg 2 - S. Johansson 1 - B. Nordström 1,3. 1 - Atomic Astrophysics, Lund Observatory ...
Astronomy and Astrophysics
Based on new, accurate photometry, radial velocities, and proper motions for the intermediate-age... more Based on new, accurate photometry, radial velocities, and proper motions for the intermediate-age open cluster NGC 3680, we identify individual single and binary cluster members and field stars in the colour-magnitude diagram (CMD). This basic step turns out to be crucial for a proper understanding of the cluster CMD: ∼60% of the stars are found to be field stars, and over 50% of the cluster stars are binaries. No bona f ide cluster star is found more than 1. m 5 below the turnoff, and cluster stars below 1.4 M are only found in binary systems. The total present mass of NGC 3680 is ∼100M , excluding any as yet unseen stellar remnants, and its half-mass radius is 3.3 (1.2 pc). Comparison with plausible IMFs indicates that only ∼3% of the original stars and < ∼ 10% of the mass now survive, ∼30% of the initial mass being in the form of massive stars that have now completed their evolution, and ∼60% in low-mass stars which may now be located in a distant cluster halo or perhaps have been lost entirely.
The catalog contains 1595 photoelectric radial-velocity observations for 790 bright southern star... more The catalog contains 1595 photoelectric radial-velocity observations for 790 bright southern stars of spectral type F5 and later. One of the purposes of this project is to make a complete southern sky radial velocity coverage using the second CORAVEL photoelectric radial velocity scanner. The first CORAVEL operating at Observatoire de Haute-Provence was used to observe the stars in the Northern
... The Inventory of F and G Dwarfs: Observational Kinematics in the Milky Way Frédéric Pont, R. ... more ... The Inventory of F and G Dwarfs: Observational Kinematics in the Milky Way Frédéric Pont, R. Fax, M. Mayor Geneva Observatory, Switzerland J. Andersen, B. Nordstrom, EH Olsen Niels Bohr Institute, Copenhagen, Denmark After an observational effort representing more than ...
Proceedings of the International Astronomical Union
ABSTRACT
We present new radial and rotational velocities for 595 nearby early F dwarfs, based on digital s... more We present new radial and rotational velocities for 595 nearby early F dwarfs, based on digital spectra cross-correlated with individually optimised synthetic template spectra. The selection of optimum templates, the determination of rotational velocities, and the extraction of velocities from the blended spectra of double-lined spectroscopic binaries are discussed in some detail. We find 170 spectroscopic binaries in the sample and determine orbits for 18 double-lined and 2 single-lined binaries, including some spectroscopic triples. 73 stars are listed with too rapid rotation to yield useful radial velocities (i.e. vsini>120km/s). We discuss the binary frequency in the sample, and the influence of unrecognised binaries on the definition of clean metallicity groups of young F dwarfs and the determination of their kinematical properties. (5 data files).
Astronomy and Astrophysics
Based on new, accurate photometry, radial velocities, and proper motions for the intermediate-age... more Based on new, accurate photometry, radial velocities, and proper motions for the intermediate-age open cluster NGC 3680, we identify individual single and binary cluster members and field stars in the colour-magnitude diagram (CMD). This basic step turns out to be crucial for a proper understanding of the cluster CMD: ~60% of the stars are found to be field stars, and over 50% of the cluster stars are binaries. No bona fide cluster star is found more than 1.5mag below the turnoff, and cluster stars below 1.4M{sun} are only found in binary systems. The total present mass of NGC 3680 is ~100M{sun}, excluding any as yet unseen stellar remnants, and its half-mass radius is 3.3' (1.2pc). Comparison with plausible IMFs indicates that only ~3% of the original stars and <~10% of the mass now survive, ~30% of the initial mass being in the form of massive stars that have now completed their evolution, and ~60% in low-mass stars which may now be located in a distant cluster halo or perhaps have been lost entirely. The single main-sequence cluster members form an extremely tight sequence in the CMD, with E(b-y)=0.034 and [Fe/H]=+0.11. A direct fit to the Hyades main sequence yields (m-M)0=10.5+/-0.2 for NGC 3680. Isochrones from several stellar models have been fit to the cluster sequence. When based on consistent uvby colour transformations and the above cluster parameters, these fits are very stable and show that standard models are not acceptable for stars with the turnoff mass of NGC 3680. Overshooting models perform much better, but further refinement of the overshooting formalism seems to be needed. The age derived for NGC 3680 is 1.45+/-0.3Gyr. The limiting factor in a precise comparison of theory and observations is now the transformation from theoretical to observed parameters, particularly (broad-band) colours. (1 data file).
We present an infrared K-band light curve and a radial velocity curve for the RR Lyrae star V9 in... more We present an infrared K-band light curve and a radial velocity curve for the RR Lyrae star V9 in the metal rich globular cluster 47 Tucanae ([Fe/H]=-0.71). Combining these new data with the optical photometry presented in Carney et al. (1993PASP..105..294C), we perform a Baade-Wesselink analysis and derive a distance modulus of 47 Tuc of 13.23mag+/-0.17 and absolute mean magnitudes of <MV>=0.32mag and <MK>=-0.57mag for V9. We also present a well populated visual-infrared color-magnitude diagram of the cluster, reaching from the upper red giant branch to the subgiant branch. (3 data files).
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Papers by Birgitta Nordström