Martin A. T. Groenewegen

Publications (6)0 Total impact

• Source

  Available from: dtic.mil

  Article: Galactic Bulge Giants: Probing Stellar and Galactic Evolution. 1. Catalogue of Spitzer IRAC and MIPS Sources (PREPRINT)

  Stefan Uttenthaler, Matthias Stute, Raghvendra Sahai, Joris A D L Blommaert, Mathias Schultheis, Kathleen E Kraemer, Martin A T Groenewegen, Stephan D Price
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  ABSTRACT: Aims. We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods. To this end, we observed seven 15 × 15 arcmin 2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results. In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue.
  01/2011;
• Source

  Available from: Matthias Stute

  Article: Galactic bulge giants: probing stellar and galactic evolution I. Catalogue of Spitzer IRAC and MIPS sources

  Stefan Uttenthaler, Matthias Stute, Raghvendra Sahai, Joris A. D. L. Blommaert, Mathias Schultheis, Kathleen E. Kraemer, Martin A. T. Groenewegen, Stephan D. Price
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  ABSTRACT: Aims: We aim at measuring mass-loss rates and the luminosities of a statistically large sample of Galactic bulge stars at several galactocentric radii. The sensitivity of previous infrared surveys of the bulge has been rather limited, thus fundamental questions for late stellar evolution, such as the stage at which substantial mass-loss begins on the red giant branch and its dependence on fundamental stellar properties, remain unanswered. We aim at providing evidence and answers to these questions. Methods: To this end, we observed seven 15 times 15 arcmin^2 fields in the nuclear bulge and its vicinity with unprecedented sensitivity using the IRAC and MIPS imaging instruments on-board the Spitzer Space Telescope. In each of the fields, tens of thousands of point sources were detected. Results: In the first paper based on this data set, we present the observations, data reduction, the final catalogue of sources, and a detailed comparison to previous mid-IR surveys of the Galactic bulge, as well as to theoretical isochrones. We find in general good agreement with other surveys and the isochrones, supporting the high quality of our catalogue. Comment: 21 pages, accepted for publication in A&A. A version with high-resolution figures, as well as the data catalogues (including cross-id with GLIMPSE and GALCEN) and image mosaics are available at the anonymous ftp://ftp.ster.kuleuven.be/dist/stefan/Spitzer/
  02/2010;
• Article: TP-AGB stars in population synthesis models

  Paola Marigo, Léo Girardi, Alessandro Bressan, Bernhard Aringer, Marco Gullieuszik, Enrico V. Held, Martin A.T. Groenewegen, Laura Silva, Gian Luigi Granato
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  ABSTRACT: In spite of its relevance, the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase is one of the most uncertain phases of stellar evolution, and a major source of disagreement between the results of different population synthesis models of galaxies. I will briefly review the existing literature on the subject, and recall the basic prescriptions that have been used to fix the contribution of TP-AGB stars to the integrated light of stellar populations. The simplicity of these prescriptions greatly contrasts with the richness of details provided by present-day databases of AGB stars in the Magellanic Clouds, which are now being extended to other nearby galaxies. I will present the first results of an ongoing study aimed at simulating photometry, chemistry, pulsation, mass loss, dust properties of AGB star populations in resolved and un-resolved galaxies. We test our predictions against observations from various surveys of the Magellanic Clouds (DENIS, 2MASS, OGLE, MACHO, Spitzer, and AKARI). I will discuss the implications and outline the plan of future developments.
  Proceedings of the International Astronomical Union 07/2009; 5:36 - 43.
• Article: Thermally-pulsing asymptotic giant branch stars in the Magellanic Clouds

  Paola Marigo, Léo Girardi, Alessandro Bressan, Martin A. T. Groenewegen, Bernhard Aringer, Laura Silva, Gian Luigi Granato
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  ABSTRACT: We present the latest results of a theoretical project aimed at investigating the properties of thermally-pulsing asymptotic giant branch (TP-AGB) stars in different host systems. For this purpose, we have recently calculated calibrated synthetic TP-AGB tracks — covering a wide range of metallicities (0.0001 ≤ Z ≤ 0.03) up to the complete ejection of the envelope by stellar winds (Marigo & Girardi 2007) — and used them to generate new sets of stellar isochrones (Marigo et al. 2008). The latter are converted to about 25 different photometric systems, including the mid-infrared filters of Spitzer and AKARI as the effect of circumstellar dust from AGB stars is taken into account. First comparisons with AGB data in the MC field and stellar clusters are discussed.
  Proceedings of the International Astronomical Union 06/2008; 4:385 - 390.
• Source

  Available from: ArXiv

  Article: Evolution of asymptotic giant branch stars II. Optical to far-infrared isochrones with improved TP-AGB models

  Paola Marigo, Leo Girardi, Alessandro Bressan, Martin A. T. Groenewegen, Laura Silva, Gian Luigi Granato
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  ABSTRACT: We present a large set of theoretical isochrones, whose distinctive features mostly reside on the greatly improved treatment of the thermally pulsing asymptotic giant branch (TP-AGB) phase. Essentially, we have coupled the TP-AGB tracks described in Paper I, at their stages of pre-flash quiescent H-shell burning, with the evolutionary tracks for the previous evolutionary phases from Girardi et al. (2000). Theoretical isochrones for any intermediate value of age and metallicity are then derived by interpolation in the grids. We take care that the isochrones keep, to a good level of detail, the several peculiarities present in these TP-AGB tracks. Theoretical isochrones are then converted to about 20 different photometric systems -- including traditional ground-based systems, and those of recent major wide-field surveys such as SDSS, OGLE, DENIS, 2MASS, UKIDSS, etc., -- by means of synthetic photometry applied to an updated library of stellar spectra, suitably extended to include C-type stars. Finally, we correct the predicted photometry by the effect of circumstellar dust during the mass-losing stages of the AGB evolution, which allows us to improve the results for the optical-to-infrared systems, and to simulate mid- and far-IR systems such as those of Spitzer and AKARI. Access to the data is provided both via a web repository of static tables (http://stev.oapd.inaf.it/dustyAGB07 and CDS), and via an interactive web interface (http://stev.oapd.inaf.it/cmd) that provides tables for any intermediate value of age and metallicity, for several photometric systems, and for different choices of dust properties. Comment: 25 pages, accepted for publication in A&A, revised according to the latest referee's indications, isochrones are available at http://stev.oapd.inaf.it/cmd
  11/2007;
• Source

  Available from: Jacco van Loon

  Article: ISO Mid-Infrared Spectroscopy of Galactic Bulge AGB Stars

  Joris A. D. L. Blommaert, Martin A. T. Groenewegen, Koryo Okumura, Shashikiran Ganesh, Alain Omont, Jan Cami, Ian S. Glass, Harm J. Habing, Mathias Schultheis, Guy Simon, Jacco Th. van Loon
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  ABSTRACT: To study the nature of Bulge AGB stars and in particular their circumstellar dust, we have analysed mid-infrared spectra obtained with the ISOCAM CVF spectrometer in three Bulge fields. The ISOCAM 5-16.5 micron CVF spectra were obtained as part of the ISOGAL infrared survey of the inner Galaxy. A classification of the shape of the 10 micron dust feature was made for each case. The spectra of the individual sources were modelled using a radiative transfer model. Different combinations of amorphous silicates and aluminium-oxide dust were used in the modelling. Spectra were obtained for 29 sources of which 26 are likely to be Bulge AGB stars. Our modelling shows that the stars suffer mass loss rates in the range of 10^{-8} - 5 x 10^{-7} Msun / yr, which is at the low end of the mass-loss rates experienced on the Thermally Pulsing AGB. The luminosities range from 1,700 to 7,700 Lsun as expected for a population of AGB stars with Minit of 1.5 - 2Msun. In agreement with the condensation sequence scenario, we find that the dust content is dominated by Al_2O_3 grains in this sample of low mass-loss rate stars. Comment: Small modifications to the text. Table 2 corrected
  09/2006;