M. F. Sterzik

European Southern Observatory, Arching, Bavaria, Germany

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Publications (225)458.2 Total impact

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    ABSTRACT: Context. Young loose nearby associations are unique samples of close (<150 pc), young (approx 5-100 Myr) pre-main sequence (PMS) stars. A significant number of members of these associations have been identified in the SACY collaboration. We can use the proximity and youth of these members to investigate key ingredients in star formation processes, such as multiplicity. Aims. We present the statistics of identified multiple systems from 113 confirmed SACY members. We derive multiplicity frequencies, mass-ratio, and physical separation distributions in a consistent parameter space, and compare our results to other PMS populations and the field. Methods. We have obtained adaptive-optics assisted near-infrared observations with NACO (ESO/VLT) and IRCAL (Lick Observatory) for at least one epoch of all 113 SACY members. We have identified multiple systems using co-moving proper-motion analysis and using contamination estimates. We have explored ranges in projected separation and mass-ratio of a [3-1000 au], and q [0.1-1], respectively. Results. We have identified 31 multiple systems (28 binaries and 3 triples). We derive a multiplicity frequency (MF) of MF_(3-1000au)=28.4 +4.7, -3.9% and a triple frequency (TF) of TF_(3-1000au)=2.8 +2.5, -0.8% in the separation range of 3-1000 au. We do not find any evidence for an increase in the MF with primary mass. The estimated mass-ratio of our statistical sample (with power-law index gamma=-0.04 +/- 0.14) is consistent with a flat distribution (gamma = 0). Conclusions. We show further similarities (but also hints of discrepancies) between SACY and the Taurus region: flat mass-ratio distributions and statistically similar MF and TF values. We also compared the SACY sample to the field (in the separation range of 19-100 au), finding that the two distributions are indistinguishable, suggesting a similar formation mechanism.
    Full-text · Article · May 2015 · Astronomy and Astrophysics
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    ABSTRACT: Context. T and Y-dwarfs are among the coolest and least luminous objects detected, and they can help to understand the properties of giant planets. Up to now, there are more than 350 T dwarfs that have been identified thanks to large imaging surveys in the infrared, and their multiplicity properties can shed light on the formation process. Aims. The aim of this work is to look for companions around a sample of seven ultracoool objects. Most of them have been discovered by the WISE observatory and have not been studied before for multiplicity. Methods. We observed a sample six T dwarfs and one L9 dwarf with the Laser Guide Star (LGS) and NAOS-CONICA, the adaptive optics (AO) facility, and the near infrared camera at the ESO Very Large Telescope. We observed all the objects in one or more near-IR filters (JHKs). Results. From the seven observed objects, we have identified a subarcsecond binary system, WISE J0612-3036, composed of two similar components with spectral types of T6. We measure a separation of ρ = 350±5mas and a position angle of PA = 235 ± 1◦. Using the mean absolute magnitudes of T6 dwarfs in the 2MASS JHKs bands, we estimate a distance of d=31±6 pc and derive a projected separation of ρ ∼ 11 ± 2 au. Another target, WISE J2255-3118, shows a very faint object at 1."3 in the Ks image. The object is marginally detected in H, and we derive a near infrared color of H − K_s> 0.1mag. HS T/WFC3 public archival data reveals that the companion candidate is an extended source. Together with the derived color, this suggests that the source is most probably a background galaxy. The five other sources are apparently single, with 3-σ sensitivity limits between H=19–21 for companions at separations ≥ 0."5. Conclusions. WISE0612-3036 is probably a new T-dwarf binary composed of two T6 dwarfs. As in the case of other late T-dwarf binaries, it shows a mass ratio close to 1, although its projected separation, ∼11 au, is larger than the average (∼ 5 au). Additional observations are needed to confirm that the system is bound.
    Full-text · Article · Apr 2015 · Astronomy and Astrophysics
  • S. Bagnulo · A. Cellino · M.F. Sterzik
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    ABSTRACT: The surfaces of the atmosphere-less objects of our solar system are traditionally probed via reflectance measurements and/or broadband linear polarimetry. Little attention has been paid so far to the wavelength dependence of the linear polarization of the scattered light. We decided to explore the potential of spectropolarimetry as a remote sensing tool for asteroids in addition to the more traditional reflectance measurements, and we carried out a spectropolarimetric survey of asteroids - to our best knolwedge, the first of its kind. We observed a sample of asteroids of different albedo and taxonomic classes, as well as a few regions at the limb of the Moon. We show that objects exhibiting similar reflectance spectra may display totally different polarization spectra, and we suggest that both intensity and polarization spectra should be used for asteroid classification. We also found that in some cases the Umov law is violated, that is, in contrast to what is expected from simple physical considerations, the fraction of linear polarization and the reflectance spectra may be correlated positively. We conclude that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectance and polarization spectra.
    No preview · Article · Jan 2015 · Proceedings of the International Astronomical Union
  • Stefano Bagnulo · Michael F. Sterzik · Alberto Cellino
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    ABSTRACT: Linear broadband polarimetry is used to characterize the objects of our solar system, and has also been proposed as a diagnostic tool for the atmospheres of exo-solar planets. Homochirality characterizes life as we know it and induces circular polarization in the diffuse reflectance spectra of biotic material. Hence it has been suggested that circular polarimetry may be used as a remote sensing tool for the search of extra-terrestrial life. With this motivation in mind we have decided to explore the potential of both linear and circular spectropolarimetry as a diagnostic tool for remote sensing of biotic material. We have used the calibration unit of the EFOSC2 instrument of the La Silla Observatory to obtain low resolution, but high signal to noise circular and linear spectropolarimetric measurements of a number of inorganic and organic materials. We then compare our laboratory data with spectropolarimetric observations of atmosphere-less bodies of our solar system and of Earthshine obtained with instruments very similar to that one used for our laboratory samples. We conclude that linear polarization measurements are more suitable than circular polarization measurements for the characterization of planetary surfaces and atmospheres, and for the search of extra-terrestrial life.
    No preview · Article · Jan 2015 · Proceedings of the International Astronomical Union
  • M.F. Sterzik · S. Bagnulo · C. Emde
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    ABSTRACT: Polarimetry is routinely used to characterise the surfaces of bodies in our solar system. In the near future, polarisation measurements of the starlight reflected by exoplanets will become a common and powerful tool to constrain the atmospheres and the surface properties of other worlds. If extra-terrestial life has similar signatures as the life we know, then astronomical observations of planet Earth represent a benchmark to eventually probe bio-signatures also on other planets. In fact, linear polarisation spectra of Earthshine (the sunlight that has been first reflected by Earth and then reflected back to Earth by the Moon), allow us to detect the presence of oxygen, ozone, and water in the atmosphere of our planet. Surface properties such as fractional contributions of clouds and ocean, as well as vegetation can be inferred. Ultimately, Earthshine observations provide strong observational constraints on model predictions for Earth-like exoplanets. In this contribution, we review the most recent observations of Earthshine by polarimetry. We highlight some advances in the interpretation and modelling of whole Earth polarisation, which will be of paramount importance to interpret possible bio-signatures of Earth-like planets in the habitable zone of nearby stars in the future.
    No preview · Article · Jan 2015 · Proceedings of the International Astronomical Union
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    ABSTRACT: There are several ways planets can survive the giant phase of the host star, hence one can consider the case of Earth-like planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU from the star would remain in the continuous habitable zone (CHZ) for about 8 Gyr. Polarisation due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 10 2 (10 4 ) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a powerful tool to detect close-in planets around white dwarfs. Multi-band polarimetry would also allow one to reveal the presence of a planet atmosphere, even providing a first characterisation. With current facilities a super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue. Preliminary habitability study show also that photosynthetic processes can be sustained on Earth-like planets orbiting CWDs and that the DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, hence white dwarfs are compatible with the persistence of complex life from the perspective of UV irradiation.
    No preview · Conference Paper · Dec 2014
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    S. Bagnulo · A. Cellino · M. F. Sterzik
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    ABSTRACT: We explore the use of spectro-polarimetry as a remote sensing tool for asteroids in addition to traditional reflectance measurements. In particular we are interested in possible relationships between the wavelength-dependent variation of linear polarization and the properties of the surfaces, including albedo and composition. We have obtained optical spectro-polarimetric measurements of a dozen asteroids of different albedo and taxonomic classes and of two small regions at the limb of the Moon. We found that objects with marginally different relative reflectance spectra (in the optical) may have totally different polarization spectra. This suggests that spectro-polarimetry may be used to refine the classification of asteroids. We also found that in some cases the Umov law may be violated, that is, in contrast to what is expected from basic physical considerations, the fraction of linear polarization and the reflectance may be positively correlated. In agreement with a few previous studies based on multi-colour broadband polarimetry, we found that the variation of linear polarization with wavelength and with phase-angle is correlated with the albedo and taxonomic class of the objects. Finally, we have serendipitously discovered that spinel-rich asteroid (599) Luisa, located very close to the Watsonia family, is a member of the rare class of Barbarian asteroids. We suggest that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectance and polarization spectra.
    Full-text · Article · Sep 2014 · Monthly Notices of the Royal Astronomical Society Letters
  • P Elliott · A Bayo · C Melo · C Torres · M Sterzik · G Quast

    No preview · Conference Paper · Sep 2014
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    ABSTRACT: Context. Our study is a follow-up of the SACY project, an extended high spectral resolution survey of more than two thousand optical counterparts to X-ray sources in the southern hemisphere targeted to search for young nearby association. Nine associations have either been newly identified, or have had their member list revised. Groups belonging to the Sco-Cen-Oph complex are not considered in the present study.Aims. These nine associations, with ages of between about 6 Myr and 70 Myr, form an excellent sample to study the Li depletion in the pre-main sequence (PMS) evolution. In the present paper, we investigate the use of Li abundances as an independent clock to constrain the PMS evolution.Methods. Using our measurements of the equivalent widths of the Li resonance line and assuming fixed metallicities and microturbulence, we calculated the LTE Li abundances for 376 members of various young associations. In addition, we considered the effects of their projected stellar rotation.Results. We present the Li depletion as a function of age in the first hundred million years for the first time for the most extended sample of Li abundances in young stellar associations.Conclusions. A clear Li depletion can be measured in the temperature range from 5000 K to 3500 K for the age span covered by the nine associations studied in this paper. The age sequence based on the Li-clock agrees well with the isochronal ages, the $\epsilon$Cha association being the only possible exception. The lithium depletion patterns for the associations presented here resemble those of the young open clusters with similar ages, strengthening the notion that the members proposed for these loose young associations have indeed a common physical origin. The observed scatter in the Li abundances hampers the use of Li in determining reliable ages for individual stars. For velocities above 20 km s$^{-1}$, rotation seems to play an important role in inhibiting the Li depletion.
    Full-text · Article · Aug 2014 · Astronomy and Astrophysics
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    ABSTRACT: Context: Dynamically undisrupted, young populations of stars are crucial to study the role of multiplicity in relation to star formation. Loose nearby associations provide us with a great sample of close ($<$150 pc) Pre-Main Sequence (PMS) stars across the very important age range ($\approx$5-70 Myr) to conduct such research. Aims: We characterize the short period multiplicity fraction of the SACY (Search for Associations Containing Young stars) accounting for any identifiable bias in our techniques and present the role of multiplicity fractions of the SACY sample in the context of star formation. Methods: Using the cross-correlation technique we identified double-lined spectroscopic systems (SB2), in addition to this we computed Radial Velocity (RV) values for our subsample of SACY targets using several epochs of FEROS and UVES data. These values were used to revise the membership of each association then combined with archival data to determine significant RV variations across different data epochs characteristic of multiplicity; single-lined multiple systems (SB1). Results: We identified 7 new multiple systems (SB1s: 5, SB2s: 2). We find no significant difference between the short period multiplicity fraction ($F_\mathrm{m}$) of the SACY sample and that of nearby star forming regions ($\approx$1-2 Myr) and the field ($F_\mathrm{m}\leq$10%) both as a function of age and as a function of primary mass, $M_1$, in the ranges $P$ [1:200 day] and $M_2$ [0.08 $M_{\odot}$-$ M_1$]. Conclusions: Our results are consistent with the picture of universal star formation, when compared to the field and nearby star forming regions (SFRs). We comment on the implications of the relationship between increasing multiplicity fraction with primary mass, within the close companion range, in relation to star formation.
    Full-text · Article · Jun 2014 · Astronomy and Astrophysics
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    ABSTRACT: We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identified by the search for associations containing young stars survey. In addition to common kinematics and ages between these two systems, here we explore their chemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogeneous high-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argus association using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba.All stars in the open cluster and Argus association were found to share similar abundances with the scatter well within the uncertainties, where [Fe/H]=-0.04+/-0.03 for cluster stars and [Fe/H]=-0.06+/-0.05 for Argus stars. Effects of overionization/excitation were seen for stars cooler than roughly 5200K as previously noted in the literature. Also, enhanced Ba abundances of around 0.6dex were observed in both systems. The common ages, kinematics and chemical abundances strongly support the fact that the Argus association stars originated from the open cluster IC 2391. Simple modelling of this system finds this dissolution to be consistent with two-body interactions.(4 data files).
    No preview · Article · Dec 2013
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    ABSTRACT: Stars in young nearby associations are the only targets allowing giant planet searches at all separations in the near future, by coupling indirect techniques such as radial velocity and deep imaging. These stars are first priorities targets for the forthcoming planets imagers on 10-m class telescopes. Young stars rotate more rapidly and are more active than their older counterparts. Both effects can limit the capability to detect planets using RV. We wish to explore the planet detection capabilities of a representative sample of stars in close and young associations with radial velocity data and explore the complementarity between this technique and direct imaging. We observed 26 such targets with spectral types from A to K and ages from
    Full-text · Article · Apr 2013 · Astronomy and Astrophysics
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    ABSTRACT: We explore the possible connection between the open cluster IC 2391 and the unbound Argus association identified by the SACY survey. In addition to common kinematics and ages between these two systems, here we explore their chemical abundance patterns to confirm if the two substructures shared a common origin. We carry out a homogenous high-resolution elemental abundance study of eight confirmed members of IC 2391 as well as six members of the Argus association using UVES spectra. We derive spectroscopic stellar parameters and abundances for Fe, Na, Mg, Al, Si, Ca, Ti, Cr, Ni and Ba. All stars in the open cluster and Argus association were found to share similar abundances with the scatter well within the uncertainties, where [Fe/H] = -0.04 +/-0.03 for cluster stars and [Fe/H] = -0.06 +/-0.05 for Argus stars. Effects of over-ionisation/excitation were seen for stars cooler than roughly 5200K as previously noted in the literature. Also, enhanced Ba abundances of around 0.6 dex were observed in both systems. The common ages, kinematics and chemical abundances strongly support that the Argus association stars originated from the open cluster IC 2391. Simple modeling of this system find this dissolution to be consistent with two-body interactions.
    Full-text · Article · Jan 2013 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Since there are several ways planets can survive the giant phase of the host star, we examine the habitability and detection of planets orbiting white dwarfs. As a white dwarf cools from 6000 K to 4000 K, a planet orbiting at 0.01 AU would remain in the continuous habitable zone (CHZ) for ~8 Gyr. We show that photosynthetic processes can be sustained on such planets. The DNA-weighted UV radiation dose for an Earth-like planet in the CHZ is less than the maxima encountered on Earth, and hence non-magnetic white dwarfs are compatible with the persistence of complex life. Polarization due to a terrestrial planet in the CHZ of a cool white dwarf (CWD) is 102 (104) times larger than it would be in the habitable zone of a typical M-dwarf (Sun-like star). Polarimetry is thus a viable way to detect close-in rocky planets around white dwarfs. Multi-band polarimetry would also allow us to reveal the presence of a planet atmosphere, providing a first characterization. Planets in the CHZ of a 0.6 M ☉ white dwarf will be distorted by Roche geometry, and a Kepler-11d analog would overfill its Roche lobe. With current facilities a super-Earth-sized atmosphereless planet is detectable with polarimetry around the brightest known CWD. Planned future facilities render smaller planets detectable, in particular by increasing the instrumental sensitivity in the blue.
    Full-text · Article · Jul 2012 · The Astrophysical Journal Letters
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    ABSTRACT: We used high-precision Harps data collected over eight years since 2003 to measure and analyse β Pic radial velocities. (1 data file).
    No preview · Article · Jul 2012
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    ABSTRACT: This second edition of the Observing Planetary Systems workshop was aimed at bringing together the two communities of Solar System and exoplanetary system scientists to review the recent progress made in our understanding of the formation of the Solar System and its early chemistry, and how this picture fits with our current knowledge of the formation and evolution of planetary systems in general.
    No preview · Article · Jun 2012
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    ABSTRACT: We present a study of the large-scale spatial distribution of 6482 RASS X-ray sources in approximately 5000 deg^2 in the direction of Orion. We examine the astrophysical properties of a sub-sample of ~100 optical counterparts, using optical spectroscopy. This sub-sample is used to investigate the space density of the RASS young star candidates by comparing X-ray number counts with Galactic model predictions. We characterize the observed sub-sample in terms of spectral type, lithium content, radial and rotational velocities, as well as iron abundance. A population synthesis model is then applied to analyze the stellar content of the RASS in the studied area. We find that stars associated with the Orion star-forming region do show a high lithium content. A population of late-type stars with lithium equivalent widths larger than Pleiades stars of the same spectral type (hence younger than ~70-100 Myr) is found widely spread over the studied area. Two new young stellar aggregates, namely "X-ray Clump 0534+22" (age~2-10 Myr) and "X-ray Clump 0430-08" (age~2-20 Myr), are also identified. The spectroscopic follow-up and comparison with Galactic model predictions reveal that the X-ray selected stellar population in the direction of Orion is characterized by three distinct components, namely the clustered, the young dispersed, and the widespread field populations. The clustered population is mainly associated with regions of recent or ongoing star formation and correlates spatially with molecular clouds. The dispersed young population follows a broad lane apparently coinciding spatially with the Gould Belt, while the widespread population consists primarily of active field stars older than 100 Myr. We expect the "bi-dimensional" picture emerging from this study to grow in depth as soon as the distance and the kinematics of the studied sources will become available from the future Gaia mission.
    Full-text · Article · Apr 2012 · Astronomy and Astrophysics
  • S. Bagnulo · M. F. Sterzik · E. Palle
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    ABSTRACT: One of the next most important goals of astronomy is the characterization of exo-solar planets and the search for extra terrestrial life. Traditional spectroscopic measurements cannot be easily applied to the study of the atmospheres of the exo-solar planets, because the light reflected by the planet is overwhelmed by the radiation of the hosting star. Polarimetric techniques offer an attractive solution to this problem. Since the light reflected by the planet is highly polarised, it can be distinguished from the nearly unpolarised stellar radiation, provided that the observations are obtained with sufficiently high signal-to-noise ratio. Theoretical models have been developed to predict what the polarised spectrum of an Earth-like planet would look like if observed in linear polarization from space [1]. Model predictions appear to be very sensitive to the percentage of ocean, vegetation, and clouds that cover the visible area of the planet. Here we present polarised spectra of the Earthshine, which simulate the observations of the planet Earth as seen from space. Interpreted with theoretical models, our observations clearly reveal bio-markers, and practically demonstrate that spectro-polarimetry may be a key diagnostic tool not only for the study of the exoplanets, but also for the search of extra-terrestrial life. [1] Stam, D.M., 2008, Astronomy and Astrophysics, 484, 989.
    No preview · Article · Apr 2012
  • I. Pascucci · M. Sterzik · R. Alexander · G. Sacco
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    ABSTRACT: We present the first observational evidence for disk photoevaporation driven by the central star and discuss the implications of star-driven photoevaporation on the architecture of planetary systems.
    No preview · Article · Mar 2012
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    ABSTRACT: The formation of spectroscopic binaries (SB) may be a natural byproduct of star formation. The early dynamical evolution of multiple stellar systems after the initial fragmentation of molecular clouds leaves characteristic imprints on the properties of young, multiple stars. The discovery and the characterization of the youngest SB will allow us to infer the mechanisms and timescales involved in their formation. Our work aims to find spectroscopic companions around young stellar objects (YSO). We present a near-IR high-resolution (R ~ 60 000) multi-epoch radial velocity survey of seven YSO in the star-forming region (SFR) ρ Ophiuchus. The radial velocities of each source were derived using a two-dimensional cross-correlation function, using the zero-point established by the Earth's atmosphere as reference. More than 14 spectral lines in the CO Δν = (0-2) bandhead window were used in the cross-correlation against LTE atmospheric models to compute the final results. We found that the spectra of the protostars in our sample agree well with the predicted stellar photospheric profiles, indicating that the radial velocities derived are indeed of stellar nature. Three of the targets analyzed exhibit large radial velocity variations during the three observation epochs. These objects - pending further confirmation and orbital characteristics - may become the first evidence for proto-spectroscopic binaries, and will provide important constraints on their formation. Our preliminary binary fraction (BF) of ~71% (when merging our results with those of previous studies) is in line with the notion that multiplicity is very high at young ages and therefore a byproduct of star formation. Based on observations collected with the CRIRES spectrograph at the VLT/UT1 8.2-m Antu Telescope (ESO run ID. 081.C-0395(A)) at the Paranal Observatory, Chile.Table 1 is available in electronic form at http://www.aanda.org
    Full-text · Article · Mar 2012 · Astronomy and Astrophysics

Publication Stats

3k Citations
458.20 Total Impact Points

Institutions

  • 1998-2015
    • European Southern Observatory
      Arching, Bavaria, Germany
    • University of Hamburg
      • Hamburg Observatory
      Hamburg, Hamburg, Germany
  • 1970-2015
    • University of Santiago, Chile
      CiudadSantiago, Santiago Metropolitan, Chile
  • 2010
    • Pontifical Catholic University of Chile
      CiudadSantiago, Santiago, Chile
  • 2003
    • Max Planck Institute for Astronomy
      Heidelburg, Baden-Württemberg, Germany
  • 1997-2003
    • Indiana University Bloomington
      • Department of Astronomy
      Bloomington, IN, United States
  • 2000
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
    • University of Vienna
      • Department of Astrophysics
      Wien, Vienna, Austria
  • 1995-1999
    • Max Planck Institute for Extraterrestrial Physics
      Arching, Bavaria, Germany
    • University of California, Santa Barbara
      Santa Barbara, California, United States
  • 1994
    • University of Tuebingen
      Tübingen, Baden-Württemberg, Germany