A5036114004- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astronomical Observations and Instrumentation
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Solar and Space Plasma Dynamics
- Galaxies: Formation, Evolution, Phenomena
- Astronomical and nuclear sciences
- History and Developments in Astronomy
- Geophysics and Gravity Measurements
- CCD and CMOS Imaging Sensors
- Atmospheric Ozone and Climate
- Calibration and Measurement Techniques
- Astrophysical Phenomena and Observations
- Historical Astronomy and Related Studies
- SAS software applications and methods
- Magnetic Properties and Applications
- Methane Hydrates and Related Phenomena
- Relativity and Gravitational Theory
- Astrophysics and Cosmic Phenomena
- Space Exploration and Technology
- Spectroscopy Techniques in Biomedical and Chemical Research
- High-pressure geophysics and materials
Aarhus University
2015-2024
Netherlands Institute for Radio Astronomy
2023
Vilnius University
2019-2022
University of Victoria
1999-2016
KU Leuven
2009
University of British Columbia
2009
University of Copenhagen
2004
Institute of Astronomy
2002
Czech Academy of Sciences, Institute of Physics
2002
Dominion Astrophysical Observatory
1998-1999
High dispersion spectra () for a quite large number of stars at the main sequence turn-off and base giant branch in NGC 6397 6752 were obtained with UVES on Kueyen (VLT UT2). The [Fe/H] values we found are respectively, where first error bars refer to internal second ones systematic errors (within abundance scale defined by our analysis 25 subdwarfs good Hipparcos parallaxes). In both clusters [Fe/H]'s TO-stars agree perfectly few percent) that RGB. value obtain is low, but it agrees...
We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to September 2009, for total 76 GRBs, and present an additional three pre-Swift not included in earlier sample. Furthermore, we publish 840 new points 42 GRB afterglows, sets 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A 080810. analyzed light curves all derived spectral energy distributions with best quality, allowing us estimate host...
Mass-loss of red giant branch (RGB) stars is still poorly determined, despite its crucial role in the chemical enrichment galaxies. Thanks to recent detection solar-like oscillations G–K giants open clusters with Kepler, we can now directly determine stellar masses for a statistically significant sample old NGC 6791 and 6819. The aim this work constrain integrated RGB mass-loss by comparing average mass clump (RC) that low-luminosity portion [i.e. L≲L(RC)]. Stellar were determined combining...
(Abridged). We present a sample of 77 optical afterglows (OAs) Swift detected GRBs for which spectroscopic follow-up observations have been secured. provide linelists and equivalent widths all lines redward Ly-alpha. discuss to what extent the current bursts with OA spectroscopy is biased subsample GRBs. For that purpose we define an X-ray selected optimal conditions ground-based follow up from period March 2005 September 2008; 146 fulfill our criteria. derive redshift distribution this...
The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of art Doppler precision and identified critical path challenges for reaching 10 cm s−1 measurement precision. presentations discussion key issues instrumentation data analysis workshop recommendations achieving this bold are summarized here. Beginning with High Accuracy Velocity Planet Searcher spectrograph, technological advances radial velocity (RV) measurements have focused building extremely stable...
New improved distances and absolute ages for the Galactic globular clusters NGC 6397, 6752, 47 Tuc are obtained using Main Sequence Fitting Method. We derived accurate estimates of reddening metal abundance these three a strictly differential procedure, where Johnson Strömgren colours UVES high resolution spectra turn-off stars early subgiants belonging to were compared similar data field subdwarfs with parallaxes measured by Hipparcos. The use free temperature indicator (the profile Hα)...
We present a homogeneous photometric and spectroscopic analysis of 18 stars along the evolutionary sequence metal-poor globular cluster NGC 6397 ([Fe/H] = -2), from main-sequence turnoff point to red giants below bump. The stellar parameters, in particular stellar-parameter differences between groups stars, are good agreement with broad-band Stroemgren photometry calibrated on infrared-flux method. abundance reveals, for first time, systematic trends iron stage. Iron is found be 31% less...
<i>Context. <i/>To alleviate the discrepancy between prediction of primordial lithium abundance in universe and abundances observed Pop II dwarfs subgiant stars, it has been suggested that stars observable today have undergone photospheric depletion lithium.<i>Aims. identify cause this depletion, is important to accurately establish behaviour with effective temperature evolutionary phase. Stars globular clusters are ideal objects for such an analysis, because relative stellar parameters can...
Multi-band Hubble Space Telescope photometry reveals that the main sequence, sub-giant, and red-giant branch of globular cluster NGC 6752 splits into three components in close analogy with distinct segments along its horizontal stars. These triple sequences are consistent stellar groups: a population chemical composition similar to field-halo stars (Population a), Population (c) enhanced sodium nitrogen, depleted carbon oxygen, an helium abundance (ΔY ∼ 0.03), (b) intermediate (between...
We present the chemical compositions for eight bright giants in globular cluster NGC 1851. Our analysis reveals large star-to-star abundance variations and correlations of light elements O, Na, Al, a feature found every well-studied cluster. However, 1851 also exhibits s-process Zr La. These are correlated with Al anticorrelated O. Furthermore, La abundances appear to around two distinct values. A recent study revealed double subgiant branch data reinforce notion that there stellar...
We present a general overview and the first results of SUMO project (a SUrvey Multiple pOpulations in Globular Clusters). The objective this survey is study multiple stellar populations largest sample globular clusters homogeneously analysed to date. To aim we obtained high signal-to-noise (S/N > 50) photometry for main sequence stars with mass down ∼0.5 M⊙ large using both archival proprietary U, B, V I data from ground-based telescopes. In paper, focus on occurrence 23 clusters. define new...
We present initial results on some of the properties open clusters NGC 6791 and 6819 derived from asteroseismic data obtained by NASA's Kepler mission. In addition to estimating mass, radius log g stars red-giant branch these clusters, we estimate distance their ages. Our model-independent modulus is (m-M)_0= 13.11\pm 0.06. find 11.85\pm 0.05 for 6819. The average mass 1.20 \pm 0.01 M_sun, while that 1.68\pm 0.03M_sun. It should be noted do not have cover entire actual will somewhat lower....
We present CN and CH indices CaII triplet metallicities for 34 giant stars chemical abundances 33 elements in 14 giants the globular cluster M2. Assuming program are members, our analysis reveals (i) an extreme variation line strengths, (ii) a metallicity dispersion with dominant peak at [Fe/H] = -1.7 smaller peaks -1.5 -1.0, (iii) star-to-star abundance variations correlations light O, Na, Al Si (iv) large (and possibly bimodal) distribution of all produced mainly via s-process solar system...
Models of stellar structure and evolution can be constrained by measuring accurate parameters detached eclipsing binaries in open clusters. Multiple binary stars provide the means to determine helium abundances these old systems, turn, improve estimates their age. In first paper this series, we demonstrated how measurements multiple cluster NGC6791 sets tighter constraints on properties models than has previously been possible, thereby potentially improving both accuracy precision Here add...
Asteroseismology has the capability of precisely determining stellar properties that would otherwise be inaccessible, such as radii, masses, and thus ages stars. When coupling this information with classical determinations parameters, metallicities, effective temperatures, angular diameters, powerful new diagnostics for Galactic studies can obtained. The ongoing Strömgren survey Archaeology goal transforming Kepler field into a benchmark studies, similar to solar neighborhood. Here we...
We present the discovery of TOI-197.01, first transiting planet identified by Transiting Exoplanet Survey Satellite (TESS) for which asteroseismology host star is possible. TOI-197 (HIP116158) a bright (V=8.2 mag), spectroscopically classified subgiant oscillates with an average frequency about 430 muHz and displays clear signature mixed modes. The oscillation amplitude confirms that redder TESS bandpass compared to Kepler has small effect on oscillations, supporting expected yield thousands...
We aim to establish and improve the accuracy level of asteroseismic estimates mass, radius, age giant stars. This can be achieved by measuring independent, accurate, precise masses, radii, effective temperatures metallicities long period eclipsing binary stars with a red component that displays solar-like oscillations. measured properties three systems KIC 7037405, 9540226, 9970396 estimated their ages $5.3\pm0.5$, $3.1\pm0.6$, $4.8\pm0.5$ Gyr. The measurements were compared corresponding...
We present broadband BVI photometry for the open cluster NGC 6791, based upon analysis of 1764 individual CCD images. discuss in detail transformation instrumental magnitudes to standard photometric system Landolt and then methods selecting a subset stars whose indices are most likely be high reliability. Color‐magnitude color‐color diagrams presented discussed. A detailed comparison this with results previous observational studies is presented. make preliminary comparisons theoretical...
A "jump" in the blue horizontal-branch (HB) distribution (V, u-y) color-magnitude diagram has recently been detected globular cluster (GC) M13 (NGC 6205) by Grundahl and coworkers. Such an effect is morphologically best characterized as a discontinuity (u, locus, with stars range 11,500 K ≲ Teff 20,000 deviating systematically from (in sense of appearing brighter and/or hotter than) canonical zero-age HB models. In this article, we present Strömgren u, y photometry 14 GCs obtained three...
We make use of high resolution, signal-to-noise ratio spectra 12 turn-off stars in the metal-poor globular cluster NGC 6397 to measure its lithium content. conclude that they all have same abundance A(Li with a standard deviation 0.056 dex. this result, together Monte Carlo simulations, estimate maximum allowed intrinsic scatter is order 0.035 This new stringent constraint be fulfilled by stellar models which predict Li depletion. argue although mild depletion 0.1–0.2 dex, as predicted...
établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics privés.
We present N abundances for 21 bright giants in the globular cluster NGC 6752 based on high-resolution UVES spectra of 3360A NH lines. confirm that Stromgren c1 index traces abundance and find star-to-star variation is 1.95 dex, at sample's luminosity. statistically significant correlations, but small amplitude variations, between alpha-, Fe-peak, s-process elements. Analyses using model atmospheres with appropriate N, O, Na, Al would strengthen, rather than mute, these correlations. If...
Studying star clusters offers significant advances in stellar astrophysics due to the combined power of having many stars with essentially same distance, age, and initial composition. This makes excellent test benches for verification evolution theory. To fully exploit this potential, it is vital that sample uncontaminated by are not members cluster. Techniques determining cluster membership therefore play a key role investigation clusters. We present results on three Kepler field view based...