Cantat-Gaudin T.,University of Padua |
Cantat-Gaudin T.,National institute for astrophysics |
Vallenari A.,National institute for astrophysics |
Zaggia S.,National institute for astrophysics |
And 55 more authors.
Astronomy and Astrophysics | Year: 2014
Context. Chemically inhomogeneous populations are observed in most globular clusters, but not in open clusters. Cluster mass seems to play a key role in the existence of multiple populations. Aims. Studying the chemical homogeneity of the most massive open clusters is needed to better understand the mechanism of their formation and determine the mass limit under which clusters cannot host multiple populations. Here we studied NGCâ‰ 6705, which is a young and massive open cluster located towards the inner region of the Milky Way. This cluster is located inside the solar circle. This makes it an important tracer of the inner disk abundance gradient. Methods. This study makes use of BVI and ri photometry and comparisons with theoretical isochrones to derive the age of NGCâ‰ 6705. We study the density profile of the cluster and the mass function to infer the cluster mass. Based on abundances of the chemical elements distributed in the first internal data release of the Gaia-ESO Survey, we study elemental ratios and the chemical homogeneity of the red clump stars. Radial velocities enable us to study the rotation and internal kinematics of the cluster. Results. The estimated ages range from 250 to 316â‰ Myr, depending on the adopted stellar model. Luminosity profiles and mass functions show strong signs of mass segregation. We derive the mass of the cluster from its luminosity function and from the kinematics, finding values between 3700 M and 11 000 M. After selecting the cluster members from their radial velocities, we obtain a metallicity of [Fe/H] = 0.10 ± 0.06 based on 21 candidate members. Moreover, NGC 6705 shows no sign of the typical correlations or anti-correlations between Al, Mg, Si, and Na, which are expected in multiple populations. This is consistent with our cluster mass estimate, which is lower than the required mass limit proposed in the literature to develop multiple populations. © 2014 ESO .
Singh K.,University of Groningen |
Singh K.,Vrije Universiteit Brussel |
Singh K.,University of Alberta |
Mevius M.,University of Groningen |
And 111 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2012
When an ultra-high energy neutrino or cosmic-ray strikes the Lunar surface a radio-frequency pulse is emitted. We plan to use the LOFAR radio telescope to detect these pulses. In this work we propose an efficient trigger implementation for LOFAR optimized for the observation of short radio pulses. © 2011 Elsevier B.V. All rights reserved.
Stratta G.,Science Data Center |
Pozanenko A.,Space Research Institute IKI |
Atteia J.L.,French National Center for Scientific Research |
Klotz A.,Hoffmann-La Roche |
And 16 more authors.
Advances in Space Research | Year: 2011
The detection of a bright optical emission measured with good temporal resolution during the prompt phase makes GRB 060111B a rare event that is especially useful for constraining theories of the prompt optical emission. Comparing this burst with other GRBs with evidence of optical peaks, we find that the optical peak epoch (tp) is anti-correlated with the high energy burst energetic assuming an isotropic energy release (Eiso) in agreement with Liang et al. (2009), and that the steeper is the post-peak afterglow decay, the less is the agreement with the correlation. GRB 060111B is among the latters and it does not match the correlation. The Cannonball scenario is also discussed and we find that this model cannot be excluded for GRB 060111B. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.
Evans C.J.,Astronomy Technology Center |
Puech M.,University Paris Diderot |
Barbuy B.,University of Sao Paulo |
Bonifacio P.,University Paris Diderot |
And 55 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014
Over the past 18 months we have revisited the science requirements for a multi-object spectrograph (MOS) for the European Extremely Large Telescope (E-ELT). These efforts span the full range of E-ELT science and include input from a broad cross-section of astronomers across the ESO partner countries. In this contribution we summarise the key cases relating to studies of high-redshift galaxies, galaxy evolution, and stellar populations, with a more expansive presentation of a new case relating to detection of exoplanets in stellar clusters. A general requirement is the need for two observational modes to best exploit the large (≥40 arcmin2) patrol field of the E-ELT. The first mode ('high multiplex') requires integrated-light (or coarsely resolved) optical/near-IR spectroscopy of >100 objects simultaneously. The second ('high definition'), enabled by wide-field adaptive optics, requires spatially-resolved, near-IR of >10 objects/sub-fields. Within the context of the conceptual study for an ELT-MOS called MOSAIC, we summarise the toplevel requirements from each case and introduce the next steps in the design process. © 2014 SPIE.
Grigahcene A.,University of Porto |
Antoci V.,Institute fuer Astronomie |
Balona L.,South African Astronomical Observatory |
Catanzaro G.,National institute for astrophysics |
And 38 more authors.
Astrophysical Journal Letters | Year: 2010
Observations of the pulsations of stars can be used to infer their interior structure and test theoretical models. The main-sequence γDoradus (Dor) and δScuti (Sct) stars with masses 1.2-2.5M are particularly useful for these studies. The γDor stars pulsate in high-order g-modes with periods of order 1day, driven by convective blocking at the base of their envelope convection zone. The δSct stars pulsate in low-order g- and p-modes with periods of order 2 hr, driven by the κ mechanism operating in the He II ionization zone. Theory predicts an overlap region in the Hertzsprung-Russell diagram between instability regions, where "hybrid" stars pulsating in both types of modes should exist. The two types of modes with properties governed by different portions of the stellar interior provide complementary model constraints. Among the known γDor and δSct stars, only four have been confirmed as hybrids. Now, analysis of combined Quarter 0 and Quarter 1 Kepler data for hundreds of variable stars shows that the frequency spectra are so rich that there are practically no pure δSct or γDor pulsators, i.e., essentially all of the stars show frequencies in both the δSct and the γDor frequency range. A new observational classification scheme is proposed that takes into account the amplitude as well as the frequency and is applied to categorize 234 stars as δSct, γDor, δSct/γDor or γDor/δSct hybrids. © 2010. The American Astronomical Society. All rights reserved.