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Saint-Martin-Boulogne, France

Monier R.,CNRS Laboratory for Space Studies and Astrophysical Instrumentation | Monier R.,Sophia University | Gebran M.,Notre Dame University - Louaize | Royer F.,GEPI
Astronomy and Astrophysics | Year: 2015

Context. We have discovered four new HgMn stars while monitoring a sample of apparently slowly rotating superficially normal bright late-B and early-A stars in the northern hemisphere. Aims. Important classification lines of Hg ii and Mn ii are found as conspicuous features in the high resolution SOPHIE spectra of these stars (R = 75 000). Methods. Several lines of Hg ii, Mn ii and Fe ii were synthesized using model atmospheres and the spectrum synthesis code SYNSPEC48, including hyperfine structure of various isotopes when relevant. These synthetic spectra were compared to high-resolution observations of these stars that have a high signal-to-noise ratio to derive abundances of these key elements. Results. The four stars are found to have distinct enhancements of Hg and Mn, which shows that they are not superficially normal B and A stars, but are new HgMn stars and need to be reclassified as such. © 2015 ESO. Source

Desmurs J.-F.,Observatorio Astronomico Nacional | Baudry A.,Laboratory Observatoire Aquitain Des Science Of Lunivers | Sivagnanam P.,GEPI | Henkel C.,MPIfR | And 2 more authors.
Astronomy and Astrophysics | Year: 2010

Aims. The aim of this study is to investigate the physical properties of molecular envelopes of planetary nebulae (PNe) in their earliest stages of evolution. Methods. Using the 100 m telescope at Effelsberg, we have undertaken a high sensitivity discrete source survey for the first excited state of OH maser emission (J = 5/2, 2Π3/2 at 6 GHz) in the direction of PNe and proto-planetary nebulae (PNe) exhibiting 18 cm OH emission (main and/or satellite lines), and we further validate our detections using the Nançay radio telescope at 1.6-1.7 GHz and MERLIN interferometer at 1.6-1.7 and 6 GHz. Results. Two sources have been detected at 6035 MHz (5 cm), both of them are young (or very young) PNe. The first one is a confirmation of the detection of a weak 6035 MHz line in Vy 2-2. The second one is a new detection, in K 3-35, which was already known to be an exceptional late type star because it exhibits 1720 MHz OH emission. The detection of 6035 MHz OH maser emission is confirmed by subsequent observations made with the MERLIN interferometer. These lines are very rarely found in evolved stars. The 1612 MHz masers surround but are offset from the 1720 and 6035 MHz masers which in turn lie close to a compact 22 GHz continuum source embedded in the optical nebula. © 2010 ESO. Source

Welsh B.Y.,University of California at Berkeley | Wheatley J.,University of California at Berkeley | Lallement R.,GEPI
Publications of the Astronomical Society of the Pacific | Year: 2011

We present medium-resolution ultraviolet interstellar absorption measurements recorded with the HST-COS and FUSE spectrographs toward the post-AGB star Barnard 29 in the M13 globular cluster. Inspection of the UV spectra has revealed absorption at V LSR ∼ -60 km s -1 in the absorption profiles of the C I, C II, C II *, C IV, N I, N II, N V, O I, ALII, Si II, Si IV, S II and Fe II ions. This component can be associated with an intermediatevelocity cloud (IVC), previously identified by both radio and visible observations. More importantly, these data have newly revealed high-velocity absorption at V LSR = -121 ± 3 km s -1 in the UVions of C II, C III, C IV, N II, Si II, and Si IV. This absorption is thought to arise in a highly ionized, multiphase high-velocity cloud (HVC) located a distance of 0.46 < z < 4.7 kpc and has no measurable counterpart in the 21 cm neutral H I emission profile or the normal tracers of neutral gas in the ISM such as Na I, N I or O I. This makes it one of the four nearest highly ionized HVCs yet discovered. The observed column density ratios of the H V components to the C IV and Si IV lines are consistent with values predicted for a turbulent mixing layer or shock ionization of a gas cloud. We have derived estimates of the abundance ratios of C and Si with respect to N relative to their corresponding solar values. Our results indicate values of [Si/N] > +0.40 ± 0.21 and [C/N] = +0.10 ± 0.25 for the HVC gas component. These values indicate that the H V gas has higher than solar relative abundances, consistent with gas of a supersolar metallicity. Several other highly ionized HVCs with distances of less than 7.5 kpc have recently been shown to possess similarly high-metallicity values that are consistent with an origin in condensing returning gas from a galactic fountain. © 2011. The Astronomical Society of the Pacific. Source

Rettura A.,Johns Hopkins University | Rosati P.,European Southern Observatory | Nonino M.,National institute for astrophysics | Fosbury R.A.E.,ST ECF | And 6 more authors.
Astrophysical Journal | Year: 2010

We derive stellar masses, ages, and star formation histories (SFHs) of massive early-type galaxies in the z = 1.237 RDCS1252.9-2927 cluster and compare them with those measured in a similarly mass-selected sample of field contemporaries drawn from the Great Observatories Origin Deep Survey South Field. Robust estimates of these parameters are obtained by comparing a large grid of composite stellar population models with 8-9 band photometry in the rest-frame near-ultraviolet, optical, and IR, thus sampling the entire relevant domain of emission of the different stellar populations. Additionally, we present new, deep U-band photometry of both fields, giving access to the critical far-ultraviolet rest frame, in order to empirically constrain the dependence of the most recent star formation processes on the environment. We also analyze the morphological properties of both samples to examine the dependence of their scaling relations on their mass and environment. We find that early-type galaxies, both in the cluster and in the field, show analogous optical morphologies, follow comparable mass versus size relation, have congruent average surface stellar mass densities, and lie on the same Kormendy relation. We also show that a fraction of early-type galaxies in the field employ longer timescales, τ, to assemble their mass than their cluster contemporaries. Hence, we conclude that while the formation epoch of early-type galaxies only depends on their mass, the environment does regulate the timescales of their SFHs. Our deep U-band imaging strongly supports this conclusion. We show that cluster galaxies are at least 0.5mag fainter than their field contemporaries of similar mass and optical-to-infrared colors, implying that the last episode of star formation must have happened more recently in the field than in the cluster. © 2010. The American Astronomical Society. All rights reserved. Source

Hill V.,University of Nice Sophia Antipolis | Lecureur A.,GEPI | Gomez A.,GEPI | Zoccali M.,University of Santiago de Chile | And 7 more authors.
Astronomy and Astrophysics | Year: 2011

Aims. We seek to constrain the formation of the Galactic bulge by analysing the detailed chemical composition of a large sample of red clump stars in Baade's window. These stars were selected to minimise the contamination by other Galactic components, so they are good tracers of the bulge metallicity distribution in Baade's window, at least for stars more metal-rich than ∼-1.5. Methods. We used an automatic procedure to measure [Fe/H] differentially with respect to the metal-rich star μLeo in a sample of 219 bulge red clump stars from R = 20 000 resolution spectra obtained with FLAMES/GIRAFFE at the VLT. For a subsample of 162 stars, we also derived [Mg/H] from spectral synthesis xaround the Mg  i triplet at λ 6319 Å. Results. The Fe and Mg metallicity distributions are both asymmetric with median values of +0.16 and +0.21, respectively. They show only a small proportion of stars at low metallicities, extending down to [Fe/H] =-1.1 or [Mg/H] =-0.7. The iron distribution is clearly bimodal, as revealed both by a deconvolution (from observational errors) and a Gaussian decomposition. The decomposition of the observed Fe and Mg metallicity distributions into Gaussian components yields two populations of equal sizes (50% each): a metal-poor component centred on [Fe/H] =-0.30 and [Mg/H] =-0.06 with a large dispersion and a narrow metal-rich component centred on [Fe/H] = +0.32 and [Mg/H] = +0.35. The metal-poor component shows high [Mg/Fe] ratios (around 0.3), while stars in the metal-rich component are found to have nearly solar ratios. Kinematical differences between the two components have also been found: the metal-poor component shows kinematics compatible with an old spheroid, while the metal-rich component is consistent with a population supporting a bar. In view of their chemical and kinematical properties, we suggest different formation scenarii for the two populations: a rapid formation time scale as an old spheroid for the metal-poor component (old bulge) and for the metal-rich component, a formation on a longer time scale driven by the evolution of the bar (pseudo-bulge). The observations are described well by a simple model consisting of two components: a simple closed box model to predict the metal-poor population contribution and a local thin disc metallicity distribution, shifted in metallicity, to represent the metal-rich population. The pseudo-bulge is compatible with its being formed from the inner thin disc, assuming high (but plausible) values of the gradients in the early Galactic disc. © 2011 ESO. Source

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