Eric Josselin | Université Montpellier 2 - Sciences et Techniques du Languedoc (original) (raw)

Papers by Eric Josselin

ESA's Gaia mission will collect low resolution spectroscopy in the optical range for ∼10 9 object... more ESA's Gaia mission will collect low resolution spectroscopy in the optical range for ∼10 9 objects. Complete and up-to-date libraries of synthetic stellar spectra are needed to built algorithms aimed to automatically derive the classification and the parametrization of this huge amount of data. In addition, libraries of stellar spectra are one of the main ingredients of stellar population synthesis models, aiming to derive the properties of unresolved stellar populations from their integrated light. We present (a) the newly computed libraries of synthetic spectra built by the Gaia community, covering the whole optical range (300-1100 nm) at medium-high resolution of (0.3 nm) for stars spanning the most different types, from M to O, from Apeculiar to Emission lines to White Dwarfs, and (b) the implementation of those libraries in our SSP code (Tantalo in The Initial Mass Function 50 Years Later, 327:235 2005), exploring different stellar evolution models.

We use moderate-resolution optical spectrophometry and the new MARCS stellar atmosphere models to... more We use moderate-resolution optical spectrophometry and the new MARCS stellar atmosphere models to determine the effective temperatures of 74 Galactic 1

ESO Astrophysics Symposia

Astronomy and Astrophysics, 2000

Abstract. We present the analysis of infrared photometry andmillimeterspectroscopyofasampleof74la... more Abstract. We present the analysis of infrared photometry andmillimeterspectroscopyofasampleof74late-typesupergiants.These observations are particularly suitable to study the massloss and the circumstellar envelopes of evolved massive stars.In particular, we quantify the circumstellar infrared excess, therelation of mass loss with stellar properties, using the K-[12]colour index as mass-loss indicator. We do not ﬁnd any clearcorrelationbetweenmasslossrateandluminosity.Wealsoshowthat the K-band magnitude is a simple luminosity indicator, be-cause of the relative constancy of the K-band bolometric cor-rection.Keywords:stars:circumstellarmatter–stars:mass-loss–stars:supergiants – infrared: stars1. IntroductionRed supergiants represent a key-phase in the evolution of mas-sive (10 . M init . 40 M ) stars, preceding Wolf-Rayet starsand/or supernovae. A good knowledge of their properties isnecessary to compute reliable stellar evolutionary tracks andpopulation synthesis models. For example,...

ABSTRACT During the AGB phase, stars lose mass at high rates. The effect of metallicity on this m... more ABSTRACT During the AGB phase, stars lose mass at high rates. The effect of metallicity on this mass-loss is poorly known. We expect mass-loss rates and expansion velocities of AGB stars to be lower at low metallicty as the mass-loss is due to radiation pressure on dust grains and less grains are expected. Just one low metallicity carbon AGB star has a known expansion velocity and mass-loss rate, measured through CO. We propose to enlarge this sample by observing 6 to 10 newly discovered Halo carbon stars. These observations are key observations to understand the mass-loss from AGB stars.

In the solar limb, linear polarisation is due to anisotropy of the radiation field induced by lim... more In the solar limb, linear polarisation is due to anisotropy of the radiation field induced by limb darkening. It is maximal when it is seen parallel to the limb and it vanishes when it is integrated over the spherically-symmetric solar disk. Therefore for distant stars, that present spherical symmetry, linear polarisation signatures are very difficult to observe. However strong linear polarisation features have been reported in the prototypical red supergiant star alpha Ori (Betelgeuse). With an analytical model we propose to explain them.

Astronomische Nachrichten

Astronomy & Astrophysics, 2017

Context. Red supergiant (RSG) stars are very massive cool evolved stars. Recently, a weak magneti... more Context. Red supergiant (RSG) stars are very massive cool evolved stars. Recently, a weak magnetic field was measured at the surface of α Ori and this is so far the only M-type supergiant for which a direct detection of a surface magnetic field has been reported. Aims. By extending the search for surface magnetic field in a sample of late-type supergiants, we want to determine whether the surface magnetic field detected on α Ori is a common feature among the M-type supergiants. Methods. With the spectropolarimeter Narval at Télescope Bernard-Lyot we undertook a search for surface magnetic fields in a sample of cool supergiant stars, and we analysed circular polarisation spectra using the least-squares deconvolution technique. Results. We detect weak Zeeman signatures of stellar origin in the targets CE Tau, α1 Her and μ Cep. For the latter star, we also show that cross-talk from the strong linear polarisation signals detected on this star must be taken into account. For CE Tau and μ...

Sf2a 2003 Semaine De L Astrophysique Francaise, 2003

Red supergiants (RSG) constitute a key-phase in the evolution of massive stars (10 ˜< initial ... more Red supergiants (RSG) constitute a key-phase in the evolution of massive stars (10 ˜< initial mass ˜<40 solar masses), characterized by strong mass-loss, and rich nucleosynthetic processes. They play a decisive role in the chemical evolution of the Galaxy. Our knowledge of these objects is however still limited, in particular because of the complexity of their atmospheres. We present an analysis of high-resolution spectra of a sample of 20 RSG, probing the velocity structure of their atmosphere. We interpret lineshifts as due to motions of probable convective origin and we show that convection must play an essential role in the mass-loss process. We also discuss indications of chromospheric activity and we present preliminary results from multi-epoch spectroscopy of some representative objects.

Http Www Theses Fr, 1997

La connaissance des populations stellaires est fondamentale pour l'etude de l'evolution s... more La connaissance des populations stellaires est fondamentale pour l'etude de l'evolution stellaire et des galaxies. Les etoiles evoluees, etoiles agb et supergeantes infrarouges, sont caracterisees par une forte perte de masse (m 10#-#7 10#-#4 m#$$/an), phenomene-cle pour l'evolution stellaire et l'evolution chimique des galaxies. Il est cependant encore mal compris. Les travaux exposes dans cette these se divisent en trois parties. Tout d'abord, nous avons recherche des criteres de distinction entre les etoiles agb et les supergeantes infrarouges, a partir des observations des deux composantes de leurs enveloppes circumstellaires, le gaz, trace par la molecule co, et la poussiere, emettant dans l'infrarouge. Nous avons pu etablir un critere de reconnaissance des etoiles agb : un objet avec un rapport r = s#6#0/t#m#b (co(1 0)) inferieur a 100 jy/k a un progeniteur de faible masse. Par contre, si les plus grandes valeurs de ce rapport sont observees pour des supergeantes, on trouve egalement des etoiles agb avec des valeurs anormalement elevees, ce qui souleve des questions sur les proprietes de l'etoile et le processus de perte de masse. La deuxieme partie presente une etude de supergeantes froides, basee sur des donnees photometriques infrarouges et spectroscopiques radio. Nous avons en particulier constate que le taux de perte de masse est apparemment independant de la masse de l'etoile. Par ailleurs, nous avons pu identifier une nouvelle supergeante a enveloppe optiquement epaisse. Ces objets sont tres rares, puisque seulement trois etaient connus jusqu'alors. Enfin, nous presentons l'analyse preliminaire d'observations infrarouges terrestres (denis) et spatiales (iso) d'un champ situe dans la barre du grand nuage de magellan. Ces donnees couvrent le domaine spectral dans lequel les etoiles evoluees emettent l'essentiel de leur rayonnement. On peut ainsi calculer leur flux bolometrique. Par ailleurs, la sensibilite des programmes denis et iso permet de detecter les etoiles agb avec des taux de perte de masse tres differents et d'etudier l'histoire de ce processus.

The post-main sequence evolution of stars of intermediate or large masses is notoriously complex.... more The post-main sequence evolution of stars of intermediate or large masses is notoriously complex. In the recent past, a number of workshops and meetings have focused on either the Asymptotic Giant Branch of intermediate mass stars, or the evolution of massive stars. But how well defined is the boundary between these categories of objects defined? How would an observer proceed to classify stars into one or the other category? How do objects near the boundary evolve, die, and contribute to the chemical evolution of their environment? During this 3-day international workshop 1 , 26 high quality presentations were given by specialists in the relevant fields of astrophysics, and stimulating discussions followed. It is technically impossible to provide an exhaustive census of the results and ideas that emerged. In this brief article, we choose to point to key elements of the workshop, some of which are now the topic of new collaborations and will lead to publications elsewhere. For the sake of brevity, we deliberately cite only the contributors to the workshop and no external references. Many bibliographic references can be found in the original presentations, which can be retrieved through:

Astron Astrophys, 2000

We report high-sensitivity millimeter-wave CO observations of recently discovered bipolar planeta... more We report high-sensitivity millimeter-wave CO observations of recently discovered bipolar planetary nebulae (PNe). Three objects (BV 5-1, K 3-94 and K 3-24) have been detected, and one of them (BV 5-1) is resolved by the ∼10 telescope beam. The envelopes of the three newly detected objects display values of the molecular to ionized mass ratio of ∼ 0.2, and sizes of ∼ 0.1 pc. This indicates that these PNe are rather evolved, with K 3-24 being the youngest of the three (∼ 10 3 years) according to its CO line profile and kinematic ages. In BV 5-1, the molecular gas appears to be distributed in an irregular disk or ring surrounding the central star and perpendicular to the bipolar nebula. This is similar to the situation found in other better studied bipolar PNe (e.g. NGC 2346, M 2-9, KjPn8), and thus seems to be the rule in this class of objects. This suggests a common mechanism for the rings and the bipolar flows that shape the optical nebula.

Proceedings of the International Astronomical Union, 2003

Our understanding of red supergiants is still limited due to the complexity of their atmospheres,... more Our understanding of red supergiants is still limited due to the complexity of their atmospheres, their circumstellar envelopes and the connexion between them, e.g. dynamics of the atmosphere, chromospheric activity, mass loss. We present an analysis of high-resolution (R ∼ 40000) echelle spectra of a sample of 20 galactic M supergiants. From correlation of the observed spectra with numerical masks (following Alvarez et al. 2001), we probe the velocity structure of their atmosphere. We find atmospheric motions, probably of convective origin, with a velocity correlated with the massloss rate. This suggests that convection plays a key-role in the mass-loss process of red supergiants. We also present a preliminary analysis of the H α line profiles in terms of chromospheric activity.

Proceedings of the International Astronomical Union, 2009

The french committee linking astronomers and teachers (CLEA, http://clea-astro.eu) has been activ... more The french committee linking astronomers and teachers (CLEA, http://clea-astro.eu) has been active for more than 30 years in the formation of teachers (from primary to high school) in the field of astronomy.

13Th Cambridge Workshop on Cool Stars Stellar Systems and the Sun, Feb 27, 2005

Red supergiant stars (RSG) constitute a key-phase in the evolution of massive stars, characterize... more Red supergiant stars (RSG) constitute a key-phase in the evolution of massive stars, characterized by strong mass loss of unknown origin. Ongoing radiative hydrodynamics (RHD) simulations of these stars with CO 5 BOLD show a peculiar convection pattern, with giant cells. We present high-resolution, multi-epoch spectroscopy of a sample of RSG, which provides a diagnostic of their atmospheric dynamics. We show synthetic spectra based on 3D RHD models. We suggest that convective motions are important in the generation of the observed mass-loss rates.

ABSTRACT *Downward* pure rotational and ro-vibrational rates are provided for the 5 lowest vibrat... more ABSTRACT *Downward* pure rotational and ro-vibrational rates are provided for the 5 lowest vibrational levels of H2O and 11 temperatures (from 200 to 5000K). This corresponds to all possible transitions among the lowest 824th levels of H2O below 5000cm-1. Upward rates can be computed using the detailed balance relation (see article). Rate files are denoted as p-h2o-h2-vi-vf.dat and o-h2o-h2-vi-vf.dat for para-H20 and ortho-H20 colliding with H2, respectively, and p-h2o-e-vi-vf.dat or o-h2o-e-vi-vf.dat for para-H20 and ortho-H20 colliding with electrons, respectively. The notation 'vi-vf' corresponds to transitions from an initial vibrational state vi to a final vibrational state vf. The standard notation v1v2v3, e.g vi=010 and vf=000, is employed. It represents vibrational quanta in normal modes v1 (symmetric stretch), v2 (bending) and v3 (antisymmetric stretch), respectively. The labelling of para- and ortho-H2O levels in rate files correspond to the labelling in files p-h2o.xxx.levels and o-h2o.xxx.levels where 'xxx' is a vibrational level, e.g. 010. (3 data files).

European Journal of Physics, 2015

This article presents an on-line tool and its accompanying software resources for the numerical s... more This article presents an on-line tool and its accompanying software resources for the numerical solution of basic radiation transfer out of local thermodynamic equilibrium (LTE). State-of-the-art stationary iterative methods such as Accelerated Λ-Iteration and Gauss-Seidel schemes, using a short characteristics-based formal solver are used. We also comment on typical numerical experiments associated to the basic non-LTE radiation problem. These resources are intended for the largest use and benefit, in support to more classical radiation transfer lectures usually given at the Master level.