The pre- versus post-main sequence evolutionary phase of B[e] stars: Constraints from 13CO band emission

Many galactic B[e] stars suffer from improper distance determinations, which make it difficult to distinguish between a pre- and post-main sequence evolutionary phase on the basis of luminosity arguments. In addition, these stars have opaque circumstellar material, obscuring the central star, so that no detailed surface abundance studies can be performed. We propose a different indicator for the supergiant status of a B[e] star, based on the enrichment of its circumstellar matter by 13C, and detectable via its 13CO band emission in the K band spectra. Based on stellar evolution models, we calculate the variation of the 12C/13C isotopic surface abundance ratio during the evolution of non-rotating stars with different initial masses. For different values of the 12C/13C ratio we then compute synthetic first-overtone vibration-rotational band spectra from both the 12CO and 13CO molecule at different spectral resolutions. We further discuss the influence of stellar rotation on the variation of the surface 12C/13C ratio. The surface 12C/13C isotope ratio is found to decrease strongly during the post-main sequence evolution of non-rotating stars, from its interstellar value of about 70 to a value of about 15-20 for stars with initial masses higher than 7 M_sun, and to a value of less than 5 for stars with initial masses higher than 25 M_sun. We find that detectable 13CO band head emission is produced for isotope ratios 12C/13C < 20, and can most easily be detected with a spectral resolution of R ~ 1500...3000. For the rotating stellar models, the drop in 12C/13C already occurs for all stars with M > 9 M_sun during the main-sequence evolution. The detection of 13CO band head emission in such mid-resolution K band spectra of a B[e] star thus favours an evolved rather than a young nature of the object.Comment: 10 pages, 6 figures, accepted for publication in A&

Analysis of physical processes in eruptive YSOs with near-infrared spectra and multiwavelength light curves

The decade-long Vista Variables in the Via Lactea (VVV) survey has detected numerous highly variable young stellar objects (YSOs). We present a study of 61 highly variable VVV YSOs (ΔKs = 1–5 mag), combining near-infrared spectra from Magellan and ESO Very Large Telescope with VVV and NEOWISE light curves to investigate physical mechanisms behind eruptive events. Most sources are spectroscopically confirmed as eruptive variables (typically Class I YSOs) but variable extinction is also seen. Among them, magnetically controlled accretion, identified by H i recombination emission (usually accompanied by CO emission), is observed in 46 YSOs. Boundary layer accretion, associated with FU Ori-like outbursts identified by CO overtone and H2O absorption, is observed only in longer duration events (≥5 yr total duration). However, even in long duration events, the magnetically controlled accretion mode predominates, with amplitudes similar to the boundary layer mode. Shorter (100–700 d) eruptive events usually have lower amplitudes and these events are generally either periodic accretors or multiple time-scale events, wherein large photometric changes occur on time-scales of weeks and years. We find that the ratio of amplitudes in Ks and W2 can distinguish between variable accretion and variable extinction. Several YSOs are periodic or quasi-periodic variables. We identify examples of periodic accretors and extinction-driven periodicity among them (with periods up to 5 yr) though more data are needed to classify some cases. The data suggest that dynamic interactions with a companion may control the accretion rate in a substantial proportion of eruptive systems, although star–disc interactions should also be considered

Ostéonécrose et VIH (étude rétrospective de 13 cas)

LE KREMLIN-B.- PARIS 11-BU Méd (940432101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

RELAXATION COLLISIONNELLE DE L'ETAT B 3 G DE N 2. ETUDE PAR SPECTROSCOPIE DE FOURIER RESOLUE EN TEMPS

ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Étude du spectre à haute résolution de la bande ν

La bande ν1 de CD3CI a été enregistrée dans le domaine spectral de 2100 à 2200 cm-1 sur un spectromètre par Transformée de Fourier dont le pouvoir séparateur est de 0,0055 cm-1. Plus de 1800 raies appartenant aux deux espèces isotopiques du chlore ont été attribuées. Plusieurs perturbations locales ont été clairement mises en évidence. Un calcul global portant sur l'ensemble des niveaux d'énergie a permis de déterminer avec précision les constantes moléculaires du niveau ν1 = 1

SELECTIVE FOURIER TRANSFORM SPECTROSCOPY OF RADICALS

Author Institution: Laboratoire d'Infrarouge, Associ\'{e} au C.N.R.S., B\^{a}t. 350, Universit\'{e} Paris XI; Laboratoire de Physique Moleculaire et Atmospherique, C.N.R.S. et Universite Pierre et Marie CurieTwo types of selective detection of paramagnetic species, based on Zeeman effect, have been examined with both Fourier transform and diode laser spectrometers. A magnetic modulation requires both a constant and a periodic magnetic fields: however a variation of the magnetic field in a plasma induces, in addition to Zeeman modulation, a non selective modulation concentration. This effect is avoided with a polarization modulation which needs a polarizing system and a constant magnetic field only. We present here experimental results obtained using these technics

Lasers moléculaires à excitation haute fréquence; coefficient d’amplification et d’absorption dans les gaz excités vibrationnellement

Cet exposé présente les résultats obtenus en utilisant un laser à CO2 pour étudier, d’une part, l’absorption de CO2 non excité pour la transition 10°0-00°1, d’autre part l’amplification du rayonnement laser dans CO2 (pur ou mélangé à l’azote) excité vibrationnellement par une décharge haute fréquence.Les niveaux d’absorption dans CO2 non excité ont conduit à déterminer le moment de transition de vibration pure : [math] = 3,31.10–2 debye et le facteur d’interaction vibration-rotation : F(m) = 1 — 0,0044 m.Les expériences d’amplification semblent pouvoir permettre une détermination de la température rotationnelle et du taux d’inversion dans le milieu excité

Approche sociologique et psychopathologique du cannibalisme

indispensable à l établissement d un diagnostic anténatal. Une meilleure connaissance des aspects anthropologiques spécifiques à la culture polynésienne concernant la conception, la maladie et la mort, nous permettra de tenter d expliquer les difficultés diagnostiques auxquelles nous avons été confrontés.LIMOGES-BU Médecine pharmacie (870852108) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF