Hubble Space Telescope imaging of the WR 38/WR 38a cluster

We are conducting a high angular resolution imaging survey of Galactic Wolf-Rayet stars using the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope (HST). We have found a small stellar cluster associated with the faint, close pair WR 38 and WR 38a. We present astrometric measurements and photometry in the wideband F336W (U), F439W (5), and F555W (V) filter system for the cluster and nearby stars. We combine our photometry with Johnson and IR magnitudes and compare the observations with calibrated model results for reddened stars to adjust the HST zero points and to identify five probable main-sequence members of the cluster. A least-squares fit of the colors and magnitudes of this set yields a cluster reddening of E(B - V) = 1.63 ±0.05 mag and a distance of 10 -4 +12 kpc for an assumed ratio of total to selective extinction of R = 3.1. We discuss the relationship of this cluster to other objects along the line of sight. If situated at a distance of ≈8 kpc, then the cluster would reside in a dense region of the Carina spiral arm, close to a giant molecular cloud and the starburst cluster NGC 3603.Facultad de Ciencias Astronómicas y Geofísica

The puzzle of HD 104994 (WR 46)

Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica

The puzzle of HD 104994 (WR 46)

Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica

Hubble Space Telescope imaging of the WR 38/WR 38a cluster

We are conducting a high angular resolution imaging survey of Galactic Wolf-Rayet stars using the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope (HST). We have found a small stellar cluster associated with the faint, close pair WR 38 and WR 38a. We present astrometric measurements and photometry in the wideband F336W (U), F439W (5), and F555W (V) filter system for the cluster and nearby stars. We combine our photometry with Johnson and IR magnitudes and compare the observations with calibrated model results for reddened stars to adjust the HST zero points and to identify five probable main-sequence members of the cluster. A least-squares fit of the colors and magnitudes of this set yields a cluster reddening of E(B - V) = 1.63 ±0.05 mag and a distance of 10 -4 +12 kpc for an assumed ratio of total to selective extinction of R = 3.1. We discuss the relationship of this cluster to other objects along the line of sight. If situated at a distance of ≈8 kpc, then the cluster would reside in a dense region of the Carina spiral arm, close to a giant molecular cloud and the starburst cluster NGC 3603.Facultad de Ciencias Astronómicas y Geofísica

The puzzle of HD 104994 (WR 46)

Intense coordinated spectroscopic and photometric monitoring of the suspected Wolf-Rayet binary WR 46 in 1999 reveals clear periodic variations, P = 0.329 ± 0.013 days, in the radial velocities of the emission lines of highest ionization potential, O VI and N V, found deepest in the Wolf-Rayet wind and thus least likely to be perturbed by a companion. These are accompanied by coherent variability in the profiles of lines with lower ionization/excitation potential and in the continuum flux. Most probably originating from orbital motion of the Wolf-Rayet component of the binary, this periodic radial velocity signal disappears from time to time, thus creating a puzzle yet to be solved. We show that the entangled patterns of the line profile variability are mainly governed by transitions between high and low states of the system's continuum flux.Facultad de Ciencias Astronómicas y Geofísica

Etude de la variabilité des étoiles massives à l'aide de la photométrie et de la spectroscopie

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

BRITE-Constellation High-Precision Time-Dependent Photometry of the Early O-Type Supergiant ζ Puppis Unveils the Photospheric Drivers of Its Small- and Large-Scale Wind Structures

From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He IIλ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He II λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability

Advanced binary evolution

We discuss recent progress in the modeling and understanding of the mass-transfer process in massive close binary systems and its consequences for their advanced evolution. We then highlight the spin evolution of both binary components and its dependence on accretion, mass loss and internal angular-momentum transport processes. In particular, we consider the influence of an internal magnetic field, which appears to be required on observational and theoretical grounds. We find that while magnetic fields lead to an agreement of predicted with observed rotation frequencies of white dwarfs and neutron stars, accretion does not always lead to rapidly spinning cores - as they are required within the collapsar model for gamma-ray bursts

The Chandra survey of Carina OB stars

audience: researcher, professionalWe have combined 22 deep Chandra ACIS-I pointings to map over one square degree of the Carina complex. Our x-ray survey detects 69 of 70 known O-type stars and 61 of 130 known early B stars. The majority of single O stars display soft X-ray spectra and have a mean log L[SUB]X[/SUB]/L[SUB]bol[/SUB] ~ -7.5 suggesting shocks embedded in the O-star winds. Over OB stars show unusually high X-ray luminosities, high shock temperatures or time variability, not predicted for embedded wind shocks