TY  - CHAP
A1  - Romero, G. E.
A1  - Owocki, S. P.
A1  - Araudo, A. T.
A1  - Townsend, R. H. D.
A1  - Benaglia, P.
T1  - Using gamma-rays to probe the clumped structure of stellar winds
N2  - Gamma-rays can be produced by the interaction of a relativistic jet and the matter of the stellar wind in the subclass of massive X-ray binaries known as “microquasars”. The relativistic jet is ejected from the surroundings of the compact object and interacts with cold protons from the stellar wind, producing pions that then quickly decay into gamma-rays. Since the resulting gamma-ray emissivity depends on the target density, the detection of rapid variability in microquasars with GLAST and the new generation of Cherenkov imaging arrays could be used to probe the clumped structure of the stellar wind. In particular, we show here that the relative fluctuation in gamma rays may scale with the square root of the ratio of porosity length to binary separation, $\sqrt{h/a}$, implying for example a ca. 10% variation in gamma ray emission for a quite moderate porosity, h/a ∼ 0.01.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-18210
ER  - 
TY  - CHAP
A1  - Vink, J. S.
A1  - Benaglia, P.
A1  - Davies, B.
A1  - de Koter, A.
A1  - Oudmaijer, R. D.
T1  - Advances in mass-loss predictions
N2  - We present the results of Monte Carlo mass-loss predictions for massive stars covering a wide range of stellar parameters. We critically test our predictions against a range of observed massloss rates – in light of the recent discussions on wind clumping. We also present a model to compute the clumping-induced polarimetric variability of hot stars and we compare this with observations of Luminous Blue Variables, for which polarimetric variability is larger than for O and Wolf-Rayet stars. Luminous Blue Variables comprise an ideal testbed for studies of wind clumping and wind geometry, as well as for wind strength calculations, and we propose they may be direct supernova progenitors.
Y1  - 2007
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-17948
ER  - 
TY  - JOUR
A1  - De Becker, M.
A1  - del Valle, Maria Victoria
A1  - Romero, G. E.
A1  - Peri, C. S.
A1  - Benaglia, P.
T1  - X- ray study of bow shocks in runaway stars
JF  - Monthly notices of the Royal Astronomical Society
N2  - Massive runaway stars produce bow shocks through the interaction of their winds with the interstellar medium, with the prospect for particle acceleration by the shocks. These objects are consequently candidates for non-thermal emission. Our aim is to investigate the X-ray emission from these sources. We observed with XMM-Newton a sample of five bow shock runaways, which constitutes a significant improvement of the sample of bow shock runaways studied in X-rays so far. A careful analysis of the data did not reveal any X-ray emission related to the bow shocks. However, X-ray emission from the stars is detected, in agreement with the expected thermal emission from stellar winds. On the basis of background measurements we derive conservative upper limits between 0.3 and 10 keV on the bow shocks emission. Using a simple radiation model, these limits together with radio upper limits allow us to constrain some of the main physical quantities involved in the non-thermal emission processes, such as the magnetic field strength and the amount of incident infrared photons. The reasons likely responsible for the non-detection of non-thermal radiation are discussed. Finally, using energy budget arguments, we investigate the detectability of inverse Compton X-rays in a more extended sample of catalogued runaway star bow shocks. From our analysis we conclude that a clear identification of non-thermal X-rays from massive runaway bow shocks requires one order of magnitude (or higher) sensitivity improvement with respect to present observatories.
KW  - acceleration of particles
KW  - radiation mechanisms: non-thermal
KW  - stars: earlytype
KW  - X-rays: stars
Y1  - 2017
U6  - https://doi.org/10.1093/mnras/stx1826
SN  - 0035-8711
SN  - 1365-2966
VL  - 471
SP  - 4452
EP  - 4464
PB  - Oxford Univ. Press
CY  - Oxford
ER  -