Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...422..336c&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 422, no. 1, p. 336-350
Astronomy and Astrophysics
Astronomy
19
Eclipsing Binary Stars, Interstellar Extinction, Interstellar Matter, Pulsars, Radiation Absorption, Stellar Winds, X Ray Spectra, X Ray Stars, Ginga Satellite, Monte Carlo Method, Proportional Counters, Pulse Amplitude, X Ray Astronomy
Scientific paper
From measurements of the X-ray eclipse phenomena of the binary X-ray pulsar 4U 1538-52, we derive properties of the stellar wind of its B0 I companion, QV Nor, and a constraint on models of interstellar grains. Estimates of the wind density as a function of the distance from the center of QV Nor are obtained from an analysis of the variation of X-ray attenuation during an eclipse egress. A Monte Carlo computation of the absorption and scattering of X-rays in the X-ray-ionized wind accounts for approximately two-thirds of the spectrum of X-rays with energies above 4.5 keV observed during the eclipse. Our upper limit on RXV is 0.06/mag, which implies that the X-ray scattering efficiency of interstellar dust is less than expected for solid grains with a size distribution of the form ng(a) approximately a-3.5 in the range from 0.005 to 0.25 microns and composed of silicate (RXV = 0.22/mag) or a silicate-graphite mixture (RXV = 0.11/mag) as derived from the calculations of Martin & Rouleau (1991). This lends support to the idea (Mathis & Whiffen 1989) that interstellar grains are 'fluffy' aggregates with an average bulk density less than that of their constitutent particles. Such aggregates would have a smaller ratio of X-ray scattering efficiency to optical extinction efficiency compared with solid grains of the same material.
Clark George W.
Nagase Fumiaki
Woo Jonathan Wonha
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