The X-Ray Light Curve of η Carinae: Refinement of the Orbit and Evidence for Phase-dependent Mass Loss

Details The X-Ray Light Curve of η Carinae: Refinement of the Orbit and Evidence for Phase-dependent Mass Loss The X-Ray Light Curve of η Carinae: Refinement of the Orbit and Evidence for Phase-dependent Mass Loss

Feb 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001apj...547.1034c&link_type=abstract

The Astrophysical Journal, Volume 547, Issue 2, pp. 1034-1039.

Other

107

Stars: Binaries: General, Stars: Individual: Constellation Name: Η Carinae, Stars: Variables: Other, X-Rays: Stars

Scientific paper

We solve the Rossi X-Ray Timing Explorer X-ray light curve of the extremely luminous and massive star η Carinae with a colliding-wind emission model to refine the ground-based orbital elements. The sharp decline to X-ray minimum at the end of 1997 fixes the date of the last periastron passage at 1997.95+/-0.05, not 1998.13 as derived from ground-based radial velocities. This helps resolve a discrepancy between the ground-based radial velocities and spatially resolved velocity measures obtained by Space Telescope Imaging Spectograph (STIS). The X-ray data are consistent with a mass function f(M)~1.5, lower than the value f(M)~7.5 previously reported, so that the masses of η Carinae and the companion are Mη>=80 Msolar and Mc~30 Msolar, respectively. In addition, the X-ray data suggest that the mass-loss rate from η Carinae is generally less than 3×10-4 Msolar yr-1, about a factor of 5 lower than that derived from some observations in other wave bands. We could not match the duration of the X-ray minimum with any standard colliding-wind model in which the wind is spherically symmetric and the mass-loss rate is constant. However, we show that we can match the variations around X-ray minimum if we include an increase of a factor of ~20 in the mass-loss rate from η Carinae for approximately 80 days following periastron. If real, this excess in M would be the first evidence of enhanced mass flow off the primary when the two stars are close (presumably driven by tidal interactions). Our interpretation of the X-ray data suggests that the ASCA and RXTE X-ray spectra near the X-ray minimum are significantly contaminated by unresolved hard emission (E>=2 keV) from some other nearby source, probably associated with scattering of the colliding-wind emission by circumstellar dust. Based on the X-ray fluxes, the distance to η Carinae is 2300 pc with formal uncertainties of only ~10%.

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