The CHANDRA HETGS X-ray Grating Spectrum of η Carinae

η Carinae may be the most massive and luminous star in the Galaxy and is suspected to be a massive, colliding wind binary system. The CHANDRA X-ray observatory has obtained a calibrated, high-resolution X-ray spectrum of the star uncontaminated by the nearby extended soft X-ray emisssion. Our 89 ksec CHANDRA observation with the High Energy Transmission Grating Spectrometer (HETGS) shows that the hot gas near the star is non-isothermal. The temperature distribution may represent the emission on either side of the colliding wind bow shock, effectively “resolving” the shock. If so, the pre-shock wind velocities are ∼ 700 and ∼ 1800 km s in our analysis, and these velocities may be interpreted as the terminal velocities of the winds from η Carinae and from the hidden companion star. The forbidden-to-intercombination (f/i) line ratios for the He-like ions of S, Si and Fe are large, indicating that the line forming region lies far from the stellar photosphere. The iron fluorescent line at 1.93Å, first detected by ASCA, is clearly resolved from the thermal iron line in the CHANDRA grating spectrum. The Fe fluorescent line is weaker in our CHANDRA observation than in any of the ASCA spectra. The CHANDRA observation also provides an uninterrupted hightime resolution lightcurve of the stellar X-ray emission from η Carinae and suggests that there was no significant, coherent variability during the CHANDRA observation. The η Carinae CHANDRA grating spectrum is unlike recently published X-ray grating spectra Universities Space Research Association, 7501 Forbes Blvd, Ste 206, Seabrook, MD 20706 Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt MD 20771 National Research Council, Laboratory For Astronomy and Space Physics, Goddard Space Flight Center, Greenbelt, MD 20771 Astronomy Department, University of Minnesota, Minneapolis, MN, 55455 Department of Astronomy, Pennsylvania State University, State College, PA Harvard-Smithsonian Center for Astrophysics, Cambridge, MA Department of Astronomy, University of Maryland, College Park, MD, 20742 Istituto di Astrofisica Spaziale, CNR, Area di Ricerca Tor Vergata, 00133 Roma, Italy Instituto Astronômico e Geofisico da USP,Av. Miguel Stefano 4200, 04301-904 São Paulo, Brazil