1. Collisional Ionization and Doppler Lines in the Ultra-compact Binary 4U1626-67 50 years or X-ray Binaries, Chandra Workshop, July 10-12, 2012, Boston MA

2. Collisional Ionization and Doppler Lines in the Ultra-compact Binary 4U1626-67 - Ionization properties in X-ray Binaries: Reflection, ADC Emissions, Jets, Discs, …and - Properties of 4U 1626-67: Torque Reversals, X-rayVariability, Doppler and Fe Lines - Fe Line Fluorescence before and after the 2008 Torque Reversal - Fitting Ionization Models: Photo-ionization vs Collisional Ionization - Possible Interpretations: Fe in the System, Ultracompact CO Disks, Magnetospheres 50 years or X-ray Binaries, Chandra Workshop, July 10-12, 2012, Boston MA

3. Previous HETG Observations of the the Ultra-compact Binary 4U1626-67 Previous HETG GTO observations: - Schulz et al. 2001: Double Peaked X-ray Lines from the O/Ne-rich Accretion Disk in 4U 1626-67: OBSIDs 104, 39 ksec - Krauss et al. 2007: High Resolution X-ray Spectroscopy of the Ultra-compact LMXB Pulsar 4U 1626-67: OBSIDs 104, 39 ksec 3504, 97 ksec

4. X-ray Spectra and Long-term Lightcurve of the Ultra-compact Binary 4U1626-67 New HETG GTO observations: -Chakrabarty & Schulz 2009 Cycle 11 GO time: OBSIDs 11058, 80 ksec, Jan 14. 2010 Camero-Arranz et al. 2012 Schulz et al. 2012

5. Continuum Properties of the Ultra-compact Binary 4U1626-67 before and after Torque Reversal Tbnew (Powerlaw + Bbodyrad): N H = 1.2x10 21 cm -1 A  = 0.0084 ph cm -2 s -1  = 0.80 A bb = 593 (R 2 km / D 2 kpc ) kT bb = 0.20 keV Tbnew (Powerlaw + Bbodyrad): N H = 1.2x10 21 cm -1 (0.2) A  = 0.0384 ph cm -2 s -1  = 1.19 (0.90) A bb = 83 (R 2 km / D 2 kpc ) kT bb = 0.48 keV (0.52) Camero-Arranz et al. 2012 Schulz et al. 2012

6. Fe Fluorescence in the Ultra-compact Binary 4U1626-67 before and after Torqure Reversal Schulz et al. 2012Camero-Arranz et al. 2012

7. Fe Fluorescence in the Ultra-compact Binary 4U1626-67 Schulz et al. 2012

8. Flares and Dips in the New Light Curve of 4U1626-67 Obsid 11058: Obsid 3504: Schulz et al. 2012

9. Doppler Lines in the Ultra-compact Binary 4U1626-67 before and after 2008 Torque Reversal

10. Doppler Lines in the Ultra-compact Binary 4U1626-67 Schulz et al. 2012

11. Ionization Model Fits to the X-ray Spectrum of 4U1626-67 Photo-ionized modeling: Collisional-ionized modeling:

12. Aped_density = 13: Collisional Ionization Model Fits to the X-ray Spectrum of 4U1626-67 Schulz et al. 2012

13. Pure C/O/Ne disk?: 1)Cannot maintain C I/Ne I/O I : log  > 2 @ r~10 9 cm 2)Pure C/O disk model predicts T = 28000 K @ 20000 km (Werner et al. 2006) Model CO Disk Properties in the Ultra-compact Binary 4U1626-67

14. Magnetospheric Accretion Shocks in the Ultra-compact Binary 4U1626-67 Emission Volumes:

15. In conclusion we propose the following: Doppler Lines in the Ultra-compact Binary 4U1626-67 Magnetospheric Accretion Shocks R co = 8.5x10 8 cm R co = R mag V shift ~ 2000 km/s ~ V co V co ~ V shock T jump < 60 MK CO plasma < 20 deg impact V shift = V ion T shock < 10 K

16. In conclusion we propose the following: Doppler Lines in the Ultra-compact Binary 4U1626-67 The light curve before torque reversal is featureless. The light curve after torque reversal shows enhance variability which includes type II flaring, intensity dips, and periods of quiescence. The X-ray flux at the time of the observation in 2009 is at about the same level as it was in 1994. The X-ray continuum after torque reversal is fit by the same spectrum as before, however with a higher blackbody temperature and a smaller emission radius. The spectrum shows a narrow Fe K fluorescence line, which was not observed before torque reversal. A photo-ionized plasma cannot fit the Ne and O Doppler line emissions. The large ratio between the Ne X Lα line and the upper limit to the Ne X Lβ line rules out significant contributions due to resonance scattering. A collisions ionized plasma fits both Ne and O line ratios very well with enhanced plasma densities and plasma temperature between 1 MK and 10 MK. Magnetospheric Accretion Shocks