1. Trends in the Chandra X-Ray Spectra of O and Early B Stars June 24, 2008

2. Spectra of Stars We know that spectra result from physical processes within stars. They often reflect physical properties of the stars that created them. ex. Optical Spectra

3. X-Ray Spectra of O and Early B Stars The spectra on the left are a representative sampling of O and early B star spectra, with earlier spectral types at top. The spectra were taken on the Chandra X- Ray telescope using the high energy transmission grating (HETG) on the advanced camera for imaging spectroscopy (ACIS). Nolan Walborn suggested in a 2006 paper that these spectra may reveal a temperature trend similar to that observed for optical spectra. I will be looking for evidence that tends to confirm or disprove this hypothesis.

4. X-Ray Production in Hot Stars X-Ray emission arises in the stellar winds of these stars. The stellar winds are radiatively driven. The line-driven stellar winds are inherently unstable. Shocks in the wind arise from the instability and produce x-rays.

5. X-Ray Spectra and Temperature Line strength ratios Differential Emission Measure dEM= n e n H dV In a plasma with a single well-defined temperature, or D(T)= n e (T)n H (T)(dV/d logT) in a plasma with a temperature distribution.

6. Stars and Parameters HD93129AB O2 If* + (2x) O3.5 V((f + )) T eff = 50000 K R= 20 R sun M=120 M sun v inf = 3200 km/s dM/dt = 1.8 * 10 -5 M sun /yr Xi Persei O7.5 III(n)((f)) T eff = 36000 K R= 12 R sun M=34 M sun v inf = 2450 km/s dM/dt = 2.0 * 10 -6 M sun /yr Delta Orionis O9.5 II + B0.5 III T eff = 33000 K R= 17 R sun M=23 M sun v inf = 2000 km/s dM/dt = 1.07 * 10 -6 M sun /yr

7. Silicon XIV/Silicon XIII Ratios HD93129AB 0.05 ± 0.02 Xi Persei 0.05 ± 0.02 Delta Orionis 0.21 ± 0.06

8. Magnesium XIV/Magnesium XIII Ratios Xi Persei 0.12 ± 0.02 HD93129AB 0.27 ± 0.04 Delta Orionis 0.24 ± 0.03

9. Conclusions (for now) Line ratios of stars in our sample seem to have little to do with effective temperature. This tends to disprove Walborn’s suggestion that the trend in the spectrum is temperature- related. However, there does appear to be some slight tendency for individual lines to become broader and more blueshifted in the hotter stars.

10. Some Directions for Research Continue to measure line ratios in more stars. Possibly explore measuring line ratios for other elements. Look into measuring emission measures for our sample stars as another probe of temperature.