1. X-ray Diagnostics and Their Relationship to Magnetic Fields David Cohen Swarthmore College

2. X-rays in massive stars are associated with their radiation-driven winds

3. Power in these winds: erg s -1 while the x-ray luminosity To account for the x-rays, only one part in 10 -4 of the wind’s mechanical power is needed to heat the wind

4. Three models for massive star x-ray emission 1. Instability driven shocks 2. Magnetically channeled wind shocks 3. Wind-wind interaction in close binaries

5. M 17: The Omega Nebula

6. CEN1AB - Kleinmann’s Anonymous Star – is an O4+O4 binary system – with 1.8” separation

7. simulated Chandra grating spectrum 1.Line ratios for location of the X-ray emitting plasma 2.Line widths for the plasma kinematics

8. The Chandra X-ray Observatory started taken the data yesterday

13. The X-ray spectrum will tell us: 1.Line ratios for location of the X-ray emitting plasma 2.Line widths for the plasma kinematics

14.  Pup  1 Ori C Si XIII Si XIV Mg XI Mg XII H-like/He-like ratio is temperature sensitive

15.  Pup  1 Ori C Si XIII Si XIV Mg XI Mg XII  1 Ori C – is hotter H/He > 1 in  1 Ori C

16. Differential Emission Measure (temperature distribution) Wojdowski & Schulz (2005)  1 Ori C is much hotter

17. 1000 km s -1 Emission lines are significantly narrower, too  1 Ori C (O7 V)  Pup (O4 If)

18. Mg XII Ly-  in  1 Ori C compared to instrumental profile

19. Ne X Ly-  in  1 Ori C : cooler plasma, broader – some contribution from “standard” instability wind shocks

20. The X-ray properties of  1 Ori C can be understood in the context of its magnetic field and the magnetically channeled wind shock (MCWS) mechanism

21. Wade et al. 2008 Dipole magnetic field

22. Shore & Brown, 1990

23. MCWS: Babel & Montmerle 1997

24. Dynamical models (ud-Doula; Townsend): color scale shows emission measure in different temperature regimes astro.swarthmore.edu/~cohen/presentations/MiMeS2/zeus-movie.avi

25. Looking at individual physical variables: Note that the hot, post-shock plasma: has relatively low density,has relatively low density, is concentrated near the tops of the largest closed-loop regions (~2R star ),is concentrated near the tops of the largest closed-loop regions (~2R star ), and is very slow moving (due to confinement)and is very slow moving (due to confinement)

26. temperature emission measure MHD simulation summary Channeled collision is close to head-on:  v > 1000 km s -1 : T > 10 7 K Gagné et al. (2005)

27. Differential emission measure (temperature distribution) MHD simulation of  1 Ori C reproduces the observed differential emission measure Wojdowski & Schulz (2005)

28. There are Chandra observations at many different phases

29. 0.0 0.5 1.0 1.5 Simulation EM (10 56 cm -3 ) 0.0 0.1 0.2 0.3 0.4 θ 1 Ori C ACIS-I count rate (s -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 Rotational phase (P=15.422 days) Chandra broadband count rate vs. rotational phase Model from MHD simulation

30. 0.0 0.5 1.0 1.5 Simulation EM (10 56 cm -3 ) 0.0 0.1 0.2 0.3 0.4 θ 1 Ori C ACIS-I count rate (s -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 Rotational phase (P=15.422 days) The star itself occults the hot plasma in the magnetosphere The closer the hot plasma is to the star, the deeper the dip in the x-ray light curve

31. 0.0 0.5 1.0 1.5 Simulation EM (10 56 cm -3 ) 0.0 0.1 0.2 0.3 0.4 θ 1 Ori C ACIS-I count rate (s -1 ) 0.0 0.2 0.4 0.6 0.8 1.0 Rotational phase (P=15.422 days) The star itself occults the hot plasma in the magnetosphere hot plasma is too far from the star in the simulation – the dip is not deep enough

32.  1 Ori C column density (from x-ray absorption) vs. phase equator-onpole-on

33. Emission measure contour encloses T > 10 6 K

34. Helium-like species’ forbidden-to-intercombination line ratios – f/i or z/(x+y) – provide information about the location of the hot plasma

35. g.s. 1s 2 1 S 1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) 10-20 eV 1-2 keV Helium-like ions (e.g. O +6, Ne +8, Mg +10, Si +12, S +14 ) – schematic energy level diagram

36. 1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S Ultraviolet light from the star’s photosphere drives photoexcitation out of the 3 S level UV

37. 1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S Weakening the forbidden line and strengthening the intercombination line UV

38. 1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S The f/i ratio is thus a diagnostic of the local UV mean intensity… UV

39. 1s2s 3 S 1s2p 3 P 1s2p 1 P resonance (w) intercombination (x+y) forbidden (z) g.s. 1s 2 1 S …and thus the distance of the x-ray emitting plasma from the photosphere UV

40.  1 Ori C Mg XI

41. R fir =1.2 R * R fir =4.0 R * R fir =2.1 R *

42. He-like f/i ratios and the x-ray light curve both indicate that the hot plasma is somewhat closer to the photosphere of  1 Ori C than the MHD models predict.

43. So, in  1 Ori C, the X-rays tell us about the magnetospheric conditions in several ways: High X-ray luminosityHigh X-ray luminosity X-ray hardness (high plasma temperatures)X-ray hardness (high plasma temperatures) Periodic variability (rotation and occultation)Periodic variability (rotation and occultation) Narrow emission lines (confinement)Narrow emission lines (confinement) f/i ratios quantify locationf/i ratios quantify location

44. What about other magnetic massive stars?

45. What about confinement? Recall:  1 Ori C:  * ~ 20 : decent confinement

46. What about confinement? Recall:  1 Ori C:  * ~ 20 : decent confinement  Ori:  * ~ 0.1 : poor confinement  Ori E:  * ~ 10 7 : excellent confinement

47.  1 Ori C has a hard X-ray spectrum with narrow lines …HD191612 and  Ori have soft X-ray spectra with broad lines Fe XVII in  Ori -v inf +v inf o

48.  1 Ori C  Ori

49.  Sco does have a hard spectrum and narrow lines Ne Ly  compared to instrumental response: narrow

50.  Sco: closed loop region is near the star…

51. …f/i ratios tell us X-rays are far from the star (~3R star ) f i

52. Do He-like f/i ratios provide evidence of hot plasma near the photospheres of O stars?

53. No, I’m afraid they do not.

54.  Pup S XV Chandra MEG Features are very blended in most O stars: here, the three models are statistically indistinguishable locations span 1.1 R star to infinity

55.  Ori E (  * ~ 10 7 : RRM+RFHD)

56. Chandra ACIS (low-resolution, CCD) spectrum

57. DEM derived from Chandra ACIS spectrum

58. DEM from RFHD modeling

59. Observed & theoretical DEMs agree well

60. RFHD (Townsend, Owocki, & ud-Doula 2007, MNRAS, 382, 139 ) astro.swarthmore.edu/~cohen/presentations/MiMeS2/hav-rfhd-4p.avi

61. Conclusions MCWS dynamical scenario explains  1 Ori C well…but, in detail, MHD models do not reproduce all the observational properties Most other magnetic massive stars have X-ray emission that is different from  1 Ori C Some have soft X-ray spectra with broad lines Closed field regions may not always be associated with the X-rays (  Sco) f/i ratios, hard X-rays, variability in massive stars…not unique to magnetic field wind interaction