COOL STARS and ATOMIC PHYSICS

1. High Accuracy Atomic Physics In Astronomy COOL STARS and ATOMIC PHYSICS Andrea Dupree Harvard-Smithsonian CfA 7 Aug. 2006

2. OUTLINE How does atomic physics influence our understanding of the atmospheres of cool stars ??? Three critical examples: 1. Identifications temperatures 2. Wavelengths dynamics 3. Coll. X-sections densities Will draw from highly ionized species characteristic of 10MK, to singly ionized atomsobserved in cool star spectra….

3. Supergiants Cool , extended Giant stars Solartype S

4. Identification of Ions allows EMD Emission Measure distributions quite different from the well-known solar case (Sanz-Forcada et al. 2004)

5. Highly Ionized Species FUSE spectra of cool stars show Fe XVIII at 974.86A. Identified in solar flare spectra. Feldman and Doschek 1991 Young et al. 2001 Dupree et al. 2003 Redfield et al, 2003.

6. Radial Velocity of Fe XVIII emission lines … Reveals coincidence of Fe XVIII with the stellar photospheric velocities , Suggests that high T plasma, 6.8 K (dex) is anchored close to the stellar surface reminiscent of low-lying coronal loops…

7. High Temperature Species Anchored in Warm Wind Fe XIX Fe XVIII FUSE Cool Star Team; Redfield et al. 2003

8. Symbiotic Star: AG Dra This stellar system consists of a red giant whose wind and surrounding nebula is photoionized by a hot white dwarf companion. Spectrum is complex with narrow nebular emission, and the surprising presencs of high ionization forbidden lines. These conditions are quite different from ‘coronal’ plasmas (collisionally-dominated). HST/STIS spectra reveal forbidden lines: Ca VII, Fe VII, Mg V, Mg VI, Si VII, and for the first time, 2 transitions of Mg VII between terms of the 2s 2 2p 2 3P-1D configuration (Young, P. et al. 2006).

9. Energy levels and density diagnostics Separation of ground 3P levels (from IR astronomical spectra) plus UV wavelengths define 1D energy levels in Mg VII Four density diagnostics using Mg ion ratios do not give consistent results, although the electron density appears to be high. High ionization appears to require nearby source of photoionization. Other problems remain that might be resolved by detailed modeling. (Young et al. 2006)

10. EUV spectra offer many coronal diagnostics Spectra from the EUVE satellite contain ions Fe IX-XXIV (not FeXVII) allow both T and Ne to be defined in cool star coronas. (Sanz-Forcada et al. 2003)

11. Density diagnostics suggest small coronal structures Electron densities are high. The observed line flux in combination with the density diagnostic suggest small emitting volumes (<0.01 R) and continuous heating. FLUXobs ~ Ne 2 ΔV Sanz-Forcada et al. 2004

12. EUV radiance spectrum of the Sun CHIPS EUV spectrum of the whole Sun reveals differences from the standard solar irradiance models (red line). Courtesy of M. Hurwitz (2006)

13. Fluorescent processes in extended atmospheres Betelgeuse – a supergiant Imaged in the ultraviolet by HST Dupree and Brickhouse 1998 Narrow lines appeared in emission in far UV (ORPHEUS) spectra of cool giants and supergiants near 1140Ǻ. Possibly fluorescent lines from low ionization species.

14. Higher resolution led to confirmation Fe II can be produced by H-Lyman-α pumping from 4s a4D and cascade to 4s a6D and 3d7 a4F. May provide an indirect diagnostic of stellar Lyman-α profile . Harper et al (2004) hypothesized that Fe II lines away from H-Ly α (Δλ > 1.8Ǻ) should be weak (marked by *).

15. FUSE Spectra show puzzling differences FUSE spectra of luminous stars do not show consistent patterns. (Dupree et al. 2005)

16. Unresolved Problem: C III profiles Profiles of the C III 1176Ǻ line 3P-3P, in luminous cool stars differ substantially from the solar profile. Check center to limb behavior. (Dupree et al 2005)