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

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 atoms observed in cool star spectra….

S Giant stars Supergiants Cool, extended Solar type

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

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

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…

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

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 3 P- 1 D configuration (Young, P. et al. 2006).

Energy levels and density diagnostics Separation of ground 3 P levels (from IR astronomical spectra) plus UV wavelengths define 1 D 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)

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)

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. FLUX obs ~ N e 2 ΔV Sanz-Forcada et al. 2004

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)

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

Higher resolution led to confirmation Fe II can be produced by H-Lyman-α pumping from 4s a 4 D and cascade to 4s a 6 D and 3d 7 a 4 F. 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 *).

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

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