COOL STARS and ATOMIC PHYSICS

Andrea Dupree

Harvard-Smithsonian CfA 7 Aug. 2006

High Accuracy Atomic PhysicsIn Astronomy

OUTLINEHow does atomic physics influence our understanding of the atmospheres of cool stars ???

Three critical examples:1. Identifications temperatures2. Wavelengths dynamics3. 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

SupergiantsCool , 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 974.86A.Identified in solar flare spectra.

Feldman and Doschek 1991Young et al. 2001Dupree et al. 2003Redfield 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 closeto the stellar surface reminiscentof 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 DraThis stellar system consists of a red giant whose wind and surroundingnebula is photoionized by a hot white dwarf companion. Spectrum is complex with narrow nebular emission, and the surprising presencs of high ionizationforbidden lines. These conditions are quite different from ‘coronal’ plasmas(collisionally-dominated).

HST/STIS spectra revealforbidden lines: Ca VII, Fe VII, Mg V, Mg VI, Si VII, and for the first time,2 transitions of Mg VII between termsof the 2s 2 2p 2 3P-1D configuration(Young, P. et al. 2006).

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 usingMg ion ratios do not give consistent results,although the electron density appears to be high.High ionization appears to require nearby sourceof 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 ionsFe IX-XXIV (not FeXVII)allow both T and Ne tobe 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 densitydiagnostic suggest small emitting volumes (<0.01 R)and continuous heating.

FLUXobs ~ Ne 2 ΔV

Sanz-Forcada et al. 2004

EUV radiance spectrum of the Sun

CHIPS EUV spectrum of the whole Sun revealsdifferences 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 fluorescentlines from low ionization species.

Dupree and Brickhouse 1998Betelgeuse – a supergiantImaged in the ultraviolet by HST

Higher resolution led to confirmation

Fe II can be produced by H-Lyman-α pumping from4s 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 fromH-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 line3P-3P, in luminous cool stars differsubstantially from the solar profile.Check center to limb behavior.

(Dupree et al 2005)