COOL STARS

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 atoms observed in cool star spectra.
3
Supergiants Cool , extended
Giant stars
Solar type
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 (lt0.01 R?) and
continuous heating. FLUXobs Ne 2
?V 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 1140?. Possibly fluorescent lines from low
ionization species.
14
Higher resolution led to confirmation
Fe II can be produced by H-Lyman-a pumping
from 4s a4D and cascade to 4s a6D and 3d7
a4F. May provide an indirect diagnostic of
stellar Lyman-a profile . Harper et al (2004)
hypothesized that Fe II lines away from H-Ly a
(?? gt 1.8?) 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 1176? line 3P-3P, in
luminous cool stars differ substantially from the
solar profile. Check center to limb
behavior. (Dupree et al 2005)