Wavelength shifts in solar-type spectra
Dainis Dravins (Lund Observatory, Sweden)
Lennart Lindegren, Hans-Günter Ludwig, Søren Madsen (Lund Observatory, Sweden)
Spectral-line displacements away from the wavelengths naively expected from the
Doppler shift caused by stellar radial motion may originate as convective shifts
(correlated velocity and brightness patterns in the photosphere), or as
gravitational redshifts. Absolute lineshifts, in the past studied only for the
Sun, are now accessible for other stars thanks to astrometric determination of
stellar radial motion, and spectrometers with accurate wavelength calibration.
Comparisons between spectroscopic apparent radial velocities and astrometrically
determined radial motions reveal greater spectral blueshifts in F-type stars
than in the Sun (as theoretically expected from more vigorous convection),
further increasing in A-type stars (possibly due to atmospheric shockwaves).
Work is in progress to survey the spectra of the Sun and several solar-type
stars for "unblended" photospheric lines of most atomic species with accurate
laboratory wavelengths. One aim is to understand in what detail it will be
feasible to verify hydrodynamic stellar models. These may predict bisectors and
shifts for different classes of lines, but there will not result any comparison
with observations if such lines do not exist in real spectra, or are too blended
for meaningful measurement.
http://www.astro.lu.se/~dainis/