Doppler Imaging of Stellar Surface Structure
Typical Doppler Image (HD218153 by M.Weber).
That's what's possible today.
SISP simulation (by K.Schrijver).
That's what we hope for from future space interferometry. This image was
composed by remapping a solar image onto a sphere.
Scientific Goals of this Project
One of the most challenging observational goals of today's stellar
activity research is to obtain
two-dimensional images of inhomogeneous stellar surfaces to relate
disk integrated observations to spatially resolved surface
features. Spots cooler than the undisturbed photosphere of a late-type
star are a manifestation of surface magnetic fields and a time-dependent
study of their latitudinal and longitudinal behavior provides a direct
link to the internal stellar dynamo. Our long-term objective is thus to
provide conclusive observational constraints for a generalized theory of
The near-term goal, however, is to enlarge
the available sample of stars with a Doppler map and
to investigate the surface spot morphology as a function of stellar rotation.
What is Doppler imaging?
Doppler imaging is an inversion technique to recover a 2-D image of a
rapidly rotating star from a series of high-resolution spectral line profiles.
The inverse problem for stars with cool spots amounts to solving the integral
equation relating the surface temperature distribution to the observed line
profiles and light and color curve variations, while controlling the effects
of noise in the data through a regularizing
functional. Note that we solve for the photometric variations
simultaneously with the line profiles, but that we can handle only
one line per solution. If the spectroscopic phase coverage contains
gaps of more than 25 degr on the stellar surface more weight is
shifted to the photometry. In a
recent application to the K-dwarf LQ Hya (Strassmeier, Rice, Wehlau et al.
1993, A&A 268, 671)
we made up an average map from nine spectral lines and two broad-band colors.
This ensured that spurious features from a single line, caused by noise or
any other systematic error, will be suppressed in the final map.
Download PDF file (19MB): Resolving stellar surface spots (K.G. Strassmeier, Stellar Coronae, MPIfR, 2006 December)
Optical, Ultraviolet, and X-ray Observations Planned and in
The first star investigated in this project was the well-known
FK Comae star HD 199178 = V1794 Cyg, the second star was UZ Librae, a
RS CVn binary with a K giant as the target star. Other targets
currently being observed include T Tauri stars, young single main-sequence
stars, RS CVn binaries, and single rapidly-rotating field giants (see
The optical observations are being conducted at KPNO, NSO, CFHT, and ESO.
X-ray observations were made or are in progress with the HRI on board of
ROSAT. Ultraviolet observations are scheduled in cycle-5 with the Hubble
Space Telescope. This will enable us to obtain Doppler maps at different
heights in the stellar atmosphere and thereby obtain 3-D information on
the temperature/magnetic flux distribution.
February 26, 1995
update: June 6, 2001
Doppler Imaging: Results
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