2,373 research outputs found
Scaled oscillation frequencies and echelle diagrams as a tool for comparative asteroseismology
We describe a method for comparing the frequency spectra of oscillating
stars. We focus on solar-like oscillations, in which mode frequencies generally
follow a regular pattern. On the basis that oscillation frequencies of similar
stars scale homologously, we show how to display two stars on a single echelle
diagram. The result can be used to infer the ratio of their mean densities very
precisely, without reference to theoretical models. In addition, data from the
star with the better signal-to-noise ratio can be used to confirm weaker modes
and reject sidelobes in data from the second star. Finally, we show that scaled
echelle diagrams provide a solution to the problem of ridge identification in
F-type stars, such as those observed by the CoRoT space mission.Comment: accepted for publication in Communications in Asteroseismolog
Observations of solar-like oscillations
There has been tremendous progress in observing oscillations in solar-type
stars. In a few short years we have moved from ambiguous detections to firm
measurements. We briefly review the recent results, most of which have come
from high-precision Doppler measurements. We also review briefly the results on
giant and supergiant stars and the prospects for the future.Comment: Invited review talk at the "Vienna Workshop on the Future of
Asteroseismology", 20-22 September 2006, to appear in Communications in
Asteroseismolog
Correcting stellar oscillation frequencies for near-surface effects
In helioseismology, there is a well-known offset between observed and
computed oscillation frequencies. This offset is known to arise from improper
modeling of the near-surface layers of the Sun, and a similar effect must occur
for models of other stars. Such an effect impedes progress in asteroseismology,
which involves comparing observed oscillation frequencies with those calculated
from theoretical models. Here, we use data for the Sun to derive an empirical
correction for the near-surface offset, which we then apply three other stars
(alpha Cen A, alpha Cen B and beta Hyi). The method appears to give good
results, in particular providing an accurate estimate of the mean density of
each star.Comment: accepted for publication in ApJ Letter
Measuring stellar oscillations using equivalent widths of absorption lines
Kjeldsen et al. (1995, AJ 109, 1313; astro-ph/9411016) have developed a new
technique for measuring stellar oscillations and claimed a detection in the G
subgiant eta Boo. The technique involves monitoring temperature fluctuations in
a star via their effect on the equivalent width of Balmer lines. In this paper
we use synthetic stellar spectra to investigate the temperature dependence of
the Balmer lines, Ca II, Fe I, the Mg b feature and the G~band. We present a
list of target stars likely to show solar-like oscillations and estimate their
expected amplitudes. We also show that centre-to-limb variations in Balmer-line
profiles allow one to detect oscillation modes with l<=4, which accounts for
the detection by Kjeldsen et al. of modes with degree l=3 in integrated
sunlight.Comment: MNRAS (accepted); 7 pages, LaTeX with necessary style file and
PostScript figures in a single uuencoded Z-compressed .tar fil
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