393 research outputs found
On the Detectability of Oxygen X-ray Fluorescence and its Use as a Solar Photospheric Abundance Diagnostic
Monte Carlo calculations of the O Kalpha line fluoresced by coronal X-rays
and emitted just above the temperature minimum region of the solar atmosphere
have been employed to investigate the use of this feature as an abundance
diagnostic. While quite weak, we estimate line equivalent widths in the range
0.02-0.2 AA, depending on the X-ray plasma temperature. The line remains
essentially uncontaminated by blends for coronal temperatures T =< 3e6 K and
should be quite observable, with a flux >~ 2 ph/s/arcmin^2. Model calculations
for solar chemical mixtures with an O abundance adjusted up and down by a
factor of 2 indicate 35-60% changes in O Kalpha line equivalent width,
providing a potentially useful O abundance diagnostic. Sensitivity of
equivalent width to differences between recently recommended chemical
compositions with ``high'' and ``low'' complements of the CNO trio important
for interpreting helioseismological observations is less accute, amounting to
20-26% at coronal temperatures T ~< 2e6 K. While still feasible for
discriminating between these two mixtures, uncertainties in measured line
equivalent widths and in the models used for interpretation would need to be
significantly less than 20%. Provided a sensitive X-ray spectrometer with
resolving power >= 1000 and suitably well-behaved instrumental profile can be
built, X-ray fluorescence presents a viable means for resolving the solar
``oxygen crisis''.Comment: To appear in the Astrophysical Journa
The Stellar Activity - Rotation Relationship
Using a new catalog of 824 solar and late-type stars with X-ray luminosities
and rotation periods we have studied the relationship between rotation and
stellar activity. From an unbiased subset of this sample the power law slope of
the unsaturated regime, , is fit as
. This is inconsistent with the canonical slope
to a confidence of 5 and argues for an interface-type dynamo.
Super-saturation is observed for the fastest rotators in our sample and its
parametric dependencies are explored. Significant correlations are found with
both the corotation radius and the excess polar updraft, the latter theory
being supported by other observations. We also present a new X-ray population
synthesis model of the mature stellar component of our Galaxy and use it to
reproduce deep observations of a high Galactic latitude field. The model,
XStar, can be used to test models of stellar spin-down and dynamo decay, as
well as for estimating stellar X-ray contamination rates for non-stellar
studies.Comment: 4 pages, 4 figures. To appear in the proceedings of Cool Stars 17:
17th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, AN 334,
1-2, Eds Klaus Strassmeier and Mercedes Lopez-Morale
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