The nature of the light variability of the silicon star HR 7224
Authors:
J. Krticka, Z. Mikulasek, G. W. Henry, J. Zverko, J. Ziznovsky, J. Skalicky, and P. Zverina
Image & caption:
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Image caption::
The emergent intensity (in the y band, μ = 1) from individual
surface elements of HR 7224 at various rotational phases.
Description:
Although photometric variations of chemically peculiar (CP) stars are frequently used to determine their rotational periods,the detailed mechanism of their light variability remains poorly understood.
We simulate the light variability of the star HR 7224 using the observed
surface distribution of silicon and iron.
We used the TLUSTY model atmospheres calculated for the appropriate silicon
and iron abundances to obtain the emergent flux and to predict the
rotationally modulated light curve of the star. We also obtained additional
photometric measurements and
employed our own regression procedure to derive a more precise estimate of
the light elements.
We show that the light variation of the star can be explained as a result of
i) the uneven surface distribution of the elements, ii) the flux
redistribution from the ultraviolet to the visible part of the spectrum, and
iii) rotation of the star. We show that the silicon bound-free transitions
and iron bound-bound transitions provide the main contribution to the flux
redistribution, although an additional
source of opacity is needed. We confirm that numerous iron lines
significantly contribute to the well-known depression at 5200 Å and discuss
the connection between iron abundance and the value of peculiarity index a.
The uneven surface distribution of silicon and iron is able to explain most
of the rotationally modulated light variation in the star HR 7224.
This paper was introduced among the highlights of the week in Astronomy and
Astrphysics.
SK
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