J/A+A/499/567 BV differential photometry of HR 7224 (Krticka+, 2009)
The nature of the light variability of the silicon star HR 7224.
Krticka J., Mikulasek Z., Henry G.W., Zverko J., Ziznovsky J., Skalicky J.,
Zverina P.
<Astron. Astrophys. 499, 567 (2009)>
=2009A&A...499..567K 2009A&A...499..567K
ADC_Keywords: Stars, peculiar ; Photometry, UBV
Keywords: stars: chemically peculiar - stars: early type -
stars: variables: general - stars: individual HR 7224
Abstract:
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 5200Å 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.
Description:
Johnson BV photometric observations of HR 7224 obtained using T3
automatic photoelectric telescope at Fairborn Observatory are
presented.
Objects:
---------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------
18 58 52.6 +69 31 53 HR 7224 = V* EE Dra
---------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
bmag.dat 20 478 B differential photometry
vmag.dat 20 462 V differential photometry
--------------------------------------------------------------------------------
See also:
J/A+AS/122/249 : uvby photometry of 4 CP stars (Adelman, 1997)
J/A+A/457/1033 : Radial velocity of HR 7224 (Lehmann+, 2006)
Byte-by-byte Description of file: bmag.dat vmag.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 F12.4 d HJD Heliocentric Julian day
14- 20 F7.4 mag Dmag Differential magnitude (in B or V)
--------------------------------------------------------------------------------
Acknowledgements:
Jiri Krticka, krticka(at)physics.muni.cz
Gregory W. Henry, henry(at)schwab.tsuniv.edu
(End) Patricia Vannier [CDS] 08-Apr-2009