J/A+A/457/1033 Radial velocity of HR 7224 (Lehmann+, 2006)
The helium-weak silicon star HR 7224
I. Radial velocity and line profile variations.
Lehmann H., Tsymbal V., Mkrtichian D.E., Fraga L.
<Astron. Astrophys. 457, 1033 (2006)>
=2006A&A...457.1033L 2006A&A...457.1033L
ADC_Keywords: Stars, peculiar; Spectroscopy; Radial velocities
Keywords: stars: chemically peculiar - stars: variables: general -
stars: atmospheres - stars: abundances - stars: individual: HR 7224
Abstract:
HR 7224 is a rapidly rotating He-weak silicon star known as
photometrically variable with a period of 1.123d. Drastic changes of
photometric amplitude and period were reported in 2003. We investigate
the star spectroscopically to determine the time scales of
variability, to derive basic atmospheric parameters, and to give first
estimates on possible surface structures. We investigate time series
of more then 570 high-resolution spectra of HR 7224 for radial
velocity and line profile variations. The rotation period is
determined from period analysis of data. Comparing radial velocity and
line profile variations we draw first conclusions on possible surface
structures in terms of line strengths. From Balmer and metal lines we
determine Teff, log(g), vsini and metal abundances depending on
rotation phase. The star shows a remarkable half-amplitude of radial
velocity variation of 6km/s. From this variation we deduce a rotation
period of 1.12324d. The period and the double-wave shaped radial
velocity curve are in agreement with earlier photometric findings. The
observed radial velocity variations can be explained by the rotation
period and its harmonics and no further periodic contributions were
found in the residuals. HR 7224 has enhanced Si and Fe abundances
whereas He is extremely depleted. The star shows line strength
variations of all observed elements with the rotation period.
Variations of radial velocity, line strength and line shape of silicon
lines and their relationships can be explained by assuming two large
spots on the stellar surface showing enhanced line strength. From
Balmer lines we deduce different temperatures of the star for
different rotation phases. The observed difference in amplitudes of
the variation of Mg II and Si II lines supports the assumption of
surface regions of different temperature on this presumably magnetic
CP star. Synthetic uvby colors computed from adapted synthetic spectra
confirm the high photometric amplitude reported for the 2003 light
curves.
Description:
Heliocentric radial velocities (RVs) of the rapidly rotating CpSi star
HR 7224 are presented. High-resolution spectra were taken with the
Coude-Echelle spectrograph attached to the 2-m telescope of the
Thueringer Landessternwarte Tautenburg with a spectral resolution of
63000. RVs were derived from a cross-correlation of metallic lines in
the 4960 to 5880Å region and are on a relative scale.
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
table.dat 27 577 Radial velocities
--------------------------------------------------------------------------------
See also:
J/A+AS/122/249 : HD 32633, 25 Sex, HR 7224, HD 200311 uvby phot. (Adelman 1997)
Byte-by-byte Description of file: table.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 F14.6 --- HJD Heliocentric Julian date
16- 21 F6.3 km/s HRV Relative heliocentric radial velocity
23- 27 F5.3 km/s e_HRV Internal error of HRV from cross-correlation
--------------------------------------------------------------------------------
Acknowledgements: Holger Lehmann, lehm(at)tls-tautenburg.de
(End) Holger Lehmann [TLS, Germany], Patricia Vannier [CDS] 28-Aug-2006