Issue |
A&A
Volume 430, Number 1, January IV 2005
|
|
---|---|---|
Page(s) | 263 - 278 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20034547 | |
Published online | 12 January 2005 |
Radial velocity variations in pulsating Ap stars*
IV. First results on HR 1217
1
Astrophysical Research Center for the Structure and Evolution of the Cosmos, Sejong University, Seoul 143-747, Korea e-mail: david@arcsec.sejong.ac.kr
2
Astronomical Observatory, Odessa National University, Shevchenko Park, Odessa 65014, Ukraine
3
Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: artie@tls-tautenburg.de
Received:
21
October
2003
Accepted:
28
June
2004
In this paper we present the first results from
a high-precision radial velocity (RV) study of the rapidly oscillating
Ap (roAp) star HR 1217. Data spanning a complete rotation period
were acquired on 9 nights in late 1997 and early
1998 using the Harlan J. Smith 2.7 m telescope at McDonald Observatory.
The RVs were measured using the wavelength range of each spectral
order (≈100 Å) of the “2dcoude” echelle spectrograph. Most
of the pulsational modes can be seen in all spectral regions but the amplitude varies by factors of
ten or more between the different wavelength intervals.
A detailed analysis of the spectral order centered on 5825 Å, which
had the largest amplitudes, showed the presence of all published
photometric frequencies f1–f7.
The multi-mode oscillations were also found in the RV variations of
the high amplitude Nd III 5294 Å feature. Our RV data reveal two new excited modes at
frequencies c d-1 (2585.3 μHz) and
c d-1 (2553.0 μHz) that follow the odd and even
alternative mode spacing with
μHz.
An analysis of individual nights shows strong amplitude and
phase modulation of all excited modes, including the two newly
discovered ones. The
amplitudes of the
c d-1 (2652.9 μHz) and
c d-1 (2720.85 μHz) modes are modulated
with the published magnetic field variations and reach their maximum and
minimum at magnetic extrema.
However, the phase variability is in disagreement with that expected from
the standard oblique pulsator model.
The phase jumps for the f2 mode occur exactly at
magnetic maximum and close to the phase of magnetic minimum,
while the f3 and f4 modes have a continuous change.
The peculiar phase variability is attributed to strong
vertical phase changes in the line-forming layers of atmosphere.
An echelle-diagram for all known excited modes in
HR 1217 is constructed. We interpret the
c d-1 (2805.7 μHz) mode with the “peculiar” spacing as due
to a mode of degree
that is the only observed member of
another system of equally-spaced frequencies. We predict
the existence of modes belonging to this system that should
be equally spaced at 68 μHz with f7.
Key words: techniques: radial velocities / techniques: spectroscopic / stars: chemically peculiar / stars: oscillations / stars: individual: HR 1217
© ESO, 2005
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.