Issue |
A&A
Volume 383, Number 2, FebruaryIV 2002
|
|
---|---|---|
Page(s) | 519 - 523 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20011684 | |
Published online | 15 February 2002 |
Search for variations in circular-polarization spectra of the magnetic white dwarf LP 790–29*
1
Institut für Theoretische Physik und Astrophysik, Universität Kiel, 24098 Kiel, Germany
2
Universitäts-Sternwarte, Geismarlandstraße 11, 37083 Göttingen, Germany,
3
Institut für Astronomie und Astrophysik, Sand 1, 72076 Tübingen, Germany e-mail: jordan@astro.uni-tuebingen.de
4
Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: sfriedrich@aip.de
Corresponding author: S. Jordan, jordan@astrophysik.uni-kiel.de
Received:
21
September
2001
Accepted:
22
November
2001
We present highly time resolved circular-polarization and flux spectra
of the magnetic white dwarf LP 790–29 taken with the VLT UT1 in order to test
the hypothesis that LP 790–29 is a fast rotator with a period of the order of
seconds to
minutes. Due to low time resolution of former observations this might have
been overlooked – leading to the conclusion that LP 790–29 has a rotational
period of
over 100 years. The optical spectrum exhibits one prominent
absorption feature with minima at about 4500, 4950, and 5350 Å,
which are most likely
C2 Swan-bands shifted by about 180 Å in a magnetic field between
50 MG and 200 MG.
At the position of the absorption structures the degree of circular
polarization varies
between and +1%, whereas it amounts to +8 to +10% in the blue and
red continuum. With this very high degree of polarization
LP 790–29 is very well suited to a search for short
time variations, since a variation of several percent in the polarization
can be expected for a magnetic field oblique to the rotational axis.
From our analysis we conclude that variations on time scales from
50 to 2500 s must have amplitudes ≲0.7% in the continuum and
≲2% in the
strongest absorption feature at 4950 Å.
While no short-term variations could
be found a careful comparison of our polarization data of LP 790–29
with those in the literatures indicates significant variations on time
scales of decades with a possible period of about 24–28 years.
Key words: stars: individual: LP 790–29 / stars: rotation / stars: white dwarfs / stars: magnetic fields
© ESO, 2002
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