15 research outputs found
First measurement of the magnetic field on FK Com and its relation to the contemporaneous starspot locations
In this study we present simultaneous low-resolution longitudinal magnetic
field measurements and high-resolution spectroscopic observations of the cool
single giant FK Com. The variation of the magnetic field over the rotational
period of 2.4 days is compared with the starspot location obtained using
Doppler imaging techniques, V-band photometry and V-I colours. The
chromospheric activity is studied simultaneously with the photospheric activity
using high resolution observations of the Halpha, Hbeta and Hgamma line
profiles. Both the maximum (272 +/- 24 G) and minimum (60 +/- 17 G) in the mean
longitudinal magnetic field, , are detected close to the phases where cool
spots appear on the stellar surface. A possible explanation for such a
behaviour is that the active regions at the two longitudes separated by 0.2 in
phase have opposite polarities.Comment: 10 Pages, 11 figures (quality of Figures 7,8 and 10 reduced),
accepted for publication in MNRA
Ellipsoidal primary of the RS CVn binary zeta And: Investigation using high-resolution spectroscopy and optical interferometry
We have obtained high-resolution spectroscopy, optical interferometry, and
long-term broad band photometry of the ellipsoidal primary of the RS CVn-type
binary system zeta And. Based on the optical interferometry the apparent limb
darkened diameter of zeta And is 2.55 +/- 0.09 mas using a uniform disk fit.
The Hipparcos distance and the limb-darkened diameter obtained with a uniform
disk fit give stellar radius of 15.9 +/- 0.8 Rsolar, and combined with
bolometric luminosity, it implies an effective temperature of 4665 +/- 140 K.
The temperature maps obtained from high resolution spectra using Doppler
imaging show a strong belt of equatorial spots and hints of a cool polar cap.
The equatorial spots show a concentration around the phase 0.75. This spot
configuration is reminiscent of the one seen in the earlier published
temperature maps of zeta And. Investigation of the Halpha line reveals both
prominences and cool clouds in the chromosphere. Long-term photometry spanning
12 years shows hints of a spot activity cycle, which is also implied by the
Doppler images, but the cycle length cannot be reliably determined from the
current data.Comment: 9 pages, 9 figures, accepted for A&
First measurement of the magnetic field on FK Com and its relation to the contemporaneous star-spot locations
In this study, we present simultaneous low-resolution longitudinal magnetic field measurements and high-resolution spectroscopic observations of the cool single giant FK Com. The variation of the magnetic field over the rotational period of 2.4 d is compared with the star-spot location obtained using Doppler imaging techniques, V-band photometry and V−I colours. The chromospheric activity is studied simultaneously with the photospheric activity using high-resolution observations of the Hα, Hβ and Hγ line profiles. Both the maximum (272 ± 24 G) and minimum (60 ± 17 G) in the mean longitudinal magnetic field, 〈Bz〉, are detected close to the phases where cool spots appear on the stellar surface. A possible explanation for such a behaviour is that the active regions at the two longitudes separated by 0.2 in phase have opposite polaritie
Optical photometry and X-ray monitoring of the "Cool Algol" BD+05 706: Determination of the physical properties
We present new photometric observations in the BVRI bands of the double-lined
eclipsing binary BD+05 706 conducted over three observing seasons, as well as
new X-ray observations obtained with the ROSAT satellite covering a full
orbital cycle (P = 18.9 days). A detailed light-curve analysis of the optical
data shows the system to be semidetached, confirming indications from an
earlier analysis by Torres et al. (1998), with the less massive and cooler star
filling its Roche lobe. The system is a member of the rare class of cool Algol
systems, which are different from the "classical" Algol systems in that the
mass-gaining component is also a late-type star rather than a B- or A-type
star. By combining the new photometry with a reanalysis of the spectroscopic
observations reported by Torres et al. (1998) we derive accurate absolute
masses for the components of M1 = 2.633 +/- 0.028 Msun and M2 = 0.5412 +/-
0.0093 Msun, radii of R1 = 7.55 +/- 0.20 Rsun and R2 = 11.02 +/- 0.21 Rsun, as
well as effective temperatures of 5000 +/- 100 K and 4640 +/- 150 K for the
primary and secondary, respectively. There are obvious signs of activity
(spottedness) in the optical light curve of the binary. Our X-ray light curve
clearly shows the primary eclipse but not the secondary eclipse, suggesting
that the primary star is the dominant source of the activity in the system. The
depth and duration of the eclipse allow us to infer some of the properties of
the X-ray emitting region around that star.Comment: 38 pages including 8 figures and 11 tables. To appear in The
Astronomical Journal, June 200
Multisite observations of SU Aurigae
We present results from the 1996 MUSICOS (MUlti-SIte COntinuous Spectroscopy)
campaign on the T Tauri star SU Aurigae. We find a 2.7-d periodicity in the He
I (587.6 nm) line and somewhat longer, less well-pronounced periodicities in
the Balmer lines and in Na D. Our observations support the suggestion that the
wind and infall signatures are out of phase on SU Aur. We present Doppler
images of SU Aur that have been obtained from least-squares deconvolved
profiles. Images taken about one rotation apart show only limited overlap, in
particular at low latitudes. This is in part due to limitations in
signal-to-noise, and in part due to line profile deformations that arise from
short-lived and/or non-surface features. The agreement at high latitudes is
better and suggests that at least some longer-lived features are present. The
analysis of Stokes V profiles yields a marginal magnetic field detection during
one of the phases.Comment: 22 pages, 20 figures, accepted for publication in MNRA
Starspot photometry with robotic telescopes.
We present continuous multicolor photometry for 47 stars from October
1996 through June 1997. Altogether, 7073 , UBV, and by data
points, each the average of three individual readings, were acquired with
three automatic photoelectric telescopes (APTs) at Fairborn Observatory in
southern Arizona. Most of our targets are chromospherically active single
and binary stars of spectral type G to K but there are also four
pre-main-sequence objects and three pulsating stars in our sample.
The light variability is generally due to rotational modulation of an
asymmetrically spotted stellar surface and therefore precise rotational
periods and their seasonal variations are determined from Fourier analysis.
We also report on photometric variations of γ CrB (A0V)
with a period of 0.44534 days. All data are available in numerical
form
Orbital period modulation in close binaries due to cyclic
The question is answered whether dynamo-generated magnetic fields are
able to produce such quadrupole terms in the gravity potential which can
explain the observed cyclic orbital variation of RS CVn stars. We start with spherical
dynamo models with outer convection zones but without any differential
rotation, i.e. with α
2-dynamos which are known as nonoscillating. With
the known anisotropic α-tensor of rapidly rotating stars the magnetic modes
with the lowest dynamo numbers are nonaxisymmetric with a slow azimuthal
drift. We also find, however, stable (i.e. with the lowest dynamo number)
axisymmetric oscillating modes but only for a very special, highly inhomogeneous α-tensor.
The dynamo model is a
linear one with an arbitrary field amplitude which can be scaled in order
to reproduce the observations. The star proves to be as prolate during
the maximum of the toroidal field energy and it proves to be as oblate
during the maximum of the poloidal field energy. In the time average the
influence of the toroidal field dominates and the star is slightly prolate.
From the
computed temporal variations of the gravitation quadrupole moment a magnetic
field of more than 105
G is found in order to produce the period modulation of
order 10-5 which has been observed
The Vienna-KPNO search for Doppler-imaging candidate stars
We present the results from a spectroscopic Ca i
Ellipsoidal primary of the RSÂ CVn binary
Aims. We have obtained high-resolution spectroscopy, optical interferometry, and
long-term broad band photometry of the ellipsoidal primary of the
RS CVn-type binary system ζ And. These observations are used to
obtain fundamental stellar parameters and to study surface structures and
their temporal evolution.
Methods. Temperature maps of the stellar surface were obtained from
high-resolution spectra with Doppler imaging techniques. These spectra were
also used to investigate the chromospheric activity using the HαÂ
line and to correlate it with the photospheric activity. The possible
cyclicity in the spot activity was investigated from the long-term broad
 band photometry. Optical interferometry was obtained during the same time
period as the high-resolution spectra. These observations were used to
derive the size and fundamental parameters of ζ And.
Results. Based on the optical interferometry the apparent limb darkened diameter of
ζ And is 2.55 ± 0.09 mas using a uniform disk fit. The expected
~4% maximum difference between the long and short axes of the
ellipsoidal stellar surface cannot be confirmed from the current data which
have 4% errors. The Hipparcos distance and the limb-darkened diameter
obtained with a uniform disk fit give stellar radius of
15.9 ± 0.8 , and combined with bolometric luminosity, it
implies an effective temperature of 4665 ± 140 K. The temperature maps
obtained from Doppler imaging show a strong belt of equatorial spots and
hints of a cool polar cap. The equatorial spots show a concentration around
the phase 0.75, i.e., 0.25 in phase from the secondary, and another
concentration spans the phases 0.0–0.4. This spot configuration is
reminiscent of the one seen in the earlier published temperature maps of
ζ And. Investigation of the Hα line reveals both prominences
and cool clouds in the chromosphere. These features do not seem to have a
clearly preferred location in the binary reference frame, nor are they
strongly associated with the cool photospheric spots. The investigation of
the long-term photometry spanning 12 years shows hints of a spot activity
cycle, which is also implied by the Doppler images, but the cycle length
cannot be reliably determined from the current data