13 research outputs found
Doppler maps and surface differential rotation of EI Eri from the MUSICOS 1998 observations
We present time-series Doppler images of the rapidly-rotating active binary
star EI Eri from spectroscopic observations collected during the MUSICOS
multi-site campaign in 1998, since the critical rotation period of 1.947 days
makes it impossible to obtain time-resolved images from a single site. From the
surface reconstructions a weak solar-type differential rotation, as well as a
tiny poleward meridional flow are measured.Comment: 4 pages, 3 figures, 1 table, proceedings of Cool Stars 15, St
Andrews, July 2008, to be published in the Conference Proceedings Series of
the AI
The Blazhko behaviour of RR Geminorum I - CCD photometric results in 2004
Extended CCD monitoring of RR Gem revealed that it is a Blazhko type RRab
star with the shortest Blazhko period (7.23d) and smallest modulation amplitude
(Delta Mmax<0.1 mag) currently known. The short period of the modulation cycle
enabled us to obtain complete phase coverage of the pulsation at each phase of
the modulation. This is the first multicolour observation of a Blazhko star
which is extended enough to define accurate mean magnitudes and colours of the
variable at different Blazhko phases. Small, but real, changes in the intensity
mean colours at different Blazhko phases have been detected. The Fourier
analysis of the light curves shows that, in spite of the mmag and smaller order
of the amplitudes, the triplet structure is noticeable up to about the 14th
harmonic. The modulation is concentrated to a very narrow, 0.2 phase range of
the pulsation, centred on the supposed onset of the H emission during rising
light. These observational results raise further complications for theoretical
explanation of the long known but poorly understood Blazhko phenomenon.Comment: 10 pages, 12 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysic
A study of X-ray flares - II. RS CVn type Binaries
We present an analysis of seven flares detected from five RS CVn-type
binaries (UZ Lib, \sigma Gem, \lambda And, V711 Tau and EI Eri) observed with
XMM-Newton observatory. The quiescent state X-ray luminosities in the energy
band of 0.3-10.0 keV of these stars were found to be 10^{30.7-30.9} erg/s. The
exponential decay time in all the sample of flares range from ~ 1 to 8 hrs. The
luminosity at peak of the flares in the energy band of 0.3-10.0 keV were found
to be in the range of 10^{30.8} - 10^{31.8} erg/s. The great sensitivity of the
XMM-EPIC instruments allowed us to perform time resolved spectral analysis
during the flares and also in the subsquent quiescent phases. The derived metal
abundances of coronal plasma were found to vary during the flares observed from
\sigma Gem, V771 Tau and EI Eri. In these flares elemental abundances found to
be enhanced by factors of ~ 1.3-1.5 to the quiescent states. In most of the
flares, the peak temperature was found to be more than 100 MK whereas emission
measure increased by factors of 1.5 - 5.5. Significant sustained heating was
present in the majority of flares. The loop lengths (L) derived for flaring
structure were found to be of the order of 10^{10 -11} cm and are smaller than
the stellar radii (R*) i.e. L/R* \lesssim 1. The flare from \sigma Gem showed a
high and variable absorption column density during the flare.Comment: Accepted for publication in MNRA
Doppler imaging of stellar surface structure
We present a simultaneous photometric and spectroscopic imaging analysis
of the long-period RS CVn binary Ï Gem, covering 3.6 consecutive
rotation cycles with high time resolution. From six overlapping but
consecutive Doppler maps we trace the evolution of
individual spots throughout the time range covered. All spots group either
along a band at approximately +45°latitude and a width of
30°, or appear centered at the equator. No polar spot is detected.
We did not find a conclusive migration pattern from the cross-correlation
maps from one rotation to the next and attribute this to a masking effect of
short-term spot changes
Doppler imaging of stellar surface structure. Pt. 16: A time-series analysis of the moderately-rotating K1-giant #sigma# Geminorum
SIGLEAvailable from TIB Hannover: RR 7310(2001-18) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Doppler imaging of stellar surface structure
Aims.We present the first Doppler images of the bright
RS CVn-type binary ζ And. The star is a magnetically active K1
giant with its rotation synchronized to the 17.8-day orbital period.
Our revised lithium abundance of places ζ And in
the vicinity of Li-rich RGB stars but it is nevertheless a Li-normal
chromospherically active binary star. The star seems to undergo its
first standard dredge-up dilution.
Methods.Four consecutive Doppler images
were obtained from a continuous 67-night observing run at NSO-McMath
in 1996/97. An additional single image was obtained from a
continuous 19-night run at KPNO in 1997/98. These unique data allow
to compute a small time series of the evolution of the star's
surface structure. All line-profile inversions are done with a
modified TempMap version that takes into account the non-spherical
shape of the star. Representative test reconstructions are performed
and demonstrate the code's reliability and robustness.
Results.High and
low-latitude spot activity was recovered together with an asymmetric
polar cap-like feature. The latter dominated the first half of the
two-month time series in 1996/97. The second half showed mostly
medium-to-high latitude activity and only a fainter polar spot. The
coolest areas were restored with a temperature contrast of about
âK. Some weaker features at equatorial latitudes were
also recovered but these could be partially spurious and appear
blurred due to imperfect phase coverage. We use our line profiles to
reconstruct an average non-sphericity of which would, if not taken into account, mimic a
temperature difference pole-to-equator of â220âK, especially
at the phases of quadrature. Finally, we apply two different methods
for restoring surface differential rotation and found a weak
solar-type rotation law with a shear °/day
(), i.e. roughly
a factor of four weaker at a rotation rate roughly 1.5Â times faster
than the Sun's