470 research outputs found
Mapping EK Draconis with PEPSI - Possible evidence for starspot penumbrae
We present the first temperature surface map of EK Dra from
very-high-resolution spectra obtained with the Potsdam Echelle Polarimetric and
Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope. Changes in
spectral line profiles are inverted to a stellar surface temperature map using
our Map code. The long-term photometric record is employed to compare our
map with previously published maps. Four cool spots were reconstructed, but no
polar spot was seen. The temperature difference to the photosphere of the spots
is between 990 and 280K. Two spots are reconstructed with a typical solar
morphology with an umbra and a penumbra. For the one isolated and relatively
round spot (A), we determine an umbral temperature of 990K and a penumbral
temperature of 180K below photospheric temperature. The umbra to photosphere
intensity ratio of EK Dra is approximately only half of that of a comparison
sunspot. A test inversion from degraded line profiles showed that the higher
spectral resolution of PEPSI reconstructs the surface with a temperature
difference that is on average 10% higher than before and with smaller surface
areas by 10-20%. PEPSI is therefore better suited to detecting and
characterising temperature inhomogeneities. With ten more years of photometry,
we also refine the spot cycle period of EK Dra to 8.90.2 years with a
continuing long-term fading trend. The temperature morphology of spot A so far
appears to show the best evidence for the existence of a solar-like penumbra
for a starspot. We emphasise that it is more the non-capture of the true umbral
contrast rather than the detection of the weak penumbra that is the limiting
factor. The relatively small line broadening of EK Dra, together with the only
moderately high spectral resolutions previously available, appear to be the
main contributors to the lower-than-expected spot contrasts when comparing to
the Sun.Comment: Accepted for A&
Carbon 12C/13C isotope ratio of alpha Aurigae revised
Context. Capella ({\alpha} Aur) is one of the few binaries in the sky with
two cool giant stars. With spectral types of G8III and G0III, the two
components appear at different but distinct stages in their evolution. The G0
secondary star is a Hertzsprung-gap giant, and the G8 primary star is thought
to be a clump giant. Aims. We present a new measure of the carbon 12 C/ 13 C
isotope ratio of the primary component of Capella using high-resolution R
250 000 spectra obtained with the Potsdam Echelle Polarimetric and
Spectroscopic Instrument (PEPSI) with both the Vatican Advanced Technology
Telescope (VATT) and the Large Binocular Telescope (LBT). Methods.
Signal-to-noise ratios of up to 2 700 were obtained by averaging nightly
spectra. These average spectra were used to disentangle the two binary
components. The isotope ratio was derived with the use of spectrum synthesis
from the CN lines at 8004 {\AA}. Results. We found that the 12 C/ 13 C ratio of
the primary component of Capella is 17.81.9. Our measurement precision is
now primarily limited by the spectral-line data and by the grid-step size of
the model atmospheres rather than the data. The separated spectrum of the
secondary component does not show distinguishable 12 CN and 13 CN lines because
of its v sin i and higher temperature. Conclusions. Our new 12 C/ 13 C value is
significantly lower than the previous value of 274 but now agrees better
with the recent model prediction of 18.8 - 20.7.Comment: accepted to A&A Letters to the Edito
Doppler images and the underlying dynamo. The case of AF Leporis
The (Zeeman-)Doppler imaging studies of solar-type stars very often reveal
large high-latitude spots. This also includes F stars that possess relatively
shallow convection zones, indicating that the dynamo operating in these stars
differs from the solar dynamo. We aim to determine whether mean-field dynamo
models of late-F type dwarf stars can reproduce the surface features recovered
in Doppler maps. In particular, we wish to test whether the models can
reproduce the high-latitude spots observed on some F dwarfs. The photometric
inversions and the surface temperature maps of AF Lep were obtained using the
Occamian-approach inversion technique. Low signal-to-noise spectroscopic data
were improved by applying the least-squares deconvolution method. The locations
of strong magnetic flux in the stellar tachocline as well as the surface fields
obtained from mean-field dynamo solutions were compared with the observed
surface temperature maps. The photometric record of AF Lep reveals both long-
and short-term variability. However, the current data set is too short for
cycle-length estimates. From the photometry, we have determined the rotation
period of the star to be 0.9660+-0.0023 days. The surface temperature maps show
a dominant, but evolving, high-latitude (around +65 degrees) spot. Detailed
study of the photometry reveals that sometimes the spot coverage varies only
marginally over a long time, and at other times it varies rapidly. Of a suite
of dynamo models, the model with a radiative interior rotating as fast as the
convection zone at the equator delivered the highest compatibility with the
obtained Doppler images.Comment: accepted for publication in Astronomy & Astrophysic
Robot-assisted pyeloplasty with buccal mucosa graft for the management of an extended recurrent ureteropelvic junction stricture
A clinical case of robot-assisted pyeloplasty with buccal mucosa graft of an extended recurrent stricture of the left ureteropelvic junction is presented. The patient had previously undergone left-sided laparoscopic antevasal pyeloplasty and retrograde endopyelotomies with ureteral stenting. However, after these interventions, the dilatation of the left pelvicalyceal system persisted, the patient complained of lumbar pain and periodic exacerbations of chronic pyelonephritis. Transperitoneal robotic access isolated the ureteral upper third and the ureteropelvic junction from scar tissue, after dissecting the narrowed ureteral section, its length was about 3.0 cm. In this regard, plastic surgery was performed with a buccal mucosa graft, the ureter was drained with a stent. There were no postoperative complications, and on day 3 the patient was discharged. The stent was removed 4 weeks after. During the control ultrasound examination, the renal pelvicalyceal system was relatively reduced, and the patient did not notice any pain
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