63 research outputs found
Lithium enrichment on the single active K1-giant DI Piscium -- Possible joint origin of differential rotation and Li enrichment
We investigate the surface spot activity of the rapidly rotating,
lithium-rich active single K-giant DI Psc to measure the surface differential
rotation and understand the mechanisms behind the Li-enrichment. Doppler
imaging was applied to recover the surface temperature distribution of DI Psc
in two subsequent rotational cycles using the individual mapping lines Ca I
6439, Fe I 6430, Fe I 6421 and Li I 6708. Surface differential rotation was
derived by cross-correlation of the subsequent maps. Difference maps are
produced to study the uniformity of Li-enrichment on the surface. These maps
are compared with the rotational modulation of the Li I 6708 line equivalent
width. Doppler images obtained for the Ca and Fe mapping lines agree well and
reveal strong polar spottedness, as well as cool features at lower latitudes.
Cross-correlating the consecutive maps yields antisolar differential rotation
with shear coefficient -0.083 +- 0.021. The difference of the average and the
Li maps indicates that the lithium abundance is non-activity related. There is
also a significant rotational modulation of the Li equivalent width.Comment: 8 pages, 7 figures, accepted in A&
Magnitude-range brightness variations of overactive K giants
We study three representative, overactive spotted K giants (IL Hya, XX Tri,
and DM UMa) known to exhibit V-band light variations between 0.65-1.05 mags.
Our aim is to find the origin of their large brightness variation. We employ
long-term phase-resolved multicolor photometry, mostly from automatic
telescopes, covering 42 yr for IL Hya, 28 yr for XX Tri, and 34 yr for DM UMa.
For one target, IL Hya, we present a new Doppler image from NSO data taken in
late 1996. Effective temperatures for our targets are determined from all
well-sampled observing epochs and are based on a V-I_C color-index calibration.
The effective temperature change between the extrema of the rotational
modulation for IL Hya and XX Tri is in the range 50-200 K. The bolometric flux
during maximum of the rotational modulation, i.e., the least spotted states,
varied by up to 39% in IL Hya and up to 54% in XX Tri over the course of our
observations. We emphasize that for IL Hya this is just about half of the total
luminosity variation that can be explained by the photospheric temperature
(spots/faculae) changes, while for XX Tri it is even about one third. The
long-term, 0.6 mag V-band variation of DM UMa is more difficult to explain
because little or no B-V color index change is observed on the same timescale.
Placing the three stars with their light and color variations into H-R
diagrams, we find that their overall luminosities are generally too low
compared to predictions from current evolutionary tracks. A change in the
stellar radius due to strong and variable magnetic fields during activity
cycles likely plays a role in explaining the anomalous brightness and
luminosity of our three targets. At least for IL Hya, a radius change of about
9% is suggested from m_bol and T_eff, and is supported by independent vsin(i)
measurements.Comment: 13 pages, 8 figures, accepted in A&
Time-series Doppler images and surface differential rotation of the effectively-single rapidly-rotating K-giant KU Pegasi
According to most stellar dynamo theories, differential rotation (DR) plays a
crucial role for the generation of toroidal magnetic fields. Numerical models
predict surface differential rotation to be anti-solar for rapidly-rotating
giant stars, i.e., their surface angular velocity could increase with stellar
latitude. However, surface differential rotation has been derived only for a
handful of individual giant stars to date.
The spotted surface of the K-giant KU Pegasi is investigated in order to
detect its time evolution and quantify surface differential rotation.
We present altogether 11 Doppler images from spectroscopic data collected
with the robotic telescope STELLA between 2006--2011. All maps are obtained
with the surface reconstruction code iMap. Differential rotation is extracted
from these images by detecting systematic (latitude-dependent) spot
displacements. We apply a cross-correlation technique to find the best
differential rotation law.
The surface of KU Peg shows cool spots at all latitudes and one persistent
warm spot at high latitude. A small cool polar spot exists for most but not all
of the epochs. Re-identification of spots in at least two consecutive maps is
mostly possible only at mid and high latitudes and thus restricts the
differential-rotation determination mainly to these latitudes. Our
cross-correlation analysis reveals solar-like differential rotation with a
surface shear of , i.e., approximately five times weaker
than on the Sun. We also derive a more accurate and consistent set of stellar
parameters for KU Peg including a small Li abundance of ten times less than
solar.Comment: 13 pages, 12 figures, accepted for publication in A&
New skeletal tuberculosis cases in past populations from Western Hungary (Transdanubia)
The distribution, antiquity and epidemiology of tuberculosis (TB) have previously been studied in osteoarchaeological material in the eastern part of Hungary, mainly on the Great Plain. The purpose of this study is to map the occurrence of skeletal TB in different centuries in the western part of Hungary, Transdanubia, and to present new cases we have found. Palaeopathological analysis was carried out using macroscopic observation supported by radiographic and molecular methods. A large human osteoarchaeological sample (n = 5684) from Transdanubian archaeological sites ranging from the 2nd to the 18th centuries served as a source of material. Spinal TB was observed in seven individuals (in three specimens with Pott's disease two of which also had cold abscess) and hip TB was assumed in one case. The results of DNA for Mycobacterium tuberculosis were positive in seven of the eight cases identified by paleopathology, and negative in the assumed case of hip TB. However, the molecular results are consistent with highly fragmented DNA, which limited further analysis. Based on the present study and previously published cases, osteotuberculosis was found in Transdanubia mainly during the 9th–13th centuries. However, there are no signs of TB in many other 9th–13th century sites, even in those that lie geographically close to those where osteotuberculous cases were found. This may be due to a true absence of TB caused by the different living conditions, way of life, or origin of these populations. An alternative explanation is that TB was present in some individuals with no typical paleopathology, but that death occurred before skeletal morphological features could develop
Token Jumping in minor-closed classes
Given two -independent sets and of a graph , one can ask if it
is possible to transform the one into the other in such a way that, at any
step, we replace one vertex of the current independent set by another while
keeping the property of being independent. Deciding this problem, known as the
Token Jumping (TJ) reconfiguration problem, is PSPACE-complete even on planar
graphs. Ito et al. proved in 2014 that the problem is FPT parameterized by
if the input graph is -free.
We prove that the result of Ito et al. can be extended to any
-free graphs. In other words, if is a -free
graph, then it is possible to decide in FPT-time if can be transformed into
. As a by product, the TJ-reconfiguration problem is FPT in many well-known
classes of graphs such as any minor-free class
Antisolar differential rotation with surface lithium enrichment on the single K-giant V1192 Ori
Context: Stars with about 12 solar masses at the red giant branch (RGB)
represent an intriguing period of stellar evolution, i.e. when the convective
envelope interacts with the fast-rotating core. During these mixing episodes
freshly synthesized lithium can come up to the stellar surface along with high
angular momentum material. This high angular momentum may alter the surface
rotation pattern.
Aims: The single rapidly rotating K-giant V1192 Ori is revisited to determine
its surface differential rotation, lithium abundance, and basic stellar
properties such as a precise rotation period. The aim is to independently
verify the antisolar differential rotation of the star and possibly find a
connection to the surface lithium abundance.
Methods: We applied time-series Doppler imaging to a new multi-epoch data
set. Altogether we reconstructed 11 Doppler images from spectroscopic data
collected with the STELLA robotic telescope between 2007--2016. We used our
inversion code iMap to reconstruct all stellar surface maps. We extracted the
differential rotation from these images by tracing systematic spot migration as
a function of stellar latitude from consecutive image cross-correlations.
Results: The position of V1192 Ori in the Hertzsprung-Russell diagram
suggests that the star is in the helium core-burning phase just leaving the RGB
bump. We measure , i.e. a value close to the
anticipated transition value of 1.5 from Li-normal to Li-rich giants. Doppler
images reveal extended dark areas arranged quasi-evenly along an equatorial
belt. No cool polar spot is found during the investigated epoch. Spot
displacements clearly suggest antisolar surface differential rotation with
shear coefficient.
Conclusions: The surface Li enrichment and the peculiar surface rotation
pattern may indicate a common origin.Comment: Accepted for publication in Astronomy and Astrophysic
EI Eridani: a star under the influence -- The effect of magnetic activity in the short and long term
We use our photometric time series of more than forty years to analyze the
long-term behaviour of EI Eri. Flare activity is investigated using space-borne
photometric data obtained with TESS. The MUSICOS campaign aimed to achieve
high-resolution spectroscopic observations from many sites around the globe, so
that uninterrupted phase coverage of EI Eri became available. We use these data
to reconstruct successive surface temperature maps of the star in order to
study the changes of starspots on a very short timescale.
We use long-term, seasonal period analysis of our photometric time series to
study changes in the rotational period. Short-term Fourier-transform is also
applied to look for activity cycle-like changes. We also study the phase and
frequency distribution of hand-selected flares. We apply our multi-line Doppler
imaging code to reconstruct four consecutive Doppler images. These images are
also used to measure surface differential rotation by our cross-correlation
technique. In addition, we carry out tests to demonstrate how Doppler imaging
is affected by the fact that the data came from several different instruments
with different spectral resolutions.
Seasonal period analysis of the light curve reveals a smooth, significant
change in period, possibly indicating the evolution of active latitudes.
Temperature curves from and show slight differences, indicating the
activity of EI Eri is spot dominated. Short-term Fourier transform reveals
smoothly changing cycles between 4.5--5.5 and 8.9--11.6 years. The
time-resolved spotted surface of EI Eri from Doppler imaging enabled us to
follow the evolution of the different surface features. Cross-correlating the
consecutive Doppler maps reveal surface shear of . Our
tests validate our approach and show that the surface temperature distribution
is adequately reconstructed by our method.Comment: 14 pages, 13 figures, A&A accepte
Magnetic activity of the young solar analog V1358 Orinis
Context. Young, fast-rotating single stars can show dramatically different magnetic signatures and levels of magnetic activity as compared with the Sun. While losing angular momentum due to magnetic breaking and mass loss through stellar winds, the stars gradually spin down resulting in decreasing levels of activity. Studying magnetic activity on such solar analogues plays a key role in understanding the evolution of solar-like stars and allows a glimpse into the past of the Sun as well. Aims: In order to widen our knowledge of the magnetic evolution of the Sun and solar-like stars, magnetic activity of the young solar analog V1358 Ori is investigated. Methods: Fourier analysis of long-term photometric data is used to derive rotational period and activity cycle length, while spectral synthesis is applied to high-resolution spectroscopic data in order to derive precise astrophysical parameters. Doppler imaging is performed to recover surface-temperature maps for two subsequent intervals. Cross-correlation of the consecutive Doppler maps is used to derive surface differential rotation. The rotational modulation of the chromospheric activity indicators is also investigated. Results: An activity cycle of 1600 days is detected for V1358 Ori. Doppler imaging revealed a surface-temperature distribution dominated by a large polar cap with a few weaker features around the equator. This spot configuration is similar to other maps of young solar analogs from the literature, and supports recent model predictions. We detected solar-like surface differential rotation with a surface shear parameter of α = 0.016 ± 0.010, which is in close agreement with our recently proposed empirical relation between rotation and differential rotation. The chromospheric activity indicators showed rotational modulation
- …