pinecone/core-2020-05-10-deduplication huggingface dataset:
Numerical simulations of fast and slow coronal mass ejections

Solar coronal mass ejections (CMEs) show a large variety in their kinematic
properties. CMEs originating in active regions and accompanied by strong flares
are usually faster and accelerated more impulsively than CMEs associated with
filament eruptions outside active regions and weak flares. It has been proposed
more than two decades ago that there are two separate types of CMEs, fast
(impulsive) CMEs and slow (gradual) CMEs. However, this concept may not be
valid, since the large data sets acquired in recent years do not show two
distinct peaks in the CME velocity distribution and reveal that both fast and
slow CMEs can be accompanied by both weak and strong flares. We present
numerical simulations which confirm our earlier analytical result that a
flux-rope CME model permits describing fast and slow CMEs in a unified manner.
We consider a force-free coronal magnetic flux rope embedded in the potential
field of model bipolar and quadrupolar active regions. The eruption is driven
by the torus instability which occurs if the field overlying the flux rope
decreases sufficiently rapidly with height. The acceleration profile depends on
the steepness of this field decrease, corresponding to fast CMEs for rapid
decrease, as is typical of active regions, and to slow CMEs for gentle
decrease, as is typical of the quiet Sun. Complex (quadrupolar) active regions
lead to the fastest CMEs.Comment: 4 pages, 3 figures, published in Astron. Nachr. 328, 743 (2007).
  Minor update to conform to published paper, with minor language improvements
  and citation updates include
Are extrasolar oceans common throughout the Galaxy?

Light and cold extrasolar planets such as OGLE 2005-BLG-390Lb, a 5.5
Earth-mass planet detected via microlensing, could be frequent in the Galaxy
according to some preliminary results from microlensing experiments. These
planets can be frozen rocky- or ocean-planets, situated beyond the snow line
and, therefore, beyond the habitable zone of their system. They can nonetheless
host a layer of liquid water, heated by radiogenic energy, underneath an ice
shell surface for billions of years, before freezing completely. These results
suggest that oceans under ice, like those suspected to be present on icy moons
in the Solar system, could be a common feature of cold low-mass extrasolar
planets.Comment: Accepted in Astronomische Nachrichten (Astronomical Notes
Imaging the cool stars in the interacting binaries AE Aqr, BV Cen and
  V426 Oph

It is well known that magnetic activity in late-type stars increases with
increasing rotation rate. Using inversion techniques akin to medical imaging,
the rotationally broadened profiles from such stars can be used to reconstruct
`Doppler images' of the distribution of cool, dark starspots on their stellar
surfaces. Interacting binaries, however, contain some of the most rapidly
rotating late-type stars known and thus provide important tests of stellar
dynamo models. Furthermore, magnetic activity is thought to play a key role in
their evolution, behaviour and accretion dynamics. Despite this, we know
comparatively little about the magnetic activity and its influence on such
binaries. In this review we summarise the concepts behind indirect imaging of
these systems, and present movies of the starspot distributions on the cool
stars in some interacting binaries. We conclude with a look at the future
opportunities that such studies may provide.Comment: 4 pages, 3 figures. Conference proceedings for the N+N+N Workshop,
  "From our star to far stars: Variation and Variability". Accepted for
  publication in Astronomische Nachrichte
Results of the photometry of the spotted dM1-2e star EY Draconis

We have observed EY Draconis with the 24`` telescope of Konkoly Observatory
in Budapest for 64 nights. In the first obse rving season the star produced a
stable light curve for more than 60 rotation periods, however, the light curves
observe d in the next season and the spot modelling show clear evidence of the
evolution of the spotted stellar surface. The chan ges of the maximum
brightness level suggests the existence of a longer period of about 300 days,
which seems to be confir med by the ROTSE archival data.Comment: 4 pages, 7 figures with 12 image files, N+N+N conference, accepted
  for publication in A
Study of the effect of metallicity on the amplitudes of Cepheids

Results concerning the dependence of photometric and radial velocity
amplitudes on metallicity are presented based on about 200 Galactic classical
Cepheids pulsating in the fundamental mode. The Galactic distribution of the
[Fe/H] value of Cepheids is also studied. We show that the photometric
amplitude ratio $A_\mathrm{I}/A_\mathrm{V}$ is independent of metallicity. The
observed dependence of this ratio on the pulsation period does not correspond
to the theoretical predictions.Comment: Accepted for publication in Astronomische Nachrichten (Astronomical
  Notes). 4 pages, 5 figure
On the possibility of a bimodal solar dynamo

A simple way to couple an interface dynamo model to a fast tachocline model
is presented, under the assumption that the dynamo saturation is due to a
quadratic process and that the effect of finite shear layer thickness on the
dynamo wave frequency is analoguous to the effect of finite water depth on
surface gravity waves. The model contains one free parameter which is fixed by
the requirement that a solution should reproduce the helioseismically
determined thickness of the tachocline. In this case it is found that, in
addition to this solution, another steady solution exists, characterized by a
four times thicker tachocline and 4-5 times weaker magnetic fields. It is
tempting to relate the existence of this second solution to the occurrence of
grand minima in solar activity.Comment: 4 pages, 1 figure; Astr. Nachr., in pres
Searching Extra Dimensions in Compact Stars

The electro-magnetic and particle radiation detected from the direction of
Cygnus X3 raise the question of the existence of special long-lived, neutral
particles. We investigate the origin of these particles in a special approach:
the source object may contain compactified extra dimension and these particles
are messengers of this state. We describe hyperon stars in 3+1 dimension and
introduce the description of a compact stars in 3+1_c+1 dimensional space-time.Comment: 4 pages, 3 figures, submitted to Astron. Nachrichte
Studying Blazhko RR Lyrae stars with the 24-inch telescope of the
  Konkoly Observatory

About a dozen field RR Lyrae stars have been observed with the 24-inch
Heyde-Zeiss telescope of the Konkoly Observatory at Sv\'abhegy, Budapest, since
its refurbishment in 2003. Most of the observing time is allocated for the
investigation of the Blazhko modulation, a phenomenon that still does not have
a satisfactory explanation. The obtained multicolour CCD observations are
unique in extent. The accuracy of the measurements makes it possible to detect
low amplitude modulation of the light curve as well. The discovery of Blazhko
stars with low modulation amplitudes warns that the incidence rate of the
Blazhko modulation is, in fact, much larger than it was previously expected.
This makes the efforts exploring the cause of the modulation even more
important. A summary of our measurements and results achieved during the last 3
years is presented.Comment: Accepted for publication in Astronomische Nachrichten (Astronomical
  Notes). 4 pages, 3 fig
The double-mode RR Lyrae variable BS Com

We present the frequency analysis of the multicolour time series photometry
of the field RRd variable BS Comae. The large number of data points in each of
the BV(RI)_c bands and the ~0.01 magnitude accuracy of the individual
measurements allow us a high precision analysis of the properties of the
combination frequencies due to nonlinear coupling. Through the combination of
the frequency spectra in different colors we show that except for the
components corresponding to the linear combinations of the two pulsation modes,
there are no other components present above the millimagnitude amplitude level.Comment: 4 pages, 7 figures, accepted for publication in A
Pulsation and orbit of AU Pegasi

AU Pegasi is a pulsating star in a spectroscopic binary system with an
orbital period of 53.26 days. Between 1960 and 1990 an extremely rapid period
increase was observed in the value of the pulsation period, but in the last 15
years the observation show that the period set in 2.411 days. Fourier analysis
of photometric data obtained during the ASAS project and those taken at the
Piszkesteto Mountain Station of the Konkoly Observatory during 1994-2005
indicate that AU Pegasi is pulsating in two modes simultaneously, and the ratio
of the frequencies of the two modes is 0.706, a value common for double-mode
classical Cepheids. A careful analysis of other photometric observations
obtained during the era of the strong period increase also revealed existence
of a second mode. This may suggest that this star is not a Type II Cepheid,
despite its galactic position.Comment: 4 pages, 10 figure
The Blazhko behavior of RV UMa

RV UMa is one of the most extensively studied RR Lyrae stars showing Blazhko
modulation. Its photometric observations cover more than 90 years. The
published photoelectric observations of RV UMa obtained at the Konkoly
Observatory (Kanyo, 1976) were re-considered and completed with previously
unpublished data. During the time interval of the observations the periods of
both the pulsation and the modulation varied within the ranges of 0.000007 and
0.9 days, respectively. We have found a definite but not strict inverse
relation between the pulsation and modulation periods of RV UMa.Comment: 4 pages, 5 figures, accepted for publication in A
More frequencies of KUV 02464+3239

Preliminary results on KUV 02464+3239, a pulsating DA white dwarf are
presented. Located near the red edge of the DAV instability strip, KUV
02464+3239 shows large amplitude and long period pulsation modes. Up to now
only one mode was known from a 50-minute-long light curve. Our more extended
observations allowed the identification of three additional frequencies. The
presence of previously known harmonics were confirmed and weak subharmonics are
also noticeable at some parts of the light curve. This suggests the dominance
of nonlinear pulsation effects from time to time.Comment: 3 pages, 3 eps figures; has been accepted for publication in
  Astronomische Nachrichten (Vol. 8, 2007), proceedings of the
  British-Hungarian-French N+N+N Workshop for Young Researcher
J1128+592: a highly variable IDV source

Short time-scale radio variations of compact extragalactic radio quasars and
blazars known as IntraDay Variability (IDV) can be explained in at least some
sources as a propagation effect; the variations are interpreted as
scintillation of radio waves in the turbulent interstellar medium of the Milky
Way. One of the most convincing observational arguments in favor of a
propagation-induced variability scenario is the observed annual modulation in
the characteristic time scale of the variation due to the Earth's orbital
motion. So far there are only two sources known with a well-constrained
seasonal cycle. Annual modulation has been proposed for a few other less
well-documented objects. However, for some other IDV sources source-intrinsic
structural variations which cause drastic changes in the variability time scale
were also suggested. J1128+592 is a recently discovered, highly variable IDV
source. Previous, densely time-sampled flux-density measurements with the
Effelsberg 100-m radio telescope (Germany) and the Urumqi 25-m radio telescope
(China), strongly indicate an annual modulation of the time scale. The most
recent 4 observations in 2006/7, however, do not fit well to the annual
modulation model proposed before. In this paper, we investigate a possible
explanation of this discrepancy.Comment: 5 pages, to be appear in the Astronomische Nachrichten as part of the
  conference proceeding of the N+N+N 2007 Workshop for Young Researche
Radial velocities of five globular clusters obtained with AAOmega

Using the recently commissioned multi-object spectrograph AAOmega on the 3.9m
AAT we have obtained medium-resolution near-infrared spectra for 10,500 stars
in and around five southern globular clusters. The targets were 47 Tuc, M12,
M30, M55 and NGC 288. We have measured radial velocities to +/- 1 km/s with the
cross correlation method and estimated metallicity, effective temperature,
surface gra vity and rotational velocity for each star by fitting synthetic
model spectra. An analysis of the velocity maps and velocity dispersion of
member stars revealed systemic rotation in four of the target clusters.Comment: 4 pages, 6 figures, accepted for publication by Astronomische
  Nachrichte
Front- vs. back-illuminated CCD cameras for photometric surveys: a noise
  budget analysis

Exoplanetary transit and stellar oscillation surveys require a very high
precision photometry. The instrumental noise has therefore to be minimized.
First, we perform a semi-analytical model of different noise sources. We show
that the noise due the CCD electrodes can be overcome using a Gaussian PSF
(Point Spread Function) of full width half maximum larger than 1.6 pixels. We
also find that for a PSF size of a few pixels, the photometric aperture has to
be at least 2.5 times larger than the PSF full width half maximum. Then, we
compare a front- with a back-illuminated CCD through a Monte-Carlo simulation.
Both cameras give the same results for a PSF full width half maximum larger
than 1.5 pixels. All these simulations are applied to the A STEP (Antarctica
Search for Transiting Extrasolar Planets) project. As a result, we choose a
front-illuminated camera for A STEP because of its better resolution and lower
price, and we will use a PSF larger than 1.6 pixels
Recent photometry of symbiotic stars - XII

We present new photometric observations of 15 symbiotic stars (EG And, Z And,
AE Ara, BF Cyg, CH Cyg, CI Cyg, V1329 Cyg, TX CVn, AG Dra, Draco C-1, RW Hya,
SY Mus, AR Pav, AG Peg, AX Per) covering their last orbital cycle(s) from
2003.9 to 2007.2. We obtained our data by both classical photoelectric and CCD
photometry. Main results are: EG And brightened by about 0.3 mag in U from
2003. A 0.5 mag deep primary minimum developed in the U light curve (LC) at the
end of 2006. Z And continues its recent activity that began during the 2000
autumn. A new small outburst started in summer of 2004 with the peak
U-magnitude of about 9.2. During the spring of 2006 the star entered a massive
outburst. It reached its historical maximum at U = 8.0 in 2006 July. AE Ara
erupted in 2006 February with Dm(vis) approx. 1.2 mag. BF Cyg entered a new
active stage in 2006 August. A brightness maximum (U approx. 9.4) was measured
during 2006 September. CH Cyg persists in a quiescent phase. During 2006 June -
December about 2 mag decline in all colours was measured. CI Cyg started a new
active phase during 2006 May - June. After 31 years it erupted by about 2 mag
in U. TX CVn maintains a bright stage with U approx. 10.5 from 2003. AG Dra
entered a new major outburst in 2006 June. It reached its maximum at U = 8.0 in
2006 September. AR Pav persists at a low level of the activity. AG Peg's LC
profile varies markedly during different orbital cycles. AX Per continues its
quiescent phase.Comment: 4 pages text, 12 figures, 18 tables, accepted for publication in
  Astron. Nachrichte
On the Distance to the Ophiuchus Star-Forming Region

The Ophiuchus molecular cloud complex has produced in Lynds 1688 the richest
known embedded cluster within ~300 pc of the Sun. Unfortunately, distance
estimates to the Oph complex vary by nearly ~40% (~120-165 pc). Here I
calculate a new independent distance estimate of 135 +- 8 pc to this benchmark
star-forming region based on Hipparcos trigonometric parallaxes to stars
illuminating reflection nebulosity in close proximity to Lynds 1688. Combining
this value with recent distance estimates from reddening studies suggests a
consensus distance of 139 +- 6 pc (4% error), situating it within ~11 pc of the
centroid of the ~5 Myr old Upper Sco OB subgroup of Sco OB2 (145 pc). The
velocity vectors for Oph and Upper Sco are statistically indistinguishable
within ~1 km/s in each vector component. Both Oph and Upper Sco have negligible
motion (<1 km/s) in the Galactic vertical direction with respect to the Local
Standard of Rest, which is inconsistent with the young stellar groups having
formed via the high velocity cloud impact scenario.Comment: to appear in Jan 2008 AN (5 pages), note added in proof regarding new
  distance estimate (131+-3 pc) using revised Hipparcos parallaxe
Modelling the time variation of the surface differential rotation in AB
  Doradus and LQ Hydrae

Sequences of Doppler images of the young, rapidly rotating late-type stars AB
Dor and LQ Hya show that their equatorial angular velocity and the amplitude of
their surface differential rotation vary versus time. Such variations can be
modelled to obtain information on the intensity of the azimuthal magnetic
stresses within stellar convection zones. We introduce a simple model in the
framework of the mean-field theory and discuss briefly the results of its
application to those solar-like stars.Comment: 4 pages, 1 figures, accepted by Astronomical Notes (Astronomische
  Nachrichten
Differential rotation and meridional circulation in global models of
  solar convection

In the outer envelope of the Sun and in other stars, differential rotation
and meridional circulation are maintained via the redistribution of momentum
and energy by convective motions. In order to properly capture such processes
in a numerical model, the correct spherical geometry is essential. In this
paper I review recent insights into the maintenance of mean flows in the solar
interior obtained from high-resolution simulations of solar convection in
rotating spherical shells. The Coriolis force induces a Reynolds stress which
transports angular momentum equatorward and also yields latitudinal variations
in the convective heat flux. Meridional circulations induced by baroclinicity
and rotational shear further redistribute angular momentum and alter the mean
stratification. This gives rise to a complex nonlinear interplay between
turbulent convection, differential rotation, meridional circulation, and the
mean specific entropy profile. I will describe how this drama plays out in our
simulations as well as in solar and stellar convection zones.Comment: 5 pages, 2 figures (one color
Magnetic field evolution in neutron stars

Neutron stars contain persistent, ordered magnetic fields that are the
strongest known in the Universe. However, their magnetic fluxes are similar to
those in magnetic A and B stars and white dwarfs, suggesting that flux
conservation during gravitational collapse may play an important role in
establishing the field, although it might also be modified substantially by
early convection, differential rotation, and magnetic instabilities. The
equilibrium field configuration, established within hours (at most) of the
formation of the star, is likely to be roughly axisymmetric, involving both
poloidal and toroidal components. The stable stratification of the neutron star
matter (due to its radial composition gradient) probably plays a crucial role
in holding this magnetic structure inside the star. The field can evolve on
long time scales by processes that overcome the stable stratification, such as
weak interactions changing the relative abundances and ambipolar diffusion of
charged particles with respect to neutrons. These processes become more
effective for stronger magnetic fields, thus naturally explaining the magnetic
energy dissipation expected in magnetars, at the same time as the longer-lived,
weaker fields in classical and millisecond pulsars.Comment: To appear in Astronomische Nachrichten (Astronomical Notes) as part
  of the Proceedings of the 5th Potsdam Thinkshop, "Meridional Circulation,
  Differential Rotation, Solar and Stellar Activity", held 2007 June 24-29. 5
  pages, no figure
Differential Rotation in F Stars

Differential rotation can be detected in single line profiles of stars
rotating more rapidly than about $v \sin{i} = 10$ km s$^{-1}$ with the Fourier
transform technique. This allows to search for differential rotation in large
samples to look for correlations between differential rotation and other
stellar parameters. I analyze the fraction of differentially rotating stars as
a function of color, rotation, and activity in a large sample of F-type stars.
Color and rotation exhibit a correlation with differential rotation in the
sense that more stars are rotating differentially in the cooler, less rapidly
rotating stars. Effects of rotation and color, however, cannot be disentangled
in the underlying sample. No trend with activity is found.Comment: 4 pages, overview talk at the 5th Potsdam thinkshop, accepted by A
Ultra-Cool and Extra-Vigorous: Rotation and Activity in M and L dwarfs

The study of rotation and activity in low-mass stars or brown dwarfs of
spectral classes M and L has seen enormous progress during the last years. I
summarize the results from different works that measured activity, rotation,
and sometimes magnetic fields. The generation of magnetic activity seems to be
unchanged at the threshold to completely convective stars, i.e. no change in
the efficiency of the magnetic dynamos is observed. On the other hand, a sudden
change in the strength of rotational braking appears at the threshold mass to
full convection, and strong evidence exists for rotational braking weakening
with lower mass. A probable explanation is that the field topology changes from
dipolar to small scale structure as the objects become fully convective.Comment: 3 pages, talk given at the 5th Potsdam Thinkshop, accepted by A
Searching for the Missing Baryons in the Warm-Hot Intergalactic Medium

Proceedings of the "XMM-Newton: the next decade", to appear in Astronomische Nachrichten.At low redshift (z<2), almost half of the baryons in the Universe are not found in bound structures like galaxies and clusters and therefore most likely reside in a Warm-Hot Intergalactic Medium (WHIM), as predicted by simulations. Attempts to detect WHIM filaments at cosmological distances in absorption towards bright background sources have yielded controversial results that I review here. I argue that a secure detection of absorption features by the WHIM is at the limit of the XMM-Newton capabilities, but feasible. A proper characterisation of the whole WHIM belongs to the realm of future X-ray missions.Financial support for this work has been provided by the Spanish Ministry of Education and Science under project ESP2006-13608-C02-01.Peer reviewe
Using X-ray observations to identify the particle acceleration
  mechanisms in VHE SNRs and "dark" VHE sources

Very high energy (VHE) gamma-ray observations have proven to be very
successful in localizing Galactic acceleration sites of VHE particles.
Observations of shell-type supernova remnants have confirmed that particles are
accelerated to VHE energies in supernova blast waves; the interpretation of the
gamma-ray data in terms of hadronic or leptonic particle components in these
objects relies nevertheless strongly on input from X-ray observations. The
largest identified Galactic VHE source class consists of pulsar wind nebulae,
as detected in X-rays. Many of the remaining VHE sources remain however
unidentified until now. With X-ray observations of these enigmatic "dark"
objects one hopes to solve the following questions: What is the astrophysical
nature of these sources? Are they predominantly electron or hadron
accelerators? And what is their contribution to the overall cosmic ray energy
budget? The paper aims to provide an overview over the identification status of
the Galactic VHE source population.Comment: 4 pages, no figures, solicited talk at the conference "XMM-Newton:
  The Next Decade" held at ESAC (Villafranca del Castillo, Madrid, Spain), 4th
  - 6th June 200