pinecone/core-2020-05-10-deduplication huggingface dataset:
Helical Kink Instability in the confined Solar Eruption on 2002 May 27

This paper presents an improved MHD modeling of the confined filament
eruption in solar active region NOAA~9957 on 2002 May~27 by extending the
parametric studies of the event in Torok & Kliem 2005 and Hassanin & Kliem
2016. Here the initial flux rope equilibrium is chosen to possess a small apex
height identical to the observed initial filament height, which implies a more
realistic inclusion of the photospheric line tying. The model matches the
observations as closely as in the preceding studies, with the closest agreement
again being obtained for an initial average flux rope twist of about $4\pi$.
Thus, the model for strongly writhing confined solar eruptions, which assumes
that a kink-unstable flux rope in the stability domain of the torus instability
exists at the onset of the eruption's main acceleration phase, is further
substantiated.Comment: Astron. Nachr. (Astron. News; AN) 337, 1082, 201
Long-term variations in sunspot magnetic field - area relation

Using observations of sunspot magnetic field strengths (H) from the Crimean
Astrophysical Observatory (CrAO) and area (S) of sunspots from the Kislovodsk
Mountain Astronomical Station of Pulkovo Observatory, we investigate the
changes in the relation between H and S over the period of about two solar
cycles (1994-2013). The data were fitted by H = A + B log S, where A =
(778+/-46) and B = (778+/-25). We show that the correlation between H and S
varies with the phase of solar cycle, and $A$ coefficient decreases
significantly after year 2001, while B coefficient does not change
significantly. Furthermore, our data confirm the presence of two distinct
populations in distribution of sunspots (small sunspots with weaker field
strength and large sunspots with stronger field). We show that relative
contribution of each component to the distribution of sunspots by their area
changes with the phase of solar cycle and on longer-then-cycle periods. We
interpret these changes as a signature of a long-term (centennial) variations
in properties of sunspots.Comment: 8 pages, 7 figures, accepted for publication in Astron. Nachrichte
KIC011764567: An evolved object showing substantial flare-activity

We intensively studied the flare activity on the stellar object KIC011764567.
The star was thought to be solar type, with a temperature of $T_{eff} = (5640
\pm 200)\,$K, $\log(g) = (4.3 \pm 0.3)\,$dex and a rotational period of Prot 22
d (Brown et al. 2011). High resolution spectra turn the target to an evolved
object with Teff = (5300 \pm 150) K, a metalicity of $[m/H] = (-0.5 \pm 0.2)$,
a surface gravity of $log(g) = (3.3 \pm 0.4)\,$dex, and a projected rotational
velocity of $v sin i = (22 \pm 1)\,kms^{-1}$. Within an observing time span of
4 years we detected 150 flares in Kepler data in an energy range of $10^{36} -
10^{37}$ erg. From a dynamical Lomb-Scargle periodogram we have evidence for
differential rotation as well as for stellar spot evolution and migration.
Analysing the occurrence times of the flares we found hints for a periodic
flare frequency cycle of $430 - 460 $d, the significance increases with an
increasing threshold of the flares equivalent duration. One explanation is a
very short activity cycle of the star with that period. Another possibility,
also proposed by others in similar cases, is that the larger flares may be
triggered by external phenomena, such as magnetically interaction with an
unseen companion. Our high resolution spectra show that KIC011764567 is not a
short period binary star
Interpretation of the historic Yemeni reports of supernova SN 1006:
  early discovery in mid-April 1006 ?

The recently published Yemeni observing report about SN 1006 from al-Yamani
clearly gives AD 1006 Apr $17 \pm 2$ (mid-Rajab 396h) as first observation
date. Since this is about 1.5 weeks earlier than the otherwise earliest reports
(Apr 28 or 30) as discussed so far, we were motivated to investigate an early
sighting in more depth. We searched for additional evidences from other areas
like East Asia and Europe. We found that the date given by al-Yamani is fully
consistent with other evidence, including: (a) SN 1006 "rose several times half
an hour after sunset" (al-Yamani), which is correct for the location of Sana in
Yemen for the time around Apr 17, but it would not be correct for late Apr or
early May; (b) the date (3rd year, 3rd lunar month, 28th day wuzi, Ichidai
Yoki) for an observation of a guest star in Japan is inconsistent (there is no
day wuzi in that lunar month), but may be dated to Apr 16 by reading wuwu date
rather than a wuzi date; (c) there is observational evidence that SN 1006 was
observed in East Asia early or mid April; for the second half of April, a bad
weather (early monsoon) period is not unlikely -- there is a lack of night
reports; (d) the observer in St. Gallen reported to have seen SN 1006 "for
three months", which must have ended at the very latest on AD 1006 Jul 10,
given his northern location, so that his observations probably started in
April. We conclude that the correctly reported details give quite high
confidence in the fully self-consistent report of al-Yamani, so that the early
discovery date should be considered seriously.Comment: 11 pages, 2 figures, 1 table (in press) in Astronomical Notes 201
On a correlation among azimuthal velocities and the flyby anomaly sign

Data of six flybys, those of Galileo I, Galileo II, NEAR, Cassini, Rosetta
and Messenger were reported by Anderson et al \citep{Anderson}. Four of them:
Galileo I, NEAR, Rosetta and Messenger gain Newtonian energy during the flyby
transfer, while Galileo II and Cassini lose energy. This is, in both cases, a
surprising anomaly since Newtonian forces derive from a potential and they are,
therefore, conservative. We show here that the gravitational field of a
rotating planet as derived from a new model introduces a non conservative force
that gives a partial, but in our opinion satisfactory, explanation of these
anomalies and suggests a correlation between the sign of the anomaly and the
sign of the azimuthal velocity at perigee.Comment: 12 pages, 3 figure
An Arabic report about supernova SN 1006 by Ibn Sina (Avicenna)

We present here an Arabic report about supernova 1006 (SN 1006) written by
the famous Persian scholar Ibn Sina (Lat. Avicenna, AD 980-1037), which was not
discussed in astronomical literature before. The short observational report
about a new star is part of Ibn Sina's book called al-Shifa', a work about
philosophy including physics, astronomy, and meteorology. We present the Arabic
text and our English translation. After a detailed discussion of the dating of
the observation, we show that the text specifies that the transient celestial
object was stationary and/or tail-less ("a star among the stars"), that it
"remained for close to three months getting fainter and fainter until it
disappeared", that it "threw out sparks", i.e. it was scintillating and very
bright, and that the color changed with time. The information content is
consistent with the other Arabic and non-Arabic reports about SN 1006. Hence,
it is quite clear that Ibn Sina refers to SN 1006 in his report, given as an
example for transient celestial objects in a discussion of Aristotle's
"Meteorology". Given the wording and the description, e.g. for the color
evolution, this report is independent from other reports known so far.Comment: 7 pages with 1 figure, paper in press, Astronomical Notes 201
Hamburger Sternwarte plate archives: Historic long-term variability
  study of active galaxies based on digitized photographic plates

At the Hamburger Sternwarte an effort was started in 2010 with the aim of
digitizing its more than 45000 photographic plates and films stored in its
plate archives. At the time of writing, more than 31000 plates have already
been made available on the Internet for researchers, historians, as well as for
the interested public. The digitization process and the Internet presentation
of the plates and accompanying hand written material (plate envelopes,
logbooks, observer notes) are presented here. To fully exploit the unique
photometric and astrometric data, stored on the plates, further processing
steps are required including registering the plate to celestial coordinates,
masking of the plates, and a calibration of the photo-emulsion darkening curve.
To demonstrate the correct functioning of these procedures, historical light
curves of two bright BL Lac type active galactic nuclei are extracted. The
resulting light curve of the blazar 1ES 1215+303 exhibits a large decrease in
the magnitude from $14.25^{+0.07}_{-0.12}$ to $15.94^{+0.09}_{-0.13}$ in about
300 days, which proves the variability in the optical region. Furthermore, we
compare the measured magnitudes for the quasar 3C~273 with contemporaneous
measurements.Comment: Accepted in A
Time series analysis of long-term photometry of BM Canum Venaticorum

Studying RS CVn binaries is challenging, because in addition to spot
activity, other effects such as mass transfer between the components and
gravitational distortion of their spherical forms may distort their light
curves. Such effects can, however, be removed from the data by subtracting a
mean light curve phased with the orbital period. We study a quarter of a
century of standard Johnson differential V photometry of the RS CVn binary BM
CVn. Our main aims are to determine the activity cycles, the rate of surface
differential rotation and the rotation period of the active longitudes of BM
CVn. The Continuous Period Search (CPS) is applied to the photometry. The
changes of the mean and amplitude of the light curves are used to search for
activity cycles. The rotation period changes give an estimate of the rate of
surface differential rotation. The Kuiper method is applied to the epochs of
the primary and secondary minima to search for active longitudes. The
photometry reveals the presence of a stable mean light curve (MLC) connected to
the orbital period P_orb = 20d.6252 of this binary. We remove this MLC from the
original V magnitudes which gives us the corrected V' magnitudes. These two
samples of V and V' data are analysed separately with CPS. The fraction of
unreliable CPS models decreases when the MLC is removed. The same significant
activity cycle of approximately 12.5 years is detected in both V and V'
samples. The estimate for the surface differential rotation coefficient, k >=
0.10, is the same for both samples, but the number of unrealistic period
estimates decreases after removing the MLC. The same active longitude period of
P_al = 20d.511 +- 0d.005 is detected in the V and V' magnitudes. This long-term
regularity in the epochs of primary and secondary minima of the light curves is
not caused by the MLC. On the contrary, the MLC hampers the detection of active
longitudes.Comment: 11 pages, 13 figure
Affordable echelle spectroscopy of the eccentric HAT-P-2, WASP-14 and
  XO-3 planetary systems with a sub-meter-class telescope

A new off-shelf low-cost echelle spectrograph was installed recently on the
0.6m telescope at the Star\'a Lesn\'a Observatory (Slovakia). In this paper we
describe in details the radial velocity (RV) analysis of the first three
transiting planetary systems, HAT-P-2, WASP-14 and XO-3, observed with this
instrument. Furthermore, we compare our data with the RV data achieved with
echelle spectrographs of other sub-meter-, meter- and two-meter-class
telescopes in terms of their precision. Finally, we investigate the
applicability of our RV data for modeling orbital parameters.Comment: AN accepte
Study of the variability of Nova V5668 Sgr, based on high resolution
  spectroscopic monitoring

We present results of our dense spectroscopic monitoring of Nova V5668 Sgr.
Starting on March 19 in 2015, only a few days after discovery, we have obtained
a series of spectra with the TIGRE telescope and its HEROS echelle spectrograph
which offers a resolution of R = 20,000 and covers the optical wavelength range
from 3800 to 8800 {\AA}. We performed a line identification of the discernible
features for four spectra which are representative for the respective phases in
the light curve evolution of that nova. By simultaneously analysing the
variations in the visual light curve and the corresponding spectra of Nova
V5668 Sgr, we found that during the declining phases of the nova the absorption
features in all hydrogen and many other lines had shifted to higher expansion
velocities of -2000 km s^-1. Conversely, during the rise towards the following
maximum, these observed absorption features had returned to lower expansion
velocities.We found that the absorption features of some Fe II lines displayed
the same behaviour, but in addition disappeared for a few days during some
declining phases. Features of several N I lines also disappeared while new N II
lines appeared in emission for a few days during some of the declining phases
of the light curve of Nova V5668 Sgr. The shape of the emission features is
changing during the evolution and shows a clear double peak structure after the
deep minimum.Comment: 13 pages, 11 figures, accepted for publication in A
V-type Near-Earth asteroids: dynamics, close encounters and impacts with
  terrestrial planets

Asteroids colliding with planets vary in composition and taxonomical type.
Among Near-Earth Asteroids (NEAs) are the V-types, basaltic asteroids that are
classified via spectroscopic observations. In this work, we study the
probability of
  V-type NEAs colliding with Earth, Mars and Venus, as well as the Moon. We
perform a correlational analysis of possible craters produced by V-type NEAs.
To achieve this, we performed numerical simulations and statistical analysis of
close encounters and impacts between V-type NEAs and the terrestrial planets
over the next 10 Myr. We find that V-type NEAs can indeed have impacts with all
the planets, the Earth in particular, at an average rate of once per 12 Myr.
  There are four candidate craters on Earth that were likely caused by V-type
NEAs.Comment: The article has been accepted by "Astronomical Notes / Astronomische
  Nachrichten" 201
Another look at the size of the low-surface brightness galaxy VCC 1661
  in the Virgo Cluster

We present new wide-field images of the low-surface brightness Virgo Cluster
dwarf galaxy VCC 1661. The extant literature lists a broad range of radii for
this object, covering a factor of more than four, depending on the filters used
and the details of the analyses. While some studies find a radius typical of
other Virgo dwarfs and note the normality of this object, any larger spatial
extent, taken at face value, would render this galaxy the largest dwarf in the
Virgo Cluster samples. Confirmation of a large extent of dwarf galaxies has
often led to the discovery of tidal tails and would then, also in VCC 1661,
indicate a severe state of tidal disruption. Given the importance of galactic
sizes for assessing tidal interactions of the satellites with their hosts, we
thus combine our surface brightness profile with data from the literature to
investigate further the nature of this galaxy. However, our new characteristic
radius for VCC 1661 of $r_e=24.1$"$\pm7.7$" and the previously noted smooth
appearance of its isophotes are fully consistent with the remainder of the
ACSVCS dwarf galaxy population without any need to invoke tidal perturbations.Comment: 8 pages, 6 figures, accepted for publication in Astronomische
  Nachrichte
Climatological and UV-based Habitability of Possible Exomoons in F-star
  Systems

We explore the astrobiological significance of F-type stars of spectral type
between F5 V and F9.5 V, which possess Jupiter-type planets within or close to
their climatological habitable zones. These planets, or at least a subset of
those, may also possess rocky exomoons, which potentially offer habitable
environments. Our work considers eight selected systems. The Jupiter-type
planets in these systems are in notably differing orbits with eccentricities
between 0.08 (about Mars) and 0.72. We consider the stellar UV environments
provided by the photospheric stellar radiation, which allows us to compute the
UV habitable zones for the systems. Following previous studies, DNA is taken as
a proxy for carbon-based macromolecules following the paradigm that
extraterrestrial biology might be based on hydrocarbons. We found that the
damage inflicted on DNA is notably different for the range of systems studied,
and also varies according to the orbit of the Jupiter-type planet, especially
for systems of high ellipticity, as expected. For some systems excessive values
of damage are attained compared to today's Earth or during the Archean eon.
Considering that the detection of exomoons around different types of stars will
remain challenging in the foreseeable future, we view our work also as an
example and template for investigating the combined requirements of
climatological and UV-based habitability for exosolar objects.Comment: 38 pages, 8 figures, 5 tables; accepted by Astronomical Note
New Aspects of Photon Propagation in Expanding Universes

According to present cosmological views the energy density of CMB (Cosmic
Microwave Background) photons, freely propagating through the expanding cosmos,
varies proportional to 1/S^4 with S being the scale factor of the universe.
This behavior is expected, because General Theory of Relativity, in application
to FLRW- (Friedmann-Lemaitre-Robertson-Walker) cosmological universes, leads to
the conclusion that the photon wavelengths increase during their free passage
through the spacetime metrics of the universe by the same factor as does the
scale factor S. This appears to be a reasonable explanation for the presently
observed Planckian CMB spectrum with its actual temperature of about 2.7 K,
while at the time of its origin after the last scattering during the
recombination phase its temperature should have been about 3000 K, at an epoch
of about 380 ky after the Big Bang, when the scale of the universe S_r was
smaller by roughly a factor of S/S_r = 1+z_r = 1100 compared to the present
scale S = S_0 of the universe. In this paper we start from putting the question
whether the scale-behavior of the CMB energy density that enters the
energy-momentum tensor of the field equations describing the expanding universe
is really falling off like 1/S^4 and, if in fact a deviation from a behavior
according to 1/S^4 would occur, why do we nevertheless presently observe a CMB
energy density which appears to be in accordance with such a 1/S^4-scaling?
This question arises from another basic and fundamental question, namely: Can
we really assume that the wavelength of the freely propagating photon during
its travel all the way along its light geodetic is permanently affected by the
expansion of the universe, i.e continuously recognizes the expansion of the
cosmic scale S? With other words: Do freely propagating photons ........Comment: 6 page
A Dynamical Evolution Study of 40 2MASS Open Clusters

We investigate the dynamical evolution of 40 open clusters (OCs) by means of
their astrophysical parameters derived from field-decontaminated 2MASS
photometry. We find a bifurcation in the planes core radius vs. age and cluster
radius vs. age, in which part of the clusters appear to expand with time
probably due to the presence of stellar black holes while others seem to shrink
due to dynamical relaxation. Mass functions (MFs) are built for 3$/$4 of the
sample (31 OCs), which are used to search for indications of mass segregation
and external dynamical processes by means of relations among astrophysical,
structural and evolutionary parameters. We detect a flattening of MF slopes
ocurring at the evolutionary parameters $\tau_{core}\leq 32$ and
$\tau_{overall}\leq 30$, respectively. Within the uncertainties involved, the
overall MF slopes of 14 out of 31 OCs with $m_{overall} > 500~M_{\odot}$ are
consistent with Kroupa's initial mass function, implying little or no dynamical
evolution for these clusters. The remaining 17 OCs with MF slopes departing
from that of Kroupa show mild/large scale mass segregation due to dynamical
evolution.Comment: Accepted by AN. 48 pages, 36 figures and 11 table
Distinguishing between order and chaos in a simple barred galaxy model

We use a simple dynamical model in order to investigate the regular or
chaotic character of orbits in a barred galaxy with a central, spherically
symmetric, dense nucleus and a flat disk. In particular, we explore how the
total orbital energy influences the overall orbital structure of the system, by
computing in each case the percentage of regular, sticky and chaotic orbits. In
an attempt to distinguish safely and with certainty between ordered and chaotic
motion, we apply the Smaller ALingment Index (SALI) as a chaos detector to
extensive samples of orbits obtained by integrating numerically the basic
equations of motion as well as the variational equations. We integrate large
sets of initial conditions of orbits in several types of two dimensional planes
for better understanding of the orbital properties. Our numerical calculations
suggest, that the value of the energy has a huge impact on the percentages of
the orbits, thus indicating that a rotating barred galaxy is indeed a very
interesting stellar quantity.Comment: Published in Astronomische Nachrichten (AN) journal. arXiv admin
  note: previous papers with related context: arXiv:1506.01496,
  arXiv:1505.03968, arXiv:1502.02510, arXiv:1604.04622, arXiv:1604.0461
Chaos Control with Ion Propulsion

The escape dynamics around the triangular Lagrangian point L5 in the real
Sun-Earth-Moon-Spacecraft system is investigated. Appearance of the finite time
chaotic behaviour suggests that widely used methods and concepts of dynamical
system theory can be useful in constructing a desired mission design. Existing
chaos control methods are modified in such a way that we are able to protect a
test particle from escape. We introduce initial condition maps in order to have
a suitable numerical method to describe the motion in high dimensional phase
space. Results show that the structure of initial condition maps can be split
into two well-defined domains. One of these two parts has a regular contiguous
shape and is responsible for long time escape; it is a long-lived island. The
other one shows a filamentary fractal structure in initial condition maps. The
short time escape is governed by this object. This study focuses on a low-cost
method which successfully transfers a reference trajectory between these two
regions using an appropriate continuous control force. A comparison of the
Earth-Moon transfer is also presented to show the efficiency of our method.Comment: 14 pages, 11 figures, accepted for publication in Astronomische
  Nachrichte
Magnetic field gradient effects on the magnetorotational instability

The magnetorotational instability (MRI), also known as the Balbus -- Hawley
instability, is thought to have an important role on the initiation of
turbulence and angular momentum transport in accretion discs. In this work, we
investigate the effect of the magnetic field gradient in the azimuthal
direction on MRI. We solve the magnetohydrodynamic equations by including the
azimuthal component of the field gradient. We find the dispersion relation and
calculate the growth rates of the instability numerically. The inclusion of the
azimuthal magnetic field gradient produces a new unstable region on wavenumber
space. It also modifies the growth rate and the wavelength range of the
unstable mode: the higher the magnitude of the field gradient, the greater the
growth rate and the wider the unstable wavenumber range. Such a gradient in the
magnetic field may be important in T Tauri discs where the stellar magnetic
field has an axis which is misaligned with respect to the rotation axis of the
disc.Comment: 8 pages, 3 figures, accepted for publication in A