pinecone/core-2020-05-10-deduplication huggingface dataset:
V391 Peg: identification of the two main pulsation modes from ULTRACAM
  u'g'r' amplitudes

V391 Peg (HS2201+2610) is an extreme horizontal branch subdwarf B (sdB) star,
it is an hybrid pulsator showing p- and g-mode oscillations, and hosts a
3.2/sini M_Jup planet at an orbital distance of about 1.7 AU. In order to
improve the characterization of the star, we measured the pulsation amplitudes
in the u'g'r' SLOAN photometric bands using ULTRACAM at the William Herschel
4.2 m telescope and we compared them with theoretical values. The preliminary
results presented in this article conclusively show that the two main pulsation
periods at 349.5 and 354.1 s are a radial and a dipole mode respectively. This
is the first time that the degree index of multiple modes has been uniquely
identified for an sdB star as faint as V391 Peg (B=14.4), proving that
multicolor photometry is definitely an efficient technique to constrain mode
identification, provided that the data have a high enough quality.Comment: Proceedings of the 4th HELAS Conference (Lanzarote, 1-5 Feb. 2010),
  Astron. Nachrichten, in pres
P-modes in rapidly rotating stars -- looking for regular patterns in
  synthetic asymptotic spectra

According to a recent ray-based asymptotic theory, the high-frequency p-mode
spectrum of rapidly rotating stars is a superposition of frequency subsets
associated with dynamically independent regions of the ray-dynamics phase
space. At high rotation rates corresponding to typical $\delta$ Scuti stars,
two frequency subsets are expected to be visible : a regular frequency subset
described by a Tassoul like formula and an irregular frequency subset with
specific statistical properties. In this paper, we investigate whether the
regular patterns can be detected in the resulting spectrum. We compute the
autocorrelation function of synthetic spectra where the frequencies follow the
asymptotic theory, the relative amplitudes are simply given by the modes'
disk-averaging factors, and the frequency resolution is that of a CoRoT long
run. Our first results are that (i) the detection of regular patterns strongly
depends on the ratio of regular over irregular modes, (ii) low inclination
angle configurations are more favorable than near equator-on configurations,
(iii) in the absence of differential rotation, the $2 \Omega$ rotational
splitting between $m=1$ and $m=-1$ modes is an easy feature to detect.Comment: 4 pages, 4 figures, proceedings of the HELAS-IV International
  Conference, accepted for publication in Astronomische Nachrichte
Is macroturbulent broadening in OB Supergiants related to pulsations?

The spectrum of O and B Supergiants is known to be affected by an important
extra line-broadening (usually called macroturbulence) that adds to stellar
rotation. Recent analysis of high resolution spectra has shown that the
interpretation of this line-broadening as a consequence of large-scale
turbulent motions would imply highly super-sonic velocity fields, making this
scenario quite improbable. Stellar oscillations have been proposed as a likely
alternative explanation. We present first encouraging results of an
observational project aimed at investigating the $macroturbulent$ broadening in
O and B Supergiants, and its possible connection with spectroscopic variability
phenomena and stellar oscillations: a) all the studied B Supergiants show line
profile variations, quantified by means of the first (< v >) and third velocity
(< v^3 >) moments of the lines, b) there is a strong correlation between the
peak-to-peak amplitudes of the < v > and < v^3 > variability and the size of
the extra-broadening.Comment: 4 pages, 2 figures, 1 table. Proceeding of the IV Helas International
  Conference: "Seismological challeges for stellar structure". Editors:Teodoro
  Roca Cort\'es, Pere Pall\'e and Sebasti\'an Jim\'enez Reye
On the use of rotational splitting asymmetries to probe the internal
  rotation profile of stars. Application to $\beta$ Cephei stars

Rotationally-split modes can provide valuable information about the internal
rotation profile of stars. This has been used for years to infer the internal
rotation behavior of the Sun. The present work discusses the potential
additional information that rotationally splitting asymmetries may provide when
studying the internal rotation profile of stars. We present here some
preliminary results of a method, currently under development, which intends: 1)
to understand the variation of the rotational splitting asymmetries in terms of
physical processes acting on the angular momentum distribution in the stellar
interior, and 2) how this information can be used to better constrain the
internal rotation profile of the stars. The accomplishment of these two
objectives should allow us to better use asteroseismology as a test-bench of
the different theories describing the angular momentum distribution and
evolution in the stellar interiors.Comment: 4 pages, 2 figures; IV International Helas conference proceedings
  (refereed). To be published in Astronomical Note
Towards ensemble asteroseismology of the young open clusters Chi Persei
  and NGC 6910

As a result of the variability survey in Chi Persei and NGC6910, the number
of Beta Cep stars that are members of these two open clusters is increased to
twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational
properties, in particular the frequency spectra, of Beta Cep stars in both
clusters and explain the differences in terms of the global parameters of the
clusters. We also indicate that the more complicated pattern of the variability
among B type stars in Chi Persei is very likely caused by higher rotational
velocities of stars in this cluster. We conclude that the sample of pulsating
stars in the two open clusters constitutes a very good starting point for the
ensemble asteroseismology of Beta Cep-type stars and maybe also for other
B-type pulsators.Comment: 4 pages, Astronomische Nachrichten, HELAS IV Conference, Arecife,
  Lanzarote, Feb 2010, submitte
Challenges and Opportunities for Helio- and Asteroseismology

I consider some of the challenges and opportunities facing helio- and
asteroseismology, which reflect major themes of presentation and discussion
from the HELAS IV international conference "Seismological Challenges for
Stellar Structure". I concentrate in particular on the exciting prospects for
asteroseismology, now that the field is being provided with data of
unprecedented quality and in unprecedented volumes.Comment: Closing review, HELAS IV international conference "Seismological
  Challenges for Stellar Structure", accepted for publication in Astronomische
  Nachrichten (5 pages, no figures
Energy oscillations and a possible route to chaos in a modified Riga
  dynamo

Starting from the present version of the Riga dynamo experiment with its
rotating magnetic eigenfield dominated by a single frequency we ask for those
modifications of this set-up that would allow for a non-trivial magnetic field
behaviour in the saturation regime. Assuming an increased ratio of azimuthal to
axial flow velocity, we obtain energy oscillations with a frequency below the
eigenfrequency of the magnetic field. These new oscillations are identified as
magneto-inertial waves that result from a slight imbalance of Lorentz and
inertial forces. Increasing the azimuthal velocity further, or increasing the
total magnetic Reynolds number, we find transitions to a chaotic behaviour of
the dynamo.Comment: 8 pages, 8 figures, submitted to Astronomische Nachrichte
The shapes of light curves of Mira-type variables

Using a sample of 454 mira light curves from the ASAS survey we study the
shape of the light variations in this kind of variable stars. Opposite to
earlier studies, we choose a general approach to identify any deviation from a
sinusoidal light change. We find that about 30% of the studied light curves
show a significant deviation from the sinusoidal reference shape. Among these
stars two characteristic light curve shapes of comparable frequency could be
identified. Some hint for a connection between atmospheric chemistry and light
curve shape was found, but beside that no or only very weak relations between
light curve shape and other stellar parameters seem to exist.Comment: 7 pages, 7 figures, accepted for publication in A
A web-tool for population synthesis of near-by cooling neutron stars: An
  on-line test for cooling curves

We present a new web-tool - Net-PSICoNS - for population synthesis of
isolated near-by cooling neutron stars (NSs). The main aim is to provide an
easy test of models of the NS thermal evolution which can be used by groups
studying this subject. A user can upload cooling curves for a set of masses,
modify the mass spectrum if necessary, change radii to fit the EoS used for
cooling curve calculations, and then a population synthesis of close-by
isolated cooling NSs is performed. The output includes the Log N -- Log S
distribution confronted with the ROSAT observations and several other sets of
data. In this paper, we summarize the idea of the test proposed by Popov et al.
(2006), and present a user's manual for the web-tool.Comment: 6 pages, accepted to A
Dissipation in dynamos at low and high magnetic Prandtl numbers

Using simulations of helically driven turbulence, it is shown that the ratio
of kinetic to magnetic energy dissipation scales with the magnetic Prandtl
number in power law fashion with an exponent of approximately 0.6. Over six
orders of magnitude in the magnetic Prandtl number the magnetic field is found
to be sustained by large-scale dynamo action of alpha-squared type. This work
extends a similar finding for small magnetic Prandtl numbers to the regime of
large magnetic Prandtl numbers. At large magnetic Prandtl numbers, most of the
energy is dissipated viscously, lowering thus the amount of magnetic energy
dissipation, which means that simulations can be performed at magnetic Reynolds
numbers that are large compared to the usual limits imposed by a given
resolution. This is analogous to an earlier finding that at small magnetic
Prandtl numbers, most of the energy is dissipated resistively, lowering the
amount of kinetic energy dissipation, so simulations can then be performed at
much larger fluid Reynolds numbers than otherwise. The decrease in magnetic
energy dissipation at large magnetic Prandtl numbers is discussed in the
context of underluminous accretion found in some quasars.Comment: 6 pages, 4 figures, published in Astron.Nach
The kinematic characteristics of magnetic O-type stars

Although magnetic fields have been discovered in ten massive O-type stars
during the last years, the origin of their magnetic fields remains unknown.
Among the magnetic O-type stars, two stars, HD36879 and HD57682, were
identified as candidate runaway stars in the past, and theta^1 Ori C was
reported to move rapidly away from its host cluster. We search for an
explanation for the occurrence of magnetic fields in O-type stars by examining
the assumption of their runaway status. We use the currently best available
astrometric, spectroscopic, and photometric data to calculate the kinematical
status of seven magnetic O-type stars with previously unknown space velocities.
The results of the calculations of space velocities suggest that five out of
the seven magnetic O-type stars can be considered as candidate runaway stars.
Only two stars, HD155806 and HD164794, with the lowest space velocities, are
likely members of Sco OB4 and NGC6530, respectively. However, the non-thermal
radio emitter HD164794 is a binary system with colliding winds, for which the
detected magnetic field has probably a different origin in comparison to other
magnetic O-type stars.Comment: 5 pages, 2 tables, accepted for publication in Astronomische
  Nachrichte
Magnetic fields of Ap stars as a result of an instability

Ap star magnetism is often attributed to fossil magnetic fields which have
not changed much since the pre-main-sequence epoch of the stars. Stable
magnetic field configurations are known which could persist probably for the
entire main-sequence life of the star, but they may not show the complexity and
diversity exhibited by the Ap stars observed. We suggest that the Ap star
magnetism is not a result of stable configurations, but is the result of an
instability based on strong toroidal magnetic fields buried in the stars. The
highly nonaxisymmetric remainders of the instability are reminiscent of the
diversity of fields seen on Ap stars. The strengths of these remnant magnetic
fields is actually between a few per cent up to considerable fractions of the
internal toroidal field; this means field strengths of the order of kGauss
being compatible with what is observed. The magnetic fields emerge at the
surface rather quickly; rough estimates deliver time-scales of the order of a
few years. Since rotation stabilizes the instability, normal A stars may still
host considerable, invisible toroidal magnetic fields.Comment: 7 pages, 8 figures, submitted to Astron. Nachr., color figures at
  http://www.aip.de/People/rarlt/a
The Tayler instability of toroidal magnetic fields in a columnar gallium
  experiment

The nonaxisymmetric Tayler instability of toroidal magnetic fields due to
axial electric currents is studied for conducting incompressible fluids between
two coaxial cylinders without endplates. The inner cylinder is considered as so
thin that even the limit of R_in \to 0 can be computed. The magnetic Prandtl
number is varied over many orders of magnitudes but the azimuthal mode number
of the perturbations is fixed to m=1. In the linear approximation the critical
magnetic field amplitudes and the growth rates of the instability are
determined for both resting and rotating cylinders. Without rotation the
critical Hartmann numbers do {\em not} depend on the magnetic Prandtl number
but this is not true for the growth rates. For given product of viscosity and
magnetic diffusivity the growth rates for small and large magnetic Prandtl
number are much smaller than those for Pm=1. For gallium under the influence of
a magnetic field at the outer cylinder of 1 kG the resulting growth time is 5
s. The minimum electric current through a container of 10 cm diameter to excite
the kink-type instability is 3.20 kA. For a rotating container both the
critical magnetic field and the related growth times are larger than for the
resting column.Comment: 7 pages, 9 figures, submitted to Astron. Nach
Identifying star clusters in a field: A comparison of different
  algorithms

Star clusters are often hard to find, as they may lie in a dense field of
background objects or, because in the case of embedded clusters, they are
surrounded by a more dispersed population of young stars. This paper discusses
four algorithms that have been developed to identify clusters as stellar
density enhancements in a field, namely stellar density maps from star counts,
the neareast neighbour method and the Voronoi tessellation, and the separation
of minimum spanning trees. These methods are tested and compared to each other
by applying them to artificial clusters of different sizes and morphologies.
While distinct centrally concentrated clusters are detected by all methods,
clusters with low overdensity or highly hierarchical structure are only
reliably detected by methods with inherent smoothing (star counts and nearest
neighbour method). Furthermore, the algorithms differ strongly in computation
time and additional parameters they provide. Therefore, the method to choose
primarily depends on the size and character of the investigated area and the
purpose of the study.Comment: 13 pages, 7 tables, 6 figures; accepted by Astronomische Nachrichte
Hard and soft spectral states of ULXs

I discuss some differences between the observed spectral states of
ultraluminous X-ray sources (ULXs) and the canonical scheme of spectral states
defined in Galactic black holes. The standard interpretation of ULXs with a
curved spectrum, or a moderately steep power-law with soft excess and
high-energy downturn, is that they are an extension of the very high state, up
to luminosities ~ 1 to 3 L_{Edd}. Two competing models are Comptonization in a
warm corona, and slim disk; I suggest bulk motion Comptonization in the
radiatively-driven outflow as another possibility. The interpretation of ULXs
with a hard power-law spectrum is more problematic. Some of them remain in that
state over a large range of luminosities; others switch directly to a curved
state without going through a canonical high/soft state. I suggest that those
ULXs are in a high/hard state not seen in Galactic black holes; that state may
overlap with the low/hard state at lower accretion rates, and extend all the
way to Eddington accretion rates. If some black holes can reach Eddington
accretion rates without switching to a standard-disk-dominated state, it is
also possible that they never quench their steady jets.Comment: 6 pages, accepted for publication in the Astronomische Nachrichten,
  to appear in the proceedings of the conference "Ultra-Luminous X-ray sources
  and Middle Weight Black Holes" (Madrid, May 24-26, 2010
Six years of XMM-Newton observations of NGC 1313 X-1 and X-2

We present a systematic analysis of the X-ray spectra of NGC 1313 X-1 and NGC
1313 X-2, using six years of XMM-Newton observations (17 observations). We
fitted the continuum with a Comptonization model plus a multicolor blackbody
disc, that describes the effects of an accretion disc plus an optically thick
corona. We checked the consistency of this spectral model on the basis of the
variability patterns of its spectral parameters. We found that the two sources
show different spectral states. We tentatively interpret the observed behaviour
of NGC 1313 X-1 within the framework of super-Eddington accretion and that of
NGC 1313 X-2 within the framework of near Eddington accretion. We also
attempted to determine the chemical abundances in the local environment of NGC
1313 X-1 and X-2, analyzing the RGS spectra of the longest observation
available (122 ksec). The results appear to indicate solar metallicity for the
local environment of NGC 1313 X-1 and sub-solar metallicity for NGC 1313 X-2.Comment: 5 pages, 6 figures. Accepted for publication in the Astronomische
  Nachrichten (Astronomical Notes), to appear in the proceedings of the
  conference "Ultra-Luminous X-ray sources and Middle Weight Black Holes"
  (Madrid, May 24-26, 2010
The collective X-ray luminosity of HMXB as a SFR indicator

We study the relation between the X-ray luminosity of compact sources and the
SFR of the host galaxy. Our sample includes 38 galaxies for which a uniform set
of X-ray, infra-red and ultraviolet data from Chandra, Spitzer and GALEX has
been collected. Our primary goals are (i) to obtain a more accurate calibration
of the Lx-SFR relation and (ii) to understand the origin of the dispersion in
the Lx-SFR relation observed in previous studies. Preliminary results of this
project are reported below.Comment: 4 pages, 2 figures, accepted for publication in the Astronomische
  Nachrichten, to appear in the proceedings of the conference "Ultra-Luminous
  X-ray sources and Middle Weight Black Holes" (Madrid, May 24-26, 2010
A Large Catalogue of Ultraluminous X-ray Source Candidates in Nearby
  Galaxies

Since their discovery, Ultraluminous X-ray sources (ULXs) have attracted
attention due to their combination of extreme luminosities and extra-nuclear
locations. However, they are a fairly rare phenomenon, and attempts to
investigate the general properties of the population have been hindered by a
relative lack of known sources. Here, we present a large catalogue of ULX
candidates including 655 detections of 475 discrete sources, based on the 2XMM
Serendipitous Survey. To demonstrate the potential of such a resource, we
present some scientific analysis of this population, focusing on the spectral
turnover seen, often at ~6 keV, in the highest quality ULX data. We also
demonstrate how the recent reflection and Comptonisation interpretations of
this feature may be distinguished observationally in the future, specifically
using NGC 4517 ULX1, a previously unanalysed source with high quality data, as
an example case.Comment: 4 pages, accepted for publication in the Astronomische Nachrichten,
  to appear in the proceedings of the conference "Ultra-Luminous X-ray sources
  and Middle Weight Black Holes" (Madrid, May 24-26, 2010
The population of ULXs in the spiral galaxy NGC 2276

We present results for X-ray point sources in the Sc galaxy NGC 2276,
obtained by analyzing Chandra data. The galaxy is known to be very active in
many wavelengths, possibly due to gravitational interaction with the central
elliptical of the group, NGC 2300. However, previous XMM-Newton observations
resulted in the detection of only one bright ULX and extended hot gas emission.
We present here the X-ray population in NGC 2276 which comprises 17 sources. We
found that 6 of them are new ULX sources in this spiral galaxy resolved for the
first time by Chandra. We constructed the Luminosity Function that can be
interpreted as mainly due of High Mass X-ray binaries, and estimate the Star
Formation rate (SFR) to be SFR ~ 5-10 M_sun/yr.Comment: 4 pages, 4 figures, Proceedings of the meeting 'Ultra-Luminous X-ray
  sources and Middle Weight Black Holes', ESAC, Madrid, Spain, May 201
The supergiant optical counterpart of ULX P13 in NGC7793

We have identified the optical counterpart of the ULX source P13 in the
nearby spiral galaxy NGC 7793. The object is a V ~ 20.5 mag star, ten times
brighter than any other established counterpart of a ULX in nearby galaxies.
Medium resolution optical spectroscopy carried out in 2008 and 2009 with the
ESO-VLT reveals the presence of narrow high order Balmer, HeI and MgII
absorption lines indicating a late B type supergiant companion star with mass
between 10 and 20 Msol. Stellar H beta and HeII 4686 emission lines are also
seen superposed on the photospheric spectrum. We detect different patterns of
radial velocity variations from the emission and absorption lines over a time
interval of one month. The velocity of the high order Balmer absorption lines
changes by ~ 100 km/s while the H beta and HeI 4686 emission components vary by
about the same amount but with a different phasing. Assuming that the observed
velocity changes trace the motion of the mass-donor star and of the X-ray
source implies a mass of the accreting black hole in the range of 3 to 100 Msol
with a most probable value of ~ 10 to 20 Msol. We expect an orbital period in
the range of 20 to 40 days based on the low density of the supergiant star. P13
is likely in a short-lived, and thus rare high X-ray luminosity evolutionary
state associated with the ascension of the donor star onto the supergiant
stage.Comment: 4 pages, 5 figures, accepted for publication in the Astronomische
  Nachrichten, to appear in the proceedings of the conference "Ultra-Luminous
  X-ray sources and Middle Weight Black Holes" (Madrid, May 24-26, 2010
Optical variability of the ultraluminous X-ray source NGC 1313 X-2

We analyzed the longest phase-connected photometric dataset available for NGC
1313 X-2, looking for the ~6 day modulation reported by Liu et al. (2009). The
folded B band light curve shows a 6 days periodicity with a significance
slightly larger than 3 sigma. The low statistical significance of this
modulation, along with the lack of detection in the V band, make its
identification uncertain.Comment: 4 pages, 2 figures. Accepted for publication in the Astronomische
  Nachrichten (Astronomical Notes), to appear in the proceedings of the
  conference "Ultra-Luminous X-ray sources and Middle Weight Black Holes"
  (Madrid, May 24-26, 2010