pinecone/core-2020-05-10-deduplication huggingface dataset:
Instrument and data analysis challenges for imaging spectropolarimetry

The next generation of solar telescopes will enable us to resolve the
fundamental scales of the solar atmosphere, i.e., the pressure scale height and
the photon mean free path. High-resolution observations of small-scale
structures with sizes down to 50 km require complex post-focus instruments,
which employ adaptive optics (AO) and benefit from advanced image restoration
techniques. The GREGOR Fabry-Perot Interferometer (GFPI) will serve as an
example of such an instrument to illustrate the challenges that are to be
expected in instrumentation and data analysis with the next generation of solar
telescopes.Comment: 4 pages, 1 figure, accepted for publication in Astronomische
  Nachrichten/AN, special issue of the 1st EAST-ATST Workshop: "Science with
  large solar telescopes" in Freiburg, Germany, October 14-16, 200
Transformations between 2MASS, SDSS and BVI photometric systems for
  late-type giants

We present colour transformations from Two Micron All Sky Survey (2MASS)
photometric system to Johnson-Cousins system and to Sloan Digital Sky Survey
(SDSS) system for late-type giants and vice versa. The giant star sample was
formed using surface gravity constraints ($2 < \log g \leq 3$) to Cayrel de
Strobel et al.\rq s (2001) spectroscopic catalogue. 2MASS, SDSS and
Johnson-Cousins photometric data was taken from Cutri et al. (2003), Ofek
(2008) and van Leeuwen (2007), respectively. The final sample was refined
applying the following steps: (1) the data were dereddened, (2) the sample
stars selected are of the highest photometric quality. We give two--colour
dependent transformations as a function of metallicity as well as independent
of metallicity. The transformations provide absolute magnitudes and distance
determinations which can be used in space density evaluations at relatively
short distances where some or all of the SDSS magnitudes of late-type giants
are saturated.Comment: The variables and "f" parameters in the equations 15-17 and 27-29
  were change
Photometric and spectroscopic observations of three rapidly rotating
  late-type stars: EY Dra, V374 Peg and GSC 02038-00293

Here, BV(RI)c broad band photometry and intermediate resolution spectroscopy
in Halpha region are presented for two rapidly rotating late-type stars: EY Dra
and V374 Peg. For a third rapid rotator, GSC 02038-00293, intermediate
resolution Halpha spectroscopy and low resolution spectroscopy are used for
spectral classification and stellar parameter investigation of this poorly
known object. The low resolution spectrum of GSC 02038-00293 clearly indicates
that it is a K-type star. Its intermediate resolution spectrum can be best
fitted with a model with Teff=4750K and vsini=90km/s, indicating a very rapidly
rotating mid-K star. The Halpha line strength is variable, indicating changing
chromospheric emission on GSC 02038-00293. In the case of EY Dra and V374 Peg,
the stellar activity in the photosphere is investigated from the photometric
observations, and in the chromosphere from the Halpha line. The enhanced
chromospheric emission in EY Dra correlates well with the location of the
photospheric active regions, indicating that these features are spatially
collocated. Hints of this behaviour are also seen in V374 Peg, but it cannot be
confirmed from the current data. The photospheric activity patterns in EY Dra
are stable during one observing run lasting several nights, whereas in V374 Peg
large night-to-night variations are seen. Two large flares, one in the Halpha
observations and one from the broadband photometry, and twelve smaller ones
were detected in V374 Peg during the observations spanning nine nights. The
energy of the photometrically detected largest flare is estimated to be
4.25x10^31 - 4.3x10^32 ergs, depending on the waveband. Comparing the activity
patterns in these two stars, which are just below and above the mass limit of
full convection, is crucial for understanding dynamo operation in stars with
different internal structures.Comment: Accepted for publication in Astronomische Nachrichten (Astronomical
  Notes
Secular variation of hemispheric phase differences in the solar cycle

We investigate the phase difference of the sunspot cycles in the two
hemispheres and compare it with the latitudinal sunspot distribution. If the
north-south phase difference exhibits a long-term tendency, it should not be
regarded as a stochastic phenomenon.
  We use datasets of historical sunspot records and drawings made by
Staudacher, Hamilton, Gimingham, Carrington, Spouml;rer, and Greenwich
observers, as well as the sunspot activity during the Maunder minimum
reconstructed by Ribes and Nesme-Ribes.
  We employ cross-recurrence plots to analyse north-south phase differences. We
show that during the last 300 years, the persistence of phase-leading in one of
the hemispheres exhibits a secular variation. Changes from one hemisphere to
the other leading in phase were registered near 1928 and 1968 as well as two
historical ones near 1783 and 1875.
  A long-term anticorrelation between the hemispheric phase differences in the
sunspot cycles and the latitudinal distribution of sunspots was traced since
1750.Comment: 7 pages, 4 figure
Seismological challenges for stellar structure

Helioseismology has provided very detailed information about the solar
interior, and extensive data on a large number of stars, although at less
detail, are promised by the ongoing and upcoming asteroseismic projects. In the
solar case there remain serious challenges in understanding the inferred solar
structure, particularly in the light of the revised determinations of the solar
surface composition. Also, a secure understanding of the origins of solar
rotation as inferred from helioseismology, both in the radiative interior and
in the convection zone, is still missing. In the stellar case challenges are
certain to appear as the data allow more detailed inferences of the properties
of stellar cores. Large remaining uncertainties in modelling concerns the
properties of convective cores and other processes that may cause mixing. As a
result of developing asteroseismic signatures addressing these and other
issues, we can look forward to a highly challenging, and hence exciting, era of
stellar astrophysics.Comment: Proc. HELAS IV Conference, Lanzarote, January 2010. Eds T. Roca
  Cort\'es, P. Pall\'e and S. Jim\'enez Reyes. To appear in Astron. Nach
Local helioseismology and the active Sun

The goal of local helioseismology is to elicit three-dimensional information
about the sub-surface (or far-side) structure and dynamics of the Sun from
observations of the helioseismic wave field at the surface. The physical
quantities of interest include flows, sound-speed deviations and magnetic
fields. However, strong surface magnetic fields induce large perturbations to
the waves making inversions difficult to interpret. The purpose of this paper
is to outline the methods of analysis used in local helioseismology, review
discoveries associated with the magnetic Sun made using local helioseismology
from the past three years, and highlight the efforts towards imaging the
interior in the presence of strong magnetic fields.Comment: 6 pages, 4th HELAS International Conference, Lanzarote, Spain, 1-5
  February 201
A new code for Fourier-Legendre analysis of large datasets: first
  results and a comparison with ring-diagram analysis

Fourier-Legendre decomposition (FLD) of solar Doppler imaging data is a
promising method to estimate the sub-surface solar meridional flow. FLD is
sensible to low-degree oscillation modes and thus has the potential to probe
the deep meridional flow. We present a newly developed code to be used for
large scale FLD analysis of helioseismic data as provided by the Global
Oscillation Network Group (GONG), the Michelson Doppler Imager (MDI)
instrument, and the upcoming Helioseismic and Magnetic Imager (HMI) instrument.
First results obtained with the new code are qualitatively comparable to those
obtained from ring-diagram analyis of the same time series.Comment: 4 pages, 2 figures, 4th HELAS International Conference "Seismological
  Challenges for Stellar Structure", 1-5 February 2010, Arrecife, Lanzarote
  (Canary Islands
Magneto-acoustic wave propagation and mode conversion in a magnetic
  solar atmosphere: comparing results from the CO5BOLD code with ray theory

We present simulations of magneto-acoustic wave propagation in a magnetic,
plane-parallel stratified solar model atmosphere, employing the CO5BOLD-code.
The tests are carried out for two models of the solar atmosphere, which are
similar to the ones used by Cally (2007) and Schunker & Cally (2006). The two
models differ only in the orientation of the magnetic field. A qualitative
comparison shows good agreement between the numerical results and the results
from ray theory. The tests are done in view of the application of the present
numerical code for the computation of energy fluxes of propagating acoustic
waves into a dynamically evolving magnetic solar atmosphere. For this, we
consider waves with frequencies above the acoustic cut-off frequency.Comment: 4 pages, 4 figures, will appear in HELAS-IV Conference Proceedin
Constraints on the core mu-gradient of the solar-like star HD 49385 via
  low-degree mixed modes

The existence of an l=1 avoided crossing in the spectrum of the solar-like
pulsator CoRoT-target HD 49385 was established by Deheuvels & Michel (2009). It
is the first confirmed detection of such a phenomenon. The authors showed in a
preliminary modeling of the star that it was in a post main sequence status.
Being a 1.3 Msun-star, HD 49385 has had a convective core during its main
sequence phase. The mu-gradient left by the withdrawal of this core bears
information about the processes of transport at the boundary of the core. We
here investigate the constraints that the observed avoided crossing brings on
the mu-gradient in the core of the star.Comment: 5 pages, 5 figures, accepted in Astron. Nach. This work was presented
  at the HELAS Conference in Lanzarote in February 201
Current methods for analyzing light curves of solar-like stars

CoRoT has allowed a quantitative leap for the solar-like-star seismology
thanks to 5-month-long uninterrupted timeseries of high-precision photometric
data. Kepler is also starting to deliver similar data. Now, several F and G
main-sequence stars have been analyzed. The techniques developed to interpret
light curves directly inherit from the experience got on the Sun with
helioseismology. I describe in this review the methods currently used to
analyze these light curves. First, these data provide an accurate determination
of the stellar rotation rate. This is possible thanks to the magnetic activity
of stars. The power spectra of light curves put also constraints on the stellar
granulation, which can be directly compared to 3-D stellar atmosphere models;
this shows still unexplained discrepancies. I then detailed a standard method
for extracting p-mode characteristics (frequency, amplitude and lifetime).
CoRoT has revealed unexpected short life times for F stars. Last, I also
discuss errors and biases of mode frequencies, especially the ones due to the
simplified description of the rotation generally used.Comment: 7 pages, 4 figures, invited review for the proceedings of the
  HELAS-IV International Conference, accepted for publication in Astronomische
  Nachrichte
Seismic signatures of stellar cores of solar-like pulsators: dependence
  on mass and age

Useful information from the inner layers of stellar pulsators may be derived
from the study of their oscillations. In this paper we analyse three diagnostic
tools suggested in the literature built from the oscillation frequencies
computed for a set of main sequence models with masses between $1.0\, {\rm
M}_{\odot}$ and $1.6\, {\rm M}_{\odot}$, to check what information they may
hold about stellar cores. For the models with convective cores ($M \geq
1.2\,{\rm M}_{\odot}$) we find a relation between the frequency slopes of the
diagnostic tools and the size of the jump in the sound speed at the edge of the
core. We show that this relation is independent of the mass of the models. In
practice, since the size of the jump in the sound speed is related to the age
of the star, using these seismic tools we may, in principle, infer the star's
evolutionary state. We also show that when combining two of the three
diagnostic tools studied, we are able to distinguish models with convective
cores from models without a convective core but with strong sound-speed
gradients in the inner layers
An alternative to mode fitting

The space mission CoRoT provides us with a large amount of high-duty cycle
long-duration observations. Mode fitting has proven to be efficient for the
complete and detailed analysis of the oscillation pattern, but remains time
consuming. Furthermore, the photometric background due to granulation severely
complicates the analysis. Therefore, we attempt to provide an alternative to
mode fitting, for the determination of large separations. With the envelope
autocorrelation function and a dedicated filter, it is possible to measure the
variation of the large separation independently for the ridges with even and
odd degrees. The method appears to be as accurate as the mode fitting. It can
be very easily implemented and is very rapid.Comment: Proceedings of the 4th HELAS International Conference held in
  Lanzarote, 201
Constraints of a pulsation frequency on stellar parameters in the
  eclipsing spectroscopic binary system: V577 Oph

We present a preliminary spectroscopic analysis of the binary system V577Oph,
observed during the summer of 2007 on the 2.6m NOT telescope on La Palma. We
have obtained time series spectroscopic observations, which show clear binary
motion as well as radial velocity variations due to pulsation in the primary
star. By modelling the radial velocities we determine a full orbital solution
of the system, which yields M_A sin^3 i = 1.562 +/- 0.012 M_solar and M_B sin^3
i = 1.461 +/- 0.020 M_solar. An estimate of inclination from photometry yields
a primary mass of 1.6 M_solar. Using this derived mass, and the known pulsation
frequency we can impose a lower limit of 1 Gyr on the age of the system, and
constrain the parameters of the oscillation mode. We show that with further
analysis of the spectra (extracting the atmospheric parameters), tighter
constraints could be imposed on the age, metallicity and the mode parameters.
This work emphasizes the power that a single pulsation frequency can have for
constraining stellar parameters in an eclipsing binary system.Comment: Accepted by A
The Kepler Asteroseismic Investigation: Scientific goals and the first
  results

Kepler is a NASA mission designed to detect exoplanets and characterize the
properties of exoplanetary systems. Kepler also includes an asteroseismic
programme which is being conducted through the Kepler Asteroseismic Science
Consortium (KASC), whose 400 members are organized into 13 working groups by
type of variable star. So far data have been available from the first 7 month
of the mission containing a total of 2937 targets observed at a 1-min. cadence
for periods between 10 days and 7 months. The goals of the asteroseismic part
of the Kepler project is to perform detailed studies of stellar interiors. The
first results of the asteroseismic analysis are orders of magnitude better than
seen before, and this bodes well for how the future analysis of Kepler data for
many types of stars will impact our general understanding of stellar structure
and evolution.Comment: Proc. HELAS IV Conference, Lanzarote, January 2010. Eds T. Roca
  Cort\'es, P. Pall\'e and S. Jim\'enez Reyes. To appear in Astron. Nach
Asteroseismology of Solar-type Stars with Kepler I: Data Analysis

We report on the first asteroseismic analysis of solar-type stars observed by
Kepler. Observations of three G-type stars, made at one-minute cadence during
the first 33.5d of science operations, reveal high signal-to-noise solar-like
oscillation spectra in all three stars: About 20 modes of oscillation can
clearly be distinguished in each star. We discuss the appearance of the
oscillation spectra, including the presence of a possible signature of faculae,
and the presence of mixed modes in one of the three stars.Comment: 5 pages, 4 figure, submitted to Astronomische Nachrichte
Asteroseismology of Solar-type stars with Kepler II: Stellar Modeling

Observations from the Kepler satellite were recently published for three
bright G-type stars, which were monitored during the first 33.5d of science
operations. One of these stars, KIC 11026764, exhibits a characteristic pattern
of oscillation frequencies suggesting that the star has evolved significantly.
We have derived initial estimates of the properties of KIC 11026764 from the
oscillation frequencies observed by Kepler, combined with ground-based
spectroscopic data. We present preliminary results from detailed modeling of
this star, employing a variety of independent codes and analyses that attempt
to match the asteroseismic and spectroscopic constraints simultaneously.Comment: 4 pages, 3 figures, 1 table, Astronomische Nachrichte
Asteroseismology of Solar-type stars with Kepler III. Ground-based Data

We report on the ground-based follow-up program of spectroscopic and
photometric observations of solar-like asteroseismic targets for the Kepler
space mission. These stars constitute a large group of more than thousand
objects which are the subject of an intensive study of the Kepler Asteroseismic
Science Consortium Working Group 1 (KASC WG-1). The main goal of this
coordinated research is the determination of the fundamental stellar
atmospheric parameters, which are used for the computing of their asteroseismic
models, as well as for the verification of the Kepler Input Catalogue (KIC).Comment: 4 pages, 2 figures, 1 tabl
Ground-based follow-up in relation to Kepler Asteroseismic Investigation

The Kepler space mission, successfully launched in March 2009, is providing
continuous, high-precision photometry of thousands of stars simultaneously. The
uninterrupted time-series of stars of all known pulsation types are a precious
source for asteroseismic studies. The Kepler data do not provide information on
the physical parameters, such as effective temperature, surface gravity,
metallicity, and vsini, which are crucial for successful asteroseismic
modelling. Additional ground-based time-series data are needed to characterize
mode parameters in several types of pulsating stars. Therefore, ground-based
multi-colour photometry and mid/high-resolution spectroscopy are needed to
complement the space data. We present ground-based activities within KASC on
selected asteroseismic Kepler targets of several pulsation types.
  (Based on observations made with the Isaac Newton Telescope, William Herschel
Telescope, Nordic Optical Telescope, Telescopio Nazionale Galileo, Mercator
Telescope (La Palma, Spain), and IAC-80 (Tenerife, Spain). Also based on
observations taken at the observatories of Sierra Nevada, San Pedro Martir,
Vienna, Xinglong, Apache Point, Lulin, Tautenburg, Loiano, Serra la Nave,
Asiago, McDonald, Skinakas, Pic du Midi, Mauna Kea, Steward Observatory, Mt
Wilson, Bialkow Observatory of the Wroclaw University, Piszkesteto Mountain
Station, Observatoire de Haute Provence, and Centro Astronomico Hispano Aleman
at Calar Alto. Based on data from the AAVSO International Database.)Comment: 4 pages, 1 figure, Astronomische Nachrichten, HELASIV conference,
  Lanzarote, February 2010, submitte
Convection and oscillations

In this short review on stellar convection dynamics I address the following,
currently very topical, issues: (1) the surface effects of the Reynolds
stresses and nonadiabaticity on solar-like pulsation frequencies, and (2)
oscillation mode lifetimes of stochastically excited oscillations in red giants
computed with different time-dependent convection formulations.Comment: Accepted for publication in Astronomische Nachrichten, HELA IV
  proceedings, T. Roca Cort\'es, P. Pall\'e, S. Jim\'enez Reyes, eds, 7 figure
Observations and interpretation of solar-like oscillations in red-giant
  stars

Over the past decade the study of solar-like oscillations in red-giant stars
has developed significantly. Not only the number of red-giant stars for which
solar-like oscillations have been observed has increased, but the quality of
these observations has improved as well. These steps forward were possible
thanks to the development of instrumentation to measure radial velocity
variations with a precision of the order of m/s, as well as the launch of
dedicated space missions, which provide timeseries of data with unprecedented
photometric precision. Many more exciting discoveries are to be expected in the
(near) future. This article provides an overview of the development of the
field over the last decade, discusses difficulties encountered and overcome in
interpreting the observational data, and addresses some challenges and
opportunities for further research.Comment: 6 pages, 3 figures, invited review for the proceedings of the
  HELAS-IV International Conference, accepted for publication in Astronomische
  Nachrichte
Inference from adiabatic analysis of solar-like oscillations in Red
  giants

The clear detection with CoRoT and KEPLER of radial and non-radial solar-like
oscillations in many red giants paves the way to seismic inferences on the
structure of such stars. We present an overview of the properties of the
adiabatic frequencies and frequency separations of radial and non-radial
oscillation modes, highlighting how their detection allows a deeper insight
into the properties of the internal structure of red giants. In our study we
consider models of red giants in different evolutionary stages, as well as of
different masses and chemical composition. We describe how the large and small
separations computed with radial modes and with non-radial modes mostly trapped
in the envelope depend on the stellar global parameters and evolutionary state,
and we compare our theoretical predictions and first KEPLER data.Finally, we
find that the properties of dipole modes constitute a promising seismic
diagnostic of the evolutionary state of red-giant stars.Comment: 6 pages, 5 figures. Proceedings of IV Helas International Conference:
  "Seismological Challenges for Stellar Structure", Lanzarote (Canary Islands,
  Spain), 1-5 February 201
Structure and evolution of pulsating hot subdwarfs

Hot subdwarfs are evolved low--mass stars that have survived core helium
ignition and are now in (or recently finished with) the core helium burning
stage. At the hot end of the Horizontal Branch (HB), many of these stars are
multiperiodic pulsators. These pulsations have revealed details of their global
and internal structure, and provide important constraints on the origin of hot
HB stars. While many features of their structure deduced from seismic fits have
confirmed what we expected from evolutionary considerations, there have been
some surprises as well.Comment: 6 pages, invited review from Fourth HELAS International Conference:
  Seismological Challenges for Stellar Structure (February 2010