pinecone/core-2020-05-10-deduplication huggingface dataset:
Broadband short term variability of the quasar PDS 456

We present a detailed analysis of a recent $500$ ks net exposure
\textit{Suzaku} observation, carried out in 2013, of the nearby ($z=0.184$)
luminous (L$_{\rm bol}\sim10^{47}$ erg s$^{-1}$) quasar PDS 456 in which the
X-ray flux was unusually low. The short term X-ray spectral variability has
been interpreted in terms of variable absorption and/or intrinsic continuum
changes. In the former scenario, the spectral variability is due to variable
covering factors of two regions of partially covering absorbers. We find that
these absorbers are characterised by an outflow velocity comparable to that of
the highly ionised wind, i.e. $\sim0.25$ c, at the $99.9\%$ $(3.26\sigma)$
confidence level. This suggests that the partially absorbing clouds may be the
denser clumpy part of the inhomogeneous wind. Following an obscuration event we
obtained a direct estimate of the size of the X-ray emitting region, to be not
larger than $20~R_{\rm g}$ in PDS 456.Comment: 6 pages, 5 figures, Proceedings of the 2015 XMM-Newton workshop: "The
  Extremes of Black Hole Accretion". Published in Astronomische
  Nachrichten/Astronomical Note
The Origin of UV-optical Variability in AGN and Test of Disc Models:
  XMM-Newton and ground based observations of NGC4395

The origin of short timescale (weeks/months) variability of AGN, whether due
to intrinsic disc variations or reprocessing of X-ray emission by a surrounding
accretion disc, has been a puzzle for many years. However recently a number of
observational programmes, particularly of NGC5548 with Swift, have shown that
the UV/optical variations lag behind the X-ray variations in a manner strongly
supportive of X-ray reprocessing. Somewhat surprisingly the implied size of the
accretion disc is ~3x greater than expected from a standard, smooth,
Shakura-Sunyaev thin disc model. Although the difference may be explained by a
clumpy accretion disc, it is not clear whether the difference will occur in all
AGN or whether it may change as, eg, a function of black hole mass, accretion
rate or disc temperature. Measurements of interband lags for most AGN require
long timescale monitoring, which is hard to arrange. However for low mass (<1
million solar mass) AGN, the combination of XMM-Newton EPIC (X-rays) with the
optical monitor in fast readout mode allows an X-ray/UV-optical lag to be
measured within a single long observation. Here we summarise previous related
observations and report on XMM-Newton observations of NGC4395 (mass ~100x lower
and accretion rate ~20x lower than for NGC5548). We find that the UVW1 lags the
X-rays by ~470s. Simultaneous observations at 6 different ground based
observatories also allowed the g-band lag (~800s) to be measured. These
observations are in agreement with X-ray reprocessing but initial analysis
suggests that, for NGC4395, they do not differ markedly from the predictions of
the standard thin disc model.Comment: 6 pages, 16 figures, accepted for publication in Astronomische
  Nachrichte
Variability of the X-ray Broad Iron Spectral Features in Active Galactic
  Nuclei and Black-hole Binaries

The "broad iron spectral features" are often seen in X-ray spectra of Active
Galactic Nuclei (AGN) and black-hole binaries (BHB). These features may be
explained either by the "relativistic disc reflection" scenario or the "partial
covering" scenario: It is hardly possible to determine which model is valid
from time-averaged spectral analysis. Thus, X-ray spectral variability has been
investigated to constrain spectral models. To that end, it is crucial to study
iron structure of BHBs in detail at short time-scales, which is, for the first
time, made possible with the Parallel-sum clocking (P-sum) mode of XIS
detectors on board Suzaku. This observational mode has a time-resolution of
7.8~ms as well as a CCD energy-resolution. We have carried out systematic
calibration of the P-sum mode, and investigated spectral variability of the BHB
GRS 1915+105. Consequently, we found that the spectral variability of GRS
1915+105 does not show iron features at sub-seconds. This is totally different
from variability of AGN such as 1H0707--495, where the variation amplitude
significantly drops at the iron K-energy band. This difference can be naturally
explained in the framework of the "partial covering" scenario.Comment: 5 pages, 7 figures, Accepted for publication in Astronomische
  Nachrichten (Proceedings of "The Extremes of Black Hole Accretion" workshop,
  held at ESAC, Madrid, in June 2015
High ionisation absorption in low mass X-ray binaries

The advent of the new generation of X-ray telescopes yielded a significant
step forward in our understanding of ionised absorption generated in the
accretion discs of X-ray binaries. It has become evident that these relatively
weak and narrow absorption features, sporadically present in the X-ray spectra
of some systems, are actually the signature of equatorial outflows, which might
carry away more matter than that being accreted. Therefore, they play a major
role in the accretion phenomenon. These outflows (or ionised atmospheres) are
ubiquitous during the softer states but absent during the power-law dominated,
hard states, suggesting a strong link with the state of the inner accretion
disc, presence of the radio-jet and the properties of the central source. Here,
we discuss the current understanding of this field.Comment: Accepted for publication in Astronomical Notes (Proceedings of "The
  Extremes of Black Hole Accretion" workshop, held at ESAC, Madrid, in June
  2015
Eclipsing the innermost X-ray emitting regions in AGN

Variable X-ray absorption has been observed in active galactic nuclei (AGN)
on several time scales. Observations allow us to identify the absorber with
clouds associated either with the clumpy torus (parsec scales, long timescales)
or with the broad line region (BLR) (short timescales). In the latter, the
cloud size has been estimated to be of the order of few gravitational radii
from the observed absorption variability. Such small cloud sizes are comparable
to the X-ray emitting regions so that a detailed modeling of occultation events
in AGN has the potential of enabling us to infer accurately the geometry of the
system. We have developed a relativistic X-ray spectral model for occultation
events and we present here theoretical predictions on the different observables
that can be inferred by studying X-ray eclipses in simulated XMM-Newton data.
These include the size of the X-ray emitting regions as well as more
fundamental parameters such as the black hole spin and the system inclination.
We find that absorption varies as a function of the energy range and that its
maximum takes place when the approaching part of the accretion disc is covered.
Therefore we study the hard-to-soft (H/S) ratio light curves produced during an
eclipse and use them to characterise the properties of the inner accretion disc
in a new model-independent way.Comment: 6 pages, 3 figures, conference The Extremes of Black Hole Accretion
  (ESAC, Madrid, Spain, 8th - 10th June 2015
High-energy monitoring of Seyfert galaxies: the case of NGC 4593

We discuss preliminary results from a joint XMM-Newton and NuSTAR monitoring
program on the active galactic nucleus NGC 4593, consisting of 5x20 ks
observations, spaced by two days, performed in January 2015. The source is
found to be variable, both in flux and spectral shape, on time scales as short
as a few ks. The spectrum clearly softens when the source brightens. A simple
timing analysis suggests the presence of a variable soft excess that correlates
with the primary continuum.Comment: Proceedings of the XMM Science Workshop 2015; to appear in
  Astronomische Nachrichte
Astronomical technology - the past and the future

The past fifty years have been an epoch of impressive progress in the field
of astronomical technology. Practically all the technical tools, which we use
today, have been developed during that time span. While the first half of this
period has been dominated by advances in the detector technologies, during the
past two decades innovative telescope concepts have been developed for
practically all wavelength ranges where astronomical observations are possible.
Further important advances can be expected in the next few decades. Based on
the experience of the past, some of the main sources of technological progress
can be identified.Comment: 9 pages, 9 figures, Review article associated with the Karl
  Schwarzschild Award Lecture 2015, Published in Astron. Nachrichten; doi:
  10.1002/asna.20161236
Multiwavelength and parsec-scale properties of extragalactic jets

Extragalactic jets originating from the central supermassive black holes of
active galaxies are powerful, highly relativistic plasma outflows, emitting
light from the radio up to the gamma-ray regime. The details of their
formation, composition and emission mechanisms are still not completely clear.
The combination of high-resolution observations using very long baseline
interferometry (VLBI) and multiwavelength monitoring provides the best insight
into these objects. Here, such a combined study of sources of the TANAMI sample
is presented, investigating the parsec-scale and high-energy properties. The
TANAMI program is a multiwavelength monitoring program of a sample of the radio
and gamma-ray brightest extragalactic jets in the southern sky, below -30deg
declination. We obtain the first-ever VLBI images for most of the sources,
providing crucial information on the jet kinematics and brightness distribution
at milliarcsecond resolution. Two particular sources are discussed in detail:
PMN J1603-4904, which can be classified either as an atypical blazar or a
gamma-ray loud (young) radio galaxy, and Centaurus A, the nearest radio-loud
active galaxy. The VLBI kinematics of the innermost parsec of Centaurus A's jet
result in a consistent picture of an accelerated jet flow with a spine-sheath
like structure.Comment: Doctoral Thesis Award Lecture 2015, AN 2016, 337,
Constraining the Milky Way assembly history with Galactic Archaeology.
  Ludwig Biermann Award Lecture 2015

The aim of Galactic Archaeology is to recover the evolutionary history of the
Milky Way from its present day kinematical and chemical state. Because stars
move away from their birth sites, the current dynamical information alone is
not sufficient for this task. The chemical composition of stellar atmospheres,
on the other hand, is largely preserved over the stellar lifetime and, together
with accurate ages, can be used to recover the birthplaces of stars currently
found at the same Galactic radius. In addition to the availability of large
stellar samples with accurate 6D kinematics and chemical abundance
measurements, this requires detailed modeling with both dynamical and chemical
evolution taken into account. An important first step is to understand the
variety of dynamical processes that can take place in the Milky Way, including
the perturbative effects of both internal (bar and spiral structure) and
external (infalling satellites) agents. We discuss here (1) how to constrain
the Galactic bar, spiral structure, and merging satellites by their effect on
the local and global disc phase-space, (2) the effect of multiple patterns on
the disc dynamics, and (3) the importance of radial migration and merger
perturbations for the formation of the Galactic thick disc. Finally, we discuss
the construction of Milky Way chemo-dynamical models and relate to
observations.Comment: 25 p., 17 fig., Review article associated with Ludwig Biermann Award
  Lecture 2015, Published in Astron. Nach
Asteroseismology of red giants: from analysing light curves to
  estimating ages

Asteroseismology has started to provide constraints on stellar properties
that will be essential to accurately reconstruct the history of the Milky Way.
Here we look at the information content in data sets representing current and
future space missions (CoRoT, Kepler, K2, TESS, and PLATO) for red giant stars.
We describe techniques for extracting the information in the frequency power
spectrum and apply these techniques to {\it Kepler} data sets of different
observing length to represent the different space missions. We demonstrate that
for KIC 12008916, a low-luminosity red giant branch star, we can extract useful
information from all data sets, and for all but the shortest data set we obtain
good constraint on the g-mode period spacing and core rotation rates. We
discuss how the high precision in these parameters will constrain the stellar
properties of stellar radius, distance, mass and age. We show that high
precision can be achieved in mass and hence age when values of the g-mode
period spacing are available. We caution that tests to establish the accuracy
of asteroseismic masses and ages are still "work in progress".Comment: To appear in Astronomische Nachrichten, special issue "Reconstruction
  the Milky Way's History: Spectroscopic surveys, Asteroseismology and
  Chemo-dynamical models", Guest Editors C. Chiappini, J. Montalb\'an, and M.
  Steffen, AN 2016 (in press
Seismic indices -- a deep look inside evolved stars

Independent of stellar modelling, global seismic parameters of red giants
provide unique information on the individual stellar properties as well as on
stellar evolution. They allow us to measure key stellar parameters, such as the
stellar mass and radius, or to derive the distance of field stars. Furthermore,
oscillations with a mixed character directly probe the physical conditions in
the stellar core. Here, we explain how very precise seismic indices are
obtained, and how they can be used for monitoring stellar evolution and
performing Galactic archeology.Comment: To appear in Astronomische Nachrichten, special issue "Reconstruction
  the Milky Way's History: Spectroscopic surveys, Asteroseismology and
  Chemo-dynamical models", Guest Editors C. Chiappini, J. Montalb\'an, and M.
  Steffen, AN 2016 (in press
Towards 21st Century Stellar Models: Star Clusters, Supercomputing, and
  Asteroseismology

Stellar models provide a vital basis for many aspects of astronomy and
astrophysics. Recent advances in observational astronomy -- through
asteroseismology, precision photometry, high-resolution spectroscopy, and
large-scale surveys -- are placing stellar models under greater quantitative
scrutiny than ever. The model limitations are being exposed and the next
generation of stellar models is needed as soon as possible. The current
uncertainties in the models propagate to the later phases of stellar evolution,
hindering our understanding of stellar populations and chemical evolution. Here
we give a brief overview of the evolution, importance, and substantial
uncertainties of core helium burning stars in particular and then briefly
discuss a range of methods, both theoretical and observational, that we are
using to advance the modelling.Comment: To appear in Astronomische Nachrichten, special issue "Reconstruction
  the Milky Way's History: Spectroscopic surveys, Asteroseismology and
  Chemo-dynamical models", Guest Editors C. Chiappini, J. Montalb\'an, and M.
  Steffen, AN 2016 (in press
Testing Asteroseismic Scaling Relations using Eclipsing Binaries in Star
  Clusters and the Field

The accuracy of stellar masses and radii determined from asteroseismology is
not known! We examine this issue for giant stars by comparing classical
measurements of detached eclipsing binary systems (dEBs) with asteroseismic
measurements from the Kepler mission. For star clusters, we extrapolate
measurements of dEBs in the turn-off region to the red giant branch and the red
clump where we investigate the giants as an ensemble. For the field stars, we
measure dEBs with an oscillating giant component. These measurements allow a
comparison of masses and radii calculated from a classical eclipsing binary
analysis to those calculated from asteroseismic scaling relations and/or other
asteroseismic methods. Our first results indicate small but significant
systematic differences between the classical and asteroseismic measurements. In
this contribution we show our latest results and summarize the current status
and future plans. We also stress the importance of realizing that for giant
stars mass cannot always be translated to age, since an unknown fraction of
these evolved through a blue straggler phase with mass transfer in a binary
system. Rough estimates of how many such stars to expect are given based on our
findings in the open clusters NGC6819 and NGC6791.Comment: To appear in Astronomische Nachrichten, special issue "Reconstruction
  the Milky Way's History: Spectroscopic surveys, Asteroseismology and
  Chemo-dynamical models", Guest Editors C. Chiappini, J. Montalb\'an, and M.
  Steffen, AN 2016 (in press)
Asteroseismic age determination for dwarfs and giants

Asteroseismology can make a substantial contribution to our understanding of
the formation history and evolution of our Galaxy by providing precisely
determined stellar properties for thousands of stars in different regions of
the Milky Way. We present here the different sets of observables used in
determining asteroseismic stellar properties, the typical level of precision
obtained, the current status of results for ages of dwarfs and giants and the
improvements than can be expected in the near future in the context of Galactic
archaeology.Comment: 4 pages, 4 figures, to appear in Astronomische Nachrichten special
  issue "Reconstruction the Milky Way's History: Spectroscopic surveys,
  Asteroseismology and Chemo-dynamical models
Impact of rotation on stellar models

After a brief recall of the main impacts of stellar rotation on the structure
and the evolution of stars, four topics are addressed: 1) the links between
magnetic fields and rotation; 2) the impact of rotation on the age
determination of clusters; 3) the exchanges of angular momentum between the
orbit of a planet and the star due to tides; 4) the impact of rotation on the
early chemical evolution of the Milky Way and the origin of the
Carbon-Enhanced-Metal-Poor stars.Comment: 5 pages, 2 figures, To appear in Astronomische Nachrichten, special
  issue "Reconstruction the Milky Way's History: Spectroscopic surveys,
  Asteroseismology and Chemo-dynamical models", Guest Editors C. Chiappini, J.
  Montalban, and M. Steffen, AN 2016 (in press
Automated Pipelines for Spectroscopic Analysis

The Gaia mission will have a profound impact on our understanding of the
structure and dynamics of the Milky Way. Gaia is providing an exhaustive census
of stellar parallaxes, proper motions, positions, colors and radial velocities,
but also leaves some flaring holes in an otherwise complete data set. The
radial velocities measured with the on-board high-resolution spectrograph will
only reach some 10% of the full sample of stars with astrometry and photometry
from the mission, and detailed chemical information will be obtained for less
than 1%. Teams all over the world are organizing large-scale projects to
provide complementary radial velocities and chemistry, since this can now be
done very efficiently from the ground thanks to large and mid-size telescopes
with a wide field-of-view and multi-object spectrographs. As a result,
automated data processing is taking an ever increasing relevance, and the
concept is applying to many more areas, from targeting to analysis. In this
paper, I provide a quick overview of recent, ongoing, and upcoming
spectroscopic surveys, and the strategies adopted in their automated analysis
pipelines.Comment: 7 pages, 1 figure. To appear in Astronomische Nachrichten, special
  issue "Reconstruction the Milky Way's History: Spectroscopic surveys,
  Asteroseismology and Chemo-dynamical models", Guest Editors C. Chiappini, J.
  Montalban, and M. Steffen, AN 2016 (in press
Hydrodynamical model atmospheres: Their impact on stellar spectroscopy
  and asteroseismology of late-type stars

Hydrodynamical, i.e. multi-dimensional and time-dependent, model atmospheres
of late-type stars have reached a high level of realism. They are commonly
applied in high-fidelity work on stellar abundances but also allow the study of
processes that are not modelled in standard, one-dimensional hydrostatic model
atmospheres. Here, we discuss two observational aspects that emerge from such
processes, the photometric granulation background and the spectroscopic
microturbulence. We use CO5BOLD hydrodynamical model atmospheres to
characterize the total granular brightness fluctuations and characteristic time
scale for FGK stars. Emphasis is put on the diagnostic potential of the
granulation background for constraining the fundamental atmospheric parameters.
We find a clear metallicity dependence of the granulation background. The
comparison between the model predictions and available observational
constraints at solar metallicity shows significant differences, that need
further clarification. Concerning microturbulence, we report on the derivation
of a theoretical calibration based on CO5BOLD models, which shows good
correspondence with the measurements for stars in the Hyades. We emphasize the
importance of a consistent procedure when determining the microturbulence, and
point to limitations of the commonly applied description of microturbulence in
hydrostatic model atmospheres.Comment: 6 pages, 6 figures, accepted for publication in A
Non-LTE iron abundances in cool stars: The role of hydrogen collisions

In the aim of determining accurate iron abundances in stars, this work is
meant to empirically calibrate H-collision cross-sections with iron, where no
quantum mechanical calculations have been published yet. Thus, a new iron model
atom has been developed, which includes hydrogen collisions for excitation,
ionization and charge transfer processes. We show that collisions with hydrogen
leading to charge transfer are important for an accurate non-LTE modeling. We
apply our calculations on several benchmark stars including the Sun, the
metal-rich star {\alpha} Cen A and the metal-poor star HD140283
Gaia Benchmark stars and their twins in the Gaia-ESO Survey

The Gaia benchmark stars are stars with very precise stellar parameters that
cover a wide range in the HR diagram at various metallicities. They are meant
to be good representative of typical FGK stars in the Milky Way. Currently,
they are used by several spectroscopic surveys to validate and calibrate the
methods that analyse the data. I review our recent activities done for these
stars. Additionally, by applying our new method to find stellar twins on the
Gaia-ESO Survey, I discuss how good representatives of Milky Way stars the
benchmark stars are and how they distribute in space.Comment: To appear in Astronomische Nachrichten, special issue "Reconstruction
  the Milky Way's History: Spectroscopic surveys, Asteroseismology and
  Chemo-dynamical models", Guest Editors C. Chiappini, J. Montalb\'an, and M.
  Steffen, AN 2016 (in press