pinecone/core-2020-05-10-deduplication huggingface dataset:
Solar system X‐rays from charge exchange processes

While X‐ray astronomy began in 1962 and has made fast progress since then in expanding our knowledge about where in the Universe X‐rays are generated by which processes, it took one generation before the importance of a fundamentally different process was recognized. This happened in our immediate neighborhood, when in 1996 comets were discovered as a new class of X‐ray sources, directing our attention to charge exchange reactions. Charge exchange is fundamentally different from other processes which lead to the generation of X‐rays, because the X‐rays are not produced by hot electrons, but by ions picking up electrons from cold gas. Thus it opens up a new window, making it possible to detect cool gas in X‐rays (like in comets), while all the other processes require extremely high temperatures or otherwise extreme conditions. After having been overlooked for a long time, the astrophysical importance of charge exchange for the generation of X‐rays is now receiving increased general attention. In our solar system, charge exchange induced X‐rays have now been established to originate in comets, in all the planets from Venus to Jupiter, and even in the heliosphere itself. In addition to that, evidence for this X‐ray emission mechanism has been found at various locations across the Universe. Here we summarize the current knowledge about solar system X‐rays resulting from charge exchange processes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
Solar wind charge exchange and local hot bubble X‐ray emission with the DXL sounding rocket experiment

The Diffuse X‐ray emission from the Local Galaxy (DXL) sounding rocket is a NASA approved mission with a scheduled first launch in December 2012. Its goal is to identify and separate the X‐ray emission of the solar wind charge exchange (SWCX) from that of the local hot bubble (LHB) to improve our understanding of both. To separate the SWCX contribution from the LHB, DXL will use the SWCX signature due to the helium focusing cone at  l  = 185°,  b  = –18°. DXL uses large area proportional counters, with an area of 1000 cm 2  and grasp of about 10 cm 2  sr both in the 1/4 and 3/4 keV bands. Thanks to the large grasp, DXL will achieve in a 5‐minute flight what cannot be achieved by current and future X‐ray satellites (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim
On the soft X-ray emission of M82

We present a spatial analysis of the soft X-ray and H{\alpha} emissions from
the outflow of the starburst galaxy M82. We find that the two emissions are
tightly correlated on various scales. The O VII triplet of M82, as resolved by
X-ray grating observations of XMM-Newton, is dominated by the forbidden line,
inconsistent with the thermal prediction. The O VII triplet also shows some
spatial variations. We discuss three possible explanations for the observed O
VII triplet, including the charge exchange at interfaces between the hot
outflow and neutral cool gas, a collisional non-equilibrium-ionization
recombining plasma, and resonance scattering.Comment: 4 pages, published in Astronomical Notes, for "Charge exchange in the
  Universe" workshop, Paris 201
Charge-exchange emission in the starburst galaxies M82 and NGC3256

Charge-exchange (CE) emission produces features which are detectable with the
current X-ray instrumentation in the brightest near galaxies. We describe these
aspects in the observed X-ray spectra of the star forming galaxies M82 and NGC
3256, from the Suzaku and XMM-Newton telescopes. Emission from both ions (O, C)
and neutrals (Mg, Si) is recognised. We also describe how microcalorimeter
instrumentation on future missions will improve CE observations.Comment: 4 pages. Proc. Workshop "Charge-exchange in the Universe", Paris,
  Nov. 2011. To appear in Astron.Nach
Linear stability analysis of the Hall magnetorotational instability in a
  spherical domain

We investigate the stability of the Hall-MHD system and determine its
importance for neutron stars at their birth, when they still consist of
differentially rotating plasma permeated by extremely strong magnetic fields.
We solve the linearised Hall-MHD equations in a spherical shell threaded by a
homogeneous magnetic field. With the fluid/flow coupling and the Hall effect
included, the magnetorotational instability and the Hall effect are both acting
together. Results differ for magnetic fields aligned with the rotation axis and
anti-parallel magnetic fields. For a positive alignment of the magnetic field
the instability grows on a rotational time-scale for any sufficiently large
magnetic Reynolds number. Even the magnetic fields which are stable against the
MRI due to the magnetic diffusion are now susceptible to the shear-Hall
instability. In contrast, the negative alignment places strong restrictions on
the growth and the magnitude of the fields, hindering the effectiveness of the
Hall-MRI. While non-axisymmetric modes of the MRI can be suppressed by strong
enough rotation, there is no such restriction when the Hall effect is present.
The implications for the magnitude and the topology of the magnetic field of a
young neutron star may be significant.Comment: 7 pages, 10 figures, Astron. Nachr. 333, 202 (2012
Milky Way simulations: the Galaxy, its stellar halo and its satellites -
  insights from a hybrid cosmological approach

Our 'home galaxy' - the Milky Way - is a fairly large spiral galaxy,
prototype of the most common morphological class in the local Universe.
Although being only a galaxy, it is the only one that can be studied in unique
detail: for the MilkyWay and for a number of members of the Local Group, a
wealth of observational data is available about the ages and chemical
abundances of their stars. Much more information is expected to come in the
next few years, from ongoing and planned spectroscopic and astrometric surveys,
providing a unique benchmark for modern theories of galaxy formation. In this
review, I will summarize recent results on the formation of our Milky Way, its
stellar halo, and its satellite galaxies. I will focus, in particular, on
results obtained in the framework of hybrid models of galaxy formation, and
refer to other reviews in this issue for studies based on hydrodynamical
simulations.Comment: 10 pages, 10 figures, invited plenary review at the Astronomische
  Gesellschaft meeting (Heidelberg 2011), to appear in Reviews in Modern
  Astronomy Vol.24 - typos correcte
MUCHFUSS - Massive Unseen Companions to Hot Faint Underluminous Stars
  from SDSS

The project Massive Unseen Companions to Hot Faint Underluminous Stars from
SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact
companions (white dwarfs with masses $M>1.0 {\rm M_{\odot}}$, neutron stars or
black holes). The existence of such systems is predicted by binary evolution
calculations and some candidate systems have been found. We identified
$\simeq1100$ hot subdwarf stars from the Sloan Digital Sky Survey (SDSS). Stars
with high velocities have been reobserved and individual SDSS spectra have been
analysed. About 70 radial velocity variable subdwarfs have been selected as
good candidates for follow-up time resolved spectroscopy to derive orbital
parameters and photometric follow-up to search for features like eclipses in
the light curves. Up to now we found nine close binary sdBs with short orbital
periods ranging from $\simeq0.07 {\rm d}$ to $1.5 {\rm d}$. Two of them are
eclipsing binaries with companions that are most likely of substellar nature.Comment: 6 pages, 4 figures, AN, in pres
AGN jets under the microscope: A divide?

A new paradigm for active galactic jet kinematics has emerged through
detailed investigations of BL Lac objects using very long baseline radio
interferometry. In this new scheme, most, if not all, jet components appear to
remain stationary with respect to the core but show significant non-radial
motions. This paper presents results from our kinematic investigation of the
jets of a statistically complete sample of radio-loud flat-spectrum active
galaxies, focusing on the comparison between the jet kinematic properties of BL
Lacs and flat-spectrum radio-quasars. It is shown that there is a statistically
significant difference between the kinematics of the two AGN classes, with BL
Lacs showing more bent jets, that are wider and show slower movement along the
jet axis, compared to flat-spectrum radio-quasars. This is interpreted as
evidence for helically structured jets.Comment: Doctoral thesis award lecture 2011, German Astronomical Society, 14
  pages, 13 figures, will appear in special edition of Astronomische
  Nachrichten "Reviews in Modern Astronomy
A wider audience: Turning VLBI into a survey instrument

Radio observations using the Very Long Baseline Interferometry (VLBI)
technique typically have fields of view of only a few arcseconds, due to the
computational problems inherent in imaging larger fields. Furthermore,
sensitivity limitations restrict observations to very compact and bright
objects, which are few and far between on the sky. Thus, while most branches of
observational astronomy can carry out sensitive, wide-field surveys, VLBI
observations are limited to targeted observations of carefully selected
objects. However, recent advances in technology have made it possible to carry
out the computations required to target hundreds of sources simultaneously.
Furthermore, sensitivity upgrades have dramatically increased the number of
objects accessible to VLBI observations. The combination of these two
developments have enhanced the survey capabilities of VLBI observations such
that it is now possible to observe (almost) any point in the sky with
milli-arcsecond resolution. In this talk I review the development of wide-field
VLBI, which has made significant progress over the last three years.Comment: Invited review at the General Assembly of the Astronomische
  Gesellschaf
The Galactic thin and thick disk

The ongoing large spectroscopic surveys of the Milky Way such as SEGUE and
RAVE have enabled us to take a fresh look at the structure of the Galactic thin
and thick disks, and how their structure fits within the framework of structure
formation via hierarchical clustering. In this article I will summarize some
recent results mainly based in the RAVE survey with respect to the structure of
the Galactic disks, their possible origin as well as indications of
substructure and asymmetries.Comment: Invited review given at the Annual Meeting of the German Astronomical
  Society, Heidelberg, Sept 19-23, 201
Principles of High-Dimensional Data Visualization in Astronomy

Astronomical researchers often think of analysis and visualization as separate tasks. In the case of high-dimensional data sets, though, interactive exploratory data visualization can give far more insight than an approach where data processing and statistical analysis are followed, rather than accompanied, by visualization. This paper attempts to charts a course toward “linked view” systems, where multiple views of high-dimensional data sets update live as a researcher selects, highlights, or otherwise manipulates, one of several open views. For example, imagine a researcher looking at a 3D volume visualization of simulated or observed data, and simultaneously viewing statistical displays of the data set's properties (such as an x -y plot of temperature vs. velocity, or a histogram of vorticities). Then, imagine that when the researcher selects an interesting group of points in any one of these displays, that the same points become a highlighted subset in all other open displays. Selections can be graphical or algorithmic, and they can be combined, and saved. For tabular (ASCII) data, this kind of analysis has long been possible, even though it has been under-used in astronomy. The bigger issue for astronomy and other “high-dimensional” fields, though, is that no extant system allows for full integration of images and data cubes within a linked-view environment. The paper concludes its history and analysis of the present situation with suggestions that look toward cooperatively-developed open-source modular software as a way to create an evolving, flexible, high-dimensional, linked-view visualization environment useful in astro-physical research.Astronom
Relative astrometric and photometric measurements of visual binaries made with the Nice 76-cm refractor in 2008

8 pages dans la version publiée sans les tables 55 pages dans la version avec les tables complètesInternational audienceWe present relative astrometric and photometric measurements of visual binaries made in 2008, with the 76-cm refractor of Côte d'Azur Observatory. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. Three different techniques were used for obtaining measurements: Lucky imaging, speckle interferometry and the Direct Vector Autocorrelation method. We obtained 2420 new measurements of the relative position of 2225 objects, with angular separations in the range 0.07 arcsec-11.5 arcsec, and an average accuracy of 0.02 arcsec. The mean error on the position angles is 0.6 deg. We managed to observe faint systems (m_V ≈ 12) with large magnitude difference (up to Δ m_V ≈ 5). We have thus been able to measure many systems containing red dwarf stars that had been poorly monitored since their discovery. We also measured the difference of magnitude of the two components of 376 objects with an estimated error of 0.1 mag. Finally, we provide a list of 33 newly discovered components of multiple or binary systems, which is a significant complement to our GII catalog. } %% end abstrac
The Opacity of Spiral Galaxy Disks IX; Dust and Gas Surface Densities

Our aim is to explore the relation between gas, atomic and molecular, and
dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO
line emission maps. To estimate the dust content, we use the disk opacity as
inferred from the number of distant galaxies identified in twelve HST/WFPC2
fields of ten nearby spiral galaxies. The observed number of distant galaxies
is calibrated for source confusion and crowding with artificial galaxy counts
and here we verify our results with sub-mm surface brightnesses from archival
Herschel-SPIRE data. We find that the opacity of the spiral disk does not
correlate well with the surface density of atomic (Hi) or molecular hydrogen
(H2) alone implying that dust is not only associated with the molecular clouds
but also the diffuse atomic disk in these galaxies. Our result is a typical
dust-to-gas ratio of 0.04, with some evidence that this ratio declines with
galactocentric radius, consistent with recent Herschel results. We discuss the
possible causes of this high dust-to-gas ratio; an over-estimate of the dust
surface-density, an under-estimate of the molecular hydrogen density from CO
maps or a combination of both. We note that while our value of the mean
dust-to-gas ratio is high, it is consistent with the metallicity at the
measured radii if one assumes the Pilyugin & Thuan calibration of gas
metallicity.Comment: Accepted by AN, 15 pages, 10 figures, 1 tabl
Simultaneous UBVRI observations of the cataclysmic variable AE Aquarii:
  temperature and mass of fireballs

We report simultaneous multicolour observations in 5 bands (UBVRI) of the
flickering variability of the cataclysmic variable AE Aqr. Our aim is to
estimate the parameters (colours, temperature, size) of the fireballs that
produce the optical flares.
  The observed rise time of the optical flares is in the interval 220 - 440
sec. We estimate the dereddened colours of the fireballs: (U-B)_0 in the range
0.8-1.4, (B-V)_0 ~ 0.03-0.24, (V-I)_0 ~ 0.26-0.78. We find for the fireballs a
temperature in the range 10000 - 25000 K, mass (7-90).10^{19} g, size
(3-7).10^9 cm (using a distance of d=86 pc). These values refer to the peak of
the flares observed in UBVRI bands.
  The data are available upon request from the authors.Comment: 8 pages, accepted in A
Rotation, activity, and lithium abundance in cool binary stars

We have used two robotic telescopes to obtain time-series high-resolution
spectroscopy and V I and/or by photometry for a sample of 60 active stars.
Orbital solutions are presented for 26 SB2 and 19 SB1 systems with
unprecedented phase coverage and accuracy. The total of 6,609 R=55,000 echelle
spectra are also used to systematically determine effective temperatures,
gravities, metallicities, rotational velocities, lithium abundances and
absolute H{\alpha}-core fluxes as a function of time. The photometry is used to
infer unspotted brightness, V - I and/or b - y colors, spot-induced brightness
amplitudes and precise rotation periods. Our data are complemented by
literature data and are used to determine rotation-temperature-activity
relations for active binary components. We also relate lithium abundance to
rotation and surface temperature. We find that 74% of all known
rapidly-rotating active binary stars are synchronized and in circular orbits
but 26% are rotating asynchronously of which half have Prot > Porb and e > 0.
Because rotational synchronization is predicted to occur before orbital
circularization active binaries should undergo an extra spin-down besides tidal
dissipation. We suspect this to be due to a magnetically channeled wind with
its subsequent braking torque. We find a steep increase of rotation period with
decreasing effective temperature for active stars. For inactive, single giants
with Prot > 100 d, the relation is much weaker. Our data also indicate a
period-activity relation for H{\alpha} of the form RH{\alpha} \propto P - 0.24
for binaries and RH{\alpha} \propto P -0.14 for singles. Lithium abundances in
our sample increase with effective temperature. On average, binaries of
comparable effective temperature appear to exhibit 0.25 dex less surface
lithium than singles. We also find a trend of increased Li abundance with
rotational period of form log n(Li) \propto - 0.6 log Prot
The DWARF project: Eclipsing binaries - precise clocks to discover
  exoplanets

We present a new observational campaign, DWARF, aimed at detection of
circumbinary extrasolar planets using the timing of the minima of low-mass
eclipsing binaries. The observations will be performed within an extensive
network of relatively small to medium-size telescopes with apertures of ~20-200
cm. The starting sample of the objects to be monitored contains (i) low-mass
eclipsing binaries with M and K components, (ii) short-period binaries with sdB
or sdO component, and (iii) post-common-envelope systems containing a WD, which
enable to determine minima with high precision. Since the amplitude of the
timing signal increases with the orbital period of an invisible third
component, the timescale of project is long, at least 5-10 years. The paper
gives simple formulas to estimate suitability of individual eclipsing binaries
for the circumbinary planet detection. Intrinsic variability of the binaries
(photospheric spots, flares, pulsation etc.) limiting the accuracy of the
minima timing is also discussed. The manuscript also describes the best
observing strategy and methods to detect cyclic timing variability in the
minima times indicating presence of circumbinary planets. First test
observation of the selected targets are presented.Comment: 12 pages, 2 figures, submitted to Astron. Nachrichte
A retrospective of the GREGOR solar telescope in scientific literature

In this review, we look back upon the literature, which had the GREGOR solar
telescope project as its subject including science cases, telescope subsystems,
and post-focus instruments. The articles date back to the year 2000, when the
initial concepts for a new solar telescope on Tenerife were first presented at
scientific meetings. This comprehensive bibliography contains literature until
the year 2012, i.e., the final stages of commissioning and science
verification. Taking stock of the various publications in peer-reviewed
journals and conference proceedings also provides the "historical" context for
the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.Comment: 6 pages, 2 color figures, this is the pre-peer reviewed version of
  Denker et al. 2012, Astron. Nachr. 333, 81
The GREGOR Fabry-P\'erot Interferometer

The GREGOR Fabry-P\'erot Interferometer (GFPI) is one of three first-light
instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio
del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated
mounting. Thanks to its large-format, high-cadence CCD detectors with
sophisticated computer hard- and software it is capable of scanning spectral
lines with a cadence that is sufficient to capture the dynamic evolution of the
solar atmosphere. The field-of-view (FOV) of 50" x 38" is well suited for quiet
Sun and sunspot observations. However, in the vector spectropolarimetric mode
the FOV reduces to 25" x 38". The spectral coverage in the spectroscopic mode
extends from 530-860 nm with a theoretical spectral resolution R of about
250,000, whereas in the vector spectropolarimetric mode the wavelength range is
at present limited to 580-660 nm. The combination of fast narrow-band imaging
and post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales down to
about 50 km on the solar surface.Comment: 14 pages, 17 figures, 4 tables; pre-print of AN 333, p.880-893, 2012
  (AN special issue to GREGOR
Fundamental properties of lower main-sequence stars

The field of exoplanet research has revitalized interest in M dwarfs, which
have become favorite targets of Doppler and transit surveys. Accurate
measurements of their basic properties such as masses, radii, and effective
temperatures have revealed significant disagreements with predictions from
stellar evolution theory in the sense that stars are larger and cooler than
expected. These anomalies are believed to be due to high levels of activity in
these stars. The evidence for the radius discrepancies has grown over the years
as more and more determinations have become available; however, fewer of these
studies include accurate determinations of the temperatures. The ubiquitous
mass-radius diagrams featured in many new discovery papers are becoming more
confusing due to increased scatter, which may be due in part to larger than
realized systematic errors affecting many of the published measurements. A
discussion of these and other issues is given here from an observer's
perspective, along with a summary of theoretical efforts to explain the radius
and temperature anomalies.Comment: 7 pages, to appear in the Proceedings of the 17th Cambridge Workshop
  on Cool Stars, Stellar Systems, and the Sun, eds. K. Strassmeier & M.
  Lopez-Morales (AN, Vol. 334
Evolution of solar-type stellar wind

By extending our self-consistent MHD simulations for the solar wind, we study
the evolution of stellar winds of solar-type stars from early main sequence
stage to red giant phase. Young solar-type stars are active and the mass loss
rates are larger by up to ~ 100 times than that of the present-day sun. We
investigate how the stellar wind is affected when the magnetic field strength
and fluctuation amplitude at the photosphere increase. While the mass loss rate
sensitively depends on the input energy from the surface because of the global
instability related to the reflection and nonlinear dissipation of Alfven
waves, it saturates at ~ 100 times because most of the energy is used up for
the radiative losses rather than the kinetic energy of the wind. After the end
of the main sequence phase when the stellar radius expands by ~ 10 times, the
steady hot corona with temperature $10^6$ K, suddenly disappears. Chromospheric
materials, with hot bubbles embedded owing to thermal instability, directly
stream out; the red giant wind is not a steady stream but structured outflow.Comment: 4 pages, Astronomische Nachrichten in press, based on a talk in "Cool
  Stars 17" in Barcelona, Jun 201