93 research outputs found
Catalog of 93 Nova Light Curves: Classification and Properties
We present a catalog of 93 very-well-observed nova light curves. The light
curves were constructed from 229,796 individual measured magnitudes, with the
median coverage extending to 8.0 mag below peak and 26% of the light curves
following the eruption all the way to quiescence. Our time-binned light curves
are presented in figures and as complete tabulations. We also calculate and
tabulate many properties about the light curves, including peak magnitudes and
dates, times to decline by 2, 3, 6, and 9 magnitudes from maximum, the time
until the brightness returns to quiescence, the quiescent magnitude, power law
indices of the decline rates throughout the eruption, the break times in this
decline, plus many more properties specific to each nova class. We present a
classification system for nova light curves based on the shape and the time to
decline by 3 magnitudes from peak (t3). The designations are S for smooth light
curves (38% of the novae), P for plateaus (21%), D for dust dips (18%), C for
cusp-shaped secondary maxima (1%), O for quasi-sinusoidal oscillations
superposed on an otherwise smooth decline (4%), F for flat-topped light curves
(2%), and J for jitters or flares superposed on the decline (16%). Our
classification consists of this single letter followed by the t3 value in
parentheses; so for example V1500 Cyg is S(4), GK Per is O(13), DQ Her is
D(100), and U Sco is P(3).Comment: Astronomical Journal, in press, 19 figures, 73 page
The Behavior of Novae Light Curves Before Eruption
In 1975, E. R. Robinson conducted the hallmark study of the behavior of
classical nova light curves before eruption, and this work has now become part
of the standard knowledge of novae. He made three points; that 5 out of 11
novae showed pre-eruption rises in the years before eruption, that one nova
(V446 Her) showed drastic changes in the variability across eruptions, and that
all but one of the novae (excepting BT Mon) have the same quiescent magnitudes
before and after the outburst. This work has not been tested since it came out.
We have now tested these results by going back to the original archival
photographic plates and measuring large numbers of pre-eruption magnitudes for
many novae using comparison stars on a modern magnitude scale. We find in
particular that four out of five claimed pre-eruption rises are due to simple
mistakes in the old literature, that V446 Her has the same amplitude of
variations across its 1960 eruption, and that BT Mon has essentially unchanged
brightness across its 1939 eruption. Out of 22 nova eruptions, we find two
confirmed cases of significant pre-eruption rises (for V533 Her and V1500 Cyg),
while T CrB has a deep pre-eruption dip. These events are a challenge to
theorists. We find no significant cases of changes in variability across 27
nova eruptions beyond what is expected due to the usual fluctuations seen in
novae away from eruptions. For 30 classical novae plus 19 eruptions from 6
recurrent novae, we find that the average change in magnitude from before the
eruption to long after the eruption is 0.0 mag. However, we do find five novae
(V723 Cas, V1500 Cyg, V1974 Cyg, V4633 Sgr, and RW UMi) that have significantly
large changes, in that the post-eruption quiescent brightness level is over ten
times brighter than the pre-eruption level.Comment: 91 pages (preprint), AJ accepte
Lattice Boltzmann simulations of soft matter systems
This article concerns numerical simulations of the dynamics of particles
immersed in a continuum solvent. As prototypical systems, we consider colloidal
dispersions of spherical particles and solutions of uncharged polymers. After a
brief explanation of the concept of hydrodynamic interactions, we give a
general overview over the various simulation methods that have been developed
to cope with the resulting computational problems. We then focus on the
approach we have developed, which couples a system of particles to a lattice
Boltzmann model representing the solvent degrees of freedom. The standard D3Q19
lattice Boltzmann model is derived and explained in depth, followed by a
detailed discussion of complementary methods for the coupling of solvent and
solute. Colloidal dispersions are best described in terms of extended particles
with appropriate boundary conditions at the surfaces, while particles with
internal degrees of freedom are easier to simulate as an arrangement of mass
points with frictional coupling to the solvent. In both cases, particular care
has been taken to simulate thermal fluctuations in a consistent way. The
usefulness of this methodology is illustrated by studies from our own research,
where the dynamics of colloidal and polymeric systems has been investigated in
both equilibrium and nonequilibrium situations.Comment: Review article, submitted to Advances in Polymer Science. 16 figures,
76 page
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
The Properties of X-Ray and Optical Light Curves of X-Ray Novae
We have collected the available data from the literature and from public data
archives covering the past two decades for the long-term X-ray and optical
light curves of X-ray nova (XN) outbursts, and carry out for the first time a
systematic, statistical study of XN light curves which are classified into 5
morphological types. Basic light curve parameters, e.g., the outburst peak
flux, amplitude, luminosity, rise and decay timescales, the observed and
expected outburst durations, and total energy radiated, are tabulated and
discussed. The rise timescales are found to have a flat distribution while the
decay timescales have a much narrower and near-Gaussian distribution, centered
around 30 days and dominated by the strongest outbursts. The peak luminosity is
also distributed like a Gaussian, centered around 0.2 in Eddington units, while
the total energy released has a much broader distribution around 10E44 ergs.
We identify and discuss additional light curve features, such as precursors,
plateaus, and secondary maxima. The plateaus exhibited in the light curves of
black hole sources are found to have, on average, longer durations and they are
followed by longer decays. The identified secondary maxima seem to occur mostly
in black hole systems. For the frequency of outbursts, we find that the average
XN outburst rate is about 2.6 per year for events >0.3 Crab, and that the mean
recurrence time between outbursts from a single source is 6 years. The spatial
and logN-logS distribution of the XN sources, with limited statistics, agrees
with a source population in the Galactic disk, as observed from a point at a
distance of 8.5 kpc from the Galactic center. Finally, we point out that the
observed XN light curve properties can in general be explained by a disk
thermal instability model, although some important problems still remain.Comment: 68 pages including 27 Postscript figures and 12 tables. To be
published in the Astrophysical Journal, Part
AE Aquarii represents a new subclass of Cataclysmic Variables
We analyze properties of the unique nova-like star AE Aquarii identified with
a close binary system containing a red dwarf and a very fast rotating
magnetized white dwarf. It cannot be assigned to any of the three commonly
adopted sub-classes of Cataclysmic Variables: Polars, Intermediate Polars, and
Accreting non-magnetized White Dwarfs. Our study has shown that the white dwarf
in AE Aqr is in the ejector state and its dipole magnetic moment is . It switched into this state due to intensive mass
exchange between the system components during a previous epoch. A high rate of
disk accretion onto the white dwarf surface resulted in temporary screening of
its magnetic field and spin-up of the white dwarf to its present spin period.
Transition of the white dwarf to the ejector state had occurred at a final
stage of the spin-up epoch as its magnetic field emerged from the accreted
plasma due to diffusion. In the frame of this scenario AE Aqr represents a
missing link in the chain of Polars evolution and the white dwarf resembles a
recycled pulsar.Comment: accepted for publication in Astronomy Reports (July 2012
Central European habitats and their Auchenorrhyncha communities
Basierend auf eigenen Daten und einer Literaturauswertung wird eine Übersicht über die Habitate der mitteleuropäischen Zikadenfauna gegeben. Besiedelt werden nahezu alle semiaquatischen und terrestrischen Lebenräume von Schwimmblattgürteln und Röhrichten bis hin zum Trockenrasen und vom Mineralboden bis in die Baumkronen hinauf. 61% der Arten leben permanent in der Krautschicht, rund 27% in der Baum- und Strauchschicht. Rund 11% bewohnen mehrere Straten, der Großteil davon macht einen obligaten Wechsel durch, meist vom Boden oder von der Krautschicht in die Baumschicht. Als Nährpflanzen spielen krautige Monokotyle und Gehölze mit Abstand die wichtigste Rolle. Von weitaus geringerer Bedeutung sind krautige Dikotyle und Zwergsträucher. Von jeweils nur einzelnen Zikaden-Arten werden Farnpflanzen, Gymnospermen und Pilze genutzt. Generell sind die höchsten Artenzahlen auf biomassereichen, also hochwuchsigen oder weit verbreiteten und häufigen Pflanzenarten anzutreffen. Wichtige Habitatfaktoren für einen Großteil der Arten sind Feuchte, Störung und die oftmals spezifischen Nährpflanzen. Weiterhin können Temperatur, Sonnenexposition, pH-Wert und Nährstoffgehalt des Bodens, Meereshöhe, Bodeneigenscliaften und Salinität eine Rolle spielen, sind aber z.T. miteinander korreliert. Dementsprechend gibt es besonders spezialisierte Zikadenarten in Lebensräumen, in denen extreme Verhältnisse hinsichtlich dieser Faktoren herrschen, also Ufer, Moore, Trockenrasen, Dünen, Salzwiesen und alpine Matten. In stark gestörten Lehensräumen kommen nur noch wenige eurytope, polyphage und gut flugfähige Arten mit hohem Fortpflanzungspotential vor. Eine Ausnahme hiervon bilden allerdings die regelmäßig überfüllten Kiesbänke der Alpenflüsse, die trotz intensiver Störung eine Anzahl stenotoper, monophager und monovoltiner Arten, oft mit nur eingeschränkter Flugfähigkeit, aufweisen.We present an overview of the habitats of the central European Auchenorrhynclia fauna, based upon our own data and an analysis of the available literature. Almost all types of semi-aquatic and terrestrial habitats are utilized, ranging from floating vegetation and reeds along shores to dry grassland and from the mineral soil up to the tree canopy. 61% of the species live permanently in the herbaceous layer, 27% in the shrub or tree layer. 11% utilize several Strata, most of them performing an obligatory migration from the soil or herbaceous vegetation up to the canopy layer. Herbaceous monocots and woody plants are by far the most important food plants. Herbaceous dicots and dwarf shrubs only play a minor role; furthermore, a few species live on pteridophytes, gymnosperms, and fungi, respectively. In general, highest species numbers are found on plants rich in biomass, i.e. tall or widespread and abundant. We discuss and present overviews of Auchenorrhyncha communities of the following habitat types: 1. Forests, scrub and their margins: 1.1. Trees and slirubs, 1.2. Herbaceous layer of forests, 1.3. Woody riverside vegetation, 1.4. Xerothermic margins of forests and scrub, 1.5, Early successional stages. 2. Natural and near-natural non-wooded habitats: 2.1. Rocks, 2.2. Dunes and other dry and sandy habitats, 2.3. Coastal and inland salt marshes, 2.4. Peatlands (with 2.4.1, Ombrotrophic and transitional bogs, and 2.4.2, Fens and spring mires), 2.5, Semiaquatic habitats (with 2.5.1. Mud and gravel banks, 2.5.2. Floating vegetation and reeds, 2.5.3. Flood plain depressions and 2.5.4. Banks of alpine rivers), 2.6. Alpine habitats (with 2.6.1. Mountains in general, 2.6.2. Alpine grassland 2.6.3. and Subalpine scrub). 3. Non-wooded habitats of anthropogenic origin: 3.1. Meadows and pastures, 3.2. Dry grassland, 3.3. Ruderal habitats and fallows, 3.4. Fields. Important habitat factors include moisture, disturbance, and food plants, which are specific in many cases, Temperature, sun exposure, soil pH and nutrient content, altitude, soil properties, and salinity may also play a role, although they are partially intercorrelated. Accordingly, habitat specificity of Auchenorrhyiicha is most pronounced under extreme conditions, notably along sliores, in bogs, dry grassland, dunes, salt marslies, and alpine grassland. Only a few eurytopic and polyphagous species witli a marked flight capability and a high reroductive potential manage to survive in strongly disturbed habitats. Gravel banks of alpine rivers, however, which are subject to periodical flooding, are an exception to this rule in holding a number of stenotopic, monopha. gous, monovoltine species with reduced flight capability
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