1,362 research outputs found
Analysis of the Early-time Optical Spectra of SN 2011fe in M101
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s^(β1)) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^(β1). This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I Ξ»7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s^(β1). The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta
Weak Prezygotic Isolating Mechanisms in Threatened Caribbean Acropora Corals
The Caribbean corals, Acropora palmata and A. cervicornis, recently have undergone drastic declines primarily as a result of disease. Previous molecular studies have demonstrated that these species form a hybrid (A. prolifera) that varies in abundance throughout the range of the parental distribution. There is variable unidirectional introgression across loci and sites of A. palmata genes flowing into A. cervicornis. Here we examine the efficacy of prezygotic reproductive isolating mechanisms within these corals including spawning times and choice and no-choice fertilization crosses. We show that these species have subtly different mean but overlapping spawning times, suggesting that temporal isolation is likely not an effective barrier to hybridization. We found species-specific differences in gametic incompatibilities. Acropora palmata eggs were relatively resistant to hybridization, especially when conspecific sperm are available to outcompete heterospecific sperm. Acropora cervicornis eggs demonstrated no evidence for gametic incompatibility and no evidence of reduced viability after aging four hours. This asymmetry in compatibility matches previous genetic data on unidirectional introgression
Phase resolved spectroscopy and Kepler photometry of the ultracompact AM CVn binary SDSS J190817.07+394036.4
{\it Kepler} satellite photometry and phase-resolved spectroscopy of the
ultracompact AM CVn type binary SDSS J190817.07+394036.4 are presented. The
average spectra reveal a variety of weak metal lines of different species,
including silicon, sulphur and magnesium as well as many lines of nitrogen,
beside the strong absorption lines of neutral helium. The phase-folded spectra
and the Doppler tomograms reveal an S-wave in emission in the core of the He I
4471 \AA\,absorption line at a period of \,sec
identifying this as the orbital period of the system. The Si II, Mg II and the
core of some He I lines show an S-wave in absorption with a phase offset of
compared to the S-wave in emission. The N II, Si III and some
helium lines do not show any phase variability at all. The spectroscopic
orbital period is in excellent agreement with a period at \,sec detected in the three year {\it Kepler} lightcurve. A
Fourier analysis of the Q6 to Q17 short cadence data obtained by {\it Kepler}
revealed a large number of frequencies above the noise level where the majority
shows a large variability in frequency and amplitude. In an O-C analysis we
measured a xs\,s for some of
the strongest variations and set a limit for the orbital period to be
s\,s. The shape of the phase folded
lightcurve on the orbital period indicates the motion of the bright spot.
Models of the system were constructed to see whether the phases of the radial
velocity curves and the lightcurve variation can be combined to a coherent
picture. However, from the measured phases neither the absorption nor the
emission can be explained to originate in the bright spot.Comment: Accepted for publication in MNRAS, 15 pages, 14 figures, 5 table
Solution of the Fokker-Planck equation with a logarithmic potential and mixed eigenvalue spectrum
Motivated by a problem in climate dynamics, we investigate the solution of a
Bessel-like process with negative constant drift, described by a Fokker-Planck
equation with a potential V(x) = - [b \ln(x) + a\, x], for b>0 and a<0. The
problem belongs to a family of Fokker-Planck equations with logarithmic
potentials closely related to the Bessel process, that has been extensively
studied for its applications in physics, biology and finance. The Bessel-like
process we consider can be solved by seeking solutions through an expansion
into a complete set of eigenfunctions. The associated imaginary-time
Schroedinger equation exhibits a mix of discrete and continuous eigenvalue
spectra, corresponding to the quantum Coulomb potential describing the bound
states of the hydrogen atom. We present a technique to evaluate the
normalization factor of the continuous spectrum of eigenfunctions that relies
solely upon their asymptotic behavior. We demonstrate the technique by solving
the Brownian motion problem and the Bessel process both with a negative
constant drift. We conclude with a comparison with other analytical methods and
with numerical solutions.Comment: 21 pages, 8 figure
Orbital periods and accretion disc structure of four AM CVn systems
Phase-resolved spectroscopy of four AM CVn systems obtained with the William Herschel Telescope and the Gran Telescopio de Canarias is presented. SDSS J120841.96+355025.2 was found to have an orbital period of 52.96 Β± 0.40 min and shows the presence of a second bright spot in the accretion disc. The average spectrum contains strong Mg i and Si i/ii absorption lines most likely originating in the atmosphere of the accreting white dwarf. SDSS J012940.05+384210.4 has an orbital period of 37.555 Β± 0.003 min. The average spectrum shows the Stark-broadened absorption lines of the DB white dwarf accretor. The orbital period is close to the previously reported superhump period of 37.9 min. Combined, this results in a period excess Ο΅ = 0.0092 Β± 0.0054 and a mass ratio q = 0.031 Β± 0.018. SDSS J164228.06+193410.0 displays an orbital period of 54.20 Β± 1.60 min with an alias at 56.35 min. The average spectrum also shows strong Mg i absorption lines, similar to SDSS J120841.96+355025.2. SDSS J152509.57+360054.50 displays a period of 44.32 Β± 0.18 min. The overall shape of the average spectrum is more indicative of shorter period systems in the 20β35 min range. The accretor is still clearly visible in the pressure-broadened absorption lines most likely indicating a hot donor star and/or a high-mass accretor. Flux ratios for several helium lines were extracted from the Doppler tomograms for the disc and bright spot region, and compared with single-slab Local Thermodynamic Equilibrium (LTE) models with variable electron densities and path lengths to estimate the disc and bright spot temperature. Good agreement between data and the model in three out of four systems was found for the disc region. All three systems show similar disc temperatures of βΌ10 500 K. In contrast, only weak agreement between observation and models was found for the bright spot region
Genetic, Spatial, and Temporal Components of Precise Spawning Synchrony in Reef Building Corals of the Montastraea annularis Species Complex
When organisms release gametes into the sea, synchrony must be precise to increase fertilization and decrease hybridization. We tagged and genotyped over 400 spawning corals from the three species in the Montastraea annularis species complex. We report on the influence of species, individuals, and genotypes on timing of spawning from 2002 through 2009. During their annual spawning event M. franksi spawns on average 2 h after sunset, whereas M. annularis and M. faveolata spawn 3.5 h after sunset. Only M. franksi and M. annularis have compatible gametes. Individual colonies of the same genotype spawn at approximately the same time after sunset within and across years (within minutes), but different genotypes have significantly different spawning times. Neighboring colonies, regardless of genotype, spawn more synchronously than individuals spaced further apart. At a given distance, clone-mates spawn more synchronously than nonclone-mates. A transplant experiment indicates a genetic and environmental influence on spawn time. There is strong, but not absolute, concordance between spawn time, morphology, and genetics. Tight precision in spawning is achieved via a combination of external cues, genetic precision, and perhaps conspecific signaling. These mechanisms are likely to influence reproductive success and reproductive isolation in a density-dependent manner
Genuine converging solution of self-consistent field equations for extended many-electron systems
Calculations of the ground state of inhomogeneous many-electron systems
involve a solving of the Poisson equation for Coulomb potential and the
Schroedinger equation for single-particle orbitals. Due to nonlinearity and
complexity this set of equations, one believes in the iterative method for the
solution that should consist in consecutive improvement of the potential and
the electron density until the self-consistency is attained. Though this
approach exists for a long time there are two grave problems accompanying its
implementation to infinitely extended systems. The first of them is related
with the Poisson equation and lies in possible incompatibility of the boundary
conditions for the potential with the electron density distribution. The
analysis of this difficulty and suggested resolution are presented for both
infinite conducting systems in jellium approximation and periodic solids. It
provides the existence of self-consistent solution for the potential at every
iteration step due to realization of a screening effect. The second problem
results from the existence of continuous spectrum of Hamiltonian eigenvalues
for unbounded systems. It needs to have a definition of Hilbert space basis
with eigenfunctions of continuous spectrum as elements, which would be
convenient in numerical applications. The definition of scalar product
specifying the Hilbert space is proposed that incorporates a limiting
transition. It provides self-adjointness of Hamiltonian and, respectively, the
orthogonality of eigenfunctions corresponding to the different eigenvalues. In
addition, it allows to normalize them effectively to delta-function and to
prove in the general case the orthogonality of the 'right' and 'left'
eigenfunctions belonging to twofold degenerate eigenvalues.Comment: 12 pages. Reported on Interdisciplinary Workshop "Nonequilibrium
Green's Functions III", August 22 - 26, 2005, University Kiel, Germany. To be
published in Journal of Physics: Conference Series, 2006; Typos in Eqs. (37),
(53) and (54) are corrected. The content of the footnote is changed.
Published version available free online at
http://www.iop.org/EJ/abstract/1742-6596/35/1/01
Inverse Spectral-Scattering Problem with Two Sets of Discrete Spectra for the Radial Schroedinger Equation
The Schroedinger equation on the half line is considered with a real-valued,
integrable potential having a finite first moment. It is shown that the
potential and the boundary conditions are uniquely determined by the data
containing the discrete eigenvalues for a boundary condition at the origin, the
continuous part of the spectral measure for that boundary condition, and a
subset of the discrete eigenvalues for a different boundary condition. This
result extends the celebrated two-spectrum uniqueness theorem of Borg and
Marchenko to the case where there is also a continuous spectru
PTF1 J085713+331843, a new post common-envelope binary in the orbital period gap of cataclysmic variables
We report the discovery and analysis of PTF1 J085713+331843, a new eclipsing post common-envelope detached white-dwarf red-dwarf binary with a 2.5h orbital period discovered by the Palomar Transient Factory. ULTRACAM multicolour photometry over multiple orbital periods reveals a light curve with a deep flat-bottomed primary eclipse and a strong reflection effect. Phase-resolved spectroscopy shows broad Balmer absorption lines from the DA white dwarf and phase-dependent Balmer emission lines originating on the irradiated side of the red dwarf. The temperature of the DA white dwarf is K and the spectral type of the red dwarf is M3-5. A combined modelling of the light curve and the radial velocity variations results in a white dwarf mass of and radius of , and a red dwarf mass and radius of and . The system is either a detached cataclysmic variable or has emerged like from the common envelope phase at nearly its current orbital period. In Myr, this system will become a cataclysmic variable in the period gap
- β¦