808 research outputs found
Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?
A unified semiclassical time propagator is used to calculate the
semiclassical time-correlation function in three cartesian dimensions for a
particle moving in an attractive Coulomb potential. It is demonstrated that
under these conditions the singularity of the potential does not cause any
difficulties and the Coulomb interaction can be treated as any other
non-singular potential. Moreover, by virtue of our three-dimensional
calculation, we can explain the discrepancies between previous semiclassical
and quantum results obtained for the one-dimensional radial Coulomb problem.Comment: 8 pages, 4 figures (EPS
Semiclassical description of multiphoton processes
We analyze strong field atomic dynamics semiclassically, based on a full
time-dependent description with the Hermann-Kluk propagator. From the
properties of the exact classical trajectories, in particular the accumulation
of action in time, the prominent features of above threshold ionization (ATI)
and higher harmonic generation (HHG) are proven to be interference phenomena.
They are reproduced quantitatively in the semiclassical approximation.
Moreover, the behavior of the action of the classical trajectories supports the
so called strong field approximation which has been devised and postulated for
strong field dynamics.Comment: 10 pages, 11 figure
Extensive HST Ultraviolet Spectra and Multi-wavelength Observations of SN 2014J in M82 Indicate Reddening and Circumstellar Scattering by Typical Dust
SN 2014J in M82 is the closest detected Type Ia supernova (SN Ia) in at least
28 years and perhaps in 410 years. Despite its small distance of 3.3 Mpc, SN
2014J is surprisingly faint, peaking at V = 10.6 mag, and assuming a typical SN
Ia luminosity, we infer an observed visual extinction of A_V = 2.0 +/- 0.1 mag.
But this picture, with R_V = 1.6 +/- 0.2, is too simple to account for all
observations. We combine 10 epochs (spanning a month) of HST/STIS ultraviolet
through near-infrared spectroscopy with HST/WFC3, KAIT, and FanCam photometry
from the optical to the infrared and 9 epochs of high-resolution TRES
spectroscopy to investigate the sources of extinction and reddening for SN
2014J. We argue that the wide range of observed properties for SN 2014J is
caused by a combination of dust reddening, likely originating in the
interstellar medium of M82, and scattering off circumstellar material. For this
model, roughly half of the extinction is caused by reddening from typical dust
(E(B-V ) = 0.45 mag and R_V = 2.6) and roughly half by scattering off LMC-like
dust in the circumstellar environment of SN 2014J.Comment: 17 pages (excluding references and tables), 15 figures, accepted to
MNRAS. A high-resolution HST image of SN 2014J in M82 is available upon
reques
The structural properties and star formation history of Leo T from deep LBT photometry
We present deep, wide-field g and r photometry of the transition type dwarf
galaxy Leo T, obtained with the blue arm of the Large Binocular Telescope. The
data confirm the presence of both very young (5
Gyr) stars. We study the structural properties of the old and young stellar
populations by preferentially selecting either population based on their color
and magnitude. The young population is significantly more concentrated than the
old population, with half-light radii of 104+-8 and 148+-16 pc respectively,
and their centers are slightly offset. Approximately 10% of the total stellar
mass is estimated to be represented by the young stellar population. Comparison
of the color-magnitude diagram (CMD) with theoretical isochrones as well as
numerical CMD-fitting suggest that star formation began over 10 Gyr ago and
continued in recent times until at least a few hundred Myr ago. The CMD-fitting
results are indicative of two distinct star formation bursts, with a quiescent
period around 3 Gyr ago, albeit at low significance. The results are consistent
with no metallicity evolution and [Fe/H] ~ -1.5 over the entire age of the
system. Finally, the data show little if any sign of tidal distortion of Leo T.Comment: 8 pages, 9 figures, some small textual changes, accepted for
publication in the Astrophysical Journa
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Early Observations And Analysis Of The Type Ia SN 2014J In M82
We present optical and near infrared (NIR) observations of the nearby Type Ia SN 2014J. Seventeen optical and 23 NIR spectra were obtained from 10 days before (-10d) to 10 days after (+10d) the time of maximum B-band brightness. The relative strengths of absorption features and their patterns of development can be compared at one day intervals throughout most of this period. Carbon is not detected in the optical spectra, but we identify C I lambda 1.0693 in the NIR spectra. Mg II lines with high oscillator strengths have higher initial velocities than other Mg II lines. We show that the velocity differences can be explained by differences in optical depths due to oscillator strengths. The spectra of SN 2014J show that it is a normal SN Ia, but many parameters are near the boundaries between normal and high-velocity subclasses. The velocities for OI, Mg II, Si II, S Ca a, and Fell suggest that SN 2014J has a layered structure with little or no mixing. That result is consistent with the delayed detonation explosion models. We also report photometric observations, obtained from -10d to +29d, in the UBVRIJH and K-s bands. The template fitting package SNooPy is used to interpret the light curves and to derive photometric parameters. Using R-v = 1.46, which is consistent with previous studies, SNooPy finds that A(v) = 1.80 for E(B - V)(host) = 1.23 +/- 0.06 mag. The maximum B-band brightness of -19.19 +/- 0.10 mag was reached on February 1.74 UT +/- 0.13 days and the supernova has a decline parameter, Delta m(15), of 1.12 +/- 0.02 mag.Department of Space, Government of IndiaHungarian OTKA NN-107637NSF AST-1109801, AST-1151462, AST-1211196NSF Astronomy and Astrophysics Postdoctoral Fellowship AST-1302771NASA through a grant from the Space Telescope Science Institute GO-12540NASA NAS5-26555Swedish Research CouncilSwedish National Space BoardDanish Agency for Science and Technology and Innovation realized through a Sapere Aude Level 2 grantAstronom
Early Observations and Analysis of the Type Ia SN 2014J in M82
We present optical and near infrared (NIR) observations of the nearby Type Ia
SN 2014J. Seventeen optical and twenty-three NIR spectra were obtained from 10
days before (10d) to 10 days after (+10d) the time of maximum -band
brightness. The relative strengths of absorption features and their patterns of
development can be compared at one day intervals throughout most of this
period. Carbon is not detected in the optical spectra, but we identify CI
1.0693 in the NIR spectra. We find that MgII lines with high
oscillator strengths have higher initial velocities than other MgII lines. We
show that the velocity differences can be explained by differences in optical
depths due to oscillator strengths. The spectra of SN 2014J show it is a normal
SN Ia, but many parameters are near the boundaries between normal and
high-velocity subclasses. The velocities for OI, MgII, SiII, SII, CaII and FeII
suggest that SN 2014J has a layered structure with little or no mixing. That
result is consistent with the delayed detonation explosion models. We also
report photometric observations, obtained from 10d to +29d, in the
and bands. SN 2014J is about 3 magnitudes fainter than a normal SN Ia at
the distance of M82, which we attribute to extinction in the host. The template
fitting package SNooPy is used to interpret the light curves and to derive
photometric parameters. Using = 1.46, which is consistent with previous
studies, SNooPy finds that for mag.
The maximum -band brightness of mag was reached on
February 1.74 UT days and the supernova had a decline parameter of
mag.Comment: 6 figures, 6 tables, submitted to the Ap
The Very Young Type Ia Supernova 2013dy: Discovery, and Strong Carbon Absorption in Early-Time Spectra
The Type Ia supernova (SN Ia) 2013dy in NGC 7250 (d ~ 13.7 Mpc) was
discovered by the Lick Observatory Supernova Search. Combined with a
prediscovery detection by the Italian Supernova Search Project, we are able to
constrain the first-light time of SN 2013dy to be only 0.10 +/- 0.05 d (2.4 +/-
1.2 hr) before the first detection. This makes SN 2013dy the earliest known
detection of an SN Ia. We infer an upper limit on the radius of the progenitor
star of R_0 < 0.25 R_sun, consistent with that of a white dwarf. The light
curve exhibits a broken power law with exponents of 0.88 and then 1.80. A
spectrum taken 1.63 d after first light reveals a C II absorption line
comparable in strength to Si II. This is the strongest C II feature ever
detected in a normal SN Ia, suggesting that the progenitor star had significant
unburned material. The C II line in SN 2013dy weakens rapidly and is undetected
in a spectrum 7 days later, indicating that C II is detectable for only a very
short time in some SNe Ia. SN 2013dy reached a B-band maximum of M_B = -18.72
+/- 0.03 mag ~17.7 d after first light.Comment: Accepted for Publication in ApJ Letter
On the physical origin of dark matter density profiles
The radial mass distribution of dark matter haloes is investigated within the
framework of the spherical infall model. We present a new formulation of
spherical collapse including non-radial motions, and compare the analytical
profiles with a set of high-resolution N-body simulations ranging from galactic
to cluster scales. We argue that the dark matter density profile is entirely
determined by the initial conditions, which are described by only two
parameters: the height of the primordial peak and the smoothing scale. These
are physically meaningful quantities in our model, related to the mass and
formation time of the halo. Angular momentum is dominated by velocity
dispersion, and it is responsible for the shape of the density profile near the
centre. The phase-space density of our simulated haloes is well described by a
power-law profile, rho/sigma^3 = 10^{1.46\pm0.04} (rho_c/Vvir^3)
(r/Rvir)^{-1.90\pm0.05}. Setting the eccentricity of particle orbits according
to the numerical results, our model is able to reproduce the mass distribution
of individual haloes.Comment: 12 pages, 13 figures, submitted to MNRA
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