6,394 research outputs found
Jet-cloud interations and the brightening of the narrow line region in Seyfert galaxies
We study the kinematical and brightness evolution of emission line clouds in
the narrow line region (NLR) of Seyfert galaxies during the passage of a jet.
We derive a critical density above which a cloud remains radiative after
compression by the jet cocoon. The critical density depends mainly on the
cocoon pressure. Super-critical clouds increase in emission line brightness,
while sub-critical clouds generally are highly overheated reducing their
luminosity below that of the inter-cloud medium. Due to the pressure
stratification in the bow-shock of the jet, a cylindrical structure of nested
shells develops around the jet. The most compact and brightest compressed
clouds surround the cloud-free channel of the radio jet. To support our
analytical model we present a numerical simulation of a supersonic jet
propagating into a clumpy NLR. The position-velocity diagram of the simulated
H_alpha emission shows total line widths of the order of 500 km/s with
large-scale variations in the radial velocities of the clouds due to the
stratified pressure in the bow-shock region of the jet. Most of the luminosity
is concentrated in a few dense clouds surrounding the jet. These morphological
and kinematic signatures are all found in the well observed NLR of NGC1068 and
other Seyfert galaxies.Comment: 11 pages, 3 figures, accepted for publication in The Astrophysical
Journal Letter
Primordial nucleosynthesis as a probe of fundamental physics parameters
We analyze the effect of variation of fundamental couplings and mass scales
on primordial nucleosynthesis in a systematic way. The first step establishes
the response of primordial element abundances to the variation of a large
number of nuclear physics parameters, including nuclear binding energies. We
find a strong influence of the n-p mass difference (for the 4He abundance), of
the nucleon mass (for deuterium) and of A=3,4,7 binding energies (for 3He, 6Li
and 7Li). A second step relates the nuclear parameters to the parameters of the
Standard Model of particle physics. The deuterium, and, above all, 7Li
abundances depend strongly on the average light quark mass hat{m} \equiv
(m_u+m_d)/2. We calculate the behaviour of abundances when variations of
fundamental parameters obey relations arising from grand unification. We also
discuss the possibility of a substantial shift in the lithium abundance while
the deuterium and 4He abundances are only weakly affected.Comment: v2: 34 pages, 2 figures, typo in last GUT scenario corrected, added
discussion and graph of nonlinear behaviour in GUT scenarios, added short
section discussing binding of dineutron and 8Be, refs added, conclusions
unaltered. Accepted for publication, Phys. Rev.
Submillimeter-wave emission of three Galactic red novae: cool molecular outflows produced by stellar mergers
Red novae are optical transients erupting at luminosities typically higher
than those of classical novae. Their outbursts are believed to be caused by
stellar mergers. We present millimeter/submillimeter-wave observations with
ALMA and SMA of the three best known Galactic red novae, V4332 Sgr, V1309 Sco,
and V838 Mon. The observations were taken 22, 8, and 14 yr after their
respective eruptions and reveal the presence of molecular gas at excitation
temperatures of 35-200 K. The gas displays molecular emission in rotational
transitions with very broad lines (full width 400 km\s). We found
emission of CO, SiO, SO, SO (in all three red novae), HS (covered only
in V838 Mon) and AlO (present in V4332 Sgr and V1309 Sco). No anomalies were
found in the isotopic composition of the molecular material and the chemical
(molecular) compositions of the three red novae appear similar to those of
oxygen-rich envelopes of classical evolved stars (RSGs, AGBs, post-AGBs). The
minimum masses of the molecular material that most likely was dispersed in the
red-nova eruptions are 0.1, 0.01, and 10 M for V838 Mon, V4332
Sgr, and V1309 Sco, respectively. The molecular outflows in V4332 Sgr and V1309
Sco are spatially resolved and appear bipolar. The kinematic distances to V1309
Sco and V4332 Sgr are 2.1 and 4.2 kpc, respectively. The kinetic energy stored
in the ejecta of the two older red-nova remnants of V838 Mon and V4332 Sgr is
of order erg, similar to values found for some post-AGB (pre-PN)
objects whose bipolar ejecta were also formed in a short-duration eruption. Our
observations strengthen the link between these post-AGB objects and red novae
and support the hypothesis that some of the post-AGB objects were formed in a
common-envelope ejection event or its most catastrophic outcome, a merger.Comment: 19 pages, 13 figures, accepted to A&
Stability of Localized Wave Fronts in Bistable Systems
Localized wave fronts are a fundamental feature of biological systems from cell biology to ecology. Here, we study a broad class of bistable models subject to self-activation, degradation, and spatially inhomogeneous activating agents. We determine the conditions under which wave-front localization is possible and analyze the stability thereof with respect to extrinsic perturbations and internal noise. It is found that stability is enhanced upon regulating a positional signal and, surprisingly, also for a low degree of binding cooperativity. We further show a contrasting impact of self-activation to the stability of these two sources of destabilization. DOI: 10.1103/PhysRevLett.110.03810
The three-dimensional structure of the Eta Carinae Homunculus
We investigate, using the modeling code SHAPE, the three-dimensional
structure of the bipolar Homunculus nebula surrounding Eta Carinae, as mapped
by new ESO VLT/X-Shooter observations of the H2 micron
emission line. Our results reveal for the first time important deviations from
the axisymmetric bipolar morphology: 1) circumpolar trenches in each lobe
positioned point-symmetrically from the center and 2) off-planar protrusions in
the equatorial region from each lobe at longitudinal (~55 degrees) and
latitudinal (10-20 degrees) distances from the projected apastron direction of
the binary orbit. The angular distance between the protrusions (~110 degrees)
is similar to the angular extent of each polar trench (~130 degrees) and nearly
equal to the opening angle of the wind-wind collision cavity (~110 degrees). As
in previous studies, we confirm a hole near the centre of each polar lobe and
no detectable near-IR H2 emission from the thin optical skirt seen prominently
in visible imagery. We conclude that the interaction between the outflows
and/or radiation from the central binary stars and their orientation in space
has had, and possibly still has, a strong influence on the Homunculus. This
implies that prevailing theoretical models of the Homunculus are incomplete as
most assume a single star origin that produces an axisymmetric nebula. We
discuss how the newly found features might be related to the Homunculus
ejection, the central binary and the interacting stellar winds. We also include
a 3D printable version of our Homunculus model.Comment: 14 pages, 7 color figures, 1 interactive 3D figure (Figure 5,
requires Adobe Reader), published in MNRAS. A 3D printable version of our
Homunculus model can be downloaded from
http://svs.gsfc.nasa.gov/vis/a010000/a011500/a011568/Eta_Car_Homunuculus_3D_model.zip
or from the 'Supporting Information' link in the electronic version of the
MNRAS articl
The Changing AGN Population
We investigate how the fraction of broad-line sources in the AGN population
changes with X-ray luminosity and redshift. We first construct the rest-frame
hard-energy (2-8 keV) X-ray luminosity function (HXLF) at z=0.1-1 using Chandra
Lockman Hole-Northwest wide-area data, Chandra Deep Field-North 2 Ms data,
other Chandra deep field data, and the ASCA Large Sky Survey data. We find that
broad-line AGNs dominate above 3e43 ergs/s and have a mean luminosity of 1.3e44
ergs/s. Type II AGNs can only become an important component of the X-ray
population at Seyfert-like X-ray luminosities. We then construct z=0.1-0.5 and
z=0.5-1 HXLFs and compare them with both the local HXLF measured from HEAO-1 A2
survey data and the z=1.5-3 HXLF measured from soft-energy (0.5-2 keV) Chandra
and ROSAT data. We find that the number density of >1e44 ergs/s sources
(quasars) steadily declines with decreasing redshift, while the number density
of 1e43-1e44 ergs/s sources peaks at z=0.5-1. Strikingly, however, the number
density of broad-line AGNs remains roughly constant with redshift while their
average luminosities decline at the lower redshifts, showing another example of
cosmic downsizing.Comment: Accepted by The Astrophysical Journal Letters, 5 page
Stability Properties of Strongly Magnetized Spine Sheath Relativistic Jets
The linearized relativistic magnetohydrodynamic (RMHD) equations describing a
uniform axially magnetized cylindrical relativistic jet spine embedded in a
uniform axially magnetized relativistically moving sheath are derived. The
displacement current is retained in the equations so that effects associated
with Alfven wave propagation near light speed can be studied. A dispersion
relation for the normal modes is obtained. Analytical solutions for the normal
modes in the low and high frequency limits are found and a general stability
condition is determined. A trans-Alfvenic and even a super-Alfvenic
relativistic jet spine can be stable to velocity shear driven Kelvin-Helmholtz
modes. The resonance condition for maximum growth of the normal modes is
obtained in the kinetically and magnetically dominated regimes. Numerical
solution of the dispersion relation verifies the analytical solutions and is
used to study the regime of high sound and Alfven speeds.Comment: 42 pages includes 7 figures, to appear in Ap
Radio Frequency Models of Novae in eruption. I. The Free-Free Process in Bipolar Morphologies
Observations of novae at radio frequencies provide us with a measure of the
total ejected mass, density profile and kinetic energy of a nova eruption. The
radio emission is typically well characterized by the free-free emission
process. Most models to date have assumed spherical symmetry for the eruption,
although it has been known for as long as there have been radio observations of
these systems, that spherical eruptions are to simplistic a geometry. In this
paper, we build bipolar models of the nova eruption, assuming the free-free
process, and show the effects of varying different parameters on the radio
light curves. The parameters considered include the ratio of the minor- to
major-axis, the inclination angle and shell thickness (further parameters are
provided in the appendix). We also show the uncertainty introduced when fitting
spherical model synthetic light curves to bipolar model synthetic light curves.
We find that the optically thick phase rises with the same power law () for both the spherical and bipolar models. In the bipolar case
there is a "plateau" phase -- depending on the thickness of the shell as well
as the ratio of the minor- to major-axis -- before the final decline, that
follows the same power law () as in the spherical case.
Finally, fitting spherical models to the bipolar model synthetic light curves
requires, in the worst case scenario, doubling the ejected mass, more than
halving the electron temperature and reducing the shell thickness by nearly a
factor of 10. This implies that in some systems we have been over predicting
the ejected masses and under predicting the electron temperature of the ejecta.Comment: 9 pages, 6 figures, accepted for publication in ApJ, accompanying
movie to figure 3 available at
http://www.ast.uct.ac.za/~valerio/papers/radioI
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