1,138 research outputs found
The spectroscopic evolution of the -ray emitting classical nova Nova Mon 2012. I. Implications for the ONe subclass of classical novae
Nova Mon 2012 was the first classical nova to be detected as a high energy
-ray transient, by Fermi-LAT, before its optical discovery. We study a
time sequence of high resolution optical echelle spectra (Nordic Optical
Telescope) and contemporaneous NOT, STIS UV, and CHIRON echelle spectra (Nov
20/21/22). We use [O III] and H line fluxs to constrain the properties
of the ejecta. We derive the structure from the optical and UV line profiles
and compare our measured line fluxes for with predictions using Cloudy with
abundances from other ONe novae. Mon 2012 is confirmed as an ONe nova. We find
E(B-V)=0.850.05 and hydrogen column density
cm. The corrected continuum luminosity is nearly the same in the entire
observed energy range as V1974 Cyg, V382 Mon, and Nova LMC 2000 at the same
epoch after outburst. The distance, about 3.6 kpc, is quite similar to V1974
Cyg. The line profiles can be modeled using an axisymmetric bipolar geometry
for the ejecta with various inclinations of the axis to the line of sight, 60
\le i \le 80 degrees, an opening angle of \approx\Delta
R/R(t)\approx 0.4f\approx 0.1-0.3\leq 6\times
10^{-5}_\odot\gamma$-ray emission may be a generic phenomenon, common to all ONe novae,
possibly to all classical novae, and connected with acceleration and emission
processes within the ejecta (abstract severely truncated).Comment: Submitted to A&A 9/1/2013; Accepted 27/2/2013 (in press
The spectroscopic evolution of the recurrent nova T Pyxidis during its 2011 outburst. II.The optically thin phase and the structure of the ejecta in recurrent novae
We continue our study of the physical properties of the recurrent nova T Pyx,
focussing on the structure of the ejecta in the nebular stage of expansion
during the 2011 outburst. The nova was observed contemporaneously with the
Nordic Optical Telescope (NOT), at high resolution spectroscopic resolution (R
~ 65000) on 2011 Oct. 11 and 2012 Apr. 8 (without absolute flux calibration),
and with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble
Space Telescope, at high resolution (R ~ 30000) on 2011 Oct. 10 and 2012 Mar.
28 (absolute fluxes). We use standard plasma diagnostics (e.g. [O III] and [N
II] line ratios and the H line fluxes) to constrain electron densities
and temperatures. Using Monte Carlo modeling of the ejecta, we derive the
structure and filling factor from comparisons to the optical and ultraviolet
line profiles. The ejecta can be modeled using an axisymmetric conical --
bipolar -- geometry with a low inclination of the axis to the line of sight,
i=15+/-5 degrees, compatible with published results from high angular
resolution optical spectro-interferometry. The structure is similar to that
observed in the other short orbital period recurrent novae during their nebular
stages. We show that the electron density scales as as expected from a
ballistically ejected constant mass shell; there is no need to invoke a
continuing mass outflow following the eruption. The derived mass for the ejecta
with filling factor f ~ 3%, M_ej ~ 2E-6$M_sun is similar to that obtained for
other recurrent nova ejecta but inconsistent with the previously reported
extended optically thick epoch of the explosion. We suggest that the system
underwent a common envelope phase following the explosion that produced the
recombination event. Implications for the dynamics of the recurrent novae are
discussed. (truncated)Comment: accepted for publication in A&A (10 Nov. 2012), 10 pgs, 16 fig
Long term pasture alters carbon stocks and organic matter dynamics in Brazilian Southwestern Amazon.
The main objective of this work was to evaluate the impact of pasture introduction on the C stocks and SOM dynamics in Acrisol profiles under long-term pastures in the Brazilian Southwestern Amazon
Fighting or supporting corruption? The role of public sector audit organizations in Brazil
Public sector audit organizations are usually expected to fight corruption. Yet they may also end up being involved in, and contributing to, sustaining corruption. Relying on multiple interviews, this paper sheds new light on the concrete mechanisms through which corruption is sustained by Brazilian regional Courts of Accounts and their members. Our findings show how politico-economic elitesâ private interests infiltrate the Courts via the appointment of high-ranked officials and how those officials may resort to a variety of actions to perpetrate forms of selective justice and to weaken the audit findings of these organizations â which ends up strengthening and supporting corruption. Additionally, we provide evidence of collective action emerging to challenge the current situation and reinforce the role Courts could play as watchdogs of the public interest. We contribute to the literature by highlighting the deleterious role of the interface between political and economic interests and the functioning of audit organizations. Moreover, relying on the literature of first- and second-order corruption, we discuss the specific conditions and mechanisms which enable corruption in public audit organizations. Finally, we present practical implications providing alternative views to the status quo
Electronic plasma diffusion with radiation reaction force and time-dependent electric field
In this work the explicit solution of the electronic plasma diffusion with
radiation reaction force, under the action of an exponential decay external
electric field is given. The electron dynamics is described by a classical
generalized Langevin equation characterized by an Ornstein-Uhlenbeck-type
friction memory kernel, with an effective memory time which accounts for the
effective thermal interaction between the electron and its surroundings
(thermal collisions between electrons + radiation reaction force). The incident
electric field exerts an electric force on the electron, which in turn can
induce an additional damping to the braking radiation force, allowing a delay
in the electron characteristic time. This fact allows that the effective memory
time be finite and positive, and as a consequence, obtaining physically
admissible solutions of the stochastic Abraham-Lorentz-like equation. It is
shown that the diffusion process is quasi-Markovian which includes the
radiation effects.Comment: 16 pages, 8 figure
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