183 research outputs found
Multicolor Photometry of the Vela Pulsar
Multicolor photometry of the Vela pulsar (PSR B0833-45), updated by recent
HST/WFPC2 observations obtained in the 555W, 675W and 814W filters, is
presented. The available data provide the best characterization so far of the
pulsar spectral shape, which is dominated by a flat power law continuum with
spectral index \alpha = -0.2 +/- 0.2, consistent with the extrapolation in the
optical domain of the power law component of the X-ray spectrum detected by
Chandra. In addition, a marginally significant dip (~ 3 sigma) seems to be
present at about 6500 AA. Spectroscopic observations with the VLT, now in
progress, will undoubtly provide a much better assessment of the reality and
characteristics of this feature.Comment: 4 pages, LaTex, 2 Postscript figures. Astronomy & Astrophysics,
accepte
Search for the Optical Counterpart of the Vela Pulsar X-ray Nebula
Observations of the Vela pulsar region with the Chandra X-ray observatory
have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN),
which showed an overall similarity with the Crab PWN. However, contrary to the
Crab, no firm detection of the Vela PWN in optical has been reported yet. To
search for the optical counterpart of the X-ray PWN, we analyzed deep optical
observations performed with different telescopes. We compared the optical
images with those obtained with the Chandra ACIS to search for extended
emission patterns which could be identified as counterparts of the X-ray nebula
elements. Although some features are seen in the optical images, we find no
correlation with the X-ray structure. Thus, we conclude that the diffuse
optical emission is more likely associated with filaments in the host Vela SNR.
The derived upper limits on the optical flux from the PWN are compatibile,
within the uncertainties, with the values expected on the basis of the
extrapolations of the X-ray data.Comment: 19 pages, 6 figures. Accepted for publication in Ap
The Optical Spectrum of the Vela Pulsar
Our knowledge of the optical spectra of Isolated Neutron Stars (INSs) is
limited by their intrinsic faintness. Among the fourteen optically identified
INSs, medium resolution spectra have been obtained only for a handful of
objects. No spectrum has been published yet for the Vela pulsar (PSR B0833-45),
the third brightest (V=23.6) INS with an optical counterpart. Optical
multi-band photometry underlines a flat continuum.In this work we present the
first optical spectroscopy observations of the Vela pulsar, performed in the
4000-11000 A spectral range.Our observations have been performed at the ESO VLT
using the FORS2 instrument. The spectrum of the Vela pulsar is characterized by
a flat power-law (alpha = -0.04 +/- 0.04), which compares well with the values
obtained from broad-band photometry. This confirms, once more, that the optical
emission of Vela is entirely of magnetospheric origin. The comparison between
the optical spectral indeces of rotation-powered INSs does not show evidence
for a spectral evolution suggesting that, as in the X-rays, the INS aging does
not affect the spectral properties of the magnetospheric emission. At the same
time, the optical spectral indeces are found to be nearly always flatter then
the X-rays ones, clearly suggesting a general spectral turnover at lower
energies.Comment: 7 pages, 8 figures, accepted for publication in A&
Implications of the Optical Observations of Neutron Stars
We show that observations of pulsars with pulsed optical emission indicate
that the peak flux scales according to the magnetic field strength at the light
cylinder. The derived relationships indicate that the emission mechanism is
common across all of the observed pulsars with periods ranging from 33ms to 385
ms and ages of 1000-300,000 years. It is noted that similar trends exist for
ray pulsars. Furthermore the model proposed by Pacini (1971) and
developed by Pacini and Salvati (1983,1987) still has validity and gives an
adequate explanation of the optical phenomena.Comment: 23 pages, 6 figures, accepted for publication in the Astrophysical
Journa
The distance to the Vela pulsar gauged with HST parallax oservations
The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed
to be 500 pc. Although affected by a significant uncertainty, this value stuck
to both the pulsar and the SNR. In an effort to obtain a model free distance
measurement, we have applied high resolution astrometry to the pulsar V~23.6
optical counterpart. Using a set of five HST/WFPC2 observations, we have
obtained the first optical measurement of the annual parallax of the Vela
pulsar. The parallax turns out to be 3.4 +/- 0.7 mas, implying a distance of
294(-50;+76) pc, i.e. a value significantly lower than previously believed.
This affects the estimate of the pulsar absolute luminosity and of its emission
efficiency at various wavelengths and confirms the exceptionally high value of
the N_e towards the Vela pulsar. Finally, the complete parallax data base
allows for a better measurement of the Vela pulsar proper motion
(mu_alpha(cos(delta))=-37.2 +/- 1.2 mas/yr; mu_delta=28.2 +/- 1.3 mas/yr after
correcting for the peculiar motion of the Sun) which, at the parallax distance,
implies a transverse velocity of ~65 km/s. Moreover, the proper motion position
angle appears specially well aligned with the axis of symmetry of the X-ray
nebula as seen by Chandra. Such an alignment allows to assess the space
velocity of the Vela pulsar to be ~81 km/s.Comment: LaTeX, 21 pages, 5 figures. Accepted for publication in Ap
The X-ray Spectrum of the Vela Pulsar Resolved with Chandra
We report the results of the spectral analysis of two observations of the
Vela pulsar with the Chandra X-ray observatory. The spectrum of the pulsar does
not show statistically significant spectral lines in the observed 0.25-8.0 keV
band. Similar to middle-aged pulsars with detected thermal emission, the
spectrum consists of two distinct components. The softer component can be
modeled as a magnetic hydrogen atmosphere spectrum - for the pulsar magnetic
field G and neutron star mass and radius
km, we obtain \tef^\infty =0.68\pm 0.03 MK, erg s, pc (the
effective temperature, bolometric luminosity, and radius are as measured by a
distant observer). The effective temperature is lower than that predicted by
standard neutron star cooling models. A standard blackbody fit gives MK,
erg s ( is the distance in units of 250 pc); the blackbody
temperature corresponds to a radius, km, much
smaller than realistic neutron star radii. The harder component can be modeled
as a power-law spectrum, with parameters depending on the model adopted for the
soft component - , erg s and , erg s for the hydrogen atmosphere and blackbody soft
component, respectively ( is the photon index, is the luminosity
in the 0.2--8 keV band). The extrapolation of the power-law component of the
former fit towards lower energies matches the optical flux at --1.45.Comment: Submitted to ApJ, three figures; color figure 1 can be found at
http://www.xray.mpe.mpg.de/~zavlin/pub_list.htm
Dopaminergic system modulation, behavioral changes, and oxidative stress after neonatal administration of pyrethroids
Pyrethroids are a class of insecticides involved in different neurological disorders. They cross the blood–brain barrier and exert
their effect on dopaminergic system, contributing to the burden of oxidative stress in Parkinson’s disease through several pathways.
The aim of the present study was to evaluate the effect of neonatal exposition to permethrin and cypermethrin (1/10 of DL50) in rats
from the eighth to the fifteenth day of life. Open-field studies showed increased spontaneous locomotor activity in the groups treated
with permethrin and the one treated with cypermethrin, while a higher number of center entries and time spent in the center was
observed for the cypermethrin-treated group. Lower dopamine and higher homovanillic acid levels were measured in the striatum
from both treated groups. A reduction of blood glutathione peroxidase content was measured, while no change in blood superoxide
dismutase was observed. Carbonyl group formation increased in striatum, but not in erythrocytes. Lipid peroxidation occurred in
erythrocytes, but not in striatum. No changes in fluidity at different depths of plasma membrane were measured in striatum or
erythrocytes. The activation of monocyte NADPH oxidase by phorbol esters (PMA) shows that superoxide anion production was
reduced in the pyrethroid-treated groups compared to the control group. Our studies suggest that neonatal exposition to permethrin or
cypermethrin induces long-lasting effects after developmental exposure giving changes in open-field behaviors, striatal monoamine
level, and increased oxidative stress. Although the action of pyrethroids on various target cells is different, a preferential interaction
with the extracellular side of plasma membrane proteins can be observed
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