1,572 research outputs found
Relative astrometry of the J=1-0, v=1 and v=2 SiO masers towards R Leonis Minoris using VERA
Oxygen-rich Asymptotic Giant Branch (AGB) stars are intense emitters of SiO
and HO maser lines at 43 (J=1-0, v=1 and 2) and 22 GHz, respectively. VLBI
observations of the maser emission provides a unique tool to sample the
innermost layers of the circumstellar envelopes in AGB stars. Nevertheless, the
difficulties in achieving astrometrically aligned v=1 and v=2 SiO maser maps
have traditionally prevented a unique interpretation of the observations in
terms of physical underlying conditions, which depend on the nature of the SiO
pumping mechanism.
We have carried out observations of the SiO and HO maser emission towards
RLMi, using the astrometric capabilities of VERA. Due to the too-weak emission
of the reference calibrator we had to develop a special method to accurately
relate the coordinates for both transitions. We present relative
astrometrically aligned v=1 and v=2 J=1-0 SiO maser maps, at multiple epochs,
and discuss the astrophysical results. The incorporation of astrometric
information into the maps of SiO masers challenges the weak points in the
current theoretical models, which will need further refinements to address the
observations results.Comment: 17 pages, 8 figure
Multi-transition study and new detections of class II methanol masers
We have used the ATNF Mopra antenna and the SEST antenna to search in the
directions of several class II methanol maser sources for emission from six
methanol transitions in the frequency range 85-115 GHz. The transitions were
selected from excitation studies as potential maser candidates. Methanol
emission at one or more frequencies was detected from five of the maser
sources, as well as from Orion KL. Although the lines are weak, we find
evidence of maser origin for three new lines in G345.01+1.79, and possibly one
new line in G9.62+0.20.
The observations, together with published maser observations at other
frequencies, are compared with methanol maser modelling for G345.01+1.79 and
NGC6334F. We find that the majority of observations in both sources are
consistent with a warm dust (175 K) pumping model at hydrogen density ~10^6
cm^-3 and methanol column density ~5 x 10^17 cm^-2. The substantial differences
between the maser spectra in the two sources can be attributed to the geometry
of the maser region.Comment: 13 pages, 6 figures, Accepted for publication in MNRA
X-ray Spectrum and Pulsations of the Vela Pulsar
We report the results of the spectral and timing analysis of observations of
the Vela pulsar with the Chandra X-ray Observatory. The spectrum shows no
statistically significant spectral lines in the observed 0.25--8.0 keV band. It
consists of two distinct continuum components. The softer component can be
modeled as either a magnetic hydrogen atmosphere spectrum with kT = 59 +- 3 eV,
R = 15.5 +- 1.5 km, or a standard blackbody with kT = 129 +- 4 eV, R = 2.1 +-
0.2 km (the radii are for a distance of 250 pc). The harder component, modeled
as a power-law spectrum, gives photon indices depending on the model adopted
for the soft component: gamma = 1.5 +- 0.3 for the magnetic atmosphere soft
component, and gamma = 2.7 +- 0.4 for the blackbody soft component. Timing
analysis shows three peaks in the pulse profile, separated by about 0.3 in
phase. Energy-resolved timing provides evidence for pulse profile variation
with energy. The higher energy (E > 1.8 keV) profile shows significantly higher
pulsed fraction.Comment: 4 pages, 2 figures, To appear in "Neutron Stars in Supernova
Remnants" (ASP Conference Proceedings), eds P. O. Slane and B. M. Gaensler
Corrected TYPO
The Complex Wind Torus and Jets of PSR B1706-44
We report on Chandra ACIS imaging of the pulsar wind nebula (PWN) of the
young Vela-like PSR B1706-44, which shows the now common pattern of an
equatorial wind and polar jets. The structure is particularly rich, showing a
relativistically boosted termination shock, jets with strong confinement, a
surrounding radio/X-ray PWN and evidence for a quasi-static `bubble nebula'.
The structures trace the pulsar spin geometry and illuminate its possible
relation to SNR G343.1-2.3. We also obtain improved estimates of the pulsar
flux and nebular spectrum, constraining the system age and energetics.Comment: To appear in the Astrophysical Journal. 15pp, 4 figures in 7 file
Integrated Diamond Optics for Single Photon Detection
Optical detection of single defect centers in the solid state is a key
element of novel quantum technologies. This includes the generation of single
photons and quantum information processing. Unfortunately the brightness of
such atomic emitters is limited. Therefore we experimentally demonstrate a
novel and simple approach that uses off-the-shelf optical elements. The key
component is a solid immersion lens made of diamond, the host material for
single color centers. We improve the excitation and detection of single
emitters by one order of magnitude, as predicted by theory.Comment: 10 pages, 3 figure
GPS positioning errors during the space weather event of October 2003
Due to the configuration of the Earth’s magnetic field and its reconnection with the Interplanetary Magnetic Field (IMF), the high latitudes ionosphere is directly connected with outer space and, consequently, highly sensitive to the enhancement of the electromagnetic radiation and energetic particles coming from the Sun. Under such conditions the ionosphere may show the presence of small-scale structures or irregularities imbedded in the large-scale ambient plasma. These irregularities can produce short term phase and amplitude fluctuations in the carrier frequency of the radio waves which pass through them, commonly called ionospheric phase and amplitude scintillations. Since September 2003 a GPS Ionospheric Scintillation and TEC Monitor (GISTM) receiver has been deployed at the Italian Arctic station “Dirigibile Italia” in Ny Alesund (79.9° N, 11.9° E, Svalbard, Norway), in the frame of the ISACCO (Ionospheric Scintillations Arctic Campaign Coordinated Observation) project. The receiver computes and records GPS phase and amplitude scintillation parameters, as well as TEC (Total Electron Content). The measurements made by ISACCO during the superstorm of October 2003 have been here used to assess the positioning errors affecting GNSS (Global Navigation Satellite Systems, such as GPS and the European Galileo) users and their correlation with the occurrence of observed levels of scintillation
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