6,519 research outputs found
Deep into the Water Fountains: The case of IRAS 18043-2116
(Abridged) The formation of large-scale (hundreds to few thousands of AU)
bipolar structures in the circumstellar envelopes (CSEs) of post-Asymptotic
Giant Branch (post-AGB) stars is poorly understood. The shape of these
structures, traced by emission from fast molecular outflows, suggests that the
dynamics at the innermost regions of these CSEs does not depend only on the
energy of the radiation field of the central star. Deep into the Water
Fountains is an observational project based on the results of programs carried
out with three telescope facilities: The Karl G. Jansky Very Large Array
(JVLA), The Australia Telescope Compact Array (ATCA), and the Very Large
Telescope (SINFONI-VLT). Here we report the results of the observations towards
the WF nebula IRAS 180432116: Detection of radio continuum emission in the
frequency range 1.5GHz - 8.0GHz; HO maser spectral features and radio
continuum emission detected at 22GHz, and H ro-vibrational emission lines
detected at the near infrared. The high-velocity HO maser spectral
features, and the shock-excited H emission detected could be produced in
molecular layers which are swept up as a consequence of the propagation of a
jet-driven wind. Using the derived H column density, we estimated a
molecular mass-loss rate of the order of Myr. On the
other hand, if the radio continuum flux detected is generated as a consequence
of the propagation of a thermal radio jet, the mass-loss rate associated to the
outflowing ionized material is of the order of 10Myr.
The presence of a rotating disk could be a plausible explanation for the
mass-loss rates estimated.Comment: 10 pages, 5 figures. Accepted for publication in A&
Flux-cutting and flux-transport effects in type-II superconductor slabs in a parallel rotating magnetic field
The magnetic response of irreversible type-II superconductor slabs subjected
to in-plane rotating magnetic field is investigated by applying the circular,
elliptic, extended-elliptic, and rectangular flux-line-cutting critical-state
models. Specifically, the models have been applied to explain experiments on a
PbBi rotating disk in a fixed magnetic field , parallel to the flat
surfaces. Here, we have exploited the equivalency of the experimental situation
with that of a fixed disk under the action of a parallel magnetic field,
rotating in the opposite sense. The effect of both the magnitude of the
applied magnetic field and its angle of rotation upon the
magnetization of the superconductor sample is analyzed. When is smaller
than the penetration field , the magnetization components, parallel and
perpendicular to , oscillate with increasing the rotation angle. On
the other hand, if the magnitude of the applied field, , is larger than
, both magnetization components become constant functions of at
large rotation angles. The evolution of the magnetic induction profiles inside
the superconductor is also studied.Comment: 12 pages, 29 figure
Submillimeter H2O masers in water-fountain nebulae
We report the first detection of submillimeter water maser emission toward
water-fountain nebulae, which are post-AGB stars that exhibit high-velocity
water masers. Using APEX we found emission in the ortho-H2O (10_29-9_36)
transition at 321.226 GHz toward three sources: IRAS 15445-5449, IRAS
18043-2116 and IRAS 18286-0959. Similarly to the 22 GHz masers, the
submillimeter water masers are expanding with a velocity larger than that of
the OH masers, suggesting that these masers also originate in fast bipolar
outflows. In IRAS 18043-2116 and IRAS 18286-0959, which figure among the
sources with the fastest water masers, the velocity range of the 321 GHz masers
coincides with that of the 22 GHz masers, indicating that they likely coexist.
Towards IRAS 15445-5449 the submillimeter masers appear in a different velocity
range, indicating that they are tracing different regions. The intensity of the
submillimeter masers is comparable to that of the 22 GHz masers, implying that
the kinetic temperature of the region where the masers originate should be Tk >
1000 K. We propose that the passage of two shocks through the same gas can
create the conditions necessary to explain the presence of strong high-velocity
321 GHz masers coexisting with the 22 GHz masers in the same region.Comment: 4 pages, 1 figure. Accepted for publication in A&A Letter
Temporal and spatial variations of the absolute reflectivity of Jupiter and Saturn from 0.38 to 1.7 m with PlanetCam-UPV/EHU
We provide measurements of the absolute reflectivity of Jupiter and Saturn
along their central meridians in filters covering a wide range of visible and
near-infrared wavelengths (from 0.38 to 1.7 m) that are not often
presented in the literature. We also give measurements of the geometric albedo
of both planets and discuss the limb-darkening behavior and temporal
variability of their reflectivity values for a period of four years
(2012-2016). This work is based on observations with the PlanetCam-UPV/EHU
instrument at the 1.23 m and 2.2 m telescopes in Calar Alto Observatory
(Spain). The instrument simultaneously observes in two channels: visible (VIS;
0.38-1.0 m) and short-wave infrared (SWIR; 1.0--1.7 m). We obtained
high-resolution observations via the lucky-imaging method. We show that our
calibration is consistent with previous independent determinations of
reflectivity values of these planets and, for future reference, provide new
data extended in the wavelength range and in the time. Our results have an
uncertainty in absolute calibration of 10--20\%. We show that under the
hypothesis of constant geometric albedo, we are able to detect absolute
reflectivity changes related to planetary temporal evolution of about 5-10\%.Comment: 13 pages, 18 figures, (in press
Evidence of ongoing radial migration in NGC 6754: Azimuthal variations of the gas properties
Understanding the nature of spiral structure in disk galaxies is one of the
main, and still unsolved questions in galactic astronomy. However, theoretical
works are proposing new testable predictions whose detection is becoming
feasible with recent development in instrumentation. In particular, streaming
motions along spiral arms are expected to induce azimuthal variations in the
chemical composition of a galaxy at a given galactic radius. In this letter we
analyse the gas content in NGC 6754 with VLT/MUSE data to characterise its 2D
chemical composition and H line-of-sight velocity distribution. We find
that the trailing (leading) edge of the NGC 6754 spiral arms show signatures of
tangentially-slower, radially-outward (tangentially-faster, radially-inward)
streaming motions of metal-rich (poor) gas over a large range of radii. These
results show direct evidence of gas radial migration for the first time. We
compare our results with the gas behaviour in a -body disk simulation
showing spiral morphological features rotating with a similar speed as the gas
at every radius, in good agreement with the observed trend. This indicates that
the spiral arm features in NGC 6754 may be transient and rotate similarly as
the gas does at a large range of radii.Comment: 8 pages, 4 figures, accepted for publication in ApJL 2016 September
2
Self-organization of ultrasound in viscous fluids
We report the theoretical and experimental demonstration of pattern formation
in acoustics. The system is an acoustic resonator containing a viscous fluid.
When the system is driven by an external periodic force, the ultrasonic field
inside the cavity experiences different pattern-forming instabilities leading
to the emergence of periodic structures. The system is also shown to possess
bistable regimes, in which localized states of the ultrasonic field develop.
The thermal nonlinearity in the viscous fluid, together with the
far-from-equilibrium conditions, are is the responsible of the observed
effects
Molecular gas at supernova local environments unveiled by EDGE
CO observations allow estimations of the gas content of molecular clouds,
which trace the reservoir of cold gas fuelling star formation, as well as to
determine extinction via H column density, N(H). Here, we studied
millimetric and optical properties at 26 supernovae (SNe) locations of
different types in a sample of 23 nearby galaxies by combining molecular
CO (J = 1 0) resolved maps from the EDGE survey and
optical Integral Field Spectroscopy from the CALIFA survey. We found an even
clearer separation between type II and type Ibc SNe in terms of molecular gas
than what we found in the optical using H emission as a proxy for
current SF rate, which reinforces the fact that SNe Ibc are more associated
with SF-environments. While A at SN locations is similar for SNe II and SNe
Ibc, and higher compared to SNe Ia, N(H) is significantly higher for SNe
Ibc than for SNe II and SNe Ia. When compared to alternative extinction
estimations directly from SN photometry and spectroscopy, we find that our SNe
Ibc have also redder color excess but showed standard Na I D absorption
pseudo-equivalent widths (1 \AA). In some cases we find no extinction
when estimated from the environment, but high amounts of extinction when
measured from SN observations, which suggests that circumstellar material or
dust sublimation may be playing a role. This work serves as a benchmark for
future studies combining last generation millimeter and optical IFS instruments
to reveal the local environmental properties of extragalactic SNe.Comment: MNRAS accepted, 17 pages, 8 Figures, 4 Table
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