709 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&
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
Bow shocks in water fountain jets
We briefly introduce the VLBI maser astrometric analysis of IRAS 18043-2116
and IRAS 18113-2503, two remarkable and unusual water fountains with
spectacular bipolar bow shocks in their high-speed collimated jet-driven
outflows. The 22 GHz H2O maser structures and velocities clearly show that the
jets are formed in very short-lived, episodic outbursts, which may indicate
episodic accretion in an underlying binary system.Comment: To appear in the proceedings of the IAU Symposium 336: Astrophysical
Masers: Unlocking the Mysteries of the Universe (4-8 September 2017,
Cagliari, Italy) - IAU Proceedings Series, eds. A. Tarchi, M. J. Reid, and P.
Castangi
Kinematics of the Outflow From The Young Star DG Tau B: Rotation in the vicinities of an optical jet
We present CO(2-1) line and 1300 m continuum observations made
with the Submillimeter Array (SMA) of the young star DG Tau B. We find, in the
continuum observations, emission arising from the circumstellar disk
surrounding DG Tau B. The CO(2-1) line observations, on the other hand,
revealed emission associated with the disk and the asymmetric outflow related
with this source. Velocity asymmetries about the flow axis are found over the
entire length of the flow. The amplitude of the velocity differences is of the
order of 1 -- 2 km s over distances of about 300 -- 400 AU. We interpret
them as a result of outflow rotation. The sense of the outflow and disk
rotation is the same. Infalling gas from a rotating molecular core cannot
explain the observed velocity gradient within the flow. Magneto-centrifugal
disk winds or photoevaporated disk winds can produce the observed rotational
speeds if they are ejected from a keplerian disk at radii of several tens of
AU. Nevertheless, these slow winds ejected from large radii are not very
massive, and cannot account for the observed linear momentum and angular
momentum rates of the molecular flow. Thus, the observed flow is probably
entrained material from the parent cloud. DG Tau B is a good laboratory to
model in detail the entrainment process and see if it can account for the
observed angular momentum.Comment: Accepted to Ap
Spatio-kinematical model of the collimated molecular outflow in the water-fountain nebula IRAS 16342-3814
Context. Water-fountain nebulae are asymptotic giant branch (AGB) and post-AGB objects that exhibit high-velocity outflows traced by water-maser emission. Their study is important for understanding the interaction between collimated jets and the circumstellar material that leads to the formation of bipolar and/or multi-polar morphologies in evolved stars. Aims. The aim of this paper is to describe the three-dimensional morphology and kinematics of the molecular gas of the water-fountain nebula IRAS 16342-3814. Methods. Data was retrieved from the ALMA archive for analysis using a simple spatio-kinematical model. The software SHAPE was employed to construct a three-dimensional, spatio-kinematical model of the molecular gas in IRAS 16342-3814, and to then reproduce the intensity distribution and position-velocity diagram of the CO emission from the ALMA observations to derive the morphology and velocity field of the gas. Data from CO(J = 1 -> 0) supported the physical interpretation of the model. Results. A spatio-kinematical model that includes a high-velocity collimated outflow embedded within material expanding at relatively lower velocity reproduces the images and position-velocity diagrams from the observations. The derived morphology is in good agreement with previous results from IR and water-maser emission observations. The high-velocity collimated outflow exhibits deceleration across its length, while the velocity of the surrounding component increases with distance. The morphology of the emitting region, the velocity field, and the mass of the gas as function of velocity are in excellent agreement with the properties predicted for a molecular outflow driven by a jet. The timescale of the molecular outflow is estimated to be similar to 70-100 yr. The scalar momentum carried by the outflow is much larger than it can be provided by the radiation of the central star. An oscillating pattern was found associated with the high-velocity collimated outflow. The oscillation period of the pattern is T approximate to 60-90 yr and its opening angle is theta(op) approximate to 2 degrees. Conclusions. The CO (J= 3 -> 2) emission in IRAS 16342-3814 is interpreted in terms of a jet-driven molecular outflow expanding along an elongated region. The position-velocity diagram and the mass spectrum reveal a feature due to entrained material that is associated with the driving jet. This feature is not seen in other more evolved objects that exhibit more developed bipolar morphologies. It is likely that the jet in those objects has already disappeared since it is expected to last only for a couple hundred years. This strengthens the idea that water fountain nebulae are undergoing a very short transition during which they develop the collimated outflows that shape the circumstellar envelopes. The oscillating pattern seen in the CO high-velocity outflow is interpreted as due to precession with a relatively small opening angle. The precession period is compatible with the period of the corkscrew pattern seen at IR wavelengths. We propose that the high-velocity molecular outflow traces the underlying primary jet that produces such a pattern
The Magnetic Field of the H~II Region NGC 6334A
We have studied the polarization characteristics and Faraday rotation of the
extragalactic radio source J172043554, that appears projected on the north
lobe of the galactic H II region NGC 6334A. From observations made with the
Very Large Array at 6.0 and 3.6 cm in three different epochs (1994, 1997, and
2006), we estimate a rotation measure of +5100900 rad m for the
extragalactic source. This large rotation measure implies a line-of-sight
average magnetic field of G, the largest
obtained by this method for an H II region. NGC 6334A is significantly denser
than other H II regions studied and this larger magnetic field is expected on
the grounds of magnetic flux conservation. The ratio of thermal to magnetic
pressure is 5, in the range of values determined for more diffuse H II
regions.Comment: 5 pages, 0 figure
Radio interferometric observations of candidate water-maser-emitting planetary nebulae
We present Very Large Array (VLA) observations of H2O and OH masers, as well
as radio continuum emission at 1.3 and 18 cm toward three sources previously
cataloged as planetary nebulae (PNe) and in which single-dish detections of H2O
masers have been reported: IRAS 17443-2949, IRAS 17580-3111, and IRAS
18061-2505. Our goal was to unambiguously confirm their nature as
water-maser-emitting PNe, a class of objects of which only two bona-fide
members were previously known. We detected and mapped H2O maser emission toward
all three sources, while OH maser emission is detected in IRAS 17443-2949 and
IRAS 17580-3111 as well as in other two objects within the observed fields:
IRAS 17442-2942 (unknown nature) and IRAS 17579-3121 (also cataloged as a
possible PN). We found radio continuum emission associated only with IRAS
18061-2505. Our results confirm IRAS 18061-2505 as the third known case of a PN
associated with H2O maser emission. The three known water-maser-emitting PNe
have clear bipolar morphologies, which suggests that water maser emission in
these objects is related to non-spherical mass-loss episodes. We speculate that
these bipolar PNe would have ``water-fountain'' Asymptotic Giant Branch (AGB)
and post-AGB stars as their precursors. A note of caution is given for other
objects that have been classified as OHPNe (objects with both OH maser and
radio continuum emission, that could be extremely young PNe) based on
single-dish observations, since interferometric data of both OH masers and
continuum are necessary for a proper identification as members of this class.Comment: 33 pages, 10 figures. Accepted by The Astronomical Journa
Towards the deformation quantization of linearized gravity
We present a first attempt to apply the approach of deformation quantization
to linearized Einstein's equations. We use the analogy with Maxwell equations
to derive the field equations of linearized gravity from a modified Maxwell
Lagrangian which allows the construction of a Hamiltonian in the standard way.
The deformation quantization procedure for free fields is applied to this
Hamiltonian. As a result we obtain the complete set of quantum states and its
discrete spectrum.Comment: 13 pages, no figures **preliminary entry **
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