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J/A+A/612/A48 4 oxygen-rich evolved stars NH3 spectra (Wong+, 2018)
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Circumstellar ammonia in oxygen-rich evolved stars.
Wong K.T., Menten K.M., Kaminski T., Wyrowski F., Lacy J.H., Greathouse T.K.
<Astron. Astrophys. 612, A48 (2018)>
=2018A&A...612A..48W (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, emission ; Stars, radio ; Planetary nebulae ;
Stars, giant ; Stars, supergiant ; Radio lines ;
Spectra, millimetric/submm ; Spectra, infrared
Keywords: stars: AGB and post-AGB - circumstellar matter - supergiants -
tars: winds, outflows - ISM: molecules - stars: mass-loss
Abstract:
The circumstellar ammonia (NH_3_) chemistry in evolved stars is poorly
understood. Previous observations and modelling showed that NH_3_
abundance in oxygen-rich stars is several orders of magnitude above
that predicted by equilibrium chemistry.
We would like to characterise the spatial distribution and excitation
of NH_3_ in the oxygen-rich circumstellar envelopes (CSEs) of four
diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420.
We observed NH_3_ emission from the ground state in the inversion
transitions near 1.3cm with the Very Large Array (VLA) and
submillimetre rotational transitions with the Heterodyne Instrument
for the Far-Infrared (HIFI) aboard Herschel Space Observatory from all
four targets. For IK Tau and VY CMa, we observed NH_3_ rovibrational
absorption lines in 2 band near 10.5um with the Texas Echelon Cross
Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility
(IRTF).We also attempted to search for the rotational transition
within the excited vibrational state (v_2_=1) near 2mm with the
IRAM 30m Telescope. Non-LTE radiative transfer modelling, including
radiative pumping to the vibrational state, was carried out to derive
the radial distribution of NH_3_ in the CSEs of these targets.
We detected NH_3_ inversion and rotational emission in all four
targets. IK Tau and VY CMa show blueshifted absorption in the
rovibrational spectra. We did not detect vibrationally excited
rotational transition from IK Tau. Spatially resolved VLA images of
IK Tau and IRC +10420 show clumpy emission structures; unresolved
images of VY CMa and OH 231.8+4.2 indicate that the spatial-kinematic
distribution of NH_3_ is similar to that of assorted molecules, such
as SO and SO2, that exhibit localised and clumpy emission. Our
modelling shows that the NH_3_ abundance relative to molecular
hydrogen is generally of the order of 10^-7^, which is a few times
lower than previous estimates that were made without considering
radiative pumping and is at least ten times higher than that in the
carbon-rich CSE of IRC +10216. NH_3_ in OH 231.8+4.2 and IRC +10420 is
found to emit in gas denser than the ambient medium. Incidentally, we
also derived a new period of IK Tau from its V-band light curve.
NH_3_ is again detected in very high abundance in evolved stars,
especially the oxygen-rich ones. Its emission mainly arises from
localised spatial-kinematic structures that are probably denser than
the ambient gas. Circumstellar shocks in the accelerated wind may
contribute to the production of NH_3_. Future mid-infrared
spectroscopy and radio imaging studies are necessary to constrain the
radii and physical conditions of the formation regions of NH_3_.
Description:
The catalogue contains radio (VLA), submillimetre (Herschel/HIFI), and
mid-infrared (NASA IRTF/TEXES) spectra of ammonia emission or
absorption from four oxygen-rich evolved stars, including IK Tau (AGB
star), VY CMa (red supergiant), OH 231.8+4.2 (pre-planetary nebular),
and IRC +10420 (yellow hypergiant). The scales of the VLA,
Herschel/HIFI, and IRTF/TEXES are total flux (Jansky), main-beam
brightness temperature (Kelvin), and relative intensity, respectively.
The X-axis of the IRTF/TEXES spectra are in LSR velocity while that of
the other spectra are in stellar rest frame (as in the paper). The
positions of the objects are determined from the radio continuum of
the VLA observations except for IRC +10420 of which the coordinates
are taken from SIMBAD. The spectra are generated in FITS format with
the GILDAS/CLASS software.
Objects:
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RA (2000) DE Designation(s)
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03 53 28.93 +11 24 21.5 IK Tau = V* IK Tau
07 22 58.33 -25 46 03.0 VY CMa = V* VY CMa
07 42 16.94 -14 42 49.8 OH 231.8+4.2 = V* QX Pup
19 26 48.10 +11 21 16.7 IRC +10420 = V* V1302 Aql
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