scholarly journals Circumstellar ammonia in oxygen-rich evolved stars

2018 ◽  
Vol 612 ◽  
pp. A48 ◽  
Author(s):  
K. T. Wong ◽  
K. M. Menten ◽  
T. Kamiński ◽  
F. Wyrowski ◽  
J. H. Lacy ◽  
...  
Keyword(s):  
Vibrational State ◽  
Ambient Medium ◽  
Far Infrared ◽  
Rotational Transition ◽  
Echelle Spectrograph ◽  
Vibrationally Excited ◽  
Excited Vibrational State ◽  
Very Large Array ◽  
Evolved Stars ◽  
Infrared Telescope

Context. The circumstellar ammonia (NH3) chemistry in evolved stars is poorly understood. Previous observations and modelling showed that NH3 abundance in oxygen-rich stars is several orders of magnitude above that predicted by equilibrium chemistry.Aims. We would like to characterise the spatial distribution and excitation of NH3 in the oxygen-rich circumstellar envelopes (CSEs) of four diverse targets: IK Tau, VY CMa, OH 231.8+4.2, and IRC +10420. Methods. We observed NH3 emission from the ground state in the inversion transitions near 1.3 cm 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 NH3 rovibrational absorption lines in the ν2 band near 10.5 μm 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 (v2 = 1) near 2 mm 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 NH3 in the CSEs of these targets. Results. We detected NH3 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 NH3 is similar to that of assorted molecules, such as SO and SO2, that exhibit localised and clumpy emission. Our modelling shows that the NH3 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. NH3 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. Conclusions. NH3 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 NH3. Future mid-infrared spectroscopy and radio imaging studies are necessary to constrain the radii and physical conditions of the formation regions of NH3.

scholarly journals Vibrationally excited water emission at 658 GHz from evolved stars

2017 ◽  
Vol 609 ◽  
pp. A25 ◽  
Author(s):  
A. Baudry ◽  
E. M. L. Humphreys ◽  
F. Herpin ◽  
K. Torstensson ◽  
W. H. T. Vlemmings ◽  
...  
Keyword(s):  
Vibrational State ◽  
Line Emission ◽  
Central Star ◽  
Rotational Transition ◽  
Asymptotic Giant Branch ◽  
Time Variability ◽  
Vibrationally Excited ◽  
Physical Conditions ◽  
Evolved Stars ◽  
Water Layers

Context. Several rotational transitions of ortho- and para-water have been identified toward evolved stars in the ground vibrational state as well as in the first excited state of the bending mode (v2 = 1 in (0, 1, 0) state). In the latter vibrational state of water, the 658 GHz J = 11,0−10,1 rotational transition is often strong and seems to be widespread in late-type stars. Aims. Our main goals are to better characterize the nature of the 658 GHz emission, compare the velocity extent of the 658 GHz emission with SiO maser emission to help locate the water layers and, more generally, investigate the physical conditions prevailing in the excited water layers of evolved stars. Another goal is to identify new 658 GHz emission sources and contribute in showing that this emission is widespread in evolved stars. Methods. We have used the J = 11,0−10,1 rotational transition of water in the (0, 1, 0) vibrational state nearly 2400 K above the ground-state to trace some of the physical conditions of evolved stars. Eleven evolved stars were extracted from our mini-catalog of existing and potential 658 GHz sources for observations with the Atacama Pathfinder EXperiment (APEX) telescope equipped with the SEPIA Band 9 receiver. The 13CO J = 6−5 line at 661 GHz was placed in the same receiver sideband for simultaneous observation with the 658 GHz line of water. We have compared the ratio of these two lines to the same ratio derived from HIFI earlier observations to check for potential time variability in the 658 GHz line. We have compared the 658 GHz line properties with our H2O radiative transfer models in stars and we have compared the velocity ranges of the 658 GHz and SiO J = 2−1, v = 1 maser lines. Results. Eleven stars have been extracted from our catalog of known or potential 658 GHz evolved stars. All of them show 658 GHz emission with a peak flux density in the range ≈50–70 Jy (RU Hya and RT Eri) to ≈2000–3000 Jy (VY CMa and W Hya). Five Asymptotic Giant Branch (AGB) stars and one supergiant (AH Sco) are new detections. Three AGBs and one supergiant (VY CMa) exhibit relatively weak 13CO J = 6−5 line emission while o Ceti shows stronger 13CO emission. We have shown that the 658 GHz line is masing and we found that the 658 GHz velocity extent tends to be correlated with that of the SiO maser suggesting that both emission lines are excited in circumstellar layers close to the central star. Broad and stable line profiles are observed at 658 GHz. This could indicate maser saturation although we have tentatively provided first information on time variability at 658 GHz.

A Far Infrared Photometer (FIRP) for the Infrared Telescope in Space (IRTS)

1993 ◽  
Vol 13 (12) ◽  
pp. 505-508
Author(s):  
M.M. Freund ◽  
T. Hirao ◽  
T. Matsumoto ◽  
S. Sato ◽  
T. Watabe ◽  
...  
Keyword(s):  
Far Infrared ◽  
Infrared Telescope

scholarly journals Probing the cold magnetised Universe with SPICA-POL (B-BOP)

2019 ◽  
Vol 36 ◽  
Author(s):  
Ph. André ◽  
A. Hughes ◽  
V. Guillet ◽  
F. Boulanger ◽  
A. Bracco ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
European Space Agency ◽  
Dust Emission ◽  
Far Infrared ◽  
High Dynamic Range ◽  
Wide Field ◽  
Infrared Telescope ◽  
Nearby Galaxies

Abstract Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a ‘Phase A’ concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100–350 $\mu$ m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 $\mu$ m images will also have a factor $\sim $ 30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.

scholarly journals Ionized gas in the NGC 5253 supernebula: high spatial and spectral resolution observations with the JVLA and TEXES

2020 ◽  
Vol 497 (2) ◽  
pp. 1675-1683
Author(s):  
Sara C Beck ◽  
John Lacy ◽  
Jean Turner ◽  
Hauyu Baobab Liu ◽  
Thomas Greathouse ◽  
...  
Keyword(s):  
Spectral Resolution ◽  
Large Scale ◽  
Massive Star ◽  
Dwarf Galaxy ◽  
Data Cube ◽  
Test Case ◽  
Echelle Spectrograph ◽  
Full Data ◽  
Ionized Gas ◽  
Very Large Array

ABSTRACT The youngest, closest, and most compact embedded massive star cluster known excites the supernebula in the nearby dwarf galaxy NGC 5253. It is a crucial target and test case for studying the birth and evolution of the most massive star clusters. We present observations of the ionized gas in this source with high spatial and spectral resolution. The data include continuum images of free–free emission with ≈0.15 arcsec resolution made with the Karl G. Jansky Very Large Array (JVLA) at 15, 22, and 33 GHz, and a full data cube of the [S iv] 10.5 μm  fine-structure emission line with ≈4.5 km s−1 velocity resolution and 0.3 arcsec beam, obtained with the Texas Echelon Cross Echelle Spectrograph (TEXES) on Gemini North. We find that (1) the ionized gas extends out from the cluster in arms or jets, and (2) the ionized gas comprises two components offset both spatially and in velocity. We discuss mechanisms that may have created the observed velocity field; possibilities include large-scale jets or a subcluster falling on to the main source.

VLA Observations of a Sample of Low-Brightness 6.7 GHz Methanol Masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 311-312
Author(s):  
Luca Olmi ◽  
Esteban D. Araya ◽  
Jason Armstrong
Keyword(s):  
New Mexico ◽  
Star Formation ◽  
Far Infrared ◽  
Large Array ◽  
Very Large Array ◽  
Early Stages ◽  
Methanol Masers ◽  
Infrared Sources ◽  
Massive Cores

AbstractIn 2014 we conducted a survey for 6.7 GHz methanol masers with the Arecibo Telescope toward far infrared sources selected from the Hi-GAL catalog of massive cores. We found a number of sources with weak 6.7 GHz methanol masers, possibly indicating regions in early stages of star formation. Here we describe the results of follow-up observations that were conducted with the Very Large Array in New Mexico to characterize this new population of “weak” 6.7 GHz methanol masers.

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