ORCID Profile
0000-0001-6078-786X
Current Organisation
University of Leeds
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Publisher: EDP Sciences
Date: 21-10-2019
DOI: 10.1051/0004-6361/201935340
Abstract: Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity that are intimately connected to the evolution of protoplanetary disks and the formation of planets. We carried out sensitive continuum observations toward the Ophiuchus A star-forming region, using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6′ and with a spatial resolution of θ maj × θ min ~ 0.′′4 × 0.′′2. We achieved a 5 μ Jy beam −1 rms noise level at the center of our mosaic field of view. Among the 18 sources we detected, 16 were YSOs (three Class 0, five Class I, six Class II, and two Class III) and two were extragalactic candidates. We find that thermal dust emission generally contributed less than 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission, such as gyro-synchrotron radiation from active magnetospheres, free–free emission from thermal jets, free–free emission from the outflowing photoevaporated disk material, and synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections for Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve over time. The sensitivity of our data cannot exclude photoevaporation due to the role of X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys using the Square Kilometre Array (SKA) will have the capacity to provide significant constraints to disk photoevaporation.
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3FD00046J
Abstract: The reaction of NH 2 and CH 3 CHO becomes fast at low temperatures, and may be a potential source of CH 3 CO radicals in the interstellar medium.
Publisher: American Astronomical Society
Date: 09-2022
Abstract: The first experimental study of the low-temperature kinetics of the gas-phase reaction of NH 2 with formaldehyde (CH 2 O) has been performed. This reaction has previously been suggested as a source of formamide (NH 2 CHO) in interstellar environments. A pulsed Laval nozzle equipped with laser-flash photolysis and laser-induced fluorescence spectroscopy was used to create and monitor the temporal decay of NH 2 in the presence of CH 2 O. No loss of NH 2 could be observed via reaction with CH 2 O, and we place an upper limit on the rate coefficient of × 10 −12 cm 3 molecule −1 s −1 at 34 K. Ab initio calculations of the potential energy surface were combined with Rice–R sberger–Kassel–Marcus (RRKM) calculations to predict a rate coefficient of 6.2 × 10 −14 cm 3 molecule −1 s −1 at 35 K, consistent with the experimental results. The presence of a significant barrier, 18 kJ mol −1 , for the formation of formamide as a product, means that only the H-abstraction channel producing NH 3 + CHO, in which the transfer of an H atom can occur by quantum mechanical tunneling through a 23 kJ mol −1 barrier, is open at low temperatures. These results are in contrast with a recent theoretical study, which suggested that the reaction could proceed without a barrier and was therefore a viable route to gas-phase formamide formation. The calculated rate coefficients were used in an astrochemical model, which demonstrated that this reaction produces only negligible amounts of gas-phase formamide under interstellar and circumstellar conditions. The reaction of NH 2 with CH 2 O is therefore not an important source of formamide at low temperatures in interstellar environments.
Publisher: American Chemical Society (ACS)
Date: 17-08-2023
Publisher: Oxford University Press (OUP)
Date: 13-08-2015
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Catherine Walsh.