66 research outputs found
Understanding Accretion Outbursts in Massive Protostars through Maser Imaging
The bright maser emission produced by several molecular species at centimeter
to long millimeter wavelengths provides an essential tool for understanding the
process of massive star formation. Unimpeded by the high dust optical depths
that affect shorter wavelength observations, the high brightness temperature of
these emission lines offers a way to resolve accretion and outflow motions down
to scales below 1 au in deeply embedded Galactic star-forming regions at
kiloparsec distances. The recent identification of extraordinary accretion
outbursts in two high-mass protostars, both of which were heralded by maser
flares, has rapidly impacted the traditional view of massive protostellar
evolution, leading to new hydrodynamic simulations that can produce such
episodic outbursts. In order to understand how these massive protostars evolve
in response to such events, larger, more sensitive ground-based centimeter
wavelength interferometers are needed that can simultaneously image multiple
maser species in the molecular gas along with faint continuum from the central
ionized gas. Fiducial observations of a large sample of massive protostars will
be essential in order to pinpoint the progenitors of future accretion
outbursts, and to quantify the outburst-induced changes in their protostellar
photospheres and outflow and accretion structures. Knowledge gained from these
studies will have broader impact on the general topic of accretion onto massive
objects.Comment: Science white paper submitted to the Astro2020 Decadal Survey. arXiv
admin note: substantial text overlap with arXiv:1806.0698
First Image of the Sun with MeerKAT Solar Observations: Opening a New Frontier in Solar Physics
Solar radio emissions provide several unique diagnostics to estimate
different physical parameters of the solar corona, which are otherwise simply
inaccessible. However, imaging the highly dynamic solar coronal emissions
spanning a large range of angular scales at radio wavelengths is extremely
challenging. At GHz frequencies, the MeerKAT radio telescope is possibly
globally the best-suited instrument at the present time and can provide
high-fidelity spectroscopic snapshot solar images. Here, we present the first
images of the Sun made using the observations with the MeerKAT at L-band (856
-- 1711 MHz). This work demonstrates the high fidelity of the MeerKAT solar
images through a comparison with simulated radio images at the MeerKAT
frequencies. The observed images show extremely good mophological similarities
with the simulated images. A detailed comparison between the simulated radio
map and observed MeerKAT radio images demonstrates that there is significant
missing flux density in MeerKAT images at the higher frequencies of the
observing band, though it can potentially be estimated and corrected for. We
believe once solar observations with the MeerKAT are commissioned, they will
not only enable a host of novel studies but also open the door to a large
unexplored phase space with significant discovery potential.Comment: Preparing for submission, 14 pages, 9 figure
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