72 research outputs found
Statistical Analysis of Water Masers in Star-Forming Regions: Cepheus A and W75 N
We have done a statistical analysis of Very Long Baseline Array (VLBA) data
of water masers in the star-forming regions (SFRs) Cepheus A and W75 N, using
correlation functions to study the spatial clustering and Doppler-velocity
distribution of these masers. Two-point spatial correlation functions show a
characteristic scale size for clusters of water maser spots < or ~1 AU, similar
to the values found in other SFRs. This suggests that the scale for water maser
excitation tends to be < or ~1 AU. Velocity correlation functions show
power-law dependences with indices that can be explained by regular velocity
fields, such as expansion and/or rotation. These velocity fields are similar to
those indicated by the water maser proper-motion measurements; therefore, the
velocity correlation functions appear to reveal the organized motion of water
maser spots on scales larger than 1 AU.Comment: 16 pages, 8 figures, and 3 tables. Accepted by The Astrophysical
Journa
ALMA sub-mm maser and dust distribution of VY Canis Majoris
Cool, evolved stars have copious, enriched winds. The structure of these
winds and the way they are accelerated is not well known. We need to improve
our understanding by studying the dynamics from the pulsating stellar surface
to about 10 stellar radii, where radiation pressure on dust is fully effective.
Some red supergiants have highly asymmetric nebulae, implicating additional
forces. We retrieved ALMA Science Verification data providing images of sub-mm
line and continuum emission from VY CMa. This enables us to locate water masers
with milli-arcsec precision and resolve the dusty continuum. The 658-, 321- and
325-GHz masers lie in irregular, thick shells at increasing distances from the
centre of expansion. For the first time this is confirmed as the stellar
position, coinciding with a compact peak offset to the NW of the brightest
continuum emission. The maser shells (and dust formation zone) overlap but
avoid each other on tens-au scales. Their distribution is broadly consistent
with excitation models but the conditions and kinematics appear to be
complicated by wind collisions, clumping and asymmetries.Comment: Letter 4 pages, 5 figures plus appendix with 3 figures. Accepted by
Astronomy and Astrophysics Letter
Kinematics of the H2O masers at the centre of the PN K3-35
We have studied the kinematics traced by the water masers located at the
centre of the planetary nebula (PN) K3-35, using data from previous Very Large
Array (VLA) observations. An analysis of the spatial distribution and
line-of-sight velocities of the maser spots allows us to identify typical
patterns of a rotating and expanding ring in the position-velocity diagrams,
according to our kinematical model. We find that the distribution of the masers
is compatible with tracing a circular ring with a ~0.021 arcsec (~100 AU)
radius, observed with an inclination angle with respect to the line of sight of
55 degrees. We derive expansion and rotation velocities of 1.4 and 3.1 km/s,
respectively. The orientation of the ring projected on the plane of the sky, at
PA 158 degrees, is almost orthogonal to the direction of the innermost region
of the jet observed in K3-35, suggesting the presence of a disc or torus that
may be related to the collimation of the outflow.Comment: 7 pages, 4 figures, 2 tables. Accepted by MNRA
GASKAP -- The Galactic ASKAP Survey
A survey of the Milky Way disk and the Magellanic System at the wavelengths
of the 21-cm atomic hydrogen (HI) line and three 18-cm lines of the OH molecule
will be carried out with the Australian Square Kilometre Array Pathfinder
telescope. The survey will study the distribution of HI emission and absorption
with unprecedented angular and velocity resolution, as well as molecular line
thermal emission, absorption, and maser lines. The area to be covered includes
the Galactic plane (|b|< 10deg) at all declinations south of delta = +40deg,
spanning longitudes 167deg through 360deg to 79deg at b=0deg, plus the entire
area of the Magellanic Stream and Clouds, a total of 13,020 square degrees. The
brightness temperature sensitivity will be very good, typically sigma_T ~ 1 K
at resolution 30arcsec and 1 km/s. The survey has a wide spectrum of scientific
goals, from studies of galaxy evolution to star formation, with particular
contributions to understanding stellar wind kinematics, the thermal phases of
the interstellar medium, the interaction between gas in the disk and halo, and
the dynamical and thermal states of gas at various positions along the
Magellanic Stream.Comment: 45 pages, 8 figures, Pub. Astron. Soc. Australia (in press
Is diet partly responsible for differences in COVID-19 death rates between and within countries?
Correction: Volume: 10 Issue: 1 Article Number: 44 DOI: 10.1186/s13601-020-00351-w Published: OCT 26 2020Reported COVID-19 deaths in Germany are relatively low as compared to many European countries. Among the several explanations proposed, an early and large testing of the population was put forward. Most current debates on COVID-19 focus on the differences among countries, but little attention has been given to regional differences and diet. The low-death rate European countries (e.g. Austria, Baltic States, Czech Republic, Finland, Norway, Poland, Slovakia) have used different quarantine and/or confinement times and methods and none have performed as many early tests as Germany. Among other factors that may be significant are the dietary habits. It seems that some foods largely used in these countries may reduce angiotensin-converting enzyme activity or are anti-oxidants. Among the many possible areas of research, it might be important to understand diet and angiotensin-converting enzyme-2 (ACE2) levels in populations with different COVID-19 death rates since dietary interventions may be of great benefit.Peer reviewe
A Keplerian disk with a four-arm spiral birthing an episodically accreting high-mass protostar
High-mass protostars (M⋆ > 8M⊙) are thought to gain the majority of their mass via short, intense bursts of growth. This episodic accretion is thought to be facilitated by gravitationally unstable and subsequently inhomogeneous accretion disks. Limitations of observational capabilities, paired with a lack of observed accretion burst events, have withheld affirmative confirmation of the association between disk accretion, instability and the accretion burst phenomenon in high-mass protostars. Following its 2019 accretion burst, a heatwave driven by a burst of radiation propagated outward from the high-mass protostar G358.93-0.03-MM1. Six very long baseline interferometry observations of the radiatively pumped 6.7 GHz methanol maser were conducted during this period, tracing ever increasing disk radii as the heatwave propagated outward. Concatenating the very long baseline interferometry maps provided a sparsely sampled, milliarcsecond view of the spatio-kinematics of the accretion disk covering a physical range of ~50–900 AU. We term this observational approach ‘heatwave mapping’. We report the discovery of a Keplerian accretion disk with a spatially resolved four-arm spiral pattern around G358.93-0.03-MM1. This result positively implicates disk accretion and spiral arm instabilities into the episodic accretion high-mass star formation paradigm
Impact of volatile phenols and their precursors on wine quality and control measures of Brettanomyces/Dekkera yeasts
Volatile phenols are aromatic compounds and one of the key molecules responsible for olfactory defects in wine. The yeast genus Brettanomyces is the only major microorganism that has the ability to covert hydroxycinnamic acids into important levels of these compounds, especially 4-ethylphenol and 4-ethylguaiacol, in red wine. When 4-ethylphenols reach concentrations greater than the sensory threshold, all wine’s organoleptic characteristics might be influenced or damaged. The aim of this literature review is to provide a better understanding of the physicochemical, biochemical, and metabolic factors that are related to the levels of p-coumaric acid and volatile phenols in wine. Then, this work summarizes the different methods used for controlling the presence of Brettanomyces in wine and the production of ethylphenols
Dietary supplementation with hydrolyzed yeast and its effect on the performance, intestinal microbiota, and immune response of weaned piglets.
The objective of this study was to evaluate the effects of autolyzed yeast on performance, cecal microbiota, and leukogram of weaned piglets. A total of 96 piglets of commercial line weaned at 21-day-old were used. The experimental design was a randomized block design with four treatments (diets containing 0.0%, 0.3%, 0.6%, and 0.9% autolyzed yeast), eight replicates, and three animals per pen in order to evaluate daily weight gain, daily feed intake, and feed conversion in periods of 0 to 15, 0 to 26, and 0 to 36 days. Quadratic effects of autolyzed yeast inclusion were observed on the feed conversion from 0 to 15 days, on daily weight gain from 0 to 15 days, 0 to 26 days and, 0 to 36 days, indicating an autolyzed yeast optimal inclusion level between 0.4% and 0.5%. No effect from autolyzed yeast addition was observed on piglet daily feed intake, cecal microbiota, and leukogram; however, i.m. application of E. coli lipopolysaccharide reduced the values of total leukocytes and their fractions (neutrophils, eosinophils, lymphocytes, monocytes, and rods). Therefore, autolyzed yeast when provided at levels between 0.4% and 0.5% improved weaned piglets’ performance.info:eu-repo/semantics/publishedVersio
Comparison of Infectious Agents Susceptibility to Photocatalytic Effects of Nanosized Titanium and Zinc Oxides: A Practical Approach
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