1,541 research outputs found
ALMA CO J=6-5 observations of IRAS16293-2422: Shocks and entrainment
Observations of higher-excited transitions of abundant molecules such as CO
are important for determining where energy in the form of shocks is fed back
into the parental envelope of forming stars. The nearby prototypical and
protobinary low-mass hot core, IRAS16293-2422 (I16293) is ideal for such a
study. The source was targeted with ALMA for science verification purposes in
band 9, which includes CO J=6-5 (E_up/k_B ~ 116 K), at an unprecedented spatial
resolution (~0.2", 25 AU). I16293 itself is composed of two sources, A and B,
with a projected distance of 5". CO J=6-5 emission is detected throughout the
region, particularly in small, arcsecond-sized hotspots, where the outflow
interacts with the envelope. The observations only recover a fraction of the
emission in the line wings when compared to data from single-dish telescopes,
with a higher fraction of emission recovered at higher velocities. The very
high angular resolution of these new data reveal that a bow shock from source A
coincides, in the plane of the sky, with the position of source B. Source B, on
the other hand, does not show current outflow activity. In this region, outflow
entrainment takes place over large spatial scales, >~ 100 AU, and in small
discrete knots. This unique dataset shows that the combination of a
high-temperature tracer (e.g., CO J=6-5) and very high angular resolution
observations is crucial for interpreting the structure of the warm inner
environment of low-mass protostars.Comment: Accepted for publication in A&A Letter
In-situ spectroscopy of intrinsic Bi2Te3 topological insulator thin films and impact of extrinsic defects
Combined in-situ x-ray photoemission spectroscopy, scanning tunnelling
spectroscopy and angle resolved photoemission spectroscopy of molecular beam
epitaxy grown Bi2Te3 on lattice mismatched substrates reveal high quality
stoichiometric thin films with topological surface states without a
contribution from the bulk bands at the Fermi energy. The absence of bulk
states at the Fermi energy is achieved without counter doping. We observe that
the surface morphology and electronic band structure of Bi2Te3 are not affected
by in-vacuo storage and exposure to oxygen, whereas major changes are observed
when exposed to ambient conditions. These films help define a pathway towards
intrinsic topological devices.Comment: 8 pages, 5 figure
Carina's Pillars of Destruction: the view from ALMA
Forming high-mass stars have a significant effect on their natal environment.
Their feedback pathways, including winds, outflows, and ionising radiation,
shape the evolution of their surroundings which impacts the formation of the
next generation of stars. They create or reveal dense pillars of gas and dust
towards the edges of the cavities they clear. They are modelled in feedback
simulations, and the sizes and shapes of the pillars produced are consistent
with those observed. However, these models predict measurably different
kinematics which provides testable discriminants. Here we present the first
ALMA Compact Array (ACA) survey of 13 pillars in Carina, observed in CO,
CO and CO J=2-1, and the 230 GHz continuum. The pillars in this
survey were chosen to cover a wide range in properties relating to the amount
and direction of incident radiation, proximity to nearby irradiating clusters
and cloud rims, and whether they are detached from the cloud. With these data,
we are able to discriminate between models. We generally find pillar velocity
dispersions of 1 km s and that the outer few layers of molecular
emission in these pillars show no significant offsets from each other,
suggesting little bulk internal motions within the pillars. There are instances
where the pillars are offset in velocity from their parental cloud rim, and
some with no offset, hinting at a stochastic development of these motions.Comment: 24 Pages, 19 figures. Accepted to MNRA
ALMA and NACO observations towards the young exoring transit system J1407 (V1400 Cen)
Our aim was to directly detect the thermal emission of the putative exoring
system responsible for the complex deep transits observed in the light curve
for the young Sco-Cen star 1SWASP J140747.93-394542.6 (V1400 Cen, hereafter
J1407), confirming it as the occulter seen in May 2007, and to determine its
orbital parameters with respect to the star. We used the Atacama Large
Millimeter/submillimeter Array (ALMA) to observe the field centred on J1407 in
the 340 GHz (Band 7) continuum in order to determine the flux and astrometric
location of the ring system relative to the star. We used the VLT/NACO camera
to observe the J1407 system in March 2019 and to search for the central
planetary mass object at thermal infrared wavelengths. We detect no point
source at the expected location of J1407, and derive an upper limit
level of . There is a point source detected at an angular
separation consistent with the expected location for a free-floating ring
system that occulted J1407 in May 2007, with a flux of
consistent with optically thin dust surrounding a massive substellar companion.
At 3.8 microns with the NACO camera, we detect the star J1407 but no other
additional point sources within 1.3 arcseconds of the star, with a lower bound
on the sensitivity of at the location of the ALMA source, and down
to in the sky background limit. The ALMA upper limit at the location
of J1407 implies that a hypothesised bound ring system is composed of dust
smaller than in size, implying a young ring structure. The detected
ALMA source has multiple interpretations, including: (i) it is an unbound
substellar object surrounded by warm dust in Sco-Cen with an upper mass limit
of , or (ii) it is a background galaxy.Comment: Accepted for publication in A&A (6 pages, 5 figures). Reduced data
and reduction scripts on GitHub at
https://github.com/mkenworthy/j1407_alma_detectio
Strong Pinning in High Temperature Superconductors
Detailed measurements of the critical current density jc of YBa2Cu3O7 films
grown by pulsed laser deposition reveal the increase of jc as function of the
filmthickness. Both this thickness dependence and the field dependence of the
critical current are consistently described using a generalization of the
theory of strong pinning of Ovchinnikov and Ivlev [Phys. Rev. B 43, 8024
(1991)]. From the model, we deduce values of the defect density (10^21 m^-3)
and the elementary pinning force, which are in good agreement with the
generally accepted values for Y2O3-inclusions. In the absence of clear evidence
that the critical current is determined by linear defects or modulations of the
film thickness, our model provides an alternative explanation for the rather
universal field dependence of the critical current density found in YBa2Cu3O7
films deposited by different methods.Comment: 11 pages; 8 Figures; Published Phys. Rev. B 66, 024523 (2002
Weak negative associations between avian influenza virus infection and movement behaviour in a key host species, the mallard Anas platyrhynchos
Animal movements may contribute to the spread of pathogens. In the case of avian influenza virus, [migratory] birds have been suggested to play a role in the spread of some highly pathogenic strains (e.g. H5N1, H5N8), as well as their low pathogenic precursors which circulate naturally in wild birds. For a better understanding of the emergence and spread of both highly pathogenic (HPAIV) and low pathogenic avian influenza virus (LPAIV), the potential effects of LPAIVs on bird movement need to be evaluated. In a key host species, the mallard Anas platyrhynchos, we tested whether LPAIV infection status affected daily local ( 100 m) movements by comparing movement behaviour 1) within individuals (captured and sampled at two time points) and 2) between individuals (captured and sampled at one time point). We fitted free-living adult males with GPS loggers throughout the autumn LPAIV infection peak, and sampled them for LPAIV infection at logger deployment and at logger removal on recapture. Within individuals, we found no association between LPAIV infection and daily local and regional movements. Among individuals, daily regional movements of LPAIV infected mallards in the last days of tracking were lower than those of non-infected birds. Moreover, these regional movements of LPAIV infected birds were additionally reduced by poor weather conditions (i.e. increased wind and/or precipitation and lower temperatures). Local movements of LPAIV infected birds in t
Hydrogen atom moving across a strong magnetic field: analytical approximations
Analytical approximations are constructed for binding energies,
quantum-mechanical sizes and oscillator strengths of main radiative transitions
of hydrogen atoms arbitrarily moving in magnetic fields 10^{12}-10^{13} G.
Examples of using the obtained approximations for determination of maximum
transverse velocity of an atom and for evaluation of absorption spectra in
magnetic neutron star atmospheres are presented.Comment: 17 pages, 3 figures, 5 tables, LaTeX with IOP style files (included).
In v.2, Fig.1 and Table 5 have been corrected. In v.3, a misprint in the fit
for oscillator strengths, Eq.(21), has been correcte
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