2,726 research outputs found
A 10- YSO with a Keplerian disk and a nonthermal radio jet
We previously observed the star-forming region G16.590.05 through
interferometric observations of both thermal and maser lines, and identified a
high-mass young stellar object (YSO) which is surrounded by an accretion disk
and drives a nonthermal radio jet. We performed high-angular-resolution (beam
FWHM ~0.15") 1.2-mm continuum and line observations towards G16.590.05 with
the Atacama Large Millimeter Array (ALMA). The main dust clump, with size
~10 au, is resolved into four relatively compact (diameter ~2000 au)
millimeter (mm) sources. The source harboring the high-mass YSO is the most
prominent in molecular emission. By fitting the emission profiles of several
unblended and optically thin transitions of CHOCH and CHOH, we
derived gas temperatures inside the mm-sources in the range 42--131 K, and
calculated masses of 1--5 . A well-defined Local Standard of Rest
velocity (Vlsr) gradient is detected in most of the high-density molecular
tracers at the position of the high-mass YSO, pinpointed by compact 22-GHz
free-free emission. This gradient is oriented along a direction forming a large
(~70 degree) angle with the radio jet, traced by elongated 13-GHz continuum
emission. The butterfly-like shapes of the P-V plots and the linear pattern of
the emission peaks of the molecular lines at high velocity confirm that this
Vlsr gradient is due to rotation of the gas in the disk surrounding the
high-mass YSO. The disk radius is ~500 au, and the Vlsr distribution along the
major axis of the disk is well reproduced by a Keplerian profile around a
central mass of 102 . The position of the YSO is offset by >~
0.1" from the axis of the radio jet and the dust emission peak. To explain this
displacement we argue that the high-mass YSO could have moved from the center
of the parental mm source owing to dynamical interaction with one or more
companions.Comment: 16 pages, 12 figures, accepted by Astronomy & Astrophysics, Main
Journa
Planar infall of CH3OH gas around Cepheus A HW2
Aims: In order to test the nature of an (accretion) disk in the vicinity of
Cepheus A HW2, we measured the three-dimensional velocity field of the CH3OH
maser spots, which are projected within 1000au of the HW2 object, with an
accuracy of the order of 0.1km/s. Methods: We made use of the European VLBI
Network (EVN) to image the 6.7GHz CH3OH maser emission towards Cepheus A HW2
with 4.5 milli-arcsecond resolution (3au). We observed at three epochs spaced
by one year between 2013 and 2015. During the last epoch, on mid-march 2015, we
benefited from the new deployed Sardinia Radio Telescope. Results: We show that
the CH3OH velocity vectors lie on a preferential plane for the gas motion with
only small deviations of 12+/-9 degrees away from the plane. This plane is
oriented at a position angle of 134 degrees east of north, and inclined by 26
degrees with the line-of-sight, closely matching the orientation of the
disk-like structure previously reported by Patel et al.(2005). Knowing the
orientation of the equatorial plane, we can reconstruct a face-on view of the
CH3OH gas kinematics onto the plane. CH3OH maser emission is detected within a
radius of 900au from HW2, and down to a radius of about 300au, the latter
coincident with the extent of the dust emission at 0.9mm. The velocity field is
dominated by an infall component of about 2km/s down to a radius of 300au,
where a rotational component of 4km/s becomes dominant. We discuss the nature
of this velocity field and the implications for the enclosed mass. Conclusions:
These findings bring direct support to the interpretation that the high-density
gas and dust emission, surrounding Cepheus A HW2, trace an accretion disk.Comment: 9 pages, 4 figures, 2 tables, accepted by Astronomy & Astrophysic
Social Cognition in Schizophrenia: An Overview
The purpose of this column is to provide an overview of social cognition in schizophrenia. The column begins with a short introduction to social cognition. Then, we describe the application of social cognition to the study of schizophrenia, with an emphasis on key domains (i.e., emotion perception, Theory of Mind, and attributional style). We conclude the column by discussing the relationship of social cognition to neurocognition, negative symptoms, and functioning, with an eye toward strategies for improving social cognition in schizophrenia
Theoretical Investigation of Optical Conductivity in Ba [Fe(1-x)Co(x)]2 As2
We report on theoretical calculations of the optical conductivity of Ba
[Fe(1-x)Co(x)]2 As2, as obtained from density functional theory within the full
potential LAPW method. A thorough comparison with experiment shows that we are
able to reproduce most of the observed experimental features, in particular a
magnetic peak located at about 0.2 eV which we ascribe to antiferromagnetic
ordered magnetic stripes. We also predict a large in-plane anisotropy of this
feature, which agrees very well with measurements on detwinned crystals. The
effect of Co doping as well as the dependence of plasma frequency on the
magnetic order is also investigated
A sub-arcsecond study of the hot molecular core in G023.01-00.41
(Abridged) METHODS: We performed SMA observations at 1.3 mm with both the
most extended and compact array configurations, providing sub-arcsecond and
high sensitivity maps of various molecular lines, including both hot-core and
outflow tracers. We also reconstruct the spectral energy distribution of the
region from millimeter to near infrared wavelengths, using the Herschel/Hi-GAL
maps, as well as archival data. RESULTS: From the spectral energy distribution,
we derive a bolometric luminosity of about 4x10^4 Lsun. Our interferometric
observations reveal that the distribution of dense gas and dust in the HMC is
significantly flattened and extends up to a radius of 8000 AU from the center
of radio continuum and maser emission in the region. The equatorial plane of
this HMC is strictly perpendicular to the elongation of the collimated bipolar
outflow, as imaged on scales of about 0.1-0.5 pc in the main CO isotopomers as
well as in the SiO(5-4) line. In the innermost HMC regions (ca. 1000 AU), the
velocity field traced by the CH3CN(12_K-11_K) line emission shows that
molecular gas is both expanding along the outflow direction following a
Hubble-law, and rotating about the outflow axis, in agreement with the (3-D)
velocity field traced by methanol masers. The velocity field associated with
rotation indicates a dynamical mass of 19 Msun at the center of the core. The
latter is likely to be concentrated in a single O9.5 ZAMS star, consistent with
the estimated bolometric luminosity of G023.01-00.41. The physical properties
of the CO(2-1) outflow emission, such as its momentum rate 6x10^-3 Msun km/s
/yr and its outflow rate 2x10^-4 Msun/yr, support our estimates of the
luminosity (and mass) of the embedded young stellar object.Comment: 24 pages, 11 figures, 6 tables, accepted by Astronomy & Astrophysic
A revised distance to IRAS 162932422 from VLBA astrometry of associated water masers
IRAS 16293-2422 is a very well studied young stellar system seen in
projection towards the L1689N cloud in the Ophiuchus complex. However, its
distance is still uncertain with a range of values from 120 pc to 180 pc. Our
goal is to measure the trigonometric parallax of this young star by means of
HO maser emission. We use archival data from 15 epochs of VLBA observations
of the 22.2 GHz water maser line. By modeling the displacement on the sky of
the HO maser spots, we derived a trigonometric parallax of mas,
corresponding to a distance of pc. This new distance is in
good agreement with recent values obtained for other magnetically active young
stars in the L1689 cloud. We relate the kinematics of these masers with the
outflows and the recent ejections powered by source A in the system.Comment: 14 pages, 6 tables, 8 figures. Accepted to be published in Astronomy
\& Astrophysic
Evidence of magnetic mechanism for cuprate superconductivity
A proper understanding of the mechanism for cuprate superconductivity can
emerge only by comparing materials in which physical parameters vary one at a
time. Here we present a variety of bulk, resonance, and scattering measurements
on the (Ca_xLa_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_y high temperature
superconductors, in which this can be done. We determine the superconducting,
Neel, glass, and pseudopage critical temperatures. In addition, we clarify
which physical parameter varies, and, equally important, which does not, with
each chemical modification. This allows us to demonstrate that a single energy
scale, set by the superexchange interaction J, controls all the critical
temperatures of the system. J, in-turn, is determined by the in plane Cu-O-Cu
buckling angle.Comment: 17 pages, 13 figure
Electronic correlations in iron-pnictide superconductors and beyond; what can we learn from optics
The Coulomb repulsion, impeding electrons' motion, has an important impact on
the charge dynamics. It mainly causes a reduction of the effective metallic
Drude weight (proportional to the so-called optical kinetic energy),
encountered in the optical conductivity, with respect to the expectation within
the nearly-free electron limit (defining the so-called band kinetic energy), as
evinced from band-structure theory. In principle, the ratio between the optical
and band kinetic energy allows defining the degree of electronic correlations.
Through spectral weight arguments based on the excitation spectrum, we provide
an experimental tool, free from any theoretical or band-structure based
assumptions, in order to estimate the degree of electronic correlations in
several systems. We first address the novel iron-pnictide superconductors,
which serve to set the stage for our approach. We then revisit a large variety
of materials, ranging from superconductors, to Kondo-like systems as well as
materials close to the Mott-insulating state. As comparison we also tackle
materials, where the electron-phonon coupling dominates. We establish a direct
relationship between the strength of interaction and the resulting reduction of
the optical kinetic energy of the itinerant charge carriers
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