1,006 research outputs found
Serendipitous Discovery of An Infrared Bow Shock Near PSR J1549-4848 with Spitzer
We report on the discovery of an infrared cometary nebula around PSR
J15494848 in our Spitzer survey of a few middle-aged radio pulsars.
Following the discovery, multi-wavelength imaging and spectroscopic
observations of the nebula were carried out. We detected the nebula in Spitzer
IRAC 8.0, MIPS 24 and 70 m imaging and in Spitzer IRS 7.5--14.4 m
spectroscopic observations, and also in the WISE all-sky survey at 12 and 22
m.These data were analyzed in detail, and we find that the nebula can be
described with a standard bow-shock shape, and that its spectrum contains
polycyclic aromatic hydrocarbon and H emission features. However, it is not
certain which object drives the nebula. We analyze the field stars and conclude
that none of them can be the associated object because stars with a strong wind
or mass ejection that usually produce bow shocks are much brighter than the
field stars. The pulsar is approximately 15\arcsec\ away from the region in
which the associated object is expected to be located. In order to resolve the
discrepancy, we suggest that a highly collimated wind could be emitted from the
pulsar and produce the bow shock. X-ray imaging to detect the interaction of
the wind with the ambient medium and high-spatial resolution radio imaging to
determine the proper motion of the pulsar should be carried out, which will
help verify the association of the pulsar with the bow shock nebula.Comment: 9 pages, 5 figures, accepted for publication in Ap
"More than just a medical student”: a mixed methods exploration of a structured volunteering programme for undergraduate medical students
Background As a result of the COVID-19 pandemic Imperial College School of Medicine developed a structured volunteering programme involving 398 medical students, across eight teaching hospitals. This case study aims to illuminate the experiences of volunteers, mechanisms of learning and draw lessons for future emergencies and curriculum improvements. Methods Using an illuminative approach to evaluation we invited all volunteers and supervisors to complete a mixed-methods survey. This gathered nominal demographic information and qualitative data related to motivations, experiences, insights into learning, processual and contextual factors. Qualitative responses were coded, thematically organised, and categorised into an overarching framework. Mann-Whitney U tests determined whether volunteers’ overall rating of the experience varied according to demographic features and modulating factors. Spearman’s rank correlation assessed the relationship between aspects of induction and supervision, and overall volunteering rating. Follow up interviews were carried out with students to check back findings and co-create conclusions. Results Modulating factors identified through thematic analysis include altruistic motivation, engaged induction and supervision, feeling valued, having responsibility and freedom from the formal curriculum. Statistically significant positive correlations are identified between volunteers overall rating and being a year 1 or 2 student, ability to discuss role and ask questions during induction, being male, and having regular meetings and role support from supervisors. Qualitatively reported impacts include improved wellbeing, valuable contribution to service and transformative learning. Transformative learning effects included reframing of role within the multidisciplinary team, view of effective learning and view of themselves as competent clinicians. The number of weeks, number of shifts per week, and the role the volunteers performed, did not significantly impact experiences. Conclusions While acknowledging the uniqueness of the situation presented by the first wave COVID-19, we suggest the features of a successful service-learning programme include: a learner-centred induction, engaged and appreciative supervisors, and the entrustment of students with meaningful work with reciprocal benefits to services. Programmes in similar settings may find that 1) volunteering is best appreciated in years 1 or 2, 2) students with altruistic motivations and meaningful work may flourish without formal outcomes and assessments, and 3) that female volunteers may experience emergency learning differently to men
Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28 2561
We report magnetic and spectroscopic observations and modeling of the Of?p
star CPD -28 2561. Using more than 75 new spectra, we have measured the
equivalent width variations and examined the dynamic spectra of photospheric
and wind-sensitive spectral lines. A period search results in an unambiguous
73.41 d variability period. High resolution spectropolarimetric data analyzed
using Least-Squares Deconvolution yield a Zeeman signature detected in the mean
Stokes V profile corresponding to phase 0.5 of the spectral ephemeris.
Interpreting the 73.41 d period as the stellar rotational period, we have
phased the equivalent widths and inferred longitudinal field measurements. The
phased magnetic data exhibit a weak sinusoidal variation, with maximum of about
565 G at phase 0.5, and a minimum of about -335 G at phase 0.0, with extrema
approximately in phase with the (double-wave) Halpha equivalent width
variation. Modeling of the Halpha equivalent width variation assuming a
quasi-3D magnetospheric model produces a unique solution for the ambiguous
couplet of inclination and magnetic obliquity angles: (i, beta) or (beta,
i)=(35 deg,90 deg). Adopting either geometry, the longitudinal field variation
yields a dipole polar intensity Bd=2.6\pm 0.9~kG, consistent with that obtained
from direct modelling of the Stokes V profiles. We derive a wind magnetic
confinement parameter eta*\simeq 100, leading to an Alfv\'en radius RA\simeq
3-5~R*, and a Kepler radius RK\simeq 20~R*. This supports a physical scenario
in which the Halpha emission and other line variability have their origin in an
oblique, co-rotating 'dynamical magnetosphere' structure resulting from a
magnetically channeled wind. Nevertheless, the details of the formation of
spectral lines and their variability within this framework remain generally
poorly understood.Comment: 18 pages, accepted by MNRAS Replaced 28 March 2015 to include
corrected figure 10 (see MNRAS erratum to this effect
Leukocytes Breach Endothelial Barriers by Insertion of Nuclear Lobes and Disassembly of Endothelial Actin Filaments
Israel Science Foundation (grant 87/12)
Flight Attendant Medical Research Institute Foundation (FAMRI) (grant FAMRI032001_CoE), USA
Minerva Foundation, Germany
Wellcome Trust (grant 098291/Z/12/Z to S.N.
SN2007ax : An Extremely Faint Type Ia Supernova
We present multi-band photometric and optical spectroscopic observations of
SN2007ax, the faintest and reddest Type Ia supernova (SNIa) yet observed. With
M_B = -15.9 and (B-V)max = 1.2, this SN is over half a magnitude fainter at
maximum light than any other SNIa. Similar to subluminous SN2005ke, SN2007ax
also appears to show excess in UV emission at late time. Traditionally,
Delta-m_15(B) has been used to parameterize the decline rate for SNeIa.
However, the B-band transition from fast to slow decline occurs sooner than 15
days for faint SNeIa. Therefore we suggest that a more physically motivated
parameter, the time of intersection of the two slopes, be used instead. Only by
explaining the faintest (and the brightest) supernovae, we can thoroughly
understand the physics of thermonuclear explosions. We suggest that future
surveys should carefully design their cadence, depth, pointings and follow-up
to find an unbiased sample of extremely faint members of this subclass of faint
SNeIa.Comment: Accepted for publication in ApJ
Quantum Monte Carlo calculations of the one-body density matrix and excitation energies of silicon
Quantum Monte Carlo (QMC) techniques are used to calculate the one-body
density matrix and excitation energies for the valence electrons of bulk
silicon. The one-body density matrix and energies are obtained from a
Slater-Jastrow wave function with a determinant of local density approximation
(LDA) orbitals. The QMC density matrix evaluated in a basis of LDA orbitals is
strongly diagonally dominant. The natural orbitals obtained by diagonalizing
the QMC density matrix resemble the LDA orbitals very closely. Replacing the
determinant of LDA orbitals in the wave function by a determinant of natural
orbitals makes no significant difference to the quality of the wave function's
nodal surface, leaving the diffusion Monte Carlo energy unchanged. The Extended
Koopmans' Theorem for correlated wave functions is used to calculate excitation
energies for silicon, which are in reasonable agreement with the available
experimental data. A diagonal approximation to the theorem, evaluated in the
basis of LDA orbitals, works quite well for both the quasihole and
quasielectron states. We have found that this approximation has an advantageous
scaling with system size, allowing more efficient studies of larger systems.Comment: 13 pages, 4 figures. To appear in Phys. Rev.
A multispectral view of the periodic events in eta Carinae
A full description of the 5.5-yr low excitation events in Eta Carinae is
presented. We show that they are not as simple and brief as previously thought,
but a combination of two components. The first, the 'slow variation' component,
is revealed by slow changes in the ionization level of circumstellar matter
across the whole cycle and is caused by gradual changes in the wind-wind
collision shock-cone orientation, angular opening and gaseous content. The
second, the 'collapse' component, is restricted to around the minimum, and is
due to a temporary global collapse of the wind-wind collision shock. High
energy photons (E > 16 eV) from the companion star are strongly shielded,
leaving the Weigelt objects at low ionization state for >6 months. High energy
phenomena are sensitive only to the 'collapse', low energy only to the 'slow
variation' and intermediate energies to both components. Simple eclipses and
mechanisms effective only near periastron (e.g., shell ejection or accretion
onto the secondary star) cannot account for the whole 5.5-yr cycle.
We find anti-correlated changes in the intensity and the radial velocity of P
Cygni absorption profiles in FeII 6455 and HeI 7065 lines, indicating that the
former is associated to the primary and the latter to the secondary star. We
present a set of light curves representative of the whole spectrum, useful for
monitoring the next event (2009 January 11).Comment: 16 pages, 7 EPS figures, accepted for publication on MNRA
A three-decade outburst of the LMC luminous blue variable R127 draws to a close
The paradigmatic luminous blue variable R127 in the Large Magellanic Cloud has been found in the intermediate, peculiar early-B state, and substantially fainter in visual light, signaling the final decline from its major outburst that began between 1978 and 1980. This transformation was detected in 2008 January, but archival data show that it began between early 2005 and early 2007. In fact, significant changes from the maximum, peculiar A-type spectrum, which was maintained from 1986 through 1998, had already begun the following year, coinciding with a steep drop in visual light. We show detailed correspondences between the spectrum and light, in which the decline mimics the rise. Moreover, these trends are not monotonic but are characterized by multiple spikes and dips, which may provide constraints on the unknown outburst mechanism. Intensive photometric and spectroscopic monitoring of R127 should now resume, to follow the decline presumably back to the quiescent Ofpe/WN9 state, in order to fully document the remainder of this unique observational opportunity.Facultad de Ciencias Astronómicas y GeofísicasConsejo Nacional de Investigaciones Científicas y Técnica
Abundance Analysis of HE2148-1247, A Star With Extremely Enhanced Neutron Capture Elements
Abundances for 27 elements in the very metal poor dwarf star HE2148-1247 are
presented, including many of the neutron capture elements. We establish that
HE2148-1247 is a very highly s-process enhanced star with anomalously high Eu
as well, Eu/H about half Solar, demonstrating the large addition of heavy
nuclei at [Fe/H] = -2.3 dex. Ba and La are enhanced by a somewhat larger factor
and reach the solar abundance, while Pb significantly exceeds it. Ba/Eu is ten
times the solar r-process ratio but much less than that of the s-process,
indicating a substantial r-process addition as well. C and N are also very
highly enhanced. We have found that HE2148-1247 is a radial velocity variable.
The C, N and the s-process element enhancements thus presumably were produced
through mass transfer from a former AGB binary companion. The large enhancement
of heavy r-nuclides also requires an additional source as this is far above any
inventory in the ISM at such low [Fe/H]. We further hypothesize that accretion
onto the white dwarf from the envelope of the star caused accretion induced
collapse of the white dwarf, forming a neutron star, which then produced heavy
r-nuclides and again contaminated its companion. (abridged)Comment: Accepted by the Astrophysical Journal. Companion paper by Qian and
Wasserburg follow
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