469 research outputs found
Discovery of the first tau Sco analogues: HD 66665 and HD 63425
The B0.2 V magnetic star tau Sco stands out from the larger population of
massive OB stars due to its high X-ray activity, peculiar wind diagnostics and
highly complex magnetic field. This paper presents the discovery of the first
two tau Sco analogues - HD 66665 and HD 63425, identified by the striking
similarity of their UV spectra to that of tau Sco. ESPaDOnS spectropolarimetric
observations were secured by the Magnetism in Massive Stars CFHT Large Program,
in order to characterize the stellar and magnetic properties of these stars.
CMFGEN modelling of optical ESPaDOnS spectra and archived IUE UV spectra showed
that these stars have stellar parameters similar to those of tau Sco. A
magnetic field of similar surface strength is found on both stars, reinforcing
the connection between the presence of a magnetic field and wind peculiarities.
However, additional phase-resolved observations will be required in order to
assess the potential complexity of the magnetic fields, and verify if the wind
anomalies are linked to this property.Comment: 6 pages, 2 tables, 3 figures. Accepted for publication in MNRAS. The
definitive version will be available at www.blackwel-synergy.co
Combining M-FISH and Quantum Dot technology for fast chromosomal assignment of transgenic insertions
<p>Abstract</p> <p>Background</p> <p>Physical mapping of transgenic insertions by Fluorescence in situ Hybridization (FISH) is a reliable and cost-effective technique. Chromosomal assignment is commonly achieved either by concurrent G-banding or by a multi-color FISH approach consisting of iteratively co-hybridizing the transgenic sequence of interest with one or more chromosome-specific probes at a time, until the location of the transgenic insertion is identified.</p> <p>Results</p> <p>Here we report a technical development for fast chromosomal assignment of transgenic insertions at the single cell level in mouse and rat models. This comprises a simplified 'single denaturation mixed hybridization' procedure that combines multi-color karyotyping by Multiplex FISH (M-FISH), for simultaneous and unambiguous identification of all chromosomes at once, and the use of a Quantum Dot (QD) conjugate for the transgene detection.</p> <p>Conclusions</p> <p>Although the exploitation of the unique optical properties of QD nanocrystals, such as photo-stability and brightness, to improve FISH performance generally has been previously investigated, to our knowledge this is the first report of a purpose-designed molecular cytogenetic protocol in which the combined use of QDs and standard organic fluorophores is specifically tailored to assist gene transfer technology.</p
The spectral variability and magnetic field characteristics of the Of?p star HD 148937
We report magnetic and spectroscopic observations and modeling of the Of?p
star HD 148937 within the context of the MiMeS LP at the CFHT. Thirty-two high
signal-to-noise ratio circularly polarised (Stokes V) spectra and 13
unpolarised (Stokes I) spectra of HD 148937 were acquired in 2009 and 2010. A
definite detection of a Stokes V Zeeman signature is obtained in the grand mean
of all observations (in both LSD mean profiles and individual spectral lines).
The longitudinal magnetic field inferred from the Stokes V LSD profiles is
consistently negative, in contrast to the essentially zero field strength
measured from the diagnostic null profiles. A period search of equivalent width
measurements confirms the previously-reported 7.03 d variability period. The
variation of equivalent widths is not strictly periodic: we present evidence
for evolution of the amount or distribution of circumstellar plasma.
Interpreting the 7.03 d period as the stellar rotational period within the
context of the ORM, we have phased the equivalent widths and longitudinal field
measurements. The longitudinal field measurements show a weak sinusoidal
variation of constant sign, with extrema out of phase with the H{\alpha}
variation by about 0.25 cycles. The inferred magnetic configuration confirms
the suggestion of Naz\'e et al (2010), who proposed that the weaker variability
of HD 148937 as compared to other members of this class is a consequence of the
stellar geometry. Based on the derived magnetic properties and published wind
characteristics, we find a wind magnetic confinement parameter \eta\ast \simeq
20 and rotation parameter W = 0.12, supporting a picture in which the Halpha
emission and other line variability have their origin in an oblique, rigidly
rotating magnetospheric structure resulting from a magnetically channeled wind.
(Abridged.)Comment: 13 pages, MNRAS. Version 2, small change to Fig. 1
A fluid-walled microfluidic platform for human neuron microcircuits and directed axotomy †
In our brains, different neurons make appropriate connections; however, there remain few in vitro models of such circuits. We use an open microfluidic approach to build and study neuronal circuits in vitro in ways that fit easily into existing bio-medical workflows. Dumbbell-shaped circuits are built in minutes in standard Petri dishes; the aqueous phase is confined by fluid walls – interfaces between cell-growth medium and an immiscible fluorocarbon, FC40. Conditions are established that ensure post-mitotic neurons derived from human induced pluripotent stem cells (iPSCs) plated in one chamber of a dumbbell remain where deposited. After seeding cortical neurons on one side, axons grow through the connecting conduit to ramify amongst striatal neurons on the other – an arrangement mimicking unidirectional cortico-striatal connectivity. We also develop a moderate-throughput non-contact axotomy assay. Cortical axons in conduits are severed by a media jet; then, brain-derived neurotrophic factor and striatal neurons in distal chambers promote axon regeneration. As additional conduits and chambers are easily added, this opens up the possibility of mimicking complex neuronal networks, and screening drugs for their effects on connectivity
Delivery of the 135kb human frataxin genomic DNA locus gives rise to different frataxin isoforms
© 2015 Elsevier Inc. Friedreich's ataxia (FRDA) is the most common form of hereditary ataxia caused by recessive mutations in the FXN gene. Recent results have indicated the presence of different frataxin isoforms due to alternative gene expression mechanisms. Our previous studies demonstrated the advantages of using high-capacity herpes simplex virus type 1 (HSV-1) amplicon vectors containing the entire FXN genomic locus (iBAC-FXN) as a gene-delivery vehicle capable of ensuring physiologically-regulated and long-term persistence. Here we describe how expression from the 135. kb human FXN genomic locus produces the three frataxin isoforms both in cultured neuronal cells and also in vivo. Moreover, we also observed the correct expression of these frataxin isoforms in patient-derived cells after delivery of the iBAC-. FXN. These results lend further support to the potential use of HSV-1 vectors containing entire genomic loci whose expression is mediated by complex transcriptional and posttranscriptional mechanisms for gene therapy applications.Spanish National Research Plan (SAF 2012-38042) and the Autonomous Government of Madrid (S2010/BMD-2331). The Center for Biomedical Research on Rare Diseases (“Centro de Investigación Biomédica en Red sobre Enfermedades Raras”, CIBERER) is an initiative supported by the “Instituto de Salud Carlos III”.Peer Reviewe
NGC 1624-2: A slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field
This paper presents a first observational investigation of the faint Of?cp
star NGC 1624-2, yielding important new constraints on its spectral and
physical characteristics, rotation, magnetic field strength, X-ray emission and
magnetospheric properties. Modeling the spectrum and spectral energy
distribution, we conclude that NGC 1624-2 is a main sequence star of mass M
{\simeq} 30 M{\odot}, and infer an effective temperature of 35 {\pm} 2 kK and
log g = 4.0 {\pm} 0.2. Based on an extensive time series of optical spectral
observations we report significant variability of a large number of spectral
lines, and infer a unique period of 157.99 {\pm} 0.94 d which we interpret as
the rotational period of the star. We report the detection of a very strong -
5.35 {\pm} 0.5 kG - longitudinal magnetic field , coupled with probable
Zeeman splitting of Stokes I profiles of metal lines confirming a surface field
modulus of 14 {\pm} 1 kG, consistent with a surface dipole of polar
strength >~ 20 kG. This is the largest magnetic field ever detected in an
O-type star, and the first report of Zeeman splitting of Stokes I profiles in
such an object. We also report the detection of reversed Stokes V profiles
associated with weak, high-excitation emission lines of O iii, which we propose
may form in the close magnetosphere of the star. We analyze archival Chandra
ACIS-I X-ray data, inferring a very hard spectrum with an X-ray efficiency log
Lx/Lbol = -6.4, a factor of 4 larger than the canonical value for O-type stars
and comparable to that of the young magnetic O-type star {\theta}1 Ori C and
other Of?p stars. Finally, we examine the probable magnetospheric properties of
the star, reporting in particular very strong magnetic confinement of the
stellar wind, with {\eta}* {\simeq} 1.5 {\times} 10^4, and a very large Alfven
radius, RAlf = 11.4 R*.Comment: 17 pages, MNRAS accepted and in pres
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
Discovery Of A Magnetic Field In The Rapidly Rotating O-Type Secondary Of The Colliding-Wind Binary HD 47129 (Plaskett\u27s Star)
We report the detection of a strong, organized magnetic field in the secondary component of the massive O8III/I+O7.5V/III double-lined spectroscopic binary system HD 47129 (Plaskett\u27s star) in the context of the Magnetism in Massive Stars survey. Eight independent Stokes V observations were acquired using the Echelle SpectroPolarimetric Device for the Observations of Stars (ESPaDOnS) spectropolarimeter at the Canada-France-Hawaii Telescope and the Narval spectropolarimeter at the Telescope Bernard Lyot. Using least-squares deconvolution we obtain definite detections of signal in Stokes V in three observations. No significant signal is detected in the diagnostic null (N) spectra. The Zeeman signatures are broad and track the radial velocity of the secondary component; we therefore conclude that the rapidly rotating secondary component is the magnetized star. Correcting the polarized spectra for the line and continuum of the (sharp-lined) primary, we measured the longitudinal magnetic field from each observation. The longitudinal field of the secondary is variable and exhibits extreme values of -810 +/- 150 and +680 +/- 190 G, implying a minimum surface dipole polar strength of 2850 +/- 500 G. In contrast, we derive an upper limit (3 sigma) to the primary\u27s surface magnetic field of 230 G. The combination of a strong magnetic field and rapid rotation leads us to conclude that the secondary hosts a centrifugal magnetosphere fed through a magnetically confined wind. We revisit the properties of the optical line profiles and X-ray emission - previously interpreted as a consequence of colliding stellar winds - in this context. We conclude that HD 47129 represents a heretofore unique stellar system - a close, massive binary with a rapidly rotating, magnetized component - that will be a rich target for further study
The writing on the wall: the concealed communities of the East Yorkshire horselads
This paper examines the graffiti found within late nineteenth and early-twentieth century farm buildings in the Wolds of East Yorkshire. It suggests that the graffiti were created by a group of young men at the bottom of the social hierarchy - the horselads – and was one of the ways in which they constructed a distinctive sense of communal identity, at a particular stage in their lives. Whilst it tells us much about changing agricultural regimes and social structures, it also informs us about experiences and attitudes often hidden from official histories and biographies. In this way, the graffiti are argued to inform our understanding, not only of a concealed community, but also about their hidden histor
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