1,032 research outputs found
The radio lighthouse CU Virginis: the spindown of a single main sequence star
The fast rotating star CU Virginis is a magnetic chemically peculiar star
with an oblique dipolar magnetic field. The continuum radio emission has been
interpreted as gyrosyncrotron emission arising from a thin magnetospheric
layer. Previous radio observations at 1.4 GHz showed that a 100% circular
polarized and highly directive emission component overlaps to the continuum
emission two times per rotation, when the magnetic axis lies in the plane of
the sky. This sort of radio lighthouse has been proposed to be due to cyclotron
maser emission generated above the magnetic pole and propagating
perpendicularly to the magnetic axis. Observations carried out with the
Australia Telescope Compact Array at 1.4 and 2.5 GHz one year after this
discovery show that this radio emission is still present, meaning that the
phenomenon responsible for this process is steady on a timescale of years. The
emitted radiation spans at least 1 GHz, being observed from 1.4 to 2.5 GHz. On
the light of recent results on the physics of the magnetosphere of this star,
the possibility of plasma radiation is ruled out. The characteristics of this
radio lighthouse provides us a good marker of the rotation period, since the
peaks are visible at particular rotational phases. After one year, they show a
delay of about 15 minutes. This is interpreted as a new abrupt spinning down of
the star. Among several possibilities, a quick emptying of the equatorial
magnetic belt after reaching the maximum density can account for the magnitude
of the breaking. The study of the coherent emission in stars like CU Vir, as
well as in pre main sequence stars, can give important insight into the angular
momentum evolution in young stars. This is a promising field of investigation
that high sensitivity radio interferometers such as SKA can exploit.Comment: Accepted to MNRAS, 8 pages, 7 figures, updated versio
Localisation of the human hSuv3p helicase in the mitochondrial matrix and its preferential unwinding of dsDNA
We characterised the human hSuv3p protein belonging to the family of NTPases/helicases. In yeast mitochondria the hSUV3 orthologue is a component of the degradosome complex and participates in mtRNA turnover and processing, while in Caenorhabditis elegans the hSUV3 orthologue is necessary for viability of early embryos. Using immunofluorescence analysis, an in vitro mitochondrial uptake assay and subâfractionation of human mitochondria we show hSuv3p to be a soluble protein localised in the mitochondrial matrix. We expressed and purified recombinant hSuv3p protein from a bacterial expression system. The purified enzyme was capable of hydrolysing ATP with a Km of 41.9 ”M and the activity was only modestly stimulated by polynucleotides. hSuv3p unwound partly hybridised dsRNA and dsDNA structures with a very strong preference for the latter. The presented analysis of the hSuv3p NTPase/helicase suggests that new functions of the protein have been acquired in the course of evolution
X-ray rotational modulation of a supersaturated star in IC 2391
We present evidence of X-ray rotational modulation on VXR45, a young fast
rotator star, member of IC 2391. It is a dG9 spectral type star whose
rotational period and X-ray luminosity make it a supersaturated star. Our X-ray
observation, made with EPIC/PN on XMM-Newton, covers about two photometric
rotational periods. The detection of rotational modulation implies the presence
of structural inhomogeneities. Possible interpretations are presented and
discussed.Comment: 4 pages with 4 PostScript figures. Accepted for publication in
Astronomy & Astrophysics Letter
Four ultra-short period eclipsing M-dwarf binaries in the WFCAM Transit Survey
We report on the discovery of four ultra-short period (P<0.18 days) eclipsing
M-dwarf binaries in the WFCAM Transit Survey. Their orbital periods are
significantly shorter than of any other known main-sequence binary system, and
are all significantly below the sharp period cut-off at P~0.22 days as seen in
binaries of earlier type stars. The shortest-period binary consists of two M4
type stars in a P=0.112 day orbit. The binaries are discovered as part of an
extensive search for short-period eclipsing systems in over 260,000 stellar
lightcurves, including over 10,000 M-dwarfs down to J=18 mag, yielding 25
binaries with P<0.23 days. In a popular paradigm, the evolution of short period
binaries of cool main-sequence stars is driven by loss of angular momentum
through magnetised winds. In this scheme, the observed P~0.22 day period
cut-off is explained as being due to timescales that are too long for
lower-mass binaries to decay into tighter orbits. Our discovery of low-mass
binaries with significantly shorter orbits implies that either these timescales
have been overestimated for M-dwarfs, e.g. due to a higher effective magnetic
activity, or that the mechanism for forming these tight M-dwarf binaries is
different from that of earlier type main-sequence stars.Comment: 22 pages, 17 figures, 3 tables Accepted for publication in MNRA
Stellar model atmospheres with magnetic line blanketing
Model atmospheres of A and B stars are computed taking into account magnetic
line blanketing. These calculations are based on the new stellar model
atmosphere code LLModels which implements direct treatment of the opacities due
to the bound-bound transitions and ensures an accurate and detailed description
of the line absorption. The anomalous Zeeman effect was calculated for the
field strengths between 1 and 40 kG and a field vector perpendicular to the
line of sight. The model structure, high-resolution energy distribution,
photometric colors, metallic line spectra and the hydrogen Balmer line profiles
are computed for magnetic stars with different metallicities and are discussed
with respect to those of non-magnetic reference models. The magnetically
enhanced line blanketing changes the atmospheric structure and leads to a
redistribution of energy in the stellar spectrum. The most noticeable feature
in the optical region is the appearance of the 5200 A depression. However, this
effect is prominent only in cool A stars and disappears for higher effective
temperatures. The presence of a magnetic field produces opposite variation of
the flux distribution in the optical and UV region. A deficiency of the UV flux
is found for the whole range of considered effective temperatures, whereas the
``null wavelength'' where flux remains unchanged shifts towards the shorter
wavelengths for higher temperatures.Comment: accepted by Astronomy & Astrophysic
Nitrogen turnover in the leaf litter and fine roots of sugar maple
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117199/1/ecy201091123456.pd
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