6,120 research outputs found
Temporal fluctuations in the differential rotation of cool active stars
This paper reports positive detections of surface differential rotation on
two rapidly rotating cool stars at several epochs, by using stellar surface
features (both cool spots and magnetic regions) as tracers of the large scale
latitudinal shear that distorts the convective envelope in this type of stars.
We also report definite evidence that this differential rotation is different
when estimated from cool spots or magnetic regions, and that it undergoes
temporal fluctuations of potentially large amplitude on a time scale of a few
years. We consider these results as further evidence that the dynamo processes
operating in these stars are distributed throughout the convective zone rather
than being confined at its base as in the Sun. By comparing our observations
with two very simple models of the differential rotation within the convective
zone, we obtain evidence that the internal rotation velocity field of the stars
we investigated is not like that of the Sun, and may resemble that we expect
for rapid rotators. We speculate that the changes in differential rotation
result from the dynamo processes (and from the underlying magnetic cycle) that
periodically converts magnetic energy into kinetic energy and vice versa. We
emphasise that the technique outlined in this paper corresponds to the first
practical method for investigating the large scale rotation velocity field
within convective zones of cool active stars, and offers several advantages
over asteroseismology for this particular purpose and this specific stellar
class.Comment: 14 pages, 4 figure
The Effect of Co-feeding Methyl Acetate on the H-ZSM5 Catalysed Methanol-to-Hydrocarbons Reaction
Funding Information: Johnson Matthey plc and the EPSRC are thanked for postgraduate student support (A.P.H., A.Z.) via the Industrial CASE scheme (EP/P510506/1). Johnson Matthey plc is additionally thanked for provision of the ZSM-5 catalyst. The Science and Technology Facilities Council is thanked for the provision of neutron beam time (RB1820116, https://doi.org/10.5286/isis.e.97999822 ). The resources and support provided by the UK Catalysis Hub via Membership of the UK Catalysis Hub Consortium and funded by EPSRC (Grants EP/K014706/1, EP/K014668/1, EP/ K014854/1, EP/K014714/1, and EP/M013219/1) are gratefully acknowledged.Peer reviewedPublisher PD
The first magnetic maps of a pre-main sequence binary star system - HD 155555
We present the first maps of the surface magnetic fields of a pre-main
sequence binary system. Spectropolarimetric observations of the young, 18 Myr,
HD 155555 (V824 Ara, G5IV + K0IV) system were obtained at the Anglo-Australian
Telescope in 2004 and 2007. Both datasets are analysed using a new binary
Zeeman Doppler imaging (ZDI) code. This allows us to simultaneously model the
contribution of each component to the observed circularly polarised spectra.
Stellar brightness maps are also produced for HD 155555 and compared to
previous Doppler images. Our radial magnetic maps reveal a complex surface
magnetic topology with mixed polarities at all latitudes. We find rings of
azimuthal field on both stars, most of which are found to be non-axisymmetric
with the stellar rotational axis. We also examine the field strength and the
relative fraction of magnetic energy stored in the radial and azimuthal field
components at both epochs. A marked weakening of the field strength of the
secondary star is observed between the 2004 and 2007 epochs. This is
accompanied by an apparent shift in the location of magnetic energy from the
azimuthal to radial field. We suggest that this could be indicative of a
magnetic activity cycle. We use the radial magnetic maps to extrapolate the
coronal field (by assuming a potential field) for each star individually - at
present ignoring any possible interaction. The secondary star is found to
exhibit an extreme tilt (~75 deg) of its large scale magnetic field to that of
its rotation axis for both epochs. The field complexity that is apparent in the
surface maps persists out to a significant fraction of the binary separation.
Any interaction between the fields of the two stars is therefore likely to be
complex also. Modelling this would require a full binary field extrapolation.Comment: 17 pages, 12 figures, accepted for publication in MNRA
Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
We present a sample of 1317 Infrared-Faint Radio Sources (IFRSs) that, for
the first time, are reliably detected in the infrared, generated by
cross-correlating the Wide-Field Infrared Survey Explorer (WISE) all-sky survey
with major radio surveys. Our IFRSs are brighter in both radio and infrared
than the first generation IFRSs that were undetected in the infrared by the
Spitzer Space Telescope. We present the first spectroscopic redshifts of IFRSs,
and find that all but one of the IFRSs with spectroscopy has z > 2. We also
report the first X-ray counterparts of IFRSs, and present an analysis of radio
spectra and polarization, and show that they include Gigahertz-Peaked Spectrum,
Compact Steep Spectrum, and Ultra-Steep Spectrum sources. These results,
together with their WISE infrared colours and radio morphologies, imply that
our sample of IFRSs represents a population of radio-loud Active Galactic
Nuclei at z > 2. We conclude that our sample consists of lower-redshift
counterparts of the extreme first generation IFRSs, suggesting that the fainter
IFRSs are at even higher redshift.Comment: 23 pages, 17 figures. Submitted to MNRA
The first WASP public data release
The WASP (wide angle search for planets) project is an exoplanet transit survey that has been automatically taking wide field images since 2004. Two instruments, one in La Palma and the other in South Africa, continually monitor the night sky, building up light curves of millions of unique objects. These light curves are used to search for the characteristics of exoplanetary transits. This first public data release (DR1) of the WASP archive makes available all the light curve data and images from 2004 up to 2008 in both the Northern and Southern hemispheres. A web interface () to the data allows easy access over the Internet. The data set contains 3â631â972 raw images and 17â970â937 light curves. In total the light curves have 119â930â299â362 data points available between them
Multi-frequency observations of a superbubble in the LMC: The case of LHA 120-N 70
We present a detailed study of new Australia Telescope Compact Array (ATCA)
and XMM-Newton observations of LHA 120-N 70 (hereafter N 70), a spherically
shaped object in the Large Magellanic Cloud (LMC) classified as a superbubble
(SB). Both archival and new observations were used to produce high quality
radio-continuum, X-ray and optical images. The radio spectral index of N 70 is
estimated to be indicating that while a supernova or
supernovae have occurred in the region at some time in the distant past, N70 is
not the remnant of a single specific supernova. N70 exhibits limited
polarisation with a maximum fractional polarisation of 9% in a small area of
the north west limb. We estimate the size of N 70 to have a diameter of 104 pc
( pc). The morphology of N 70 in X-rays closely follows that in radio
and optical, with most X-ray emission confined within the bright shell seen at
longer wavelengths. Purely thermal models adequately fit the soft X-ray
spectrum which lacks harder emission (above 1 keV). We also examine the
pressure output of N 70 where the values for the hot (PX) and warm (PHii) phase
are consistent with other studied Hii regions. However, the dust-processed
radiation pressure (PIR) is significantly smaller than in any other object
studied in Lopez et al. (2013). N70 is a very complex region that is likely to
have had multiple factors contributing to both the origin and evolution of the
entire region.Comment: 21 pages 8 figures accepted for publication in A
Doppler tomography of transiting exoplanets: A prograde, low-inclined orbit for the hot Jupiter CoRoT-11b
We report the detection of the Doppler shadow of the transiting hot Jupiter
CoRoT-11b. Our analysis is based on line-profile tomography of time-series,
Keck/HIRES high-resolution spectra acquired during the transit of the planet.
We measured a sky-projected, spin-orbit angle of 0.1 +/- 2.6 degrees, which is
consistent with a very low-inclined orbit with respect to the stellar rotation
axis. We refined the physical parameters of the system using a Markov chain
Monte Carlo simultaneous fitting of the available photometric and spectroscopic
data. An analysis of the tidal evolution of the system shows how the currently
measured obliquity and its uncertainty translate into an initial absolute value
of less than about 10 degrees on the zero-age main sequence, for an expected
average modified tidal quality factor of the star Q'* > 4 x 10^6. This is
indicative of an inward migration scenario that would not have perturbed the
primordial low obliquity of CoRoT-11b. Taking into account the effective
temperature and mass of the planet host star (Teff=6440 K, M*=1.23 MSun), the
system can be considered a new telling exception to the recently proposed
trend, according to which relatively hot and massive stars (Teff>6250 K, M*>1.2
MSun) seem to be preferentially orbited by hot Jupiters with high obliquity.Comment: 5 pages, 4 figures, accepted for publication in A&A Letter
Studies of propene conversion over H-ZSM-5 demonstrate the importance of propene as an intermediate in methanol-to-hydrocarbons chemistry
Funding Information: Johnson Matthey plc. is thanked for supplying the ZSM-5 zeolite and for financial support through the provision of industrial CASE studentships in partnership with the EPSRC (APH (EP/P510506/1), AZ (EP/N509176/1)). Experiments at the ISIS Neutron and Muon Source were made possible by a beam time allocation from the Science and Technologies Facilities Council. 53 The resources and support provided by the UK Catalysis Hubviamembership of the UK Catalysis Hub consortium and funded by EPSRC grants EP/R026815/1 and EP/R026939/1 are gratefully acknowledged. This research has been performed with the use of facilities and equipment at the Research Complex at Harwell; the authors are grateful to the Research Complex for this access and support.Peer reviewedPublisher PD
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