17,037 research outputs found
On gravity from SST, geoid from Seasat, and plate age and fracture zones in the Pacific
A composite map produced by combining 90 passes of SST data show good agreement with conventional GEM models. The SEASAT altimeter data were deduced and found to agree with both the SST and GEM fields. The maps are dominated (especially in the east) by a pattern of roughly east-west anomalies with a transverse wavelength of about 2000 km. Comparison with regional bathymetric data shows a remarkedly close correlation with plate age. Most anomalies in the east half of the Pacific could be partly caused by regional differences in plate age. The amplitude of these geoid or gravity anomalies caused by age differences should decrease with absolute plate age, and large anomalies (approximately 3 m) over old, smooth sea floor may indicate a further deeper source within or perhaps below the lithosphere. The possible plume size and ascent velocity necessary to supply deep mantle material to the upper mantle without complete thermal equilibration was considered. A plume emanating from a buoyant layer 100 km thick and 10,000 times less viscous than the surrounding mantle should have a diameter of about 400 km and must ascend at about 10 cm/yr to arrive still anomalously hot in the uppermost mantle
Spin-resolved spectroscopy of the intermediate polar DQ Her
We present high-speed spectroscopic observations of the intermediate polar (IP) DQ Herculis. Doppler tomography of two He I lines reveals a spiral density structure in the accretion disc around the white dwarf (WD) primary. The spirals look very similar to the spirals seen in dwarf novae during outburst. DQ Her is the first well-established IP in which spirals are seen, which are in addition likely persistent because of the system's high mass transfer rate. Spiral structures give an alternative explanation for sidebands of the WD spin frequency that are found in IP light curves. The Doppler tomogram of He II lambda 4686 indicates that a large part of the emission is not disc-like.
Spin trails of spectra reveal a pulsation in the He II lambda 4686 emission that is believed to result from reprocessing of X-rays from the WD's magnetic poles in the accretion flow close to the WD. We confirm the previous finding that the pulsation is only visible in the redshifted part of the line when the beam points to the back side of the disc. The absence of reprocessed light from the front side of the disc can be explained by obscuration by the front rim of the disc, but the absence of extra emission from the blueshifted back side of the disc is puzzling. Reprocessing in accretion curtains can be an answer to the problem and can also explain the highly non-Keplerian velocity components that are found in the He II lambda 4686 line. Our spin trails can form a strong test for future accretion curtain models, with the possibility of distinguishing between a spin period of 71 or 142 s. Spin trails of data taken at selected orbital phases show little evidence for a significant contribution of the bright spot to the pulsations and allow us to exclude a recent suggestion that 71 s is the beat period and 70.8 s the spin period
KIC 2856960: the impossible triple star
KIC 2856960 is a star in the Kepler field which was observed by Kepler for 4
years. It shows the primary and secondary eclipses of a close binary of 0.258d
as well as complex dipping events that last for about 1.5d at a time and recur
on a 204d period. The dips are thought to result when the close binary passes
across the face of a third star. In this paper we present an attempt to model
the dips. Despite the apparent simplicity of the system and strenuous efforts
to find a solution, we find that we cannot match the dips with a triple star
while satisfying Kepler's laws. The problem is that to match the dips the
separation of the close binary has to be larger than possible relative to the
outer orbit given the orbital periods. Quadruple star models can get round this
problem but require the addition of a so-far undetected intermediate period of
order 5 -- 20d that has be a near-perfect integer divisor of the outer 204d
period. Although we have no good explanation for KIC 2856960, using the full
set of Kepler data we are able to update several of its parameters. We also
present a spectrum showing that KIC 2856960 is dominated by light from a K3- or
K4-type star.Comment: 11 pages, 13 figures, accepted for publication in MNRAS August 21,
201
The crystal and molecular structure of Hydridotetrakis(diethyl phenylphosphonite)cobalt(I)
An X-ray structure determination of the title compound shows that the co-ordination about the cobalt atom is approximately trigonal bipyramidal; n.m.r. data indicate that the complex is non-rigid in solution
Searching for nova shells around cataclysmic variables
We present the results of a search for nova shells around 101 cataclysmic
variables (CVs), using Halpha images taken with the 4.2-m William Herschel
Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric Halpha Survey
of the Northern Galactic Plane (IPHAS). Both telescopes are located on La
Palma. We concentrated our WHT search on nova-like variables, whilst our IPHAS
search covered all CVs in the IPHAS footprint. We found one shell out of the 24
nova-like variables we examined. The newly discovered shell is around V1315 Aql
and has a radius of approx.2.5 arcmin, indicative of a nova eruption
approximately 120 years ago. This result is consistent with the idea that the
high mass-transfer rate exhibited by nova-like variables is due to enhanced
irradiation of the secondary by the hot white dwarf following a recent nova
eruption. The implications of our observations for the lifetime of the
nova-like variable phase are discussed. We also examined 4 asynchronous polars,
but found no new shells around any of them, so we are unable to confirm that a
recent nova eruption is the cause of the asynchronicity in the white dwarf
spin. We find tentative evidence of a faint shell around the dwarf nova V1363
Cyg. In addition, we find evidence for a light echo around the nova V2275 Cyg,
which erupted in 2001, indicative of an earlier nova eruption approx.300 years
ago, making V2275 Cyg a possible recurrent nova.Comment: 14 pages, 50 figures, 3 Table
Tracing the spiral arms in IP Pegasi
We report the analysis of time-resolved spectroscopy of IP Pegasi in outburst with eclipse mapping techniques to investigate the location and geometry of the observed spiral structures. We were able to obtain an improved view of the spiral structures with the aid of light curves extracted in velocity bins matching the observed range of velocities of the spiral arms combined with a double default map tailored for reconstruction of asymmetric structures. Two-armed spiral structures are clearly seen in all eclipse maps. The arms are located at different distances from the disc centre. The “blue” arm is farther out in the disc (R = 0.55 ± 0.05 R L1 ) than the “red” arm (R = 0.30 ± 0.05 R L1 ). There is evidence that
the velocity of the emitting gas along the spiral pattern is lower than the Keplerian velocity for the same disc radius. The discrepancy is smaller in the outer arm (measured velocities 10–15 per cent lower than Keplerian) and is more significant in the inner arm (observed velocities up to 40 per cent lower than Keplerian). We measured the opening angle of the spirals from the azimuthal intensity distribution of the eclipse maps to
be φ = 25◦ ± 3◦ . A comparison with similar measurements on data at different outburst stages reveals that the opening angle of the spiral arms in IP Peg decreases while the outbursting accretion disc cools and shrinks, in agreement with the expected evolution of a tidally driven spiral
wave. The sub-Keplerian velocities along the spiral pattern and the clear correlation between the opening angle of the spirals and the outburst stage favors the interpretation of these asymmetric structures as tidally-induced spiral shocks
Fermented beverages with health-promoting potential: Past and future perspectives
peer-reviewedFermentation is an ancient form of food preservation, which also improves the nutritional content of foods. In many regions of the world, fermented beverages have become known for their health-promoting attributes. In addition to harnessing traditional beverages for commercial use, there have recently been innovative efforts to develop non-dairy probiotic fermented beverages from a variety of substrates, including soy milk, whey, cereals and vegetable and fruit juices. On the basis of recent developments, it is anticipated that fermented beverages will continue to be a significant component within the functional food market
New results on GP Com
We present high resolution optical and UV spectra of the 46 min orbital
period, helium binary, GP Com. Our data contains simultaneous photometric
correction which confirms the flaring behaviour observed in previous optical
and UV data. In this system all lines show a triple peaked structure where the
outer two peaks are associated with the accretion disc around the compact
object. The main aim of this paper is to constrain the origin of the central
peak, also called ``central spike''. We find that the central spike contributes
to the flare spectra indicating that its origin is probably the compact object.
We also detect that the central spike moves with orbital phase following an
S-wave pattern. The radial velocity semiamplitude of the S-wave is ~10 km/s
indicating that its origin is near the centre of mass of the system, which in
this case lies very close to the white dwarf. Our resolution is higher than
that of previous data which allows us to resolve structure in the central peak
of the line. The central spike in three of the HeI lines shows another peak
blueshifted with respect to the main peak. We propose that one of the peaks is
a neutral helium forbidden transition excited in a high electron density
region. This forbidden transition is associated with the permitted one (the
stronger peak in two of the lines). The presence of a high electron density
region again favours the white dwarf as their origin.Comment: 14 pages, 16 figures. Accepted for publication in A&
Evidence for bimodal orbital separations of white dwarf-red dwarf binary stars
We present the results of a radial velocity survey of 20 white dwarf plus M
dwarf binaries selected as a follow up to a \textit{Hubble Space Telescope}
study that aimed to spatially resolve suspected binaries. Our candidates are
taken from the list of targets that were spatially unresolved with
\textit{Hubble}. We have determined the orbital periods for 16 of these compact
binary candidates. The period distribution ranges from 0.14 to 9.16\,d and
peaks near 0.6\,d. The original sample therefore contains two sets of binaries,
wide orbits (\,au) and close orbits (\,au), with
no systems found in the \,au range. This observational evidence
confirms the bimodal distribution predicted by population models and is also
similar to results obtained in previous studies. We find no binary periods in
the months to years range, supporting the post common envelope evolution
scenario. One of our targets, WD\,1504+546, was discovered to be an eclipsing
binary with a period of 0.93\,d
A Radial Velocity Study of CTCV J1300-3052
We present time-resolved spectroscopy of the eclipsing, short period
cataclysmic variable CTCV J1300-3052. Using absorption features from the
secondary star, we determine the radial velocity semi-amplitude of the
secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity
to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo
techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf
primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These
parameters are found to be in excellent agreement with previous mass
determinations found via photometric fitting techniques, supporting the
accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9
figures (black and white
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