12,987 research outputs found
The mass ratio distribution of short period double degenerate stars
Short period double degenerates (DDs) are close white dwarf - white dwarf
binary stars which are the result of the evolution of interacting binary stars.
We present the first definitive measurements of the mass ratio for two DDs,
WD0136+768 and WD1204+450, and an improved measurement of the mass ratio for
WD0957-666. We compare the properties of the 6 known DDs with measured mass
ratios to the predictions of various theoretical models. We confirm the result
that standard models for the formation of DDs do not predict sufficient DDs
with mass ratios near 1. We also show that the observed difference in cooling
ages between white dwarfs in DDs is a useful constraint on the initial mass
ratio of the binary. A more careful analysis of the properties of the white
dwarf pair WD1704+481.2 leads us to conclude that the brighter white dwarf is
older than its fainter companion. This is the opposite of the usual case for
DDs and is caused by the more massive white dwarf being smaller and cooling
faster. The mass ratio in the sense (mass of younger star)/(mass of older star)
is then 1.43+-0.06 rather than the value 0.70+-0.03 given previously.Comment: Accepted for publication in MNRA
The triple degenerate star WD1704+481
WD1704+481 is a visual binary in which both components are white dwarfs. We
present spectra of the H-alpha line of both stars which show that one component
(WD1704+481.2 = Sanduleak B = GR 577) is a close binary with two white dwarf
components. Thus, WD1704+481 is the first known triple degenerate star. From
radial velocity measurements of the close binary we find an orbital period of
0.1448d, a mass ratio, q=Mbright/Mfaint of q=0.70+-0.03 and a difference in the
gravitational redshifts of 11.5+-2.3km/s. The masses of the close pair of white
dwarfs predicted by the mass ratio and gravitational redshift difference
combined with theoretical cooling curves are 0.39+-0.05 solar mass and
0.56+-0.07 solar masses. WD1704+481 is therefore also likely to be the first
example of a double degenerate in which the less massive white dwarf is
composed of helium and the other white dwarf is composed of carbon and oxygen.Comment: 5 pages, 4 figure
Orbital periods of the binary sdB stars PG0940+068 and PG1247+554
We have used the radial velocity variations of two sdB stars previously
reported to be binaries to establish their orbital periods. They are
PG0940+068, (P=8.33d) and PG1247+554 (P=0.599d). The minimum masses of the
unseen companions, assuming a mass of 0.5 solar masses for the sdB stars, are
0.090 +/- 0.003 solar masses for PG1247+554 and 0.63 +/- 0.02 solar masses for
PG0940+068. The nature of the companions is not constrained further by our
data.Comment: 5 pages, 2 figure
A mystery solved: the mass ratio of the dwarf nova EM Cygni
We have discovered that the spectrum of the well-known dwarf nova EM Cyg is
contaminated by light from a K2-5V star (in addition to the K-type mass donor
star). The K2-5V star contributes approximately 16 per cent of the light from
the system and if not taken into account has a considerable effect upon radial
velocity measurements of the mass donor star. We obtain a new radial velocity
amplitude for the mass donor star of K2 = 202 +/- 3 km/s, which compares with
the value of K2 = 135 +/- 3 km/s obtained in Stover, Robinson & Nather's
classic 1981 study of EM Cyg. The revised value of the amplitude combined with
a measurement of rotational broadening of the mass donor vsini = 140 +/- 6
km/s, leads to a new mass ratio of q = M2/M1 = 0.88 +/- 0.05. This solves a
long standing problem with EM Cyg because Stover et al.'s measurements
indicated a mass ratio q > 1, a value which should have led to dynamically
unstable mass transfer for the secondary mass deduced by Stover et al. The
revised value of the mass ratio combined with the orbital inclination i = 67
+/- 2 degrees leads to masses of 0.99 +/- 0.12 Msun and 1.12 +/- 0.08 Msun for
the mass donor and white dwarf respectively. The mass donor is evolved, since
it has a later spectral type (K3) than its mass would imply. We discuss whether
the K star could be physically associated with EM Cyg or not, and present the
results of the spectroscopic study.Comment: 10 pages, 12 figures, accepted for publication in MNRA
The 3-53 keV Spectrum of the Quasar 1508+5714: X-rays from z = 4.3
We present a high-quality X-ray spectrum in the 3--53 keV rest-frame band of
the radio-loud quasar 1508+5714, by far the brightest known X-ray source at z >
4. A simple power-law model with an absorption column density equal to the
Galactic value in the direction of the source provides an excellent and fully
adequate fit to the data; the measured power-law photon index Gamma = 1.42
(+0.13,-0.10). Upper limits to Fe K alpha line emission and Compton-reflection
components are derived. We offer evidence for both X-ray and radio variability
in this object and provide the first contemporaneous radio spectrum (alpha =
-0.25). The data are all consistent with a picture in which the emission from
this source is dominated by a relativistically beamed component in both the
X-ray and radio bands.Comment: 8 pages, TeX, 2 postscript figures; to appear in ApJ Letter
Self-aligned 0.12mm T-gate In.53Ga.47As/In.52Al.48As HEMT Technology Utilising a Non Annealed Ohmic Contact Strategy
An InGaAs/InAlAs based HEMT structure, lattice matched to an InP substrate, is presented in which drive current and transconductance has been optimized through a double-delta doping strategy. Together with an increase in channel carrier density, this allows the use of a non-annealed ohmic contact process. HEMT devices with 120 nm standard and self-aligned T-gates were fabricated using the non-annealed ohmic process. At DC, self-aligned and standard devices exhibited transconductances of up to 1480 and 1100 mS/mm respectively, while both demonstrated current densities in the range 800 mA/mm. At RF, a cutoff frequency f/sub T/ of 190 GHz was extracted for the self-aligned device. The DC characteristics of the standard devices were then calibrated and modelled using a compound semiconductor Monte Carlo device simulator. MC simulations provide insight into transport within the channel and illustrate benefits over a single delta doped structure
The applicability of nature-based interventions to support mothersâ postnatal wellbeing: A conceptual review
Nature-based interventions represent promising candidates for supporting mothers and infants in the postnatal period, which is a vulnerable time for mothers to experience mental health difficulties. Possible mechanisms by which nature-based interventions may support postnatal health include those of a biological/physiological nature (for example natural light optimising circadian rhythm, improving microbiome health, providing opportunities for physical activity), relational/social pathways, and cognitive and creative pathways. A conceptual understanding of these possible mechanisms will aid the design and evaluation of postnatal nature-based interventions
ANALYSIS OF THE JOINT KINEMATICS OF THE 5 IRON GOLF SWING
The purpose of this study was to identify the performance determining factors of the 5-iron golf swing. Joint kinematics were obtained from thirty male golfers using a twelve camera motion analysis system. Participants were divided into two groups, based on their ball launch speed (high vs. low). Those in the high ball speed group were deemed to be the more skillful group. Statistical analysis was used to identify the variables which differed significantly between the two groups, and could therefore be classified as the performance determining factors. The following factors were important to performance success: (i) the ability of the golfer to maintain a large X Factor angle and generate large X Factor angular velocity throughout the downswing, (ii) maintain the left arm as straight as possible throughout the swing, (iii) utilise greater movement of the hips in the direction of the target and a greater extension of the right hip during the downswing and (iv) greater flexion of both shoulders and less left shoulder internal rotation during the backswing
Review of Engaging Education: Developing Emotional Literacy, Equity and Co-education. Brian Matthews. (Book Review)
The book is only about a fraction of its title Engaging Education. His section on âengaging the emotionsâ sums this up: whereas the book is largely about engaging the emotions positively, the definition of âEngagingâ is more far reaching: âthat pupils should be involved in their learning; be active and absorbed and not just passive recipients of a set curriculum. Additionally, they should feel engaged in the processes of education and have some input into creating their own agendas for learningâ (p.2). Exploring the full impact of this statement across the curriculum really needs a different book
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