327 research outputs found
Study of Eclipsing Binary and Multiple Systems in OB Associations II. The Cygnus OB Region: V443 Cyg, V456 Cyg and V2107 Cyg
Three presumably young eclipsing binary systems in the direction of the
Cygnus OB1, OB3 and OB9 associations are studied. Component spectra are
reconstructed and their orbits are determined using light curves and spectra
disentangling techniques. V443 Cyg and V456 Cyg have circular orbits, while the
light curve of V2107\,Cyg imposes a slightly eccentric orbit
(. V443 Cyg harbours F-type stars, and not young early-A stars
as previously suggested in the literature based on photometry solely. It
appears to be situated in the foreground (distance kpc) of the
young stellar populations in Cygnus. V456 Cyg, at a distance of
kpc consists of a slightly metal-weak A--type and an early--F star. The age of
both systems, on or very near to the main sequence, remains uncertain by an
order of magnitude. V2107 Cyg is a more massive system ( and
) at kpc and, also kinematically, a strong
candidate-member of Cyg OB1. The more massive component is slightly evolved and
appears to undergo non-radial -type pulsations. The Doppler signal
of the secondary is barely detectable. A more extensive study is important to
fix masses more precisely, and an asteroseismological study would then become
appropriate. Nevertheless, the position of the primary in the HR-diagram
confines the age already reasonably well to Myr, indicating for Cyg
OB1 a similar extent of star formation history as established for Cyg OB2.Comment: 27 pages, including 9 figures and 6 tables, accepted for publication
in Astronomical Journa
The Spectroscopic Orbits of Three Double-lined Eclipsing Binaries: I. BG Ind, IM Mon, RS Sgr
We present the spectroscopic orbit solutions of three double-lines eclipsing
binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs)
of the components were determined using high resolution echelle spectra
obtained at Mt. John University Observatory in New Zealand. The RVs of the
components of BG Ind and RS Sgr were measured using Gaussian fittings to the
selected spectral lines, whereas two-dimensional cross-correlation technique
was preferred to determine the RVs of IM Mon since it has relatively short
orbital period among the other targets and so blending of the lines is more
effective. For all systems, the Keplerian orbital solution was used during the
analysis and also circular orbit was adopted because the eccentricities for all
targets were found to be negligible. The first precise orbit analysis of these
systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325,
respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio
values, orbital sizes and minimum masses of the components of the systems
indicates that all systems should have different physical, dynamical and
probable evolutionary status.Comment: 17 pages, 6 figures and 4 tables, accepted for publication in New
Astronom
All-optical attoclock: accessing exahertz dynamics of optical tunnelling through terahertz emission
The debate regarding attosecond dynamics of optical tunneling has so far been
focused on time delays associated with electron motion through the potential
barrier created by intense ionizing laser fields and the atomic core.
Compelling theoretical and experimental arguments have been put forward to
advocate the polar opposite views, confirming or refuting the presence of
tunnelling time delays. Yet, such delay, whether present or ot, is but a single
quantity characterizing the tunnelling wavepacket; the underlying dynamics are
richer. Here we propose to complement photo-electron detection with detecting
light, focusing on the so-called Brunel adiation -- the near-instantaneous
nonlinear optical response triggered by the tunnelling event. Using the
combination of single-color and two-color driving fields, we determine not only
the ionization delays, but also the re-shaping of the tunnelling wavepacket as
it emerges from the classically forbidden region. Our work introduces a new
type of attoclock for optical tunnelling, one that is based on measuring light
rather than photo-electrons. All-optical detection paves the way to
time-resolving multiphoton transitions across bandgaps in solids, on the
attosecond time-scale
Scattering of first and second sound waves by quantum vorticity in superfluid Helium
We study the scattering of first and second sound waves by quantum vorticity
in superfluid Helium using two-fluid hydrodynamics. The vorticity of the
superfluid component and the sound interact because of the nonlinear character
of these equations. Explicit expressions for the scattered pressure and
temperature are worked out in a first Born approximation, and care is exercised
in delimiting the range of validity of the assumptions needed for this
approximation to hold. An incident second sound wave will partly convert into
first sound, and an incident first sound wave will partly convert into second
sound. General considerations show that most incident first sound converts into
second sound, but not the other way around. These considerations are validated
using a vortex dipole as an explicitely worked out example.Comment: 24 pages, Latex, to appear in Journal of Low Temperature Physic
Magnus and Iordanskii Forces in Superfluids
The total transverse force acting on a quantized vortex in a superfluid is a
problem that has eluded a complete understanding for more than three decades.
In this letter I propose a remarkably simple argument, somewhat reminiscent of
Laughlin's beautiful argument for the quantization of conductance in the
quantum Hall effect, to define the superfluid velocity part of the transverse
force. This term is found to be . Although
this result does not seem to be overly controversial, this thermodynamic
argument based only on macroscopic properties of the superfluid does offer a
robust derivation. A recent publication by Thouless, Ao and Niu has
demonstrated that the vortex velocity part of the transverse force in a
homogeneous neutral superfluid is given by the usual form . A combination of these two independent results and the required
Galilean invariance yields that there cannot be any transverse force
proportional to the normal fluid velocity, in apparent conflict with
Iordanskii's theory of the transverse force due to phonon scattering by the
vortex.Comment: RevTex, 1 Encapsulated Postscript figur
Binary coalescence from case A evolution -- mergers and blue stragglers
We constructed some main-sequence mergers from case A binary evolution and
studied their characteristics via Eggleton's stellar evolution code. Both total
mass and orbital angular momentum are conservative in our binary evolutions.
Some mergers might be on the left of the ZAMS as defined by normal surface
composition on a CMD because of enhanced surface helium content. The study also
shows that central hydrogen content of the mergers is independent of mass. As a
consequence, we fit the formula of magnitude and B-V of the mergers when they
return back to thermal equilibrium with maximum error 0.29 and 0.037,
respectively. Employing the consequences above, we performed Monte Carlo
simulations to examine our models in NGC 2682 and NGC 2660. In NGC 2682, binary
mergers from our models cover the region with high luminosity, but its
importance is much less than that of AML. Our results are well-matched to the
observations of NGC2660 if there is about 0.5Mo of mass loss in the merger
process.Comment: 14 pages, 12 figures. accepted by MNRA
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