354 research outputs found
Star formation in the S233 region
The main objective of this paper is to study the possibility of triggered
star formation on the border of the HII region S233, which is formed by a
B-star. Using high-resolution spectra we determine the spectral class of the
ionizing star as B0.5 V and the radial velocity of the star to be -17.5(1.4)
km/s. This value is consistent with the velocity of gas in a wide field across
the S233 region, suggesting that the ionizing star was formed from a parent
cloud belonging to the S233 region. By studying spatial-kinematic structure of
the molecular cloud in the S233 region, we detected an isolated clump of gas
producing CO emission red-shifted relative to the parent cloud. In the UKIDSS
and WISE images, the clump of gas coincides with the infrared source containing
a compact object and bright-rimmed structure. The bright-rimmed structure is
perpendicular to the direction of the ionizing star. The compact source
coincides in position with IRAS source 05351+3549. All these features indicate
a possibility of triggering formation of a next-generation star in the S233
region. Within the framework of a theoretical one-dimensional model we conclude
that the "collect-and-collapse" process is not likely to take place in the S233
region. The presence of the bright-rimmed structure and the compact infrared
source suggest that the "collapse of the pre-existing clump" process is taking
place.Comment: 12 pages, 10 figure
THz parametric gain in semiconductor superlattices in the absence of electric domains
We theoretically show that conditions for THz gain and conditions for
formation of destructive electric domains in semiconductor superlattices are
fairly different in the case of parametric generation and amplification. Action
of an unbiased high-frequency electric field on a superlattice causes a
periodic variation of energy and effective mass of miniband electrons. This
parametric effect can result in a significant gain at some even harmonic of the
pump frequency without formation of electric domains and corruption from pump
harmonics.Comment: 4 pages, 3 figures. Accepted to Appl. Phys. Let
Optical solitons in -symmetric nonlinear couplers with gain and loss
We study spatial and temporal solitons in the symmetric
coupler with gain in one waveguide and loss in the other. Stability properties
of the high- and low-frequency solitons are found to be completely determined
by a single combination of the soliton's amplitude and the gain/loss
coefficient of the waveguides. The unstable perturbations of the high-frequency
soliton break the symmetry between its active and lossy components which
results in a blowup of the soliton or a formation of a long-lived breather
state. The unstable perturbations of the low-frequency soliton separate its two
components in space blocking the power drainage of the active component and
cutting the power supply to the lossy one. Eventually this also leads to the
blowup or breathing.Comment: 14 pages, 11 figure
Orbital and physical parameters of the spectroscopic binary HD37737
We report the physical and orbital parameters of the visible component of the spectroscopic binary HD37737 (m V = 8.03). The observations were performed with the 1.2-m telescope of the Kourovka Astronomical Observatory of the Ural Federal University in 2012 and the 6-m BTA telescope of the SAO RAS in 2007 and 2009. Radial velocities were measured separately from each spectral line of the list by the cross-correlation method with a synthetic spectrum. The latter was calculated using the grids of non-LTE model atmospheres with solar chemical compositions. A significant difference in the epochs of observations (2005-2012) allowed to refine the orbital period of the star (7· d84705) and the orbital elements of the binary system. We obtained an estimate of the mass function f(m) = 0.23 ± 0.02M ⊙. The best agreement between the synthetic and observed spectra is achieved at T eff = 30 000 K and log g = 3.50 according to the observations on both instruments. The obtained parameters correspond to a star of spectral type O9.5 III, with mass estimated at 26 ± 2M ⊙. The minimum mass estimate of the secondary component of the binary is 6.2 ± 0.5M ⊙. We have discovered a fact that the velocities, obtained from different spectral lines, differ, which is typical for giant stars. Engaging additional spectra, obtained in 2005 with the 2.1-m KPNO telescope, we investigated the effect of this fact on the estimate of the speed of the system's center of mass. The difference in the velocities of various lines is approximately the same in the spectra, obtained at all the three instruments. The obtained ratios suggest that the deeper layers of the atmosphere of the star are moving with a greater velocity than the outer layers. Depending on the line, the estimate of the heliocentric velocity of the binary's center of mass varies in the range from -11 to 1 km/s. © 2013 Pleiades Publishing, Ltd
Terahertz Bloch oscillator with a modulated bias
Electrons performing Bloch oscillations in an energy band of a dc-biased
superlattice in the presence of weak dissipation can potentially generate THz
fields at room temperature. The realization of such Bloch oscillator is a
long-standing problem due to the instability of a homogeneous electric field in
conditions of negative differential conductivity. We establish the theoretical
feasibility of stable THz gain in a long superlattice device in which the bias
is quasistatically modulated by microwave fields. The modulation waveforms must
have at least two harmonics in their spectra.Comment: 5 page
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