960 research outputs found
Revealing the nature of central emission nebulae in the dwarf galaxy NGC 185
In this paper we present new optical observations of the galaxy NGC 185
intended to reveal the status of supernova remnants (SNRs) in this dwarf
companion of the Andromeda galaxy. Previously, it was reported that this galaxy
hosts one SNR. Our deep photometric study with the 2m telescope at Rozhen
National Astronomical Observatory using narrow-band H and [SII] filters
revealed complex structure of the interstellar medium in the center of the
galaxy. To confirm the classification and to study the kinematics of the
detected nebulae, we carried out spectroscopic observations using the SCORPIO
multi-mode spectrograph at the 6m telescope at the Special Astrophysical
Observatory of the Russian Academy of Science, both in low- and high-resolution
modes. We also searched the archival X-ray and radio data for counterparts of
the candidate SNRs identified by our optical observations. Our observations
imply the presence of one more SNR, one possible HII region previously
cataloged as part of an SNR, and the presence of an additional source of shock
ionization in one low-brightness PN. We detected enhanced [SII]/H_alpha and
[NII]/H_alpha line ratios, as well as relatively high (up to 90 km s)
expansion velocities of the two observed nebulae, motivating their
classification as SNRs (with diameters of 45 pc and 50 pc), confirmed by both
photometric and spectral observations. The estimated electron density of
emission nebulae is 30 - 200 cm. Archival XMM-Newton observations
indicate the presence of an extended, low-brightness, soft source in projection
of one of the optical SNRs, whereas the archival VLA radio image shows weak,
unresolved emission in the center of NGC 185.Comment: 15 pages, 14 figures, accepted for publication in A&
The Anti-Coincidence Detector for the GLAST Large Area Telescope
This paper describes the design, fabrication and testing of the
Anti-Coincidence Detector (ACD) for the Gamma-ray Large Area Space Telescope
(GLAST) Large Area Telescope (LAT). The ACD is LAT first-level defense against
the charged cosmic ray background that outnumbers the gamma rays by 3-5 orders
of magnitude. The ACD covers the top and 4 sides of the LAT tracking detector,
requiring a total active area of ~8.3 square meters. The ACD detector utilizes
plastic scintillator tiles with wave-length shifting fiber readout. In order to
suppress self-veto by shower particles at high gamma-ray energies, the ACD is
segmented into 89 tiles of different sizes. The overall ACD efficiency for
detection of singly charged relativistic particles entering the tracking
detector from the top or sides of the LAT exceeds the required 0.9997.Comment: 33 pages, 19 figure
The optimal form of the scanning near-field optical microscopy probe
A theoretical approach to determine the optimal form of the near-field
optical microscope probe is proposed. An analytical expression of the optimal
probe form with subwavelength aperture has been obtained. The advantages of the
probe with the optimal form are illustrated using numerical calculations. The
conducted calculations show 10 times greater light throughput and the reception
possibility of the more compactly localized light at the output probe aperture
which could indicate better spatial resolution of the optical images in
near-field optical technique using optimal probe.Comment: 12 pages, 6 figure
Apollo asteroids (1566) Icarus and 2007 MK6: Icarus family members?
Although it is more complicated to search for near-Earth object (NEO)
families than main belt asteroid (MBA) families, since differential orbital
evolution within a NEO family can cause current orbital elements to drastically
differ from each other, we have found that Apollo asteroids (1566) Icarus and
the newly discovered 2007 MK6 are almost certainly related. Specifically, their
orbital evolutions show a similar profile, time shifted by only ~1000 yr, based
on our time-lag theory. The dynamical relationship between Icarus and 2007 MK6
along with a possible dust band, the Taurid-Perseid meteor swarm, implies the
first detection of an asteroidal NEO family, namely the "Icarus asteroid
family".Comment: 11 pages, 1 figure, to appear on Astrophysical Journal Letters
(journal info added
A Region of Violent Star Formation in the Irr Galaxy IC 10: Structure and Kinematics of Ionized and Neutral Gas
We have used observations of the galaxy IC 10 at the 6-m telescope of the
Special Astrophysical Observatory with the SCORPIO focal reducer in the
Fabry-Perot interferometer mode and with the MPFS spectrograph to study the
structure and kinematics of ionized gas in the central region of current
intense star formation. Archive VLA 21-cm observations are used to analyze the
structure and kinematics of neutral gas in this region. High-velocity wings of
the H-alpha and [SII] emission lines were revealed in the inner cavity of the
nebula HL 111 and in other parts of the complex of violent star formation. We
have discovered local expanding neutral-gas shells around the nebulae HL 111
and HL 106.Comment: 22 pages, 10 figures; accepted in Astronomy Report
Large-scale instability in a sheared nonhelical turbulence: formation of vortical structures
We study a large-scale instability in a sheared nonhelical turbulence that
causes generation of large-scale vorticity. Three types of the background
large-scale flows are considered, i.e., the Couette and Poiseuille flows in a
small-scale homogeneous turbulence, and the "log-linear" velocity shear in an
inhomogeneous turbulence. It is known that laminar plane Couette flow and
antisymmetric mode of laminar plane Poiseuille flow are stable with respect to
small perturbations for any Reynolds numbers. We demonstrate that in a
small-scale turbulence under certain conditions the large-scale Couette and
Poiseuille flows are unstable due to the large-scale instability. This
instability causes formation of large-scale vortical structures stretched along
the mean sheared velocity. The growth rate of the large-scale instability for
the "log-linear" velocity shear is much larger than that for the Couette and
Poiseuille background flows. We have found a turbulent analogue of the
Tollmien-Schlichting waves in a small-scale sheared turbulence. A mechanism of
excitation of turbulent Tollmien-Schlichting waves is associated with a
combined effect of the turbulent Reynolds stress-induced generation of
perturbations of the mean vorticity and the background sheared motions. These
waves can be excited even in a plane Couette flow imposed on a small-scale
turbulence when perturbations of mean velocity depend on three spatial
coordinates. The energy of these waves is supplied by the small-scale sheared
turbulence.Comment: 12 pages, 14 figures, Phys. Rev. E, in pres
Use of Physicochemical Method for Evaluation of Mucilage Producing Ability of the Linum Usitatissimum L. Seeds
Abstract In the modern medicine of many European countries flax is used as a medicament with a wide range of use. Wholesome effect of flax seeds is determined by the large amount of enveloping substances. This property is connected with content of mucilage up to 10% and glycoside linamarin. Flaxseed polysaccharides also possess antiinflammatory effect. Furthermore, mucilage production can be a chemosystematic characteric of intraspecific taxons. In literature intervarietal variability data is limited. Therefore, comparative evaluation of mucilage producing ability of flax seeds with different morphotypes is of interest. The research of micromorphological characteristics of seed coat and mucilage production dynamics was carried out and it was established that mucilage-producing cells are localized predominantly in the external layer of seed coat. It was established that Bahmalskiy, Nebesnyj, Kustanayskiy yantar varieties possess the highest level of mucilage production. Morphotype and varietal specificity of mucilage production are determined, consequently it can be used as a marker feature of L. usitatissimum new forms. The proposed technique is based on the determination of seed physicochemical characteristics and can be used for express analysis of the vegetal samples and their differentiation by the directions of use: as a fatty oil or mucilage-containing raw material.
Keywords: Linum usitatissimum L. varieties, seeds, mucilage production, hydration dynamics, physicochemical method
Propagating Star Formation in the Collisional Ring Galaxy Arp 10
Propagating star formation in a collisional ring galaxy Arp10 is investigated
by a complex approach, which includes the broad- and narrow-band photometry,
long- slit spectroscopy, and scanning Fabry-Perot spectroscopy. The ionized gas
velocity field obtained with best spatial resolution to date indicates a non-
isotropic expansion of the outer ring with a maximum velocity 110km/s. Strong
vertical and non-circular motions are also seen in the vicinity of the inner
ring. Our kinematic data suggest that Arp10 has a small inclination i=22\degr
and high total (luminous plus dark matter) mass of about
within a 50 kpc radius.The abundance of oxygen 12 + log(O/H) in both star-
forming rings is about 8.6.The analysis of spectral indices provides an
estimate on the propagation velocities of both rings and metallicity of the
pre-collision stellar population.A small "knot" near the nucleus of Arp10,which
was previously suspected as a possible candidate for collision, is now
unambiguously identified as the "intruder" of at least 1/4 of the total mass of
Arp~10.We use a simplified two-dimensional hydrodynamic modeling of galaxy
collisions to test a collisional origin of Arp10. We confirm that the sizes of
the inner and outer rings, maximum expansion velocity of the outer ring, and
radial profile of the gas circular velocity can be reproduced by a near-central
collision with the intruder galaxy, which occurred approximately 85Myr ago. We
acknowledge that an apparent crescent- shaped distribution of H
emission in the outer ring is caused by a star formation threshold in the gas
disk of Arp10.Comment: 17 pages, 17 figures, accepted by Ap
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