146 research outputs found
Possibly interacting Vorontsov-Velyaminov galaxies. I. Observations of VV432, VV543 and VV747
Among the galaxies which were included in the Atlas and Catalogue of
Interacting galaxies by Vorontsov-Velyaminov (hereafter VV) as multiple systems
("nests", "chains" and similarly looking systems), there are many objects,
where the interaction is not evident. Some of them are single objects,
including low-mass galaxies with active star formation (SF). In this work we
present the description of observations and results of the long-slit
spectrophotometry with the Russian 6-m telescope of three VV-galaxies looking
like double or multiple systems, and HI-observations of one of them in order to
elucidate their nature, determine their metallicity, kinematic properties and
the evolution status. Galaxies VV432 and VV747 are found to be dwarf systems
with low oxygen abundance (O/H = 1/22 and 1/12 of the solar value,
respectively). Their velocity curves indicate quite slow rotation with
respective maximum velocities of about 60 and 80 km/s, in agreement with their
low luminosities. The distance to VV432 is rather uncertain. If it is a member
of Virgo Cluster, this is the most metal-deficient known galaxy of this
aggregate. For galaxy VV543 the measured emission-line redshift 0.047 appeared
ten times larger than it was given in the original paper and is cited in
databases. This "system" evidently represents an optical pair of two galaxies
with large velocity difference. The fainter western component is an HII-galaxy,
while the brighter one is an absorption-line early-type galaxy with the radial
velocity being 1600 km/s lower.Comment: 11 pages, A&AS in press. Version of the paper with Figures 1-3 of the
higher quality is available via
http://precise.sao.ru/Laboratory/Publications/2000_pub.htm
Local Volume dwarf KK242: radial velocity, SF region, and metallicity
KK242 is a LV dwarf of transition type residing in the void environment. Koda
et al. present clear indications on its connection with Scd galaxy NGC6503.
This implies the distance to KK242 of ~6.3 Mpc and its M_B = -10.5 mag. Its
radial velocity, known from the Effelsberg radio telescope \HI\ observations,
reveals, however, the difference with that of NGC6503, dV ~ 400 km/s. If real,
this fact implies the substantial constraints on its origin. To clear-up the
issue of KK242 radial velocity, we obtained with the SAO 6-m telescope spectra
of its faint star-forming (SF) complex. H-alpha and H-beta emission is detected
in two adjacent compact regions, the southern and northern, separated by ~2"
(~60 pc). Their mean radial velocity is V_hel = -66 km/s, ~100 km/s lower than
that of NGC6503. We use the HST Legacy Archive images and photometry of
individual stars from the Extragalactic Distance Database, available for KK242,
to identify in the SF complex the exciting hot stars, the probable BHeB and
RHeB stars and a supernova remnant. We address, based on the possible range of
its gas metallicity, the probable evolutionary paths of KK242. Using package
Cloudy and parameters of the exciting B0V stars, we conclude that the observed
flux ratio of [Sii] doublet to H-alpha is consistent with the value of
12+log(O/H) ~7.35+/-0.18 dex, expected for a stripped void dIrr galaxy.Comment: 15 pages, 8 figures, 4 tables, published at MNRA
Discovery of a massive variable star with Z=Zo/36 in the galaxy DDO 68
The Local Volume dwarf galaxy DDO 68, from the spectroscopy of its two
brightest HII regions (Knots 1 and 2) was designated as the second most
metal-poor star-forming galaxy [12+log(O/H)=7.14]. In the repeated spectral
observations in 2008 January with the 6-m telescope (BTA) of the HII region
Knot 3 [having 12+log(O/H)=7.10+-0.06], we find a strong evidence of a
transient event related to a massive star evolution. From the follow-up
observation with the higher spectral resolution in 2008 February, we confirm
this phenomenon, and give parameters of its emission-line spectrum comprising
of Balmer HI and HeI lines. The luminosities of the strongest transient lines
(Ha, Hb) are of a few 10^36 erg s^-1. We also detected an additional continuum
component in the new spectrum of Knot 3, which displays the spectral energy
distribution raising to ultraviolet. The estimate of the flux of this continuum
leads us to its absolute V-band magnitude of ~-7.1. Based on the spectral
properties of this transient component, we suggest that it is related to an
evolved massive star of luminous blue variable type with Z=Zo/36. We briefly
discuss observational constraints on parameters of this unique (in the aspect
of the record low metallicity of the progenitor massive star) event and propose
several lines of its study.Comment: 6 pages, 5 Postscript figures, to appear in MNRAS Letters in June
2008 issu
Electronic Transport in a Three-dimensional Network of 1-D Bismuth Quantum Wires
The resistance R of a high density network of 6 nm diameter Bi wires in
porous Vycor glass is studied in order to observe its expected semiconductor
behavior. R increases from 300 K down to 0.3 K. Below 4 K, where R varies
approximately as ln(1/T), the order-of-magnitude of the resistance rise, as
well as the behavior of the magnetoresistance are consistent with localization
and electron-electron interaction theories of a one-dimensional disordered
conductor in the presence of strong spin-orbit scattering. We show that this
behaviour and the surface-enhanced carrier density may mask the proposed
semimetal-to-semiconductor transition for quantum Bi wires.Comment: 19 pages total, 4 figures; accepted for publication in Phys. Rev.
Single electron emission in two-phase xenon with application to the detection of coherent neutrino-nucleus scattering
We present an experimental study of single electron emission in ZEPLIN-III, a
two-phase xenon experiment built to search for dark matter WIMPs, and discuss
applications enabled by the excellent signal-to-noise ratio achieved in
detecting this signature. Firstly, we demonstrate a practical method for
precise measurement of the free electron lifetime in liquid xenon during normal
operation of these detectors. Then, using a realistic detector response model
and backgrounds, we assess the feasibility of deploying such an instrument for
measuring coherent neutrino-nucleus elastic scattering using the ionisation
channel in the few-electron regime. We conclude that it should be possible to
measure this elusive neutrino signature above an ionisation threshold of
3 electrons both at a stopped pion source and at a nuclear reactor.
Detectable signal rates are larger in the reactor case, but the triggered
measurement and harder recoil energy spectrum afforded by the accelerator
source enable lower overall background and fiducialisation of the active
volume
3-D Wave Propagation in Cylindrical Single Crystal Solid-Liquid Bodies
The large difference in the ultrasonic velocity between the solid and the liquid phases of most semiconducting materials results in reflection/refraction of ultrasound at solid-liquid interfaces and an interest in using laser ultrasonics for sensing solid-liquid interfaces during single crystal growth. Using a ray tracing analysis, a set of measured ultrasonic time of flight (TOF) projection data can yield the ray paths connecting the source to the receiver, which can subsequently be used to reconstruct the solid-liquid interface. In previous work [1] 2-D wave propagation in cylindrical single crystal solid-liquid bodies was used to explore the feasibility of using ultrasound to characterize solid-liquid interfaces during vertical Bridgman growth of semiconductor materials. Detailed study of ray paths, wavefronts and TOF for ultrasound propagating in both transverse and diametral planes of liquid-solid single crystal (Ge) bodies was reported. Numerical simulations indicated that the magnitude and direction of the group velocity, the solid:liquid velocity ratio and the curvature of the interface together controlled the ray bending behavior and thus determined the ultrasonic data across the interface. Knowledge of ray paths at the interface enabled reconstruction of the interface using a small set of ultrasonic TOF’s
Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC 5548
We present the results of three years of ground-based observations of the
Seyfert 1 galaxy NGC 5548, which combined with previously reported data, yield
optical continuum and broad-line H-beta light curves for a total of eight
years. The light curves consist of over 800 points, with a typical spacing of a
few days between observations. During this eight-year period, the nuclear
continuum has varied by more than a factor of seven, and the H-beta emission
line has varied by a factor of nearly six. The H-beta emission line responds to
continuum variations with a time delay or lag of 10-20 days, the precise value
varying somewhat from year to year. We find some indications that the lag
varies with continuum flux in the sense that the lag is larger when the source
is brighter.Comment: 29 pages, 6 figures. Accepted for publication in ApJ (1999 Jan 10
A simple radionuclide-driven single-ion source
We describe a source capable of producing single barium ions through nuclear
recoils in radioactive decay. The source is fabricated by electroplating 148Gd
onto a silicon {\alpha}-particle detector and vapor depositing a layer of BaF2
over it. 144Sm recoils from the alpha decay of 148Gd are used to dislodge Ba+
ions from the BaF2 layer and emit them in the surrounding environment. The
simultaneous detection of an {\alpha} particle in the substrate detector allows
for tagging of the nuclear decay and of the Ba+ emission. The source is simple,
durable, and can be manipulated and used in different environments. We discuss
the fabrication process, which can be easily adapted to emit most other
chemical species, and the performance of the source
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