5,651 research outputs found
Transient Gamma Ray Spectrometer Measurements of Gamma-Ray Lines from Novae. II. Constraining the Galactic Nova Rate from a Survey of the Southern Sky during 1995-1997
The good energy resolution (3--4 keV FWHM) of the Transient Gamma Ray
Spectrometer (TGRS) on board the WIND spacecraft makes it sensitive to
Doppler-shifted outbursts of 511 keV electron-positron annihilation radiation,
the reason being that the Doppler shift causes the cosmic line to be slightly
offset from a strong instrumental background 511 keV line at rest, which is
ubiquitous in space environments. Such a cosmic line (blueshifted) is predicted
to arise in classical novae due to the annihilation of positrons from
-decay on a timescale of a few hours in an expanding envelope. A further
advantage of TGRS - its broad field of view, containing the entire southern
ecliptic hemisphere - has enabled us to make a virtually complete and unbiased
3-year search for classical novae at distances up to ~1 kpc. We present
negative results of this search, and estimate its implications for the
highly-uncertain Galactic classical nova rate and for future space missions.Comment: 22 pp. + 3 fig
Viscosity effects on liquid-liquid dispersion in laminar flows
Efficiency of liquid/liquid dispersion is an important stake in numerous sectors, such as
the chemical, food, cosmetic and environmental industries. In the present study, dispersion is achieved
in an open-loop reactor consisting of simple curved pipes, either helically coiled or chaotically twisted.
In both configurations, we investigate the drop breakup process of two immiscible fluids (W/O) and
especially the effect of the continuous phase viscosity, which is varied by addition of different fractions
of butanol in the native sunflower oil. The global Reynolds numbers vary between 40 and 240, so that
the flow remains laminar while the Dean roll-cells in the bends develop significantly. Different
fractions of butanol are added to the oil in each case to examine the influence of the continuous phase
viscosity on the drop size distribution of the dispersed phase (water). When the butanol fraction is
decreased, the dispersion process is intensified and smaller drops are created. The Sauter mean
diameters obtained in the chaotic twisted pipe are compared with those in a helically coiled pipe flow.
The results show that chaotic advection intensifies the droplet breakup till 20% in droplet size
reduction, and also reduces polydispersity
Quasi Harmonic Lattice Dynamics and Molecular Dynamics calculations for the Lennard-Jones solids
We present Molecular Dynamics (MD), Quasi Harmonic Lattice Dynamics (QHLD)
and Energy Minimization (EM) calculations for the crystal structure of Ne, Ar,
Kr and Xe as a function of pressure and temperature. New Lennard-Jones (LJ)
parameters are obtained for Ne, Kr and Xe to reproduce the experimental
pressure dependence of the density. We employ a simple method which combines
results of QHLD and MD calculations to achieve densities in good agreement with
experiment from 0 K to melting. Melting is discussed in connection with
intrinsic instability of the solid as given by the QHLD approximation. (See
http://www.fci.unibo.it/~valle for related papers)Comment: 7 pages, 5 figures, REVte
Early spectral evolution of Nova Sgr 2004 (V5114 Sgr)
We present optical and near-infrared spectral evolution of the Galactic nova
V5114 Sgr (2004) during few months after the outburst. We use multi-band
photometry and line intensities derived from spectroscopy to put constrains on
the distance and the physical conditions of the ejecta of V5114 Sgr. The nova
showed a fast decline (t_2 \simeq 11 days) and spectral features of FeII
spectroscopic class. It reached M_V = -8.7 \pm 0.2 mag at maximum light, from
which we derive a distance of 7700 \pm 700 kpc and a distance from the galactic
plane of about 800 pc. Hydrogen and Oxygen mass of the ejecta are measured from
emission lines, leading to 10^{-6} and 10^{-7} M_\odot, respectively. We
compute the filling factor of the ejecta to be in the range 0.1 -- 10^{-3} . We
found the value of the filling factor to decrease with time. The same is also
observed in other novae, then giving support to the idea that nova shells are
not homogeneously filled in, rather being the material clumped in relatively
higher density blobs less affected by the general expanding motion of the
ejecta.Comment: accepted for publication in Astronomy & Astrophysics, 16 pages and 8
figure
Type Ia supernova SN 2003du: optical observations
UBVRI photometry and optical spectra of type Ia supernova SN 2003du obtained
at the Indian Astronomical Observatory for nearly a year since discovery are
presented.
The apparent magnitude at maximum was B=13.53 +/- 0.02 mag, and the colour
(B-V) = -0.08 +/- 0.03 mag. The luminosity decline rate, Delta(m_{15}(B)) =
1.04 +/- 0.04 mag indicates an absolute B magnitude at maximum of M_B = -19.34
+/- 0.3 mag and the distance modulus to the parent galaxy as mu=32.89 +/-
0.4.The light curve shapes are similar, though not identical, to those of SNe
1998bu and 1990N, both of which had luminosity decline rates similar to that of
SN 2003du and occurred in spiral galaxies. The peak bolometric luminosity
indicates that 0.9 Msun mass of 56Ni was ejected by the supernova. The spectral
evolution and the evolution of the Si II and Ca II absorption velocities
closely follows that of SN 1998bu, and in general, is within the scatter of the
velocities observed in normal type Ia supernovae.
The spectroscopic and photometric behaviour of SN 2003du is quite typical for
SNe Ia in spirals.
A high velocity absorption component in the Ca II (H & K) and IR-triplet
features, with absorption velocities of ~20,000 km/s and ~22,000 km/s
respectively, is detected in the pre-maximum spectra of days -11 and -7.Comment: 10 pages, 10 figures; Accepted for publication in A&
Photometric Confirmation of MACHO Large Magellanic Cloud Microlensing Events
We present previously unpublished photometry of three Large Magellanic Cloud
(LMC) microlensing events and show that the new photometry confirms the
microlensing interpretation of these events. These events were discovered by
the MACHO Project alert system and were also recovered by the analysis of the
5.7 year MACHO data set. This new photometry provides a substantial increase in
the signal-to-noise ratio over the previously published photometry and in all
three cases, the gravitational microlensing interpretation of these events is
strengthened. The new data consist of MACHO-Global Microlensing Alert Network
(GMAN) follow-up images from the CTIO 0.9 telescope plus difference imaging
photometry of the original MACHO data from the 1.3m "Great Melbourne" telescope
at Mt. Stromlo. We also combine microlensing light curve fitting with
photometry from high resolution HST images of the source stars to provide
further confirmation of these events and to show that the microlensing
interpretation of event MACHO-LMC-23 is questionable. Finally, we compare our
results with the analysis of Belokurov, Evans & Le Du who have attempted to
classify candidate microlensing events with a neural network method, and we
find that their results are contradicted by the new data and more powerful
light curve fitting analysis for each of the four events considered in this
paper. The failure of the Belokurov, Evans & Le Du method is likely to be due
to their use of a set of insensitive statistics to feed their neural networks.Comment: 29 pages with 8 included postscript figures, accepted by the
Astrophysical Journa
A Black Hole in the X-Ray Nova Velorum 1993
We have obtained 17 moderate-resolution (~2.5 A) optical spectra of the
Galactic X-ray Nova Velorum 1993 in quiescence with the Keck-II telescope. The
orbital period (P) is 0.285206 +/- 0.0000014 d, and the semiamplitude (K_2) is
475.4 +/- 5.9 km/s. Our derived mass function, f(M_1) = PK_2^3 /2 pi G = 3.17
+/- 0.12 M_sun, is close to the conventional absolute limiting mass for a
neutron star (~ 3.0-3.2 M_sun) -- but if the orbital inclination i is less than
80 degrees (given the absences of eclipses), then M_1 is greater than 4.2-4.4
M_sun for nominal secondary-star masses of 0.5 M_sun (M0) to 0.65 M_sun (K6).
The primary star is therefore almost certainly a black hole rather than a
neutron star. The velocity curve of the primary from H-alpha emission has a
semiamplitude (K_1) of 65.3 +/- 7.0 km/s, but with a phase offset by 237
degrees (rather than 180 degrees) from that of the secondary star. The nominal
mass ratio q = M_2/M_1 = K_1/K_2 = 0.137 +/- 0.015, and hence for M_2 =
0.5-0.65 M_sun we derive M_1 = 3.64-4.74 M_sun. An adopted mass M_1 ~ 4.4 M_sun
is significantly below the typical value of ~ 7 M_sun found for black holes in
other low-mass X-ray binaries.
Keck observations of MXB 1659-29 (V2134 Oph) in quiescence reveal a probable
optical counterpart at R = 23.6 +/- 0.4 mag.Comment: 16 pages, 9 figures, added references, revised per. referee's
comments Accepted for publication in August 1999 issue of PAS
Testing the neutrality of matter by acoustic means in a spherical resonator
New measurements to test the neutrality of matter by acoustic means are
reported. The apparatus is based on a spherical capacitor filled with gaseous
SF excited by an oscillating electric field. The apparatus has been
calibrated measuring the electric polarizability. Assuming charge conservation
in the decay of the neutron, the experiment gives a limit of
for the electron-proton charge
difference, the same limit holding for the charge of the neutron. Previous
measurements are critically reviewed and found incorrect: the present result is
the best limit obtained with this technique
A very faint core-collapse supernova in M85
An anomalous transient in the early Hubble-type (S0) galaxy Messier 85 (M85)
in the Virgo cluster was discovered by Kulkarni et al. (2007) on 7 January 2006
that had very low luminosity (peak absolute R-band magnitude MR of about -12)
that was constant over more than 80 days, red colour and narrow spectral lines,
which seem inconsistent with those observed in any known class of transient
events. Kulkarni et al. (2007) suggest an exotic stellar merger as the possible
origin. An alternative explanation is that the transient in M85 was a type
II-plateau supernova of extremely low luminosity, exploding in a lenticular
galaxy with residual star-forming activity. This intriguing transient might be
the faintest supernova that has ever been discovered.Comment: 7 pages, 2 figures. Submitted to Nature "Brief Communication Arising"
on 18 July 2007, Accepted on 17 August 2007. Arising from: Kulkarni et al.
2007, Nature, 447, 458-46
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