829 research outputs found
Variability of Massive Stars with Known Spectral Types in the Small Magellanic Cloud Using 8 Years of OGLE-III Data
We present a variability study of 4646 massive stars in the Small Magellanic
Cloud (SMC) with known spectral types from the catalog of Bonanos et al. (2010)
using the light curves from the OGLE-III database. The goal is to exploit the
time domain information available through OGLE-III to gain insight into the
processes that govern the evolution of massive stars. This variability survey
of massive stars with known spectral types is larger than any previous survey
by a factor of 7. We find that 60% of our sample (2766 stars) show no
significant variability and 40% (1880 stars) exhibit variability distributed as
follows: 807 stars display low-amplitude stochastic variability with
fluctuations in I-band of up to 0.05 mag, 443 stars present irregular
variability of higher amplitude (76% of these are reported as variables for the
first time), 205 are eclipsing binaries (including 101 newly discovered
systems), 50 are candidate rotating variables, 126 are classical Cepheids, 188
stars exhibit short-term sinusoidal periodicity (P < 3 days) making them
candidate "slowly pulsating B stars" and non-radial Be pulsators, and 61
periodic stars exhibit longer periods. We demonstrate the wealth of information
provided in the time domain, by doubling the number of known massive eclipsing
binary systems and identifying 189 new candidate early-type Be and 20 Oe stars
in the SMC. In addition, we find that ~80% of Be stars are photometrically
variable in the OGLE-III time domain and provide evidence that short-term
pulsating stars with additional photometric variability are rotating close to
their break-up velocity.Comment: 46 pages, 18 figures, 11 tables. A&A in press. See
http://media.wix.com/ugd/d2ba94_1596d7db762b496c89f21d03891f46c3.pdf for a
version with full resolution figure
Optical reference geometry of the Kerr-Newman spacetimes
Properties of the optical reference geometry related to Kerr-Newman
black-hole and naked-singularity spacetimes are illustrated using embedding
diagrams of their equatorial plane. Among all inertial forces defined in the
framework of the optical geometry, just the centrifugal force plays a
fundamental role in connection to the embedding diagrams because it changes
sign at the turning points of the diagrams. The limits of embeddability are
given, and it is established which of the photon circular orbits hosted the by
Kerr-Newman spacetimes appear in the embeddable regions. Some typical embedding
diagrams are constructed, and the Kerr-Newman backgrounds are classified
according to the number of embeddable regions of the optical geometry as well
as the number of their turning points. Embedding diagrams are closely related
to the notion of the radius of gyration which is useful for analyzing fluid
rotating in strong gravitational fields.Comment: 28 pages, 17 figure
A gravitationally lensed quasar discovered in OGLE
Indexación: Scopus; Web of Science.We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the ~670deg2 area encompassing the Magellanic Clouds. The source was selected as one of ~60 'red W1-W2' mid-infrared objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made 'the other way around', meaning we first measured the time delay between the two lensed quasar images of -132 < tAB < -76 d (90 per cent CL), with the median tAB ~-102 d (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5 arcsec on the sky, with I ~20.0mag and I ~19.6mag, respectively, and a lensing galaxy that becomes detectable as I ~21.5 mag source, 1.0 arcsec from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at z=2.16 in the New Technology Telescope spectra. The spectral energy distribution (SED) fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of z ~0.9 ± 0.2 (90 per cent CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model). © 2018 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.https://academic.oup.com/mnras/article/476/1/663/483368
Bubbling and bistability in two parameter discrete systems
We present a graphical analysis of the mechanisms underlying the occurrences
of bubbling sequences and bistability regions in the bifurcation scenario of a
special class of one dimensional two parameter maps. The main result of the
analysis is that whether it is bubbling or bistability is decided by the sign
of the third derivative at the inflection point of the map function.Comment: LaTeX v2.09, 14 pages with 4 PNG figure
Overexpression of adrenomedullin gene markedly inhibits proliferation of PC3 prostate cancer cells in vitro and in vivo
The expression of the gene encoding adrenomedullin (AM), a multifunctional peptide hormone, in the prostate is localized to the epithelial cells. Prostate cancer cells are derived from prostatic epithelial cells. To elucidate the potential role of the AM gene in prostate cancer progression, we have stably-transfected the PC3 human prostate cancer cell line with an AM gene expression vector. The AM-transfected PC3 sublines were studied along with parental and empty vector transfected PC3 cells as controls. The average level of AM in the conditioned media of AM-transfected cells was 0.959+/-0.113 nM, a physiologically relevant concentration. The ectopic expression of AM gene inhibited the proliferation of PC3 cells in culture dishes. In addition, anchorage-independent growth of the transfected sublines was virtually abolished in soft agar assays. Flow cytometry studies showed that overexpression of AM gene caused a very significant G(1)/G(0) cell cycle arrest. In vivo experiments demonstrated that AM gene expression markedly inhibited the growth of xenograft tumors in nude mice. Our in vivo and in vitro studies suggest that AM could strongly suppress the malignancy of prostate cancer cells, via autocrine and/or paracrine mechanisms
SDWFS-MT-1: A Self-Obscured Luminous Supernova at z~0.2
We report the discovery of a six-month-long mid-infrared transient,
SDWFS-MT-1 (aka SN 2007va), in the Spitzer Deep, Wide-Field Survey of the NOAO
Deep Wide-Field Survey Bootes field. The transient, located in a z=0.19 low
luminosity (M_[4.5]~-18.6 mag, L/L_MilkyWay~0.01) metal-poor (12+log(O/H)~7.8)
irregular galaxy, peaked at a mid-infrared absolute magnitude of M_[4.5]~-24.2
in the 4.5 micron Spitzer/IRAC band and emitted a total energy of at least
10^51 ergs. The optical emission was likely fainter than the mid-infrared,
although our constraints on the optical emission are poor because the transient
peaked when the source was "behind" the Sun. The Spitzer data are consistent
with emission by a modified black body with a temperature of ~1350 K. We rule
out a number of scenarios for the origin of the transient such as a Galactic
star, AGN activity, GRB, tidal disruption of a star by a black hole and
gravitational lensing. The most plausible scenario is a supernova exploding
inside a massive, optically thick circumstellar medium, composed of multiple
shells of previously ejected material. If the proposed scenario is correct,
then a significant fraction (~10%) of the most luminous supernova may be
self-enshrouded by dust not only before but also after the supernova occurs.
The spectral energy distribution of the progenitor of such a supernova would be
a slightly cooler version of eta Carina, peaking at 20-30 microns.Comment: 26 pages, 5 figures, 1 table, accepted for publication in Ap
Precise Measurement of the Pi+ -> Pi0 e+ nu Branching Ratio
Using a large acceptance calorimeter and a stopped pion beam we have made a
precise measurement of the rare Pi+ -> Pi0 e+ Nu,(pi_beta) decay branching
ratio. We have evaluated the branching ratio by normalizing the number of
observed pi_beta decays to the number of observed Pi+ -> e+ Nu, (pi_{e2})
decays. We find the value of Gamma(Pi+ -> Pi0 e+ Nu)/Gamma(total) = [1.036 +/-
0.004(stat.) +/- 0.004(syst.) +/- 0.003(pi_{e2})] x 10^{-8}$, where the first
uncertainty is statistical, the second systematic, and the third is the pi_{e2}
branching ratio uncertainty. Our result agrees well with the Standard Model
prediction.Comment: 4 pages, 5 figures, 1 table, revtex4; changed content; updated
analysi
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