4,902 research outputs found
The pursuit of the Hubble Constant using Type II Supernovae
The use of multiple independent methods with their own systematic
uncertainties is crucial for resolving the ongoing tension between local and
distant measurements of the Hubble constant (). While type Ia supernovae
(SNe Ia) have historically been the most widely used distance indicators,
recent studies have shown that type II supernovae (SNe II) can provide
independent measurements of extragalactic distances with different systematic
uncertainties. Unlike SNe Ia, the progenitors of SNe II are well understood,
arising from the explosion of red supergiants in late-type galaxies via
core-collapse. While SNe II do not exhibit the same level of uniformity in peak
luminosity as SNe Ia, their differences can be calibrated using theoretical or
empirical methods. Overall, this chapter presents a comprehensive overview of
the use of SNe II as extragalactic distance indicators, with a particular focus
on their application to measuring and addressing the Hubble tension. We
describe the underlying theory of each method, discuss the challenges
associated with them, including uncertainties in the calibration of the
supernova absolute magnitude, and present a comprehensive list of the most
updated Hubble constant measurements.Comment: Invited chapter for the edited book "Hubble Constant Tension" (Eds.
E. Di Valentino and D. Brout, Springer Singapore, expected in 2024
Born's rule from measurements of classical signals by threshold detectors which are properly calibrated
The very old problem of the statistical content of quantum mechanics (QM) is
studied in a novel framework. The Born's rule (one of the basic postulates of
QM) is derived from theory of classical random signals. We present a
measurement scheme which transforms continuous signals into discrete clicks and
reproduces the Born's rule. This is the sheme of threshold type detection.
Calibration of detectors plays a crucial role.Comment: The problem of double clicks is resolved; hence, one can proceed in
purely wave framework, i.e., the wave-partcile duality has been resolved in
favor of the wave picture of prequantum realit
Silicates in D-type symbiotic stars: an ISO overview
We investigate the IR spectral features of a sample of D-type symbiotic
stars. Analyzing unexploited ISO-SWS data, deriving the basic observational
parameters of dust bands and comparing them with respect to those observed in
other astronomical sources, we try to highlight the effect of environment on
grain chemistry and physic. We find strong amorphous silicate emission bands at
10 micron and 18 micron in a large fraction of the sample. The analysis of the
10 micron band, along with a direct comparison with several astronomical
sources, reveals that silicate dust in symbiotic stars shows features between
the characteristic circumstellar environments and the interstellar medium. This
indicates an increasing reprocessing of grains in relation to specific
symbiotic behavior of the objects. A correlation between the central wavelength
of the 10 and 18 micron dust bands is found. By the modeling of IR spectral
lines we investigate also dust grains conditions within the shocked nebulae.
Both the unusual depletion values and the high sputtering efficiency might be
explained by the formation of SiO moleculae, which are known to be a very
reliable shock tracer. We conclude that the signature of dust chemical
disturbance due to symbiotic activity should be looked for in the outer,
circumbinary, expanding shells where the environmental conditions for grain
processing might be achieved. Symbiotic stars are thus attractive targets for
new mid-infrared and mm observations.Comment: 24 pages, 6 figures, 5 tables - to be published in A
Low temperature mobility in hafnium-oxide gated germanium p-channel metal-oxide-semiconductor field-effect transistors
Effective mobility measurements have been made at 4.2 K on high performance high-k gated germanium p-type metal-oxide-semiconductor field effect transistors with a range of Ge/gate dielectric interface state densities. The mobility is successfully modelled by assuming surface roughness and interface charge scattering at the SiO2 interlayer/Ge interface. The deduced interface charge density is approximately equal to the values obtained from the threshold voltage and subthreshold slope measurements on each device. A hydrogen anneal reduces both the interface state density and the surface root mean square roughness by 20%
Type II supernovae as probes of environment metallicity: observations of host HII regions
Spectral modelling of SNII atmospheres indicates a clear dependence of metal
line strengths on progenitor metallicity. This motivates further work to
evaluate the accuracy with which these SNe can be used as metallicity
indicators. To assess this accuracy we present a sample of SNII HII-region
spectroscopy, from which environment abundances are derived. These environment
abundances are compared to the observed strength of metal lines in SN spectra.
Combining our sample with measurements from the literature, we present oxygen
abundances of 119 host HII regions, by extracting emission line fluxes and
using abundance diagnostics. Then, following Dessart et al., these abundances
are compared to equivalent widths of Fe 5018 A at various time and colour
epochs. Our distribution of inferred SNII host HII-region abundances has a
range of ~0.6 dex. We confirm the dearth of SNeII exploding at metallicities
lower than those found (on average) in the Large Magellanic Cloud. The
equivalent width of Fe 5018 A at 50 days post explosion shows a statistically
significant correlation with host HII-region oxygen abundance. The strength of
this correlation increases if one excludes abundance measurements derived far
from SN explosion sites. The correlation significance also increases if we only
analyse a 'gold' IIP sample, and if a colour epoch is used in place of time. In
addition, no evidence is found of correlation between progenitor metallicity
and SN light-curve or spectral properties - except for that stated above with
respect to Fe 5018 A equivalent width - suggesting progenitor metallicity is
not a driving factor in producing the diversity observed in our sample. This
study provides observational evidence of the usefulness of SNII as metallicity
indicators. We finish with a discussion of the methodology needed to use SN
spectra as independent metallicity diagnostics throughout the Universe.Comment: Accepted for publication in Astronomy and Astrophyci
On the complexity of some birational transformations
Using three different approaches, we analyze the complexity of various
birational maps constructed from simple operations (inversions) on square
matrices of arbitrary size. The first approach consists in the study of the
images of lines, and relies mainly on univariate polynomial algebra, the second
approach is a singularity analysis, and the third method is more numerical,
using integer arithmetics. Each method has its own domain of application, but
they give corroborating results, and lead us to a conjecture on the complexity
of a class of maps constructed from matrix inversions
Serendipitous discovery of RR Lyrae stars in the Leo V ultra-faint galaxy
During the analysis of RR Lyrae stars discovered in the High cadence
Transient Survey (HiTS) taken with the Dark Energy Camera at the 4-m telescope
at Cerro Tololo Inter-American Observatory, we found a group of three very
distant, fundamental mode pulsator RR Lyrae (type ab). The location of these
stars agrees with them belonging to the Leo V ultra-faint satellite galaxy, for
which no variable stars have been reported to date. The heliocentric distance
derived for Leo V based on these stars is 173 +/- 5 kpc. The pulsational
properties (amplitudes and periods) of these stars locate them within the locus
of the Oosterhoff II group, similar to most other ultra-faint galaxies with
known RR Lyrae stars. This serendipitous discovery shows that distant RR Lyrae
stars may be used to search for unknown faint stellar systems in the outskirts
of the Milky Way.Comment: Accepted in ApJ Letter
Granular Avalanches in Fluids
Three regimes of granular avalanches in fluids are put in light depending on
the Stokes number St which prescribes the relative importance of grain inertia
and fluid viscous effects, and on the grain/fluid density ratio r. In gas (r >>
1 and St > 1, e.g., the dry case), the amplitude and time duration of
avalanches do not depend on any fluid effect. In liquids (r ~ 1), for
decreasing St, the amplitude decreases and the time duration increases,
exploring an inertial regime and a viscous regime. These regimes are described
by the analysis of the elementary motion of one grain
Fluctuation-Dissipation theorems and entropy production in relaxational systems
We show that for stochastic dynamical systems out of equilibrium the
violation of the fluctuation-dissipation equality is bounded by a function of
the entropy production. The result applies to a much wider situation than `near
equilibrium', comprising diffusion as well as glasses and other macroscopic
systems far from equilibrium. For aging systems this bounds the age-frequency
regimes in which the susceptibilities satisfy FDT in terms of the rate of decay
of the H-function, a question intimately related to the reading of a
thermometer placed in contact with the system.Comment: 4 pages, RevTex; formula and reference added plus various minor
changes in the tex
- …