25 research outputs found
Public health impact and cost effectiveness of mass vaccination with live attenuated human rotavirus vaccine (RIX4414) in India: model based analysis
Objectives To examine the public health impact of mass vaccination with live attenuated human rotavirus vaccine (RIX4414) in a birth cohort in India, and to estimate the cost effectiveness and affordability of such a programme
Ionization of the diffuse gas in galaxies: Hot low-mass evolved stars at work
We revisit the question of the ionization of the diffuse medium in late type
galaxies, by studying NGC 891, the prototype of edge-on spiral galaxies. The
most important challenge for the models considered so far was the observed
increase of [OIII]/Hbeta, [OII]/Hbeta, and [NII]/Halpha with increasing
distance to the galactic plane. We propose a scenario based on the expected
population of massive OB stars and hot low-mass evolved stars (HOLMES) in this
galaxy to explain this observational fact. In the framework of this scenario we
construct a finely meshed grid of photoionization models. For each value of the
galactic latitude z we look for the models which simultaneously fit the
observed values of the [OIII]/Hbeta, [OII]/Hbeta, and [NII]/Halpha ratios. For
each value of z we find a range of solutions which depends on the value of the
oxygen abundance. The models which fit the observations indicate a systematic
decrease of the electron density with increasing z. They become dominated by
the HOLMES with increasing z only when restricting to solar oxygen abundance
models, which argues that the metallicity above the galactic plane should be
close to solar. They also indicate that N/O increases with increasing z.Comment: Accepted for publication in MNRA
The origin of the light distribution in spiral galaxies
We analyse a high-resolution, fully cosmological, hydrodynamical disc galaxy simulation, to study the source of the double-exponential light profiles seen in many stellar discs, and the effects of stellar radial migration upon the spatiotemporal evolution of both the disc age and metallicity distributions. We find a ‘break’ in the pure exponential stellar surface brightness profile, and trace its origin to a sharp decrease in the star formation per unit surface area, itself produced by a decrease in the gas volume density due to a warping of the gas disc. Star formation in the disc continues well beyond the break. We find that the break is more pronounced in bluer wavebands. By contrast, we find little or no break in the mass density profile. This is, in part, due to the net radial migration of stars towards the external parts of the disc. Beyond the break radius, we find that ∼60 per cent of the resident stars migrated from the inner disc, while ∼25 per cent formed in situ. Our simulated galaxy also has a minimum in the age profile at the break radius but, in disagreement with some previous studies, migration is not the main mechanism producing this shape. In our simulation, the disc metallicity gradient flattens with time, consistent with an ‘inside-out’ formation scenario. We do not find any difference in the intensity or the position of the break with inclination, suggesting that perhaps the differences found in empirical studies are driven by dust extinction
Galactic Gradients, Postbiological Evolution and the Apparent Failure of SETI
Motivated by recent developments impacting our view of Fermi's paradox
(absence of extraterrestrials and their manifestations from our past light
cone), we suggest a reassessment of the problem itself, as well as of
strategies employed by SETI projects so far. The need for such reevaluation is
fueled not only by the failure of searches thus far, but also by great advances
recently made in astrophysics, astrobiology, computer science and future
studies, which have remained largely ignored in SETI practice. As an example of
the new approach, we consider the effects of the observed metallicity and
temperature gradients in the Milky Way on the spatial distribution of
hypothetical advanced extraterrestrial intelligent communities. While,
obviously, properties of such communities and their sociological and
technological preferences are entirely unknown, we assume that (1) they operate
in agreement with the known laws of physics, and (2) that at some point they
typically become motivated by a meta-principle embodying the central role of
information-processing; a prototype of the latter is the recently suggested
Intelligence Principle of Steven J. Dick. There are specific conclusions of
practical interest to be drawn from coupling of these reasonable assumptions
with the astrophysical and astrochemical structure of the Galaxy. In
particular, we suggest that the outer regions of the Galactic disk are most
likely locations for advanced SETI targets, and that intelligent communities
will tend to migrate outward through the Galaxy as their capacities of
information-processing increase, for both thermodynamical and astrochemical
reasons. This can also be regarded as a possible generalization of the Galactic
Habitable Zone, concept currently much investigated in astrobiology.Comment: 30 pages, 2 figure
TESS spots a mini-neptune interior to a hot saturn in the TOI-2000 system
Hot jupiters (P 60 ) are almost always found
alone around their stars, but four out of hundreds known have inner companion
planets. These rare companions allow us to constrain the hot jupiter's
formation history by ruling out high-eccentricity tidal migration. Less is
known about inner companions to hot Saturn-mass planets. We report here the
discovery of the TOI-2000 system, which features a hot Saturn-mass planet with
a smaller inner companion. The mini-neptune TOI-2000 b (, ) is in a 3.10-day
orbit, and the hot saturn TOI-2000 c (, ) is in a
9.13-day orbit. Both planets transit their host star TOI-2000 (TIC 371188886, V
= 10.98, TESS magnitude = 10.36), a metal-rich ([Fe/H] =
) G dwarf 174 pc away. TESS observed the two planets
in sectors 9-11 and 36-38, and we followed up with ground-based photometry,
spectroscopy, and speckle imaging. Radial velocities from CHIRON, FEROS, and
HARPS allowed us to confirm both planets by direct mass measurement. In
addition, we demonstrate constraining planetary and stellar parameters with
MIST stellar evolutionary tracks through Hamiltonian Monte Carlo under the PyMC
framework, achieving higher sampling efficiency and shorter run time compared
to traditional Markov chain Monte Carlo. Having the brightest host star in the
V band among similar systems, TOI-2000 b and c are superb candidates for
atmospheric characterization by the JWST, which can potentially distinguish
whether they formed together or TOI-2000 c swept along material during
migration to form TOI-2000 b.Comment: v3 adds RV frequency analysis; 25 pages, 11 figures, 14 tables;
revision submitted to MNRAS; machine-readable tables available as ancillary
files; posterior samples available from Zenodo at
https://doi.org/10.5281/zenodo.7683293 and source code at
https://doi.org/10.5281/zenodo.798826