162 research outputs found
Influence of temperature on extreme rainfall intensity in Sicily (Italy)
Some climate model experiments suggest an intensification of short-duration extreme precipitation in many parts of the world associated with a warming climate. This behavior could have a physical motivation due to the fact that warmer air has the potential to hold more atmospheric moisture and, then, to provide more water to rainfall events. The theoretical basis of the relationship that links air temperature and atmospheric humidity is provided by the Clausius-Clapeyron relation, according to which, if the relative humidity remains constant, then atmospheric humidity will increase with temperature at a rate (often referred to as CC-rate) in the order of 6-7% C-1, following the saturation vapour pressure curve as a function of temperature. The study of the relationship between extreme rainfall events and surface temperature could be of capital importance for evaluating the effects of global warming on future precipitation, since it may have important impacts on society with relevant fallouts on several aspects (e.g. flooding, risk protection, etc.). Different approaches have been proposed for the study at different locations of the scaling relationship between extreme rainfall intensity and surface temperature. In some cases, it has been observed a rate consistent with the thermodynamic Clausius-Clapeyron relation (CC-rate). Nevertheless, in many cases, the existence of scaling rate between temperature and extreme precipitation has been demonstrated with significantly different values with respect to the theoretical CC-rate, being in some cases sensibly higher (super-CC) and in other relevantly lower (sub-CC). In this work, an analysis of the scaling relationship between sub-daily extreme rainfall and surface temperature in a semi-arid region (Sicily, Italy) is carried out, also investigating the role of different factors, such as the duration of maximum rainfall depths for fixed duration (i.e. 10, 30 and 60 minutes), the type of adopted regression models (exponential regression, two-segments piecewise regression and LOESS - Locally-weighted scatterplot smoothing - regression), and the climate seasonality (unique season for the entire hydrological year; dry season from April to September and wet season for the remaining part of the year). The original dataset is constituted by hourly temperature and 10-minutes rainfall data collected from 2003 to 2015 by the regional agency SIAS (Servizio Informativo Agrometeorologico Siciliano) through 107 weather stations spread over the region. The results demonstrate that in Sicily the scaling rates are generally lower than the CC-rate; however, the observed tendency towards sub-CC rates is smoothed by the consideration of shorter duration for rainfall maximum depths (higher rates for 10-minutes durations) and under wetter periods (higher rates considering only wet season values), demonstrating how such factors play a fundamental role
Effetto combinato di cambiamenti climatici ed urbanizzazione sugli estremi di portata
Il termine “cambiamento idrologico” (hydrological change) è spesso utilizzato per sintetizzare quell’insieme di alterazioni della risposta idrologica dei bacini indotte da fattori naturali o antropici. ll ruolo fondamentale di tali alterazioni nel determinare fenomeni di dissesto ha stimolato l’International Association of Hydrological Scienses (IAHS) a dedicare la decade scientifica 2013-2022 (denominata “Phanta Rhei”) ai cambiamenti idrologici e all’analisi dei diversi fattori perturbanti.
I cambiamenti climatici e l’urbanizzazione sono fra i fattori antropici perturbanti più influenti e, allo stesso tempo, più diffusi a livello globale.
Il cambiamento climatico è stato abbondantemente studiato in passato, con chiare evidenze di trend sugli estremi (es. Burn et al., 2011; Arnone et al., 2013) e con numerosi esempi attestanti i possibili cambiamenti idrologici indotti (es. Wang and Alimohammadi, 2012; Francipane et al., 2015; Chiarelli et al., 2016; Pumo et al. 2016). Molto più recente è l’analisi degli effetti dell’urbanizzazione sulla risposta idrologica dei bacini (es. Salvadore et al., 2015). Il processo di urbanizzazione è associato a una perdita di “superfici permeabili” (suoli naturali), con conseguente impoverimento dei processi d’infiltrazione, alterazione ai sistemi di drenaggio naturale e ai processi di trasferimento (alterazione dei percorsi idrici e delle velocità di deflusso).
La valutazione dell’impatto di tali perturbazioni sulle portate di picco durante eventi estremi, può risultare particolarmente utile nel definire e orientare efficaci politiche di pianificazione urbana e gestione di eventi di inondazione, nonché in attività di verifica delle infrastrutture idrauliche esistenti e di progettazione di quelle future.
L’obiettivo di questo lavoro è quello di investigare gli effetti dell'interazione delle suddette perturbazioni sugli eventi estremi di deflusso.
A tale scopo, è stato ideato un esperimento numerico, applicato ad un piccolo bacino fluviale, che ha permesso di generare e confrontare serie temporali di deflusso orario sotto diversi ipotetici scenari di cambiamento.
Gli scenari, generati attraverso l’uso combinato di un modello di cambiamento di uso del suolo opportunamente implementato e di un modello di generazione di serie climatiche già esistente (Fatichi et al., 2011), descrivono situazioni estreme sia in termini di espansione delle aree urbane che in termini di variazioni (aumento o diminuzione) della precipitazione media annua (MAP). Nella creazione degli scenari climatici si è anche tenuto conto di un aumento della temperatura media, e, a parità di MAP, sono state create diverse configurazioni, caratterizzate da diversa frequenza e/o l’intensità media degli eventi di pioggia. La risposta idrologica del bacino ai vari scenari è stata riprodotta mediante il tRIBS (Ivanov et al., 2004), un modello idrologico, fisicamente basato e distribuito, in grado di simulare, con alta risoluzione temporale, anche le diverse componenti di deflusso.
I risultati mostrano un’alta sensibilità degli indicatori della risposta idrologica utilizzati alle variazioni delle caratteristiche di pioggia. In termini di deflusso totale, gli effetti dei cambiamenti climatici sembrano essere prevalenti rispetto a quelli indotti dall’espansione urbana, anche se, a una maggiore frazione di suoli impermeabili, corrisponde un chiaro aumento della componente di scorrimento veloce, i cui effetti sul deflusso totale vengono parzialmente smorzati da una simultanea riduzione della componente di deflusso lento e profondo
SNe 2013K and 2013am: observed and physical properties of two slow, normal Type IIP events
We present one year of optical and near-infrared photometry and spectroscopy
of the Type IIP SNe 2013K and 2013am. Both objects are affected by significant
extinction, due to their location in dusty regions of their respective host
galaxies, ESO 009-10 and NGC 3623 (M65). From the photospheric to nebular
phases, these objects display spectra congruent with those of underluminous
Type IIP SNe (i.e. the archetypal SNe 1997D or 2005cs), showing low
photospheric velocities (~2 X 10**3 km/s at 50d) together with features arising
from Ba II which are particularly prominent in faint SNe IIP. The peak V-band
magnitudes of SN 2013K (-15.6 mag) and SN 2013am (-16.2 mag) are fainter than
standard-luminosity Type IIP SNe. The ejected Nickel masses are 0.012+-0.010
and 0.015+-0.006 Msol for SN 2013K and SN 2013am, respectively. The physical
properties of the progenitors at the time of explosion are derived through
hydrodynamical modelling. Fitting the bolometric curves, the expansion velocity
and the temperature evolution, we infer total ejected masses of 12 and 11.5
Msol, pre-SN radii of ~460 and ~360 Rsol, and explosion energies of 0.34 foe
and 0.40 foe for SN 2013K and SN 2013am. Late time spectra are used to estimate
the progenitor masses from the strength of nebular emission lines, which turn
out to be consistent with red supergiant progenitors of ~15 Msol. For both SNe,
a low-energy explosion of a moderate-mass red supergiant star is therefore the
favoured scenario.Comment: accepted for publication MNRA
SN 2009E: a faint clone of SN 1987A
In this paper we investigate the properties of SN 2009E, which exploded in a
relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest
1987A-like supernova discovered so far. Spectroscopic observations which
started about 2 months after the supernova explosion, highlight significant
differences between SN 2009E and the prototypical SN 1987A. Modelling the data
of SN 2009E allows us to constrain the explosion parameters and the properties
of the progenitor star, and compare the inferred estimates with those available
for the similar SNe 1987A and 1998A. The light curve of SN 2009E is less
luminous than that of SN 1987A and the other members of this class, and the
maximum light curve peak is reached at a slightly later epoch than in SN 1987A.
Late-time photometric observations suggest that SN 2009E ejected about 0.04
solar masses of 56Ni, which is the smallest 56Ni mass in our sample of
1987A-like events. Modelling the observations with a radiation hydrodynamics
code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an
initial radius of ~7 x 10^12 cm and an ejected mass of ~19 solar masses. The
photospheric spectra show a number of narrow (v~1800 km/s) metal lines, with
unusually strong Ba II lines. The nebular spectrum displays narrow emission
lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively
strong compared to the [Ca II] doublet. The overall spectroscopic evolution is
reminiscent of that of the faint 56Ni-poor type II-plateau supernovae. This
suggests that SN 2009E belongs to the low-luminosity, low 56Ni mass, low-energy
tail in the distribution of the 1987A-like objects in the same manner as SN
1997D and similar events represent the faint tail in the distribution of
physical properties for normal type II-plateau supernovae.Comment: 19 pages, 9 figures (+7 in appendix); accepted for publication in A&A
on 3 November 201
Nickel-Rich Outflows Produced by the Accretion-Induced Collapse of White Dwarfs: Lightcurves and Spectra
The accretion-induced collapse (AIC) of a white dwarf to form a neutron star
can leave behind a rotationally supported disk with mass of up to ~ 0.1 M_sun.
The disk is initially composed of free nucleons but as it accretes and spreads
to larger radii, the free nucleons recombine to form helium, releasing
sufficient energy to unbind the remaining disk. Most of the ejected mass fuses
to form Ni56 and other iron group elements. We present spherically symmetric
radiative transfer calculations of the transient powered by the radioactive
heating of this ejecta. For an ejecta mass of 1e-2 M_sun (3e-3 M_sun), the
lightcurve peaks after <~ 1 day with a peak bolometric luminosity ~ 2e41 erg/s
(~ 5e40 erg/s), i.e., a "kilonova"; the decay time is ~ 4 (2) days. Overall,
the spectra redden with time reaching U-V ~ 4 after ~ 1 day; the optical colors
(B-V) are, however, somewhat blue. Near the peak in the lightcurve, the spectra
are dominated by Doppler broadened Nickel features, with no distinct spectral
lines present. At ~ 3-5 days, strong Calcium lines are present in the infrared,
although the Calcium mass fraction is only ~ 1e-4.5. If rotationally supported
disks are a common byproduct of AIC, current and upcoming transient surveys
such as the Palomar Transient Factory should detect a few AIC per year for an
AIC rate of ~ 1e-2 of the Type Ia rate. We discuss ways of distinguishing AIC
from other rapid, faint transients, including .Ia's and the ejecta from binary
neutron star mergers.Comment: 9 pages, 4 figures, 1 table, now accepted to MNRA
The supernova CSS121015:004244+132827: a clue for understanding super-luminous supernovae
We present optical photometry and spectra of the super luminous type II/IIn
supernova CSS121015:004244+132827 (z=0.2868) spanning epochs from -30 days
(rest frame) to more than 200 days after maximum. CSS121015 is one of the more
luminous supernova ever found and one of the best observed. The photometric
evolution is characterized by a relatively fast rise to maximum (~40 days in
the SN rest frame), and by a linear post-maximum decline. The light curve shows
no sign of a break to an exponential tail. A broad Halpha is first detected at
~ +40 days (rest-frame). Narrow, barely-resolved Balmer and [O III] 5007 A
lines, with decreasing strength, are visible along the entire spectral
evolution. The spectra are very similar to other super luminous supernovae
(SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes
considered a type Ia interacting with H-rich CSM. The spectra are also similar
to a subsample of H-deficient SLSNe. We propose that the properties of
CSS121015 are consistent with the interaction of the ejecta with a massive,
extended, opaque shell, lost by the progenitor decades before the final
explosion, although a magnetar powered model cannot be excluded. Based on the
similarity of CSS121015 with other SLSNe (with and without H), we suggest that
the shocked-shell scenario should be seriously considered as a plausible model
for both types of SLSN.Comment: 17 pages, 10 figures and 5 tables. In press to MNRAS. This version
matches the accepted one. Main conclusions are unchange
The bright Type IIP SN 2009bw, showing signs of interaction
We present photometry and spectroscopy of the type IIP supernova 2009bw in
UGC 2890 from few days after the outburst to 241 days. The light curve of SN
2009bw during the photospheric phase is similar to that of normal SNe IIP but
with brighter peak and plateau (Mmax R = -17.82 mag, Mplateau R = -17.37 mag).
The luminosity drop from the photospheric to the nebular phase is one of the
fastest ever observed, ~2.2 mag in about 13 days. The radioactive tail of the
bolometric light curve indicates that the amount of ejected 56 Ni is \approx
0.022 M\odot. The photospheric spectra reveal high velocity lines of H{\alpha}
and H{\beta} until about 105 days after the shock breakout, suggesting a
possible early interaction between the SN ejecta and pre-existent circumstellar
material, and the presence of CNO elements. By modeling the bolometric light
curve, ejecta expansion velocity and photospheric temperature, we estimate a
total ejected mass of 8-12M\odot, a kinetic energy of ~0.3 foe and an initial
radius of ~ 3.6 - 7 \times 10^13 cm.Comment: Accepted for publication in MNRAS, 19 pages, 13 figures, 9 table
Low luminosity Type II supernovae - IV. SN 2020cxd and SN 2021aai, at the edges of the sub-luminous supernovae class
Photometric and spectroscopic data for two Low Luminosity Type IIP Supernovae (LL SNe IIP) 2020cxd and 2021aai are presented. SN 2020cxd was discovered 2 d after explosion at an absolute magnitude of Mr = -14.02 ± 0.21 mag, subsequently settling on a plateau which lasts for ∼120 d. Through the luminosity of the late light curve tail, we infer a synthesized 56Ni mass of (1.8 ± 0.5) × 10-3 M⊙. During the early evolutionary phases, optical spectra show a blue continuum (8000 K) with broad Balmer lines displaying a P Cygni profile, while at later phases, Ca ii, Fe ii, Sc ii, and Ba ii lines dominate the spectra. Hydrodynamical modelling of the observables yields 575 R⊙ for the progenitor star, with Mej = 7.5 M⊙ and 0.097 foe emitted during the explosion. This low-energy event originating from a low-mass progenitor star is compatible with both the explosion of a red supergiant (RSG) star and with an Electron Capture Supernova arising from a super asymptotic giant branch star. SN 2021aai reaches a maximum luminosity of Mr = -16.57 ± 0.23 mag (correcting for AV = 1.92 mag), at the end of its remarkably long plateau (∼140 d). The estimated 56Ni mass is (1.4 ± 0.5) × 10-2 M⊙. The expansion velocities are compatible with those of other LL SNe IIP (few 103 km s-1). The physical parameters obtained through hydrodynamical modelling are 575 R⊙, Mej = 15.5 M⊙, and E = 0.4 foe. SN 2021aai is therefore interpreted as the explosion of an RSG, with properties that bridge the class of LL SNe IIP with standard SN IIP events.GV acknowledges INAF for funding his PhD fellowship within the PhD School in Astronomy at the University of Padova. MLP acknowledges support from the plan ‘programma ricerca di ateneo UNICT 2020-22 linea 2” of the University of Catania. AR acknowledges support from ANID BECAS/DOCTORADO NACIONAL 21202412. NER acknowledges partial support from MIUR, PRIN 2017 (grant 20179ZF5KS), from the Spanish MICINN grant PID2019-108709GB-I00 and FEDER funds, and from the programme Unidad de Excelencia María de Maeztu CEX2020-001058-M. LG acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) ‘Investing in your future’ under the 2019 Ramón y Cajal programme RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016, and the programme Unidad de Excelencia María de Maeztu CEX2020-001058-M. TMB acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033 under the PID2020-115253GA-I00 HOSTFLOWS project, and from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016, and the programme Unidad de Excelencia María de Maeztu CEX2020-001058-M. Y-ZC is funded by China Postdoctoral Science Foundation (grant no. 2021M691821
On the origin of the helium-rich population in Omega Centauri
To study the possible origin of the huge helium enrichment attributed to the
stars on the blue main sequence of Omega Centauri, we make use of a chemical
evolution model that has proven able to reproduce other major observed
properties of the cluster, namely, its stellar metallicity distribution
function, age-metallicity relation and trends of several abundance ratios with
metallicity. In this framework, the key condition to satisfy all the available
observational constraints is that a galactic-scale outflow develops in a much
more massive parent system, as a consequence of multiple supernova explosions
in a shallow potential well. This galactic wind must carry out preferentially
the metals produced by explosive nucleosynthesis in supernovae, whereas
elements restored to the interstellar medium through low-energy stellar winds
by both asymptotic giant branch (AGB) stars and massive stars must be mostly
retained. Assuming that helium is ejected through slow winds by both AGB stars
and fast rotating massive stars (FRMSs), the interstellar medium of Omega
Centauri's parent galaxy gets naturally enriched in helium in the course of its
evolution.Comment: 10 pages, 5 figures, accepted for publication in MNRA
SN 2009N: linking normal and subluminous Type II-P Sne
We present ultraviolet, optical, near-infrared photometry and spectroscopy of
SN 2009N in NGC 4487. This object is a type II-P supernova with spectra
resembling those of subluminous II-P supernovae, while its bolometric
luminosity is similar to that of the intermediate luminosity SN 2008in. We
created SYNOW models of the plateau phase spectra for line identification and
to measure the expansion velocity. In the near-infrared spectra we find signs
indicating possible weak interaction between the supernova ejecta and the
pre-existing circumstellar material. These signs are also present in the
previously unpublished near-infrared spectra of SN 2008in. The distance to SN
2009N is determined via the expanding photosphere method and the standard
candle method as . The produced nickel-mass
is estimated to be . We infer the
physical properties of the progenitor at the explosion through hydrodynamical
modelling of the observables. We find the values of the total energy as , the ejected mass as , and the initial radius as .Comment: 23 pages, 18 figures, accepted for publication by MNRA
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