A Preliminary Analysis for Understanding Variations in Mountain Springs’ Water Availability under Climate Change in Aosta Valley

The availability of freshwater resources in alpine mountain areas has been affected by the impacts of climate change on groundwater storage mechanisms. A web of complex interactions characterizes climate systems, and several potential effects of climate change in such areas remain largely unknown. Therefore, examining how groundwater storage mechanisms are changing in response to climate-driven agents is becoming increasingly crucial. To comprehend the existing relationship between changes in weather conditions and water availability in the Aosta Valley region (Northwestern Italy) and how their trends have changed over the last decade, a 7-year discharge series of different Aosta Valley springs (Promise, Alpe Perrot, Promiod, Cheserod) and precipitation data of the related meteorological stations (Aymaville-Viayes, La Thuile-Villaret, Champdepraz, Sant Vincent) were analyzed. The extent of the correlations between springs discharge measurements and hydrometeorological data was investigated. Besides, precipitation and flow rate trend analyses using the Mann–Kendall and Sen’s slope trend detection tests were performed. The Aymaville-Viayes, La Thuile-Villaret, Champdepraz, and Sant Vincent meteorological stations revealed an overall decreasing trend in annual rainfall (mm), with a slight increase in intensity (mm/day) as a result of the reduction in rainfall events (number of rainy days). Nonetheless, based on the analysis of flow rate data relating to the associated springs, Alpe Perrot, Cheserod, and Promise show an overall increasing trend of discharge over time. Although the Cheserod and Promise springs were not found to be highly correlated with rainfall, their aquifers appear to positively respond to the modified climate conditions, increasing the amount of groundwater stored. The moderate correlation values of these two springs can be a consequence of several factors such as aquifer features, distance from the weather station, and solid precipitation amounts that supply water in the following hydrogeological year. Being able to continuously monitor the effects induced by changed climatic conditions on water reserves through simplified analysis approaches such as those presented in this paper is increasingly necessary. Moreover, implementing future studies through in-depth analyses of soil infiltration, groundwater recharge and storage mechanisms are required to predict the mountain aquifers’ behavior in changing climatic conditions

A metallicity study of 1987A-like supernova host galaxies

The origin of the blue supergiant (BSG) progenitor of Supernova (SN) 1987A has long been debated, along with the role that its sub-solar metallicity played. We now have a sample of 1987A-like SNe that arise from the core collapse (CC) of BSGs. The metallicity of the explosion sites of the known BSG SNe is investigated, as well as their association to star-forming regions. Both indirect and direct metallicity measurements of 13 BSG SN host galaxies are presented, and compared to those of other CC SN types. Indirect measurements are based on the known luminosity-metallicity relation and on published metallicity gradients of spiral galaxies. To provide direct estimates based on strong line diagnostics, we obtained spectra of each BSG SN host both at the SN explosion site and at the positions of other HII regions. Continuum-subtracted Ha images allowed us to quantify the association between BSG SNe and star-forming regions. BSG SNe explode either in low-luminosity galaxies or at large distances from the nuclei of luminous hosts. Therefore, their indirectly measured metallicities are typically lower than those of SNe IIP and Ibc. This is confirmed by the direct estimates, which show slightly sub-solar values (12+log(O/H)=8.3-8.4 dex), similar to that of the Large Magellanic Cloud (LMC), where SN 1987A exploded. However, two SNe (1998A and 2004em) were found at near solar metallicity. SNe IIb have a metallicity distribution similar to that of BSG SNe. Finally, the association to star-forming regions is similar among BSG SNe, SNe IIP and IIn. Our results suggest that LMC metal abundances play a role in the formation of some 1987A-like SNe. This would naturally fit in a single star scenario for the progenitors. However, the existence of two events at nearly solar metallicity suggests that also other channels, e.g. binarity, contribute to produce BSG SNe.Comment: 28 pages, 17 figures; accepted for publication (Astronomy and Astrophysics); abstract abridged for arXiv submissio

Constraints on the origin of the first light from SN2014J

We study the very early lightcurve of supernova 2014J (SN 2014J) using the high-cadence broad-band imaging data obtained by the Kilodegree Extremely Little Telescope (KELT), which fortuitously observed M 82 around the time of the explosion, starting more than two months prior to detection, with up to 20 observations per night. These observations are complemented by observations in two narrow-band filters used in an H$\alpha$ survey of nearby galaxies by the intermediate Palomar Transient Factory (iPTF) that also captured the first days of the brightening of the \sn. The evolution of the lightcurves is consistent with the expected signal from the cooling of shock heated material of large scale dimensions, \gsim 1 R_{\odot}. This could be due to heated material of the progenitor, a companion star or pre-existing circumstellar environment, e.g., in the form of an accretion disk. Structure seen in the lightcurves during the first days after explosion could also originate from radioactive material in the outer parts of an exploding white dwarf, as suggested from the early detection of gamma-rays. The model degeneracy translates into a systematic uncertainty of $\pm 0.3$ days on the estimate of the first light from SN 2014J.Comment: Accepted by ApJ. Companion paper by Siverd et al, arXiv:1411.415

Reliability of spring recession curve analysis as a function of the temporal resolution of the monitoring dataset

Mountain springs represent one of the largest and most precious sources of potable water in Italy, necessary to meet the water needs of the population. Optimizing the present and future management strategies of mountain groundwater resources has become increasingly necessary. The accuracy and frequency of the flow rate (Q) measurements determine and restrict the processes that can be studied using spring hydrograph and recession curve analysis. Therefore, to properly define mountain aquifers’ hydrogeological properties, it turns out important to highlight the variation of the error in the estimation of the hydrogeological parameters as the time interval of sampling varies. In this paper, recession curve analysis was performed on two different mountain springs (Spring 1 and Spring 2) of north-western Italy, firstly considering available 4-h resolution measuring data and subsequently by resampling data to simulate longer sampling intervals of 1, 3, 7, 15, and 30 days. The resulting distribution of errors introduced by longer acquisition intervals underlined how the percentage error increases with increasing acquisition interval. For obtaining an adequate estimation of mountain aquifer hydrodynamic parameters, in place of continuous hourly data, 1-day and 3-day sampling intervals with associated errors respectively lower than 5% and 10% were found to be valid

Groundwater heat pump systems diffusion and groundwater resources protection

Geothermal Energy, being a clean and sustainable source of energy, is gaining importance worldwide due to various reasons. Geothermal power can be generated throughout the year on twenty four hour basis as it's not much dependent on ambient temperature and weather conditions. Recently there is an increased interest in exploitation of low enthalpy geothermal resources for other applications such as geothermal space heating and cooling for domestic, industrial and commercial applications.GroundWater Heat Pump systems (GWHPs) extract water from one or more wells, pass it through a heat exchanger or a heat pump, which either extracts heat from, or rejects heat, and discharge water back into the aquifer or nearby surface water.This reinjection disturbs the natural aquifer temperature, producing a local temperature anomalies (cold or heat plume) known as the thermal affected zone (TAZ).Moreover, it is important to know if the TAZ can interfere with downgradient pre-existing plants or subsurface infrastructure or with the plant itself (thermal feedback). It is then important to know, even before constructing a GWHP system, the future TAZ extent around the planned injection point.Due to these risks, the increasing number of GWHP systems enforces the need for new criteria to develop subsurface energy policies that allow planning their spatial distribution. To obtain these sustainability criteria, the results of different dedicated studies are here proposed, in order to optimize the design and operation of GWHP systems

Metallicity at the explosion sites of interacting transients

Context. Some circumstellar-interacting (CSI) supernovae (SNe) are produced by the explosions of massive stars that have lost mass shortly before the SN explosion. There is evidence that the precursors of some SNe IIn were luminous blue variable (LBV) stars. For a small number of CSI SNe, outbursts have been observed before the SN explosion. Eruptive events of massive stars are named as SN impostors (SN IMs) and whether they herald a forthcoming SN or not is still unclear. The large variety of observational properties of CSI SNe suggests the existence of other progenitors, such as red supergiant (RSG) stars with superwinds. Furthermore, the role of metallicity in the mass loss of CSI SN progenitors is still largely unexplored. Aims. Our goal is to gain insight on the nature of the progenitor stars of CSI SNe by studying their environments, in particular the metallicity at their locations. Methods. We obtain metallicity measurements at the location of 60 transients (including SNe IIn, SNe Ibn, and SN IMs), via emission-line diagnostic on optical spectra obtained at the Nordic Optical Telescope and through public archives. Metallicity values from the literature complement our sample. We compare the metallicity distributions among the different CSI SN subtypes and to those of other core-collapse SN types. We also search for possible correlations between metallicity and CSI SN observational properties. Results. We find that SN IMs tend to occur in environments with lower metallicity than those of SNe IIn. Among SNe IIn, SN IIn-L(1998S-like) SNe show higher metallicities, similar to those of SNe IIL/P, whereas long-lasting SNe IIn (1988Z-like) show lower metallicities, similar to those of SN IMs. The metallicity distribution of SNe IIn can be reproduced by combining the metallicity distributions of SN IMs (that may be produced by major outbursts of massive stars like LBVs) and SNe IIP (produced by RSGs). The same applies to the distributions of the Normalized Cumulative Rank (NCR) values, which quantifies the SN association to H II regions. For SNe IIn, we find larger mass-loss rates and higher CSM velocities at higher metallicities. The luminosity increment in the optical bands during SN IM outbursts tend to be larger at higher metallicity, whereas the SN IM quiescent optical luminosities tend to be lower. Conclusions. The difference in metallicity between SNe IIn and SN IMs suggests that LBVs are only one of the progenitor channels for SNe IIn, with 1988Z-like and 1998S-like SNe possibly arising from LBVs and RSGs, respectively. Finally, even though linedriven winds likely do not primarily drive the late mass-loss of CSI SN progenitors, metallicity has some impact on the observational properties of these transients. Key words. supernovae: general - stars: evolution - galaxies: abundancesComment: Submitted to Astronomy and Astrophysics on 28/02/2015; submitted to arXiv after the 1st referee repor

The Carnegie Supernova Project I: methods to estimate host-galaxy reddening of stripped-envelope supernovae

We aim to improve upon contemporary methods to estimate host-galaxy reddening of stripped-envelope (SE) supernovae (SNe). To this end the Carnegie Supernova Project (CSP-I) SE SNe photometry data release, consisting of nearly three dozen objects, is used to identify a minimally reddened sub-sample for each traditionally defined spectroscopic sub-types (i.e, SNe~IIb, SNe~Ib, SNe~Ic). Inspection of the optical and near-infrared (NIR) colors and color evolution of the minimally reddened sub-samples reveals a high degree of homogeneity, particularly between 0d to +20d relative to B-band maximum. This motivated the construction of intrinsic color-curve templates, which when compared to the colors of reddened SE SNe, yields an entire suite of optical and NIR color excess measurements. Comparison of optical/optical vs. optical/NIR color excess measurements indicates the majority of the CSP-I SE SNe suffer relatively low amounts of reddening and we find evidence for different R_(V)^(host) values among different SE SN. Fitting the color excess measurements of the seven most reddened objects with the Fitzpatrick (1999) reddening law model provides robust estimates of the host visual-extinction A_(V)^(host) and R_(V)^(host). In the case of the SE SNe with relatively low amounts of reddening, a preferred value of R_(V)^(host) is adopted for each sub-type, resulting in estimates of A_(V)^(host) through Fitzpatrick (1999) reddening law model fits to the observed color excess measurements. Our analysis suggests SE SNe reside in galaxies characterized by a range of dust properties. We also find evidence SNe Ic are more likely to occur in regions characterized by larger R_(V)^(host) values compared to SNe IIb/Ib and they also tend to suffer more extinction. These findings are consistent with work in the literature suggesting SNe Ic tend to occur in regions of on-going star formation.Comment: Abstract abridged to fit allowed limit. Resubmitted to A&A, 34 pages, 19 figures, 6 tables. Constructive comments welcome

The peculiar Type Ia supernova iPTF14atg: Chandrasekhar-mass explosion or violent merger?

iPTF14atg, a subluminous peculiar Type Ia supernova (SN Ia) similar to SN 2002es, is the first SN Ia for which a strong UV flash was observed in the early-time light curves. This has been interpreted as evidence for a single-degenerate (SD) progenitor system where such a signal is expected from interactions between the SN ejecta and the non-degenerate companion star. Here, we compare synthetic observables of multi-dimensional state-of-the-art explosion models for different progenitor scenarios to the light curves and spectra of iPTF14atg. From our models, we have difficulties explaining the spectral evolution of iPTF14atg within the SD progenitor channel. In contrast, we find that a violent merger of two carbon-oxygen white dwarfs with 0.9 and 0.76 solar masses, respectively, provides an excellent match to the spectral evolution of iPTF14atg from 10d before to several weeks after maximum light. Our merger model does not naturally explain the initial UV flash of iPTF14atg. We discuss several possibilities like interactions of the SN ejecta with the circum-stellar medium and surface radioactivity from a He ignited merger that may be able to account for the early UV emission in violent merger models.Comment: 12 pages, 7 figures, accepted for publication in MNRA