The initial-final mass relationship of white dwarfs in common proper motion pairs

A promising approach to decrease the uncertainties in the initial-final mass relationship, which is still poorly constrained, is to study white dwarfs for which external constraints are available, for instance, white dwarfs in common proper motion pairs (CPMPs). Important information of the white dwarf can be inferred from the study of the companion, since they were born at the same time and with the same initial chemical composition. In this contribution, we report new results obtained from spectroscopic observations of both members of several CPMPs composed of a F, G or K type star and a DA white dwarf

White dwarf dynamical interactions and fast optical transients

This is the author accepted manuscript. The final version is available from OUP via the DOI in this record.Recent advances in time-domain astronomy have uncovered a new class of optical transients with timescales shorter than typical supernovae and a wide range of peak luminosities. Several subtypes have been identi ed within this broad class, including Ca-rich transients, .Ia supernovae, and fast/bright transients. We examine the predic- tions from a state-of-the-art grid of three-dimensional simulations of dynamical white dwarf interactions in the context of these fast optical transients. We nd that for colli- sions involving carbon-oxygen or oxygen-neon white dwarfs the peak luminosities and durations of the light curves in our models are in good agreement with the properties of fast/bright transients. When one of the colliding white dwarfs is made of helium the properties of the light curves are similar to those of Ca-rich gap transients. The model lightcurves from our white dwarf collisions are too slow to reproduce those of .Ia SNe, and too fast to match any normal or peculiar Type Ia supernova.This work was partially funded by the MINECO grant AYA2014-59084-P and by the AGAUR (EG-B). CB acknowledges support from grants NASA ADAP NNX15AM03G S01 and NSF/AST-1412980. We acknowl- edge the useful comments of our referee, which helped in improving the original version of the paper

Statistical analysis of inter-arrival times of rainfall events for Italian Sub-Alpine and Mediterranean areas

Abstract. In this work a set of time-series of inter-arrival times of rainfall events, at daily scale, was analysed, with the aim to verify the issue of increasing duration of dry periods. The set consists of 12 time-series recorded at rain gauges in 1926–2005, six of them belong to an Italian Sub-Alpine area (Piedmont) and six to a Mediterranean one (Sicily). In order to overcome the problem related to limited sample size for high values of inter-arrival times, the discrete probability polylog-series distribution was used to fit the empirical data from partial (20 yr) time-series. Moreover, a simple qualitative trend analysis was applied to some high quantiles of inter-arrival times as well as to the average extent of rain clusters. The preliminary analysis seems to confirm the issue of increasing duration of dry periods for both environments, which is limited to the ''cold'' season

The variation of the fine structure constant: testing the dipole model with thermonuclear supernovae

The large-number hypothesis conjectures that fundamental constants may vary. Accordingly, the space-time variation of fundamental constants has been an active subject of research for decades. Recently, using data obtained with large telescopes a phenomenological model in which the fine structure constant might vary spatially has been proposed. We test whether this hypothetical spatial variation of alpha, which follows a dipole law, is compatible with the data of distant thermonuclear supernovae. Unlike previous works, in our calculations we consider not only the variation of the luminosity distance when a varying alpha is adopted, but we also take into account the variation of the peak luminosity of Type Ia supernovae resulting from a variation of alpha. This is done using an empirical relation for the peak bolometric magnitude of thermonuclear supernovae that correctly reproduces the results of detailed numerical simulations. We find that there is no significant difference between the several phenomenological models studied here and the standard one, in which alpha does not vary spatially. We conclude that the present set of data of Type Ia supernovae is not able to distinguish the standard model from the dipole models, and thus cannot be used to discard nor to confirm the proposed spatial variation of alpha.Peer ReviewedPostprint (published version

The last Charrua Indian; (Uruguay): analysis of the remains of Chief Vaimaca Perú.

Uruguay is the only Latin American country that at present lacks Native populations and little is known about its prehistoric populations. In the construction of National identity, the unique reference to Natives is about Charra Indians, one of the most important ethnic groups that lived in the territory and exterminated in the 1830s. In 1833, four survivors were taken to be exhibited and studied in France, becoming martyrs and a symbol of their nation. The skeletal remains of Chief Perú were preserved and studied mainly by Rivet1; these are the only remains certainly identified as belonging to a Charrúa. In 2002, the French government returned the remains to Uruguay, where they were buried with honours at the National Pantheon. Before the burial, we performed morphological studies as well as extracted samples for DNA analysis. Peru's morphology is coherent with the one of a nomadic warrior: robust body with strong muscular insertions, wounds, and healthy diet based mainly on meat. Here we show that metric and morphological data as well as maternal inherited mitochondrial DNA (mtDNA) hypervariable region I (HVRI) and restriction fragment length polymorphisms (RFLPs), indicate a close relationship with Pampa-Patagonian Indians, and specially, with prehistoric Natives buried in mounds from eastern Uruguay. This last finding is particularly important to understand Uruguayan prehistory and history, raising the debate about who the mound builders were, and showing continuity between them, historic Charrúa Indians, and present populations

The age-metallicity relation from a sample of white dwarf-main sequence binarie

The age-metallicity relation (AMR) is a fundamental observational constraint for un-derstanding how the Galactic disc formed and evolved chemically in time. However, there is not yet an agreement on the observational properties of the AMR, primarily due to the difficulty inobtaining accurate ages for individual field stars. We have started an observational campaign for providing new observational input by using wide white dwarf-main sequence (WDMS) binaries.WDs are natural clocks and can be used to derive accurate ages. Metallicities can be obtained from the MS companions. Since the progenitors of WDs and the MS stars were born at the sametime, WDMS provide a unique opportunity to constrain in a robust way the properties of the AMR. We present the AMR derived from analysing a pilot sample of 23 WDMS and provide clear evidence for the lack of correlation between age and metallicity at young and intermediate ages.Peer ReviewedPostprint (published version

Is the central binary system of the planetary nebula Henize 2-428 a type Ia supernova progenitor?

We critically discuss the recent observations of the binary system atthe center of the bipolar planetary nebula Henize 2-428. We findthat the proposed explanation of two equal-mass degenerate objects witha total mass larger than the Chandrasekhar limiting mass that supposedlywill merge in less than a Hubble time, possibly leading to a SN Ia,is controversial. This hypothesis relies on the assumption that thevariability of the He II 5412 Å spectral lineis due to two absorption components. Instead, we propose that it can beaccounted for by a broad absorption line from the central system on topof which there is a narrow emission line from the nebula. This promptedus to study if the binary system can be made of a degenerate star and alow-mass main sequence companion, or of two degenerate objects ofsmaller mass. We find that although both scenarios can account for theexistence of two symmetric broad minima in the light curve, the secondone agrees better with observations. We thus argue that the claim thatHenize 2-428 provides observational evidence supporting thedouble-degenerate scenario for SN Ia is premature.Instituto de Astrofísica de La Plat

Is the central binary system of the planetary nebula Henize 2-428 a type Ia supernova progenitor?

We critically discuss the recent observations of the binary system atthe center of the bipolar planetary nebula Henize 2-428. We findthat the proposed explanation of two equal-mass degenerate objects witha total mass larger than the Chandrasekhar limiting mass that supposedlywill merge in less than a Hubble time, possibly leading to a SN Ia,is controversial. This hypothesis relies on the assumption that thevariability of the He II 5412 Å spectral lineis due to two absorption components. Instead, we propose that it can beaccounted for by a broad absorption line from the central system on topof which there is a narrow emission line from the nebula. This promptedus to study if the binary system can be made of a degenerate star and alow-mass main sequence companion, or of two degenerate objects ofsmaller mass. We find that although both scenarios can account for theexistence of two symmetric broad minima in the light curve, the secondone agrees better with observations. We thus argue that the claim thatHenize 2-428 provides observational evidence supporting thedouble-degenerate scenario for SN Ia is premature.Instituto de Astrofísica de La Plat

Neural network interpolation of the magnetic field for the LISA Pathfinder Diagnostics Subsystem

LISA Pathfinder is a science and technology demonstrator of the European Space Agency within the framework of its LISA mission, which aims to be the first space-borne gravitational wave observatory. The payload of LISA Pathfinder is the so-called LISA Technology Package, which is designed to measure relative accelerations between two test masses in nominal free fall. Its disturbances are monitored and dealt by the diagnostics subsystem. This subsystem consists of several modules, and one of these is the magnetic diagnostics system, which includes a set of four tri-axial fluxgate magnetometers, intended to measure with high precision the magnetic field at the positions of the test masses. However, since the magnetometers are located far from the positions of the test masses, the magnetic field at their positions must be interpolated. It has been recently shown that because there are not enough magnetic channels, classical interpolation methods fail to derive reliable measurements at the positions of the test masses, while neural network interpolation can provide the required measurements at the desired accuracy. In this paper we expand these studies and we assess the reliability and robustness of the neural network interpolation scheme for variations of the locations and possible offsets of the magnetometers, as well as for changes in environmental conditions. We find that neural networks are robust enough to derive accurate measurements of the magnetic field at the positions of the test masses in most circumstances

The initial–final mass relationship of white dwarfs in common proper motion pairs and open clusters

We have studied white dwarfs in common proper motion pairs (CPMPs) to improve the semi-empirical initial–final mass relationship of white dwarfs. In this contribution, we re- port new results obtained from spectroscopic observations of both members of several CPMPs composed of a F, G or K type star and a DA white dwarf.Peer Reviewe