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Paolo Molaro

Publications and source records attributed to Paolo Molaro.

At least 37 records · Page 2Linked to original sources
arXiv2019

Search for 7Be in the outburst of four recent novae

Following the recent detection of 7Be in the outburst spectra of Classical Novae we report the search for this isotope in the outbursts of four recent bright novae by means of high resolution UVES observations. The 7BeII 313.0583, 313.1228 nm doublet resonance lines are detected in the high velocity components of Nova Mus 2018 and ASASSN-18fv during outburst. On the other hand 7BeII is neither detected in ASASSN-17hx and possibly nor in Nova Cir 2018, therefore showing that the 7BeII is not always ejected in the thermonuclear runaway. Taking into account the 7Be decay we find X(7Be)/X(H) approx 1.5 x10 ^{-5} and 2.2 x 10 ^{-5} in Nova Mus 2018 and ASASSN-18fv, respectively. A value of 7Be/H about 2 x10 ^{-5} is found in 5 out of the 7 extant measurements and it might be considered as a typical 7Be yield for novae. However, this value is almost one order of magnitude larger than predicted by current theoretical models. We argue that the variety of high 7Be/H abundances could be originated in a higher than solar content of 3He in the donor star. The cases with 7Be not detected might be related to a small mass of the WD or to relatively little mixing with the core material of the WD. The 7Be /H, or 7Li/H, abundance is about 4 dex above meteoritic thus confirming the novae as the main sources of 7Li in the Milky Way.

astro-ph.GA↗
arXiv2018

$^{7}$Li evolution in the thin and thick disks of the Milky Way

Recent detection of the isotope $^7$Be (that decays into $^7$Li) in the outburst of classical novae confirms the suggestion made in the 70s that novae could make $^7$Li. We reconsidered the role of novae as producers of Li by means of a detailed model of the chemical evolution of the Milky Way. We showed that novae could be the Galactic lithium source accounting for the observed increase of Li abundances in the thin disk with stellar metallicity. The best agreement with the upper envelope of the observed Li abundances is obtained for a delay time of ~ 1 Gyr for the nova production and for an effective Li yield of $1.8 (\pm 0.6) \times 10^{-5}$ $M_{\odot}$ over the whole nova life. Lithium in halo stars is depleted by ~ 0.35 dex, assuming the pristine abundance from standard big bang nucleosynthesis. We elaborate a model that matches the pristine stellar abundances, assuming that all stars are depleted by 0.35 dex. In this case, the delay remains the same, but the Li yields are doubled compared to the previous case. This model also has the merit to match the Li abundance in meteorites and young TTauri stars. The thick disk model, adopting the parameters derived for the thin disk, can also explain the absence of increase of Li abundances in its stars. The thick disk is old, but formed and evolved in a time shorter than that required by novae to contribute significantly to Li. Therefore, no Li enhancement is expected in thick disk stars. We show that the almost constant Li abundance in the thick disk results from the compensation of stellar astration by spallation processes.

astro-ph.SR↗
arXiv2018

Gamma-Ray Observations of Nova Sgr 2015 No. 2 with INTEGRAL

INTEGRAL observed the nova V5668 Sgr around the time of its optical maximum on March 21, 2015. Studies at UV wavelengths showed spectral lines of freshly produced Be-7. This could be measurable also in gamma-rays at 478 keV from the decay to Li-7. Novae are also expected to synthesise Na-22 which decays to Ne-22, emitting a 1275 keV photon. About one week before the optical maximum, a strong gamma-ray flash on time-scales of hours is expected from short-lived radioactive nuclei, such as N-13 and F-18. These beta-plus-unstable nuclei should yield emission up to 511 keV, but which has never been observed. The spectrometer SPI aboard INTEGRAL pointed towards V5668 by chance. We use these observations to search for possible gamma-ray emission of decaying Be-7, and to directly measure the synthesised mass during explosive burning. We also aim to constrain possible burst-like emission days to weeks before the optical maximum using the SPI anticoincidence shield (ACS). We extract spectral and temporal information to determine the fluxes of gamma-ray lines at 478 keV, 511 keV, and 1275 keV. A measured flux value directly converts into abundances produced by the nova. The SPI-ACS rates are analysed for burst-like emission using a nova model light-curve. For the obtained nova flash candidate events, we discuss possible origins. No significant excess for the expected gamma-ray lines is found. Our upper limits on the synthesised Be-7 and Na-22 mass depend on the uncertainties of the distance to the nova: The Be-7 mass is constrained to less than $4.8\times10^{-9}\,(d/kpc)^2$, and Na-22 to less than $2.4\times10^{-8}\,(d/kpc)^2$ solar masses. For the Be-7 mass estimate from UV studies, the distance to V5668 Sgr must be larger than 1.2 kpc. During three weeks before the optical maximum, we find 23 burst-like events in the ACS rate, of which six could possibly be associated with V5668 Sgr.

astro-ph.HE↗
arXiv2018

Cosmological evolution of the Nitrogen abundance

The abundance of nitrogen in the interstellar medium is a powerful probe of star for- mation processes over cosmological timescales. Since nitrogen can be produced both in massive and intermediate-mass stars with metallicity-dependent yields, its evolution is challenging to model, as evidenced by the differences between theoretical predictions and observations. In this work we attempt to identify the sources of these discrepancies using a cosmic evolution model. To further complicate matters, there is considerable dispersion in the abundances from observations of DLAs at redshift 2 - 3. We study the evolution of nitrogen with a detailed chemical evolution model and find good agreement with observations, including the relative abundances of N/O and N/Si ratios. We find that the principal contribution of nitrogen comes from intermediate mass stars, with the exception of systems with the lowest N/H, where nitrogen production might possibly be dominated by massive stars. This last result could be strengthened if stellar rotation which is important at low metallicity can produce significant amounts of nitrogen. Moreover, these systems likely reside in host galaxies with stellar masses below 10**8.5 solar mass. We also study the origin of the observed dispersion in nitrogen abundances using the cosmological hydrodynamical simulations Horizon-AGN. We conclude that this dispersion can originate from two effects: differ- ence in the masses of the DLA host galaxies, and difference in the their position inside the galaxy.

astro-ph.GA↗
arXiv2017

On the Earthshine depicted in Galileo's watercolors of the Moon

With the manuscript of the Sidereus Nuncius preserved at the Biblioteca Nazionale of Florence are included 7 watercolors of the Moon painted by Galileo himself. We suggest that some of them, and in particular the drawing of the 30 Nov 1609 of the very first Moon's observations, illustrate the phenomenon of the Earthshine of the Moon, which was discussed in some detail in the Sidereus Nuncius to provide evidence of the similarity of Earth to other celestial bodies. The watercolors were used as models for the engraving of the Moon in the Sidereus but, surprisingly, the secondary light had not been reproduced. Galileo may have decided for the inclusion of the passage on the Earthshine only at a very late stage of the editorial process. Galileo's hesitation shows how contentious was this issue already recognized as a possible discriminant between the different systems of the world.

physics.hist-ph↗
arXiv2017

Francesco Fontana and his "astronomical" Telescope

In the late 1620s the Neapolitan telescope maker Francesco Fontana was the first to observe the sky using a telescope with two convex lenses, which he had manufactured himself. Fontana succeeded in drawing the most accurate maps of the Moon's surface of his time, which were to become popular through a number of publications spread all over Europe but without acknowledging the author. At the end of 1645, in a state of declining health and pressed by the need to defend his authorship, Fontana carried out an intense observational campaign, whose results he hurriedly collected in his Novae Coelestium Terrestriumque rerum Observationis (1646), the only book he left to posterity. Fontana observed the Moon's main craters, as the crater Tycho which he named Fons Major, their radial patterns and the change in their positions due to the Moon's motions. He observed the gibbosity of Mars at quadrature and, together with the Jesuit G.B. Zupus, he described the phases of Mercury. Fontana observed the two - and occasionally three - major bands of Jupiter, and inferred the rotation movement of the major planets Mars, Jupiter and Saturn, arguing that they could not be attached to an Aristotelian sky. He came close to revealing the ring structure of Saturn. He also suggested the presence of additional moons around Jupiter, Venus and Saturn, which prompted a debate that lasted more than a hundred years. In several places of his book Fontana repeatedly claimed to have conceived the first positive eyepiece in 1608, providing a declaration by Zupus to have used his telescope since 1614. This declaration is still the oldest record mentioning such a device. We finally suggest that the telescopes depicted in the two Allegory of Sight by J. Brueghel the Elder belonging to Albert VII might have been made by Fontana, and that he might have inspired the Sight by Jusepe Ribera (c. 1616).

physics.hist-ph↗
arXiv2016

Highly Enriched 7Be in the ejecta of Nova Sagittarii 2015 No. 2 (V5668 Sgr) and the Galactic Lithium origin

We report on the evidence of highly blue-shifted resonance lines of the singly ionised isotope of 7BeII in high resolution UVES spectra of Nova Sagittarii 2015 No. 2 (V5668 Sgr). The resonance doublet lines 7BeII at lambda 313.0583, 313.1228 nm are clearly detected in several non saturated and partially resolved high velocity components during the evolution of the outburst. The total absorption identified with Beryllium has an equivalent width much larger than all other elements and comparable to hydrogen. We estimate an atomic fraction N(7Be)/N(Ca) ~ 53-69 from unsaturated and resolved absorption components. The detection of 7Be in several high velocity components shows that it has been freshly created in a thermonuclear runaway via the reaction 3He}(alpha,gamma) 7Be during the Nova explosion, as postulated by Arnould and Norgaard (1975) , however in much larger amounts than predicted by current models. 7Be decays to 7Li with a half-life of 53.22 days, comparable to the temporal span covered by the observations. The non detection of LiI requires that LiII remains ionised throughout our observations. The massive 7Be ejecta result into a 7Li production that is about 4.7-4.9 dex above the meteoritic abundance. If such a high production is common even in a small fraction (~5%) of Novae, they can make all the "stellar" 7Li of the Milky Way.

astro-ph.GA↗
arXiv2015

Early Telescopes and Ancient Scientific Instruments in the Paintings of Jan Brueghel the Elder

Ancient instruments of high interest for research on the origin and diffusion of early scientific devices in the late XVI - early XVII centuries are reproduced in three paintings by Jan Brueghel the Elder. We investigated the nature and the origin of these instruments, in particular the spyglass depicted in a painting dated 1609-1612 that represents the most ancient reproduction of an early spyglass, and the two sophisticated spyglasses with draw tubes that are reproduced in two paintings, dated 1617-1618. We suggest that these two instruments may represent early examples of keplerian telescopes. Concerning the other scientific instruments, namely an astrolabe, an armillary sphere, a nocturnal, a proportional compass, surveying instruments, a Mordente's compass, a theodolite, etc., we point out that most of them may be associated with Michiel Coignet, cosmographer and instrument maker at the Court of the Archduke Albert VII of Hapsburg in Brussels.

astro-ph.IM↗
arXiv2015

The Earth transiting the Sun as seen from Jupiter's moons: detection of an inverse Rossiter-McLaughlin effect produced by the Opposition Surge of the icy Europa

We report on a multi-wavelength observational campaign which followed the Earth's transit on the Sun as seen from Jupiter on 5 Jan the 2014. Simultaneous observations of Jupiter's moons Europa and Ganymede obtained with HARPS from La Silla, Chile, and HARPS-N from La Palma, Canary Islands, were performed to measure the Rossiter-McLaughlin effect due to the Earth's passage using the same technique successfully adopted for the 2012 Venus Transit (Molaro et al 2013). The expected modulation in radial velocities was of about 20 cm/s but an anomalous drift as large as 38 m/s, i.e. more than two orders of magnitude higher and opposite in sign, was detected instead. The consistent behaviour of the two spectrographs rules out instrumental origin of the radial velocity drift and BiSON observations rule out the possible dependence on the Sun's magnetic activity. We suggest that this anomaly is produced by the Opposition Surge on Europa's icy surface, which amplifies the intensity of the solar radiation from a portion of the solar surface centered around the crossing Earth which can then be observed as a a sort of inverse Rossiter-McLaughling effect. in fact, a simplified model of this effect can explain in detail most features of the observed radial velocity anomalies, namely the extensions before and after the transit, the small differences between the two observatories and the presence of a secondary peak closer to Earth passage. This phenomenon, observed here for the first time, should be observed every time similar Earth alignments occur with rocky bodies without atmospheres. We predict it should be observed again during the next conjunction of Earth and Jupiter in 2026.

astro-ph.EP↗
arXiv2015

Lithium evolution in metal-poor stars: from Pre-Main Sequence to the Spite plateau

Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicted by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred as the lithium problem. We here reconsider the stellar Li evolution from the pre-main sequence to the end of the main sequence phase by introducing the effects of convective overshooting and residual mass accretion. We show that $^7$Li could be significantly depleted by convective overshooting in the pre-main sequence phase and then partially restored in the stellar atmosphere by a tail of matter accretion which follows the Li depletion phase and that could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and microscopic diffusion along the main sequence we can reproduce the Spite plateau for stars with initial mass $m_0=0.62 - 0.80 M_{\odot}$, and the Li declining branch for lower mass dwarfs, e.g, $m_0=0.57 - 0.60 M_{\odot}$, for a wide range of metallicities (Z=0.00001 to Z=0.0005), starting from an initial Li abundance $A({\rm Li}) =2.72$. This environmental Li evolution model also offers the possibility to interpret the decrease of Li abundance in extremely metal-poor stars, the Li disparities in spectroscopic binaries and the low Li abundance in planet hosting stars.

astro-ph.SR↗
arXiv2015

Edgar Allan Poe: the first man to conceive a Newtonian evolving Universe

The notion that we live in an evolving universe was established only in the twentieth century with the discovery of the recession of galaxies by Hubble and with the Lemaitre and Friedmann's interpretation in the 1920s. However, the concept of an evolving universe is intrinsically tied to the law of universal gravitation, and it is surprising that it remained unrecognized for more than two centuries. A remarkable exception to this lack of awareness is represented by Poe. In Eureka (1848), the writer developed a conception of an evolving universe following the reasoning that a physical universe cannot be static and nothing can stop stars or galaxies from collapsing on each other. Unfortunately this literary work was, and still is, very little understood both by the literary critics and scientists of the time. We will discuss Poe's cosmological views in their historical scientific context, highlighting the remarkable insights of the writer, such as those dealing with the Olbers paradox, the existence of other galaxies and of a multi-universe.

physics.hist-ph↗
arXiv2014

Big-Bang Nucleosynthesis

A critical review is given of the current status of cosmological nucleosynthesis. In the framework of the Standard Model with 3 types of relativistic neutrinos, the baryon-to-photon ratio, $η$, corresponding to the inferred primordial abundances of deuterium and helium-4 is consistent with the independent determination of $η$ from observations of anisotropies in the cosmic microwave background. However the primordial abundance of lithium-7 inferred from observations is significantly below its expected value. Taking systematic uncertainties in the abundance estimates into account, there is overall concordance in the range $η= (5.7-6.7)\times 10^{-10}$ at 95% CL (corresponding to a cosmological baryon density $Ω_B h^2 = 0.021 - 0.025$). The D and He-4 abundances, when combined with the CMB determination of $η$, provide the bound $N_ν=3.28 \pm 0.28$ on the effective number of neutrino species. Other constraints on new physics are discussed briefly.

astro-ph.CO↗
arXiv2014

The ESO UVES Advanced Data Products Quasar Sample - III. Evidence of Bimodality in the [N/alpha] Distribution

We report here a study of nitrogen and $α$-capture element (O, S, and Si) abundances in 18 Damped Ly$α$ Absorbers (DLAs) and sub-DLAs drawn from the ESO-UVES Advanced Data Products (EUADP) database. We report 9 new measurements, 5 upper and 4 lower limits of nitrogen that when compiled with available nitrogen measurements from the literature makes a sample of 108 systems. The extended sample presented here confirms the [N/$α$] bimodal behaviour suggested in previous studies. Three-quarter of the systems show $\langle$[N/$α$]$\rangle=-0.85$ ($\pm$0.20 dex) and one-quarter ratios are clustered at $\langle$[N/$α$]$\rangle= -1.41$ ($\pm$0.14 dex). The high [N/$α$] plateau is consistent with the HII regions of dwarf irregular and blue compact dwarf galaxies although extended to lower metallicities and could be interpreted as the result of a primary nitrogen production by intermediate mass stars. The low [N/$α$] values are the lowest ever observed in any astrophysical site. In spite of this fact, even lower values could be measured with the present instrumentation, but we do not find them below [N/$α$] $\approx$ $-1.7$. This suggests the presence of a floor in [N/$α$] abundances, which along with the lockstep increase of N and Si may indicate a primary nitrogen production from fast rotating, massive stars in relatively young or unevolved systems.

astro-ph.GA↗
arXiv2014

Nitrogen Abundances in Damped Ly-alpha Absorbers

Nitrogen is thought to have both primary and secondary origins depending on whether the seed carbon and oxygen are produced by the star itself (primary) or already present in the interstellar medium (secondary) from which star forms. DLA and sub-DLA systems with typical metallicities of -3.0<Z/Z_sun<-0.5 are excellent tools to study nitrogen production. We made a search for nitrogen in the ESO-UVES advanced data products (EUADP) database. In the EUADP database, we find 10 new measurements and 9 upper limits of nitrogen. We further compiled DLA/sub-DLA data from the literature with estimates available of nitrogen and alpha-elements. This yields a total of 98 systems, i.e. the largest nitrogen abundance sample investigated so far. In agreement with previous studies, we indeed find a bimodal [N/alpha] behaviour: three-quarter systems show a mean value of [N/alpha]=-0.87 with a scatter of 0.21 dex and one-quarter shows ratios clustered at [N/alpha]=-1.43 with a lower dispersion of 0.13 dex. The high [N/alpha] group is consistent with the blue compact dwarves and dwarf irregular galaxies, suggesting primary nitrogen production. The low [N/alpha] group is the lowest ever observed in any astrophysical site and probably provides an evidence of the primary production by fast rotating massive stars in young sites. Moreover, we find a transition between the two [N/alpha] groups around [N/H]=-2.5. The transition is not abrupt and there are a few systems lying in the transition region. Additional observations of DLAs/sub-DLAs below [N/H]<-2.5 would provide more clues.

astro-ph.GA↗
arXiv2013

Constraints of $Δμ/μ$ based on H$_2$ observations in QSO spectra at high redshifts

This article summarizes the latest results on the proton-to-electron mass ratio $μ$ derived from H$_2$ observations at high redshift in the light of possible variations of fundamental physical constants. The focus lies on UVES observations of the past years as enormous progress was achieved since the first positive results on $Δμ/μ$ were published. With the better understanding of systematics, dedicated observation runs, and numerous approaches to improve wavelength calibration accuracy, all current findings are in reasonable good agreement with no variation and provide an upper limit of $Δμ/μ< 1\times 10^{-5}$ for the redshift range of $2 <$ z $< 3$.

astro-ph.CO↗
arXiv2012

QSO 0347-383 and the invariance of m_p/m_e in the course of cosmic time

The variation of the dimensionless fundamental physical constant mu = m_p/m_e (the proton to electron mass ratio) can be constrained via observation of Lyman and Werner lines of molecular hydrogen in the spectra of damped Lyman alpha systems (DLAs) in the line of sight to distant QSOs. Drawing on VLT-UVES high resolution data sets of QSO 0347-383 and its DLA obtained in 2009 our analysis yields dmu/mu = (4.3 +/- 7.2) * 10^-6 at z_abs =3.025. We apply corrections for the observed offsets between discrete spectra and for the first time we find indications for inter-order distortions. Current analyses tend to underestimate the impact of systematic errors. Based on the scatter of the measured redshifts and the corresponding low significance of the redshift-sensitivity correlation we estimate the limit of accuracy of line position measurements to about 220 m/s, consisting of roughly 150 m/s due to the uncertainty of the absorption line fit and about 150 m/s allocated to systematics related to instrumentation and calibration.

astro-ph.CO↗
arXiv2011

Extremely metal-poor stars in SDSS fields

Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal-poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metalllicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1000 the solar metallicity and 4 stars with about 1/10000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X-Shooter has the unique capability of performing the necessary follow-up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr,...) for EMP candidates. We here report on the results for the first two stars observed in the course of our franco-italian X-Shooter GTO. The two stars were targeted to be of metallicity around -3.0, the analysis of the X-Shooter spectra showed them to be of metallicity around -2.0, but with a low alpha to iron ratio, which explains the underestimate of the metallicity from the SDSS spectra. The efficiency of X-Shooter allows an in situ study of the outer Halo, for the two stars studied here we estimate distances of 3.9 and 9.1 Kpc, these are likely the most distant dwarf stars studied in detail to date.

astro-ph.SR↗