High-precision acoustic helium signatures in 18 low-mass low-luminosity red giants. Analysis from more than four years of Kepler observations

High-precision frequencies of acoustic modes in red giant stars are now available thanks to the long observing length and high-quality of the light curves provided by the NASA Kepler mission, thus allowing to probe the interior of evolved cool low-mass stars with unprecedented level of detail. We characterize the acoustic signature of the helium second ionization zone in a sample of 18 low-mass low-luminosity red giants by exploiting new mode frequency measurements derived from more than four years of Kepler observations. We analyze the second frequency differences of radial acoustic modes in all the stars of the sample by using the Bayesian code Diamonds. We find clear acoustic glitches due to the signature of helium second ionization in all the stars of the sample. We measure the acoustic depth and the characteristic width of the acoustic glitches with a precision level on average around $\sim$2% and $\sim$8%, respectively. We find good agreement with theoretical predictions and existing measurements from the literature. Lastly, we derive the amplitude of the glitch signal at $\nu_\mathrm{max}$ for the second differences and for the frequencies with an average precision of $\sim$6%, obtaining values in the range 0.14-0.24 $\mu$Hz, and 0.08-0.33 $\mu$Hz, respectively, which can be used to investigate the helium abundance in the stars.Comment: 12 pages, 19 figures, 3 tables. Accepted for publication in A&

Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler

The currently available Kepler light curves contain an outstanding amount of information but a detailed analysis of the individual oscillation modes in the observed power spectra, also known as peak bagging, is computationally demanding and challenging to perform on a large number of targets. Our intent is to perform for the first time a peak bagging analysis on a sample of 19 low-mass low-luminosity red giants observed by Kepler for more than four years. This allows us to provide high-quality asteroseismic measurements that can be exploited for an intensive testing of the physics used in stellar structure models, stellar evolution and pulsation codes, as well as for refining existing asteroseismic scaling relations in the red giant branch regime. For this purpose, powerful and sophisticated analysis tools are needed. We exploit the Bayesian code Diamonds, using an efficient nested sampling Monte Carlo algorithm, to perform both a fast fitting of the individual oscillation modes and a peak detection test based on the Bayesian evidence. We find good agreement for the parameters estimated in the background fitting phase with those given in the literature. We extract and characterize a total of 1618 oscillation modes, providing the largest set of detailed asteroseismic mode measurements ever published. We report on the evidence of a change in regime observed in the relation between linewidths and effective temperatures of the stars occurring at the bottom of the RGB. We show the presence of a linewidth depression or plateau around $\nu_\mathrm{max}$ for all the red giants of the sample. Lastly, we show a good agreement between our measurements of maximum mode amplitudes and existing maximum amplitudes from global analyses provided in the literature, useful as empirical tools to improve and simplify the future peak bagging analysis on a larger sample of evolved stars.Comment: 78 pages, 46 figures, 22 tables. Accepted for publication in A&

FliPer: Checking the reliability of global seismic parameters from automatic pipelines

Our understanding of stars through asteroseismic data analysis is limited by our ability to take advantage of the huge amount of observed stars provided by space missions such as CoRoT, Kepler, K2, and soon TESS and PLATO. Global seismic pipelines provide global stellar parameters such as mass and radius using the mean seismic parameters, as well as the effective temperature. These pipelines are commonly used automatically on thousands of stars observed by K2 for 3 months (and soon TESS for at least around 1 month). However, pipelines are not immune from misidentifying noise peaks and stellar oscillations. Therefore, new validation techniques are required to assess the quality of these results. We present a new metric called FliPer (Flicker in Power), which takes into account the average variability at all measured time scales. The proper calibration of FliPer enables us to obtain good estimations of global stellar parameters such as surface gravity that are robust against the influence of noise peaks and hence are an excellent way to find faults in asteroseismic pipelines.Comment: 4 pages, 3 figures, Proceedings for SF2A 2017 (Paris

Characterizing high energy explosive eruptions at Stromboli volcano using multidisciplinary data: An example from the 9 January 2005 explosion

Stromboli is well known for its persistent, normal explosive activity, consisting of intermittent, mild to moderate, Strombolian explosions that typically occur every 10–20 min. All tephras erupted during this activity usually fall back into the crater terrace, and consist of volatile-poor scoriae fed by Highly Porphyritic (HP) magma. More occasionally, large explosions or “paroxysms” eject a greater quantity of tephra, mainly consisting of HP scoriae and pumice clasts of Low Porphyritic (LP) magma, but also including large lithic blocks. In addition to this activity, between 2004 and 2006 high energy explosions, displaying an intermediate eruptive style between that of normal and paroxysmal explosions in terms of column height, duration and tephra dispersal, were observed to occur at a frequency of one to eight events per year. While many volcanological, geochemical and geophysical studies have focused in the last few years on the two endmembers of activity, i.e. normal or paroxysmal, a detailed investigation on these intermediate types of events has not been carried out yet. Here we report of a study on the 9 January 2005 explosion, one of the high energy explosions during which the main fountaining phase lasted nearly a minute causing ejection of coarse bombs up to a height of 120 m, and of ash and lapilli to N200 m. An accompanying ash plume rose up to 500 m at the end of the explosion. We present a multidisciplinary approach that integrates the results from analysis of live-camera images with compositional and textural characterization of the erupted products. Major element composition of glassy groundmass and 3D views of textures in the erupted scoriae support the hypothesis based on volcanological observations that this explosion falls between normal and paroxysmal activity, for which we use the term “intermediate”. By comparing the video-camera images of the 9 January 2005 explosion with volcanological features of other high energy explosions that occurred at Stromboli between June 2004 and October 2006, we find that three additional events can be considered intermediate explosions, suggesting that this type of activity may be fairly common on this volcano. The results of this study, although preliminary given our limited dataset, clearly indicate that the methodology used here can be successfully applied to better define the range of eruptive styles typifying the normal explosive activity, potentially improving our capability of eruption forecasting and assessing volcanic hazard at Stromboli

The December 2018 eruption at Etna volcano: a geochemical study on melt and fluid inclusions

This study focus on the Mt Etna December 2018 eruption with the aim of investigating the geochemical characteristics of the feeding magma. New data on major and trace element geochemistry of olivine-hosted melt inclusions (MI) in volcanic products are presented together with the noble gas geochemistry of fluid inclusions (FI) in olivines. The noble gas geochemistry of fluid inclusions (FIs) in olivines was also investigated. The major element composition of MIs is variable from tephrite/trachybasalt to phonotephrite/basaltic trachyandesite

Testing the asymptotic relation for period spacings from mixed modes of red giants observed with the Kepler mission

Dipole mixed pulsation modes of consecutive radial order have been detected for thousands of low-mass red-giant stars with the NASA space telescope Kepler. Such modes have the potential to reveal information on the physics of the deep stellar interior. Different methods have been proposed to derive an observed value for the gravity-mode period spacing, the most prominent one relying on a relation derived from asymptotic pulsation theory applied to the gravity-mode character of the mixed modes. Our aim is to compare results based on this asymptotic relation with those derived from an empirical approach for three pulsating red-giant stars. We developed a data-driven method to perform frequency extraction and mode identification. Next, we used the identified dipole mixed modes to determine the gravity-mode period spacing by means of an empirical method and by means of the asymptotic relation. In our methodology, we consider the phase offset, $\epsilon_{\mathrm{g}}$, of the asymptotic relation as a free parameter. Using the frequencies of the identified dipole mixed modes for each star in the sample, we derived a value for the gravity-mode period spacing using the two different methods. These differ by less than 5%. The average precision we achieved for the period spacing derived from the asymptotic relation is better than 1%, while that of our data-driven approach is 3%. Good agreement is found between values for the period spacing derived from the asymptotic relation and from the empirical method. Full abstract in PDF file.Comment: 14 pages, 13 figures, accepted for publication in A&

The HERMES Solar Atlas and the spectroscopic analysis of the seismic solar analogue KIC3241581

Solar-analog stars provide an excellent opportunity to study the Sun's evolution, i.e. the changes with time in stellar structure, activity, or rotation for solar-like stars. The unparalleled photometric data from the NASA space telescope Kepler allows us to study and characterise solar-like stars through asteroseismology. We aim to spectroscopically investigate the fundamental parameter and chromospheric activity of solar analogues and twins, based on observations obtained with the HERMES spectrograph and combine them with asteroseismology. Therefore, we need to build a solar atlas for the spectrograph, to provide accurate calibrations of the spectroscopically determined abundances of solar and late type stars observed with this instrument and thus perform differential spectral comparisons. We acquire high-resolution and high signal-to-noise spectroscopy to construct three solar reference spectra by observing the reflected light of Vesta and Victoria asteroids and Europa (100<S/N<450) with the \Hermes spectrograph. We then observe the Kepler solar analog KIC3241581 (S/N~170). We constructed three solar spectrum atlases from 385 to 900 nm obtained with the Hermes spectrograph from observations of two bright asteroids and Europa. A comparison between our solar spectra atlas to the Kurucz and HARPS solar spectrum shows an excellent agreement. KIC3241581 was found to be a long-periodic binary system. The fundamental parameter for the stellar primary component are Teff=5689+/-11K, logg=4.385+/-0.005, [Fe/H]=+0.22+/-0.01, being in agreement with the published global seismic values confirming its status of solar analogue. KIC 3241581 is a metal rich solar analogue with a solar-like activity level in a binary system of unknown period. The chromospheric activity level is compatible to the solar magnetic activity.Comment: 12 pages, 8 figures, accepted for publication in A&

Reply to comment by D. Carbone and D. Patanè on “Multi-disciplinary investigation on a lava fountain preceding a flank eruption: the 10 May 2008 Etna case”

Bonaccorso et al. [2011a] investigated the source and magma dynamics of the 10 May 2008 lava fountain at the South-East Crater (SEC) of Mount Etna through a multidisciplinary approach that integrated a wide data set ranging from bulk rock compositions of the erupted products to seismic tremor and long-period events, tilt and gravity signals. Using a large dataset, the study provided a robust framework in which the mechanism of the 10 May 2008 lava fountain is explained as a violent release of bubble-rich magma layer previously trapped at the top of a shallow reservoir located between −0.5 and 1.5 km above sea level (asl). This result is in agreement with recent relevant literature [Allard et al., 2005; Vergniolle and Ripepe, 2008; Aiuppa et al., 2010; Andronico and Corsaro, 2011; Bonaccorso et al., 2011b; Calvari et al., 2011; Vergniolle and Gaudemer, 2012]. In the introduction of their comment Carbone and Patanè [submitted] affirm that in their opinion the interpretation that “the lava fountain was generated by the fragmentation of a foam layer trapped at the top of shallow reservoir” is not soundly based. This comment’s conclusion is puzzling because one of the comment’s authors (D. Patanè) is also a co-author on the paper by Aiuppa et al. [2010] where the same conclusion, now criticized, was well supported (see figure 5 and conclusions of that paper). In particular, in the conclusions Aiuppa et al. [2010] reported that “The paroxysmal SEC episodes mark the violent release of a bubble-rich magma layer, with bubbles having relatively shallow reservoir ...", that is, the same conclusion now criticized in the comment. After this, the comment raises issues concerning the analysis and interpretation of gravity and tilt data in the multidisciplinary approach presented by Bonaccorso et al. [2011a]. The comment by Carbone and Patanè is divided into 4 paragraphs, labelled “1. Introduction”, “2. Gravity changes”, “3. Tilt changes” and “4. Concluding remarks” with only paragraphs 2 and 3 containing specific comments. In this reply, we address these two paragraphs, and we shall show how the assumptions underlying the comment are merely speculative and why the results presented by Bonaccorso et al.[2011a] remain valid

SAT0460 INGESTION OF LEMON JUICE MAY MODULATE BONE METABOLISM.

Background:An association between bone health and consumption of citrus fruits have been previously reported; however, the effect of lemon juice on bone metabolism have not been explored yet.Objectives:To investigate bone metabolic changes in postmenopausal women assuming lemon juice.Methods:Participants were postmenopausal osteoporotic women without history of clinical fractures who agreed to enrich their diet with lemon juice (Acti Lemon, Polenghi) over a 2-month period. The daily juice dose of 30 ml we suggested was equivalent to one Sicilian organic lemon. Surrogate markers of bone formation as procollagen type 1 N-propeptide (P1NP) and of bone resorption as C-terminal telopeptide of type I collagen (CTX), but also some regulators of bone metabolism as RANK-L, OPG, RANK-L/OPG ratio and sclerostin were assessed at baseline and then at 1 and 2 months after lemon juice administration. Controls were represented by a placebo group of age-matched osteoporotic postmenopausal women.Results:47 participants [mean age 60.2 ± 4.1 yr.] completed the study, without reporting any adverse events. Lemon juice was well tolerated. Over the observation period modifications of bone metabolism occurred: we detected a decreased RANK-L/OPG ratio and increased CTX levels at all time points vs. baseline. Particularly, change at month-1 of sclerostin (versus baseline) has been positively associated with change at month-1 and month-2 of CTX (r=0.46, p=0.01 and r=0.43, p=0.01, respectively). Change at month-1 of OPG was positively associated with change at month-1 of P1NP (r=0.49, p=0.006). Change at month-1 of RANKL/OPG has been related with variation at day 30 of P1NP (r=-0.44, p=0.013). Variation of P1NP at month-1 was related with sclerostin variation at day 30 (r=-0.56, p=0.02) and month-2 vs. baseline value (r=0.44, p=0.017) and with sclerostin variation between month-1 and month-2 (r=0.69, p<0.001). Variation of P1NP between month-1 and month-2 was associated with RANKL change at month-1 (r=-0.35, p=0.05), with sclerostin change at month-1 (r=-0.49, p=0.008) and with sclerostin change between month-1 and month-2 (r=0.41, p=0.028). At a multiple regression analysis the change of P1NP between month-1 and month-2 was independently predicted by the change of sclerostin at month-1 (ß=-1.5, SE 0.5, p=0.006), after correcting for age, BMI and change of RANKL and CTX levels at month-1. No significant modifications raised from controls.Conclusion:Drinking lemon juice may boost bone metabolic changes involving both bone resorption and bone formation.Disclosure of Interests:None declare