Planet transit and stellar granulation detection with interferometry: Using the three-dimensional stellar atmosphere S tagger -grid simulations

Context. Stellar activity and, in particular, convection-related surface structures, potentially cause bias in planet detection and characterisation. In the latter, interferometry can help disentangle the signal of the transiting planet. Aims. We used realistic three-dimensional (3D) radiative hydrodynamical (RHD) simulations from the Stagger-grid and synthetic images computed with the radiative transfer code Optim3D to provide interferometric observables to extract the signature of stellar granulation and transiting planets. Methods. We computed intensity maps from RHD simulations and produced synthetic stellar disk images as a nearby observer would see, thereby accounting for the centre-to-limb variations. We did this for twelve interferometric instruments covering wavelengths ranging from optical to infrared. We chose an arbitrary date and arbitrary star with coordinates, and this ensures observability throughout the night. This optimisation of observability allows for a broad coverage of spatial frequencies. The stellar surface asymmetries in the brightness distribution mostly affect closure phases, because of either convection-related structures or a faint companion. We then computed closure phases for all images and compared the system star with a transiting planet and the star alone. We considered the impact of magnetic spots with the construction of a hypothetical starspot image and compared the resulting closure phases with the system star that has a transiting planet. Results. We analysed the impact of convection at different wavelengths. All the simulation depart from the axisymmetric case (closure phases not equal to 0 or ± π) at all wavelengths. The levels of asymmetry and inhomogeneity of stellar disk images reach high values with stronger effects from the 3rd visibility lobe on. We present two possible targets (Beta Com and Procyon) either in the visible or in the infrared and find that departures up to 16° can be detected on the 3rd lobe and higher. In particular, MIRC is the most appropriate instrument because it combines good UV coverage and long baselines. Moreover, we explored the impact of convection on interferometric planet signature for three prototypes of planets with sizes corresponding to one hot Jupiter, one hot Neptune, and a terrestrial planet. The signature of the transiting planet in the closure phase is mixed with the signal due to the convection-related surface structures, but it is possible to disentangle it at particular wavelengths (either in the infrared or in the optical) by comparing the closure phases of the star at difference phases of the planetary transit. It must be noted that starspots caused by the magnetic field may pollute the granulation and the transiting planet signals. However, it is possible to differentiate the transiting planet signal because the time scale of a planet crossing the stellar disk is much smaller than the typical rotational modulation of a star. Conclusions. Detection and characterisation of planets must be based on a comprehensive knowledge of the host star, and this includes the detailed study of the stellar surface convection with interferometric techniques. In this context, RHD simulations are crucial for this aim. We emphasise that interferometric observations should be pushed at high spatial frequencies by accumulating observations on closure phases at short and long baselines

Polyvinylamine membranes containing graphene-based nanofillers for carbon capture applications

In the present study, the separation performance of new self-standing polyvinylamine (PVAm) membranes loaded with few-layer graphene (G) and graphene oxide (GO) was evaluated, in view of their use in carbon capture applications. PVAm, provided by BASF as commercial product named Lupamin\u2122, was purified obtaining PVAm films with two degrees of purification: Low Grade (PVAm-LG) and High Grade (PVAm-HG). These two-grade purified PVAm were loaded with 3 wt% of graphene and graphene oxide to improve mechanical stability: indeed, pristine tested materials proved to be brittle when dry, while highly susceptible to swelling in humid conditions. Purification performances were assessed through FTIR-ATR spectroscopy, DSC and TGA analysis, which were carried out to characterize the pristine polymer and its nanocomposites. In addition, the membranes\u2032 fracture surfaces were observed through SEM analysis to evaluate the degree of dispersion. Water sorption and gas permeation tests were performed at 35 \ub0C at different relative humidity (RH), ranging from 50% to 95%. Overall, composite membranes showed improved mechanical stability at high humidity, and higher glass transition temperature (Tg) with respect to neat PVAm. Ideal CO2/N2 selectivity up to 80 was measured, paired with a CO2 permeability of 70 Barrer. The membranes\u2019 increased mechanical stability against swelling, even at high RH, without the need of any crosslinking, represents an interesting result in view of possible further development of new types of facilitated transport composite membranes

Asymmetries on red giant branch surfaces from CHARA/MIRC optical interferometry

Context. Red giant branch (RGB) stars are very bright objects in galaxies and are often used as standard candles. Interferometry is the ideal tool to characterize the dynamics and morphology of their atmospheres. Aims. We aim at precisely characterising the surface dynamics of a sample of RGB stars. Methods. We obtained interferometric observations for three RGB stars with the MIRC instrument mounted at the CHARA interfer- ometer. We looked for asymmetries on the stellar surfaces using limb-darkening models. Results. We measured the apparent diameters of HD197989 (Epsilon Cyg) = 4.61+-0.02 mas, HD189276 (HR7633) = 2.95+-0.01 mas, and HD161096 (Beta Oph) = 4.43+-0.01 mas. We detected departures from the centrosymmetric case for all three stars with the tendency of a greater effect for lower logg of the sample. We explored the causes of this signal and conclude that a possible explanation to the interferometric signal is the convection-related and/or the magnetic-related surface activity. However, it is necessary to monitor these stars with new observations, possibly coupled with spectroscopy, in order to firmly establish the cause.Comment: Accepted for publication as a Letter in Astronomy and Astrophysics, section 1. Letters to the Editor. The official date of acceptance is 06/03/201

Searching for galactic axions through magnetized media: QUAX status report

The current status of the QUAX R\&D program is presented. QUAX is a feasibility study for a detection of axion as dark matter based on the coupling to the electrons. The relevant signal is a magnetization change of a magnetic material placed inside a resonant microwave cavity and polarized with a static magnetic field.Comment: Contributed to the 13th Patras Workshop on Axions, WIMPs and WISPs, Thessaloniki, May 15 to 19, 201

Axion search with a quantum-limited ferromagnetic haloscope

A ferromagnetic axion haloscope searches for Dark Matter in the form of axions by exploiting their interaction with electronic spins. It is composed of an axion-to-electromagnetic field transducer coupled to a sensitive rf detector. The former is a photon-magnon hybrid system, and the latter is based on a quantum-limited Josephson parametric amplifier. The hybrid system consists of ten 2.1 mm diameter YIG spheres coupled to a single microwave cavity mode by means of a static magnetic field. Our setup is the most sensitive rf spin-magnetometer ever realized. The minimum detectable field is $5.5\times10^{-19}\,$T with 9 h integration time, corresponding to a limit on the axion-electron coupling constant $g_{aee}\le1.7\times10^{-11}$ at 95% CL. The scientific run of our haloscope resulted in the best limit on DM-axions to electron coupling constant in a frequency span of about 120 MHz, corresponding to the axion mass range $42.4$-$43.1\,\mu$eV. This is also the first apparatus to perform an axion mass scanning by changing the static magnetic field.Comment: 4 pages, 4 figure

Improving the surface brightness-color relation for early-type stars using optical interferometry

The aim of this work is to improve the SBC relation for early-type stars in the $-1 \leq V-K \leq 0$ color domain, using optical interferometry. Observations of eight B- and A-type stars were secured with the VEGA/CHARA instrument in the visible. The derived uniform disk angular diameters were converted into limb darkened angular diameters and included in a larger sample of 24 stars, already observed by interferometry, in order to derive a revised empirical relation for O, B, A spectral type stars with a V-K color index ranging from -1 to 0. We also took the opportunity to check the consistency of the SBC relation up to $V-K \simeq 4$ using 100 additional measurements. We determined the uniform disk angular diameter for the eight following stars: $\gamma$ Ori, $\zeta$ Per, $8$ Cyg, $\iota$ Her, $\lambda$ Aql, $\zeta$ Peg, $\gamma$ Lyr, and $\delta$ Cyg with V-K color ranging from -0.70 to 0.02 and typical precision of about $1.5\%$. Using our total sample of 132 stars with $V-K$ colors index ranging from about $-1$ to $4$, we provide a revised SBC relation. For late-type stars ($0 \leq V-K \leq 4$), the results are consistent with previous studies. For early-type stars ($-1 \leq V-K \leq 0$), our new VEGA/CHARA measurements combined with a careful selection of the stars (rejecting stars with environment or stars with a strong variability), allows us to reach an unprecedented precision of about 0.16 magnitude or $\simeq 7\%$ in terms of angular diameter.Comment: 13 pages, 5 figures, accepted for publication in A&

Biogenesis of Pro-senescent Microparticles by Endothelial Colony Forming Cells from Premature Neonates is driven by SIRT1-Dependent Epigenetic Regulation of MKK6.

Senescent cells may exert detrimental effect on microenvironment through the secretion of soluble factors and the release of extracellular vesicles, such as microparticles, key actors in ageing and cardiovascular diseases. We previously reported that sirtuin-1 (SIRT1) deficiency drives accelerated senescence and dysfunction of endothelial colony-forming cells (ECFC) in PT neonates. Because preterm birth (PT) increases the risk for cardiovascular diseases during neonatal period as well as at adulthood, we hypothesized that SIRT1 deficiency could control the biogenesis of microparticles as part of a senescence-associated secretory phenotype (SASP) of PT-ECFC and investigated the related molecular mechanisms. Compared to control ECFC, PT-ECFC displayed a SASP associated with increased release of endothelial microparticles (EMP), mediating a paracrine induction of senescence in naïve endothelial cells. SIRT1 level inversely correlated with EMP release and drives PT-ECFC vesiculation. Global transcriptomic analysis revealed changes in stress response pathways, specifically the MAPK pathway. We delineate a new epigenetic mechanism by which SIRT1 deficiency regulates MKK6/p38 <sup>MAPK</sup> /Hsp27 pathway to promote EMP biogenesis in senescent ECFC. These findings deepen our understanding of the role of ECFC senescence in the disruption of endothelial homeostasis and provide potential new targets towards the control of cardiovascular risk in individuals born preterm

Recent inversion of the Tyrrhenian Basin

The Tyrrhenian Basin is a region created by Neogene extensional tectonics related to slab rollback of the east-southeast–migrating Apennine subduction system, commonly believed to be actively underthrusting the Calabrian arc. A compilation of >12,000 km of multichannel seismic profiles, much of them recently collected or reprocessed, provided closer scrutiny and the mapping of previously undetected large compressive structures along the Tyrrhenian margin. This new finding suggests that Tyrrhenian Basin extension recently ceased. The ongoing compressional reorganization of the basin indicates a change of the regional stress field in the area, confirming that slab rollback is no longer a driving mechanism for regional kinematics, now dominated by the Africa-Eurasia lithospheric collision

A 19 to 17 Ma amagmatic extension event at the Mid-Atlantic Ridge: Ultramafic mylonites from the Vema Lithospheric Section

A >300 km long lithospheric section (Vema Lithospheric Section or VLS) is exposed south of the Vema transform at 11°N in the Atlantic. It is oriented along a seafloor spreading flow line and represents ∼26 Ma of accretion at a single 80 km long segment (EMAR) of the Mid-Atlantic Ridge. The basal part of the VLS exposes a mantle unit made mostly of relatively undeformed coarse-grained/porphyroclastic peridotites that were sampled at close intervals. Strongly deformed mylonitic peridotites were found at 14 contiguous sites within a ∼80 km stretch (∼4.7 Ma interval); they are dominant in a time interval of 1.4 Ma, from crustal ages of 16.8 to 18.2 Ma (mylonitic stretch). Some of the mylonites are "dry," showing anhydrous high-T deformation, but most contain amphibole. The mylonitic peridotites tend to be less depleted than the porphyroclastic peridotites on the basis of mineral major and trace elements composition, suggesting that the mylonites parent was a subridge mantle that underwent a relatively low degree of melting. The Sr, Nd, and O isotopic composition of the amphiboles is MORB-like and suggests either that seawater did not contribute to their isotopic signature or that their isotopic ratios re-equilibrated during fluid circulation in the upper mantle. Four 40Ar/39Ar ages, on three amphiboles separated from the peridotites, are close to crustal ages predicted from magnetic anomalies, confirming that the amphiboles formed close to ridge axis. We propose that crustal accretion at the EMAR segment has been mostly symmetrical for the 26 Ma of its recorded history, except for the ∼1.4 Ma interval of prevalent ultramafic mylonites (mylonitic stretch) that may record a period of quasi-amagmatic asymmetric accretion of oceanic lithosphere close to the ridge–Vema transform intersection, possibly with development of detachment faults. This interval may correspond to a thermal minimum of the subridge upwelling mantle, marking the transition from a period of decreasing to one of increasing mantle melting below the EMAR segment