Characterizing CO Fourth Positive Emission in Young Circumstellar Disks

Carbon Monoxide is a commonly used IR/sub-mm tracer of gas in protoplanetary disks. We present an analysis of ultraviolet CO emission in {HST}-COS spectra for 12 Classical T Tauri stars. Several ro-vibrational bands of the CO A^1\Pi - X^1\Sigma^+ (Fourth Positive) electronic transition system are spectrally resolved from emission of other atoms and H_2. The CO A^1\Pi v'=14 state is populated by absorption of Ly\alpha photons, created at the accretion column on the stellar surface. For targets with strong CO emission, we model the Ly\alpha radiation field as an input for a simple fluorescence model to estimate CO rotational excitation temperatures and column densities. Typical column densities range from N_{CO} = 10^{18} - 10^{19} cm^{-2}. Our measured excitation temperatures are mostly below T_{CO} = 600 K, cooler than typical M-band CO emission. These temperatures and the emission line widths imply that the UV emission originates in a different population of CO than that which is IR-emitting. We also find a significant correlation between CO emission and the disk accretion rate M_{acc} and age. Our analysis shows that ultraviolet CO emission can be a useful diagnostic of CTTS disk gas

The Nature of the Secondary Star in the Black Hole X-Ray Transient V616 Mon (=A0620-00)

We have used NIRSPEC on Keck II to obtain $K$-band spectroscopy of the low mass X-ray binary V616 Mon (= A0620$-$00). V616 Mon is the proto-typical soft x-ray transient containing a black hole primary. As such it is important to constrain the masses of the binary components. The modeling of the infrared observations of ellipsoidal variations in this system lead to a derived mass of 11.0 M_{\sun} for the black hole. The validity of this derivation has been called into question due to the possiblity that the secondary star's spectral energy distribution is contaminated by accretion disk emission (acting to dilute the variations). Our new $K$-band spectrum of V616 Mon reveals a late-type K dwarf secondary star, but one that has very weak $^{\rm 12}$CO absorption features. Comparison of V616 Mon with SS Cyg leads us to estimate that the accretion disk supplies only a small amount of $K$-band flux, and the ellipsoidal variations are not seriously contaminated. If true, the derived orbital inclination of V616 Mon is not greatly altered, and the mass of the black hole remains large. A preliminary stellar atmosphere model for the $K$-band spectrum of V616 Mon reveals that the carbon abundance is approximately 50% of the solar value. We conclude that the secondary star in V616 Mon has either suffered serious contamination from the accretion of supernova ejecta that created the black hole primary, or it is the stripped remains of a formerly more massive secondary star, one in which the CNO cycle had been active.Comment: 20 pages, 5 figure

A Model-Driven Methodology Approach for Developing a Repository of Models

International audienceTo cope with the growing complexity of embedded system design, several development approaches have been proposed. The most popular are those using models as main artifacts to be constructed and maintained. The wanted role of models is to ease, systematize and standardize the approach of the construction of software-based systems. In order to enforce reuse and to interconnect the process of models’ specification and the system development with models, we promote a model-based approach coupled with a repository of models. In this paper, we propose a Model-Driven Engineering methodological approach for the development of a repository of models and an operational architecture for development tools. In particular, we show the feasibility of our own approach by reporting some preliminary prototype providing a model-based repository of security and dependability (S&D) pattern models

First observation of 55,56Zn

In an experiment at the SISSI/LISE3 facility of GANIL, the most proton-rich zinc isotopes 55,56Zn have been observed for the first time. The experiment was performed using a high-intensity 58Ni beam at 74.5 MeV/nucleon impinging on a nickel target. The identification of 55,56Zn opens the way to 54Zn, a good candidate for two-proton radioactivity according to theoretical predictions.Comment: 2 pages, 1 figure, accepted for publication in Eur. Phys. J.

Decay of proton-rich nuclei between 39Ti and 49Ni

Decay studies of very neutron-deficient nuclei ranging from 39Ti to 49Ni have been performed during a projectile fragmentation experiment at the GANIL/LISE3 separator. For all nuclei studied in this work, 39,40Ti, 42,43Cr, 46Mn, 45,46,47Fe and 49Ni, half-lives and decay spectra have been measured. In a few cases, gamma coincidence measurements helped to successfully identify the initial and final states of transitions. In these cases, partial decay scheme are proposed. For the most exotic isotopes, 39Ti, 42Cr, 45Fe and 49Ni, which are candidates for two-proton radioactivity from the ground state, no clear evidence of this process is seen in our spectra and we conclude rather on a delayed particle decay.Comment: 12 pages, 15 figures, submitted for publication in Eur. Phys. J.

Suppressed Far-UV stellar activity and low planetary mass-loss in the WASP-18 system

WASP-18 hosts a massive, very close-in Jupiter-like planet. Despite its young age (R′HK activity parameter lies slightly below the basal level; there is no significant time-variability in the log R′HK value; there is no detection of the star in the X-rays. We present results of far-UV observations of WASP-18 obtained with COS on board of HST aimed at explaining this anomaly. From the star’s spectral energy distribution, we infer the extinction (E(B − V) ≈ 0.01mag) and then the ISM column density for a number of ions, concluding that ISM absorption is not the origin of the anomaly. We measure the flux of the four stellar emission features detected in the COS spectrum (C II, C III, C IV, Si IV). Comparing the C II/C IV flux ratio measured for WASP-18 with that derived from spectra of nearby stars with known age, we see that the far-UV spectrum of WASP-18 resembles that of old (>5Gyr), inactive stars, in stark contrast with its young age. We conclude that WASP-18 has an intrinsically low activity level, possibly caused by star-planet tidal interaction, as suggested by previous studies. Re-scaling the solar irradiance reference spectrum to match the flux of the Si IV line, yields an XUV integrated flux at the planet orbit of 10.2 erg s−1 cm−2. We employ the rescaled XUV solar fluxes to model of the planetary upper atmosphere, deriving an extremely low thermal mass-loss rate of 10−20MJ Gyr−1. For such high-mass planets, thermal escape is not energy limited, but driven by Jeans escape

On the discovery of doubly-magic 48^{48}Ni

The paper reports on the first observation of doubly-magic Nickel-48 in an experimental at the SISSI/LISE3 facility of GANIL. Four Nickel-48 isotopes were identified. In addition, roughly 100 Nickel-49, 50 Iron-45, and 290 Chromium-42 isotopes were observed. This opens the possibility to search for two-proton emission from these nuclei.Comment: 4 pages, 3 figures, accepted for publication in Phys. Rev. Let

Life Beyond the Solar System: Space Weather and Its Impact on Habitable Worlds

The search of life in the Universe is a fundamental problem of astrobiology and a major priority for NASA. A key area of major progress since the NASA Astrobiology Strategy 2015 (NAS15) has been a shift from the exoplanet discovery phase to a phase of characterization and modeling of the physics and chemistry of exoplanetary atmospheres, and the development of observational strategies for the search for life in the Universe by combining expertise from four NASA science disciplines including heliophysics, astrophysics, planetary science and Earth science. The NASA Nexus for Exoplanetary System Science (NExSS) has provided an efficient environment for such interdisciplinary studies. Solar flares, coronal mass ejections and solar energetic particles produce disturbances in interplanetary space collectively referred to as space weather, which interacts with the Earth upper atmosphere and causes dramatic impact on space and ground-based technological systems. Exoplanets within close in habitable zones around M dwarfs and other active stars are exposed to extreme ionizing radiation fluxes, thus making exoplanetary space weather (ESW) effects a crucial factor of habitability. In this paper, we describe the recent developments and provide recommendations in this interdisciplinary effort with the focus on the impacts of ESW on habitability, and the prospects for future progress in searching for signs of life in the Universe as the outcome of the NExSS workshop held in Nov 29 - Dec 2, 2016, New Orleans, LA. This is one of five Life Beyond the Solar System white papers submitted by NExSS to the National Academy of Sciences in support of the Astrobiology Science Strategy for the Search for Life in the Universe.Comment: 5 pages, the white paper was submitted to the National Academy of Sciences in support of the Astrobiology Science Strategy for the Search for Life in the Univers

Mitigating impacts of the COVID-19 pandemic on primary and lower secondary children during school closures: a rapid evidence review

BACKGROUND: To control the spread of the SARS-CoV-2 virus during the COVID-19 pandemic, UK schools were closed and education activity was undertaken at home resulting in considerable disruption to children’s education. AIMS: To identify and assess evidence of harms caused to primary and lower secondary pupils during this time and identify mitigation strategies relevant to those harms. METHODS: A rapid evidence review tailored to delivery at pace, drawing on UK evidence for harms and relevant mitigation strategies. FINDINGS ON HARM: There is evidence that the patterns of disruption to education during the pandemic have impacted on children’s learning and attainment, mental health and wellbeing, physical health and nutrition and increased exposure to risk especially for those children living in potentially dangerous domestic settings. Although the quality of the evidence is uneven, it is clear that children living in poverty have been most affected, in particular through food insecurity and conditions triggering stress and anxiety in the home, alongside their more limited opportunities to access digital resources for learning, or indeed outside space for physical activity. Attempts to distinguish harms that impact in the short term from longer lasting harms may take time. It also requires schools to have access to contextually relevant diagnostic tools they can use to assess the range of harms in need of redress in their local context. FINDINGS ON MITIGATION STRATEGIES: We found no evidence for mitigation strategies directly relevant to the harms experienced by children due to school closures under COVID-19. Mitigation strategies suggested in the UK often derived their evidence of efficacy from circumstances quite unlike the prolonged patterns of disruption to education that COVID has caused. Most were designed to address the needs of a few pupils struggling under normal circumstances and were not able to demonstrate their relevance at scale. We therefore examined the primary literature on recovery from unplanned school closures in other countries focused on school-based strategies that had been evaluated as effective under similar conditions. CONCLUSION: We found some evidence of a range of harms but little research evidence on relevant mitigation strategies and an absence of evidence on those strategies that schools themselves have adopted since re-opening, tailored to local needs. Such mitigation strategies may be highly relevant for system learning, and it is important to document and evaluate their efficacy, and indeed learn from them. Closing schools during the pandemic has revealed the importance of schools in safeguarding children. School staff should be given the training and resources to be able to identify children at risk and refer pupils to appropriate services if necessary