Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Measurements of the dark energy equation-of-state parameter, <jats:italic>w</jats:italic>, have been limited by uncertainty in the selection effects and photometric calibration of <jats:italic>z</jats:italic> &lt; 0.1 Type Ia supernovae (SNe Ia). The Foundation Supernova Survey is designed to lower these uncertainties by creating a new sample of <jats:italic>z</jats:italic> &lt; 0.1 SNe Ia observed on the Pan-STARRS system. Here we combine the Foundation sample with SNe from the Pan-STARRS Medium Deep Survey and measure cosmological parameters with 1338 SNe from a single telescope and a single, well-calibrated photometric system. For the first time, both the low-<jats:italic>z</jats:italic> and high-<jats:italic>z</jats:italic> data are predominantly discovered by surveys that do not target preselected galaxies, reducing selection bias uncertainties. The <jats:italic>z</jats:italic> &gt; 0.1 data include 875 SNe without spectroscopic classifications, and we show that we can robustly marginalize over CC SN contamination. We measure Foundation Hubble residuals to be fainter than the preexisting low-<jats:italic>z</jats:italic> Hubble residuals by 0.046 ± 0.027 mag (stat + sys). By combining the SN Ia data with cosmic microwave background constraints, we find <jats:italic>w</jats:italic> = −0.938 ± 0.053, consistent with ΛCDM. With 463 spectroscopically classified SNe Ia alone, we measure <jats:italic>w</jats:italic> = −0.933 ± 0.061. Using the more homogeneous and better-characterized Foundation sample gives a 55% reduction in the systematic uncertainty attributed to SN Ia sample selection biases. Although use of just a single photometric system at low and high redshift increases the impact of photometric calibration uncertainties in this analysis, previous low-<jats:italic>z</jats:italic> samples may have correlated calibration uncertainties that were neglected in past studies. The full Foundation sample will observe up to 800 SNe to anchor the LSST and <jats:italic>WFIRST</jats:italic> Hubble diagrams.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hydration is a major mineral alteration process in primitive asteroids and it might occur in comet nuclei; however, it is poorly understood at low temperatures, especially below the freezing point of water. Long-duration experiments were performed with exposures of amorphous silicate nanoparticles and organic compounds (glycine and ribose) to D<jats:sub>2</jats:sub>O and D<jats:sub>2</jats:sub>O + NH<jats:sub>3</jats:sub> ices and vapors at temperatures of −17°C and −27°C for 10–120 days; and with exposure of amorphous silicates to H<jats:sub>2</jats:sub>O vapor/liquid at &gt;25°C for 10 days. The amorphous silicates were analyzed by X-ray diffraction and Fourier-transform infrared spectroscopy, and recovery of organic molecules was determined by liquid chromatography–mass spectrometry. No hydration of amorphous silicates or organic compounds was observed after exposure at temperatures below −17°C for 120 days to ices with or without NH<jats:sub>3</jats:sub>, whereas hydration of the amorphous silicates was observed in experiments above room temperature. The estimated thermal history of the nucleus of the short-period comet 67P/Churyumov–Gerasimenko indicates that the surface temperature does not exceed −45°C, even in a region exposed to strong solar illumination during the perihelion passage. Assuming hydration is controlled by the collision frequency between H<jats:sub>2</jats:sub>O molecules and dust particles, the present results indicate that cometary dust does not hydrate for more than 25–510 periods of comet 67P. This is consistent with the absence of phyllosilicates on 67P and suggests that amino acids and sugars have not been altered.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Exploiting a very large library of physically plausible equations of state (EOSs) containing more than 10<jats:sup>7</jats:sup> members and yielding more than 10<jats:sup>9</jats:sup> stellar models, we conduct a survey of the impact that a neutron-star radius measurement via electromagnetic observations can have on the EOS of nuclear matter. Such measurements are soon to be expected from the ongoing <jats:italic>Neutron Star Interior Composition Explorer</jats:italic> mission and will complement the constraints on the EOS from gravitational-wave detections. Thanks to the large statistical range of our EOS library, we can obtain a first quantitative estimate of the commonly made assumption that the high-density part of the EOS is best constrained when measuring the radius of the most massive, albeit rare, neutron stars with masses <jats:italic>M</jats:italic> ≳ 2.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. At the same time, we find that radius measurements of neutron stars with masses <jats:italic>M</jats:italic> ≃ 1.7–1.85 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> can provide the strongest constraints on the low-density part of the EOS. Finally, we quantify how radius measurements by future missions can further improve our understanding of the EOS of matter at nuclear densities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca <jats:sc>ii</jats:sc> 8542 Å and H<jats:italic>α</jats:italic> lines as well as in the photospheric Fe <jats:sc>i</jats:sc> line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca <jats:sc>ii</jats:sc> and H<jats:italic>α</jats:italic> channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave.</jats:p>