Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>As part of the NASA Starlight collaboration, we look at the implications of impacts with the interstellar medium (ISM) on a directed energy-driven relativistic spacecraft. The spacecraft experiences a stream of MeV/nucleon impacts along the forward edge primarily from hydrogen and helium nuclei. The accumulation of implanted slowly diffusing gas atoms in solids drives damage through the meso-scale processes of bubble formation, blistering, and exfoliation. This results in macroscopic changes to material properties and, in the cases of blistering and exfoliation, material erosion via blister rupture and delamination. Relativistic hydrogen and helium at constant velocity will stop in the material at a similar depth, as predicted by Bethe–Bloch stopping and subsequent simulations of the implantation distribution, leading to a mixed hydrogen and helium system similar to that observed within fusion plasma-facing components. However, the difference in depth of near-surface gas atoms with respect to the direction of exposure means that previously developed empirical models of blistering cannot be used to predict bubble formation or blistering onset. In this work, we present a model of the local gas concentration threshold for material blistering from exposure to the ISM at relativistic speeds. Expected effects on the spacecraft and mitigation strategies are also discussed. The same considerations apply to the Breakthrough Starshot mission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Some supernovae, such as pair-instability supernovae, are predicted to have a duration of more than a year in the observer frame. To constrain the rates of supernovae lasting for more than a year, we conducted a long-term deep transient survey using Hyper Suprime-Cam (HSC) on the 8.2 m Subaru telescope. HSC is a wide-field (a 1.75 deg<jats:sup>2</jats:sup> field-of-view) camera and it can efficiently conduct transient surveys. We observed the same 1.75 deg<jats:sup>2</jats:sup> field repeatedly using the <jats:italic>g-</jats:italic>, <jats:italic>r-</jats:italic>, <jats:italic>i-</jats:italic>, and <jats:italic>z-</jats:italic>band filters with the typical depth of 26 mag for four seasons (from late 2016 to early 2020). Using these data, we searched for transients lasting for more than a year. Two supernovae were detected in two continuous seasons, one supernova was detected in three continuous seasons, but no transients lasted for all four seasons searched. The discovery rate of supernovae lasting for more than a year with the typical limiting magnitudes of 26 mag is constrained to be <jats:inline-formula> <jats:tex-math> <?CDATA ${1.4}_{-0.7}^{+1.3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcfc0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:inline-formula> <jats:tex-math> <?CDATA $(\mathrm{stat}.){}_{-0.3}^{+0.2}(\mathrm{sys}.)\,\mathrm{events}\,{\deg }^{-2}\,{\mathrm{yr}}^{-1}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabcfc0ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. All the long-lasting supernovae we found are likely Type IIn supernovae and our results indicate that about 40% of Type IIn supernovae have long-lasting light curves. No plausible pair-instability supernova candidates lasting for more than a year are discovered. By comparing the survey results and survey simulations, we constrain the luminous pair-instability supernova rate up to <jats:italic>z</jats:italic> ≃ 3 is of the order of 100 Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup> at most, which is 0.01–0.1% of the core-collapse supernova rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Atacama Large Millimeter/submillimeter Array observations of a protoplanetary disk around the T Tauri star Sz 84 and analyses of the structures of the inner cavity in the central region of the dust disk. Sz 84's spectral energy distribution (SED) has been known to exhibit negligible infrared excess at <jats:italic>λ</jats:italic>  ≲ 10 <jats:italic>μ</jats:italic>m due to the disk’s cavity structure. Analyses of the observed visibilities of dust continuum at 1.3 mm and the SED indicate that the size of the cavity in the disk of large (millimeter size) dust grains is 8 au in radius and that in the disk of small (submicron size) dust grains is 60 au in radius. Furthermore, from the SED analyses, we estimate that the upper limit mass of small dust grains at <jats:italic>r</jats:italic> &lt; 60 au is less than ∼10<jats:sup>−3</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub>, which is ≲0.01% of the total (small + large) dust mass at <jats:italic>r</jats:italic> &lt; 60 au. These results suggest that large dust grains are dominant at <jats:italic>r</jats:italic> &lt; 60 au, implying that dust grains efficiently grow with less efficient fragmentation in this region, potentially due to weak turbulence and/or stickier dust grains. The balance of grain growth and dust fragmentation is an important factor for determining the size of large dust grains in protoplanetary disks, and thus Sz 84 could serve as a good testbed for investigations of grain growth in such disks.</jats:p>