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<jats:title>Abstract</jats:title> <jats:p>We explore the evolution of a select grid of solar metallicity stellar models from their pre-main-sequence phase to near their final fates in a neutrino Hertzsprung–Russell diagram, where the neutrino luminosity replaces the traditional photon luminosity. Using a calibrated <jats:monospace>MESA</jats:monospace> solar model for the solar neutrino luminosity (<jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\nu ,\odot }=0.02398$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7f2cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> · <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\gamma ,\odot }=9.1795$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7f2cieqn2.gif" xlink:type="simple" /> </jats:inline-formula> × 10<jats:sup>31</jats:sup> erg s<jats:sup>−1</jats:sup>) as a normalization, we identify ≃0.3 MeV electron neutrino emission from helium burning during the helium flash (peak <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\nu }/{L}_{\nu ,\odot }\simeq {10}^{4}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7f2cieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, flux <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Phi }}}_{\nu ,\mathrm{He}\mathrm{flash}}\simeq 170$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7f2cieqn4.gif" xlink:type="simple" /> </jats:inline-formula> (10 pc/<jats:italic>d</jats:italic>)<jats:sup>2</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> for a star located at a distance of <jats:italic>d</jats:italic> parsec, timescale ≃3 days) and the thermal pulse (peak <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\nu }/{L}_{\nu ,\odot }\simeq {10}^{9}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7f2cieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, flux <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Phi }}}_{\nu ,\mathrm{TP}}\simeq 1.7$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7f2cieqn6.gif" xlink:type="simple" /> </jats:inline-formula> × 10<jats:sup>7</jats:sup> (10 pc/<jats:italic>d</jats:italic>)<jats:sup>2</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, timescale ≃0.1 yr) phases of evolution in low-mass stars as potential probes for stellar neutrino astronomy. We also delineate the contribution of neutrinos from nuclear reactions and thermal processes to the total neutrino loss along the stellar tracks in a neutrino Hertzsprung–Russell diagram. We find, broadly but with exceptions, that neutrinos from nuclear reactions dominate whenever hydrogen and helium burn, and that neutrinos from thermal processes dominate otherwise.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Following the success of the first mission, the High-Resolution Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1) on 2018 May 29 from the White Sands Missile Range, NM, USA. On this occasion, 329 s of 17.2 nm data of target active region AR 12712 were captured with a cadence of ≈4 s, and a plate scale of 0.″129 pixel<jats:sup>−1</jats:sup>. Using data captured by Hi-C 2.1 and co-aligned observations from <jats:italic>SDO</jats:italic>/AIA 17.1 nm, we investigate the widths of 49 coronal strands. We search for evidence of substructure within the strands that is not detected by AIA, and further consider whether these strands are fully resolved by Hi-C 2.1. With the aid of multi-scale Gaussian normalization, strands from a region of low emission that can only be visualized against the contrast of the darker, underlying moss are studied. A comparison is made between these low-emission strands and those from regions of higher emission within the target active region. It is found that Hi-C 2.1 can resolve individual strands as small as ≈202 km, though the more typical strand widths seen are ≈513 km. For coronal strands within the region of low emission, the most likely width is significantly narrower than the high-emission strands at ≈388 km. This places the low-emission coronal strands beneath the resolving capabilities of <jats:italic>SDO</jats:italic>/AIA, highlighting the need for a permanent solar observatory with the resolving power of Hi-C.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Radio observations of some asymptotic giant branch (AGB) star envelopes show excess emission at frequencies below 100 GHz that cannot be explained by thermal dust emission (hereafter anomalous microwave emission (AME)). Moreover, AGB envelopes are a common place where gas molecules condense to form nanoparticles (e.g., polycyclic aromatic hydrocarbons) and large grains. In this paper, we study whether electric dipole emission from rapidly spinning nanoparticles can reproduce the AME observed toward AGB stars. To properly model the size distribution of nanoparticles in the AGB envelope, we take into account both the increase of nanoparticles due to rotational disruption of large grains spun up by radiative torques and the decrease of the smallest nanoparticles due to rotational disruption driven by stochastic gas collisions. We then perform detailed modeling of microwave emission from rapidly spinning nanoparticles from both C-rich and O-rich AGB envelopes using the grain-size distribution constrained by rotational disruption. We find that spinning dust emission is dominant over thermal dust emission at frequencies below 100 GHz. We attempt to fit the observational data of AME using our spinning dust model and demonstrate that spinning dust can reproduce the observed AME in six AGB stars. Finally, we discuss how microwave emission from spinning dust in AGB envelopes could be observed with high-resolution upcoming radio telescopes such the Next Generation Very Large Array and Atacama Large Millimeter/submillimeter Array Band 1. This would be a major leap for understanding AGB envelopes’ formation, evolution, and internal structures of dust. Observations would help to distinguish the carrier of AME via comparisons of C-rich and O-rich stars, because polycyclic aromatic hydrocarbons (PAHs) are formed in C-rich AGB stars, while silicates are formed in O-rich stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The scaling anisotropy is crucial to interpret the nonlinear interactions in solar wind turbulence. Previous observations provide diverse results and the structure function analyses are also reported to be an approach to investigate the scaling anisotropy based on a local magnetic field. However, the determination of the sampling angle with respect to the local background magnetic field requires that the observed time series for the average are time stationary. Whether or not this required time stationarity is compatible with the measurements has not been investigated. Here we utilize the second-order structure function method to study the scaling anisotropy with a time-stationary background field. We analyze 88 fast solar wind intervals each with time durations ≥ 2 days measured by <jats:italic>WIND</jats:italic> spacecraft in the period 2005–2018. We calculate the local magnetic field as the average of the time series <jats:inline-formula> <jats:tex-math> <?CDATA ${\boldsymbol{B}}(t^{\prime} )$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7b72ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> whose time stationarity is fulfilled by our criterion <jats:italic>ϕ</jats:italic> &lt; 10° (<jats:italic>ϕ</jats:italic> is the angle between the two averaged magnetic fields after cutting <jats:inline-formula> <jats:tex-math> <?CDATA ${\boldsymbol{B}}(t^{\prime} )$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7b72ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> into two halves). We find for the first time the isotropic scaling feature of the magnetic-trace structure functions with scaling indices <jats:inline-formula> <jats:tex-math> <?CDATA $-0.63\pm 0.08$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7b72ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA $0.70\pm 0.04$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7b72ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>, respectively, with the local magnetic field parallel and perpendicular to the solar wind velocity directions. The scaling for the velocity-trace structure functions is also isotropic and the indices are <jats:inline-formula> <jats:tex-math> <?CDATA $-0.47\pm 0.10$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7b72ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA $0.51\pm 0.09$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab7b72ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. We also find that with increasing <jats:italic>ϕ</jats:italic> threshold to 90°, the scaling index of the magnetic-trace structure function in the parallel direction decreases to −0.81, while the rms of the instantaneous angle between magnetic field and solar wind velocity increases up to 45° at the timescale 150 s, indicating a mix of perpendicular measurements into parallel ones at large scales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this work, we investigate the properties of young giant planet spectra in the optical and suggest that future space-based direct imaging missions should be considering young planets as a valuable and informative science case. While young planets are dimmer in the optical than in the infrared, they can still be brighter in the optical than a mature planet of similar mass. Therefore, an instrument designed to characterize mature planets should also be suitable for high-precision photometric imaging and spectroscopy of young self-luminous planets in a wavelength range and at a contrast ratio not currently attainable from the ground. We identify known young self-luminous companions that are feasible targets for coronagraphic instrument on the <jats:italic>Wide Field Infrared Survey Telescope</jats:italic> (<jats:italic>WFIRST</jats:italic>-CGI) and compute spectra for them, including a treatment of scattering and reflected light at optical wavelengths. Using these results, we highlight potentially diagnostic spectral features that will be present in the <jats:italic>WFIRST</jats:italic>-CGI wavelengths. Expanding to direct imaging missions beyond <jats:italic>WFIRST</jats:italic>-CGI, we also use evolutionary models across a grid of masses and planet–star separations as inputs to compute spectra of hypothetical objects, exploring when reflected light may contribute to a degree comparable to that of thermal emission from the residual heat of formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present 1.3 mm Atacama Large Millimeter/submillimeter Array observations of polarized dust emission toward the wide-binary protostellar system BHR 71 IRS1 and IRS2. IRS1 features what appears to be a natal, hourglass-shaped magnetic field. In contrast, IRS2 exhibits a magnetic field that has been affected by its bipolar outflow. Toward IRS2, the polarization is confined mainly to the outflow cavity walls. Along the northern edge of the redshifted outflow cavity of IRS2, the polarized emission is sandwiched between the outflow and a filament of cold, dense gas traced by N<jats:sub>2</jats:sub>D<jats:sup>+</jats:sup>, toward which no dust polarization is detected. This suggests that the origin of the enhanced polarization in IRS2 is the irradiation of the outflow cavity walls, which enables the alignment of dust grains with respect to the magnetic field—but only to a depth of ∼300 au, beyond which the dust is cold and unpolarized. However, in order to align grains deep enough in the cavity walls, and to produce the high polarization fraction seen in IRS2, the aligning photons are likely to be in the mid- to far-infrared range, which suggests a degree of grain growth beyond what is typically expected in very young, Class 0 sources. Finally, toward IRS1 we see a narrow, linear feature with a high (10%–20%) polarization fraction and a well-ordered magnetic field that is not associated with the bipolar outflow cavity. We speculate that this feature may be a magnetized accretion streamer; however, this has yet to be confirmed by kinematic observations of dense-gas tracers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The search for life on exoplanets is one of the grand scientific challenges of our time. The strategy to date has been to find (e.g., through transit surveys like Kepler) earthlike exoplanets in their stars’ habitable zone, then use transmission spectroscopy to measure biosignature gases, especially oxygen, in the planets’ atmospheres (e.g., using James Webb Space Telescope (JWST)). Already there are more such planets than can be observed by JWST, and missions like the Transiting Exoplanet Survey Satellite and others will find more. A better understanding of the geochemical cycles relevant to biosignature gases is needed, to prioritize targets for costly follow-up observations and to help design future missions. We define a Detectability Index to quantify the likelihood that a biosignature gas could be assigned a biological versus nonbiological origin. We apply this index to the case of oxygen gas, O<jats:sub>2</jats:sub>, on earthlike planets with varying water contents. We demonstrate that on earthlike exoplanets with 0.2 weight percent (wt%) water (i.e., no exposed continents) a reduced flux of bioessential phosphorus limits the export of photosynthetically produced atmospheric O<jats:sub>2</jats:sub> to levels indistinguishable from geophysical production by photolysis of water plus hydrogen escape. Higher water contents &gt;1 wt% that lead to high-pressure ice mantles further slow phosphorus cycling. Paradoxically, the maximum water content allowing use of O<jats:sub>2</jats:sub> as a biosignature, 0.2 wt%, is consistent with no water based on mass and radius. Thus, the utility of an O<jats:sub>2</jats:sub> biosignature likely requires the direct detection of both water and land on a planet.</jats:p>