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<jats:title>Abstract</jats:title> <jats:p>Ions that are reflected at the shock front and escape back into the upstream region can play the role of ions that start to be accelerated by a diffusive shock acceleration mechanism. Backstreaming ions have been shown to be generated from a superthermal tail of the solar wind at sufficiently high upstream temperatures. The number of such ions was found to be low and they were not found at shock angles exceeding 50°. The mechanism of production is multiple reflection when an ion changes the direction of motion inside the ramp for the first time, due to the cross-shock potential. Since pickup ions (PUIs) constitute a strongly superthermal population of protons a substantially stronger production of backstreaming PUIs can be expected. We study the reflection of PUIs in a planar stationary shock front using test particle analysis. The used model is inspired by the observed profile of the termination shock. The influence of magnetic compression, the shock angle, and the overshoot are analyzed. It is found that generation of backstreaming PUIs in this shock is substantially more efficient than the generation of backstreaming protons from thermal solar wind. The fraction of backstreaming PUIs rapidly increases with the increase of magnetic compression and the decrease of the shock angle. Overshoot enhances production of backstreaming PUIs and allows it for larger shock angles. No backstreaming ions have been found for shock angles larger than 60°. The results of the test particle analysis are supported by full-particle simulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is an unbiased, massively multiplexed spectroscopic survey, designed to measure the expansion history of the universe through low-resolution (<jats:italic>R</jats:italic> ∼ 750) spectra of Ly<jats:italic>α</jats:italic> emitters. In its search for these galaxies, HETDEX will also observe a few times 10<jats:sup>5</jats:sup> stars. In this paper, we present the first stellar value-added catalog within the internal second data release of the HETDEX Survey (HDR2). The new catalog contains 120,571 low-resolution spectra for 98,736 unique stars between 10 &lt; <jats:italic>G</jats:italic> &lt; 22 spread across the HETDEX footprint at relatively high (<jats:italic>b</jats:italic> ∼ 60°) Galactic latitudes. With these spectra, we measure radial velocities (RVs) for ∼42,000 unique FGK-type stars in the catalog and show that the HETDEX spectra are sufficient to constrain these RVs with a 1<jats:italic>σ</jats:italic> precision of 28.0 km s<jats:sup>−1</jats:sup> and bias of 3.5 km s<jats:sup>−1</jats:sup> with respect to the Large Sky Area Multi-Object Fibre Spectroscopic Telescope surveys and 1<jats:italic>σ</jats:italic> precision of 27.5 km s<jats:sup>−1</jats:sup> and bias of 14.0 km s<jats:sup>−1</jats:sup> compared to the Sloan Extension for Galactic Understanding and Exploration survey. Since these RVs are for faint (<jats:italic>G</jats:italic> ≥ 16) stars, they will be complementary to Gaia. Using t-Distributed Stochastic Neighbor Embedding (tSNE), we also demonstrate that the HETDEX spectra can be used to determine a star’s <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub>, and log <jats:italic>g</jats:italic> and its [Fe/H]. With the tSNE projection of the FGK-type stars with HETDEX spectra we also identify 416 new candidate metal-poor ([Fe/H] &lt; −1 dex) stars for future study. These encouraging results illustrate the utility of future low-resolution stellar spectroscopic surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Narrowband spikes have been observed in solar flares for several decades. However, their exact origin is still discussed. To contribute to understanding of these spikes, we analyze the narrowband spikes observed in the 800–2000 MHz range during the impulsive phase of the 2013 November 7 flare. In the radio spectrum, the spikes started with typical broadband clouds of spikes, and then their distribution in frequencies changed into unique, very narrow bands having noninteger frequency ratios. We successfully fitted frequencies of these narrow spike bands by those, calculating dispersion branches and growth rates of the Bernstein modes. For comparison, we also analyzed the model where the narrow bands of spikes are generated at the upper-hybrid frequencies. Using both models, we estimated the plasma density and magnetic field in spike sources. Then, the models are discussed, and arguments in favor of the model with the Bernstein modes are presented. Analyzing frequency profiles of this spike event by the Fourier method, we found the power-law spectra with the power-law indices varying in the −0.8 to −2.75 interval. Because at some times this power-law index was close to the Kolmogorov spectral index (−5/3), we propose that the spikes are generated through the Bernstein modes in turbulent plasma reconnection outflows or directly in the turbulent magnetic reconnection of solar flares.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a search for RR Lyrae stars using the full six-year data set from the Dark Energy Survey covering ∼5000 deg<jats:sup>2</jats:sup> of the southern sky. Using a multistage multivariate classification and light-curve template-fitting scheme, we identify RR Lyrae candidates with a median of 35 observations per candidate. We detect 6971 RR Lyrae candidates out to ∼335 kpc, and we estimate that our sample is &gt;70% complete at ∼150 kpc. We find excellent agreement with other wide-area RR Lyrae catalogs and RR Lyrae studies targeting the Magellanic Clouds and other Milky Way satellite galaxies. We fit the smooth stellar halo density profile using a broken-power-law model with fixed halo flattening (<jats:italic>q</jats:italic> = 0.7), and we find strong evidence for a break at <jats:inline-formula> <jats:tex-math> <?CDATA ${R}_{0}={32.1}_{-0.9}^{+1.1}\,\mathrm{kpc}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>32.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1.1</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mi>kpc</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe873ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with an inner slope of <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{1}=-{2.54}_{-0.09}^{+0.09}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.54</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.09</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe873ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and an outer slope of <jats:inline-formula> <jats:tex-math> <?CDATA ${n}_{2}=-{5.42}_{-0.14}^{+0.13}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>5.42</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe873ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. We use our catalog to perform a search for Milky Way satellite galaxies with large sizes and low luminosities. Using a set of simulated satellite galaxies, we find that our RR Lyrae-based search is more sensitive than those using resolved stellar populations in the regime of large (<jats:italic>r</jats:italic> <jats:sub>h</jats:sub> ≳ 500 pc), low-surface-brightness dwarf galaxies. A blind search for large, diffuse satellites yields three candidate substructures. The first can be confidently associated with the dwarf galaxy Eridanus II. The second has a distance and proper motion similar to the ultrafaint dwarf galaxy Tucana II but is separated by ∼5 deg. The third is close in projection to the globular cluster NGC 1851 but is ∼10 kpc more distant and appears to differ in proper motion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Imaging surveys of CO and other molecular transition lines are fundamental to measuring the large-scale distribution of molecular gas in the Milky Way. Due to finite angular resolution and sensitivity, however, observational effects are inevitable in the surveys, but few studies are available on the extent of uncertainties involved. The purpose of this work is to investigate the dependence of observations on angular resolution (beam sizes), sensitivity (noise levels), distances, and molecular tracers. To this end, we use high-quality CO images of a large-scale region (258 &lt; <jats:italic>l</jats:italic> &lt; 497 and ∣<jats:italic>b</jats:italic>∣ &lt; 5°) mapped by the Milky Way Imaging Scroll Painting (MWISP) survey as a benchmark to simulate observations with larger beam sizes and higher noise levels, deriving corresponding beam filling and sensitivity clip factors. The sensitivity clip factor is defined to be the completeness of observed flux. Taking the entire image as a whole object, we found that <jats:sup>12</jats:sup>CO has the largest beam filling and sensitivity clip factors and C<jats:sup>18</jats:sup>O has the lowest. For molecular cloud samples extracted from images, the beam filling factor can be described by a characteristic size, <jats:italic>l</jats:italic> <jats:sub>1/4</jats:sub> = 0.762 (in beam size), at which the beam filling factor is approximately 1/4. The sensitivity clip factor shows a similar relationship but is more correlated with the mean voxel signal-to-noise ratio of molecular clouds. This result may serve as a practical reference on beam filling and sensitivity clip factors in further analyses of the MWISP data and other observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Relic gravitational waves (GWs) can be produced by primordial magnetic fields. However, not much is known about the resulting GW amplitudes and their dependence on the details of the generation mechanism. Here we treat magnetic field generation through the chiral magnetic effect (CME) as a generic mechanism and explore its dependence on the speed of generation (the product of magnetic diffusivity and characteristic wavenumber) and the speed characterizing the maximum magnetic field strength expected from the CME. When the latter exceeds the former (regime I), which is the regime applicable to the early universe, we obtain an inverse cascade with moderate GW energy that scales with the third power of the magnetic energy. When the generation speed exceeds the CME limit (regime II), the GW energy continues to increase without a corresponding increase of magnetic energy. In the early kinematic phase, the GW energy spectrum (per linear wavenumber interval) has opposite slopes in both regimes and is characterized by an inertial range spectrum in regime I and a white noise spectrum in regime II. The occurrence of these two slopes is shown to be a generic consequence of a nearly monochromatic exponential growth of the magnetic field. The resulting GW energy is found to be proportional to the fifth power of the limiting CME speed and the first power of the generation speed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The magnetic activity of late-type stars is correlated with their rotation rates. Up to a certain limit, stars with smaller Rossby numbers, defined as the rotation period divided by the convective turnover time, have higher activity. A more detailed look at this rotation–activity relation reveals that, rather than being a simple power-law relation, the activity scaling has a shallower slope for the low-Rossby stars than for the high-Rossby ones. We find that, for the chromospheric Ca <jats:sc>II</jats:sc> H&amp;K activity, this scaling relation is well modeled by a broken two-piece power law. Furthermore, the knee point of the relation coincides with the axisymmetry to nonaxisymmetry transition seen in both the spot activity and surface magnetic field configuration of active stars. We interpret this knee point as a dynamo transition between dominating axi- and nonaxisymmetric dynamo regimes with a different dependence on rotation and discuss this hypothesis in the light of current numerical dynamo models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>M-dwarf stars are prime targets for exoplanet searches because of their close proximity and favorable properties for both planet detection and characterization. However, the potential habitability and atmospheric characterization of these exoplanetary systems depends critically on the history of high-energy stellar radiation from X-rays to NUV, which drive atmospheric mass loss and photochemistry in the planetary atmospheres. With the Far Ultraviolet M-dwarf Evolution Survey, we have assessed the evolution of the FUV radiation, specifically eight prominent emission lines, including Ly<jats:italic>α</jats:italic>, of M-dwarf stars with stellar rotation period and age. We demonstrate tight power-law correlations between the spectroscopic FUV features, and measure the intrinsic scatter of the quiescent FUV emissions. The luminosity evolution with rotation of these spectroscopic features is well-described by a broken power law, saturated for fast rotators, and decays with increasing Rossby number, with a typical power-law slope of −2, although likely shallower for Ly<jats:italic>α</jats:italic>. Our regression fits enable FUV emission-line luminosity estimates relative to bolometric from known rotation periods to within ∼0.3 dex, across eight distinct UV emission lines, with possible trends in the fit parameters as a function of source layer in the stellar atmosphere. Our detailed analysis of the UV luminosity evolution with age further shows that habitable-zone planets orbiting lower-mass stars experience much greater high-energy radiative exposure relative the same planets orbiting more massive hosts. Around early- to mid-M dwarfs, these exoplanets, at field ages, accumulate up to 10–20× more EUV energy, relative to modern Earth. Moreover, the bulk of this UV exposure likely takes place within the first Gyr of the stellar lifetime.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed study of KIC 2306740, an eccentric double-lined eclipsing binary system. Kepler satellite data were combined with spectroscopic data obtained with the 4.2 m William Herschel Telescope (WHT). This allowed us to determine precise orbital and physical parameters of this relatively long period (<jats:italic>P</jats:italic> = 10.ͩ3) and slightly eccentric (<jats:italic>e</jats:italic> = 0.3) binary system. The physical parameters have been determined to be <jats:italic>M</jats:italic> <jats:sub>1</jats:sub> = 1.194 ± 0.008 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, <jats:italic>M</jats:italic> <jats:sub>2</jats:sub> = 1.078 ± 0.007 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, <jats:italic>R</jats:italic> <jats:sub>1</jats:sub> = 1.682 ± 0.004 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>, <jats:italic>R</jats:italic> <jats:sub>2</jats:sub> = 1.226 ± 0.005 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>, <jats:italic>L</jats:italic> <jats:sub>1</jats:sub> = 2.8 ± 0.4 <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>, <jats:italic>L</jats:italic> <jats:sub>2</jats:sub> = 1.8 ± 0.2 <jats:italic>L</jats:italic> <jats:sub>⊙</jats:sub>, and orbital separation <jats:italic>a</jats:italic> = 26.20 ± 0.04 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> through simultaneous solutions of the Kepler light curves and WHT radial velocity data. Binarity effects were extracted from the light curve in order to study intrinsic variations in the residuals. Five significant and more than 100 combination frequencies were detected. We modeled the binary system assuming nonconservative evolution models with the Cambridge <jats:sc>stars (twin)</jats:sc> code, and we show the evolutionary tracks of the components in the <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}L\mbox{--}\mathrm{log}T$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>L</mml:mi> <mml:mo>–</mml:mo> <mml:mi>log</mml:mi> <mml:mi>T</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe546ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> plane, the <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}R\mbox{--}\mathrm{log}M$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>R</mml:mi> <mml:mo>–</mml:mo> <mml:mi>log</mml:mi> <mml:mi>M</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe546ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> plane, and the <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}P\mbox{--}\mathrm{age}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mi>P</mml:mi> <mml:mo>–</mml:mo> <mml:mi>age</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe546ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> plane for both spin and orbital periods together with eccentricity <jats:italic>e</jats:italic> and <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{R}_{1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>R</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe546ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. The model of the nonconservative processes in the code led the system to evolve to the observed system parameters in roughly 5.1 Gyr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The H <jats:sc>i</jats:sc> Ly<jats:italic>α</jats:italic> (1215.67 Å) emission line dominates the far-UV spectra of M dwarf stars, but strong absorption from neutral hydrogen in the interstellar medium makes observing Ly<jats:italic>α</jats:italic> challenging even for the closest stars. As part of the Far-Ultraviolet M-dwarf Evolution Survey, the Hubble Space Telescope has observed 10 early-to-mid M dwarfs with ages ranging from ∼24 Myr to several Gyr in order to evaluate how the incident UV radiation evolves through the lifetime of exoplanetary systems. We reconstruct the intrinsic Ly<jats:italic>α</jats:italic> profiles from STIS G140L and E140M spectra, and achieve reconstructed fluxes with 1<jats:italic>σ</jats:italic> uncertainties ranging from 5% to a factor of two for the low-resolution spectra (G140L) and 3%–20% for the high-resolution spectra (E140M). We observe broad, 500–1000 km s<jats:sup>−1</jats:sup> wings of the Ly<jats:italic>α</jats:italic> line profile, and analyze how the line width depends on stellar properties. We find that stellar effective temperature and surface gravity are the dominant factors influencing the line width with little impact from the star’s magnetic activity level, and that the surface flux density of the Ly<jats:italic>α</jats:italic> wings may be used to estimate the chromospheric electron density. The Ly<jats:italic>α</jats:italic> reconstructions on the G140L spectra are the first attempted on <jats:italic>λ</jats:italic>/Δ<jats:italic>λ</jats:italic> ∼ 1000 data. We find that the reconstruction precision is not correlated with the signal-to-noise ratio of the observation—rather, it depends on the intrinsic broadness of the stellar Ly<jats:italic>α</jats:italic> line. Young, low-gravity stars have the broadest lines and therefore provide more information at low spectral resolution to the fit to break degeneracies among model parameters.</jats:p>