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<jats:title>Abstract</jats:title> <jats:p>In order to address the generation of neutron star magnetic fields, with particular focus on the dichotomy between magnetars and radio pulsars, we consider the properties of dynamos as inferred from other astrophysical systems. With sufficiently low (modified) Rossby number, convective dynamos are known to produce dipole-dominated fields whose strength scales with convective flux, and we argue that these expectations should apply to the convective protoneutron stars (PNSs) at the centers of core-collapse supernovae. We analyze a suite of three-dimensional simulations of core collapse, featuring a realistic equation of state and full neutrino transport, in this context. All our progenitor models, ranging from 9 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> to 25 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, including one with initial rotation, have sufficiently vigorous PNS convection to generate dipole fields of order ∼10<jats:sup>15</jats:sup> Gauss, if the modified Rossby number resides in the critical range. Thus, the magnetar/radio pulsar dichotomy may arise naturally in part from the distribution of core rotation rates in massive stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (∼26 AB mag) optical and wide-area (∼500 deg<jats:sup>2</jats:sup>) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ∼10% solar value (O/H)<jats:sub>⊙</jats:sub>, and four sources are contaminants of moderately metal-rich galaxies or no emission-line objects. Notably, two out of the nine EMPGs have extremely low stellar masses and oxygen abundances of 5 × 10<jats:sup>4</jats:sup>–7 × 10<jats:sup>5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and 2%–3% (O/H)<jats:sub>⊙</jats:sub>, respectively. With a sample of five EMPGs with (Fe/O) measurements, two (three) of which are taken from this study (the literature), we confirm that two EMPGs with the lowest (O/H) ratios of ∼2% (O/H)<jats:sub>⊙</jats:sub> show high (Fe/O) ratios of ∼0.1, close to the solar abundance ratio. Comparing galaxy chemical enrichment models, we find that the two EMPGs cannot be explained by a scenario of metal-poor gas accretion/episodic star formation history due to their low (N/O) ratios. We conclude that the two EMPGs can be reproduced by the inclusion of bright hypernovae and/or hypothetical pair-instability supernovae (SNe) preferentially produced in a metal-poor environment. This conclusion implies that primordial galaxies at <jats:italic>z</jats:italic> ∼ 10 could have a high abundance of Fe that did not originate from Type Ia SNe with delays and that Fe may not serve as a cosmic clock for primordial galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present deep X-ray and radio observations of the fast blue optical transient (FBOT) AT 2020xnd/ZTF 20acigmel at <jats:italic>z</jats:italic> = 0.2433 from 13 days to 269 days after explosion. AT 2020xnd belongs to the category of optically luminous FBOTs with similarities to the archetypal event AT 2018cow. AT 2020xnd shows luminous radio emission reaching <jats:italic>L</jats:italic> <jats:sub> <jats:italic>ν</jats:italic> </jats:sub> ≈ 8 × 10<jats:sup>29</jats:sup> erg s<jats:sup>−1</jats:sup> Hz<jats:sup>−1</jats:sup> at 20 GHz and 75 days post-explosion, accompanied by luminous and rapidly fading soft X-ray emission peaking at <jats:italic>L</jats:italic> <jats:sub>X</jats:sub> ≈ 6 × 10<jats:sup>42</jats:sup> erg s<jats:sup>−1</jats:sup>. Interpreting the radio emission in the context of synchrotron radiation from the explosion’s shock interaction with the environment, we find that AT 2020xnd launched a high-velocity outflow (<jats:italic>v</jats:italic> ∼ 0.1<jats:italic>c</jats:italic>–0.2<jats:italic>c</jats:italic>) propagating into a dense circumstellar medium (effective <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{M}\approx {10}^{-3}\,{M}_{\odot }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mover accent="true"> <mml:mi>M</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> </mml:mrow> <mml:mo>≈</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4506ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> yr<jats:sup>−1</jats:sup> for an assumed wind velocity of <jats:italic>v</jats:italic> <jats:sub>w</jats:sub> = 1000 km s<jats:sup>−1</jats:sup>). Similar to AT 2018cow, the detected X-ray emission is in excess compared to the extrapolated synchrotron spectrum and constitutes a different emission component, possibly powered by accretion onto a newly formed black hole or neutron star. These properties make AT 2020xnd a high-redshift analog to AT 2018cow, and establish AT 2020xnd as the fourth member of the class of optically luminous FBOTs with luminous multiwavelength counterparts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present results constraining the multiplicity of the very low mass stars and substellar objects in the Orion Nebula Cluster (ONC). Our sample covers primary masses 0.012–0.1<jats:italic> M</jats:italic> <jats:sub>⊙</jats:sub> using archival Hubble Space Telescope data obtained with the Advanced Camera for Surveys using multiple filters. Studying the binary populations of clusters provides valuable constraints of how the birth environment affects binary formation and evolution. Prior surveys have shown that the binary populations of high-mass, high-density star clusters like the ONC may substantially differ from those in low-mass associations. Very low mass stellar and substellar binaries at wide separations, &gt;20 au, are statistically rare in the Galactic field and have been identified in stellar associations like Taurus-Auriga and Ophiuchus. They also may be susceptible to dynamical interactions, and their formation may be suppressed by feedback from ongoing star formation. We implement a double point-spread function (PSF) fitting algorithm using empirical, position-dependent PSF models to search for binary companions at projected separations &gt;10 au (0.″025). With this technique, we identify seven very low mass binaries, five of which are new detections, resulting in a binary frequency of <jats:inline-formula> <jats:tex-math> <?CDATA ${12}_{-3.2}^{+6} \% $?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>12</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>6</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>%</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac36d4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> over mass ratios of 0.5–1.0 and projected separations of 20–200 au. We find an excess of very low mass binaries in the ONC compared to the Galactic field, with a probability of 10<jats:sup>−6</jats:sup> that the populations are statistically consistent. The substellar population of the ONC may require further dynamical processing of the lowest binding energy binaries to resemble the field population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Extrapolations of line-of-sight photospheric field measurements predict radial interplanetary magnetic field (IMF) strengths that are factors of ∼2–4 too low. To address this <jats:italic>open flux problem</jats:italic>, we reanalyze the magnetograph measurements from different observatories, with particular focus on those made in the saturation-prone Fe <jats:sc>i</jats:sc> 525.0 nm line by the Mount Wilson Observatory (MWO) and the Wilcox Solar Observatory (WSO). The total dipole strengths, which determine the total open flux, generally show large variations among observatories, even when their total photospheric fluxes are in agreement. However, the MWO and WSO dipole strengths, as well as their total fluxes, agree remarkably well with each other, suggesting that the two data sets require the same scaling factor. As shown earlier by Ulrich et al., the saturation correction <jats:italic>δ</jats:italic> <jats:sup>−1</jats:sup> derived by comparing MWO measurements in the 525.0 nm line with those in the nonsaturating Fe <jats:sc>i</jats:sc> 523.3 nm line depends sensitively on where along the irregularly shaped 523.3 nm line wings the exit slits are placed. If the slits are positioned so that the 523.3 and 525.0 nm signals originate from the same height, <jats:italic>δ</jats:italic> <jats:sup>−1</jats:sup> ∼ 4.5 at the disk center, falling to ∼2 near the limb. When this correction is applied to either the MWO or WSO maps, the derived open fluxes are consistent with the observed IMF magnitude. Other investigators obtained scaling factors only one-half as large because they sampled the 523.3 nm line farther out in the wings, where the shift between the right- and left-circularly polarized components is substantially smaller.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Analyses of absorption from disk winds and atmospheres in accreting compact objects typically treat the central emitting regions in these systems as point sources relative to the absorber. This assumption breaks down if the absorbing gas is located within a few × 1000 <jats:italic>GM</jats:italic>/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup>, in which case a small component of the absorber’s Keplerian motion contributes to the velocity width of absorption lines. Here, we demonstrate how this velocity-broadening effect can be used to constrain the sizes of central engines in accreting compact objects via a simple geometric relationship, and develop a method for modeling this effect. We apply this method to the Chandra/HETG spectra of three ultracompact and short-period neutron star X-ray binaries in which evidence of gravitationally redshifted absorption, owing to an inner-disk atmosphere, has recently been reported. The significance of the redshift is above 5<jats:italic>σ</jats:italic> for XTE J1710−281 (this work) and 4U 1916−053, and is inconsistent with various estimates of the relative radial velocity of each binary. For our most sensitive spectrum (XTE J1710−281), we obtain a 1<jats:italic>σ</jats:italic> upper bound of 310 km s<jats:sup>−1</jats:sup> on the magnitude of this geometric effect and a central engine of size <jats:italic>R</jats:italic> <jats:sub>CE</jats:sub> &lt; 60 <jats:italic>GM</jats:italic>/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> (or &lt; 90 <jats:italic>GM</jats:italic>/<jats:italic>c</jats:italic> <jats:sup>2</jats:sup> at the 3<jats:italic>σ</jats:italic> level). These initial constraints compare favorably to those obtained via microlensing in quasars and approach the sensitivity of constraints via relativistic reflection in neutron stars. This sensitivity will increase with further exposures, as well as the launch of future microcalorimeter and grating missions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Observations of luminous quasars and their supermassive black holes at <jats:italic>z</jats:italic> ≳ 6 suggest that they formed at dense matter peaks in the early universe. However, few studies have found definitive evidence that the quasars lie at cosmic density peaks, in clear contrast with theory predictions. Here we present new evidence that the radio-loud quasar SDSS J0836+0054 at <jats:italic>z</jats:italic> = 5.8 could be part of a surprisingly rich structure of galaxies. This conclusion is reached by combining a number of findings previously reported in the literature. Bosman et al. obtained the redshifts of three companion galaxies, confirming an overdensity of <jats:italic>i</jats:italic> <jats:sub>775</jats:sub> dropouts found by Zheng et al. By comparing this structure with those found near other quasars and large overdense regions in the field at <jats:italic>z</jats:italic> ∼ 6–7, we show that the SDSS J0836+0054 field is among the densest structures known at these redshifts. One of the spectroscopic companions is a very massive star-forming galaxy (<jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}({{ \mathcal M }}_{\star }/{M}_{\odot })={10.3}_{-0.2}^{+0.3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic"></mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>10.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac448cieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) based on its unambiguous detection in a Spitzer 3.6 <jats:italic>μ</jats:italic>m image. This suggests that the quasar field hosts not one, but at least two rare, massive dark matter halos (<jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{log}}_{10}({{ \mathcal M }}_{h}/{M}_{\odot })\gtrsim 12$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="italic"></mml:mi> </mml:mrow> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊙</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≳</mml:mo> <mml:mn>12</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac448cieqn2.gif" xlink:type="simple" /> </jats:inline-formula>), corresponding to a galaxy overdensity of at least 20. We discuss the properties of the young radio source. We conclude that the environment of SDSS J0836+0054 resembles, at least qualitatively, the type of conditions that may have spurred the direct collapse of a massive black hole seed according to recent theory.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the detection of gravity modes in RR Lyrae stars. Thanks to Photometer AntarctIca eXtinction (PAIX), the first Antarctic polar photometer. Unprecedented and uninterrupted <jats:italic>UBVRI</jats:italic> time-series photometric ground-based data are collected during 150 days from the highest plateau of Antarctica. PAIX light-curve analyses reveal an even richer power spectrum with mixed modes in RR Lyrae stars. The nonlinear nature of several dominant peaks, showing lower and higher frequencies, occurs around the dominant fundamental radial pressure mode. These lower frequencies and harmonics linearly interact with the dominant fundamental radial pressure mode and its second and third overtone pressure modes, as well. Half-integer frequencies are also detected, likewise side-peak structures, demonstrating that HH Puppis is a bona-fide Blazhko star. Fourier correlations are used to derive underlying physical characteristics for HH Puppis. The most striking finding is the direct detection of gravity waves. We interpret the excitation mechanism of gravity waves in RR Lyrae stars by the penetrative convection-driving mechanism. We demonstrate that RR Lyrae stars’ pulsation is excited by several distinct mechanisms, and hence RR Lyrae stars are simultaneously <jats:italic>g-</jats:italic>mode and <jats:italic>p-</jats:italic>mode pulsators. Our discoveries make RR Lyrae stars very challenging stellar objects, and provide their potential to undergo at the same time <jats:italic>g</jats:italic> and <jats:italic>p</jats:italic> modes toward an advancement of the theory of stellar evolution and a better understanding of the universe.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We utilize the Hyper Suprime-Cam (HSC) Wide Survey to explore the properties of galaxies located in the voids identified from the Baryon Oscillation Spectroscopic Survey up to <jats:italic>z</jats:italic> ∼ 0.7. The HSC reaches <jats:italic>i</jats:italic> ∼ 25, allowing us to characterize the void galaxies down to 10<jats:sup>9.2</jats:sup> solar mass. We find that the revised void galaxy densities, when including faint galaxies in voids defined by bright galaxies, are still underdense compared to the mean density from the entire field. In addition, we classify galaxies into star-forming, quiescent, and green valley populations, and find that void galaxies tend to have slightly higher fractions of star-forming galaxies under the mass and redshift control, although the significance of this result is only moderate (2<jats:italic>σ</jats:italic>). However, when we focus on the star-forming population, the distribution of the specific star formation rate (sSFR) of void galaxies shows little difference from that of the control galaxies. Similarly, the median sSFR of star-forming void galaxies is also in good agreement with that of the star-forming control galaxies. Moreover, the effective green valley fraction of void galaxies, defined as the number of green valley galaxies over the number of nonquiescent galaxies, is comparable to that of the control ones, supporting the suggestion that void and control galaxies evolve under similar physical processes and quenching frequencies. Our results thus favor a scenario of galaxy assembly bias.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>More luminous Type Ia supernovae prefer less massive hosts and regions of higher star formation. This correlation is inverted during width–color–luminosity light-curve standardization resulting in step-like biases of distance measurements with respect to host properties. Using the PMAS/PPak Integral-field Supernovahosts COmpilation (PISCO) supernova host sample and Sloan Digital Sky Survey, Galaxy Evolution Explorer, and Two Micron All Sky Survey photometry, we compare host stellar mass and specific star-formation rate (sSFR) from different observation methods, including local versus global, and fitting techniques to measure their impact on the host step biases. Mass-step measurements for all our mass samples are consistent within a 1<jats:italic>σ</jats:italic> significance from −0.03 ± 0.02 mag to −0.04 ± 0.02 mag. Including or excluding UV information had no effect on measured mass-step size or location. sSFR step sizes are more significant than mass-step measurements and varied from 0.05 ± 0.03 mag (Hα) and 0.06 ± 0.02 mag (UV) for a 51 host sample. The sSFR step location is influenced by the mass sample used to normalize star formation and by sSFR tracer choice. The step size is reduced to 0.04 ± 0.03 mag when using all available 73 hosts with Hα measurements. This 73 PISCO host subsample overall lacked a clear step signal, but here we are searching for whether different choices of mass or sSFR estimation can create a step signal. We find no evidence that different observation or fitting techniques choices can create a distance measurement step in either mass or sSFR.</jats:p>