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<jats:title>Abstract</jats:title> <jats:p>Supernova (SN) explosions can potentially affect the structure and evolution of circumnuclear disks in active galactic nuclei (AGN). Some previous studies have suggested that a relatively low rate of SN explosions can provide an effective value of alpha viscosity between 0.1 and 1 in AGN accretion disks within a 1 pc scale. In order to test this possibility, we provide some analytic scalings of the evolution of an SN remnant embedded in a differentially rotating smooth disk. We calibrate our estimates using three-dimensional hydrodynamical simulations where the gas is modeled as adiabatic with index <jats:italic>γ</jats:italic>. Our simulations are suited to include the fact that a fraction of the momentum injected by the SN escapes from the disk into the corona. Based on these results, we calculate the contribution of SN explosions to the effective alpha viscosity, denoted by <jats:italic>α</jats:italic> <jats:sub>SNe</jats:sub>, in a model AGN accretion disk, where accretion is driven by the local viscosity <jats:italic>α</jats:italic>. We find that for AGN galaxies with a central black hole of <jats:inline-formula> <jats:tex-math> <?CDATA $\sim {10}^{8}{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca88ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and a disk with viscosity <jats:italic>α</jats:italic> = 0.1, the contribution of SN explosions may be as large as <jats:inline-formula> <jats:tex-math> <?CDATA ${\alpha }_{\mathrm{SNe}}\simeq 0.02$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca88ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, provided that <jats:inline-formula> <jats:tex-math> <?CDATA $\gamma \gtrsim 1.1$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca88ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. On the other hand, in the momentum conservation limit, which is valid when the push by the internal pressure of the SN remnant is negligible, we find <jats:inline-formula> <jats:tex-math> <?CDATA ${\alpha }_{\mathrm{SNe}}\lesssim 6\times {10}^{-4}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabca88ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this study, we investigate the spatial distribution of highly varying plasma composition around one of the largest sunspots of solar cycle 24. Observations of the photosphere, chromosphere, and corona are brought together with magnetic field modeling of the sunspot in order to probe the conditions that regulate the degree of plasma fractionation within loop populations of differing connectivities. We find that, in the coronal magnetic field above the sunspot umbra, the plasma has photospheric composition. Coronal loops rooted in the penumbra contain fractionated plasma, with the highest levels observed in the loops that connect within the active region. Tracing field lines from regions of fractionated plasma in the corona to locations of Alfvénic fluctuations detected in the chromosphere shows that they are magnetically linked. These results indicate a connection between sunspot chromospheric activity and observable changes in coronal plasma composition.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The aim of this paper is to establish a complete sample of red supergiants (RSGs) in M31 and M33. The member stars of the two galaxies are selected from the near-infrared (NIR) point sources after removing the foreground dwarfs from their obvious branch in the <jats:italic>J</jats:italic> − <jats:italic>H</jats:italic>/<jats:italic>H</jats:italic> − <jats:italic>K</jats:italic> diagram with the archival photometric data taken by the UKIRT/WFCAM. This separation by NIR colors of dwarfs from giants is confirmed by the optical/infrared color–color diagrams (<jats:italic>r</jats:italic> − <jats:italic>z</jats:italic>/<jats:italic>z</jats:italic> − <jats:italic>H</jats:italic> and <jats:italic>B</jats:italic> − <jats:italic>V</jats:italic>/<jats:italic>V</jats:italic> − <jats:italic>R</jats:italic>) and the Gaia measurement of parallax and proper motion. The RSGs are then identified by their outstanding location in the members’ <jats:italic>J</jats:italic> − <jats:italic>K</jats:italic>/<jats:italic>K</jats:italic> diagram due to high luminosity and low effective temperature. The resultant sample has 5498 and 3055 RSGs in M31 and M33 respectively, which should be complete because the lower limiting <jats:italic>K</jats:italic> magnitude of RSGs in both cases is brighter than the complete magnitude of the UKIRT photometry. Analysis of the control fields finds that the pollution rate in the RSG sample is less than 1%. The by-product is the complete sample of oxygen-rich asymptotic giant branch stars (AGBs), carbon-rich AGBs, thermally pulsing AGBs, and extreme AGBs. In addition, the tip-RGB is determined together with its implication on the distance modulus to M31 and M33.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze two-armed global spiral density wave modes generated by gravitational instability in razor-thin, nonviscous, self-gravitating protoplanetary disks to understand the dependence of spiral arm morphology (pitch angle <jats:italic>α</jats:italic> and amplitude) on various disk conditions. The morphologies of the resulting spiral density wave modes closely resemble observations. Their pitch angles and pattern speeds are insensitive to the boundary conditions adopted. Gaussian disks exhibit more tightly wound spirals (smaller pitch angle) than power-law disks under the same conditions. We find that at a fixed disk-to-star mass ratio (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>), the pitch angle increases with average Toomre’s stability parameter (<jats:inline-formula> <jats:tex-math> <?CDATA $\overline{Q}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) or average disk aspect ratio (<jats:inline-formula> <jats:tex-math> <?CDATA $\overline{h}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c5ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>). For a given <jats:inline-formula> <jats:tex-math> <?CDATA $\overline{Q}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c5ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>, density wave modes with higher <jats:italic>M</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub>/<jats:italic>M</jats:italic> <jats:sub>*</jats:sub> have larger pitch angles, while the behavior reverses for a given <jats:inline-formula> <jats:tex-math> <?CDATA $\overline{h}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c5ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. The interdependence between pitch angle and disk properties can be roughly approximated by <jats:inline-formula> <jats:tex-math> <?CDATA $\alpha \propto {c}_{s}^{2}/{M}_{d}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabc7c5ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>c</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> is the sound speed. Our gravitational instability-excited spiral density waves can be distinguished from planet-launched spirals: (1) massive cool disks have spiral pitch angle falling with radius, while low-mass hot disks have spiral pitch angle rising with radius; (2) the profile of spiral amplitude presents several dips and bumps. We propose that gravitational instability-excited density waves can serve as an alternative scenario to explain the observed spiral arms in self-gravitating protoplanetary disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic flux ropes (MFRs) rising buoyantly through the Sun’s convection zone are thought to be subject to viscous forces preventing them from rising coherently. Numerous studies have suggested that MFRs require a minimum twist in order to remain coherent during their rise. Furthermore, even MFRs that get to the photosphere may be unable to successfully emerge into the corona unless they are at least moderately twisted, since the magnetic pressure gradient needs to overcome the weight of the photospheric plasma. To date, however, no lower limit has been placed on the critical minimum twist required for an MFR to rise coherently through the convection zone or emerge through the photosphere. In this paper, we simulate an untwisted toroidal MFR that is able to rise from the convection zone and emerge through the photosphere as an active region that resembles those observed on the Sun. We show that untwisted MFRs can remain coherent during their rise and then pile up near the photosphere, triggering undular instability, allowing the MFR to emerge through the photosphere. We propose that the toroidal geometry of our MFR is critical for its coherent rise. Upon emergence, a pair of lobes rises into the corona. The two lobes then interact and reconnect, resulting in a localized high speed jet. The resulting photospheric magnetogram displays the characteristic salt-and-pepper structure often seen in observations. Our major result is that MFRs need not be twisted to rise coherently through the convection zone and emerge through the photosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Quantum chemical cluster calculations show that reactions of C<jats:sup>+</jats:sup> with HCN or HNC embedded in the surface of an icy grain mantle can account for the formation of a recently detected molecule, glycolonitrile, which is considered to be an important precursor to ribonucleic compounds. Reactions of cations deposited on ice mantles with minimal kinetic energy have been found theoretically to result in previously unknown pathways to significant organic compounds in protostellar systems and the interstellar medium. In density functional theory cluster calculations involving up to 24H<jats:sub>2</jats:sub>O, C<jats:sup>+</jats:sup> reacts consistently with HCN embedded in ice to yield the neutral HOCHNC radical with no barrier, along with H<jats:sub>3</jats:sub>O<jats:sup>+</jats:sup> as a byproduct. If HOCHNC then reacts with H, three species can be formed: HOCH<jats:sub>2</jats:sub>NC (isocyanomethanol), HOCH<jats:sub>2</jats:sub>CN (glycolonitrile), and HOCHNCH. For the C<jats:sup>+</jats:sup>+ HNC reaction on ice, the HOCHCN and H<jats:sub>2</jats:sub>OCCN radicals form as intermediates, the first of which is another direct precursor to glycolonitrile via H addition. In addition to characterizing reaction pathways, predictions are provided of the vibrational and electronic spectra of the HCN and HNC starting clusters and the HOCHNC ice-bound intermediate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The absence of high-Eddington-ratio, obscured active galactic nuclei (AGNs) in local (<jats:italic>z</jats:italic> ≲ 0.1) samples of moderate-luminosity AGNs has generally been explained to result from radiation pressure on the dusty gas governing the level of nuclear (≲10 pc) obscuration. However, very high accretion rates are routinely reported among obscured quasars at higher luminosities and may require a different feedback mechanism. We compile constraints on obscuration and Eddington ratio for samples of X-ray, optical, infrared, and submillimeter selected AGNs at quasar luminosities. Whereas moderate-luminosity, obscured AGNs in the local universe have a range of lower Eddington ratios (<jats:italic>f</jats:italic> <jats:sub>Edd</jats:sub> ∼ 0.001–0.1), the most luminous (<jats:italic>L</jats:italic> <jats:sub>bol</jats:sub> ≳ 10<jats:sup>46</jats:sup> erg s<jats:sup>−1</jats:sup>) IR/submillimeter-bright, obscured quasars out to <jats:italic>z</jats:italic> ∼ 3 commonly have very high Eddington ratios (<jats:italic>f</jats:italic> <jats:sub>Edd</jats:sub> ∼ 0.11). This apparent lack of radiation-pressure feedback in luminous, obscured quasars is likely coupled with AGN timescales, such that a higher fraction of luminous, obscured quasars are seen because of the short timescale for which quasars are most luminous. When adopting quasar evolutionary scenarios, extended (∼10<jats:sup>2–3</jats:sup> pc) obscuration may work together with the shorter timescales to explain the observed fraction of obscured, luminous quasars, while outflows driven by radiation pressure will slowly clear this material over the AGN lifetime.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study gravitomagnetic instabilities of a static homogeneous medium with an aligned magnetic field in the two contexts of relativistic magnetohydrodynamics (MHD): first, MHD with post-Newtonian (PN) corrections, and second, special relativistic (SR) MHD with weak gravity. The analysis in the PN MHD is made without taking the temporal gauge condition, thus results are gauge-invariant. The PN corrections of the internal energy, pressure, sound velocity, and the Alfvén velocity lower the critical (Jeans) wavelength. All relativistic effects tend to destabilize the system. Although the SR MHD with weak gravity is presented in the harmonic gauge, in the presence of gravity the stability analysis is strictly valid to Newtonian order. In the absence of gravity, the SR MHD is independent of the gauge condition. We present the plane wave velocities and the stability criteria in both cases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present first results of a four-epoch VLBA survey for nonthermal emission toward all 556 compact radio sources previously identified in a deep VLA survey of the Orion Nebula Cluster (ONC). We identify VLBA counterparts toward an unprecedented 123 sources. Of these, 41 do not have X-ray counterparts, of which 34 also do not display near-infrared counterparts. Since these cannot be explained by extragalactic background sources, this suggests a component of the ONC population of young stellar objects that are too deeply embedded for even X-rays to be detectable. We find pervasive variability and detect even most of the highest-S/N sources in only one out of four epochs. Neither a negative spectral index nor extreme variability in the VLA data is a good predictor of a VLBA detection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In the solar corona, the free energy, i.e., the excess in magnetic energy over a ground-state potential field, forms the reservoir of energy that can be released during solar flares and coronal mass ejections. Such free energy provides a measure of the magnetic field nonpotentiality. Recent theoretical and observational studies indicate that the presence of nonpotential magnetic fields is imprinted into the structures of infrared, off-limb, coronal polarization. In this paper, we investigate the possibility of exploiting such observations for mapping and studying the accumulation and release of coronal free magnetic energy, with the goal of developing a new tool for identifying “hot spots” of coronal free energy such as those associated with twisted and/or sheared coronal magnetic fields. We applied forward modeling of infrared coronal polarimetry to three-dimensional models of nonpotential and potential magnetic fields. From these we defined a quantitative diagnostic of nonpotentiality that in the future could be calculated from a comparison of infrared, off-limb, coronal polarization observations from, e.g., the Coronal Multi-channel Polarimeter or the Daniel K. Inouye Solar Telescope, and the corresponding polarization signal forward-modeled from a potential field extrapolated from photospheric magnetograms. We considered the relative diagnostic potential of linear and circular polarization, and the sensitivities of these diagnostics to coronal density distributions and assumed boundary conditions of the potential field. Our work confirms the capacity of polarization measurements for diagnosing nonpotentiality and free energy in the solar corona.</jats:p>