Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>C-type shocks are believed to be ubiquitous in turbulent molecular clouds thanks to ambipolar diffusion. We investigate whether the drag instability in 1D isothermal C-shocks, inferred from the local linear theory of Gu &amp; Chen, can appear in nonideal magnetohydrodynamic simulations. Two C-shock models (with narrow and broad steady-state shock widths) are considered to represent the typical environment of star-forming clouds. The ionization-recombination equilibrium is adopted for the one-fluid approach. In the 1D simulation, the inflow gas is continuously perturbed by a sinusoidal density fluctuation with a constant frequency. The perturbations clearly grow after entering the C-shock region until they start being damped at the transition to the post-shock region. We show that the profiles of a predominant Fourier mode extracted locally from the simulated growing perturbation match those of the growing mode derived from the linear analysis. Moreover, the local growth rate and wave frequency derived from the predominant mode generally agree with those from the linear theory. Therefore, we confirm the presence of the drag instability in simulated 1D isothermal C-shocks. We also explore the nonlinear behavior of the instability by imposing larger-amplitude perturbations to the simulation. We find that the drag instability is subject to wave steepening, leading to saturated perturbation growth. Issues concerning local analysis, nonlinear effects, one-fluid approach, and astrophysical applications are discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present high-resolution Karl G. Jansky Very Large Array (VLA) observations of the protostar L1527 IRS at 7 mm, 1.3 cm, and 2 cm wavelengths. We detect the edge-on dust disk at all three wavelengths and find that it is asymmetric, with the southern side of the disk brighter than the northern side. We confirm this asymmetry through analytic modeling and also find that the disk is flared at 7 mm. We test the data against models including gap features in the intensity profile, and though we cannot rule such models out, they do not provide a statistically significant improvement in the quality of fit to the data. From these fits, we can, however, place constraints on allowed properties of any gaps that could be present in the true, underlying intensity profile. The physical nature of the asymmetry is difficult to associate with physical features owing to the edge-on nature of the disk, but it could be related to spiral arms or asymmetries seen in other imaging of more face-on disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent studies suggest that the magnetic field may play an important role in the formation of giant planets during the final stage of the formation process. In this paper, we construct a circumplanetary system around a planet that is in the final formation stage to investigate the effects of the planetary magnetic field on the accretion process of the planet at this stage. We find that at the early times of our magneto-hydrodynamic (MHD) simulation, the magnetic loops connecting the planet and the circumplanetary material inflate upward due to the build-up of the toroidal field pressure with magnetic islands forming inside the loops, which changes the flow pattern above the planet in comparison with the hydrodynamic case. We find that a low-density gap, which is produced by the strong magnetic pressure, appears along the disk’s surface and expands as the system evolves. Accompanied by the accretion flow above the disk surface, the disk surface field lines can reconnect with the magnetic loops anchored on the planet. Thus, the material above the disk’s surface can permeate into the loops anchored on the planet via reconnection and can be accreted to the planet through the loops. Comparing the results in the hydrodynamic and MHD simulations, we find that the mass accretion rate and the angular momentum transport rate from the infalling gas to the planet do not change apparently when the effects of the magnetic field are included, but these rates from the circumplanetary disk to the planet increase significantly by an order of magnitude.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Vera Rubin Observatory Legacy Survey of Space and Time (LSST) is expected to process ∼10<jats:sup>6</jats:sup> transient detections per night. For precision measurements of cosmological parameters and rates, it is critical to understand the detection efficiency, magnitude limits, artifact contamination levels, and biases in the selection and photometry. Here we rigorously test the LSST Difference Image Analysis (DIA) pipeline using simulated images from the Rubin Observatory LSST Dark Energy Science Collaboration Data Challenge (DC2) simulation for the Wide-Fast-Deep survey area. DC2 is the first large-scale (300 deg<jats:sup>2</jats:sup>) image simulation of a transient survey that includes realistic cadence, variable observing conditions, and CCD image artifacts. We analyze ∼15 deg<jats:sup>2</jats:sup> of DC2 over a 5 yr time span in which artificial point sources from Type Ia supernova (SNIa) light curves have been overlaid onto the images. The magnitude limits per filter are <jats:italic>u</jats:italic> = 23.66 mag, <jats:italic>g</jats:italic> = 24.69 mag, <jats:italic>r</jats:italic> = 24.06 mag, <jats:italic>i</jats:italic> = 23.45 mag, <jats:italic>z</jats:italic> = 22.54 mag, and <jats:italic>y</jats:italic> = 21.62 mag. The artifact contamination levels are ∼90% of all detections, corresponding to ∼1000 artifacts deg<jats:sup>–2</jats:sup> in <jats:italic>g</jats:italic> band, and falling to 300 deg<jats:sup>–2</jats:sup> in <jats:italic>y</jats:italic> band. The photometry has biases &lt;1% for magnitudes 19.5 &lt; <jats:italic>m</jats:italic> &lt; 23. Our DIA performance on simulated images is similar to that of the Dark Energy Survey difference-imaging pipeline on real images. We also characterize DC2 image properties to produce catalog-level simulations needed for distance bias corrections. We find good agreement between DC2 data and simulations for distributions of signal-to-noise ratio, redshift, and fitted light-curve properties. Applying a realistic SNIa cosmology analysis for redshifts <jats:italic>z</jats:italic> &lt; 1, we recover the input cosmology parameters to within statistical uncertainties.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In studying the interstellar medium (ISM) and Galactic cosmic rays (CRs), uncertainty of the interstellar gas density has always been an issue. To overcome this difficulty, we used a component decomposition of the 21 cm H <jats:sc>i</jats:sc> emission line and used the resulting gas maps in an analysis of <jats:italic>γ</jats:italic>-ray data obtained by the Fermi Large Area Telescope (LAT) for the MBM 53, 54, and 55 molecular clouds and the Pegasus loop. We decomposed the ISM gas into intermediate-velocity clouds, narrow-line and optically thick H <jats:sc>i</jats:sc>, broad-line and optically thin H <jats:sc>i</jats:sc>, CO-bright H<jats:sub>2</jats:sub>, and CO-dark H<jats:sub>2</jats:sub> using detailed correlations with the H <jats:sc>i</jats:sc> line profiles from the HI4PI survey, the Planck dust-emission model, and the Fermi-LAT <jats:italic>γ</jats:italic>-ray data. We found the fractions of the optical depth correction to the H <jats:sc>i</jats:sc> column density and CO-dark H<jats:sub>2</jats:sub> to be nearly equal. We fitted the CR spectra directly measured at/near the Earth and the measured <jats:italic>γ</jats:italic>-ray emissivity spectrum simultaneously. We obtained a spectral break in the interstellar proton spectrum at ∼7 GeV, and found that the <jats:italic>γ</jats:italic>-ray emissivity normalization agrees with the AMS-02 proton spectrum within 10%, relaxing the tension with the CR spectra previously claimed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report results for a complete sample of 10 luminous radio-quiet quasars with large C <jats:sc>iv</jats:sc> equivalent widths (EW ≥ 150 Å). For 8/10 we performed Chandra snapshot observations. We find that, in addition to the enhanced C <jats:sc>iv</jats:sc> line EW, their He <jats:sc>ii</jats:sc> and Mg <jats:sc>ii</jats:sc> lines are enhanced, but the C <jats:sc>iii</jats:sc>] line is not. Their X-ray emission is substantially stronger than expected from their ultraviolet luminosity. Additionally, these large C <jats:sc>iv</jats:sc> EW quasars show small C <jats:sc>iv</jats:sc> blueshifts and possibly low Eddington ratios, suggesting that they are “extreme low Eigenvector 1 (EV1)” quasars. The mean excess He <jats:sc>ii</jats:sc> EW is well matched by radiation pressure compression (RPC) photoionization models, with the harder <jats:italic>α</jats:italic> <jats:sub>ox</jats:sub> ionizing spectrum. However, these results do not reproduce well the enhancement pattern of the C <jats:sc>iv</jats:sc>, Mg <jats:sc>ii</jats:sc>, and C <jats:sc>iii</jats:sc>] EWs, or the observed high C <jats:sc>iv</jats:sc>/Mg <jats:sc>ii</jats:sc> ratio. RPC calculations indicate that the C <jats:sc>iv</jats:sc>/Mg <jats:sc>ii</jats:sc> line ratio is an effective metallicity indicator, and models with subsolar-metallicity gas and a hard ionizing continuum reproduce well the enhancement pattern of all four ultraviolet lines. We find that the C <jats:sc>iv</jats:sc>/Mg <jats:sc>ii</jats:sc> line ratio in quasars is generally correlated with the excess X-ray emission. Extremely high EV1 quasars are characterized by high metallicity and suppressed X-ray emission. The underlying mechanism relating gas metallicity and X-ray emission is not clear but may be related to radiation-pressure-driven disk winds, which are enhanced at high metallicity, and consequent mass loading reducing coronal X-ray emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study spatially resolved scaling relations among stars, dust, and gas in ten nearby spiral galaxies. In a preceding paper, we have derived spatially resolved properties of the stellar population and dust by a panchromatic spectral energy distribution fitting using <jats:monospace>piXedfit</jats:monospace>. Now, we investigate resolved star formation (<jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>–Σ<jats:sub>SFR</jats:sub>–Σ<jats:sub>*</jats:sub>) and dust scaling relations. While the relations with all subgalactic regions of the galaxies are reasonably tight (<jats:italic>σ</jats:italic> ≲ 0.3 dex), we find that most of the scaling relations exhibit galaxy-to-galaxy variations in normalization and shape. Only two relations of Σ<jats:sub>dust</jats:sub>–Σ<jats:sub>gas</jats:sub> and Σ<jats:sub>dust</jats:sub>–<jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> do not show noticeable galaxy-to-galaxy variations among our sample galaxies. We further investigate the correlations among the scaling relations. We find significant correlations among the normalization of the <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>–Σ<jats:sub>SFR</jats:sub>–Σ<jats:sub>*</jats:sub> relations, which suggest that the galaxies with higher levels of resolved H<jats:sub>2</jats:sub> fraction (<jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>) tend to have higher levels of resolved star formation efficiency (SFE) and specific star formation rate (sSFR). We also observe that the galaxies with higher levels of resolved dust-to-stellar mass ratios tend to have higher levels of resolved sSFR, SFE, and <jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn5.gif" xlink:type="simple" /> </jats:inline-formula>. Moreover, we find that the galaxies with higher global sSFR and less compact morphology tend to have higher levels of the resolved sSFR, SFE, and <jats:inline-formula> <jats:tex-math> <?CDATA ${f}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>, which can explain the variations in the normalization of the <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{\Sigma }}}_{{{\rm{H}}}_{2}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Σ</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7da4ieqn7.gif" xlink:type="simple" /> </jats:inline-formula>–Σ<jats:sub>SFR</jats:sub>–Σ<jats:sub>*</jats:sub> relationships. Overall, we observe indications of the contributions of both global and local factors in governing the star formation process in galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Habitability of an exoplanet is believed to be profoundly affected by activities of the host stars, although the related coronal mass ejections (CMEs) are still rarely detected in solar-like and late-type stars. We here report an observational study on the flares of two M dwarfs triggered by the high-cadence survey performed by the Ground-based Wide Angle Camera system. In both events, the fast, time-resolved spectroscopy enables us to identify symmetric broad H<jats:italic>α</jats:italic> emission with not only a nearly zero bulk velocity, but also a large projected maximum velocity as high as ∼700–800 km s<jats:sup>−1</jats:sup>. This broadening could be resulted from either the Stark (pressure) effect or a flaring-associated CME at the stellar limb. In the context of the CME scenario, the CME mass is estimated to be ∼4 × 10<jats:sup>18</jats:sup> and 2 × 10<jats:sup>19</jats:sup> g. In addition, our spectral analysis reveals a temporal variation of the line center of the narrow H<jats:italic>α</jats:italic> emission in both events. The variation amplitudes are at tens of kilometers per second, which could be ascribed to the chromospheric evaporation in one event, and to a binary scenario in the other one. With the total flaring energy determined from our photometric monitor, we show a reinforced trend in which the larger the flaring energy, the higher the CME mass is.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The archetypical flare star UV Cet was observed by MeerKAT on 2021 October 5–6. A large radio outburst with a duration of ∼2 hr was observed between 886 and 1682 MHz, with a time resolution of 8 s and a frequency resolution of 0.84 MHz, enabling sensitive dynamic spectra to be formed. The emission is characterized by three peaks containing a multitude of broadband arcs or partial arcs in the time-frequency domain. In general, the arcs are highly right-hand circularly polarized. At the end of the third peak, brief bursts occur that are significantly elliptically polarized. We present a simple model that appears to be broadly consistent with the characteristics of the radio emission from UV Cet. Briefly, the stellar magnetic field is modeled as a dipole aligned with the rotational axis of the star. The radio emission mechanism is assumed to be due to the cyclotron maser instability, where x-mode radiation near the electron gyrofrequency is amplified. While the elliptically polarized bursts may be intrinsic to the source, rather stringent limits are imposed on the plasma density in the source and along the propagation path. We suggest that the elliptically polarized radiation may instead be the result of reflection on an overdense plasma structure at some distance from the source. The radio emission from UV Cet shares both stellar and planetary attributes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The evolution of white dwarfs (WDs) depends crucially on thermal processes. The plasma in their core can produce neutrinos that escape from the star, thus contributing to the energy loss. While in the absence of a magnetic field the main cooling mechanism is plasmon decay at high temperature and photon surface emission at low temperature, a large magnetic field in the core hiding beneath the surface even of ordinary WDs, and undetectable to spectropolarimetric measurements, could potentially leave an imprint in the cooling. In this paper, we revisit the contribution to WD cooling stemming from neutrino pair synchrotron radiation and the effects of the magnetic field on plasmon decay. Our key finding is that even if observations limit the magnetic field strength at the stellar surface, magnetic fields in the interior of WDs—with or without a surface magnetic field—can be strong enough to modify the cooling rate, with neutrino pair synchrotron emission being the most important contribution. This effect may not only be relevant for the quantification and interpretation of cooling anomalies, but suggests that the internal magnetic fields of WDs should be smaller than ∼ 6 × 10<jats:sup>11</jats:sup> G, slightly improving bounds coming from a stability requirement. While our simplified treatment of the WD structure implies that further studies are needed to reduce the systematic uncertainties, the estimates based on comparing the emissivities illustrate the potential of neutrino emission as a diagnostic tool to study the interior of WDs.</jats:p>