Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Interpreting the short-timescale variability of the accreting, young, low-mass stars known as Classical T Tauri stars remains an open task. Month-long, continuous light curves from the Transiting Exoplanet Survey Satellite (TESS) have become available for hundreds of T Tauri stars. With this vast data set, identifying connections between the variability observed by TESS and short-timescale accretion variability is valuable for characterizing the accretion process. To this end, we obtained short-cadence TESS observations of 14 T Tauri stars in the Taurus star formation region along with simultaneous ground-based, <jats:italic>UBVRI</jats:italic>-band photometry to be used as accretion diagnostics. In addition, we combine our data set with previously published simultaneous near-UV–near-IR Hubble Space Telescope spectra for one member of the sample. We find evidence that much of the short-timescale variability observed in the TESS light curves can be attributed to changes in the accretion rate, but note significant scatter between separate nights and objects. We identify hints of time lags within our data set that increase at shorter wavelengths, which we suggest may be evidence of longitudinal density stratification of the accretion column. Our results highlight that contemporaneous, multiwavelength observations remain critical for providing context for the observed variability of these stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar magnetic fields comprise an 11 yr activity cycle, represented by the number of sunspots. The maintenance of such a solar magnetic field can be attributed to fluid motion in the convection zone, i.e., a dynamo. This study conducts the mean-field analyses of the global solar dynamo simulation presented by Hotta et al. (2016). Although the study succeeds in producing coherent large-scale magnetic fields at high Reynolds numbers, the detailed physics of the maintenance of these fields have not been fully understood. This study extracts the <jats:italic>α </jats:italic>tensor and the turbulent magnetic diffusivity tensor <jats:bold> <jats:italic>β</jats:italic> </jats:bold> through mean-field analyses. The turbulent magnetic diffusivity exhibits a significant decrease toward high Reynolds numbers. The decrease in the turbulent magnetic diffusivity suppresses the energy conversion of large-scale field to small-scale field. This implies that the decrease in the turbulent magnetic diffusivity contributes to the maintenance of a large-scale magnetic field at high Reynolds numbers. A significant downward turbulent pumping is observed; it is enhanced in the weak phase of the large-scale field. This study proposes a cyclic reversal process of a large-scale field, which is dominantly driven by the <jats:italic>α </jats:italic>effect and is possibly triggered by downward pumping.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gas accretion onto the circumplanetary disks and the source region of accreting gas are important to reveal dust accretion that leads to satellite formation around giant planets. We performed local three-dimensional high-resolution hydrodynamic simulations of an isothermal and inviscid gas flow around a planet to investigate the planetary-mass dependence of the gas accretion bandwidth and gas accretion rate onto circumplanetary disks. We examined cases with various planetary masses corresponding to <jats:italic>M</jats:italic> <jats:sub>p</jats:sub> = 0.05–1<jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> at 5.2 au, where <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> is the current Jovian mass. We found that the radial width of the gas accretion band is proportional to <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{{\rm{p}}}^{1/6}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>6</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7ddfieqn1.gif" xlink:type="simple" /> </jats:inline-formula> for the low-mass regime with <jats:italic>M</jats:italic> <jats:sub>p</jats:sub> ≲ 0.2<jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> while it is proportional to <jats:italic>M</jats:italic> <jats:sub>p</jats:sub> for the high-mass regime with <jats:italic>M</jats:italic> <jats:sub>p</jats:sub> ≳ 0.2<jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub>. We found that the ratio of the mass accretion rate onto the circumplanetary disk to that into the Hill sphere is about 0.4 regardless of the planetary mass for the cases we examined. Combining our results with the gap model obtained from global hydrodynamic simulations, we derive a semi-analytical formula of mass accretion rate onto circumplanetary disks. We found that the mass dependence of our three-dimensional accretion rates is the same as the previously obtained two-dimensional case, although the qualitative behavior of accretion flow onto the circumplanetary disk is quite different between the two cases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High-resolution observations of the Perseus B5 “core” have previously revealed that this subsonic region actually consists of several filaments that are likely in the process of forming a quadruple stellar system. Since subsonic filaments are thought to be produced at the ∼0.1 pc sonic scale by turbulent compression, a detailed kinematic study is crucial to test such a scenario in the context of core and star formation. Here we present a detailed kinematic follow-up study of the B5 filaments at a 0.009 pc resolution using the VLA and GBT combined observations fitted with multicomponent spectral models. Using precisely identified filament spines, we find a remarkable resemblance between the averaged width profiles of each filament and Plummer-like functions, with filaments possessing FWHM widths of ∼0.03 pc. The velocity dispersion profiles of the filaments also show decreasing trends toward the filament spines. Moreover, the velocity gradient field in B5 appears to be locally well ordered (∼0.04 pc) but globally complex, with kinematic behaviors suggestive of inhomogeneous turbulent accretion onto filaments and longitudinal flows toward a local overdensity along one of the filaments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In a recent paper, we investigated possible systematic uncertainties related to the Cepheid color–luminosity calibration method and their influence on the tension between the Hubble constant as inferred from distances to Type Ia supernovae and the cosmic microwave background as measured with the Planck satellite. Here, we study the impact of other sources of uncertainty in the supernova distance ladder, including Cepheid temperature and metallicity variations, supernova magnitudes, and GAIA parallax distances. Using Cepheid data in 19 Type Ia supernova host galaxies from Riess et al., anchor data from Riess et al., and a set of recalibrated Milky Way Cepheid distances, we obtain <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> = 71.9 ± 2.2 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup>, 2.0<jats:italic>σ</jats:italic> from the Planck value. Excluding Cepheids with estimated color excesses <jats:inline-formula> <jats:tex-math> <?CDATA $\hat{E}(V-I)=0.15$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>ˆ</mml:mo> </mml:mrow> </mml:mover> <mml:mo stretchy="false">(</mml:mo> <mml:mi>V</mml:mi> <mml:mo>−</mml:mo> <mml:mi>I</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>0.15</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7c19ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> mag to mitigate the impact of the Cepheid color–luminosity calibration, the inferred Hubble constant is <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> = 68.1 ± 2.6 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup>, removing the tension with the Planck value.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We carried out Chandra, Hubble Space Telescope (HST), and Very Large Array observations of four MOJAVE blazars that have previously been classified as <jats:italic>hybrid</jats:italic> (FR I/II) blazars in terms of radio morphology but not total radio power. The motivation of this study is to determine the X-ray emission mechanism in jets, these being different in FR I and FR II jets. We detected X-ray jet emission with sufficient signal to noise in two blazars, viz<jats:italic>.</jats:italic> PKS 0215+015 and TXS 0730+504. We carried out spectral energy distribution modeling of the broadband emission from the jet regions in these sources and found that a single synchrotron emission model is ruled out due to the deep upper limits obtained from HST optical and IR data. The inverse Compton-cosmic microwave background model can reproduce the X-ray jet emission in both sources although the model requires extreme jet parameters. Both our sources possess FR II-like radio powers and our results are consistent with previous studies suggesting that radio power is more important than FR morphology in determining the emission mechanism of X-ray jets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The conservation of wave action in moving plasmas has been well known for over half a century. However, wave action is not conserved when multiple wave modes propagate and coexist close to the degeneration condition (where the sound speed equals the Alfvén speed, i.e., plasma <jats:italic>β</jats:italic> ∼ 1). Here, we show that the violation of conservation is due to wave mode conversion, and that the total wave action summed over the interacting modes is still conserved. Though the result is general, we focus on MHD waves and identify three distinctive mode-conversion mechanisms, i.e., degeneracy, linear mode conversion, and resonance, and provide an intuitive physical picture for the mode-conversion processes. We use one-dimensional MHD simulations with the Expanding Box Model to simulate the nonlinear evolution of monochromatic MHD waves in the expanding solar wind. The simulation results validate the theory; total wave action therefore remains an interesting diagnostic for studies of waves and turbulence in the solar wind.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report measurements of the gravitationally lensed secondary image—the first in an infinite series of so-called “photon rings”—around the supermassive black hole M87* via simultaneous modeling and imaging of the 2017 Event Horizon Telescope (EHT) observations. The inferred ring size remains constant across the seven days of the 2017 EHT observing campaign and is consistent with theoretical expectations, providing clear evidence that such measurements probe spacetime and a striking confirmation of the models underlying the first set of EHT results. The residual diffuse emission evolves on timescales comparable to one week. We are able to detect with high significance a southwestern extension consistent with that expected from the base of a jet that is rapidly rotating in the clockwise direction. This result adds further support to the identification of the jet in M87* with a black hole spin-driven outflow, launched via the Blandford–Znajek process. We present three revised estimates for the mass of M87* based on identifying the modeled thin ring component with the bright ringlike features seen in simulated images, one of which is only weakly sensitive to the astrophysics of the emission region. All three estimates agree with each other and previously reported values. Our strongest mass constraint combines information from both the ring and the diffuse emission region, which together imply a mass-to-distance ratio of <jats:inline-formula> <jats:tex-math> <?CDATA ${4.20}_{-0.06}^{+0.12}\,\mu \mathrm{as}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>4.20</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.12</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mi>μ</mml:mi> <mml:mi>as</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7c1dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and a corresponding black hole mass of (7.13 ± 0.39) × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, where the error on the latter is now dominated by the systematic uncertainty arising from the uncertain distance to M87*.</jats:p>