Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We use the Green Bank Telescope to search for <jats:sup>3</jats:sup>He<jats:sup>+</jats:sup> emission from a sample of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009. During the era of primordial nucleosynthesis, the light elements <jats:sup>2</jats:sup>H, <jats:sup>3</jats:sup>He, <jats:sup>4</jats:sup>He, and <jats:sup>7</jats:sup>Li were produced in significant amounts, and these abundances have since been modified primarily by stars. Observations of <jats:sup>3</jats:sup>He<jats:sup>+</jats:sup> in H <jats:sc>ii</jats:sc> regions located throughout the Milky Way disk reveal very little variation in the <jats:sup>3</jats:sup>He/H abundance ratio—the “<jats:sup>3</jats:sup>He Plateau”—indicating that the net effect of <jats:sup>3</jats:sup>He production in stars is negligible. This is in contrast to much higher <jats:sup>3</jats:sup>He/H abundance ratios reported for some planetary nebulae. This discrepancy is known as the “<jats:sup>3</jats:sup>He Problem.” We use radio recombination lines observed simultaneously with the <jats:sup>3</jats:sup>He<jats:sup>+</jats:sup> transition to make a robust assessment of the spectral sensitivity that these observations achieve. We detect spectral lines at ∼1–2 mK intensities, but at these levels, instrumental effects compromise our ability to measure accurate spectral line parameters. We do not confirm reports of previous detections of <jats:sup>3</jats:sup>He<jats:sup>+</jats:sup> in NGC 3242 nor do we detect <jats:sup>3</jats:sup>He<jats:sup>+</jats:sup> emission from any of our sources. This result calls into question all reported detections of <jats:sup>3</jats:sup>He<jats:sup>+</jats:sup> emission from any planetary nebula. The <jats:sup>3</jats:sup>He/H abundance upper limit we derive here for NGC 3242 is inconsistent with standard stellar production of <jats:sup>3</jats:sup>He and thus requires that some type of extra-mixing process operates in low-mass stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The polarization properties of radio sources powered by an Active Galactic Nucleus (AGN) have attracted considerable attention because of the significance of magnetic fields in the physics of these sources, their use as probes of plasma along the line of sight, and as a possible contaminant of polarization measurements of the cosmic microwave background. For each of these applications, a better understanding of the statistics of polarization in relation to source characteristics is crucial. In this paper, we derive the median fractional polarization, Π<jats:sub>0,med</jats:sub>, of large samples of radio sources with 1.4 GHz flux density 6.6 &lt; <jats:italic>S</jats:italic> <jats:sub>1.4</jats:sub> &lt; 70 mJy, by stacking 1.4 GHz NVSS polarized intensity as a function of angular size derived from the FIRST survey. Five samples with deconvolved mean angular size 1.″8 to 8.″2 and two samples of symmetric double sources are analyzed. These samples represent most sources smaller than or near the median angular size of the mJy radio source population We find that the median fractional polarization Π<jats:sub>0,med</jats:sub> at 1.4 GHz is a strong function of source angular size ≲5″ and a weak function of angular size for larger sources up to ∼8″. We interpret our results as depolarization inside the AGN host galaxy and its circumgalactic medium. The curvature of the low-frequency radio spectrum is found to anticorrelate with Π<jats:sub>0,med</jats:sub>, a further sign that depolarization is related to the source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present new X-ray and UV observations of the Wolf–Rayet + black hole (BH) binary system NGC 300 X-1 with the Chandra X-ray Observatory and the Hubble Space Telescope Cosmic Origins Spectrograph. When combined with archival X-ray observations, our X-ray and UV observations sample the entire binary orbit, providing clues to the system geometry and interaction between the BH accretion disk and the donor star wind. We measure a binary orbital period of 32.7921 ± 0.0003 hr, in agreement with previous studies, and perform phase-resolved spectroscopy using the X-ray data. The X-ray light curve reveals a deep eclipse, consistent with inclination angles of <jats:italic>i</jats:italic> = 60°–75°, and a pre-eclipse excess consistent with an accretion stream impacting the disk edge. We further measure radial velocity variations for several prominent far-UV spectral lines, most notably H <jats:sc>ii</jats:sc> <jats:italic>λ</jats:italic>1640 and C <jats:sc>iv</jats:sc> <jats:italic>λ</jats:italic>1550. We find that the He <jats:sc>ii</jats:sc> emission lines systematically lag the expected Wolf–Rayet star orbital motion by a phase difference of Δ<jats:italic>ϕ</jats:italic> ∼ 0.3, while C <jats:sc>iv</jats:sc> <jats:italic>λ</jats:italic>1550 matches the phase of the anticipated radial velocity curve of the Wolf–Rayet donor. We assume the C <jats:sc>iv</jats:sc> <jats:italic>λ</jats:italic>1550 emission line follows a sinusoidal radial velocity curve (semi-amplitude = 250 km s<jats:sup>−1</jats:sup>) and infer a BH mass of 17 ± 4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Our observations are consistent with the presence of a wind-Roche lobe overflow accretion disk, where an accretion stream forms from gravitationally focused wind material and impacts the edge of the BH accretion disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stellar-mass estimates of massive galaxies are susceptible to systematic errors in their photometry, due to their extended light profiles. In this study, we use data from the Dragonfly Wide Field Survey to accurately measure the total luminosities and colors of nearby massive galaxies. The low surface brightness limits of the survey (<jats:italic>μ</jats:italic> <jats:sub> <jats:italic>g</jats:italic> </jats:sub> ≈ 31 mag arcsec<jats:sup>−2</jats:sup> on a 1′ scale) allow us to implement a method, based on integrating the 1D surface brightness profile, that is minimally dependent on any parameterization. We construct a sample of 1188 massive galaxies with <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{* }/{M}_{\odot }\gt 10.75$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd7f8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> based on the Galaxy Mass and Assembly (GAMA) survey and measure their total luminosities and <jats:italic>g</jats:italic> − <jats:italic>r</jats:italic> colors. We then compare our measurements to various established methods applied to imaging from the Sloan Digital Sky Survey (SDSS), focusing on those favored by the GAMA survey. In general, we find that galaxies are brighter in the <jats:italic>r</jats:italic> band by an average of ∼0.05 mag and bluer in <jats:italic>g</jats:italic> − <jats:italic>r</jats:italic> colors by ∼0.06 mag compared to the GAMA measurements. These two differences have opposite effects on the stellar-mass estimates. The total luminosities are larger by 5% but the mass-to-light ratios are lower by ∼10%. The combined effect is that the stellar-mass estimate of massive galaxies decreases by 7%. This, in turn, implies a small change in the number density of massive galaxies: ≤30% at <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}{M}_{* }/{M}_{\odot }\geqslant 11$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd7f8ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the results of new dust polarization of a nearly edge-on disk in the HH 212 protostellar system, obtained with the Atacama Large Millimeter/submillimeter Array at ∼0.035″ (14 au) resolution in a continuum at <jats:italic>λ</jats:italic> ∼ 878 <jats:italic>μ</jats:italic>m. Dust polarization is detected within ∼44 au of the central source, where a rotationally supported disk has formed. The polarized emission forms V-shaped structures opening to the east, and probably to the west, arising from the disk surfaces and arm structures further away in the east and west, which could be due to potential spiral arms excited in the outer disk. The orientations of the polarization are mainly parallel to the minor axis of the disk, with some in the western part tilting slightly away from the minor axis to form a concave shape with respect to the center. This tilting of the orientations of the polarization is expected from dust self-scattering, e.g., by 50−75 <jats:italic>μ</jats:italic>m grains in a young disk. The intensity and degree of the polarization both peak near the central source with a small dip at the central source and decrease toward the edges. These decreases in the intensity and degree of polarization are expected from dichroic extinction by grains aligned by poloidal fields, but may also be consistent with dust self-scattering if the grain size decreases toward the edges. It is possible that both mechanisms are needed to produce the observed dust polarization, suggesting the presence of both grain growth and poloidal fields in the disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We discovered a new growth mode of dust grains to kilometer-size bodies in protoplanetary disks that evolve via viscous accretion and magnetically driven disk winds (MDWs). We solved an approximate coagulation equation of dust grains with time-evolving disks that consist of both gas and solid components using a one-dimensional model. With grain growth, all solid particles initially drift inward toward the central star due to the gas drag force. However, the radial profile of gas pressure, <jats:italic>P</jats:italic>, is modified by the MDW that disperses the gas in an inside-out manner. Consequently, a local concentration of solid particles is created by the converging radial flux of drifting dust grains at the location with a convex-upward profile of <jats:italic>P</jats:italic>. When the dimensionless stopping time, St, exceeds unity there, the solid particles spontaneously reach the growth-dominated state because of the positive feedback between the suppressed radial drift and the enhanced accumulation of dust particles that drift from the outer part. Once the solid particles are in the drift-limited state, the above-mentioned condition of St <jats:inline-formula> <jats:tex-math> <?CDATA $\gtrsim \,1$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd79fieqn1.gif" xlink:type="simple" /> </jats:inline-formula> for dust growth is equivalent to Σ<jats:sub>d</jats:sub>/Σ<jats:sub>g</jats:sub> ≳ <jats:italic>η</jats:italic>, where Σ<jats:sub>d</jats:sub>/Σ<jats:sub>g</jats:sub> is the dust-to-gas surface-density ratio and <jats:italic>η</jats:italic> is the dimensionless radial pressure-gradient force. As a consequence of the successful growth of dust grains, a ring-like structure containing planetesimal-size bodies is formed at the inner part of the protoplanetary disks. Such a ring-shaped concentration of planetesimals is expected to play a vital role in the subsequent planet formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate self-gravitating equilibria of halos constituted by dark matter (DM) non-minimally coupled to gravity. In particular, we consider a theoretically motivated non-minimal coupling that may arise when the averaging/coherence length <jats:italic>L</jats:italic> associated with the fluid description of the DM collective behavior is comparable to the local curvature scale. In the Newtonian limit, such a non-minimal coupling amounts to a modification of the Poisson equation by a term <jats:italic>L</jats:italic> <jats:sup>2</jats:sup>∇<jats:sup>2</jats:sup> <jats:italic>ρ</jats:italic> proportional to the Laplacian of the DM density <jats:italic>ρ</jats:italic> itself. We further adopt a general power-law equation of state <jats:italic>p</jats:italic> ∝ <jats:italic>ρ</jats:italic> <jats:sup>Γ</jats:sup> <jats:italic>r</jats:italic> <jats:sup> <jats:italic>α</jats:italic> </jats:sup> relating the DM dynamical pressure <jats:italic>p</jats:italic> to density <jats:italic>ρ</jats:italic> and radius <jats:italic>r</jats:italic>, as expected for phase-space density stratification during the gravitational assembly of halos in a cosmological context. We confirm previous findings that, in the absence of non-minimal coupling, the resulting density <jats:italic>ρ</jats:italic>(<jats:italic>r</jats:italic>) features a steep central cusp and an overall shape mirroring the outcomes of <jats:italic>N</jats:italic>-body simulations in the standard ΛCDM cosmology, as described by the classic Navarro–Frenk–White or Einasto profiles. Most importantly, we find that the non-minimal coupling causes the density distribution to develop an inner core and a shape that closely follows the Burkert profile out to several core scale radii. In fact, we highlight that the resulting mass distributions can fit, with an accuracy comparable to Burkert’s one, the coadded rotation curves of dwarf, DM-dominated galaxies. Finally, we show that non-minimally coupled DM halos are consistent with the observed scaling relation between the core radius <jats:italic>r</jats:italic> <jats:sub>0</jats:sub> and core density <jats:italic>ρ</jats:italic> <jats:sub>0</jats:sub>, in terms of a universal core surface density <jats:italic>ρ</jats:italic> <jats:sub>0</jats:sub> × <jats:italic>r</jats:italic> <jats:sub>0</jats:sub> among different galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the collimation and acceleration of jets in the nearby giant radio galaxy NGC 315, using multifrequency Very Long Baseline Array observations and archival High Sensitivity Array and Very Large Array data. We find that the jet geometry transitions from a semi-parabolic shape into a conical/hyperbolic shape at a distance of ≈10<jats:sup>5</jats:sup> gravitational radii. We constrain the frequency-dependent position of the core, from which we locate the jet base. The jet collimation profile in the parabolic region is in good agreement with the steady axisymmetric force-free electrodynamic solution for the outermost poloidal magnetic field line anchored to the black hole event horizon on the equatorial plane, similar to the nearby radio galaxies M87 and NGC 6251. The velocity field derived from the asymmetry in brightness between the jet and counterjet shows gradual acceleration up to the bulk Lorentz factor of Γ ∼ 3 in the region where the jet collimation occurs, confirming the presence of the jet acceleration and collimation zone. These results suggest that the jets are collimated by the pressure of the surrounding medium and accelerated by converting Poynting flux to kinetic energy flux. We discover limb brightening of the jet in a limited distance range where the angular resolution of our data is sufficient to resolve the jet transverse structure. This indicates that either the jet has a stratified velocity field of fast-inner and slow-outer layers or the particle acceleration process is more efficient in the outer layer owing to the interaction with the surroundings on parsec scales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>At subterahertz frequencies—i.e., millimeter and submillimeter wavelengths—there is a gap in measurements of the solar radius, as well as other parameters of the solar atmosphere. As the observational wavelength changes, the radius varies because the altitude of the dominant electromagnetic radiation is produced at different heights in the solar atmosphere. Moreover, radius variations throughout long time series are indicative of changes in the solar atmosphere that may be related to the solar cycle. Therefore, the solar radius is an important parameter for the calibration of solar atmospheric models enabling a better understanding of the atmospheric structure. In this work, we use data from the Solar Submillimeter-wave Telescope (SST) and the Atacama Large Millimeter/submillimeter Array (ALMA) at frequencies of 100, 212, 230, and 405 GHz to measure the equatorial and polar radii of the Sun. The radii measured with extensive data from the SST agree with the radius-versus-frequency trend present in the literature. The radii derived from ALMA maps at 230 GHz also agree with the radius-versus-frequency trend, whereas the 100 GHz radii are slightly above the values reported by other authors. In addition, we analyze the equatorial and polar radius behavior over the years by determining the correlation coefficient between solar activity and subterahertz radius time series at 212 and 405 GHz (SST). The variations of the SST-derived radii over 13 yr are correlated to the solar activity when considering equatorial regions of the solar atmosphere and anticorrelated when considering polar regions. The ALMA-derived radius time series for 100 and 230 GHz show very similar behaviors with those of SST.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We compare abundance ratio trends in a sample of ∼11,000 Milky Way bulge stars (<jats:italic>R</jats:italic> <jats:sub>GC</jats:sub> &lt; 3 kpc) from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) to those of APOGEE stars in the Galactic disk (5 kpc &lt; <jats:italic>R</jats:italic> <jats:sub>GC</jats:sub> &lt; 11 kpc). We divide each sample into low-Ia (high-[Mg/Fe]) and high-Ia (low-[Mg/Fe]) populations, and in each population, we examine the median trends of [X/Mg] versus [Mg/H] for elements X = Fe, O, Na, Al, Si, P, S, K, Ca, V, Cr, Mn, Co, Ni, Cu, and Ce. To remove small systematic trends of APOGEE abundances with stellar <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}(g)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd6beieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, we resample the disk stars to match the <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}(g)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd6beieqn2.gif" xlink:type="simple" /> </jats:inline-formula> distributions of the bulge data. After doing so, we find nearly identical median trends for low-Ia disk and bulge stars for all elements. High-Ia trends are similar for most elements, with noticeable (0.05–0.1 dex) differences for Mn, Na, and Co. The close agreement of abundance trends (with typical differences ≲0.03 dex) implies that similar nucleosynthetic processes enriched bulge and disk stars despite the different star formation histories and physical conditions of these regions. For example, we infer that differences in the high-mass slope of the stellar initial mass function between disk and bulge must have been ≲0.30. This agreement, and the generally small scatter about the median sequences, means that one can predict all of a bulge star's APOGEE abundances with good accuracy knowing only its measured [Mg/Fe] and [Mg/H] and the observed trends of disk stars.</jats:p>