Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>Star formation in galaxies is regulated by heating and cooling in the interstellar medium (ISM). In particular, the processing of molecular gas into stars will depend strongly on the ratio of gas heating to gas cooling in the neutral gas around sites of recent star formation. In this work, we combine mid-infrared (mid-IR) observations of polycyclic aromatic hydrocarbons (PAHs), the dominant heating mechanism of gas in the ISM, with [C <jats:sc>ii</jats:sc>], [O <jats:sc>i</jats:sc>], and [Si <jats:sc>ii</jats:sc>] fine-structure emission, the strongest cooling channels in dense, neutral gas. The ratio of IR cooling line emission to PAH emission measures the photoelectric efficiency, a property of the ISM which dictates how much energy carried by ultraviolet photons gets transferred into the gas. We find that star-forming, IR-luminous galaxies in the Great Observatories All-Sky LIRG Survey with high IR surface densities have low photoelectric efficiencies. These systems also have, on average, higher ratios of radiation field strength to gas densities, and larger average dust grain size distributions. The data support a scenario in which the most compact galaxies have more young star-forming regions per unit area that exhibit less efficient gas heating. These conditions may be more common at high <jats:italic>z</jats:italic>, and may help explain the higher star formation rates at cosmic noon. We make predictions on how this can be investigated with the James Webb Space Telescope.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This study assesses the contribution of neutral polycyclic aromatic hydrocarbons (PAHs) and hydrogenated PAHs (H<jats:sub> <jats:italic>n</jats:italic> </jats:sub>-PAHs) in H<jats:sub>2</jats:sub>O-ices to the 3 <jats:italic>μ</jats:italic>m and 5–8 <jats:italic>μ</jats:italic>m regions of the infrared absorption spectrum of the Young Stellar Object, Mon R2 IRS 3, and the Taurus dense cloud in the direction of Elias 16. We compare the astronomical spectra to the previously published laboratory data of matrix-isolated PAHs and H<jats:sub> <jats:italic>n</jats:italic> </jats:sub>-PAHs in H<jats:sub>2</jats:sub>O-ices. For the molecules in this study, the band positions, FWHMs, and integrated band strengths have been measured. For the PAHs considered here, the ratio of the experimental <jats:italic>A</jats:italic>(C–H) stretch (in H<jats:sub>2</jats:sub>O ices) to the theoretical <jats:italic>A</jats:italic>(C–H) stretch (in the gas phase) is consistently about 0.10, meaning that the trove of theoretical data can be reliably scaled to compare to the astronomical spectra. We find that the fractional percentage contribution to the 5–8 <jats:italic>μ</jats:italic>m region for Mon R2 IRS 3 ranges between 2.7 and 3.9 for neutral PAHs and 0.25–1.2 for H<jats:sub> <jats:italic>n</jats:italic> </jats:sub>-PAHs. The best match to the observed 3.25 <jats:italic>μ</jats:italic>m profile in the Mon R2 IRS 3 spectrum is accomplished with the laboratory-measured coronene:H<jats:sub>2</jats:sub>O spectrum. Using this spectrum we estimate that neutral PAHs contribute up to 12.0% of the cosmic carbon budget for Mon R2 IRS 3 and &lt;14.5% for Elias 16. Neutral hydrogenated PAHs contribute mainly to the 3.47 <jats:italic>μ</jats:italic>m absorption and very little to the 5 to 8 <jats:italic>μ</jats:italic>m region. For neutral H<jats:sub> <jats:italic>n</jats:italic> </jats:sub>-PAHs, we estimate that they contribute up to 0.6% of the cosmic carbon budget for Mon R2 IRS 3 and &lt;1% for Elias 16.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present limits on the lens flux of OGLE-2007-BLG-224 based on MagAO imaging taken seven years after the microlensing event. At the time of the observations, the lens should have been separated from the microlensing source by 292 mas. However, no new sources are detected with MagAO. We place an upper limit on the lens flux of <jats:italic>H</jats:italic> &gt; 20.57. This measurement supports the conclusion of Gould et al. that the lens in this event should be a brown dwarf. This is the first test of a prediction based on the terrestrial microlens parallax effect and the first AO confirmation of a substellar/dark microlens.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the Stromlo Stellar Tracks, a set of stellar evolutionary tracks, computed by modifying the Modules for Experiments in Stellar Astrophysics (MESA) 1D stellar evolution package, to fit the Galactic Concordance abundances for hot (<jats:italic>T</jats:italic> &gt; 8000 K) massive (≥10 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) main-sequence (MS) stars. Until now, all stellar evolution tracks have been computed at solar, scaled-solar, or <jats:italic>α</jats:italic>-element-enhanced abundances, and none of these models correctly represent the Galactic Concordance abundances at different metallicities. This paper is the first implementation of Galactic Concordance abundances to the stellar evolution models. The Stromlo tracks cover massive stars (10 ≤ <jats:italic>M</jats:italic>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> ≤ 300) with varying rotations (<jats:italic>v</jats:italic>/<jats:italic>v</jats:italic> <jats:sub>crit</jats:sub> = 0.0, 0.2, 0.4) and a finely sampled grid of metallicities (−2.0 ≤ [Z/H] ≤ +0.5; Δ[Z/H] = 0.1) evolved from the pre-main sequence to the end of <jats:sup>12</jats:sup>C burning. We find that the implementation of Galactic Concordance abundances is critical for the evolution of MS, massive hot stars in order to estimate accurate stellar outputs (<jats:italic>L</jats:italic>, <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub>, <jats:italic>g</jats:italic>), which, in turn, have a significant impact on determining the ionizing photon luminosity budgets. We additionally support prior findings of the importance that rotation plays on the evolution of massive stars and their ionizing budget. The evolutionary tracks for our Galactic Concordance abundance scaling provide a more empirically motivated approach than simple uniform abundance scaling with metallicity for the analysis of H <jats:sc>ii</jats:sc> regions and have considerable implications for determining nebular emission lines and metallicity. Therefore, it is important to refine existing stellar evolutionary models for comprehensive high-redshift extragalactic studies. The Stromlo tracks are available to the astronomical community.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Long-duration gamma-ray bursts (GRBs) are generally related to the core-collapse of massive stars. In the collapsar scenario, a rotating stellar-mass black hole (BH) surrounded by a hyperaccretion disk has been considered as one of the plausible candidates of GRB central engines. In this paper, we work on a sample including 146 long GRBs with significant jet break features in the multiband afterglows. The jet opening angles can then be obtained by the jet break time. By assuming GRB jets powered by the Blandford–Znajek (BZ) mechanism in the BH hyperaccretion system, we analyze the distributions of the long GRB luminosities and durations in the samples, and constrain the accretion rates for the different BH spins. As a result, we find that the BZ mechanism is so powerful that it is possible to interpret the long GRB prompt emissions within reasonable accretion rates.</jats:p>

<jats:title>Abstract</jats:title> <jats:p> <jats:sup>3</jats:sup>He-rich solar energetic particles (SEPs) are believed to be accelerated in solar flares or jets by a mechanism that depends on the ion charge-to-mass (<jats:italic>Q</jats:italic>/<jats:italic>M</jats:italic>) ratio. It implies that the flare plasma characteristics (e.g., temperature) may be effective in determining the elemental abundances of <jats:sup>3</jats:sup>He-rich SEPs. This study examines the relation between the suprathermal (≲0.2 MeV nucleon<jats:sup>−1</jats:sup>) abundances of the He–Fe ions measured on the Advanced Composition Explorer and temperature in the solar sources for 24 <jats:sup>3</jats:sup>He-rich SEP events in the period 2010–2015. The differential emission measure technique is applied to derive the temperature of the source regions from the extreme ultraviolet imaging observations on the Solar Dynamics Observatory. The obtained temperature distribution peaks at 2.0–2.5 MK that is surprisingly consistent with earlier findings based on in situ elemental abundance or charge state measurements. We have found a significant anticorrelation between <jats:sup>3</jats:sup>He/<jats:sup>4</jats:sup>He ratio and solar source temperature with a coefficient −0.6. It is most likely caused by non-charge-stripping processes, as both isotopes would be fully ionized in the inferred temperature range. This study shows that the elemental ratios <jats:sup>4</jats:sup>He/O, N/O, Ne/O, Si/O, S/O, Ca/O, Fe/O generally behave with temperature as expected from abundance enhancement calculations at ionization equilibrium. The C and Mg, the two species with small changes in the <jats:italic>Q</jats:italic>/<jats:italic>M</jats:italic> ratio in the obtained temperature range, show no such behavior with temperature and could be influenced by similar processes as for the <jats:sup>3</jats:sup>He/<jats:sup>4</jats:sup>He ratio.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed study of the internal structure and kinematics of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). Using machine-learning techniques, we have combined the information provided by 3300 RR Lyrae stars, more than 2000 spectroscopically observed stars, and the Gaia second data release to derive the full phase space, i.e., 3D positions and kinematics, of more than 1.2 × 10<jats:sup>5</jats:sup> member stars in the core of the galaxy. Our results show that Sgr has a bar structure ∼2.5 kpc long, and that tidal tails emerge from its tips to form what it is known as the Sgr stream. The main body of the galaxy, strongly sheared by tidal forces, is a triaxial (almost prolate) ellipsoid with its longest principal axis of inertia inclined 43° ± 6° with respect to the plane of the sky and axis ratios of 1:0.67:0.60. Its external regions are expanding mainly along its longest principal axis, yet the galaxy conserves an inner core of about 500×330×300 pc that shows no net expansion and is rotating at <jats:italic>v</jats:italic> <jats:sub>rot</jats:sub> = 4.13 ± 0.16 km s<jats:sup>−1</jats:sup>. The internal angular momentum of the galaxy forms an angle <jats:italic>θ</jats:italic> = 18° ± 6° with respect to its orbital angular momentum, meaning that Sgr is in an inclined prograde orbit around the Milky Way. We compared our results with predictions from <jats:italic>N</jats:italic>-body models with spherical, pressure-supported progenitors and a model whose progenitor is a flattened rotating disk. Only the rotating model, based on preexisting simulations aimed at reproducing the line-of-sight velocity gradients observed in Sgr, was able to reproduce the observed properties in the core of the galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We performed a systematic search for broad-velocity-width molecular features (BVFs) in the disk part of our Galaxy by using the CO <jats:italic>J</jats:italic> = 1–0 survey data obtained with the Nobeyama Radio Observatory 45 m telescope. From this search, 58 BVFs were identified. In comparisons with the infrared and radio continuum images, 36 BVFs appeared to have both infrared and radio continuum counterparts, and 15 of them are described as molecular outflows from young stellar objects in the literature. In addition, 21 BVFs have infrared counterparts only, and eight of them are described as molecular outflows in the literature. One BVF (CO 16.134–0.553) does not have any luminous counterpart in the other wavelengths, which suggests that it may be an analog of high-velocity compact clouds in the Galactic center.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stars with peculiar element abundances are important markers of chemical enrichment mechanisms. We present a simple method, tangent space projection (TSP), for the detection of <jats:italic>X</jats:italic>-enriched stars, for arbitrary elements <jats:italic>X</jats:italic>, even from blended lines. Our method does not require stellar labels, but instead directly estimates the counterfactual unenriched spectrum from other unlabeled spectra. As a case study, we apply this method to the 6708 Å Li doublet in LAMOST DR5, identifying 8428 Li-enriched stars seamlessly across evolutionary state. We comment on the explanation for Li-enrichment for different subpopulations, including planet accretion, nonstandard mixing, and youth.</jats:p>