Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We describe and discuss remarkable infrared spectra, covering key portions of the 2–5 <jats:italic>μ</jats:italic>m wavelength interval, of the probable OH/IR supergiant 2MASS J17470898−2829561 (2M1747), located in direction of the Sgr B molecular cloud complex within the Central Molecular Zone (CMZ) of the Galaxy. This star was originally singled out for examination based on its suitability for spectroscopy of lines of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{3}^{+}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabee12ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> in the CMZ. Analysis of the spectra shows that 2M1747 is deeply embedded within Sgr B1, with <jats:italic>A</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> ≳ 100 mag, making it the only star within Sgr B for which infrared spectra have been obtained at present, and thereby a unique infrared probe of the dense interstellar medium within the CMZ. Despite the high extinction, spectra of 2M1747 reveal a veiled photosphere in the <jats:italic>K</jats:italic> band and circumstellar gas in the <jats:italic>M</jats:italic> band, giving clues as to its nature. Its 3.5–4.0 <jats:italic>μ</jats:italic>m spectrum contains the strongest absorption lines of <jats:inline-formula> <jats:tex-math> <?CDATA ${{\rm{H}}}_{3}^{+}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabee12ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> observed toward any object to date. The 4.5–4.8 <jats:italic>μ</jats:italic>m spectrum has impressively deep and wide absorption lines of interstellar CO, most of which arise in dense gas within Sgr B1. The 3–5 <jats:italic>μ</jats:italic>m spectrum also contains several solid-state absorption features, which are characteristic of both dense and diffuse clouds, and which raise questions about the identifications of some of these features. We discuss the nature of the star, the extinction to it, the extinction law for dust in the CMZ, and the identifications of the various solid-state features and where they are produced along this complex line of sight.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on optical observations and modeling of HD96670, a single-line spectroscopic binary in the Carina OB2 association. We collected 10 epochs of optical spectroscopy, and optical photometry on 17 nonconsecutive nights on the source. We construct a radial velocity curve from the spectra, and update the orbital period of the binary to be <jats:italic>P</jats:italic> = 5.28388 ± 0.00046 days. The spectra show oxygen and helium absorption, consistent with an O-type primary. We see no evidence for spectral lines from the secondary star in the binary. We model the optical light curve and radial velocity curve simultaneously using the Wilson–Devinney code and find a best-fit mass of <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{1}={22.7}_{-3.6}^{+5.2}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf24cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> for the primary, and <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{2}={6.2}_{-0.7}^{+0.9}\,{M}_{\odot }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf24cieqn2.gif" xlink:type="simple" /> </jats:inline-formula> for the secondary. An object of this mass is consistent with either a B-type star, or a black hole. Given that we see no absorption lines from the secondary, in combination with an observed hard power-law X-ray spectrum with Γ = 2.6 detected past 10 keV that may have been produced by wind accretion onto the secondary, we conclude that the secondary is most likely a black hole. We see asymmetrical helium lines with a shape consistent with the presence of a third star. If the secondary is indeed a black hole, this system would add to the small sample of only four possible black hole high mass X-ray binaries in the galaxy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Plasmoids—magnetized quasi-circular structures formed self-consistently in reconnecting current sheets—were previously considered to be the graveyards of energetic particles. In this paper, we demonstrate the important role of plasmoids in shaping the particle energy spectrum in relativistic reconnection (i.e., with upstream magnetization <jats:italic>σ</jats:italic> <jats:sub>up</jats:sub> ≫ 1). Using 2D particle-in-cell simulations in pair plasmas with <jats:italic>σ</jats:italic> <jats:sub>up</jats:sub> = 10 and 100, we study a secondary particle energization process that takes place inside compressing plasmoids. We demonstrate that plasmoids grow in time, while their interiors compress, amplifying the internal magnetic field. The magnetic field felt by particles injected in an isolated plasmoid increases linearly with time, which leads to particle energization as a result of magnetic moment conservation. For particles injected with a power-law distribution function, this energization process acts in such a way that the shape of the injected power law is conserved, while producing an additional nonthermal tail <jats:italic>f</jats:italic>(<jats:italic>E</jats:italic>) ∝ <jats:italic>E</jats:italic> <jats:sup>−3</jats:sup> at higher energies, followed by an exponential cutoff. The cutoff energy, which increases with time as <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{\mathrm{cut}}\propto \sqrt{t}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabedacieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, can greatly exceed <jats:italic>σ</jats:italic> <jats:sub>up</jats:sub> <jats:italic>m</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub> <jats:italic>c</jats:italic> <jats:sup>2</jats:sup>. We analytically predict the secondary acceleration timescale and the shape of the emerging particle energy spectrum, which can be of major importance in certain astrophysical systems, such as blazar jets.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Improving the use of Type Ia supernovae (SNe Ia) as standard candles requires a better approach to incorporate the relationship between SNe Ia and the properties of their host galaxies. Using a spectroscopically confirmed sample of ∼1600 SNe Ia, we develop the first empirical model of underlying populations for SNe Ia light-curve properties that includes their dependence on host-galaxy stellar mass; we find a significant correlation between stretch population and stellar mass (99.9% confidence) and a weaker correlation between color and stellar mass (90% confidence). These populations are important inputs to simulations that are used to model selection effects and correct distance biases within the BEAMS with Bias Correction (BBC) framework. Here we improve BBC to also account for SNe Ia-host correlations, and we validate this technique on simulated data samples. We recover the input relationship between SNe Ia luminosity and host-galaxy stellar mass (the mass step, <jats:italic>γ</jats:italic>) with a bias of 0.004 ±0.001 mag, which is a factor of 5 improvement over previous methods that have a <jats:italic>γ </jats:italic>bias of ∼0.02 ± 0.001 mag. We adapt BBC for a novel dust-based model of intrinsic brightness variations, which results in a greatly reduced mass step for data (<jats:italic>γ</jats:italic> = 0.017 ± 0.008) and for simulations (<jats:italic>γ</jats:italic> = 0.006 ± 0.007). Analyzing simulated SNe Ia, the biases on the dark energy equation of state, <jats:italic>w</jats:italic>, vary from Δ<jats:italic>w</jats:italic> = 0.006(5) to 0.010(5) with our new BBC method; these biases are significantly smaller than the 0.02(5) <jats:italic>w</jats:italic> bias using previous BBC methods that ignore SNe Ia-host correlations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Giant, star-forming clumps are a common feature prevalent among high-redshift star-forming galaxies and play a critical role in shaping their chaotic morphologies and yet, their nature and role in galaxy evolution remains to be fully understood. A majority of the effort to study clumps has been focused at high redshifts, and local clump studies have often suffered from small sample sizes. In this work, we present an analysis of clump properties in the local universe, and for the first time, performed with a statistically significant sample. With the help of the citizen science-powered Galaxy Zoo: Hubble project, we select a sample of 92 <jats:italic>z</jats:italic> &lt; 0.06 clumpy galaxies in Sloan Digital Sky Survey Stripe 82 galaxies. Within this sample, we identify 543 clumps using a contrast-based image analysis algorithm and perform photometry as well as estimate their stellar population properties. The overall properties of our <jats:italic>z</jats:italic> &lt; 0.06 clump sample are comparable to the high-redshift clumps. However, contrary to the high-redshift studies, we find no evidence of a gradient in clump ages or masses as a function of their galactocentric distances. Our results challenge the inward migration scenario for clump evolution for the local universe, potentially suggesting a larger contribution of ex situ clumps and/or longer clump migration timescales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first results from a Hubble Space Telescope Wide Field Camera 3/Infrared program, which obtained direct imaging and grism observations of galaxies near quasar sightlines with a high frequency of uncorrelated foreground Mg <jats:sc>ii</jats:sc> absorption. These highly efficient observations targeted 54 Mg <jats:sc>ii</jats:sc> absorbers along the line of sight to nine quasars at <jats:italic>z</jats:italic> <jats:sub>(qso</jats:sub> ∼ 2. We find that 89% of the absorbers in the range of 0.64 &lt; <jats:italic>z</jats:italic> &lt; 1.6 can be spectroscopically matched to at least one galaxy with an impact parameter of less than 200 kpc and ∣Δ<jats:italic>z</jats:italic>∣/(1 + <jats:italic>z</jats:italic>) &lt; 0.006. We have estimated the star formation rates and measured structural parameters for all detected galaxies with impact parameters in the range of 7–200 kpc and star formation rates greater than 1.3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>. We find that galaxies associated with Mg <jats:sc>ii</jats:sc> absorption have significantly higher mean star formation rates and marginally higher mean star formation rate surface densities compared to galaxies with no detected Mg <jats:sc>ii</jats:sc>. Nearly half of the Mg <jats:sc>ii</jats:sc> absorbers match more than one galaxy, and the mean equivalent width of the Mg <jats:sc>ii</jats:sc> absorption is found to be greater for groups, compared to isolated galaxies. Additionally, we observe a significant redshift evolution in the physical extent of Mg <jats:sc>ii</jats:sc>-absorbing gas around galaxies and evidence of an enhancement of Mg <jats:sc>ii</jats:sc> within 50° of the minor axis, characteristic of outflows, which persists to 80 kpc around the galaxies, in agreement with recent predictions from simulations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The purpose of this paper is to study the behavior of magnetohydrodynamic (MHD) wave modes that propagate in compressible magnetic flux tubes with an elliptical cross section embedded in a magnetic environment. The dispersion relation that describes the behavior of MHD wave modes permitted in an elliptical magnetic flux tube is solved numerically. Distortion of the spatial structure of the purely real eigenmodes from the well-known circular flux tube model has been considered. It has been studied under both photospheric and coronal conditions. It has been shown that (i) solutions in the form of even Mathieu functions are more sensitive to the value of eccentricity than solutions with the form of odd Mathieu functions; (ii) if the ellipticity of the cross section of the magnetic flux tube increases, a sausage mode (<jats:italic>m</jats:italic> = 0) cannot be easily identified; (iii) even solutions that correspond to the fluting mode (<jats:italic>m</jats:italic> = 3) can be misinterpreted as a kink mode (<jats:italic>m</jats:italic> = 1) due to their similarities. In contrast to the fluting modes that are polarized along the major axis and strongly depend on the ellipticity of the magnetic flux tube, the kink and sausage surface modes are practically unaffected by ellipticity. Several examples of the spatial structure of the eigenmodes permitted in the pores and sunspots have been visualized. The solutions obtained in the approximation of cylindrical symmetry are in agreement with previous studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have calculated the thermonuclear <jats:sup>19</jats:sup>F(<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic> <jats:sub> <jats:italic>γ</jats:italic> </jats:sub>)<jats:sup>16</jats:sup>O reaction rate in a wide temperature region of 0.001–10 GK by re-evaluating the available experimental data. Together with recently evaluated <jats:sup>19</jats:sup>(<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic> <jats:sub>0</jats:sub>)<jats:sup>16</jats:sup>O and <jats:sup>19</jats:sup>(<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic> <jats:sub> <jats:italic>π</jats:italic> </jats:sub>)<jats:sup>16</jats:sup>O data, we have derived a new total reaction rate of <jats:sup>19</jats:sup>F(<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic>)<jats:sup>16</jats:sup>O using a Monte Carlo technique. The present rate is larger than the NACRE recommended one by factors of 36.4, 2.3, and 1.7 at temperatures of 0.01, 0.05, and 0.1 GK, respectively. This is because we have considered the enhanced low-energy astrophysical <jats:italic>S</jats:italic> factors in the (<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic> <jats:sub> <jats:italic>γ</jats:italic> </jats:sub>) channel, owing to the interference effect between an 11 keV resonance and the well-known 323 keV resonance. It shows that the (<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic> <jats:sub> <jats:italic>γ</jats:italic> </jats:sub>) channel dominates the total rate over the entire temperature region, except for a narrow region of 0.05–0.12 GK where the (<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic> <jats:sub>0</jats:sub>) channel dominates, contrary to the previous conclusion. We have investigated the impact of the <jats:sup>19</jats:sup>F(<jats:italic>p</jats:italic>, <jats:italic>α</jats:italic>)<jats:sup>16</jats:sup>O reaction rate using a simple parametric model of extra mixing in low-mass AGB stars, which would lower the fluorine abundance produced and observed in these stars. However, models considering different temperature profiles and more sophisticated approaches, such as extra mixing induced by magnetic fields, are needed to verify the results of our preliminary tests. Interestingly, our new rate has a strong impact on destruction of <jats:sup>19</jats:sup>F in the CNO cycle at low temperatures of 0.02–0.03 GK, and this general behavior needs to be analyzed further.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A small number of interplanetary coronal mass ejections (ICMEs) have been identified that contain measurable contributions from prominence plasma. In situ measurements from during these events are marked by the presence of unusually low-charge states of C, O, and Fe, representing ionization equilibrium formation temperatures of ∼10<jats:sup>4</jats:sup>–10<jats:sup>5</jats:sup> K, consistent with prominence material observed at the Sun. We present a thorough analysis of the elemental abundances of a wide variety of heavy ions, measured by Advanced Composition Explorer/SWICS, in prominence material observed in the solar wind. We find that prominence material observed in situ tends to be more enriched in heavy ions than the surrounding ICME plasma and the fast and slow solar wind. We also find that the material is on average moderately enhanced in low first ionization potential elements compared to photospheric abundances, with values that lie between fast and slow solar wind. In rare instances, where in situ prominence material is observed to have clear, persistent, low-charge states over longer periods of time, it exhibits elemental abundances that are photospheric in nature. However, in most prominence events we see indications that the associated material contains a mixture of prominence and adjacent ICME plasma. The anomalous behavior of the elemental and ionic composition in ICMEs with and without prominence material can be used to study physical processes that occur during CME initiation and release.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate ionization and heating of gas in the dense, shielded clumps/cores of molecular clouds bathed by an influx of energetic, charged cosmic rays (CRs). These molecular clouds have complex structures, with substantial variation in their physical properties over a wide range of length scales. The propagation and distribution of CRs is thus regulated accordingly, in particular, by the magnetic fields threaded through the clouds and into the dense regions within. We have found that a specific heating rate reaching 10<jats:sup>−26</jats:sup> erg cm<jats:sup>−3</jats:sup> s<jats:sup>−1</jats:sup> can be sustained in the dense clumps/cores for Galactic environments, and this rate increases with CR energy density. The propagation of CRs and heating rates in some star-forming filaments identified in IC 5146 are calculated, with the CR diffusion coefficients in these structures determined from magnetic field fluctuations inferred from optical and near-infrared polarizations of starlight, which is presumably a magnetic field tracer. Our calculations indicate that CR heating can vary by nearly three orders of magnitude between different filaments within a cloud due to different levels of CR penetration. The CR ionization rate among these filaments is similar. The equilibrium temperature that could be maintained by CR heating alone is of order 1 K in a Galactic environment, but this value would be higher in strongly star-forming environments, thus causing an increase in the Jeans mass of their molecular clouds.</jats:p>