Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We combine asteroseismology, optical high-resolution spectroscopy, and kinematic analysis for 26 halo red giant branch stars in the Kepler field in the range of −2.5 &lt; [Fe/H] &lt; −0.6. After applying theoretically motivated corrections to the seismic scaling relations, we obtain an average mass of 0.97 ± 0.03 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> for our sample of halo stars. Although this maps into an age of ∼7 Gyr, significantly younger than independent age estimates of the Milky Way stellar halo, we considered this apparently young age to be due to the overestimation of stellar mass in the scaling relations. There is no significant mass dispersion among lower red giant branch stars (log <jats:italic>g</jats:italic> &gt; 2), which constrains the relative age dispersion to &lt;18%, corresponding to &lt;2 Gyr. The precise chemical abundances allow us to separate the stars with [Fe/H] &gt; −1.7 into two [Mg/Fe] groups. While the [<jats:italic>α</jats:italic>/Fe] and [Eu/Mg] ratios are different between the two subsamples, [<jats:italic>s</jats:italic>/Eu], where <jats:italic>s</jats:italic> stands for Ba, La, Ce, and Nd, does not show a significant difference. These abundance ratios suggest that the chemical evolution of the low-Mg population is contributed by Type Ia supernovae, but not by low- to intermediate-mass asymptotic giant branch stars, providing a constraint on its star formation timescale as 100 Myr &lt; <jats:italic>τ</jats:italic> &lt; 300 Myr. We also do not detect any significant mass difference between the two [Mg/Fe] groups, thus suggesting that their formation epochs are not separated by more than 1.5 Gyr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The analysis of exoplanetary atmospheres often relies upon the observation of transit or eclipse events. While very powerful, these snapshots provide mainly one-dimensional information on the planet structure and do not easily allow precise latitude–longitude characterizations. The phase curve technique, which consists of measuring the planet emission throughout its entire orbit, can break this limitation and provide useful two-dimensional thermal and chemical constraints on the atmosphere. As of today, however, computing performances have limited our ability to perform unified retrieval studies on the full set of observed spectra from phase curve observations at the same time. Here, we present a new phase curve model that enables fast, unified retrieval capabilities. We apply our technique to the combined phase curve data from the Hubble and Spitzer space telescopes of the hot Jupiter WASP-43 b. We tested different scenarios and discussed the dependence of our solution on different assumptions in the model. Our more comprehensive approach suggests that multiple interpretations of this data set are possible, but our more complex model is consistent with the presence of thermal inversions and a metal-rich atmosphere, contrasting with previous data analyses, although this likely depends on the Spitzer data reduction. The detailed constraints extracted here demonstrate the importance of developing and understanding advanced phase curve techniques, which we believe will unlock access to a richer picture of exoplanet atmospheres.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The high-frequency radio sky has historically remained largely unexplored due to the typical faintness of sources in this regime, and the modest survey speed compared to observations at lower frequencies. However, high-frequency radio surveys offer an invaluable tracer of high-redshift star formation, as they directly target the faint radio free–free emission. We present deep continuum observations at 34 GHz in the COSMOS and GOODS-North fields from the Karl G. Jansky Very Large Array (VLA), as part of the COLD<jats:italic>z</jats:italic> survey. The deep COSMOS mosaic spans <jats:inline-formula> <jats:tex-math> <?CDATA $\sim 10\,{\mathrm{arcmin}}^{2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe6a5ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> down to <jats:italic>σ</jats:italic> = 1.3 <jats:italic>μ</jats:italic>Jy beam<jats:sup>−1</jats:sup>, while the wider GOODS-N observations cover <jats:inline-formula> <jats:tex-math> <?CDATA $\sim 50\,{\mathrm{arcmin}}^{2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabe6a5ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> to <jats:italic>σ</jats:italic> = 5.3 <jats:italic>μ</jats:italic>Jy beam<jats:sup>−1</jats:sup>. We detect a total of 18 galaxies at 34 GHz, of which nine show radio emission consistent with being powered by star formation; although for two sources, this is likely due to thermal emission from dust. Utilizing deep ancillary radio data at 1.4, 3, 5, and 10 GHz, we decompose the spectra of the remaining seven star-forming galaxies into their synchrotron and thermal free–free components, and find typical thermal fractions and synchrotron spectral indices comparable to those observed in local star-forming galaxies. We further determine free–free star formation rates (SFRs), and show that these are in agreement with SFRs from spectral energy distribution-fitting and the far-infrared/radio correlation. Our observations place strong constraints on the high-frequency radio emission in typical galaxies at high redshift, and provide some of the first insights into what is set to become a key area of study with future radio facilities, such as the Square Kilometer Array Phase 1 and next-generation VLA.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The nonthermal broadening of spectral lines formed in the solar corona is often used to seek evidence of Alfvén waves propagating in the corona. To have a better understanding of the variation of line widths at different altitudes, we measured the line widths of the strong Fe <jats:sc>xii</jats:sc> 192.4, 193.5, and 195.1 Å and Fe <jats:sc>xiii</jats:sc> 202.0 Å in an off-limb southern coronal hole up to 1.5 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> observed by the Extreme Ultraviolet Spectrometer on board the Hinode satellite. We compared our measurements to the predictions from the Alfvén Wave Solar Model (AWSoM) and the SPECTRUM module. We found that the Fe <jats:sc>xii</jats:sc> and Fe <jats:sc>xiii</jats:sc> line widths first increase monotonically below 1.1 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> and then keep fluctuating between 1.1 and 1.5 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>. The synthetic line widths of Fe <jats:sc>xii</jats:sc> and Fe <jats:sc>xiii</jats:sc> below 1.3 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> are notably lower than the observed ones. We found that the emission from a streamer in the line of sight significantly contaminates the coronal hole line profiles even up to 1.5 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> both in observations and simulations. We suggest that either the discrepancy between the observations and simulations is caused by insufficient nonthermal broadening at the streamer in the AWSoM simulation or the observations are less affected by the streamer. Our results emphasize the importance of identifying the origin of the coronal EUV emission in off-limb observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present elemental abundance results for HE 2148−2039 and HE 2155−2043 based on a detailed high-resolution spectroscopic analysis. The high-resolution Subaru/High Dispersion Spectrograph (HDS) spectra used for our analysis have a resolution of <jats:italic>R</jats:italic> ∼ 60,000. Although limited information based on photometry and low-resolution spectroscopy is available, we present for the first time an abundance analysis based on high-resolution spectra for both objects. Our analysis shows that the two objects are extremely metal-poor with [Fe/H] &lt; −3. Among the neutron-capture elements, abundances of only Sr and Ba could be determined in our program stars. For both the objects [Ba/Fe] is found to be &lt;0. While strontium is underabundant in HE 2148−2039 with [Sr/Fe] ∼ −2.02, Sr is near solar in HE 2155−2043. The locations of the program stars in the absolute carbon abundance, <jats:italic>A</jats:italic>(C) versus [Fe/H] diagram, show that HE 2148−2039 is a carbon-enhanced metal-poor (CEMP)-no Group II object and HE 2155−2043 is a CEMP-no Group III object. Observed [Sr/Ba] ratios are characteristics of a fast rotating massive star progenitor for HE 2155−2043 and a metal-poor asymptotic giant branch (AGB) star for HE 2148−2039. The estimated [Sc/Mn] as well as [C/Cr] ratios in HE 2155−2043 show that the surface chemical composition of this object is mono-enriched. The surface chemical composition of HE 2148−2039 is also found to be mono-enriched based on the [Mg/C] ratio. With respect to their locations in the [C/N] versus <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> diagram, HE 2148−2039 shows signatures of mixing, and HE 2155−2043 falls in the unmixed region of the [C/N] versus <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> plot. Kinematic analysis shows that both objects belong to the Galactic halo population.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We apply for the first time a two-dimensional fitting statistic, <jats:italic>τ</jats:italic> <jats:sup>2</jats:sup>, to rotational-evolution models (REMs) of stars (0.1–1.3 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) on the period–mass plane. The <jats:italic>τ</jats:italic> <jats:sup>2</jats:sup> statistic simultaneously considers all cluster rotation data to return a goodness of fit, allowing for data-driven improvement of REMs. We construct data sets for Upper Sco, the Pleiades, and Praesepe, to which we tune our REMs. We use consistently determined stellar masses (calculated by matching <jats:italic>K</jats:italic> <jats:sub>s</jats:sub> magnitudes to isochrones) and literature rotation periods. As a first demonstration of the <jats:italic>τ</jats:italic> <jats:sup>2</jats:sup> statistic, we find the best-fitting gyrochronology age for Praesepe, which is in good agreement with the literature. We then systematically vary three parameters that determine the dependence of our stellar wind torque law on the Rossby number in the saturated and unsaturated regimes, and the location of the transition between the two. By minimizing <jats:italic>τ</jats:italic> <jats:sup>2</jats:sup>, we find best-fit values for each parameter. These values vary slightly between clusters, mass determinations, and initial conditions, highlighting the precision of <jats:italic>τ</jats:italic> <jats:sup>2</jats:sup> and its potential for constraining REMs, gyrochronology, and our understanding of stellar physics. Our resulting REMs, which implement the best-possible fitting form of a broken-power-law torque, are statistically improved on previous REMs using similar formulations, but still do not simultaneously describe the observed rotation distributions of the lowest masses, which have both slow and fast rotators by the Praesepe age, and the shape of the converged sequence for higher masses. Further complexity in the REMs is thus required to accurately describe the data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A total of 80% of the matter in the universe is in the form of dark matter that composes the skeleton of the large-scale structure called the cosmic web. As the cosmic web dictates the motion of all matter in galaxies and intergalactic media through gravity, knowing the distribution of dark matter is essential for studying the large-scale structure. However, the cosmic web’s detailed structure is unknown because it is dominated by dark matter and warm−hot intergalactic media, both of which are hard to trace. Here we show that we can reconstruct the cosmic web from the galaxy distribution using the convolutional-neural-network-based deep-learning algorithm. We find the mapping between the position and velocity of galaxies and the cosmic web using the results of the state-of-the-art cosmological galaxy simulations of Illustris-TNG. We confirm the mapping by applying it to the EAGLE simulation. Finally, using the local galaxy sample from <jats:italic>Cosmicflows-3</jats:italic>, we find the dark matter map in the local universe. We anticipate that the local dark matter map will illuminate the studies of the nature of dark matter and the formation and evolution of the Local Group. High-resolution simulations and precise distance measurements to local galaxies will improve the accuracy of the dark matter map.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use a time-dependent hydrodynamic code and a non-LTE Monte Carlo code to model disk dissipation for the Be star 66 Ophiuchi. We compiled 63 years of observations from 1957 to 2020 to encompass the complete history of the growth and subsequent dissipation of the star’s disk. Our models are constrained by new and archival photometry, spectroscopy, and polarization observations, allowing us to model the disk dissipation event. Using Markov Chain Monte Carlo methods, we find that the properties of 66 Oph are consistent with those of a standard B2Ve star. We computed a grid of 61,568 Be star disk models to constrain the density profile of the disk before dissipation using observations of the H<jats:italic>α</jats:italic> line profile and spectral energy distribution. We find at the onset of dissipation the disk has a base density of 2.5 × 10<jats:sup>−11</jats:sup> g cm<jats:sup>−3</jats:sup> with a radial power-law index of <jats:italic>n</jats:italic> = 2.6. Our models indicate that after 21 yr of disk dissipation 66 Oph’s outer disk remained present and bright in the radio. We find an isothermal disk with constant viscosity with an <jats:italic>α</jats:italic> = 0.4 and an outer disk radius of ∼115 stellar radii best reproduces the rate of 66 Oph’s disk dissipation. We determined the interstellar polarization in the direction of the star in the <jats:italic>V</jats:italic> band is <jats:italic>p</jats:italic> = 0.63 ± 0.02% with a polarization position angle of <jats:italic>θ</jats:italic> <jats:sub> <jats:italic>IS</jats:italic> </jats:sub> ≈ 857 ± 07. Using the Stokes QU diagram, we find the intrinsic polarization position angle of 66 Oph’s disk is <jats:italic>θ</jats:italic> <jats:sub>int</jats:sub> ≈ 98° ± 3°.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>An accurate and systematic quantification of the state variables in the Mars upper atmosphere is important for the study of Mars volatile evolution. In this study, we perform a comprehensive analysis of the Ly<jats:italic>α</jats:italic> limb scans observed by MAVEN during Martian years 32–35 to quantify the Mars upper atmospheric temperature, the CO<jats:sub>2</jats:sub> density, the H density, and the H thermal escape rate. A previously uncharacterized feature of the proton aurora at Mars is reported, which affects the overall shape of the limb scans without introducing peak intensity structures. Our inversion results excluding such scans demonstrate an unambiguous and systematic consistency of the Mars exobase temperature (∼150–280 K) derived from the dayside Ly<jats:italic>α</jats:italic> emission with those derived from the CO<jats:sub>2</jats:sub> <jats:sup>+</jats:sup> airglow emission and those from atmospheric drag measurements, resolving a long-standing discrepancy between those different estimates. The temperature is shown to be highly predictable over different solar cycles and seasons. However, the H density and escape rate can be episodically enhanced by a factor of ∼2–3, likely driven by dust storms that coincided with the enhancements. During the three Martian years, the averaged thermal escape rates between Mars solar longitude 0°–180° and 210°–330° are 0.6 × 10<jats:sup>7</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup> and 9.0 × 10<jats:sup>7</jats:sup> cm<jats:sup>−2</jats:sup> s<jats:sup>−1</jats:sup>, respectively, a factor of 15 seasonal difference, with a factor of ∼7.5 and ∼2 due to temperature and H density variations, respectively. These temperatures and thermal escape rates derived from the thermospheric Ly<jats:italic>α</jats:italic> emission are generally lower than those derived from the exospheric Ly<jats:italic>α</jats:italic> emission in the literature, indicating the presence of a hot H population in the Mars exosphere.</jats:p>