Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>In beyond-Horndeski theories of gravity, the Vainshtein screening mechanism might only be partially effective inside stellar objects. This results in a modification of the pressure balance equation inside stars, often characterized by a single parameter (ϒ) in isotropic systems. We show how to constrain such theories of modified gravity, using tidal effects. We study such effects in cataclysmic variable star binaries and numerically obtain limits on the critical masses of the donor stars, below which they are tidally disrupted, by modeling them in beyond-Horndeski theories. This is contrasted with values of the donor masses, obtained using existing observational data, by a Monte Carlo error progression method. A best-fit scenario of the two yields a parametric constraint in the theories that we consider, within the approximations used. Here, we obtain the allowed range 0 ≤ ϒ ≤ 0.50.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>How and when did galaxies form and assemble their stars and stellar mass? The answer to these questions, so crucial to astrophysics and cosmology, requires the full reconstruction of the so-called cosmic star formation rate density (SFRD), i.e., the evolution of the average star formation rate per unit volume of the universe. While the SFRD has been reliably traced back to 10–11 billion years ago, its evolution is still poorly constrained at earlier cosmic epochs, and its estimate is mainly based on galaxies luminous in the ultraviolet and with low obscuration by dust. This limited knowledge is largely due to the lack of an unbiased census of all types of star-forming galaxies in the early universe. We present a new approach to finding dust-obscured star-forming galaxies based on their emission at radio wavelengths coupled with the lack of optical counterparts. Here, we present a sample of 197 galaxies selected with this method. These systems were missed by previous surveys at optical and near-infrared wavelengths, and 22 of them are at very high redshift (i.e., <jats:italic>z</jats:italic> &gt; 4.5). The contribution of these elusive systems to the SFRD is substantial and can be as high as 40% of the previously known SFRD based on UV-luminous galaxies. The mere existence of such heavily obscured galaxies in the first two billion years after the Big Bang opens new avenues to investigate the early phases of galaxy formation and evolution, and to understand the links between these systems and the massive galaxies that ceased their star formation at later cosmic times.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore changes in the adiabatic low-order g-mode pulsation periods of 0.526, 0.560, and 0.729 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> carbon–oxygen white dwarf models with helium-dominated envelopes due to the presence, absence, and enhancement of <jats:sup>22</jats:sup>Ne in the interior. The observed g-mode pulsation periods of such white dwarfs are typically given to 6−7 significant figures of precision. Usually white dwarf models without <jats:sup>22</jats:sup>Ne are fit to the observed periods and other properties. The rms residuals to the ≃150−400 s low-order g-mode periods are typically in the range of <jats:italic>σ</jats:italic> <jats:sub>rms</jats:sub> ≲ 0.3 s, for a fit precision of <jats:italic>σ</jats:italic> <jats:sub>rms</jats:sub>/<jats:italic>P</jats:italic> ≲ 0.3%. We find average relative period shifts of Δ<jats:italic>P</jats:italic>/<jats:italic>P</jats:italic> ≃ ±0.5% for the low-order dipole and quadrupole g-mode pulsations within the observed effective temperature window, with the range of Δ<jats:italic>P</jats:italic>/<jats:italic>P</jats:italic> depending on the specific g-mode, abundance of <jats:sup>22</jats:sup>Ne, effective temperature, and the mass of the white dwarf model. This finding suggests a systematic offset may be present in the fitting process of specific white dwarfs when <jats:sup>22</jats:sup>Ne is absent. As part of the fitting processes involves adjusting the composition profiles of a white dwarf model, our study on the impact of <jats:sup>22</jats:sup>Ne can provide new inferences on the derived interior mass fraction profiles. We encourage routinely including <jats:sup>22</jats:sup>Ne mass fraction profiles, informed by stellar evolution models, to future generations of white dwarf model-fitting processes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a study of 28 Type I superluminous supernovae (SLSNe) in the context of the ejecta mass and photospheric velocity. We combine photometry and spectroscopy to infer ejecta masses via the formalism of radiation diffusion equations. We present an improved method to determine the photospheric velocity by combining spectrum modeling and cross-correlation techniques. We find that Type I SLSNe can be divided into two groups according to their pre-maximum spectra. Members of the first group have a W-shaped absorption trough in their pre-maximum spectrum, usually identified as due to O <jats:sc>ii</jats:sc>. This feature is absent in the spectra of supernovae in the second group, whose spectra are similar to that of SN 2015bn. We confirm that the pre- or near-maximum photospheric velocities correlate with the velocity gradients: faster evolving SLSNe have larger photospheric velocities around maximum. We classify the studied SLSNe into the Fast or the Slow evolving group according to their estimated photospheric velocities, and find that all those objects that resemble SN 2015bn belong to the Slow evolving class, while SLSNe showing the W-like absorption are represented in both Fast and Slow evolving groups. We estimate the ejecta masses of all objects in our sample, and obtain values in the range 2.9 (±0.8)−208 (±61) <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, with a mean of 43 (±12) <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We conclude that Slow evolving SLSNe tend to have higher ejecta masses compared to the Fast SLSNe. Our ejecta mass calculations suggests that SLSNe are caused by energetic explosions of very massive stars, irrespective of the powering mechanism of the light curve.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report that the RS CVn–type star GT Mus (HR 4492, HD 101379+HD 101380) was the most active star in the X-ray sky in the last decade in terms of the scale of recurrent energetic flares. We detected 11 flares from GT Mus in 8 yr of observations with the Monitor of All-sky X-ray Image (MAXI) from 2009 August to 2017 August. The detected flare peak luminosities were 1–4 × 10<jats:sup>33</jats:sup> erg s<jats:sup>−1</jats:sup> in the 2.0–20.0 keV band for its distance of 109.6 pc. Our timing analysis showed long durations (<jats:italic>τ</jats:italic> <jats:sub>r</jats:sub> + <jats:italic>τ</jats:italic> <jats:sub>d</jats:sub>) of 2–6 days with long decay times (<jats:italic>τ</jats:italic> <jats:sub>d</jats:sub>) of 1–4 days. The released energies during the decay phases of the flares in the 0.1–100 keV band were in the range of 1–11 × 10<jats:sup>38</jats:sup> erg, which are at the upper end of the observed stellar flare. The released energies during the whole duration were in the range of 2–13 × 10<jats:sup>38</jats:sup> erg in the same band. We carried out X-ray follow-up observations for one of the 11 flares with the Neutron star Interior Composition Explorer (NICER) on 2017 July 18 and found that the flare cooled quasi-statically. On the basis of a quasi-static cooling model, the flare loop length is derived to be 4 × 10<jats:sup>12</jats:sup> cm (or 60 <jats:italic>R</jats:italic> <jats:sub>☉</jats:sub>). The electron density is derived to be 1 × 10<jats:sup>10</jats:sup> cm<jats:sup>−3</jats:sup>, which is consistent with the typical value of solar and stellar flares (10<jats:sup>10–13</jats:sup> cm<jats:sup>−3</jats:sup>). The ratio of the cooling timescales between radiative (<jats:italic>τ</jats:italic> <jats:sub>rad</jats:sub>) and conductive (<jats:italic>τ</jats:italic> <jats:sub>cond</jats:sub>) cooling is estimated to be <jats:italic>τ</jats:italic> <jats:sub>rad</jats:sub> ∼ 0.1 <jats:italic>τ</jats:italic> <jats:sub>cond</jats:sub> from the temperature; thus, radiative cooling was dominant in this flare.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The nature of shock waves in nonfundamental mode RR Lyrae stars remains a mystery because of limited spectroscopic observations. We apply a pattern recognition algorithm on spectroscopic data from SDSS and LAMOST and report the first evidence of hydrogen emission in first-overtone (RRc) and multimode (RRd) RR Lyrae stars showing the “first apparition,” which is the most prominent observational characteristic of shock in RR Lyrae variables. We find 10 RRc stars in SDSS, 10 RRc stars in LAMOST, and 3 RRd stars in LAMOST that show blueshifted Balmer emissions. The emission features possibly indicate the existence of shock waves. We calculate the radial velocities of the emission lines, which are related to the physical conditions occurring in the radiative zone of shock waves. Using photometric observations from ZTF, we present a detailed light-curve analysis for the frequency components in one of our RRd stars with hydrogen emission, RRdl3, for possible modulations. With the enormous volume of upcoming spectral observations of variable stars, our study raises the possibility of connecting the unexplained Blazhko effect to shock waves in nonfundamental mode RR Lyrae stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Water ice has a strong spectral feature at a wavelength of approximately 3 <jats:italic>μ</jats:italic>m, which plays a vital role in our understanding of the icy universe. In this study, we investigate the scattering polarization of this water-ice feature. The linear polarization degree of light scattered by micron-sized icy grains is known to be enhanced at the ice band; however, the dependence of this polarization enhancement on various grain properties is unclear. We find that the enhanced polarization at the ice band is sensitive to the presence of micron-sized grains as well as their ice abundance. We demonstrate that this enhancement is caused by the high absorbency of the water-ice feature, which attenuates internal scattering and renders the surface reflection dominant over internal scattering. Additionally, we compare our models with polarimetric observations of the low-mass protostar L1551 IRS 5. Our results show that scattering by a maximum grain radius of a few microns with a low water-ice abundance is consistent with observations. Thus, scattering polarization of the water-ice feature is a useful tool for characterizing ice properties in various astronomical environments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The use of Type Ia supernovae (SNe Ia) as cosmological tools has motivated significant effort to understand what drives the intrinsic scatter of SN Ia distance modulus residuals after standardization, characterize the distribution of SN Ia colors, and explain why properties of the host galaxies of the SNe correlate with SN Ia distance modulus residuals. We use a compiled sample of ∼1450 spectroscopically confirmed photometric light curves of SNe Ia and propose a solution to these three problems simultaneously that also explains an empirical 11<jats:italic>σ</jats:italic> detection of the dependence of Hubble residual scatter on SN Ia color. We introduce a physical model of color where intrinsic SN Ia colors with a relatively weak correlation with luminosity are combined with extrinsic dust-like colors (<jats:italic>E</jats:italic>(<jats:italic>B</jats:italic> − <jats:italic>V</jats:italic>)) with a wide range of extinction parameter values (<jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>). This model captures the observed trends of Hubble residual scatter and indicates that the dominant component of SN Ia intrinsic scatter is variation in <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub>. We also find that the recovered <jats:italic>E</jats:italic>(<jats:italic>B</jats:italic> − <jats:italic>V</jats:italic>) and <jats:italic>R</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> distributions differ based on global host-galaxy stellar mass, and this explains the observed correlation (<jats:italic>γ</jats:italic>) between mass and Hubble residuals seen in past analyses, as well as an observed 4.5<jats:italic>σ</jats:italic> dependence of <jats:italic>γ</jats:italic> on SN Ia color. This finding removes any need to ascribe different intrinsic luminosities to different progenitor systems. Finally, we measure biases in the equation of state of dark energy (<jats:italic>w</jats:italic>) up to ∣Δ<jats:italic>w</jats:italic>∣ = 0.04 by replacing previous models of SN color with our dust-based model; this bias is larger than any systematic uncertainty in previous SN Ia cosmological analyses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have conducted a search for new strong gravitational lensing systems in the Dark Energy Spectroscopic Instrument Legacy Imaging Surveys’ Data Release 8. We use deep residual neural networks, building on previous work presented by Huang et al. These surveys together cover approximately one-third of the sky visible from the Northern Hemisphere, reaching a <jats:italic>z</jats:italic>-band AB magnitude of ∼22.5. We compile a training sample that consists of known lensing systems as well as non-lenses in the Legacy Surveys and the Dark Energy Survey. After applying our trained neural networks to the survey data, we visually inspect and rank images with probabilities above a threshold. Here we present 1210 new strong lens candidates.</jats:p>