Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>In this work we derive the minimum allowed orbital periods of H-rich bodies ranging in mass from Saturn’s mass to 1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, emphasizing gas giants and brown dwarfs (BDs) over the range 0.0003–0.074 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Analytic fitting formulae for <jats:inline-formula> <jats:tex-math> <?CDATA ${P}_{\min }$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf7b0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> as a function of the mass of the body and as a function of the mean density are presented. We assume that the density of the host star is sufficiently high so as not to limit the minimum period. In many instances this implies that the host star is a white dwarf. This work is aimed, in part, toward distinguishing BDs from planets that are found transiting the host white dwarf without recourse to near-infrared or radial velocity measurements. In particular, orbital periods of ≲100 minutes are very likely to be BDs. The overall minimum period over this entire mass range is ≃37 minutes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed spectral-timing analysis of the Kilohertz quasiperiodic oscillations (kHz QPOs) in Sco X-1 using the data of the Rossi X-ray Timing Explorer (RXTE) and the Hard X-ray Modulation Telescope (Insight-HXMT). The energy band with detectable kHz QPOs is studied for the first time: on the horizontal branch, it is ∼6.89–24.01 and ∼8.68–21.78 keV for the upper and lower kHz QPOs, respectively, detected by the RXTE, and ∼9–27.5 keV for the upper kHz QPOs by the Insight-HXMT; on the lower normal branch, the energy band is narrower. The fractional root mean square (rms) of the kHz QPOs increases with energy at a lower energy, reaches a plateau at about 16 and 20 keV for the lower and upper peaks, and then levels off though with a large uncertainty. The simulation of the deadtime effect of RXTE/PCA shows that the deadtime does not affect much the search of the kHz QPOs but makes the rms amplitude underestimated. No significant QPO is detected below ∼6 keV as shown by the RXTE data, implying that the kHz QPOs do not originate from the blackbody emission of the accretion disk and neutron star surface. In addition, with the combined analysis of the energy spectra and the absolute rms spectra of kHz QPOs, we suggest that the kHz QPOs in Sco X-1 originate from the Comptonization of the inner part of the transition layer, where the rotation sets the frequency and the inward bulk motion makes the spectrum harder.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Multiwavelength analyses of spectra of active galactic nuclei provide useful information on the physical processes in the accretion disk and jets of black holes. This, however, is limited to bright sources and may not represent the population as a whole. Another approach is through the investigation of the cosmological evolution of the luminosity function (LF), which shows varied evolution (luminosity and density) at different wavelengths. These differences and the correlations between luminosities can shed light on the jet-accretion disk connection. Most such studies use forward fitting parametric methods that involve several functions and many parameters. We use nonparametric, nonbinning methods developed by Efron &amp; Petrosian and Lynden-Bell, for obtaining unbiased description of the evolution of the LF, from data truncated by observational selection effects. We present an analysis of the evolution of gamma-ray LF of blazars with a main focus on flat-spectrum radio quasars. This requires analysis of both gamma-ray and optical data, essential for redshift measurements, and a description of the joint LF. We use a new approach that divides the sample into two subsamples, each with its own flux limit. We use the Fermi Large Area Telescope and GAIA observations, and present results on the gamma-ray LF and its evolution, and determine the intrinsic correlation between the gamma-ray and optical luminosities corrected for the well-known false correlation induced by their similar redshift dependence and evolution of the two luminosities. We also present a direct estimation of the contribution of blazars to the spectrum of the extragalactic gamma-ray background.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Swing amplification is a model of spiral arm formation in disk galaxies. Previous <jats:italic>N</jats:italic>-body simulations show that the epicycle phases of stars in spiral arms are synchronized. However, the elementary process of the phase synchronization is not well understood. In order to investigate phase synchronization, we investigate the orbital evolution of stars due to gravitational scattering by a perturber under the epicycle approximation and its dependence on orbital elements and a disk parameter. We find that gravitational scattering by the perturber can cause phase synchronization of stellar orbits. The epicycle phases are better synchronized for smaller initial epicycle amplitudes of stars and larger shear rates of galactic disks. The vertical motion of stars does not affect the phase synchronization. The phase synchronization forms trailing dense regions, which may correspond to spiral arms.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present theoretical predictions for the free–free emission at centimeter wavelengths obtained from photoevaporation and magnetohydrodynamic (MHD) wind disk models adjusted to the case of the TW Hydrae young stellar object. For this system, disk photoevaporation with heating due to the high-energy photons from the star has been proposed as a possible mechanism to open the gap observed in the dust emission with the Atacama Large Millimeter/submillimeter Array. We show that the photoevaporation disk model predicts a radial profile for the free–free emission that is made of two main spatial components, one originated from the bound disk atmosphere at 0.5–1 au from the star, and another more extended component from the photoevaporative wind at larger disk radii. We also show that the stellar X-ray luminosity has a significant impact on both these components. The predicted radio emission from the MHD wind model has a smoother radial distribution which extends to closer distances to the star than the photoevaporation case. We also show that a future radio telescope such as the Next Generation Very Large Array would have enough sensitivity and angular resolution to spatially resolve the main structures predicted by these models.</jats:p>