Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title> <jats:p>We present a novel method for detrending systematic noise from time series data using Principal Component Analysis (PCA) in Fast Fourier Transforms. This method is demonstrated on time series data obtained from the inaugural campaign of the Kepler K2 mission, as well as three objects of interest from Campaign 4. Unlike previous detrending techniques that utilize PCA, this method performs the detrending in Fourier space rather than temporal space. The advantage of performing the analysis in frequency space is that the technique is sensitive purely to the periodicity of the unwanted signal and not to its morphological characteristics. This method could improve measurements of low signal-to-noise photometric features by reducing systematics. We also discuss challenges and limitations associated with this technique.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The constancy of the speed of light <jats:italic>c</jats:italic> is the foundation of most physical theories and is found to be indeed constant from local measurements. Whether or not the same is true at cosmological timescale has been of interest for some time. The measurement of time delay difference in the peaking of the luminosity between two gravitationally lensed images of a type 1a-supernova has recently been proposed to determine if <jats:italic>c</jats:italic> was different from its current value at the time the images were produced by a lensing galaxy. Since the geometrical time delay and the Shapiro time delay both scale as <jats:italic>G</jats:italic>/<jats:italic>c</jats:italic> <jats:sup>3</jats:sup> we show that this method of constraining <jats:italic>c</jats:italic> is valid only when the potential variation of the gravitational constant <jats:italic>G</jats:italic> is ignored: <jats:italic>c</jats:italic> variation is imperceptible when <jats:italic>G</jats:italic> ∼ <jats:italic>c</jats:italic> <jats:sup>3</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Vortices (flows with closed elliptic streamlines) are exact nonlinear solutions to the compressible Euler equation. In this contribution, we use differential geometry to derive the transformations between Cartesian and elliptic coordinates, and show that in elliptic coordinates a constant vorticity flow reduces to <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{\mu }=0$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>˙</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>0</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="rnaasac1867ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{\nu }=\mathrm{const}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>˙</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mi>const</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="rnaasac1867ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> along the streamline <jats:italic>μ</jats:italic> <jats:sub>0</jats:sub> that matches the vortex eccentricity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Solar Cycle 25 started in 2019 December. Different predictions for its amplitude have been published so far without general consensus. We compared the evolution of Solar Cycle 25, using the first available values of the smoothed sunspot number, with past solar cycles. Our analysis shows that Solar Cycle 25 is very similar to Solar Cycles 24 and 7. Therefore, the maximum amplitude for this Solar Cycle 25 could be small-moderate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report on archival XMM-Newton and post-outburst Swift observations of the newly discovered dwarf nova ASASSN-21kt. Its pre-outburst X-ray emission is consistent with that of a collisionally ionized, thermal plasma with <jats:inline-formula> <jats:tex-math> <?CDATA ${kT}={8.1}_{-2.5}^{+10.2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">kT</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>8.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>10.2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="rnaasac19a3ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> keV and <jats:italic>L</jats:italic> <jats:sub>X 0.2–12 keV</jats:sub> = 7 × 10<jats:sup>32</jats:sup> erg s<jats:sup>−1</jats:sup>, with no clear modulation. Multiple optical outbursts revealed by Gaia and time evolution of the last one followed by the All-Sky Automated Survey for Supernovae, and X-ray properties presented here support the dwarf nova classification of ASASSN-21kt.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Light curve comparison is a simple but statistically powerful test for the presence of gravitational lensing in gamma-ray bursts (GRBs). Since gravitational lensing does not change relative timing internal to images, all source images created by gravitational lensing should show the same light curve to within a scale factor in amplitude. Applied to the recent claim that the two pulses in GRB 090717 are lensed images of the same pulse, it was found that the light curves for these pulses actually differ at about the 5.0<jats:italic>σ</jats:italic> confidence level (99.999956%) in a <jats:italic>χ</jats:italic> <jats:sup>2</jats:sup> comparison test. Under the given assumptions, GRB 090717 therefore does not present a compelling example of gravitational lensing.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gamma-ray bursts, associated with the collapse of massive stars or the collisions of compact objects, are the most luminous events in our universe. However, there is still much to learn about the nature of the relativistic jets launched from the central engines of these objects. We examine how jet structure-that is, the energy and velocity distribution as a function of angle-affects observed GRB afterglow light curves. Using the package afterglowpy, we compute light curves arising from an array of possible jet structures, and present the suite of models that can fit the coincident electromagnetic observations of GW190814 (which is likely due to a background AGN). Our work emphasizes not only the need for broadband spectral and timing data to distinguish among jet structure models, but also the necessity for high resolution radio follow-up to help resolve background sources that may mimic a GRB afterglow.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Contained within a galaxy cluster, the Intracluster Medium is comprised of hot, X-ray emitting material between member galaxies. The nearest (∼16.1 Mpc) large galaxy cluster is Virgo. Virgo covers an approximately 12° diameter field, making it challenging to observe in its entirety. The HaloSat satellite utilized a 7° radius field of view to obtain the first full cluster observations since 1994. We then fit the cluster spectra with a plasma emission model of fixed metallicity. Our best fit temperature is <jats:italic>kT</jats:italic> = 1.39 ± 0.11 keV. We report a cluster luminosity of 5.8 ± 0.7 × 10<jats:sup>43</jats:sup> erg s<jats:sup>−1</jats:sup> and an emission measure of 5.8 ± 0.6 × 10<jats:sup>66</jats:sup> cm<jats:sup>−3</jats:sup>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The provenance of a singular picture of the nearside of the Moon made at Lick Observatory is discussed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The extragalactic background light (EBL) is the summed emission from sources beyond the Milky Way. An accurate measurement of the EBL can be used as a benchmark to search for any diffuse components in excess of the integrated light from galaxies. We have studied archival data from the Linear Etalon Imaging Spectral Array (LEISA) aboard the New Horizons spacecraft to assess its capability to measure the near-IR EBL at wavelengths between 1.2 and 2.5 <jats:italic>μ</jats:italic>m. We estimate LEISAs sensitivity to diffuse brightness to be ∼10<jats:sup>5</jats:sup> nW m<jats:sup>−2</jats:sup> sr<jats:sup>−1</jats:sup> in 1.5 s exposures, which precludes the possibility of reaching EBL signals at the level of 10 nW m<jats:sup>−2</jats:sup> sr<jats:sup>−1</jats:sup>.</jats:p>