The seismic properties of low-mass He-core white dwarf stars

We present here a detailed pulsational study applied to low-mass He-core white dwarfs, based on full evolutionary models representative of these objects. The background stellar models on which our pulsational analysis was carried out were derived by taking into account the complete evolutionary history of the progenitor stars, with special emphasis on the diffusion processes acting during the white dwarf cooling phase. We computed nonradial $g$-modes to assess the dependence of the pulsational properties of these objects with stellar parameters such as the stellar mass and the effective temperature, and also with element diffusion processes. We also performed a g- and p-mode pulsational stability analysis on our models and found well-defined blue edges of the instability domain, where these stars should start to exhibit pulsations. We found substantial differences in the seismic properties of white dwarfs with $M_* \gtrsim 0.20 M_{\odot}$ and the extremely low-mass (ELM) white dwarfs ($M_* \lesssim 0.20 M_{\odot}$). Specifically, $g$-mode pulsation modes in ELM white dwarfs mainly probe the core regions and are not dramatically affected by mode-trapping effects by the He/H interface, whereas the opposite is true for more massive He-core white dwarfs. We found that element diffusion processes substantially affects the shape of the He/H chemical transition region, leading to non-negligible changes in the period spectrum of low-mass white dwarfs. Our stability analysis successfully predicts the pulsations of the only known variable low-mass white dwarf (SDSS J184037.78+642312.3), and also predicts both $g$- and $p$-mode pulsational instabilities in a significant number of known low-mass and ELM white dwarfs.Comment: 14 pages, 15 figures, 2 tables. To be published in Astronomy & Astrophysic

Einstein y la religión

"A pesar de sus muchas declaraciones, no sabemos del todo qué quiso significar Einstein con la palabra Dios. En su obra científica Dios fue el concepto gobernante-un concepto mal definido, porque, ¿quién puede definir a Dios?- pero un símbolo no sólo de la pasión de Einstein por lo asombroso y lo bello, sino también de aquel intuitivo sentido de comunión con el Universo, que fue el distintivo de su genio." Banesh Hoffmann, Albert Einstein.  

A New Timescale for Period Change in the Pulsating DA White Dwarf WD 0111+0018

We report the most rapid rate of period change measured to date for a pulsating DA (hydrogen atmosphere) white dwarf (WD), observed in the 292.9 s mode of WD 0111+0018. The observed period change, faster than 10^{-12} s/s, exceeds by more than two orders of magnitude the expected rate from cooling alone for this class of slow and simply evolving pulsating WDs. This result indicates the presence of an additional timescale for period evolution in these pulsating objects. We also measure the rates of period change of nonlinear combination frequencies and show that they share the evolutionary characteristics of their parent modes, confirming that these combination frequencies are not independent modes but rather artifacts of some nonlinear distortion in the outer layers of the star.Comment: 10 pages, 6 figures, accepted for publication in The Astrophysical Journa

Political Science and the FDA

This essay collects and analyzes the important political science works on FDA, with an eye both to serving as a springboard for future research on FDA decision-making and to drawing conclusions from extant research

Eclipsing binary and white dwarf features associated with K2 target EPIC251248385

White dwarfs, remnants of Sun-like stars which have completed their evolution, are one of the most common types of stars in space. Despite this, very few white dwarfs have been observed in transiting or eclipsing systems, and only two planetary systems around white dwarfs are currently known, thus motivating a search for white dwarfs with transits or eclipses as seen by the Kepler telescope. A systematic search of K2 white dwarf targets revealed one candidate with regular eclipses, but additional research was necessary to confirm the transits and white dwarf signal were coming from the same astrophysical source. The software package PyKe was utilized to adjust the light curve aperture, and perform principal component analysis which revealed that the transits were originating from a single pixel. Generating a new lightcurve from this pixel revealed the absolute transit depth, which was unconstrained previously. Ten additional images taken with the 2m LCOGT telescope revealed that a potential target star in the single Kepler pixel was actually a cluster of three stars, but no clear transits were seen from any of the potential target stars in the followup images. Additionally, analysis of transit depths in the single pixel light curve and additional investigation of nearby bright sources supported the hypothesis that the transits were more likely to be coming from the white dwarf rather than the two other sources. However, the transit duration and shape appear atypical for white dwarf systems. Thus, despite determining the potential sources and relative sizes for the potential eclipsing white dwarf candidate, or whether the eclipses come from the white dwarf target cannot be confirmed without additional data.https://iopscience.iop.org/article/10.3847/2515-5172/ab5861Published versio

Phase diagrams of charged colloidal rods: can a uniaxial charge distribution break chiral symmetry?

We construct phase diagrams for charged rodlike colloids within the second-virial approximation as a function of rod concentration, salt concentration, and colloidal charge. Besides the expected isotropic-nematic transition, we also find parameter regimes with a coexistence between a nematic and a second, more highly aligned nematic phase including an isotropic-nematic-nematic triple point and a nematic-nematic critical point, which can all be explained in terms of the twisting effect. We compute the Frank elastic constants to see if the twist elastic constant can become negative, which would indicate the possibility of a cholesteric phase spontaneously forming. Although the twisting effect reduces the twist elastic constant, we find that it always remains positive. In addition, we find that for finite aspect-ratio rods the twist elastic constant is also always positive, such that there is no evidence of chiral symmetry breaking due to a uniaxial charge distribution.Comment: Added a reference to Sec. 4 and extended discussions in Secs. 4 and 7, results unchange

Tindak Pidana terhadap Konflik Antar Kampung dalam Perspektif Hukum Pidana

Tujuan dilakukannya penelitian ini adalah untuk mengetahui bagaimana perspektif sosiologis hukum terhadap konflik antar kampung di Indonesia dan bagaimana implementasi KUHP terhadap konflik antar kampung yang terjadi di Indonesia. Dengan menggunakan metode penelitian yuridis normatif, maka dapat disimpulkan: 1. Konflik antar kampung di Indonesia bisa terjadi karena tingginya faktor sosiologis dari masyarakat setempat yang melakukan peristiwa pidana tersebut, dari faktor disorganisasi sosial, individualisme dalam praktek politik dan ekonomi, mobilitas sosial dan konflik budaya. konflik antar kampung biasanya terjadi karena ketersinggungan anggota kelompok, kesalahpahaman, dendam, minuman keras, rasa solidaritas, kesenjangan sosial, penguasaan lahan dan hal-hal lain yang dapat membuat perpecahan. 2. Rumusan Pasal 170 dan Pasal 358 Kitab Undang-Undang Hukum Pidana telah jelas dan mengatur tentang konflik antar kampung, bukan saja karena telah terjadinya kekerasan terhadap orang dan barang yang dilakukan secara bersama-sama, namun juga dapa merugikan orang lain. Dalam Kitab Undang-Undang Hukum Pidana juga telah diatur dan dibagi tentang peranan dan pertanggungjawaban pelaku konflik antar kampung sesuai dengan Pasal 55 dan Pasal 56 KUHP. Namun implementasinya cukup sulit dalam memberikan sanksi yang adil dan efektif terhadap kerumunan massa yang melakukan konflik antar kampungtersebut. Hal ini karena dalam hukum pidana kita tidak mengenal pertanggungjawaban kolektif dan sanksi pidana lebih lanjut ditunjukkan kepada diri individu pelanggar. Menjatuhkan sanksi terhadap pelaku secara merata tidak mungkin dilakukan

A Status Report On A Planet Search Around White Dwarf Stars

We have continued monitoring a pilot sample of 15 isolated, pulsating DA white dwarfs for center-of-mass motion caused by a planetary companion. Roughly 7 years into our survey, we have preliminary evidence for periodic variations in pulse arrival times for at least two white dwarfs in our sample. The variations in these systems are unlikely to be caused by secular evolution and are possibly the result of motion of the white dwarf around a center of mass. We have yet to claim confirmation of a planet. GD66 is a previously published candidate system, with a modulation in pulse arrival times that could be caused by a 2.0 M-J sin i planetary companion with an 8.3 year orbital period. Another candidate system, WD1354+0108, has a phase modulation consistent with a 0.7 M-J sin i planet at 2.3 AU (a 4.5 year orbit). We see similar behavior in two independent frequencies within this star, and while a sinusoid is currently a marginally better fit to the data than a straight line (as we might expect from cooling alone in a DAV), we are hesitant to over-interpret our results. Finally, we have a third system, WD0018+0031, that shows a change in pulse arrival times inconsistent with cooling alone; a 2.7 M-J planet at an orbit of about 5 AU could cause the observed trend. Observations of these candidate systems are ongoing in order to constrain any planetary companions that may be present.Astronom

The Potential of Ketungau and Silat Shales in Ketungau and Melawi Basins, West Kalimantan: for Oil Shale and Shale Gas Exploration

DOI: 10.17014/ijog.v8i1.154The Ketungau and Melawi Basins, in West Kalimantan, are Tertiary intramontane basins of which the potential for economic conventional oil and gas discoveries have not previously been confirmed. The Ketungau Basin is bordered by the Melawi Basin in the south. Besides non-ideal trapping mechanisms, another major problem in these basins is source rock maturation. Nevertheless, both basins are promising to be explored for oil shale and shale gas energy resources. Therefore, the aim of this paper is to give some perspectives on their source rocks, as an input for the evaluation of the potential of unconventional oil and gas. About twenty samples collected from the Ketungau and Melawi Basins were analyzed using pyrolysis and organic petrographic methods. The results show a poor to good quality of source rock potential. The Ketungau shale, which is the main source rock in the Ketungau Basin, is dominated by type III, immature, and gas prone kerogen. The Silat shale, which is the main source rock in the Melawi Basin, is dominated by type II, immature to early mature, mixed gas, and oil prone kerogen. In the field, Ketungau and Silat Formations have a widespread distribution, and are typically 900 m to 1000 m thick. Both the Ketungau and Silat shales occur within synclinal structures, which have a poor trapping mechanism for conventional oil or gas targets, but are suitable for oil shale and shale gas exploration. This early stage of research clearly shows good potential for the future development of unconventional energy within the Ketungau and Melawi Basins