Evidence For Temperature Change And Oblique Pulsation From Light Curve Fits Of The Pulsating White Dwarf GD 358

Convective driving, the mechanism originally proposed by Brickhill for pulsating white dwarf stars, has gained general acceptance as the generic linear instability mechanism in DAV and dbV white dwarfs. This physical mechanism naturally leads to a nonlinear formulation, reproducing the observed light curves of many pulsating white dwarfs. This numerical model can also provide information on the average depth of a star's convection zone and the inclination angle of its pulsation axis. In this paper, we give two sets of results of nonlinear light curve fits to data on the dbV GD 358. Our first fit is based on data gathered in 2006 by the Whole Earth Telescope; this data set was multiperiodic containing at least 12 individual modes. Our second fit utilizes data obtained in 1996, when GD 358 underwent a dramatic change in excited frequencies accompanied by a rapid increase in fractional amplitude; during this event it was essentially monoperiodic. We argue that GD 358's convection zone was much thinner in 1996 than in 2006, and we interpret this as a result of a short-lived increase in its surface temperature. In addition, we find strong evidence of oblique pulsation using two sets of evenly split triplets in the 2006 data. This marks the first time that oblique pulsation has been identified in a variable white dwarf star.Delaware Asteroseismic Research CenterNational Science Foundation AST-0909107, AST-0607840Norman Hackerman Advanced Research Program 003658-0255-2007Crystal Trust FoundationMt. Cuba ObservatoryUniversity of DelawareAstronom

Periodic variations in the O-C diagrams of five pulsation frequencies of the DB white dwarf EC 20058-5234

Variations in the pulsation arrival time of five independent pulsation frequencies of the DB white dwarf EC 20058−5234 individually imitate the effects of reflex motion induced by a planet or companion but are inconsistent when considered in unison. The pulsation frequencies vary periodically in a 12.9 year cycle and undergo secular changes that are inconsistent with simple neutrino plus photon-cooling models. The magnitude of the periodic and secular variations increases with the period of the pulsations, possibly hinting that the corresponding physical mechanism is located near the surface of the star. The phase of the periodic variations appears coupled to the sign of the secular variations. The standards for pulsation-timing-based detection of planetary companions around pulsating white dwarfs, and possibly other variables such as subdwarf B stars, should be re-evaluated. The physical mechanism responsible for this surprising result may involve a redistribution of angular momentum or a magnetic cycle. Additionally, variations in a supposed combination frequency are shown to match the sum of the variations of the parent frequencies to remarkable precision, an expected but unprecedented confirmation of theoretical predictions.Web of Scienc

Pulsational Mapping of Calcium Across the Surface of a White Dwarf

We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time series spectroscopy from Gemini-North with global time series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a model for polar accretion of calcium and rules out equatorial accretion.Comment: Accepted to the Astrophysical Journal. 16 pages, 10 figures

The rate of cooling of the pulsating white dwarf star G117−-B15A: a new asteroseismological inference of the axion mass

We employ a state-of-the-art asteroseismological model of G117-B15A, the archetype of the H-rich atmosphere (DA) white dwarf pulsators (also known as DAV or ZZ Ceti variables), and use the most recently measured value of the rate of period change for the dominant mode of this pulsating star to derive a new constraint on the mass of axion, the still conjectural non-barionic particle considered as candidate for dark matter of the Universe. Assuming that G117-B15A is truly represented by our asteroseismological model, and in particular, that the period of the dominant mode is associated to a pulsation g-mode trapped in the H envelope, we find strong indications of the existence of extra cooling in this star, compatible with emission of axions of mass m_a \cos^2 \beta = 17.4^{+2.3}_{-2.7} meV.Comment: 9 pages, 5 figures and 3 tables. Accepted for publication in MNRA

Involvement of Cyclin K Posttranscriptional Regulation in the Formation of Artemia Diapause Cysts

Background: Artemia eggs tend to develop ovoviviparously to yield nauplius larvae in good rearing conditions; while under adverse situations, they tend to develop oviparously and encysted diapause embryos are formed instead. However, the intrinsic mechanisms regulating this process are not well understood. Principal Finding: This study has characterized the function of cyclin K, a regulatory subunit of the positive transcription elongation factor b (P-TEFb) in the two different developmental pathways of Artemia. In the diapause-destined embryo, Western blots showed that the cyclin K protein was down-regulated as the embryo entered dormancy and reverted to relatively high levels of expression once development resumed, consistent with the fluctuations in phosphorylation of position 2 serines (Ser2) in the C-terminal domain (CTD) of the largest subunit (Rpb1) of RNA polymerase II (RNAP II). Interestingly, the cyclin K transcript levels remained constant during this process. In vitro translation data indicated that the template activity of cyclin K mRNA stored in the postdiapause cyst was repressed. In addition, in vivo knockdown of cyclin K in developing embryos by RNA interference eliminated phosphorylation of the CTD Ser2 of RNAP II and induced apoptosis by inhibiting the extracellular signal-regulated kinase (ERK) survival signaling pathway. Conclusions/Significance: Taken together, these findings reveal a role for cyclin K in regulating RNAP II activity during diapause embryo development, which involves the post-transcriptional regulation of cyclin K. In addition, a further role wa

Primary Black Hole Spin in OJ 287 as Determined by the General Relativity Centenary Flare

OJ 287 is a quasi-periodic quasar with roughly 12 year optical cycles. It displays prominent outbursts that are predictable in a binary black hole model. The model predicted a major optical outburst in 2015 December. We found that the outburst did occur within the expected time range, peaking on 2015 December 5 at magnitude 12.9 in the optical R -band. Based on Swift /XRT satellite measurements and optical polarization data, we find that it included a major thermal component. Its timing provides an accurate estimate for the spin of the primary black hole, ##IMG## [http://ej.iop.org/images/2041-8205/819/2/L37/apjl523055ieqn1.gif] $i =0.313pm 0.01$ . The present outburst also confirms the established general relativistic properties of the system such as the loss of orbital energy to gravitational radiation at the 2% accuracy level, and it opens up the possibility of testing the black hole no-hair theorem with 10% accuracy during the present decade.Peer reviewe

A Search for QPOs in the Blazar OJ287: Preliminary Results from the 2015/2016 Observing Campaign

We analyse the light curve in the R band of the blazar OJ287, gathered during the 2015/2016 observing season. We did a search for quasi-periodic oscillations (QPOs) using several methods over a wide range of timescales. No statistically significant periods were found in the high-frequency domain both in the ground-based data and in Kepler observations. In the longer-period domain, the Lomb–Scargle periodogram revealed several peaks above the 99% significance level. The longest one—about 95 days—corresponds to the innermost stable circular orbit (ISCO) period of the more massive black hole. The 43-day period could be an alias, or it can be attributed to accretion in the form of a two-armed spiral wave.Peer reviewe

Authenticating the Presence of a Relativistic Massive Black Hole Binary in OJ 287 Using Its General Relativity Centenary Flare : Improved Orbital Parameters

Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole "no-hair theorem" at the 10% level.Peer reviewe