The quest for planets around subdwarfs and white dwarfs from Kepler space telescope fields: Part I. Techniques and tests of the methods

In this study, we independently test the presence of an exoplanet around the binary KIC 9472174, which is composed of a red dwarf and a pulsating type B subdwarf. We also present the results of our search for Jupiter-mass objects orbiting near to the eclipsing binary KIC 7975824, which is composed of a white dwarf and type B subdwarf, and the pulsating white dwarf KIC 8626021. The goal is to test analytical techniques and prepare the ground for a larger search for possible substellar survivors on tight orbits around post-common envelope binaries and stars at the end of their evolution, that is, extended horizontal branch stars and white dwarfs. We, therefore, mainly focus on substellar bodies orbiting these stars within the range of the host's former red-giant or asymptotic-giant phase envelopes. Due to the methods we use, the quest is restricted to single-pulsating type B subdwarf and white dwarf stars and short-period eclipsing binaries containing a white dwarf or a subdwarf component. Results. Based on the three objects studied in this paper, we demonstrate that these methods can be used to detect giant exoplanets orbiting around pulsating white dwarf or type B subdwarf stars as well as short-period binary systems, at distances which fall within the range of the former red-giant envelope of a single star or the common envelope of a binary. Using our analysis techniques, we reject the existence of a Jupiter-mass exoplanet around the binary KIC 9472174 at the distance and orbital period previously suggested in the literature. We also found that the eclipse timing variations observed in the binary might depend on the reduction and processing of the Kepler data. The other two objects analyzed in this work do not have Jupiter mass exoplanets orbiting within 0.7 - 1.4 AU from them, or larger-mass objects on closer orbits (the given mass limits are minimum masses).Comment: 8 page

Signatures of the disk-jet coupling in the Broad-line Radio Quasar 4C+74.26

Here we explore the disk-jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of the multiwavelength monitoring of the source. The target is unique in that its radiative output at radio wavelengths is dominated by a moderately-beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96\% and 98\%, respectively) between the optical and radio bands, with the disk lagging behind the jet by $250 \pm 42$ days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along relativistic outflow. This scenario is supported by the re-analysis of the NuSTAR data, modelled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns the inner disk radius $R_{\rm in}/R_{\rm ISCO} =35^{+40}_{-16}$. We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity $L_{\rm bol} \sim 9 \times 10^{46}$ erg s$^{-1}$ $\sim 0.2 L_{\rm Edd}$, the jet total kinetic energy $L_\textrm{j} \sim 4 \times 10^{44}$ erg s$^{-1}$, inferred from the dynamical modelling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.Comment: 9 pages and 6 figures, ApJ accepte

Constraining the degree of the dominant mode in QQ Vir

We present early results of the application of a method which uses multicolor photometry and spectroscopy for \ell discrimination. This method has been successfully applied to the pulsating hot subdwarf Balloon 090100001. Here we apply the method to QQ Vir (PG1325+101). This star was observed spectroscopically and photometrically in 2008. Details on spectroscopy can be found in Telting et al. (2010) while photometry and preliminary results on \ell discrimination are provided here. The main aim of this work was to compare the value of the \ell parameter derived for the main mode in QQ Vir to previously published values derived by using different methods.Comment: Proceedings of The Fourth Meeting on Hot Subdwarf Stars and Related Objects held in China, 20-24 July 2009. Accepted for publication in Astrophysics and Space Scienc

The quest for planets around subdwarfs and white dwarfs from Kepler space telescope fields. I. Techniques and tests of the methods

Context. In this study, we independently test the presence of an exoplanet around the binary KIC 9472174, which is composed of a red dwarf and a pulsating type B subdwarf. We also present the results of our search for Jupiter-mass objects orbiting near to the eclipsing binary KIC 7975824, which is composed of a white dwarf and type B subdwarf, and the pulsating white dwarf KIC 8626021. Aims: The goal is to test analytical techniques and prepare the ground for a larger search for possible substellar survivors on tight orbits around post-common envelope binaries and stars at the end of their evolution, that is, extended horizontal branch stars and white dwarfs. We, therefore, mainly focus on substellar bodies orbiting these stars within the range of the host's former red-giant or asymptotic-giant phase envelopes. Due to the methods we use, the quest is restricted to single-pulsating type B subdwarf and white dwarf stars and short-period eclipsing binaries containing a white dwarf or a subdwarf component. Methods: Our methods rely on the detection of exoplanetary signals hidden in photometric time series data from the Kepler space telescope, and they are based on natural clocks within the data itself, such as stellar pulsations and eclipse times. The light curves are analyzed using Fourier transforms, time-delays, and eclipse timing variations. Results: Based on the three objects studied in this paper, we demonstrate that these methods can be used to detect giant exoplanets orbiting around pulsating white dwarf or type B subdwarf stars as well as short-period binary systems, at distances which fall within the range of the former red-giant envelope of a single star or the common envelope of a binary. Using our analysis techniques, we reject the existence of a Jupiter-mass exoplanet around the binary KIC 9472174 at the distance and orbital period previously suggested in the literature. We also found that the eclipse timing variations observed in the binary might depend on the reduction and processing of the Kepler data. The other two objects analyzed in this work do not have Jupiter mass exoplanets orbiting within 0.7-1.4 AU from them, or larger-mass objects on closer orbits (the given mass limits are minimum masses). Conclusions: Depending on the detection threshold of the time-delay method and the inclination of the exoplanet orbit toward the observer, data from the primary Kepler mission allows for the detection of bodies with a minimum of ~1 Jupiter-mass orbiting these stars at ~1 AU, while data from the K2 mission extends the detection of objects with a minimum mass of ~7 Jupiter-mass on ~0.1 AU orbits. The exoplanet mass and orbital distance limits depend on the length of the available photometric time series

UVSat: a concept of an ultraviolet/optical photometric satellite

Time-series photometry from space in the ultraviolet can be presently done with only a few platforms, none of which is able to provide wide-field long-term high-cadence photometry. We present a concept of UVSat, a twin space telescope which will be capable to perform this kind of photometry, filling an observational niche. The satellite will host two telescopes, one for observations in the ultraviolet, the other for observations in the optical band. We also briefly show what science can be done with UVSat.Comment: 6 pages, 2 figures, accepted for publication in the Proceedings of the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck

Follow-up observations of pulsating subdwarf B stars: Multisite campaigns on PG 1618+563B and PG 0048+091

We present follow-up observations of pulsating subdwarf B (sdB) stars as part of our efforts to resolve the pulsation spectra for use in asteroseismological analyses. This paper reports on multisite campaigns of the pulsating sdB stars PG 1618+563B and PG 0048+091. Data were obtained from observatories placed around the globe for coverage from all longitudes. For PG 1618+563B, our five-site campaign uncovered a dichotomy of pulsation states: Early during the campaign the amplitudes and phases (and perhaps frequencies) were quite variable while data obtained late in the campaign were able to fully resolve five stable pulsation frequencies. For PG 0048+091, our five-site campaign uncovered a plethora of frequencies with short pulsation lifetimes. We find them to have observed properties consistent with stochastically excited oscillations, an unexpected result for subdwarf B stars. We discuss our findings and their impact on subdwarf B asteroseismology.Comment: 50 pages including 17 figures and 10 tables. Accepted for publication in the Astrophysical Journa

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