The HU Aqr planetary system hypothesis revisited Goździewski, K; Słowikowska, A; Dimitrov, D ...
Monthly notices of the Royal Astronomical Society,
04/2015, Letnik:
448, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We study the mid-egress eclipse timing data gathered for the cataclysmic binary HU Aquarii during the years 1993–2014. The (O−C) residuals were previously attributed to a single ∼7 Jupiter mass ...companion in ∼5 au orbit or to a stable two-planet system with an unconstrained outermost orbit. We present 22 new observations gathered between 2011 June and 2014 July with four instruments around the world. They reveal a systematic deviation of ∼60–120 s from the older ephemeris. We re-analyse the whole set of the timing data available. Our results provide an erratum to the previous HU Aqr planetary models, indicating that the hypothesis for a third and fourth body in this system is uncertain. The dynamical stability criterion and a particular geometry of orbits rule out coplanar two-planet configurations. A putative HU Aqr planetary system may be more complex, e.g. highly non-coplanar. Indeed, we found examples of three-planet configurations with the middle planet in a retrograde orbit, which are stable for at least 1 Gyr, and consistent with the observations. The (O−C) may be also driven by oscillations of the gravitational quadrupole moment of the secondary, as predicted by the Lanza et al. modification of the Applegate mechanism. Further systematic, long-term monitoring of HU Aqr is required to interpret the (O−C) residuals.
Aims. We present the results of flux density monitoring of PSR B0329+54 at the frequency of 4.8 GHz using the 32-m TCfA radiotelescope. The observations were conducted between 2002 and 2005. The main ...goal of the project was to find interstellar scintillation (ISS) parameters for the pulsar at the frequency at which it was never studied in detail. To achieve this, the 20 observing sessions consisted of 3-min integrations, which on average lasted 24 h. This gave us sufficient sensitivity to all types of flux density variations over a wide range of timescales. The character of the observations makes our project unique amongst other ISS oriented observing programs, at least at high frequency. Methods. Flux density time series obtained for each session were analysed using structure functions. For some of the individual sessions as well as for the general average structure function we were able to identify two distinctive timescales present, the timescales of diffractive and refractive scintillations. To the best of our knowledge, this is the first case when both scintillation timescales, tDISS = 42.7 min and tRISS = 305 min, were observed simultaneously in a uniform data set and estimated using the same method. Results. The obtained values of the ISS parameters combined with the data found in the literature allowed us to study the frequency dependence of these parameters over a wide range of observing frequencies, which is crucial for understanding the ISM turbulence. We found that the Kolmogorov spectrum is not best suited for describing the density fluctuations of the ISM, and a power-law spectrum with β = 4 seems to fit better with our results. We were also able to estimate the transition frequency (transition from strong to weak scintillation regimes) as νc = 10.1 GHz, much higher than was previously predicted. We were also able to estimate the strength of scattering parameter u = 2.67 and the Fresnel scale as rF = 6.7 × 108 m.
Turn-over in pulsar spectra around 1 GHz Kijak, J.; Gupta, Y.; Krzeszowski, K.
Astronomy and astrophysics (Berlin),
02/2007, Letnik:
462, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Aims.The main aim is to investigate the possibility of a high frequency turn-over in the radio spectrum of pulsars. Methods.Using the GMRT, multi-frequency flux density measurements of several ...candidate pulsars have been carried out and their spectra have been extended to lower frequencies. Results.We present the first direct evidence for turn-over in pulsar radio spectra at high frequencies. A total of 3 pulsars (including 2 new ones from this study) are now shown to have a turn-over frequency $\ga$1 GHz, and one is shown to have a turn-over at ~600 MHz.
The magnetospheric locations of pulsar radio emission region are not well known. The actual form of the so-called radius-to-frequency mapping should be reflected in the aberration–retardation (A/R) ...effects that shift and/or delay the photons depending on the emission height in the magnetosphere. Recent studies suggest that in a handful of pulsars the A/R effect can be discerned with respect to the peak of the central core emission region. To verify these effects in an ensemble of pulsars, we launched a project analysing multifrequency total intensity pulsar profiles obtained from the new observations from the Giant Meterwave Radio Telescope (GMRT), Arecibo Observatory (AO) and archival European Pulsar Network (EPN) data. For all these profiles, we measure the shift of the outer cone components with respect to the core component, which is necessary for establishing the A/R effect. Within our sample of 23 pulsars, seven show the A/R effects, 12 of them (doubtful cases) show a tendency towards this effect, while the remaining four are obvious counterexamples. The counterexamples and doubtful cases may arise from uncertainties in the determination of the location of the meridional plane and/or the core emission component. Hence, it appears that the A/R effects are likely to operate in most pulsars from our sample. We conclude that in cases where those effects are present the core emission has to originate below the conal emission region.
Aims. We aim to investigate the flux density modulation from pulsars and the specific behaviour of the modulation index versus frequency. Methods. Several pulsars were observed with the Effelsberg ...radio telescope at 8.35 GHz. Their flux density time series were corrected for interstellar scintillation effects. Results. We present measurements of modulation indices for eight pulsars. We confirm the presence of a critical frequency at ~1 GHz for these pulsars (including three new ones from this study). We derived intrinsic modulation indices for the resulting flux density time series. Our data analysis revealed strong single pulses detected from five pulsars.
We show the results of microsecond resolution radio data analysis focused on flux measurements of single pulses of PSR B1133+16. The data were recorded at 4.85 and 8.35 GHz with 0.5- and 1.1-GHz ...bandwidth, respectively, using Radio Telescope Effelsberg (Max-Planck-Institut fur Radioastronomie). The most important conclusion of the analysis is that the strongest single pulse emission at 4.85 and 8.35 GHz contributes almost exclusively to the trailing part of the leading component of the pulsar mean profile, whereas studies at lower frequencies report that the contribution is spread almost uniformly, covering all phases of the pulsar mean profile. We also estimate the radio emission heights to be around 1-2 per cent of the light-cylinder radius, which is in agreement with previous studies. Additionally, these observations allowed us to add two more measurements of the flux density to the PSR B1133+16 broad-band radio spectrum, covering frequencies from 16.7 MHz up to 32 GHz. We fit two different models to the spectrum: a broken power law and a spectrum based on the flicker-noise model, which represents the spectrum in a simpler, but similarly accurate, way. PUBLICATION ABSTRACT
Aims. We aim to investigate the flux density modulation from pulsars and the specific behaviour of the modulation index versus frequency. Methods. Several pulsars were observed with the Effelsberg ...radio telescope at 8.35 GHz. Their flux density time series were corrected for interstellar scintillation effects. Results. We present measurements of modulation indices for eight pulsars. We confirm the presence of a critical frequency at ∼1 GHz for these pulsars (including three new ones from this study). We derived intrinsic modulation indices for the resulting flux density time series. Our data analysis revealed strong single pulses detected from five pulsars.
PDF
