Calibration of the Liverpool Telescope RINGO3 polarimeter

We present an analysis of polarimetric observations of standard stars performed over the period of more than three years with the RINGO3 polarimeter mounted on the Liverpool Telescope. The main objective was to determine the instrumental polarisation of the RINGO3 polarimeter in three spectral energy ranges: blue (350--640~nm), green (650--760~nm) and red (770--1000~nm). The observations were conducted between 2012 and 2016. The total time span of 1126 days was split into five epochs due to the hardware changes to the observing system. Our results should be applied to calibrate all polarimetric observations performed with the RINGO3 polarimeter

Pulse to pulse flux density modulation from pulsars at 8.35 GHz

Aims. To investigate the flux density modulation from pulsars and the existence of specific behaviour of modulation index versus frequency. Methods. Several pulsars have been observed with the Effelsberg radio telescope at 8.35 GHz. Their flux density time series have been corrected for interstellar scintillation effects. Results. We present the measurement of modulation indices for 8 pulsars. We confirm the presence of a critical frequency at ~1 GHz for these pulsars (including 3 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 5 pulsars.Comment: accepted for publication in A&

Human Gait Recognition from Motion Capture Data in Signature Poses

Most contribution to the field of structure-based human gait recognition has been done through design of extraordinary gait features. Many research groups that address this topic introduce a unique combination of gait features, select a couple of well-known object classiers, and test some variations of their methods on their custom Kinect databases. For a practical system, it is not necessary to invent an ideal gait feature -- there have been many good geometric features designed -- but to smartly process the data there are at our disposal. This work proposes a gait recognition method without design of novel gait features; instead, we suggest an effective and highly efficient way of processing known types of features. Our method extracts a couple of joint angles from two signature poses within a gait cycle to form a gait pattern descriptor, and classifies the query subject by the baseline 1-NN classier. Not only are these poses distinctive enough, they also rarely accommodate motion irregularities that would result in confusion of identities. We experimentally demonstrate that our gait recognition method outperforms other relevant methods in terms of recognition rate and computational complexity. Evaluations were performed on an experimental database that precisely simulates street-level video surveillance environment

Diffractive and refractive timescales at 4.8 GHz in PSR B0329+54

We present the results of flux density monitoring of PSR B0329+54 at the frequency of 4.8 GHz using the 32-meter 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-minute integrations which on average lasted 24 hours. 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, t_DISS=42.7 minutes and t_RISS=305 minutes, were observed simultaneously in a uniform data set and estimated using the same method. 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 beta =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 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 6.7x10^8 meters.Comment: 11 pages, 4 figures, accepted for publication in: Astronomy and Astrophysic

The HU Aqr planetary system hypothesis revisited

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 2-planet system with an unconstrained outermost orbit. We present 22 new observations gathered between June, 2011 and July, 2014 with four instruments around the world. They reveal a systematic deviation of ~60 - 120 seconds 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 2-planet configurations. A putative HU Aqr planetary system may be more complex, e.g., highly non-coplanar. Indeed, we found examples of 3-planet configurations with the middle planet in a retrograde orbit, which are stable for at least 1Gyr, 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.Comment: 18 pages, 16 figures, 4 tables, accepted to Monthly Notices of the Royal Astronomical Society (MNRAS

On the aberration-retardation effects in pulsars

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 w.r.t the peak of the central core emission region. To verify these effects in an ensemble of pulsars we launched a project analysing multi--frequency 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 7 show the A/R effects, 12 of them (doubtful cases) show a tendency towards this effect, while the remaining 4 are obvious counter examples. The counter--examples and doubtful cases may arise from uncertainties in determination of the location of the meridional plane and/or the core emission component. It hence 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.Comment: for appendix postscript file, see http://astro.ia.uz.zgora.pl/~chriss/Krzeszowski_2009_appendix.p