Twelve type II-P supernovae seen with the eyes of Spitzer

Core-collapse supernovae (CC SNe), especially those of type II-plateau (II-P), are thought to be important contributors to cosmic dust production. The most obvious indicator of the presence of newly-formed and/or pre-existing dust is the time-dependent mid-infrared (MIR) excess coming from the environment of SNe. Our goal was to collect publicly available, previously unpublished measurements on type II-P (or peculiar IIP) SNe from the Spitzer database. The temporal changes of the observed fluxes may be indicative of the underlying supernova, while spectral energy distribution (SED) fitting to the fluxes in different IRAC channels may reveal the physical parameters of the mid-IR radiation, presumably due to warm dust. IRS spectra were extracted and calibrated with SPICE, while photometric SEDs were assembled using IRAF and MOPEX. Calculated SEDs from observed fluxes were fit with simple dust models to get basic information on the dust presumed as the source of MIR radiation. We found twelve SNe satisfying the criterion above, observed at late-time epochs (typically after +300 days). In three cases we could not identify any point source at the SN position on late time IRAC images. We found two SNe, 2005ad and 2005af, which likely have newly-formed dust in their environment, while in the other seven cases the observed MIR flux may originate from pre-existing circumstellar or interstellar dust. Our results support the previous observational conclusions that warm new dust in the environment of SNe contributes only marginally to cosmic dust content.Comment: Accepted for publication in Astronomy and Astrophysics; 15 pages, 8 figures, 9 tables (Ver. 2.: language edited version, minor corrections were made in the title, in the text, and in the reference list

A two-component model for fitting light-curves of core-collapse supernovae

We present an improved version of a light curve model, which is able to estimate the physical properties of different types of core-collapse supernovae having double-peaked light curves, in a quick and efficient way. The model is based on a two-component configuration consisting of a dense, inner region and an extended, low-mass envelope. Using this configuration, we estimate the initial parameters of the progenitor via fitting the shape of the quasi-bolometric light curves of 10 SNe, including Type IIP and IIb events, with model light curves. In each case we compare the fitting results with available hydrodynamic calculations, and also match the derived expansion velocities with the observed ones. Furthermore, we also compare our calculations with hydrodynamic models derived by the SNEC code, and examine the uncertainties of the estimated physical parameters caused by the assumption of constant opacity and the inaccurate knowledge of the moment of explosion

Robustness of BitTorrent-like VoD protocols

Besides server supported solutions for Video-on-demand, approaches based on distributed systems such as BitTorrent are being used due to their efficiency and high scalability. There are several protocol variants proposed in the literature, which are mainly concerned with providing mechanisms for piece selection and peer selection. In this paper, using the concept of Design Space Analysis, we give comparisons of the performances of several BitTorrent-like Video-on-demand protocols under the assumption that other protocol variants may also enter the system

Experimental Investigation on Condition Monitoring Opportunities of Tramway Tracks

The increasing demands for guided transportation modes in urban areas generate the need of high-frequency services. Due to the frequent services, the track deterioration process will be accelerated. Therefore, the exact knowledge of track quality is highly important for every railway company to provide high quality service level.For monitoring of tramway tracks, an unconventional vehicle dynamics measurement setup is developed, which records the data of 3-axes wireless accelerometers mounted on wheel discs of regular in-service tram. In the implementation of prototype system, the bogie side-frame and car body mounted sensors are also fitted to the instrumented vehicle to compare the efficiency of these conventional solutions with the developed arrangement. At the first test period, the instrumented vehicle works as a dedicated inspection vehicle, in order to keep the constant velocity and help to determine the influencing factors on results. Accelerations are processed to obtain the track irregularities, in order to determine whether the track needs to be repaired. Real data come from measurements taken on tram line 49 of the Budapest (Hungary) and they have been validated by comparing results to the actual state of the track provided by a track geometry monitoring trolley and visual inspection. This paper presents the developed methods used for validation and the analysis of preliminary results of the wheel discs mounted accelerometers. This vehicle dynamic measurement system is cheap to implement and no significant modification of the vehicle is required. Therefore, in-service vehicles equipped with this system may serve a good opportunity for monitoring tramway track, while it multiple passes over same track section

Towards the Coevolution of Incentives in BitTorrent

BitTorrent is a peer-to-peer file sharing system that is open to variant behavior at the peer level through modification of the client software. A number of different variants have been released and proposed. Some are successful and become widely used whereas others remain in a small minority or are not used at all. In previous work we explored the performance of a large set of client variants over a number of dimensions by applying Axelrod’s round-robin pairwise tournament approach. However, this approach does not capture the dynamics of client change over time within pairwise tournaments. In this work we extend the tournament approach to include a limited evolutionary step, within the pairwise tournaments, in which peers copy their opponents strategy (client variant) if it outperforms their own and also spontaneously change to the opponents strategy with a low mutation probability. We apply a number of different evolutionary algorithms and compare them with the previous non-evolutionary tournament results. We find that in most cases cooperative (sharing) strategies outperformed free riding strategies. These results are comparable to those previously obtained using the round-robin approach without evolution. We selected this limited form of evolution as a step towards understanding the full coevolutionary dynamics that would result from evolution between a large space of client variants in a shared population rather than just pairs of variants. We conclude with a discussion on how such future work might proceed. © 2015, Budapest Tech Polytechnical Institution. All rights reserved

Dynamical phasing of Type II Cepheids

In this paper we examine the problems of phasing using light curves and offer an alternate technique using the changes in acceleration to establish the zero point. We give astrophysical justification as to why this technique is useful and apply the technique to a selection of Type II Cepheids. We then examine some limitations of the technique which qualify its use.Comment: 6 pages, including 4 figures, accepted in MNRA

Measuring Expansion Velocities in Type II-P Supernovae

We estimate photospheric velocities of Type II-P supernovae using model spectra created with SYNOW, and compare the results with those obtained by more conventional techniques, such as cross-correlation, or measuring the absorption minimum of P Cygni features. Based on a sample of 81 observed spectra of 5 SNe, we show that SYNOW provides velocities that are similar to ones obtained by more sophisticated NLTE modeling codes, but they can be derived in a less computation-intensive way. The estimated photospheric velocities (v_model) are compared to ones measured from Doppler-shifts of the absorption minima of the Hbeta and the FeII \lambda5169 features. Our results confirm that the FeII velocities (v_Fe) have tighter and more homogeneous correlation with the estimated photospheric velocities than the ones measured from Hbeta, but both suffer from phase-dependent systematic deviations from those. The same is true for comparison with the cross-correlation velocities. We verify and improve the relations between v_Fe, v_Hbeta and v_model in order to provide useful formulae for interpolating/extrapolating the velocity curves of Type II-P SNe to phases not covered by observations. We also discuss the implications of our results for the distance measurements of Type II-P SNe, and show that the application of the model velocities is preferred in the Expanding Photosphere Method.Comment: 19 pages, 10 figures, accepted in MNRA