RAT0455+1305: another pulsating hybrid sdB star

RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in finding any variability on timescales of a few minutes to several hours. The star was found to be another sdBV star with one high amplitude mode and relatively long period. These features along with estimation of T_eff and log g makes this star very similar to Balloon 090100001. Encouraged by prominent results obtained for the latter star we have decided to perform white light photometry on RAT0455+1305. In 2009 we used the 1.5m telescope located in San Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant mode found in the discovery data, uncovered another peak close to the dominant one, and three peaks in the low frequency region. This shows that RAT0455+1305 is another hybrid sdBV star pulsating in both p- and g-modes.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 & Space Scienc

Multichannel operation of an integrated acousto-optic wavelength routing switch for WDM systems

Polarization independent acousto-optic tunable filters (PIAOTF's) can operate as transparent wavelength-selective crossconnects to route signals in wavelength division multiplexed optical networks. In this paper, a new low power PIAOTF is characterized as a switch in multiwavelength operation, using four equally spaced lightwave signals with wavelengths between 1546 nm and 1558 nm. Interchannel interference due to sidelobe excitation is lower than -11 dB for single wavelength switching and is equal to -6 dB in the extreme case of simultaneous switching of all wavelength channels. Sources of interport and interchannel crosstalk for single and multiple wavelength switching are identified

Multicolour photometry of Balloon 090100001: linking the two classes of pulsating hot subdwarfs

We present results of the multicolour UBVR photometry of the high-amplitude EC14026-type star, Balloon 090100001. The data span over a month and consist of more than a hundred hours of observations. Fourier analysis of these data led us to the detection of at least 30 modes of pulsation of which 22 are independent. The frequencies of 13 detected modes group in three narrow ranges, around 2.8, 3.8 and 4.7 mHz, where the radial fundamental mode, the first and second overtones are likely to occur. Surprisingly, we also detect 9 independent modes in the low-frequency domain, between 0.15 and 0.4 mHz. These modes are typical for pulsations found in PG1716+426-type stars, discovered recently among cool B-type subdwarfs. The modes found in these stars are attributed to the high-order g modes. As both kinds of pulsations are observed in Balloon 090100001, it represents a link between the two classes of pulsating hot subdwarfs. At present, it is probably the most suitable target for testing evolutionary scenarios and internal constitution models of these stars by means of asteroseismology. Three of the modes we discovered form an equidistant frequency triplet which can be explained by invoking rotational splitting of an $\ell$ = 1 mode. The splitting amounts to about 1.58 $\mu$Hz, leading to a rotation period of 7.1 $\pm$ 0.1 days.Comment: 12 pages, 14 figures, accepted for publication in MNRAS. For full-resolution postscript file, visit http://www.as.wsp.krakow.pl/~andy/balloon.ps.g

J08069+1527: A newly discovered high amplitude, hybrid subdwarf B pulsator

We present our discovery of a new hybrid pulsating subdwarf B star, J08069+1527. The effective temperature and surface gravity of 28,500$\pm$400\,K and 5.37$\pm$0.04\,dex, respectively, place this object inside the instability strip and also among other pulsating hot subdwarfs of a hybrid nature, right next to another fascinating star: Balloon\,090100001. From this proximity, we anticipated this star could pulsate in both high and low frequency modes. Indeed, our analysis of photometric data confirmed our prediction. We detected two peaks in the high frequency region and two other peaks at low frequencies. In addition, the amplitude of the dominant mode is very high and comparable to the dominant peaks in other hybrid subdwarf B stars. Since this star is bright, we performed time-series low resolution spectroscopy. Despite a low signal-to-noise (S/N) ratio, we were able to detect the main peak from these data. All our results strongly indicate that J08069+1527 is a high amplitude pulsating hot subdwarf B star of hybrid nature. By analogy to the other pulsating sdB star, we judge that the dominant mode we detected here has radial nature. Future stellar modeling should provide us with quite good constrains as p- and g-modes presented in this star are driven in different parts of its interior.Comment: 7 pages, 10 figures, accepted for publication in MNRA

RAT J0455+1305: A rare hybrid pulsating subdwarf B star

We present results on the second-faintest pulsating subdwarf B (sdB) star known, RAT J0455+1305, derived from photometric data obtained in 2009. It shows both short and long periods oscillations, theoretically assigned as pressure and gravity modes. We identify six short-period frequencies (with one being a combination) and six long-period frequencies. This star is the fourth hybrid sdB star discovered so far which makes it of special interest as each type of mode probes a different part of the star. This star is similar to the sdB hybrid pulsator Balloon 090100001 in that it exhibits short-period mode groupings, which can be used to identify pulsation parameters and constrain theoretical models.Comment: published in MNRA

The cranking formula and the spurious behaviour of the mass parameters

We discuss some aspects of the approach of the mass parameters by means of the simple cranking model. In particular, it is well known that the numerical application of this formula is often subject to ambiguities or contradictions. It is found that these problems are induced by the presence of two derivatives in the formula. To overcome these problems, we state a useful ansatz and we develop a number of simple arguments which tend to justify the removal of these terms. As soon as this is done, the formula becomes simpler and easier to interpret. In this respect, it is shown how the shell effects affect the mass parameters. A number of numerical tests help us in our conclusions.Comment: version 3 corrigendum of the ansatz of section V, corrigendum of the legend of Fig3. Submission = text file + 5 figure

Nuclear collective dynamics within Vlasov approach

We discuss, in an investigation based on Vlasov equation, the properties of the isovector modes in nuclear matter and atomic nuclei in relation with the symmetry energy. We obtain numerically the dipole response and determine the strength function for various systems, including a chain of Sn isotopes. We consider for the symmetry energy three parametrizations with density providing similar values at saturation but which manifest very different slopes around this point. In this way we can explore how the slope affects the collective response of finite nuclear systems. We focus first on the dipole polarizability and show that while the model is able to describe the expected mass dependence, A^{5/3}, it also demonstrates that this quantity is sensitive to the slope parameter of the symmetry energy. Then, by considering the Sn isotopic chain, we investigate the emergence of a collective mode, the Pygmy Dipole Resonance (PDR), when the number of neutrons in excess increases. We show that the total energy-weighted sum rule exhausted by this mode has a linear dependence with the square of isospin I=(N-Z)/A, again sensitive to the slope of the symmetry energy with density. Therefore the polarization effects in the isovector density have to play an important role in the dynamics of PDR. These results provide additional hints in the investigations aiming to extract the properties of symmetry energy below saturation.Comment: 7 pages, 6 figure

Classification of integrable Weingarten surfaces possessing an sl(2)-valued zero curvature representation

In this paper we classify Weingarten surfaces integrable in the sense of soliton theory. The criterion is that the associated Gauss equation possesses an sl(2)-valued zero curvature representation with a nonremovable parameter. Under certain restrictions on the jet order, the answer is given by a third order ordinary differential equation to govern the functional dependence of the principal curvatures. Employing the scaling and translation (offsetting) symmetry, we give a general solution of the governing equation in terms of elliptic integrals. We show that the instances when the elliptic integrals degenerate to elementary functions were known to nineteenth century geometers. Finally, we characterize the associated normal congruences