D.-F. Guo

PHOTOMETRIC PROPERTIES FOR SELECTED ALGOL-TYPE BINARIES. II. AO SERPENTIS AND V338 HERCULIS

We present the first multiband photometry for the semidetached eclipsing binary AO Serpentis, observed on seven nights between 2009 April and July at the Weihai Observatory of Shandong University. By using the 2003 version of the Wilson–Devinney code, the photometric solutions of AO Ser and a similar object V338 Her were (re)deduced. The spectral types and orbital periods are A2 and P = 0.8793 days for AO Ser, F1V and P = 1.3057 days for V338 Her. The results reveal that two binaries are low mass ratio systems, whose secondary components fill their Roche lobes. The fill-out factors of the primary components are f = 58.6% for AO Ser and f = 54.2% for V338 Her, respectively. From the O − C curves of AO Ser and V338 Her, it is discovered that secular period changes with cyclic variations exist. The periods and semiamplitudes are 17.32(±0.01) yr and 0.0051(±0.0001) days for AO Ser, 29.07(±0.04) yr and 0.0116(±0.0015) days for V338 Her, respectively. This kind of cyclic oscillation may be attributed to either the light-time effect via an assumed third body or perhaps cyclic magnetic activity on the secondary component. For AO Ser, the long-term period decreases at a rate of dP /dt = −5.35(±0.03) × 10 −7 days yr −1 , which may be caused by mass and angular momentum loss from the system. Considering the period decreasing, the fill-out factor of the primary for AO Ser will increase and it will finally fill its Roche lobe. Meanwhile, the secular period increase rate for V338 Her is dP /dt = +1.44(±0.24) × 10 −7 days yr −1 , indicating that mass transfers from the less massive component to the more massive component. This will also cause the fill-out factor of the primary to increase. When the primaries fill their Roche lobes, AO Ser and V338 Her may evolve into contact stars, as predicted by the theory of thermal relaxation oscillations.

Multiband Variability Analysis of Mrk 421

We have assembled the historical variability data of Mrk 421 at radio 15 GHz, X-ray and gamma-ray bands, spanning about 6.3, 10.3 and 7.5 yr, respective- ly. We analyzed the variability by using three methods. The results indicated that there is a period of 287.6 +- 4.4 days for 15 GHz, 309.5 +- 5.8 days for X- ray and 283.4+- 4.7 days for gamma-ray, respectively. This period can be reasonably explained by the nonballistic helical motion of the emitting material. The cor- relation analysis suggested that the variabilities of radio 15 GHz, X-ray and 0-ray are remarkable correlated, and the emission of radio 15 GHz lags behind that of X-ray, and the X-ray flux lags behind the gamma-ray. This suggests that the gamma-ray derives from inverse Compton (IC) scattering of the synchrotron photons, supporting the synchrotron self-Compton (SSC) model. Moreover, the time delay between different wavebands could be explained by the shock-in-jet models, in which a moving emission region produces the radio to gamma-ray activity, implying that the emission region of gamma-ray is closer to the center than ones of X-ray and radio emission.

Time-resolved GRB spectra in the complex radiation of synchrotron and Compton processes

Under the steady state condition, the spectrum of electrons is investigated by solving the continuity equation under the complex radiation of both the synchrotron and Compton processes. The resulted GRB spectrum is a broken power law in both the fast and slow cooling phases. On the basis of this electron spectrum, the spectral indices of the Band function in four different phases are presented. In the complex radiation frame, the detail investigation on physical parameters reveals that both the reverse shock photosphere model and the forward shock with strong coupling model can answer the

THE ACTIVE CONTACT BINARY TY UMA REVISITED: IS IT A QUADRUPLE STAR?

\alpha \sim -1

THE FIRST PHOTOMETRIC ANALYSIS OF THE NEAR CONTACT BINARY IR Cas

problem. A possible marginal to fast cooling phase transition in GRB 080916C is discussed. The time resolved spectra in different pulses of GRB 100724B, GRB 100826A and GRB 130606B are investigated. We found that the flux is proportional to the peak energy in almost all pulses. The phases for different pulses are determined according to the spectral index revolution. We found the strong correlations between spectral indices and the peak energy in GRB 100826A, which can be explained by the Compton effect in the fast cooling phase. However, the complex scenario predicts a steeper index for the injected electrons, which challenges the acceleration mechanism in GRBs.

Optical monitoring of the Seyfert galaxy NGC 4151 and possible periodicities in its historical light curve

TY UMa is an F-type eclipsing binary star. Four-color light curves and radial velocities of this system were presented and simultaneously analyzed using the W-D code. It is found that TY UMa is a W-subtype shallow contact binary system (f = 13.4%) with a mass ratio of q = 2.523. In order to explain the asymmetric light curve of this binary, a dark spot on the less massive component was employed. Our newly determined 31 times of minimum light, including those collected from the literature, have been used to analyze orbital period changes of TY UMa. The complicated period variation could be sorted into a secular period increase at a rate of dp/dt = +5.18(+/- 0.21) x 10(-7) days yr(-1), a 51.7 yr periodic modulation (A(3) = 0.0182 days), and a very small amplitude cyclic oscillation with a period of 10.0 yr (A(4) = 0.0015 days). The long-term increase of the period can be explained by mass transfer from the less massive component to the more massive one. The Applegate mechanism may impossibly explain the two cyclic components in the period. The two cyclic variations are very likely caused by the light travel time effect of third and fourth components, suggesting that TY UMa is a quadruple system.

A possible giant planet orbiting the cataclysmic variable LX Ser

The first photometric analysis of IR Cas was carried out based on the new observed BVRI light curves. The symmetric light curves and nearly flat secondary minimum indicate that very precise photometric results can be determined. We found that IR Cas is a near contact binary with the primary component filling its Roche lobe. An analysis of the O-C diagram based on all available times of light minimum reveals evidence for a periodic change with a semiamplitude of 0.0153 days and a period of 39.7 years superimposed on a secular decrease at a rate of dp/dt=-1.28(\pm0.09)\times10^{-7} d yr^{-1}. The most reasonable explanation for the periodic change is the light time-travel effect due to a third body. The period decrease may be caused by mass transfer from the primary component to the secondary. With the decreasing period, IR Cas would eventually evolve into a contact system.

Astrometric calibration for space debris with a small field of view

We report B , V and R band CCD photometry of the Seyfert galaxy NGC 4151 obtained with the 1.0 m telescope at Weihai Observatory of Shandong University and the 1.56 m telescope at Shanghai Astronomical Observatory from 2005 December to 2013 February. Combining all available data from literature, we have constructed a historical light curve from 1910 to 2013 to study the periodicity of the source using three different methods (the Jurkevich method, the Lomb-Scargle periodogram method and the Discrete Correlation Function method). We find possible periods of P 1 = 4 ± 0.1, P 2 = 7.5 ± 0.3 and P 3 = 15.9 ± 0.3 yr.

WES—Weihai Echelle Spectrograph

LX Ser is a deeply eclipsing cataclysmic variable with an orbital period of 0.1584325 d. 62 new eclipse times were determined by our observations and the AAVSO International Data base. Combining all available eclipse times, we analyzed the O-C behavior of LX Ser. We found that the O-C diagram of LXSer shows a sinusoidal oscillation with a period of 22.8 yr and an amplitude of 0.00035 d. Two mechanisms (i.e., the Applegate mechanism and the light-travel time effect) are applied to explain the cyclic modulation. We found that it is difficult to apply the Applegate mechanism to explain the cyclic oscillation in the orbital period. Therefore, the cyclic period change is most likely to be caused by the light-travel time effect due to the presence of a third body. The mass of the tertiary component was determined to be M-3 similar to 7.5M(Jup). We supposed that the tertiary companion is plausibly a giant planet. The stability of the giant planet was checked, and we found that the multiple system is stable.

The active W UMa type binary star V781 Tau revisited

A center-shift method is presented for astrometric calibration, which is effective for space debris astrometry in a small field of view. Its details are given, the accuracy is experimented and the result is presented. The average accuracy of astrometric calibration using center-shift method is about 0.57 arcsec. The center-shift method is applicable to images observed by equatorial mount telescopes.