Shin-ya Narusawa

Short-Period Light Variation of an Eclipsing Binary System: RZ Cassiopeiae

The eclipsing binary system RZ Cas is known to exhibit variation in its light curves at the primary minimum, usually showing a partial-eclipse–type curve but sometimes indicating a flat minimum, which is evidence for a total eclipse. We observed RZ Cas not only during the primary eclipse, but also during the out-of-eclipse phase, and we have found a short-period light variation with a frequency of 62.20 cycles day-1 (period of 23.15 minutes), whose maximum amplitude is 0.02 mag. This short-period variation can modulate the shape of the light curve at the primary minimum effectively. The brightness-color relationship of the short-period variation suggests a δ Scuti type oscillation.

Early Spectral Evolution of the Rapidly Expanding Type Ia Supernova 2006X

We present optical spectroscopic and photometric observations of Type Ia supernova (SN Ia) 2006X from 10 d before the B-band maximum to 91 d after. This object exhibits one of the highest expansion velocities ever published for SNe Ia. At its premaximum phases, the spectra show strong and broad features of intermediate-mass elements, such as Si, S, Ca, and Mg, while the O I � 7773 line is weak. The extremely high velocities of the Si II and S II lines and the weak feature of the O I line suggest that an intense nucleosynthesis might take place in the outer layers, favoring a delayed detonation model. Interestingly, the Si II � 5972 feature is quite shallow, resulting in an unusually low depth ratio of Si II � 5972 to Si II � 6355, R(Si II). The low R(Si II) is usually interpreted as being a high photospheric temperature. However, the weak Si III � 4560 line suggests a low temperature, in contradiction with an interpretation on the low R(Si II). This could imply that the Si II � 5972 line might be contaminated by underlying emission. We propose that R(Si II) may not be a good temperature indicator for a rapidly expanding SN Ia in the premaximum phases.

Spectroscopic Observations of the WZ Sge-Type Dwarf Nova GW Librae during its 2007 Superoutburst

We carried out an international spectroscopic observation campaign of the dwarf nova GW Librae (GW Lib) during its 2007 superoutburst. Our observation period covered the rising phase of the superoutburst, maximum, slowly decaying phase (plateau), and long fading tail phase after the rapid decline from the plateau. The spectral features dramatically changed during the observations. In the rising phase, only absorption lines of H˛ ,H ˇ ,a nd Hwere present. Around the maximum, the spectrum showed singly peaked emission lines of H˛ ,H e I 5876, He I 6678, He II 4686, and C III/N III as well as absorption lines of the Balmer components and He I. These emission lines significantly weakened during the latter part of the plateau phase. In the fading tail phase, all of the Balmer lines and He I 6678 were in emission, as observed in quiescence. We find that the center of the H˛ emission component was mostly stable over the whole orbital phase, being consistent with the low inclination of the system. Compared with the observational results of WZ Sagittae during its 2001 superoutburst, the same type of stars as GW Lib seen with a high inclination angle, we interpret that the change of the H˛ profile before the fading tail phase can be attributed to a photoionized region formed at the outer edge of the accretion disk, irradiated from the white dwarf and inner disk.