松本 桂

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A spectroscopic study of the SU UMa star <ASTROBJ>HS Vir</ASTROBJ> is presented. From the analysis of the radial velocities of the Hα emission line the most likely orbital period is 0\fd07692(3), although we cannot discard two aliases at 0\fd07678 and 0\fd07709. The Balmer lines follow the orbital period with a radial velocity semiamplitude K = 96 +/- 9 km s(-1) , but the He I lambda 5875 emission line shows a double wave during the orbital cycle. We found that the mean Balmer, He I and He II 4686 lines can be roughly modeled with a disk radial emissivity ~ r(-2) . A revised version of the P_o-P_s relation for SU UMa stars is also given, which is relevant for discriminating between +/- 1 c/d aliases of the orbital period. We calculated the mass ratio, derived from the tidal resonance model, of <ASTROBJ>HS Vir</ASTROBJ> (q_sh = 0.22 +/- 0.04) and 43 additional SU UMa stars. The q_sh distribution has a roughly gaussian shape with a mean 0.14, in sharp contrast with the orbital period distribution. Finally, a discussion of the possible stellar masses and inclination of <ASTROBJ>HS Vir</ASTROBJ> is given. We observe that the mass ratio derived from the dynamic solution is in disagreement with that derived from the tidal resonance model. This fact probably indicates that K does not represent the white dwarf binary motion. Based on observations obtained at ESO La Silla Observatory (ESO Proposal 61.D-0395)....

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Photometric observations of BL Lac were carried out during the large optical and X-ray outburst in 1997. Time-resolved photometry on 1997 August 2 revealed a rapid increase of brightness by about 0.6 mag within 40 min. This large-amplitude, short-time variation is the most active one among known variability of blazars in the optical wavelength. By considering a model based on the “synchrotron self-Compton model” of the relativistic jets of blazars, the size of the variable source should be R ∼ 7.2 × 1014 cm from the 40 min variation. The power-density spectrum of the light curve on the night yielded a dependence of the power to the frequency $/-^1\prime\circ$ for timescales of the variabilities and down to a possible minimum timescale of around 10 min. The clear difference between the observed $\textit{f}\sim ^{10}$ dependence from the canonical $\textit{f}\sim^{15}-\textit{f}\sim^1\prime^8$ power indices observed in X-ray variations of radio-loud AGNs suggests that different mechanisms are responsible for short-term optical variability between BL Lacs and radio-loud AGNs.

Time-resolved CCD photometric observations of a dwarf nova EG Cnc were carried out during an outburst which occurred after a 19-year quiescent interval, since 1977 November. Our observations between 1996 December 2 and 14 revealed this outburst to be a definite superoutburst, eventually enabling a definite classification of this object as an SU UMa-type dwarf nova. This outburst was characterized by its long duration of more than two weeks and a large amplitude of at least 6.7 mag. The object showed two distinct types of superhumps: double-peaked modulations attributable to “early superhumps” with a period of 0.0582±0.00025 d in the earlier stage of the current outburst, followed by fully grown typical superhumps with a period of 0.0603±0.00006 d. We regard the period of 0.0582 d as being the orbital period of the object with a 3.7% superhump excess ratio. These characteristics suggest a strong resemblance to an extreme rare class of dwarf novae including WZ Sge, HV Vir, and AL Com with some other similarities between EG Cnc and the WZ Sge-type dwarf novae. The existence of double-peaked “early superhumps” in the early stage of superoutbursts may be a new defining criterion for the WZ Sge-type dwarf novae.

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We considered the X-ray irradiated accretion disk in the galactic supersoft X-ray source RX J0019.8+2156, and estimated the contribution in UV and optical fluxes due to the reprocessing effect of X-ray radiation on the surface of the accretion disk and main sequence companion star. In the nuclear-burning white dwarf model of supersoft X-ray sources, radiation near the Eddington luminosity is generated on the white dwarf. For an assumed distance of 2 kpc to the object, however, a simple model with the standard accretion-disk model can not reproduce the observed fluxes in the UV and optical wavelengths of the object. This fact suggests the existence of reprocessing processes by the irradiated components in the binary system at relatively lower frequencies. We thus calculated the irradiation effects on the accretion disk and the mass donor companion in this system, and estimated their contributions to the flux of the lower frequency regions in the energy distribution. As a result, the reprocessed radiation from the irradiated accretion disk and companion star can well reproduce the observed fluxes.

We present the results of VRI CCD photometric observations of SS 433 and VRI light-curve modelings for SS 433. Observations were carried out in the fall of 1995 using the 51-cm relfector at Osaka Kyoiku University. Three cycles of the binary phase were covered. The mean magnitudes and colors during the observational periods were V = 14.0, R = 11.1, I = 10.5; V – R = 2.88, V – I = 3.50, R – I = 0.62. On October 17 and 18 a strong flare was observed. Theoretical light curves were also calculated using a model in which SS 433 consists of a geometrically thick torus around a compact star and a companion star filling the Roche lobe. In the torus picture VRI light curves were first calculated; for appropriate parameters VRI model light curves well reproduce the observational profiles. In addition, the extinction was first derived from the magnitude difference between the obervation and the model; AV ∼ 6–7, AR ∼ 3–4, and AI ∼ 3. These values are in good agreement with those of a previous observation.

Results obtained during the international observational campaign "TT Ari-94" are briefly discussed. During 258 hours, totally 51299 observations were obtained in 12 observatories. The moments of 68 individual maxima and 74 minima are tabulated. The linear ephemeris for the maximum is MaxHJD=2449645.4255+/-0.0003 deg +(0.133160 +/- 0.000004 deg)ṡ E for our data obtained in JD 2 449 614-690. The period value is distinctly outside the interval 0.1326-0.13298 deg obtained for previous years. It still corresponds to the 'negative superhump' state, whereas for a normal 'positive superhump' the value predicted by Tremko et al. (1996, As.Ap. 312, 121) is P=0.1426+/-0.00006 deg. The data prewhitened in respect to the superhump variations show the red noise power-law power spectrum with an index gamma=1.3...2.6....

Photometric observations of the galactic supersoft X-ray source RXJ0019.8+2156 in the B, V, R, and I bands were carried out between July and December of 1995. The observed light curves show periodic variations (Period = 15.85hr) with an amplitude of around 0.5mag in all four bands, while color curves (B – V, V – R, and V – I) show virtually no variation throughout the cycle. We find a secondary minimum which is highly variable in its shape from one cycle to another. The hump before the secondary minimum (phase ∼ 0.3–0.4) is brighter by about 0.1mag compared to that seen after the secondary minimum (phase ∼ 0.6–0.7). The primary minimum appears to be stable in depth on a timescale of several months. Furthermore, changes in brightness of about 0.15mag are observed from one cycle to another without detectable variation in the colors. The time scale of these irregular fluctuations is about one week or shorter.

Abstract A dwarf nova, AL Com, was photometrically observed during an outburst in 1995 April, which occurred for the first time since 1975. The star showed two distinct types of periodic variation: (1) a 0.05666-day variation with decaying amplitudes during the earliest stage of the outburst, and (2) 0.0572-day super humps which grew ∼ 11 d after the onset of the outburst. The present observations are the one first to clearly established the SU UMa-type nature of AL Com. Furthermore, the appearance of these two periods, together with the whole course of the superoutburst, makes AL Com an almost perfect twin of an enigmatic dwarf nova, WZ Sge. We attributed the former period to be the orbital period of this cataclysmic binary. The double-humped profile of this variation seems to preclude an explantion based on an enhanced hot spot by a mass-transfer burst from the secondary, which has been believed to be the best observational evidence of a mass-transfer burst in WZ Sge obtained during its 1978 outburst.

Abstract Optical light curves in the V, R, and I bands, starting 10 days before the maximum light, and the optical spectra near to the V maximum phase of supernova SN 1995D in NGC 2962 are presented. The spectra taken near to the optical maximum are similar to the prototypical type-la supernova SN 1981B, and show no trace of the interstellar Nal D line. The expansion velocity at the maximum phase was 10000 ± 200 km s-1. The supernova reached maximum light in the I band about four days earlier than in the V band. A distinct secondary peak is observed in the / band about 30 days after the V maximum. This secondary peak occurred about one week delayed from the published template light curve. A clear shoulder is detected in the R band light curve corresponding to the secondary peak in the I band. The initial rate of decline is slow [Δm15(V) = 0.66 mag], and it is suggested that the supernova belongs to a group of the intrinsically brightest type-la supernovae. From the initial declining rate in the V band, we estimated the absolute magnitude Mv to be −18.8 ± 0.3 mag, and the distance modulus of the parent galaxy (NGC 2962) to be 32.2 ± 0.3 mag.

From the photometric monitoring of RZ LMi for 44 days between 1995 February 5 and March 20, we identified RZ LMi as an extreme ER UMa-type dwarf nova: a subclass of SU UMa-type dwarf novae. We give a definition of ER UMa stars and clarify the difference between ER UMa stars and ordinary SU UMa stars. The most conspicuous characteristic of ER UMa stars is their extreme short cycle length of superoutbursts (supercycle), which in RZ LMi is ~ 19 days. The superhump period of RZ LMi is 0.05946 +/- 0.00004 days. The peculiar light curve of ER UMa stars suggests an extraordinarily large mass-transfer rate among SU UMa stars, which can not be explained by the current scheme concerning the origin of mass-transfer of cataclysmic variables (CVs). Moreover, the high incidence of such systems among known CVs suggests that an important course of the evolution of CVs may have been overlooked....

We present wide-band VRI photometry of supernova SN 1994I in M51 for the period April 5-May 30. Observations were carried out using a 51-cm reflector at Osaka Kyoiku University. The magnitudes were determined using a direct integration technique after removing the local sky background fitted with a quadratic surface. A nearby star (TB 135) was used as a reference star. The estimated accuracy of the results was within +/- 0.05 mag when the SN was brighter than 14 mag, while it was around +/- 0.1 mag when the SN became fainter. The brightness of the supernova declined steeply (about 0.1 mag per day) after reaching maximum brightnesses on April 8-9 (V band) and on April 10-11 (R and I bands). The rate of decline slowed down to about 0.03 mag per day about 20 d after the maximum. Our results are consistent with the classification of SN 1994I as a Type Ic event....