9 research outputs found
On the Rebrightenings of Classical Novae during the Early Phase
We report on the spectral evolution of 6 classical novae, V1186 Sco, V2540
Oph, V4745 Sgr, V5113 Sgr, V458 Vul, and V378 Ser, based on the low-resolution
spectra obtained at the Fujii-Bisei Observatory and the Bisei Astronomical
Observatory, Japan. In the light curves, these 6 novae show several
rebrightenings during the early phase lasting ~10 days after the first maximum
in fast novae, and ~100 days in slow novae. The early spectra of all of these
novae had emission lines with a P-Cygni profile at the maximum brightness. The
absorption component of the P-Cygni profiles then disappeared after the
maximum, and reappeared when the novae brightened to the next maximum. We
suggest that the re-appearance of the absorption component at the rebrightening
is attributable to re-expansion of the photosphere after it once shifts
sufficiently inside. From the light curves, we found that the time intervals of
the rebrightenings of these 6 novae show a similar systematic trend, which is
applicable to all types of novae: fast and slow, and Fe II type and hybrid
type. Moreover, we note the difference between the spectra at the
rebrightenings during the early phase and at the rebrightening in V2362 Cyg,
and at the oscillation during the transition phase in V1494 Aql, which means
difference of the physical mechanism of the rebrightening during the early
phase and the later oscillations.Comment: 11 pages, 15 figures, accepted for publication in PAS
Spectral Evolution of the Unusual Slow Nova V5558 Sgr
We report on the spectral evolution of the enigmatic, very slow nova V5558
Sgr, based on the low-resolution spectra obtained at the Fujii-Bisei
Observatory and the Bisei Astronomical Observatory, Japan during a period of
2007 April 6 to 2008 May 3. V5558 Sgr shows a pre-maximum halt and then several
flare-like rebrightenings, which is similar to another very slow nova V723 Cas.
In our observations, the spectral type of V5558 Sgr evolved from the He/N type
toward the Fe II type during the pre-maximum halt, and then toward the He/N
type again. This course of spectral transition was observed for the first time
in the long history of the nova research. In the rebrightening stage after the
initial brightness maximum, we could identify many emission lines accompanied
by a stronger absorption component of the P-Cygni profile at the brightness
maxima. We found that the velocity of the P-Cygni absorption component measured
from the emission peak decreased at the brightness maxima. Furthermore, we
compared the spectra of V5558 Sgr with V723 Cas, and other novae which
exhibited several rebrightenings during the early phase.Comment: 8 pages, 7figures, accepted for publication in PAS
Spiral Structure in WZ Sagittae around the 2001 Outburst Maximum
Intermediate resolution phase-resolved spectra of WZ Sge were obtained on
five consecutive nights (July 23 -- 27) covering the initial stage of the 2001
superoutburst. Double-peaked emission lines of He\textsc{II} at 4686 \AA, which
were absent on July 23, emerged on July 24 together with emission lines of
C\textsc{III} / N\textsc{III} Bowen blend. Analyses of the He\textsc{II}
emission lines using the Doppler tomography revealed an asymmetric spiral
structure on the accretion disk. This finding demonstrates that spiral shocks
with a very short orbital period can arise during the initial stage of an
outburst and may be present in all SU UMa stars.Comment: 5 pages, 8 figures, accepted for publication in PAS
The Type Ic Hypernova SN 2002ap
Photometric and spectroscopic data of the energetic Type Ic supernova (SN)
2002ap are presented, and the properties of the SN are investigated through
models of its spectral evolution and its light curve. The SN is
spectroscopically similar to the "hypernova" SN 1997ef. However, its kinetic
energy [ erg] and the mass ejected (2.5-5
) are smaller, resulting in a faster-evolving light curve. The SN
synthesized of Ni, and its peak luminosity was
similar to that of normal SNe. Brightness alone should not be used to define a
hypernova, whose defining character, namely very broad spectral features, is
the result of a high kinetic energy. The likely main-sequence mass of the
progenitor star was 20-25 , which is also lower than that of both
hypernovae SNe 1997ef and 1998bw. SN 2002ap appears to lie at the low-energy
and low-mass end of the hypernova sequence as it is known so far. Observations
of the nebular spectrum, which is expected to dominate by summer 2002, are
necessary to confirm these values.Comment: 10 pages, 4 figures, accepted for publication in ApJL, 30 April 2002
(minor changes to match the accepted version, with figures being colored
Superhump Evolution in the Ultrashort Period Dwarf Nova 1RXS J232953.9+062814
Abstract
We report on the evolution of superhumps and late superhumps in an ultrashort period dwarf nova, 1RXS J232953.9062814, during the superoutburst in 2001 November. Ordinary superhumps were observed throughout a plateau phase, a rapid fading phase, and a rebrightening phase. During the plateau phase, the superhump period increased with time at a large rate of . In conjunction with the rebrightening phenomenon, these characteristics indicate that an accretion disk expanded further outward from the resonance radius, which caused a large amount of left over matter at the outer disk, even after the superoutburst. In the post-outburst phase, we detected late superhumps superimposed on dominant double-peak modulations. Late superhumps were observed at least for 10 d without a significant period change. We detected the first normal outburst of this object on 2001 December 26. The interval between the superoutburst and this normal one is 53 d. This short recurrence time supports a high mass-transfer rate in this system. Concerning the evolutionary status of 1RXS J232953.9062814, we propose that it is a progenitor of AM CVn stars on the evolutionary course of the cataclysmic variable channel in which systems have a secondary star with a hydrogen-exhausted core
The Eruption of the Candidate Young Star ASASSN-15qi
Outbursts on young stars are usually interpreted as accretion bursts caused by instabilities in the disk or the star-disk connection. However, some protostellar outbursts may not fit into this framework. In this paper, we analyze optical and near-infrared spectra and photometry to characterize the 2015 outburst of the probable young star ASASSN-15qi. The mag brightening in the band was sudden, with an unresolved rise time of less than one day. The outburst decayed exponentially by 1 mag for 6 days and then gradually back to the pre-outburst level after 200 days. The outburst is dominated by emission from K gas. An explosive release of energy accelerated matter from the star in all directions, seen in a spectacular cool, spherical wind with a maximum velocity of 1000 km/s. The wind and hot gas both disappeared as the outburst faded and the source the source returned to its quiescent F-star spectrum. Nebulosity near the star brightened with a delay of 10-20 days. Fluorescent excitation of H is detected in emission from vibrational levels as high as , also with a possible time delay in flux increase. The mid-infrared spectral energy distribution does not indicate the presence of warm dust emission, although the optical photospheric absorption and CO overtone emission could be related to a gaseous disk. Archival photometry reveals a prior outburst in 1976. Although we speculate about possible causes for this outburst, none of the explanations are compelling