A report is presented on spectroscopic and multi-color photometric observations of the high Galactic latitude classical nova KT Eridani (Nova Eridani 2009). After 12.2 d from maximum light, broad and ...prominent emission lines of the Balmer series, Hei, Heii, Nii, Niii, and Oi can be seen on the spectra. The FWHM of the H
${\alpha}$
line yields an expansion velocity of approximately 3400 km s
$^{-1}$
. After 279.4 d from maximum light, we can see prominent emission lines of Heii and Oiii on the spectrum. Among them, Oiii (4959, 5007) lines show multiple peaks. From the obtained light curve, KT Eri is classified to be a very fast nova, with a decline rate by two magnitudes of 6.2
$\pm$
0.3 d and three of 14.3
$\pm$
0.7 d. We tried to estimate the absolute magnitude (
$M_V$
) using the Maximum Magnitude versus Rate of Decline relationship and distance of KT Eri. The calculated
$M_V$
is approximately
$-$
9. Accordingly, the distance and Galactic height are approximately 7 kpc and 4 kpc, respectively. Hence, KT Eri is concluded to be located outside of the Galactic disk.
We report on a discovery of “negative” superhumps during the 2011 January superoutburst of ER UMa. During the superoutburst, which started on 2011 January 16, we detected negative superhumps having a ...period of 0.062242(9) d, shorter than its orbital period by 2.2%. No evidence of a positive superhump was detected during this observation. This finding indicates that the disk exhibited retrograde precession during this superoutburst, contrary to all other known cases of superoutbursts. The duration of this superoutburst was shorter than those of ordinary superoutbursts, and the interval of its normal outbursts was longer than those of ordinary normal outbursts of ER UMa. We suggest the possibility that such unusual outburst properties are likely to be a result of a disk tilt, which is supposed to be a cause of negative superhumps; the tilted disk could prevent the disk from being filled with materials in the outmost region, which is supposed to be responsible for long-duration superoutbursts in ER UMa-type dwarf novae. This discovery signifies the importance of the classical prograde precession in sustaining long-duration superoutbursts. Furthermore, the presence of pronounced negative superhumps in this system with a high mass-transfer rate supports the hypothesis that hydrodynamical lift is the cause of the disk tilt.
Early Spectroscopy of the 2010 Outburst of U Scorpii Yamanaka, Masayuki; Uemura, Makoto; Kawabata, Koji S ...
Publications of the Astronomical Society of Japan,
10/2010, Letnik:
62, Številka:
5
Journal Article
Recenzirano
Odprti dostop
We present early spectroscopy of the recurrent nova U Sco during an outburst in 2010. We successfully obtained time-series spectra during the period of
$t_{\rm d} =$
0.37–0.44 d, where
$t_{\rm d}$
is ...the time that elapsed since the discovery of the present outburst. This is the first time-resolved spectroscopy on the first night of U Sco outbursts. At
$t_{\rm d} \sim$
0.4 d, the H
$\alpha$
line consists of a blue-shifted (
$-$
5000 km s
$^{-1}$
) narrow absorption component and a wide, triple-peak emission one: blue (
$\sim-$
3000 km s
$^{-1}$
), central (
$\sim$
0 km s
$^{-1}$
), and red (
$\sim+$
3000 km s
$^{-1}$
) peaks. The blue and red peaks developed more rapidly than the central one for the first night. This rapid variation would be caused by the growth of aspherical wind produced during the earliest stage of the outburst. At
$t_{\rm d} =$
1.4 d, the H
$\alpha$
line has a nearly flat-topped profile with weak blue and red peaks at
$\sim \pm$
3000 km s
$^{-1}$
. This profile can be attributed to a nearly spherical shell, while the asphericity growing on the first night still remains. The wind asphericity is less significant after
$t_{\rm d} =$
9 d.
We present our observational results of the recurrent nova T Pyx at its early stage of the 2011 outburst, using a low-resolution spectrograph (
$ R$
$ \approx$
400) attached to a 28 cm telescope. The ...total number of nights of our observation was 11, among which 9 nights were during the pre-maximum stage. As a result, we obtained a detailed evolutional feature of this recurrent nova on the way to its maximum light. At first, on the earliest three nights (25–21 days before maximum), broad and prominent emission lines, such as Balmer series, He I, He II, N II, N III, and O I together with the P Cyg profile, are seen on the spectra. The blueshifted absorption minima of H
$ \alpha$
yields a maximum expansion velocity of approximately 2200 km s
$ ^{-1}$
, and the velocity gradually decreases. Then, helium and nitrogen lines are weakened day by day. After that (18 days before maximum light), Fe II (multiplets) lines emerge on the spectra. These lines are then strengthened day by day, and the P Cyg profiles also become more prominent. Accordingly, the expansion velocities turn to gradual increase. In addition, during the pre-maximum stage, the nova spectral type of T Pyx is thought to evolve from the He
$ /$
N type to the Fe II one.
Abstract
We present visible and near-infrared observations of a near-Earth object (NEO), 2012 TC
4
. The NEO 2012 TC
4
approached close to Earth at a distance of about 50,000 km in 2017 October. This ...close approach provided a practical exercise for planetary defense. This apparition was also an appropriate opportunity to investigate 2012 TC
4
, which is a monolithic asteroid. We conducted the observation campaign of 2012 TC
4
using six small- and medium-sized telescopes. The multiband photometry analysis showed the taxonomic class of 2012 TC
4
to be an X type. In particular, we successfully obtained the high time resolution light curve of 2012 TC
4
with the Tomo-e Gozen camera, which is the world’s first wide-field CMOS camera, mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The shape and rotational motion models of 2012 TC
4
were derived from the light curve. When 2012 TC
4
was assumed to be a triaxial ellipsoid, the rotational and precession periods were 8.47 ± 0.01 minutes and 12.25 ± 0.01 minutes, respectively, with the long-axis mode. This indicates that 2012 TC
4
is a tumbling and monolithic asteroid. The shape models showed the plausible axial lengths to be 6.2 × 8.0 × 14.9 m or 3.3 × 8.0 × 14.3 m. The flattened and elongated shape indicates that 2012 TC
4
is a fragment produced by an impact event. We also estimated the excitation timescale, which implied that the impact event happened within ∼3 × 10
5
yr and 2012 TC
4
has a fresh surface.
We present visible and near-infrared observations of a near-Earth object (NEO), 2012 TC{sub 4}. The NEO 2012 TC{sub 4} approached close to Earth at a distance of about 50,000 km in 2017 October. This ...close approach provided a practical exercise for planetary defense. This apparition was also an appropriate opportunity to investigate 2012 TC{sub 4}, which is a monolithic asteroid. We conducted the observation campaign of 2012 TC{sub 4} using six small- and medium-sized telescopes. The multiband photometry analysis showed the taxonomic class of 2012 TC{sub 4} to be an X type. In particular, we successfully obtained the high time resolution light curve of 2012 TC{sub 4} with the Tomo-e Gozen camera, which is the world’s first wide-field CMOS camera, mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The shape and rotational motion models of 2012 TC{sub 4} were derived from the light curve. When 2012 TC{sub 4} was assumed to be a triaxial ellipsoid, the rotational and precession periods were 8.47 ± 0.01 minutes and 12.25 ± 0.01 minutes, respectively, with the long-axis mode. This indicates that 2012 TC{sub 4} is a tumbling and monolithic asteroid. The shape models showed the plausible axial lengths to be 6.2 × 8.0 × 14.9 m or 3.3 × 8.0 × 14.3 m. The flattened and elongated shape indicates that 2012 TC{sub 4} is a fragment produced by an impact event. We also estimated the excitation timescale, which implied that the impact event happened within ∼3 × 10{sup 5} yr and 2012 TC{sub 4} has a fresh surface.
Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 102 SU UMa-type dwarf novae, observed mainly during the 2014–2015 season, and ...characterized these objects. Our project has greatly improved the statistics of the distribution of orbital periods, which is a good approximation of the distribution of cataclysmic variables at the terminal evolutionary stage, and has confirmed the presence of a period minimum at a period of 0.053 d and a period spike just above this period. The number density monotonically decreased toward the longer period and there was no strong indication of a period gap. We detected possible negative superhumps in Z Cha. It is possible that normal outbursts are also suppressed by the presence of a disk tilt in this system. There was no indication of enhanced orbital humps just preceding the superoutburst, and this result favors the thermal–tidal disk instability as the origin of superoutbursts. We detected superhumps in three AM CVn-type dwarf novae. Our observations and recent other detections suggest that 8% of objects showing dwarf nova-type outbursts are AM CVn-type objects. AM CVn-type objects and EI Psc-type objects may be more abundant than previously recognized. OT J213806, a WZ Sge-type object, exhibited remarkably different features between the 2010 and 2014 superoutbursts. Although the 2014 superoutburst was much fainter, the plateau phase was shorter than the 2010 one, and the course of the rebrightening phase was similar. This object indicates that the O − C diagrams of superhumps can indeed be variable, at least in WZ Sge-type objects. Four deeply eclipsing SU UMa-type dwarf novae (ASASSN-13cx, ASASSN-14ag, ASASSN-15bu, and NSV 4618) were identified. We studied long-term trends in supercycles in MM Hya and CY UMa and found systematic variations of supercycles of ∼20%.
Abstract
We observed a stellar occultation by (3200) Phaethon, which occurred in western Japan on 2021 October 3 (UTC). This observation was requested by the DESTINY+ mission team, which plans to ...conduct a flyby of asteroid Phaethon in 2028. Overall, this research effort contributes towards a large-scale observation campaign with a total of 72 observers observing from western Japan to southern Korea. 36 stations were established, and stellar occultation by the asteroid Phaethon was detected in 18 of them. This is the first time that this many multiple chord observations have been made for such a small asteroid (it has a diameter of 5–6 km). Observational reductions show that the apparent cross-section of Phaethon at the time of the occultation could be approximated using an ellipse with a major diameter of 6.12 ± 0.07 km and a minor diameter of 4.14 ± 0.07 km, and a position angle of 117.°4 ± 1.°5. As can be seen from the small error bars of the fitted ellipse, we have succeeded in estimating the shape and size of the asteroid with an extremely high degree of accuracy. Our observation results, together with other observations, will be used to create a 3D model of Phaethon and to improve its orbit. The instruments that we used for this observation are commonly used by many amateur astronomers in Japan for occultation observations and are not difficult to obtain. This paper describes the method and results of our observations using a CMOS camera and a GPS module, so that many people can participate in occultation observations in the future.
Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 86 SU UMa-type dwarf novae, mainly observed during the 2011–2012 season. We ...confirmed general trends recorded in our previous studies, such as the relation between period derivatives and orbital periods. There are some systems showing positive period derivatives despite the long orbital period. We observed the 2011 outburst of the WZ Sge-type dwarf nova BW Scl, and recorded an
$ O$
$-$
$ C$
diagram similar to those of previously known WZ Sge-type dwarf novae. The WZ Sge-type dwarf nova OT J184228.1
$ +$
483742 showed an unusual pattern of double outbursts composed of an outburst with early superhumps and one with ordinary superhumps. We propose an interpretation that a very small growth rate of the 3:1 resonance due to an extremely low mass-ratio led to quenching the superoutburst before the ordinary superhump appeared. We systematically studied ER UMa-type dwarf novae, and found that V1159 Ori showed positive superhumps similar to ER UMa in the 1990s. The recently recognized ER UMa-type object BK Lyn dominantly showed negative superhumps, and its behavior was very similar to the present-day state of ER UMa. The pattern of period variations in AM CVn-type objects was very similar to that of short-period hydrogen-rich SU UMa-type dwarf novae, making them a helium analogue of hydrogen-rich SU UMa-type dwarf novae. SBS 1108
$ +$
574, a peculiar hydrogen-rich dwarf nova below the period minimum, showed a very similar pattern of period variations to those of short-period SU UMa-type dwarf novae. The mass-ratio derived from the detected orbital period suggests that this secondary is a somewhat evolved star whose hydrogen envelope was mostly stripped during the mass-exchange. CC Scl, MASTER OT J072948.66
$ +$
593824.4, and OT J173516.9
$ +$
154708 showed only low-amplitude superhumps with complex profiles. These superhumps are likely to be a combination of two closely separated periods.
We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of the superhump period is ...found to be composed of three distinct stages: an early evolutionary stage with a longer superhump period, a middle stage with systematically varying periods, and a final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods of less than 0.08 d show positive period derivatives. We present observational characteristics of these stages and give greatly improved statistics. Contrary to an earlier claim, we found no clear evidence for a variation of period derivatives among different superoutbursts of the same object. We present an interpretation that the lengthening of the superhump period is a result of the outward propagation of an eccentricity wave, which is limited by the radius near the tidal truncation. We interpret that late-stage superhumps are rejuvenated excitation of a 3:1 resonance when superhumps in the outer disk are effectively quenched. The general behavior of the period variation, particularly in systems with short orbital periods, appears to follow a scenario proposed in Kato, Maehara, and Monard (2008, PASJ, 60, L23). We also present an observational summary of WZ Sge-type dwarf novae. Many of them have shown long-enduring superhumps during a post-superoutburst stage having longer periods than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently with the mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives, and are excellent candidates for those systems around or after the period minimum of evolution of cataclysmic variables.
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