Tatsuharu Ono

Hokkaido University

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Planetary lightning flashes observation using ground based telescope with Photomultiplier tube

Tatsuharu Ono Yukihiro Takahashi Mitsuteru Sato Shigeto Watanabe Seiko Takagi

Lightning

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Broad-lined Supernova 2016coi with a Helium Envelope

The Astrophysical Journal (2017)

M. Yamanaka Tatsuya Nakaoka Masaomi Tanaka Keiichi Maeda Satoshi Honda

We present the early-phase spectra and the light curves of the broad-lined supernova (SN) 2016coi from $t=7$ to $67$ days after the estimated explosion date. This SN was initially reported as a broad-lined Type SN Ic (SN Ic-BL). However, we found that spectra up to $t=12$ days exhibited the He~{\sc i} $\lambda$5876, $\lambda$6678, and $\lambda$7065 absorption lines. We show that the smoothed and blueshifted spectra of normal SNe Ib are remarkably similar to the observed spectrum of SN 2016coi. The line velocities of SN 2016coi were similar to those of SNe Ic-BL and significantly faster than those of SNe Ib. Analyses of the line velocity and light curve suggest that the kinetic energy and the total ejecta mass of SN 2016coi are similar to those of SNe Ic-BL. Together with broad-lined SNe 2009bb and 2012ap for which the detection of He~{\sc i} were also reported, these SNe could be transitional objects between SNe Ic-BL and SNe Ib, and be classified as broad-lined Type `Ib' SNe (SNe `Ib'-BL). Our work demonstrates the diversity of the outermost layer in broad-lined SNe, which should be related to the variety of the evolutionary paths.

Line (geometry)

10.3847/1538-4357/aa5f57

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Status of lightning hunt in Venus with Akatsuki/LAC and Pirka telescope

Yukihiro Takahashi Mitsuteru Sato Masataka Imai R. D. Lorenz Seiko Takagi

Lightning

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Polarimetric and Photometric observations of NEAs with the 1.6m Pirka Telescope

Japan Geoscience Union (2018)

Ryo Okazaki Tomohiko Sekiguchi Akari Kamada Masateru Ishiguro Hiroyuki Naito

Source

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Polarimetric and photometric observations of NEAs; (422699) 2000 PD3 and (3200) Phaethon with the 1.6m Pirka telescope

Planetary and Space Science (2019)

Ryo Okazaki Tomohiko Sekiguchi Masateru Ishiguro Hiroyuki Naito Seitaro Urakawa

Albedo (alchemy)

Geometric albedo

Epoch (astronomy)

10.1016/j.pss.2019.104774

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Study of hydrated asteroids via their polarimetric properties at low phase angles

Astronomy and Astrophysics (2024)

Jooyeon Geem Masateru Ishiguro Hiroyuki Naito Sunao Hasegawa Jun Takahashi

Context . Ch-type asteroids are distinctive among other dark asteroids in that they exhibit deep negative polarization branches (NPBs). Nevertheless, the physical and compositional properties that cause their polarimetric distinctiveness are less investigated. Aims . We aim to investigate the polarimetric uniqueness of Ch-type asteroids by making databases of various observational quantities (i.e., spectroscopic and photometric properties as well as polarimetric ones) of dark asteroids. Methods . We conducted an intensive polarimetric survey of 52 dark asteroids (including 31 Ch-type asteroids) in the R C band to increase the size of polarimetric samples. The observed data were compiled with previous polarimetric, spectroscopic, and photometric archival data to find their correlations. Results . We find remarkable correlations between these observed quantities, particularly the depth of NPBs and their spectroscopic features associated with the hydrated minerals. The amplitude of the opposition effect in photometric properties also shows correlations with polarimetric and spectral properties. However, these observed quantities do not show noticeable correlations with the geometric albedo, thermal inertia, and diameter of asteroids. Conclusions . Based on the observational evidence, we arrive at our conclusion that the submicrometer-sized structures (fibrous or flaky puff pastry-like structures in phyllosilicates) in the regolith particles could contribute to the distinctive NPBs of hydrated asteroids.

Phase angle (astronomy)

10.1051/0004-6361/202450384

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Multicolor and multi-spot observations of Starlink’s Visorsat

Publications of the Astronomical Society of Japan (2023)

Takashi Horiuchi H. Hanayama Masatoshi Ohishi Tatsuya Nakaoka Ryo Imazawa

Abstract This study provides the results of simultaneous multicolor observations for the first Visorsat (STARLINK-1436) and the ordinary Starlink satellite (STARLINK-1113) in the U, B, V, g′, r, i, RC, IC, $z$, J, H, and Ks bands to quantitatively investigate the extent to which Visorsat reduces its reflected light. Our results are as follows: (1) in most cases, Visorsat is fainter than STARLINK-1113, and the sunshade on Visorsat therefore contributes to the reduction of the reflected sunlight; (2) the magnitude at 550 km altitude (normalized magnitude) of both satellites often reaches the naked-eye limiting magnitude (<6.0); (3) from a blackbody radiation model of the reflected flux, the peak of the reflected components of both satellites is around the $z$ band; and (4) the albedo of the near-infrared range is larger than that of the optical range. Under the assumption that Visorsat and STARLINK-1113 have the same reflectivity, we estimate the covering factor, Cf, of the sunshade on Visorsat, using the blackbody radiation model: the covering factor ranges from 0.18 ≤ Cf ≤ 0.92. From the multivariable analysis of the solar phase angle (Sun–target–observer), the normalized magnitude, and the covering factor, the phase angle versus covering factor distribution presents a moderate anti-correlation between them, suggesting that the magnitudes of Visorsat depend not only on the phase angle but also on the orientation of the sunshade along our line of sight. However, the impact on astronomical observations from Visorsat-designed satellites remains serious. Thus, new countermeasures are necessary for the Starlink satellites to further reduce reflected sunlight.

Black-body radiation

Limiting magnitude

10.1093/pasj/psad021

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SN 2019ein: New Insights into the Similarities and Diversity among High-velocity Type Ia Supernovae

The Astrophysical Journal (2020)

Miho Kawabata Keiichi Maeda M. Yamanaka Tatsuya Nakaoka Koji S. Kawabata

Abstract We present optical observations of the Type Ia supernova (SN) 2019ein, starting two days after the estimated explosion date. The spectra and light curves show that SN 2019ein belongs to a high-velocity (HV) and broad-line group with a relatively rapid decline in the light curves (Δ m 15 ( B ) = 1.36 ± 0.02 mag) and a short rise time (15.37 ± 0.55 days). The Si ii λ 6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached ∼20,000 km s −1 12 days before the B -band maximum. The line velocity, however, decreased very rapidly and smoothly toward maximum light, to ∼13,000 km s −1 , which is relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated with not only the velocity at maximum light, but also the light-curve decline rate, as is the case for normal-velocity (NV) SNe Ia. Spectral synthesis modeling shows that the outermost layer at >17,000 km s −1 is well described by an O–Ne–C burning layer extending to at least 25,000 km s −1 , and there is no unburnt carbon below 30,000 km s −1 ; these properties are largely consistent with the delayed detonation scenario and are shared with the prototypical HV SN 2002bo despite the large difference in Δ m 15 ( B ). This structure is strikingly different from that derived for the well-studied NV SN 2011fe. We suggest that the relation between the mass of 56 Ni (or Δ m 15 ) and the extent of the O–Ne–C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe.

Line (geometry)

Group velocity

10.3847/1538-4357/ab8236

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Estimation of the drift rate and intensity of Neptune's storm by Pirika telescope

Yuki Sato Yukihiro Takahashi Mitsuteru Sato S. Takagi Masataka Imai

The outermost planet Neptune is known to have a giant storm system as Jupiter's Great Red Spot (GRS). However, there are only a few observations of Neptune's storm, and the structure, formation mechanism, and lifecycle of these giant storms are poorly understood. Voyager 2 observed Neptune on May 24, 1989, and discovered the Earth-sized Great Dark Spot (GDS) with 13,000 km. GDS was located in the southern hemisphere, but GDS became extinct when the Hubble Space Telescope observed it in 1994 (Hammel et al., 1995). It is unknown whether it is a sudden thing or storms such as GDS always occur in Neptune. A huge storm of 9,000 km at the equator was observed on July 2 and June 26, 2017, by Keck observatory (Edward et al., 2019). It's considered that Neptune storms occur at mid-latitudes in the north and south that an ascending air occurs. However, this huge storm occurred near the equator. A rotation axis of Neptune is 29.6°, and the storm possibly occurred near the equator because of seasonal change. Neptune is a great distance away from the Earth, storms in Neptune can be resolved only by using large telescopes such as Keck observatory and the Hubble Space Telescope. However, it is not easy to use those telescopes for long-term continuous monitoring. In order to investigate the temporal evolution of GDSs and storms in Neptune, we developed the technique to estimate the drift rate and intensity of storms by observing Neptune's whole spectrum in this study. When seeing is bad, it's possible to observe and acquire Neptune's observation data for a long-term on a short time scale. The purpose of this study is to understand the atmosphere convection structure related to Neptune's storm and its temporal evolution. We observed Neptune by using 1.6 m Pirka telescope operated by the Faculty of Science in Hokkaido University from October 22, 2018, to November 26, 2018. The wavelength is 890, 855 nm. From this analysis, we can retrieve a weak absorption at 890 nm because the altitude of storms is higher than the surrounding areas. In addition, the apparent size of storms from the observation point changes by the rotation of Neptune, so an 890 nm flux changes by the rotation. We took the ratio of an 890 nm flux and an 855 nm flux to correct the effect of the earth atmosphere and calculated the relative intensity's theoretical values by the rotation. The bottom left figure shows the profile of the theoretical line. Here, we defined the longitude difference between the observer longitude and the storm's longitude. We assumed the storm's area and longitude of the storm at the start of our observation, and fit the observed values with the theoretical values in the method of least squares to estimate the drift rate and 890 nm albedo inside the storm. The fitting result is shown in the bottom right figure. We estimated that the drift rate of the storm is 24.6°/ day, and the 890 nm albedo is 0.055.                                                                                                                                   

Neptune

10.5194/epsc2020-80

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Ground-based Observation of planetary lightning flashes with Photomultiplier tube

Tatsuharu Ono Yukihiro Takahashi Mitsuteru Sato Shigeto Watanabe Seiko Takagi

Abstract Lightning in planetary atmospheres are generated by the convections, so the detection of lightning can be used to deduce the atmospheric dynamics and the large-scale structures on other planets. In the case of Jupiter, the lightning flashes have been observed in the dense clouds. Previous studies (e.g. Gierasch et al., 2000; Ingersoll et al., 2000) suggested that zonal jet is driven by small-scale eddies that receive their energy from moist vertical convection which similar to large thunderstorm on the Earth. Although it is difficult to know the vertical convections within the dense clouds, lightning clusters are correlated with the cumulonimbus, and thus lightning observations can be used to investigate the formation of Jupiter’s zonal jet structure. In Venus, the existence of Venusian lightning is controversial for 40 years, and the possible generation mechanisms are convection, volcanic, or aeolian triboelectric activity. In the previous study, there are radio wave observations and optical observations by CCD. Although some of the observations have detected lightning, no unambiguous lightning flash events have been detected recently by LAC (Lightning and Airglow Camera) onboard AKATSUKI Venus Climate orbiter (Lorenz et al., 2019). There is no robust evidence of existence the lightning because it is difficult to distinguish between the lightning signal and the electrical noise or other plasma waves, the observation area is limited, and the CCD’s sensitivity is not enough for lightning flashes. If we can confirm the existence of Venusian lightning like the Jovian, it could also be an indicator of Venusian atmospheric dynamics.  To reveal the relationship between lightning and atmospheric dynamics of Jupiter and Venus, we have developed the Planetary Lightning Detector (PLD), which is the high-speed and high-sensitive lightning detector mounted on a 1.6-m ground-based telescope “Pirka” by using a photomultiplier tube to observe the planetary lightning. Pirka telescope, operated by the Faculty of Science, the Hokkaido University, is primarily dedicated to observations of the planets of the Solar System. Using this telescope we can obtain an observation period at least one hour per day for several months, longer than the previous studies. We can obtain the light-curve of flash events with a sampling rate of >20 s-1to distinguish the other flashes and decrease the contamination of dayside light and sky to improve the Signal-to-Noise ratio. We will reveal the concentrate of lightning and its frequency, and then we derive the distribution of a few tens km scale vertical convections. We compare the results and the variation of wind velocity or cloud distribution to reveal the atmosphere dynamics.Figure 1: The layout of inside of PLD.  777.4 nm (atomic oxygen) is the predicted strong emission line in the Venus lightning spectra (Borucki et al. 1996). PLD equips narrowband filter (FWHM = 1 nm) of 777 nm. PLD observes the light by using a Photomultiplier tube. The minimum exposure time is 50 microseconds. The maximum time resolution is about 2x104 points/s. PLD’s FOV can be changed to 5”, 10”, 30”, 60” pinhole, and 2”x11” slit by using field stops. Slit and pinhole are used for Venus’s night-side observation. To obtain the lightning’s light curve, we operate the bandpass filter to remove noise and large time scale variation by the atmosphere. We have observed Venus by using PLD from May 2020. In our Venus observation, we could find several possible lightning events having large count values above 4-sigma of the background level. The detection frequency was 3 events per 2000 s observation period. The estimated peak energy of light-curve is about from 8.9×107 to 1.4×108 J. The calculated event rate is ~10-11 [s-1km-2], which is ten times larger than the result of previous study 2.7×10-12 [s-1km-2] (Hansell et al., 1995). Although, our observation duration is not sufficient to compare with the previous study. we will increase the observation time up to 3 hr in total.Figure 2: RAW data light-curve of a detected event on 05/18. The triggered time set to 0 s.  In this presentation, we will introduce the newly developed lightning observation instrument PLD and present our observation results obtained from May 2020. We will also show our future coordinated observation with LAC.References [1] Borucki, W. J., McKay, C. P., Jebens, D., Lakkaraju, H. S., and Vanajakshi, C. T. (1996). Spectral Irradiance Measurements of Simulated Lightning in Planetary Atmospheres. Icarus, 123, 336-441[2] Gierasch, P. J., Ingersoll, A. P., Banfield, D., Ewald, S. P., Helfenstein, P., Simon-Miller, A., Vasavada, A., Breneman, H. H., Senske, D. A., and Galileo Imaging Team (2000). Observation of moist convection in Jupiter’s atmosphere. Nature, 403(6770), 628-630[3] Hansell, S. A., Wells, W. K., and Hunten, D. M. (1995). Optical Detection of Lightning on Venus. Icarus, 117, 345-351[4] Ingersoll, A.P., Gierasch, P.J., Banfield, D., Vasavada, A.R., and Galileo Imaging Team (2000). Moist convection as an energy source for the large-scale motions in Jupiter’s atmosphere. Nature, 403, 630–632[5] Lorenz, R. D., Imai, M., Takahashi, Y., Sato, M., Yamazaki, A., Sato, T. M., et al. (2019). Constraints on Venus lightning from Akatsuki's first 3 years in orbit. Geophys. Res. Lett., 46, 7955–7961. https://doi.org/10.1029/ 2019GL0833

Lightning

Atmospheric electricity

Upper-atmospheric lightning

Light emission

10.5194/epsc2020-231

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