37 research outputs found
Faint debris disk peering through superflare light echo
We present the detectability of strong mid-infrared (MIR) light echoes from
faint debris disks illuminated by bright superflares of M-dwarf stars.
Circumstellar dust grains around an M-dwarf star are simultaneously heated by
superflare radiation. One can thus expect their re-emission in the MIR
wavelength regime. According to our model calculations for the Proxima Centauri
system, the nearest M-dwarf star system, thermal emission echos from an inner
() debris disk with a total mass down to that of the solar
system's zodiacal dust are expected to emerge at wavelengths longer than with a strength comparable to or greater than a white-light
superflare. Also, observable echos from inner- ()
debris disks irradiated by energetic ()
superflares of nearby () M-dwarfs are expected. Our simulation
results indicate that superflare monitoring using high-speed optical
instruments like OASES and its prompt follow-up using ground-based MIR
instruments, such as TAO/MIMIZUKU, can detect these MIR light echoes from
debris disks around solar neighborhood flare stars.Comment: 11 pages, 5 figures, ApJL accepte
Modelling the optical energy profile of the 2021 October Jupiter impact flash
We have conducted numerical simulations to reproduce the observed optical
energy profile of the 15 October 2021 (UT) impact flash on Jupiter, which was
the largest and the most well-observed flash event detected by ground-based
movie observations. The observed long-duration () optical
emission can be reproduced by an impact of an object with an exceptionally
small angle of entry relative to the horizontal. The apparent lack of the
impact debris feature despite the large impact object was possibly due to the
shallower angle of entry (), which resulted in the lower ablation
per unit volume at altitudes higher than , and the volume
densities of the ablated materials were too low to allow the debris
particulates to coagulate. The absence of temporal methane absorption change in
the observed flash spectrum is consistent with the best-fit results. The model
better fits the observed optical energy profile for weaker material (cometary
and stony) cases than for metallic ones. Based on the simulation results,
prospects for future observations of impact flashes are discussed.Comment: 6 pages, 5 figures, Accepted for publication in MNRA
Cloud reflection modelling for impact flashes on Jupiter: A new constraint on the bulk properties of the impact objects
We investigate optical characteristics of flashes caused by impacting meter-
to decameter-sized outer solar system objects on Jupiter and contributions of
reflected light from surface clouds at visible wavelengths to estimate more
accurate bulk parameters such as the luminous energy of the flash, the kinetic
energy, the mass, and the size of the impact object. Based on the results of
recent reflectivity studies of the Jovian surface, we develop a cloud
reflection model that calculates the contribution of the reflected light
relative to that directly from the flash. We compare the apparent luminous
energy of the previously reported flashes with the expected cloud reflection
contributions to obtain their revised bulk parameters. We found that the cloud
reflection contributions can be up to 200% of the flux directly from the flash
and thus can be the most significant uncertainty in the measurement of the bulk
parameters. The reflection contributions strongly depend on wavelength. With
our cloud reflection correction, the revised bulk parameters of the previously
reported flashes are obtained. Our cloud reflection correction provides a
better understanding of the properties of impacting objects on Jupiter and is
crucial for ongoing detailed investigations using high-sensitivity and
multi-wavelength observation systems such as PONCOTS. It will also be useful
for understanding other optical transients in Jupiter's upper atmosphere, such
as the recently discovered sprite-like events.Comment: 6 pages, 4 figures, accepted for publication in Astronomy &
Astrophysic
Detection of an extremely large impact flash on Jupiter by high-cadence multiwavelength observations
木星で超大型の衝突閃光現象を発見 --京大のとある屋上の小さな望遠鏡による大発見--. 京都大学プレスリリース. 2022-09-13.We report the detection of an optical impact flash on Jupiter on 2021 October 15 by a dedicated telescope, Planetary ObservatioN Camera for Optical Transient Surveys, for the first time. Our temporally resolved three-band observations of the flash allowed investigations of its optical energy without the need for approximations on the impact brightness temperature. The kinetic energy of the impactor was equivalent to approximately two megatons of TNT, an order of magnitude greater than that of previously detected flashes on Jupiter and comparable with the Tunguska impact on Earth in 1908. This detection indicates that Tunguska-like impact events on Jupiter occur approximately once per year, two to three orders of magnitude more frequently than terrestrial impacts. The observed flash displayed a single-temperature blackbody spectrum with an effective temperature of approximately 8300 K without clear temporal variation, possibly representing common radiative features of terrestrial Tunguska-class superbolides
Cold Molecular Gas Along the Merger Sequence in Local Luminous Infrared Galaxies
We present an initial result from the 12CO (J=1-0) survey of 79 galaxies in
62 local luminous and ultra-luminous infrared galaxy (LIRG and ULIRG) systems
obtained using the 45 m telescope at the Nobeyama Radio Observatory. This is
the systematic 12CO (J=1-0) survey of the Great Observatories All-sky LIRGs
Survey (GOALS) sample. The molecular gas mass of the sample ranges 2.2 x 10^8 -
7.0 x 10^9 Msun within the central several kiloparsecs subtending 15" beam. A
method to estimate a size of a CO gas distribution is introduced, which is
combined with the total CO flux in the literature. The method is applied to a
part of our sample and we find that the median CO radius is 1-4 kpc. From the
early stage to the late stage of mergers, we find that the CO size decreases
while the median value of the molecular gas mass in the central several kpc
region is constant. Our results statistically support a scenario where
molecular gas inflows towards the central region from the outer disk, to
replenish gas consumed by starburst, and that such a process is common in
merging LIRGs.Comment: 25 pages, 22 figures, accepted for publication in Ap