arXiv subjects

Daisuke Kuroda

Publications and source records attributed to Daisuke Kuroda.

At least 37 records · Page 2Linked to original sources

arXiv2020

Nature of bright C-complex asteroids

Most C-complex asteroids have albedo values less than 0.1, but there are some high-albedo (bright) C-complex asteroids with albedo values exceeding 0.1. To reveal the nature and origin of bright C-complex asteroids, we conducted spectroscopic observations of the asteroids in visible and near-infrared wavelength regions. As a result, the bright B-, C-, and Ch-type (Bus) asteroids, which are subclasses of the Bus C-complex, are classified as DeMeo C-type asteroids with concave curvature, B-, Xn-, and K-type asteroids. Analogue meteorites and material (CV/CK chondrites, enstatite chondrites/achondrites, and salts) associated with these spectral types of asteroids are thought to be composed of minerals and material exposed to high temperatures. A comparison of the results obtained in this study with the SDSS photometric data suggests that salts may have occurred in the parent bodies of 24 Themis and 10 Hygiea, as well as 2 Pallas. The bright C-complex asteroids in other C-complex families were likely caused by impact heating. Bright C-complex asteroids that do not belong to any families are likely to be impact metamorphosed carbonaceous chondrites, CV/CK chondrites, or enstatite chondrites/achondrites.

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arXiv2020

Type Ia SN 2019ein: New Insights into the Similarities and diversities among High-Velocity SNe Ia

We present optical observations of type Ia supernova (SN) 2019ein, starting at 2 days after the estimated explosion date. The spectra and the light curves show that SN 2019ein belongs to the High-Velocity (HV) and Bload Line groups with relatively rapid decline in the light curves (Delta m15(B) = 1.36 +- 0.02 mag) and the short rise time (15.37 +- 0.55 days). The Si II 6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached ~ 20,000 km s-1 at 12 days before the B-band maximum. The line velocity however decreased very rapidly and smoothly toward the maximum light, where it was ~ 13,000 km s-1 as relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated not only to the velocity at the maximum light, but also to the light curve decline rate like 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 the 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 Delta m15(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 56Ni (or Delta m15) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe.

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arXiv2019

Q-type asteroids: Possibility of non-fresh weathered surfaces

Itokawa particles, which are the recovered samples from the S-complex asteroid 25143 Itokawa by the Hayabusa spacecraft, demonstrate that S-complex asteroids are parent bodies of ordinary chondrite meteorites. Furthermore, they clarify that the space weathering age of the Itokawa surface is of the order of several thousand years. Traditionally, Q-type asteroids have been considered fresh-surfaced. However, as the space weathering timescale is approximately three orders of magnitude lesser than the conventionally considered age, the previously proposed formation mechanisms of Q-type asteroids cannot sufficiently explain the surface refreshening. In this study, we propose a new hypothesis on the surface state of Q-type asteroids: Q-type asteroids have a non-fresh weathered surface with a paucity of fine particles. For verifying this hypothesis, laboratory experiments on the space weathering of ordinary chondrites are performed. Based on the results of these experiments, we found that large (more than 100 μm) ordinary chondritic particles with space weathering exhibit spectra consistent with Q-type asteroids.

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arXiv2018

Physical properties of near-Earth asteroids with a low delta-${\it v}$: Survey of target candidates for the Hayabusa2 mission

Sample return from the near-Earth asteroid known as 25143 Itokawa was conducted as part of the Hayabusa mission, with a large number of scientific findings being derived from the returned samples. Following the Hayabusa mission, Hayabusa2 was planned, targeting sample return from a primitive asteroid. The primary target body of Hayabusa2 was asteroid 162173 Ryugu; however, it was also necessary to gather physical information for backup target selection. Therefore, we examined five asteroids spectroscopically, 43 asteroids spectrophotometrically, and 41 asteroids through periodic analysis. Hence, the physical properties of 74 near-Earth asteroids were obtained, which helped the Hayabusa2 backup target search and, also, furthered understanding of the physical properties of individual asteroids and their origins.

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arXiv2017

Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU$_\mathrm{2}$

We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU$_\mathrm{2}$ , which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU$_\mathrm{2}$ are 44.6 $\pm$ 0.5\% in the R$_\mathrm{C}$ band and 44.0 $\pm$ 0.6\% in the V band at a solar phase angle of 81.0\degr. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (< 0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU$_\mathrm{2}$ has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.

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arXiv2017

J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817

The first detected gravitational wave from a neutron star merger was GW170817. In this study, we present J-GEM follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5-mag decline in the $z$-band from 1.7 days to 7.7 days after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder for later epochs; the $z-H$ color changed by approximately 2.5 mag in the period of 0.7 days to 7.7 days. The rapid evolution of both the optical brightness and the color are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized $r$-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that $r$-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with the ejecta mass of 0.01 $\Msun$, which suggests a more intense mass ejection ($\sim 0.03 \Msun$) or possibly an additional energy source.

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arXiv2017

Follow-up observations for the Asteroid Catalog using AKARI Spectroscopic Observations

In the 1-2.5 micron range, spectroscopic observations are made on the AcuA-spec asteroids, whose spectra were obtained in a continuous covered mode between 2.5-5.0 micron by AKARI. Based on the Bus-DeMeo taxonomy (DeMeo et al. 2009, Icarus, 202, 160), all the AcuA-spec asteroids are classified, using the published and our observational data. Additionally, taking advantage of the Bus-DeMeo taxonomy characteristics, we constrain the characteristic each spectral type by combining the taxonomy results with the other physical observational data from colorimetry, polarimetry, radar, and radiometry. As a result, it is suggested that certain C-, Cb-, B-type, dark X-, and D-complex asteroids have spectral properties compatible with those of anhydrous interplanetary dust particles with tiny bright material, such as water ice. This supports the proposal regarding the C-complex asteroids (Vernazza et al. 2015, ApJ, 806, 204; 2017, AJ, 153, 72). A combination of the Bus-DeMeo taxonomy for AcuA-spec asteroids and the presumptions with other physical clues such as the polarimetric inversion angle, radar albedo, and mid-infrared spectroscopic spectra will be beneficial for surface material constraints, from the AcuA-spec asteroid observations.

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arXiv2017

Polarimetric Study of Near-Earth Asteroid (1566) Icarus

We conducted a polarimetric observation of the fast-rotating near-Earth asteroid (1566) Icarus at large phase (Sun-asteroid-observer's) angles $α$= 57 deg--141deg around the 2015 summer solstice. We found that the maximum values of the linear polarization degree are $P_\mathrm{max}$=7.32$\pm$0.25 % at phase angles of $α_\mathrm{max}$=124$\pm$8 deg in the $V$-band and $P_\mathrm{max}$=7.04$\pm$0.21 % at $α_\mathrm{max}$=124$\pm$6 deg in the $R_\mathrm{C}$-band. Applying the polarimetric slope-albedo empirical law, we derived a geometric albedo of $p_\mathrm{V}$=0.25$\pm$0.02, which is in agreement with that of Q-type taxonomic asteroids. $α_\mathrm{max}$ is unambiguously larger than that of Mercury, the Moon, and another near-Earth S-type asteroid (4179) Toutatis but consistent with laboratory samples with hundreds of microns in size. The combination of the maximum polarization degree and the geometric albedo is in accordance with terrestrial rocks with a diameter of several hundreds of micrometers. The photometric function indicates a large macroscopic roughness. We hypothesize that the unique environment (i.e., the small perihelion distance $q$=0.187 au and a short rotational period of $T_\mathrm{rot}$=2.27 hours) may be attributed to the paucity of small grains on the surface, as indicated on (3200) Phaethon.

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arXiv2017

OISTER Optical and Near-Infrared Monitoring Observations of a Peculiar Radio-Loud Active Galactic Nucleus SDSS J110006.07+442144.3

We present monitoring campaign observations at optical and near-infrared (NIR) wavelengths for a radio-loud active galactic nucleus (AGN) at z=0.840, SDSS~J110006.07+442144.3 (hereafter, J1100+4421), which was identified during a flare phase in late February, 2014. The campaigns consist of three intensive observing runs from the discovery to March, 2015, mostly within the scheme of the OISTER collaboration. Optical-NIR light curves and simultaneous spectral energy distributions (SEDs) are obtained. Our measurements show the strongest brightening in March, 2015. We found that the optical-NIR SEDs of J1100+4421 show an almost steady shape despite the large and rapid intranight variability. This constant SED shape is confirmed to extend to $\sim5~μ$m in the observed frame using the archival WISE data. Given the lack of absorption lines and the steep power-law spectrum of $α_ν\sim-1.4$, where $f_ν\proptoν^{α_ν}$, synchrotron radiation by a relativistic jet with no or small contributions from the host galaxy and the accretion disk seems most plausible as an optical-NIR emission mechanism. The steep optical-NIR spectral shape and the large amplitude of variability are consistent with this object being a low $ν_{\rm{peak}}$ jet-dominated AGN. In addition, sub-arcsec resolution optical imaging data taken with Subaru Hyper Suprime-Cam does not show a clear extended component and the spatial scales are significantly smaller than the large extensions detected at radio wavelengths. The optical spectrum of a possible faint companion galaxy does not show any emission lines at the same redshift and hence a merging hypothesis for this AGN-related activity is not supported by our observations.

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arXiv2017

Broad-Lined Supernova 2016coi with Helium Envelope

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} $λ$5876, $λ$6678, and $λ$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.

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arXiv2016

J-GEM Follow-Up Observations of The Gravitational Wave Source GW151226

We report the results of optical--infrared follow-up observations of the gravitational wave (GW) event GW151226 detected by the Advanced LIGO in the framework of J-GEM (Japanese collaboration for Gravitational wave ElectroMagnetic follow-up). We performed wide-field optical imaging surveys with Kiso Wide Field Camera (KWFC), Hyper Suprime-Cam (HSC), and MOA-cam3. The KWFC survey started at 2.26 days after the GW event and covered 778 deg$^2$ centered at the high Galactic region of the skymap of GW151226. We started the HSC follow-up observations from 12 days after the event and covered an area of 63.5 deg$^2$ of the highest probability region of the northern sky with the limiting magnitudes of 24.6 and 23.8 for i band and z band, respectively. MOA-cam3 covered 145 deg$^2$ of the skymap with MOA-red filter 2.5 months after the GW alert. Total area covered by the wide-field surveys was 986.5 deg$^2$. The integrated detection probability of all the observed area was $\sim$29%. We also performed galaxy-targeted observations with six optical and near-infrared telescopes from 1.61 days after the event. Total of 238 nearby (<100 Mpc) galaxies were observed with the typical I band limiting magnitude of $\sim$19.5. We detected 13 supernova candidates with the KWFC survey, and 60 extragalactic transients with the HSC survey. Two third of the HSC transients were likely supernovae and the remaining one third were possible active galactic nuclei. With our observational campaign, we found no transients that are likely to be associated with GW151226.

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arXiv2016

2014-2015 Multiple Outbursts of 15P/Finlay

Multiple outbursts of a Jupiter-family comet, 15P/Finlay, occurred from late 2014 to early 2015. We conducted an observation of the comet after the first outburst and subsequently witnessed another outburst on 2015 January 15.6-15.7. The gas, consisting mostly of C2 and CN, and dust particles expanded at speeds of 1,110 +/- 180 m/s and 570 +/- 40 m/s at a heliocentric distance of 1.0 AU. We estimated the maximum ratio of solar radiation pressure with respect to the solar gravity beta_max = 1.6 +/- 0.2, which is consistent with porous dust particles composed of silicates and organics. We found that 10^8-10^9 kg of dust particles (assumed to be 0.3 micron - 1 mm) were ejected through each outburst. Although the total mass is three orders of magnitude smaller than that of the 17P/Holmes event observed in 2007, the kinetic energy per unit mass (104 J/kg) is equivalent to the estimated values of 17P/Holmes and 332P/2010 V1 (Ikeya-Murakami), suggesting that the outbursts were caused by a similar physical mechanism. From a survey of cometary outbursts on the basis of voluntary reports, we conjecture that 15P/Finlay-class outbursts occur >1.5 times annually and inject dust particles from Jupiter-family comets and Encke-type comets into interplanetary space at a rate of ~10 kg/s or more.

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arXiv2016

J-GEM Follow-Up Observations to Search for an Optical Counterpart of The First Gravitational Wave Source GW150914

We present our optical follow-up observations to search for an electromagnetic counterpart of the first gravitational wave source GW150914 in the framework of the Japanese collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM), which is an observing group utilizing optical and radio telescopes in Japan, as well as those in New Zealand, China, South Africa, Chile, and Hawaii. We carried out a wide-field imaging survey with Kiso Wide Field Camera (KWFC) on the 1.05-m Kiso Schmidt telescope in Japan and a galaxy-targeted survey with Tripole5 on the B&C 61-cm telescope in New Zealand. Approximately 24 deg2 regions in total were surveyed in i-band with KWFC and 18 nearby galaxies were observed with Tripole5 in g-, r-, and i-bands 4-12 days after the gravitational wave detection. Median 5-sigma depths are i~18.9 mag for the KWFC data and g~18.9 mag, r~18.7 mag, and i~18.3 mag for the Tripole5 data. Probability for a counterpart to be in the observed area is 1.2% in the initial skymap and 0.1% in the final skymap. We do not find any transient source associated to an external galaxy with spatial offset from its center, which is consistent with the local supernova rate. We summarize future prospects and ongoing efforts to pin down electromagnetic counterparts of binary black hole mergers as well as neutron star mergers.

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arXiv2016

OISTER Optical and Near-Infrared Observations of the Super-Chandrasekhar Supernova Candidate SN 2012dn: Dust Emission from the Circumstellar Shell

We present extensively dense observations of the super-Chandrasekhar supernova (SC SN) candidate SN 2012dn from $-11$ to $+140$ days after the date of its $B$-band maximum in the optical and near-infrared (NIR) wavelengths conducted through the OISTER ToO program. The NIR light curves and color evolutions up to 35 days after the $B$-band maximum provided an excellent match with those of another SC SN 2009dc, providing a further support to the nature of SN 2012dn as a SC SN. We found that SN 2012dn exhibited strong excesses in the NIR wavelengths from $30$ days after the $B$-band maximum. The $H$ and $K_{s}$-band light curves exhibited much later maximum dates at $40$ and $70$ days after the $B$-band maximum, respectively, compared with those of normal SNe Ia. The $H$ and $K_{s}$-band light curves subtracted by those of SN 2009dc displayed plateaued evolutions, indicating a NIR echo from the surrounding dust. The distance to the inner boundary of the dust shell is limited to be $4.8 - 6.4\times10^{-2}$ pc. No emission lines were found in its early phase spectrum, suggesting that the ejecta-CSM interaction could not occur. On the other hand, we found no signature that strongly supports the scenario of dust formation. The mass loss rate of the pre-explosion system is estimated to be $10^{-6}-10^{-5}$ M$_{\odot}$ yr$^{-1}$, assuming that the wind velocity of the system is $10-100$ km~s$^{-1}$, which suggests that the progenitor of SN 2012dn could be a recurrent nova system. We conclude that the progenitor of this SC SN could be explained by the single-degenerate scenario.

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arXiv2015

Monitoring Observations of the Jupiter-Family Comet 17P/Holmes during 2014 Perihelion Passage

We performed a monitoring observation of a Jupiter-Family comet, 17P/Holmes, during its 2014 perihelion passage to investigate its secular change in activity. The comet has drawn the attention of astronomers since its historic outburst in 2007, and this occasion was its first perihelion passage since then. We analyzed the obtained data using aperture photometry package and derived the Afrho parameter, a proxy for the dust production rate. We found that Afrho showed asymmetric properties with respect to the perihelion passage: it increased moderately from 100 cm at the heliocentric distance r_h=2.6-3.1 AU to a maximal value of 185 cm at r_h = 2.2 AU (near the perihelion) during the inbound orbit, while dropping rapidly to 35 cm at r_h = 3.2 AU during the outbound orbit. We applied a model for characterizing dust production rates as a function of r_h and found that the fractional active area of the cometary nucleus had dropped from 20%-40% in 2008-2011 (around the aphelion) to 0.1%-0.3% in 2014-2015 (around the perihelion). This result suggests that a dust mantle would have developed rapidly in only one orbital revolution around the sun. Although a minor eruption was observed on UT 2015 January 26 at r_h = 3.0 AU, the areas excavated by the 2007 outburst would be covered with a layer of dust (<~ 10 cm depth) which would be enough to insulate the subsurface ice and to keep the nucleus in a state of low activity.

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arXiv2015

Detection of Remnant Dust Cloud Associated with the 2007 Outburst of 17P/Holmes

This paper reports a new optical observation of 17P/Holmes one orbital period after the historical outburst event in 2007. We detected not only a common dust tail near the nucleus, but also a long narrow structure that extended along the position angle 274.6+/- 0.1 degree beyond the field of view of the Kiso Wide Field Camera, i.e., >0.2 degree eastward and >2.0 degree westward from the nuclear position. The width of the structure decreased westward with increasing distance from the nucleus. We obtained the total cross section of the long extended structure in the field of view, C= (2.3 +/- 0.5)x10^10 m^2. From the position angle, morphology and the mass, we concluded that the long narrow structure consists of materials ejected during the 2007 outburst. On the basis of the dynamical behavior of dust grains in the solar radiation field, we estimated that the long narrow structure would be composed of 1 mm-1 cm grains having an ejection velocity of >50 m/s. The velocity was more than one order of magnitude faster than that of millimeter - centimeter grains from typical comets around a heliocentric distance rh of 2.5 AU. We considered that sudden sublimation of a large amount of water ice (about 10^30 mol/s) would be responsible for the high ejection velocity. We finally estimated a total mass of M=(4-8)x10^11 kg and a total kinetic energy of E=(1-6)x10^15 J for the 2007 outburst ejecta, which are consistent with those of previous studies that conducted soon after the outburst.

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arXiv2015

Optical and Near-Infrared Polarimetry for a Highly Dormant Comet 209P/LINEAR

We conducted an optical and near-infrared polarimetric observation of the highly dormant Jupiter-Family Comet, 209P/LINEAR. Because of its low activity, we were able to determine the linear polarization degrees of the coma dust particles and nucleus independently, that is $P_n$=30.3$^{+1.3}_{-0.9}$% at $α$=92.2$^\circ$ and $P_n$=31.0$^{+1.0}_{-0.7}$% at $α$=99.5$^\circ$ for the nucleus, and $P_c$=28.8$^{+0.4}_{-0.4}$% at $α$=92.2$^\circ$ and 29.6$^{+0.3}_{-0.3}$% at $α$=99.5$^\circ$ for the coma. We detected no significant variation in $P$ at the phase angle coverage of 92.2$^\circ$-99.5$^\circ$, which may imply that the obtained polarization degrees are nearly at maximum in the phase-polarization curves. By fitting with an empirical function, we obtained the maximum values of linear polarization degrees $P_\mathrm{max}$=30.8% for the nucleus and $P_\mathrm{max}$=29.6% for the dust coma. The $P_\mathrm{max}$ of the dust coma is consistent with those of dust-rich comets. The low geometric albedo of $P_v$=0.05 was derived from the slope-albedo relationship and was associated with high $P_\mathrm{max}$. We examined $P_\mathrm{max}$-albedo relations between asteroids and 209P, and found that the so-called Umov law seems to be applicable on this cometary surface.

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arXiv2015

OISTER Optical and Near-Infrared Observations of Type Iax Supernova 2012Z

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared wavelengths from immediately after the explosion until $\sim$ $260$ days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research (OISTER) Target-of-Opportunity (ToO) program and the Subaru telescope. We found that the near-infrared (NIR) light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes ($M_{J}\sim-18.1$ mag and $M_{H}\sim-18.3$ mag) and the rate of decline of the light curve ($Δ$ $m_{15}$($B$)$=1.6 \pm 0.1$ mag) are very similar to those of SN 2005hk ($M_{J}\sim-17.7$ mag, $M_{H}\sim$$-18.0$ mag, and $Δ$ $m_{15}$($B$)$\sim1.6$ mag), yet differ significantly from SNe 2008ha and 2010ae ($M_{J}\sim-14 - -15$ mag and $Δ$ $m_{15}$($B$)$\sim2.4-2.7$ mag). The estimated rise time is $12.0 \pm 3.0$ days, which is significantly shorter than that of SN 2005hk or any other Ia SNe. The rapid rise indicates that the $^{56}$Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of 6--8. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a `failed deflagration' model, although the pulsational delayed detonations is not excluded.

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