Optical Observations of Faint Meteors
with the Extremely Wide Field Mosaic CMOS Camera: Tomo-e Gozen
Ryou Ohsawa (Univ. of Tokyo)

S. Sako, A. Hirota, K. Morita, S. Abe, J. Kero, D. Kastinen, T. Nakamura,
F. Usui, Y. Sarugaku, M. Sato, Y. Fujiwara, T. Ootsubo, K. Arimatsu,
T. Kasuga, J. Watanabe, and the Tomo-e Gozen project2019.03.06

Outline
1. Brief introduction of optical meteor observations
2. Kiso Observatory and Tomo-e Gozen
3. Faint meteors captured by Tomo-e Gozen- Observations with a prototype camera in 2016
- MU radar & Tomo-e Gozen observations in 2018

4. Other science topics with Tomo-e Gozen

Summary

About 1,000 meteors can be detected in a night with the Tomo-e Gozen camera.
A small-end size distribution is provided with optical-radar simultaneous observations.
Tomo-e Gozen has a high performance in detecting faint transient events.

Self Introduction
Name: Ryou Ohsawa
Affilication: The Institute of Astronomy, The University of Tokyo
Science: Optical/Infrared Observatoinal Astronomy
Formation and Evolution of dust grains in the Universe
Development of Cameras (MIMIZUKU, Tomo-e Gozen)

Dust grains
Solid-state material in the Universe
Obscure objects, absorbing light
Carriers of heavy elements (e.g., Mg, Fe, Si)
important role in galactic chemical evolution
ingredients for planets, satellites, and lifes

Spitzer/IRAC image of M81 (nasa.gov)(B,G,Y,R) = (3.6 μm, 4.5 μm, 5.8 μm, 8.0 μm)

Ubiquitously observed
evolved stars, star-forming regions, and distant galaxies

Important sites for chemical reactions
formation of H2 and other molecules
Draine (2011), Princeton Univ. Press; Field (1974), AJ, 187, 453; Jenkins (2009) ApJ, 700, 1299

Size Distribution of Dust Grains
Important characteristics of dust grains⇆ not easy to measure the size of dust particles
Grains around evolved stars like AGB-stars- large (~μm) grains formed around evolved stars

e.g., Ohnaka et al. 2016 A&A...589A..91- dust size distribution ~ single population?

Grains in the interstellar space- size distribution ~ a single power-law function- shattering in diffuse interstellar space-q
Grains in the Solar System dN(D) ∝ D dD
- 4P/Faye: 3 μm ― 5 mm, power law (q ~ 3.5)
- 2P/Encke: 30 μm ― 110 mm, power law (q ~ 3.4)

e.g., Mathis et al. 1977ApJ...217..425
e.g., Jones et al. 1996ApJ...469..740

Sarugaku et al. 2007 PASJ...59L..25
Sarugaku et al. 2015 ApJ...804..127

Mass influx onto the Earth
Mass influx (109g yr-1)

6Interplanetary dust grains

Huge Impactors

54
32
1
0
10-15

10-10

10-5

100105Mass of particle (g)

1010

1015

from Cosmic dust in the earth's atmosphere, Plane (2012)

Single Grain Experiment
1. Using instruments onboard spacecrafts
Ulysses, Galileo, Cassini, Rosetta, DESTINY+, ...
direct measurements of mass and chemical compositions
2. Sample return missions
cometary dust (Stardust), asteroids (Hayabusa, Hayabusa-2, OSIRIS-REx), ...
3. Meteor observations
using the atmosphere/surface of the Earth (other planets) as a detector
the magnitude of the event corresponds to the mass (energy)

Grün et al. (1992), A&AS, 92, 411; Srama et al. (2004), SSR, 114, 465; Sandford et al. (2006), Science, 314, 1720

Observations of Meteors

Ionosphere

Optical observations

TailEcho

direct and passive measurement
optical brightness ∝ kinetic energy ∝ mass
trajectory from multi-site observations

Radar echo observations

direct and active measurement
volume of ionized region ∝ energy ∝ mass
trajectory from a single-site observation (head echo)

Infraso
und

Head
Echo

licat
Op

Infrasound obsrevations

indirect and passive measurement
only available for large bolides

Ionosphere disturbance observations
indirect and passive measurement
only available for large bolides

Jenniskens (2006), Cambrige Univ. Press; Mathews et al. (1997), Icarus, 126, 157
Brown et al. (2007), JASTP, 69, 600; Yang et al. (2014), Radio Sci., 49, 341

Meteor Observation Networks
Major Networks
Cameras for Allsky Meteor Surveillance (CAMS)
SonotaCo Network
European viDeo Meteor Observation Network (EDMONd)
Mostly supported by amateur astronomers
About 1,000,000 meteor orbits have been identified
Observing down to +4 mag. (~1 cm, ~1 g)Canadian Automated Meteor Observatory (CAMO)
Automated observing system operated by the University of Western Ontario
Consists of two stations with two camera systems
High Resolution Wide-field Camera / High Resolution Narrow-field Camera
Wide-field Camera

Narrow-field Camera

Weryk et al. (2013),Icarus, 225, 614-622

Canadian Automated Meteor Observatory (CAMO)
Automated observing system operated by the University of Western Ontario
Consists of two stations with two camera systems
High Resolution Wide-field Camera / High Resolution Narrow-field Camera

Weryk et al. (2013),Icarus, 225, 614-622

Cumulative Number Counts: N(<Mpg)

Luminosity Function of Sporadic Meteors
log10N(<M) = Mlog10r + log10N0

velocity correctied

1000
weightedno correction
10010r = 3.4log10N0 = -5.1-3.0-2..0-1.0

0.0+1.0+2..0

Photographic Magnitude+3.0+4..0

Luminosity function with SuperSchmidt camera, adapted from Hawkins & Upton (1958)

Luminosity Function of Faint Sporadic Meteors
2.33-1=h)>N(1000101000~12 mag.

100kh~7 mag.

Cumulative Frequency N(>h)

10000

100

10Pulse Height: h (chart units)
Luminosity function with a 10-m reflector and a Phototube, adapted from Cook, et al. (1980)

Log Cumulative Flux (m-2s-12πstr-1)

Cumulative Mass Distribution-2-4-6s =mSatellite

1.55±0.
02-8-10sm =-12Radar2.0
3±0.02Vis sua
m = l2.
62−2.89-14-16-12-10-8-6-4Log Particle Mass (g)-2-0Cumulative flux of particles to the Earth's surface, adapted from Hughes (1987)

How to detect fainter meteors
Preferred Specifications
1. Larger aperture to collect more photons
2. Larger field-of-view not to miss meteor events
3. Higher frame rate to avoid/decrease the trail loss
Possible Solution

A high-sensitive video camera + A wide-field large telescope

Kiso Observatory & Tomo-e Gozen

Kiso Observatory
Kiso Observatory
Univ. Tokyo

Kobe Univ.

Ma p d a ta ©2018 Go o gle , SK te le c o m , ZENRIN

50 km

Kiso Observatory
Kiso Observatory
Univ. Tokyo

Ma p d a ta ©2018 Go o gle , SK te le c o m , ZENRIN

50 km

Previous Instrument: Kiso Wide Field Camera

2010-2018

KWFCaImge
Circleofcope

Kiso Wide Field Camera (KWFC)
2° × 2° FOV (8 CCD sensors)

seleTtKiso Schmid

Image of KWFC from the website of Kiso Observatory

New Wide-Field CMOS Camera: Tomo-e Gozen

2010-2018

KWFCaIm

geCircleofcope

Kiso Wide Field Camera (KWFC)
2° × 2° FOV (8 CCD sensors)

sele
Tt
Kiso Schmid

Tomo-e Gozen

An overview of the camera modules
2K×1K CMOS image sensor by Canon
84 CMOS sensors are tiled to cover ~20□°
Q2

eerged9~

Q3

Q1

moon

Q4

Composed of four camera modules

Tomo-e Gozen

An overview of the camera modules

Specifications (Sako et al. Proc. SPIE, 2018)
Observatory

Kiso Observatory

Telescope

1.0-m f/3.1 Schmidt telescope

Sensor format

2160×1200pixchip-1

Field of view39′.7×22′.4 × 84chips (~20 deg )Pixel scale

19μm, 1″.189pix-1

Wavelength

350−700nm (peak at 500nm)

Filters

optical broadband (transparent)

Frame rate

2Hz (max, continuous, full frame)

Read noise~1.9e- at 2Hz

Dark current~0.1e- sec-1 pix-1 at 277K

Well depth~6,400e -5σ lim. mag.

~18.5mag. in 0.5sec exposure2

Development of Tomo-e Gozen
20142015201620172018

2019

Prototype DesignPM Assembly
PM Observation
Tomo-e Design
Q1 Assembly
Q1 Observation
Q1&3 Observation

camera8-chipamer
ip ca
4-cheraampcihc
21-eraampcchi48

Meteors with Tomo-e Gozen
2 Hz observation ⇨ meteors are captured as streaks and sometimes truncated.
Typical distance ~ 80−120 km ⇨ meteors are defocused.
Expected limiting magnitude is ~12 mag at the V-band (taking the trail loss into account).

VideoAn image contains a faint meteor (stellar sources are masked)

An image contains a faint meteor (stellar sources are masked)

An image contains a faint meteor (stellar sources are masked)

Automated detection of lines

An algorithm based on the Hough transformation
Original Image

Set of Slanted Images

Set of Compressed Arrayseor
met
cosmic ray

Stack Arrays

Converted Image
Slanted Image

angle

yRa
mic
Cos

Compressed Array

position

Ohsawa et al. (2016), Proc. SPIE, 9913, 39

Automated detection of lines

An algorithm based on the Hough transformation
Original Image

Set of Slanted Images

Set of Compressed Arrays

eormetcosmic ray

Stack Arrays
Detected

Converted Image
Slanted Image

angleyRamic
Cos

Compressed Arrayposition

Ohsawa et al. (2016), Proc. SPIE, 9913, 39

Observations with a prototype in 2016 (Ohsawa et al. submitted)

Overview of observations
Tomo-e Gozen (prototype) with 8 CMOS sensors.
2 Hz monitoring observations on 11 and 14 April, 2016.
Sidereal tracking, pointing the inside of the Earth's shadow every 2 hours.

-05:00eEarth'sshadow
fthoe

2016-04-11Siz

Declination (dd:mm)

Measure the video-rate magnitude assuming the velocity = 10°s-1 (Iye et al., 2004).

-10:00-15:00-20:00-25:0013:00 15:00 17:00

15:20

15:40

14:00

13:20

13:40

Right Ascension (hh:mm)

12:00

Ohsawa et al. (2019), P&SS, 165, 281

Details of Obeservations
Obs. Date

2016.04.11

2016.04.14

Obs. Field

Inside the Earth's shadow

Inside the Earth's shadow

Exposures

1 set = 0.5s × 360frame

1 set = 0.5s × 360frameObs. Time~5.1hours~5.5hours

FilterBlank

Blank# Frames

290880frm.

316800frm.

Unique Meteors

1514 events

706 events

Mean Rates~15events/180s~6.4events/180s

4.5−12.5mag.

4.5−11.5mag.

＊

Magnitudes＊Apparent Video rate magnitude (Iye+ 2007)

Ohsawa et al. (2019), P&SS, 165, 281

Unique Meteor Events

Event rates per 3 minutes on the first day
Event Rates (8 chips,180s) on 2016-04-11

zero mag.

Number of Events

30
25
20
15
10
50
26
24
22

12:00

13:00

14:00

15:00

16:00

17:00

Observation Time (UT)

18:00

19:00

No observations in the shaded regions.

Meteor Magnitude Distributions~50mg~0.3mg2016-04-11

250

t
limi
ion
ect
det

200
150

Number of Meteros

1005002016-04-14

250
200
150
100
50
024

6

8Magnitude (at 100km, V-band)

1012

Ohsawa et al. (2019), P&SS, 165, 281

Luminosity Function
Photographic (Hawkins & Upton, 1958)
Phototube (Cook et al., 1980)
Television (Clifton, 1973)
Television (Hawkes & Jones, 1975)
Visual (Hawkins, 1959)

Ohsawa et al. (2019), P&SS, 165, 281

Short Summary
Kiso Observatory + Tomo-e Gozen
20 deg² CMOS mosaic camera mounted on a 1-m Schmidt type telescope
detection limits in 2 Hz monitoring: ~18 mag (star) & ~12 mag (meteor)

Meteor Observation with Tomo-e Gozen (8 sensors)more than 1,000 unique meteor events in a night
meteor limiting magnitude ~12 mag. was confirmed in real observations
providing a practical tool to investigate ~0.1−10 mg interplanetary grains

Limitation of Tomo-e Gozen
Kiso Observatory + Tomo-e Gozen is unique
no counterpart for simultaneous optical observations⇨ no information on the trajectory or the apparent velocity⇨ large uncertaninty of the meteor brightness

Kiso Schmidt + Tomo-e Gozen

Non-existent counterpart

MU Radar & Tomo-e Gozen observations in 2018

RCS (ionizing mass)

Previous Works

Brightness (photometric mass)
Brown et al. (2017), P&SS, 142, 25

Nishimura et al. (2001)
Michell (2010)
Campbell-Brown et al. (2012)
Michell et al. (2015)
Brown et al. (2017)

MU radar & optical camera
PFISR & optical camera
EISCAT & two optical cameras
SAAMR & optical camera
MAARSY & two optical cameras

35 meteors / 2 nights
7 meteors / 1 night
4 meteors / 11 hours
6 meteors / 1 night
105 meteors / 242 hours

km
.1
3
7~1

KisoObservatory

Kyoto
RISHMUUniversity
radar
Ma p d a ta ©2017 ZENRIN

20 km

Collaboration with MU radar› determine ~1,000 meteor orbits and sizes per night› investigate ~100 meteor spectra per night› connect radar and optical observations

MeteoroidMeteor head

The first collaboration successfully conducted in April, 2018.

Optical Observation:brightness (size) distribution
elemental abundance by spectroscopy (optional)

Kiso Schmidt telescope

Radar Observation:
direct measurements of meteor motion
accurate time stamps

Distance ~ 173km

Kyoto Univ. MU RadarObservations
Time (JST)commentDay 1

2018-04-18 20:00 ― 2018-04-19 05:00

partly cloudy

Day 22018-04-19 20:00 ― 2018-04-20 05:00

clear skyDay 3

2018-04-20 20:00 ― 2018-04-21 05:00

clear skyDay 42018-04-21 20:00 ― 2018-04-22 05:00

clear sky

MU radar (J. Kero & S. Abe)configuration optimized for meteor head echo observations
radar beam pointed at the zenith
Akira Hirota & Kohei Morita
Tomo-e Gozen (R. Ohsawa)(Nihon Univ.)
2 Hz monitoring with 20 image sensors (one was severely affected by electric noise)Slide Title

SWW
Direction to MU radar

Image by Stellarium

Slide Title

SWW
Direction to MU radar

Image by Stellarium

Simultaneous Events
Selection by the time windows

Selection on the projected sky†#events (Tomo-e)

Day 1

1041

197

Day 2

942

265

Day 3

1031

285

Day 4

1004

207

Total

4018

954

MU radar timestamp

MU radar detection

38

Tomo-e Gozen detection
36

Elevation (deg)#events (MU)

34
30
28
26

Tomo-e Gozen frames
24

0.5s

extract streaks in these frames† these include non-meteor events (debris and LEO satellites)

228

230

232

234

236

238

Azimuth (deg)

240

242

Simultaneous Events
MU radar detection
Tomo-e Gozen detection
30

954 candidateseye inspection

Elevation (deg)29

confirmed

894 simultaneous events

28

check overwrap

27

fully-overlapped

294 simultaneous events

26

232

233

234

235

236

Azimuth (deg)

237

238

239

Meteor RCS and Magnitude conversion
30

294 events + previous works

MU + Tomo-e Gozen
MU + ICCD (2009,2010)
Linear Regression

Radar Corss Section (dBm)

10-10-20-30

Velocity (km/s)

RCS at Maximum S/N (dB)

20-40
1

2

3

4

5

6

7

8

9

V-band absolute magnitude

101112

13

G-band absolute magnitude(Right) Brown et al. (2017), P&SS, 141, 25-34

Brightness of MU-detected meteors
Applying the derived conversion law to the meteors detected by MU in 2009-2015

Present result: r = 2.80±0.02
Hawkins & Upton (1958)

3.4±0.2

Hawkins (1959)~2.5

Clifton (1973)~3.4

Hawkes & Jones (1975) ~2.5

~1g~0.1mg

Cook et al. (1980)

3.41

Rendtel (2004)

2.95±0.06

Ohsawa et al. (2019)3.10±0.4

Kero et al. (2011), MNRAS, 416, 2550; Kero et al. (2012), 425, 135

Mass DistributionN(>m)∝m -(s-1): s~2.00±0.01

Hughes (1978), COSPAR Space Research XVIII, 427

Size Distribution
N(>D)∝D -b:b~3.00±0.
01

Short Summary
Tomo-e Gozen & MU radar simultaneous observation
More than 800 simultaneous meteor events detected only in 4 nights.
We derived a RCS-magnitude relationship with confidence.
MU radar detects meteors down to ~100 μm in size or ~0.1mg in mass

Tomo-e Gozen and meteors
A CMOS mosaic camera with an extremely wide field-of-view (~20 sq-deg).
Limiting magnitude for stars: ~18 mag. / for meteors: ~12 mag.
More than 1,000 meteor events per night will be captured by Tomo-e Gozen.
We demonstrated early results of a Tomo-e Gozen and MU radar collaboration.
More than 800 simultaneous events were detected only in 4 nights.
Further collaborations (e.g., spectroscopy, meteor showers) are planned.

Tomo-e Gozen and the Solar System
Objects in the Solar System are major science targets (meteor, NEO, comet, etc...).

Ohsawa et al. (2019), P&SS; Urakawa et al. (2019), AJ; Kojima (2019), MThesis

We are always welcome for collaborations!