2023/2/28 - 3/1
第13回 光・赤外線天文学大学間連携ワークショップ

1/13

OISTER連携観測によるVisorsatの庇の効果の検証
東京大学 天文学教育研究センター
特任研究員
堀内 貴史 / Takashi Horiuchi
Co-authors
Hidekazu Hanayama, Masatoshi OHISHI, Tatsuya NAKAOKA, Ryo IMAZAWA, Koji S. KAWABATA,Jun TAKAHASHI, Hiroki ONOZATO, Tomoki SAITO, Masayuki YAMANAKA, Daisaku NOGAMI,Yusuke TAMPO, Naoto KOJIGUCHI, Jumpei ITO, Masaaki SHIBATA, Malte SCHRAMM, Yumiko OASA,Takahiro KANAI, Kohei OIDE, Katsuhiro L. MURATA, Ryohei HOSOKAWA, Yutaka TAKAMATSU,Yuri IMAI, Naohiro ITO, Masafumi NIWANO, Seiko TAKAGI, Tatsuharu ONO, and Vladimir V. KOUPRIANOVLight pollution from the Starlink satellites□ SpaceX launched the first 60 Starlink
satellites on May 24, 2019 for high-speed
internet communications.
□ However, the mega-constellation including theStarlink satellites pollutes the environment ofastronomical observations (orbital height: 550 km).

・IAU expressed the concern on that incident.
□ SpaceX plans to launch 12,000 satellites until
mid 2020s.

2/13

３/13

Light pollution countermeasures by SpaceX - Darksat and Visorsat ©SpaceX©SpaceXMallama (2021)Darksat

Origial Starlinks

Magnitude at the orbital height of 550 km(e.g., Horiuchi+2020; Tregloan-Reed+2020)

・Origial Starlink (STARLINK-1113)
5.33 (gʼ), 5.60 (Rc), 4.25 (Ic)
・Darksat
6.10 (gʼ), 6.00 (Rc), 5.65 (Ic)

Multicolor magnitudes of Visorsat are
not well known. èè Our motivation !

Observation with the OISTER collaboration
4/13© OISTER□ Simultaneous multicolor observations with theJapanese OISTER collaboration→ capture the trail of Visorsat andSTARLINK-1113 (original satellite)□ Telescopes/instruments:
・Murikabushi and Akeno 50 cm/MITSuME (g, R, I)
・SaCRA/MuSaSHI (r, i, z)
・Kanata/HONIR (B, V, H)
・Nayuta/NIC (J, H, K)
・Kyoto 40cm (B)

12 bands

・Prika/MSI (U)・PROMPT6@CTIO (V; other than OISTER)

5/13

Magnitude estimation 1
Using “Projection” in DS9, we
estimated average cross section
counts of satellite trails (fsat)

The observed ﬂux is inversely proportional
to the satellite velocity, Vsat.

Cross section
CountsRc

Horiuchi+(2020)

Elongated reference stars(fstar) by tracking off

Apparent magnitudes of the satellites, msat

Vstar = 15 cosδ arcsec s-1

Magnitude estimation 2
Using “Projection” in DS9, weestimated average cross section
counts of satellite trails (fsat)

The observed ﬂux is inversely proportional
to the satellite velocity, Vsat.

Satellite trail (streak)vs.
Point source

6/13

Cross section
CountsRc

Horiuchi+(2020)

Apparent magnitudes of the satellites, msat

Typical magnitudes of Visorsat• Magnitudes at a 550 km
height.
• U band magnitude was notable to obtain because of thesensitivity of Pirka/MSI(Hokkaido Univ.).
• Visorsat is dimmer than
STARLINK-1113 as a trend.
• The longer the observed
wavelength, the brighter thesatellite magnitudes become.

BandVisorsat
(mag)

7/13

STARLINK1113
(mag)

B

6.77

0.48

6.11

0.33

V

6.61

0.12

5.25

0.13

g‘

6.07

0.12

5.12

0.17

Rc

5.32

0.04

4.40

0.08

Ic

4.94

0.07

4.04

0.12

r

4.90

0.02

4.26

0.03

i

4.76

0.02

3.79

0.03

z

4.65

0.02

3.57

0.02

J

3.80

0.24

3.70

0.08

H

3.38

0.06

3.47

0.05

K

3.65

0.11

3.55

0.07

Phase angle dependence on magnitudes

8/13□ The satellite magnitudes are minimized around solar phase angle (Sun-Sat-Observer) of 90 .
□ The magnitudes of Visorsat are ~ 1 mag dimmer than those of STARLINK-1113.

Blackbody model of the satellite flux

9/13

□ In order to estimate the albedo, amod, ofthe starlink satellites, we construct theblackbody model of the satellite (AB)flux.
□ Assuming amod(STARLINK-1113) ~amod(Visorsat), we estimated covering
foctor, Cf, of the sun visor on Visorsat(where Uf = 1 - Cf).

FRS : sunlight reflection
FREs : earthshine reflection
FTS: thermal radiation of the satellite
FTE: reflection of Earthʼs thermal radiationBlackbody fitting to the satellite flux (ex1)10/13
STARLINK-1113
amod = 0.06
□ Model fitting to r, i, and z
band flux obtained with
SaCRA/MuSaSHI(Saitama Univ.).
□ Together with the resultswith other telescopes, therange of the coveringfactor is 0.18 < Cf < 0.92.

Visorsatamod = 0.06
Cf = 0.72
Visorsatamod = 0.06
Cf = 0.57

VisorsataUf = 0.18

Flux model for B and H bands (ex2)□ B and H bans flux obtainedwith Kanata/HONIR(Hiroshima Univ.)
・The albedo of H band isabout twice larger than thatof B band.
・・The reflectivity of satellite
surface materials likely
become higher at thelonger wavelength.

Fit to B band flux
a = 0.09

STARLINK-1113
Fit to B band flux
a = 0.09
Cf = 0.20

Visorsat

Fit to H band flux
a = 0.19

STARLINK-1113
Fit to H band flux
a = 0.19
Cf = 0.29

Visorsat

11/13

The relation between covering factor, brightness, and phase angle
12/13

The smaller the covering factor is, the brighter the magnitudes ofVisorsat tend to become.

Summary13/13□ We observed Visorsat and STARLINK-1113 with the OISTER collaboration.
・ In most cases, Visorsat (~ 6 ‒ 7 mag) is dimmer than STARLINK-1113(~ 5 ‒ 6 mag) as a trend.
・ By assuming the blackbody radiation, we estimated a covering factor, Cf,
and its range of 0.18 < Cf < 0.92.
・ The reflectivity of satellite surface materials likely become higher at thelonger wavelength.

☆ While we showed the shading effect of the sun visor of Visorsat,the observational impact from Visorsat is still profound (Horiuchi+submitted).
© OISTERBlackbody fitting to the satellite flux (ex3)Blackbody fitting to the satellite flux (ex4)□ The albedo of near infrared bands (J, H, and K) is somewhat
higher than that of optical region.

Az, El dependence of magnitudes

Cole (2021)

Simulation of the impact on astronomical
observations with a large telescope
Tyson et al. (2020) simulated the impact from the Starlink
satellites on LSST observations- Using artiﬁcial satellite trails at the level corresponding tov0.9 Starlink satellites, they showed the negative impact onCCDs-- the main trail is ~1000 times brighter than important
astronomical signals.

Tyson et al. (2020)

LSSTSimulation of the impact on astronomical
observations with a large telescope
Tyson et al. (2020)

Tyson et al. (2020) simulated the impact fromthe Starlink satellites on LSST observations-a satellite magnitude - CCD counts (e-)
relation was verified in six passbands: u, g, r, I,z, and y bands
Tyson et al. (2020)-- the CCD will saturate at ~3.5 and ~1.5 mag
in g and y bands, respectively.

LSSTRelation between time of day and number of satellites
From London

McDowell (2020)
TotalTotal

V~ 7.5 mag
V~ 7.5 mag
V~ 5.5 mag
V~ 4.5 mag
McDowell (2020)

The Starlink satellites can be observed even in the middle of the night.

The relation between covering factor, brightness, and phase angle

The smaller the covering factor is, the brighter the magnitudes ofVisorsat tend to become.