Okayama and Subaru
Planet Search Programs
Bun’ei Sato
Tokyo Institute of TechnologyOct. 7‐9 2009

Searching for Planets around
Evolved Intermediate‐Mass Stars

Understanding properties ofplanets as a function ofstellar mass, evolutionarystage, etc.

(c) Okayama Astrophysical Observatory

Why Giants?
Distribution of planet‐hosting stars

A4 V

GK giants
G9 III~30 planets

BA dwarfs
0 planets
FGK dwarfs~290 planets

M dwarfs~10 planetsSunEast‐Asian Planet Search Network(EAPSNET)Okayama 1.88m tel., Japan
300 GK giants (V<6), since 2001
10 planets and 1 brown dwarf
Xinglong 2.16m tel., China & Okayama
100 GK giants (V~6), since 2005
(1 planet and 1 brown dwarf)
Bohyunsan 1.8m tel., Korea & Okayama
140 GK giants (V<6.5), since 2005
1 brown dwarf
Subaru 8.2m tel., Japan & EAPSNET
>200 GK giants (6.5<V<7), since 2006
Several candidates
TUBITAK 1.5m tel., Turkey
50 GK giants (V~6.5), since 2008

Goal:
~100 planetsfrom 1000 stars

RV Precision with OAO/HIDES
2001～2002

2003~2005

2006~2008

σRV~4m/s

Short-term (~weeks) precision is2m/s (Kambe et al. 2008)

Discoveries from EAPSNETStar Name

Sp. Type Stellar
Mass(M~)

StellarRadius(R~)

Planetary
Mass(MJUP)

Semi‐
Eccen Metallicity
majortricity ([Fe/H])
Axis (AU)(dex)

HD 119445

G6III

3.9

20.5

37.6

1.71

0.08

＋0.04

ε Tau

K0 III

2.7

13.7

7.6

1.93

0.15

＋0.13

11 ComG8 III

2.7

19

19.4

1.29

0.23

－0.28

81 CetG5 III

2.4

115.3

2.5

0.21

＋0.06

18 DelG6 III

2.3

8.5

10.3

2.6

0.08

－0.05

HD 104985

G9 III

2.3

118.3

0.950.09－0.35

ξ Aql

K0 III

2.2

122.8

0.68

0－0.1814 AndK0 III

2.2114.8

0.83

0－0.24

HD 81688

K0 III‐IV

2.113

2.7

0.81

0－0.34

HD 173416

G8 III

2.0

13.5

2.7

1.2

0.21

－0.22

6 Lyn

K0 IV

1.7

5.2

2.4

2.2

0.13

－0.13

HD 167042

K1 IV

1.5

4.5

1.6

1.3

0.10

＋0.00

To be Submitted
OAO

OAO

OAO

All of these are subgiants
with 1.5-1.7M~ and[Fe/H]=0.0-0.1

Planet Frequency vs. Stellar Mass
Johnson et al.
(2007)

KM dwarfs
0.1‐0.7M~
2%

G dwarfs F dwarfs, G subgiants
0.7‐1.3M~
1.3‐1.9M~
4%
9%(>0.8MJUP)
17%(5/30)< 2.5MJUP> 2.5MJUPGK giants GK giants
1.9‐3M~
3‐5M~

5%
0%
(10/184) (0/61)
3.0

Semimajor Axis
100
Inside ofcentral star
Msini (MJUP)

10？

1Detection limit
0.1
0.01
0.01

▲：Red clump giants (1.7‐3.9M~)
Primordially▲：Subgiants
deficient?(1.6‐1.9M~)▲：K giants (<1.6M~)
Engulfed by ○：FGKM
the centraldwarfsstars?

0.11Semimajor Axis (AU)10

Planets vs. Metallicity
In solar‐type stars, more metal‐richstars are known to have moreplanets.

Solar‐type stars
w/o planets

w/ planets

In core‐accretion scenario, solid
cores of planets easily form in
metal‐rich circumstellar disks.
In planet‐hosting giants, however,no such metal‐rich tendency has
been seen so far.
Efficient inward migration of planetsin metal‐rich disks or metallicity
independent formation such as
gravitational instability in disks ordilution by convective envelope?

Santos et al. 2004

Giant stars
OAO Sample

w/o planets(309)

w/ planets(13)

Takeda et al. 2008

What’s next ?
• Extending baseline beyond 3 AU
• Continue OAO program• BOAO?, Xinglong??

• Enlarging samples to >1000 stars• Subaru survey + OAO, BOAO, Xinglong follow‐up• Focus on relatively short‐period planets (P<1yr)• Dedicated search for planets around >3M~ giants• Most of the current targets are <3M~
• Planet desert around >3M~? Î Omiya‐san’s talk

• Dedicated search for planets around [Fe/H]~+0.2 giants

Beyond 3 AU
Msini=4MJUP
a=5AU

OAO/HIDES

Msini=4MJUP
a=4AU
Preliminary

Frequency of planets
beyond 3 AU strongly
depends on snow-line

OAO/HIDES

Preliminary

Subaru/HDS Survey
zThree obs. each star ina half year to identify
large RV candidates
zFollow up using
2m‐telescopes ineast‐Asian countries‐ 40 @Okayama‐ a few @Xinglong, BOAOzIn 2006‐2008, 200 stars
have been screened and~70 of them show large(>20m/s) RV variations.

Toward 1000 stars in total

RV Variatiions
70/200 show σRV=20‐200 m/sÎfollow upNew Candidates
Msini=3.5MJUP
a=0.77AU

Blue: Subaru
Red: OAO

Msini=20MJUP
a=1.3AUSummary• Nine years of the Okayama Planet SearchPrograms• Nine planets, one BD, and several more candidates
within 2.5AU• Different properties of planets (frequency, mass,semimajor‐axis, host‐star’s metallicity etc.) from thosearound solar‐like stars• Future• Extending baseline beyond 3AU at Okayama• Enlarging sample to >1000 stars• Subaru survey + OAO, BOAO, Xinglong follow‐up• New dedicated planet searches