June. 4, 2015
@ NAOJ	

Probing	  the	  Dynamical	  History	  of	  Exoplanets:	  Spectroscopic	  Observa<ons	  of	  Transi<ng	  Systems	

©NASA	Teruyuki	  Hirano	  Outline	
1. Dynamical	  History	  of	  Close-­‐in	  Planets	  2. Measurements	  of	  the	  Stellar	  Obliquity	  3. Observa<on	  of	  the	  Rossiter-­‐McLaughlin	  (RM)	  Eﬀect	  4. Interpreta<on	  of	  the	  Past	  RM	  Result	  5. Towards	  Smaller	  Planets	  6. Summary	  Distribu<on	  of	  Exoplanets	  	I100planet mass [MJ]

10BA10.1

Snow Line	
0.01

0.001
0.001

C0.01

0.1
1
semi-major axis [AU]10100

Distribu<on	  of	  Exoplanets	  I	I

orbital eccentricity

10.1

0.01
0.01

0.1

1
semi-major axis [AU]10100

Forma<on	  of	  Close-­‐in	  Giant	  Planets	
The	  Standard	  Scenario	  	  →	  	  Close-­‐in	  giants	  have	  originally	  formed	  at	  a	  few	  AU	  away	  from	  their	  host	  stars,	  then	  migrated	  inward	  by	  some	  migra<on	  processes.	  	
ØWhat	  process	  can	  make	  planets	  migrate?	  
ØIs	  there	  any	  possibility	  to	  observa<onally	  	  	  	  	  	  dis<nguish	  among	  migra<on	  scenarios	  ?	  
5	Migra<on	  Processes	
1. Interac<ons	  between	  proto-­‐planets	  and	  proto-­‐plantary	  disk	  →	  	  	  Planets	  had	  gradually	  migrated	  inward	  due	  to	  gravita<onal	  interac<ons	  with	  proto-­‐planetary	  disk	  (e.g.	  Lin	  et	  al.	  1996,	  Lubow	  &	  Ida	  2010)	  	  	  	  2. Planet-­‐planet	  sca^ering	  (or	  Kozai	  cycles)	  +	  <dal	  interac<ons	  →	  	  When	  mul<ple	  planets	  form	  or	  there	  exists	  a	  companion	  star,	  they	  interact	  with	  each	  other	  and	  some<mes	  cause	  orbital	  crossing,	  which	  can	  pump	  up	  eccentrici<es.	  Subsequent	  <dal	  interac<ons	  with	  host	  stars	  may	  cause	  orbital	  circulariza<on.	  	  	  	  	  (e.g.	  	  Cha^erjee	  et	  al.	  2008,	  Wu	  et	  al.	  2007,	  Fabrycky	  &	  Tremaine	  2007)	  	  6	© Weidenschilling and Marzari 1996	Migra<on	  Processes	
1. Interac<ons	  between	  proto-­‐planets	  and	  proto-­‐plantary	  disk	  →	  	  	  Planets	  had	  gradually	  migrated	  inward	  due	  to	  gravita<onal	  interac<ons	  with	  proto-­‐planetary	  disk	  (e.g.	  Lin	  et	  al.	  1996,	  Lubow	  &	  Ida	  2010)	  	  	  	  → small e and stellar obliquity	

2. Planet-­‐planet	  sca^ering	  (or	  Kozai	  cycles)	  +	  <dal	  interac<ons	  →	  	  When	  mul<ple	  planets	  form	  or	  there	  exists	  a	  companion	  star,	  they	  interact	  with	  each	  other	  and	  some<mes	  cause	  orbital	  crossing,	  which	  can	  pump	  up	  eccentrici<es.	  Subsequent	  <dal	  interac<ons	  with	  host	  stars	  may	  cause	  orbital	  circulariza<on.	  	  	  	  	  (e.g.	  	  Cha^erjee	  et	  al.	  2008,	  Wu	  et	  al.	  2007,	  Fabrycky	  &	  Tremaine	  2007)	  	  → large e and stellar obliquity	

7	© Weidenschilling and Marzari 1996	

Measurements	  of	  the	  Stellar	  Obliquity	Measurement of the stellar obliquity is a unique method to probe
the dynamical history of exoplanets!	
a. The	  Rossiter-­‐McLaughlin	  eﬀect	  -­‐>	  High	  dispersion	  spectroscopy	  during	  planetary	  transits	  (e.g.,	  Queloz	  2002,	  Winn	  et	  al.	  2005)	  b. Spot-­‐crossing	  Method	  -­‐>	  Modeling	  of	  anomaly	  in	  transit	  light-­‐curves	  (e.g.,	  Sanchis-­‐Ojeda,	  et	  al.	  2011)	  c. VsinI	  Method	  -­‐>	  Spectroscopic	  determina<on	  of	  the	  rota<on	  velocity	  +	  photometric	  determina<on	  of	  the	  rota<on	  period	  (e.g.,	  Hirano	  et	  al.	  
2012)	  d. Asteroseismology	  -­‐>	  High	  cadence	  photometry	  of	  pulsa<ng	  stars	  (e.g.,	  Chaplin	  et	  al.	  2013)	  e. Gravity-­‐darkening	  Method	  -­‐>	  Modeling	  of	  asymmetry	  in	  transit	  light-­‐
curves	  	   → Kamiaka’s talk	The	  Rossiter-­‐McLaughlin	  (RM)	  Eﬀect	
λ = 0°approaching

λ = 50°

receding

planet’s	  orbit	

RV anomaly

RV anomaly

during	  transit	

time [h]←ver<cal	  axis:	  radial	  veliocity	  	  anomaly	  during	  a	  transit	  time [h]Through	  the	  RM	  eﬀect,	  we	  can	  es<mate	  the	  angle	  between	  	  the	  stellar	  spin	  axis	  and	  the	  planetary	  orbital	  axis,	  which	  is	  	  closely	  related	  to	  the	  planetary	  migra<on.	  

9	Results	  by	  Subaru/HDS	Subaru RV
40!v [m s-1]

200-20Subaru (this work)

Residual [m s-1]

-403020100-10-20-30

Keck (P08)

-0.04

-0.02

0
Orbital Phase

0.02↑ HAT-P-16:
Teff = 6158 ± 80 K
λ = -8.4° ± 7.0°
VsinIs = 3.9 ± 0.3 km/s
T.H. + in prep.	

0.04↑ HAT-P-7:
Teff = 6350 ± 80 K
λ = -132.6° +10.5° -16.3°
VsinIs = 2.3 ± 0.6 km/s
Narita et al. 2009	

RM	  Measurement	  for	  a	  Mul<ple	  Transi<ng	  System	  	Name	  of	  Candidate	

Orbital	  Period	Planet	  Radius	

Kepler-­‐89b	

3.7	  days	

0.13	  RJ	

Kepler-­‐89c	

10.4	  days	

0.31	  RJ	

Kepler-­‐89d	22.3	  days	

0.83	  RJ	

Kepler-­‐89e	54.3	  days	

0.49	  RJ	40∆v [m s-1]

20

Kepler-89 (KOI-94):

0

Teff = 6116 ± 30 K
λ = -6° -11° +13°
VsinIs = 8.01 ± 0.73 km/s
T.H.+ 2012b, ApJ Letters-20

Residual [m s-1]

-40
30
20
100-10-20-30

Kepler-89d	-0.01-0.005

0Orbital Phase

0.005

0.01

This result was later confirmed
by Albrecht et al. (2013)

Mul<ple	  transi<ng	  systems	  are	  generally	  aligned!	
← RM measurements for Kepler-25(multi-planet system):	

1552.0•1051.5•101051.0•10500−5−10−150.230.26

O − C (m s−1)

1050−5−20020

Teff = 6190 ± 80 K
λ = 7°±8°
VsinIs = 8.7 ± 1.3 km/s

12v sin i (km s−1)

RV (m s−1)45.0•10101210Obliquity measurements for other multi8planetsystems generally show good spinorbit alignment (Sanchis-Ojeda et al. 2012,
6Huberet al. 2013).
86−10−15

The only−20
exception
is 20
Kepler-56 (multiple,0but misaligned;λ (deg)
Huber et al. 2013).	
0−6−4−2Time (hr)0242.0•1044.0•1046.0•1048.0•1051.0•1051.2•1051.4•10

Albrecht et al. 2013, ApJ

A companion is present outside of the planetary system, which might beresponsible for the misalignment in Kepler-56. 	

Summary	  of	  RM	  Measurements	
proj. obliquity [deg]180150120|λ|	WASP-8 b
HAT-P-11 b

9060

HD 80606 b

30
HD 17156 b

05000

6000

7000

8000v sin istar [km s-1]

8060
40205000

6000

7000
Teff [K]8000

Albrecht et al. 2012	Correla<on	  between	  Stellar	  Obliquity	  and	  Rela<ve	  Tidal	  Timescale	

Albrecht et al. 2012	

180

proj. obliquity [deg]|λ|	HAT−P−7 b

150
WASP−8 b

120

WASP−33 b

HAT−P−11 b

HAT−P−32 b

90

WASP−12 b60

HD 80606 b

XO−3 b30

KOI−13 b
HD 17156 b

0100

102
104
106
relative tidal−dissipation timescales τCE τRA [yr]108

↑ relative tidal damping timescale of stellar obliquity(based on Zahn 1977)	
Assuming that planet-planet scatterings are the dominant channel for the formation of HJ
subsequent tidal interactions “realign” the stellar spin and the planet orbital axes. 	

Quiescent	  v.s.	  Chao<c	  migra<ons	• Quiescent	  migra<ons	  (i.e.,	  disk-­‐planet	  interac<ons):	  ü The	  presence	  of	  close-­‐in	  planets	  in	  mean	  mo<on	  resonance	  	  ü Mul<ple	  transi<ng	  systems	  are	  generally	  aligned.	  	  ü Misaligned	  systems	  are	  formed	  by	  stellar	  internal	  gravity	  waves	  independently	  of	  the	  planets?	  (Rogers	  et	  al.	  2012)	  • Chao<c	  migra<ons:	  ü The	  correla<on	  between	  the	  stellar	  obliquity	  and	  rela<ve	  <dal	  damping	  <mescale	  ü Existence	  of	  highly	  eccentric	  hot	  Jupiters	  (e.g.,	  HD	  80606b)	

To	  Se^le	  This	  Issue…	
Previous Targets of RM Measurements	
host	  star	Single	  Transi<ng	  System	 Mul<ple	  Transi<ng	  System	cool	  (Teﬀ	  <	  6250	  K)	many	a	  few	

hot	  (Teﬀ	  >	  6250	  K)	many	

No	  observa<on	ü There are a few hot multiple
systems detected by Kepler (e.g.,
KOI-89).

Worth a try!	

proj. obliquity [deg]ü So far, no hot multiple systems
have been investigated for
obliquity measurements.

150
120

WASP-8 b
HAT-P-11 b

9060

HD 80606 b

30
HD 17156 b

05000

6000

7000

8000

80v sin istar [km s-1]

ü One solution to partly settle thedebate is to observe the RM
effect for “hot multiple” systems.

180

60
40
20

5000

6000

7000
Teff [K]8000Towards	  Smaller	  Planets	

Limita<on	  of	  the	  RM	  Measurements	
a. The	  RM	  measurements	  have	  been	  conducted	  for	  systems	  with	  hot	  Jupiters	  (Neptunes).	  	  b. When	  the	  size	  of	  the	  transi<ng	  planet	  becomes	  small	  (~	  Earth-­‐sized	  planet),	  the	  detec<on	  of	  the	  RM	  eﬀect	  becomes	  very	  challenging.	  
→ ΔvRM 〜 - f ・ V sin Is・√(1-b^2)	

c. In	  order	  to	  conﬁrm	  or	  refute	  possible	  hypothesis	  on	  the	  planetary	  migra<on	  (and	  relevant	  <dal	  interac<on),	  we	  need	  to	  expand	  the	  parameter	  space	  for	  which	  the	  spin-­‐orbit	  angle	  is	  inves<gated.	  ü From	  such	  light-­‐curves,	  we	  can	  es<mate	  the	  rota<onal	  periods	  of	  planet	  hos<ng	  stars.	  	  KOI 988

1.0151.010
1.005
1.000
0.995
0.990
0.985
210

220230BJD−2454900 [days]240

2.0•104
1.5•104
Powerü Some	  of	  the	  light-­‐curves	  taken	  by	  Kepler	  spacecrar	  show	  periodic	  ﬂux	  varia<ons	  due	  to	  rota<on	  of	  starspots.	  	  Relative flux

Es<mate	  of	  Stellar	  Rota<on	  Periods	

1.0•104
5.0•103
005

1015
Period of rotation [days]20

Es<ma<on	  of	  Stellar	  Inclina<ons	  by	  Starspots	
12534/%-).&#+-43)46+$$-%334&)$5+/)46+$

λI$
I.

7!"#$%&'%&($)*+&%,-+./0ü The rotational period Ps of the host star is estimated by Kepler photometry.
ü The projected rotational velocity (V sin Is) and stellar radius are estimatedby spectroscopy.		
We can estimate stellar inclination Is.	
a.

Since	  the	  orbital	  inclina<on	  of	  a	  transi<ng	  exoplanet	  is	  close	  to	  90°,	  a	  small	  value	  of	  Is	  implies	  a	  spin-­‐orbit	  misalignment.	  	  

b.

This	  method	  can	  be	  applied	  regardless	  of	  the	  size	  of	  the	  planet,	  enabling	  us	  to	  discuss	  spin-­‐orbit	  alignment/misalignment	  for	  smaller	  exoplanets.	  Results	  1	We observed about 10 KOI systems and estimated VsinIs along with stellar radii.	
20V sin Is [km s-1]

Is=90omultiple	

15262269

y axis ->	
projected rotational
velocities estimatedby spectroscopy	

Is=45o974

10x axis -> rotational velocities
estimated by Kepler
photometry	257

Is=30o

280

5367

261
00510Veq [km s-1]

1520

Solid line indicates
Veq = V sin Is,
suggesting spin-orbitalignments.	

T.H.+ 2012, ApJ, 756, 66	

KOI-261 may have a possible spin-orbit misalignment along
the line-of-sight.	

Results	  2	We observed additional 25 systems. 	
2010(a) single

V sin Is [km s-1]

15V sin Is [km s-1]

Is=90oIs=45o10
2002
323

5o

Is=30

1890

0058
Is=45o6Is=30o4
2261
98822026
285

Is=90o(b) multi

304

10-1
Veq [km s ]1520002

46Veq [km s-1]

8T.H.+ 2014, ApJ	ü All the systems here have only Earth- or Neptune-sized planets.
ü Some multiple systems show possible spin-orbit misalignment. 	

10

Posterior	  distribu<ons	  of	  I	s2.5blue single
red multi

Probability Density

2black isotropic	

1.5
10.5
000.2

0.4

0.6
0.8
Is [radian]

11.2

1.4

ü We computed the posterior distribution of Is for each system.
ü The solid lines indicate the averaged posteriors for single and multiple systems.
ü The two distributions (red and blue) seem slightly different from each other.

Summary	
1. Measurements	  of	  the	  stellar	  obliquity	  have	  revealed	  a	  diversity	  in	  the	  spin-­‐orbit	  rela<on,	  and	  yielded	  new	  hypotheses	  on	  the	  dynamical	  origin	  of	  exoplanets.	  	  2. Observa<onal	  results	  of	  the	  RM	  measurement	  imply	  that	  some	  close-­‐in	  giant	  planets	  have	  experienced	  quiescent	  migra<on	  (e.g.,	  Kepler-­‐89),	  while	  others	  are	  produced	  by	  more	  chao<c	  processes.	  The	  reason	  for	  this	  discrepancy	  between	  the	  two	  dynamical	  origins	  is	  not	  known.	  	  	  3. Measurement	  of	  the	  stellar	  inclina<on	  is	  a	  unique	  technique	  to	  discuss	  spin-­‐orbit	  rela<ons	  for	  systems	  with	  smaller	  planets.	  Previous	  observa<on	  showed	  that	  transi<ng	  systems	  with	  small	  planets	  generally	  have	  good	  spin-­‐orbit	  alignment.	  The	  distribu<ons	  of	  stellar	  inclina<ons	  for	  single	  and	  mul<ple	  systems	  show	  a	  slight	  diﬀerence	  (Morton	  &	  Winn	  2014).