Re-evaluating the Very Hot Gas Giant WASP-12b

Re-evaluating the Very Hot
Gas Giant WASP-12b
Ian Crossfield (MPIA)
2012.07.17
Work done in collaboration with:
Travis Barman, Brad Hansen,
and Ichi Tanaka
1

Summary of Results:
● An M0V star located only 1'' from WASP-12 has
diluted past eclipse and transit analyses (by >1σ).
● In a narrow band (2.315 µm), WASP-12b's eclipse is
marginally deeper: T B = 3600 ± 200 K.
● WASP-12b has a nearly isothermal NIR
photosphere, and its composition cannot be
meaningfully constrained with present eclipse
measurements.
2

E
Transiting Planets with Measured Masses:
Sub-Neptunes/
Super-Earths
Hot
Jupiters
3

Transiting Planets with Measured Masses:
E
WASP-12b
4

The Extreme Planet WASP-12b:
Period ~ 1 day
Eq. Temp ~ 3,000 K
Radius ~ 1.7 R_Jup
Density ~ 0.3 g/cc
Li+2010
5

Modeling of initial eclipse photometry
suggested that C/O ≥ 1 for WASP-12b
Planet/star Flux Ratio (10 -3 )
Croll+2011
Campo+2011
Madhusudhan+2011
Madhusudhan+2011
6

Modeling of initial eclipse photometry
suggested that C/O ≥ 1 for WASP-12b
Planet/star Flux Ratio (10 -3 )
Croll+2011
Campo+2011
chi^2 ~ 10
Madhusudhan+2011
Madhusudhan+2011
7

Modeling of initial eclipse photometry
suggested that C/O ≥ 1 for WASP-12b
Planet/star Flux Ratio (10 -3 )
Croll+2011
Campo+2011
Madhusudhan+2011
Madhusudhan+2011
8

Step 1: Subaru/MOIRCS narrowband 2.3 µm
secondary eclipse photometry of WASP-12b
9

DATA &
MODEL
(photometry
binned for plotting)
RESIDUALS
TIME →
Crossfield et al.
submitted
Narrowband 2.3µm
eclipse is deeper
than expected:
0.41 +/- 0.05 %.
Duration and time of
eclipse are as expected.
10

Planet/star Flux Ratio (10 -3 )
Croll+2011
Campo+2011
Madhusudhan+2011
Madhusudhan+2011
11

Planet/star Flux Ratio (10 -3 )
Croll+2011
Cowan+2012
Campo+2011
Madhusudhan+2011
Madhusudhan+2011
12

Campo+2011
Cowan+2012
4.5µm Eclipses of WASP-12b:
0.382 ± 0.019 %
0.39 ± 0.03 %
(very prolate planet)
Or
0.50 ± 0.04 %
(non-prolate planet)
13

Campo+2011
Cowan+2012
4.5µm Eclipses of WASP-12b:
0.382 ± 0.019 %
A consistent analysis of all Spitzer data,
and further measurements, are called for!
0.39 ± 0.03 %
(very prolate planet)
Or
0.50 ± 0.04 %
(non-prolate planet)
14

A fainter star very close to WASP-12
has diluted past eclipse measurements
Δi = 4.0 mag
Bergfors et al. 2011,
Bergfors et al. submitted
Bergfors-2
See Carolina
Bergfors' poster!
15

Step 2: IRTF/SpeX Imaging of
WASP-12 and Bergfors-2.
16

IRTF/SpeX K-band imaging shows that
Bergfors-2 is redder than WASP-12
Δi = 4.0 mag
Bergfors et al. 2011
ΔK = 2.5 mag
Eclipse dilution is greater at longer λ
Crossfield et al., submitted
17

Step 3: Archival Keck2/NIRSPEC spectra of
WASP-12 and its nearby, faint companion
18

Transit/Eclipse
contamination
Keck/NIRSPEC spectra reveal
Bergfors-2 to be an M0 dwarf:
Data
Model
Crossfield et al., submitted
19

WASP-12b spectrum (as measured):
Crossfield et al., submitted
20

Dilution-corrected planetary spectrum:
Crossfield et al., submitted
21

The dilution-
corrected planetary
spectrum is very
nearly a blackbody:
chi^2 k BIC
Blackbody ~15 2 19
C/O > 1 ~10 >10 >32
Crossfield et al., submitted
22

The similarly hot (~3200 K)
planet WASP-18b also closely
matches a blackbody:
chi^2 k BIC
Blackbody 7 2 10
Rad. Transf. ~4 >6 >12
Nymeyer+2011
23

The dilution-
corrected planetary
spectrum is very
nearly a blackbody:
A high C/O ratio cannot be defended
when a two-parameter (blackbody) model fits as well
as do many-parameter (radiative-transfer) models.
chi^2 k BIC
Blackbody ~15 2 19
C/O > 1 ~10 >10 >32
Crossfield et al., submitted
24

A high C/O ratio cannot be defended
when a two-parameter (blackbody) model fits as well
as do many-parameter (radiative-transfer) models.
chi^2 k BIC
Blackbody ~25 2 29
C/O > 1 ~10 >10 >32
25

The dilution-
corrected planetary
spectrum is very
nearly a blackbody:
Preliminary!
See Ernst de
Mooij's poster.
Swain et al.,
submitted
chi^2 k BIC
Blackbody ~15 2 19
C/O > 1 ~10 >6 >23
Crossfield et al., submitted
26

Followup
observations will
confirm whether we
are seeing excess
2.3µm emission --->
Crossfield et al., submitted
27

Step 4: Keck1/MOSFIRE Multi-Object
Eclipse Spectroscopy of WASP-12b:
scheduled for Oct. 2012
28

Conclusions:
● An M0 dwarf is located only 1” from
WASP-12: observers must correct for
this object! Also: is it physically
associated with WASP-12?
● WASP-12b has a nearly isothermal
NIR photosphere, so its C/O ratio
cannot be uesfully constrained with
the present data.
● Controversies remain:
● How prolate is WASP-12b?
● What is the correct 4.5 µm flux?
● Additional Spitzer measurements can
resolve both these issues!
Crossfield et al., submitted
29

WASP-12b 2.315µm eclipse:
Residual behavior
Ingress timescale
31

de Mooij poster;
Preliminary!
Swain et al.,
submitted
??
32

Planet/Star Flux Density (10 -3 )
More physically motivated models
do not significantly improve the fit.
z J H K 3.6 4.5 5.8 8.0
A high C/O ratio cannot be defended
when a two-parameter (blackbody) model fits as well
as many-parameter (radiative-transfer) models.
33

Planet/Star Flux Density (10 -3 )
Followup observations will confirm whether we
are seeing excess narrowband emission.
z J H K 3.6 4.5 5.8 8.0
34