Avi M. Mandell NASA GSFC Collaborators :

Exoplanet Transit SpectroscopyFebruary 7, 2014

Avi M. MandellNASA GSFC

Collaborators:Korey HaynesEvan SinukoffDrake DemingAdam Burrows

Nikku Madhusudhan

Mark ClampinDon Lindler

Natasha BatalhaHeather Knutson(others as well)

Spectroscopy of Water and Organics in Exoplanet Atmospheres:

First Detections and What the Future Holds


Henry et al. 1999

What is aExoplanet Transit?


How Do We Learn About the Atmospheresof Transiting Planets?

• Exoplanet transits provide the opportunity to probe the absorption in a planet’s atmosphere

– The more absorption, the deeper the depth of the transit… but absorption depends on abundance, temperature, optical depth

– As starlight passes through the atmosphere of a planet, atoms and molecules absorb at different wavelengths Planet Cross-Section


HST / WFC3 Grism Spectroscopy: Resolving Molecular Absorption

• Wavelength range (1.1 – 1.7 μm) samples water bands at 1.15 and 1.4 μm as well as several hydrocarbons and continuum regions on either side

• Can answer major questions about temperature and chemistry

• But at LOW resolution over a NARROW bandpass, degeneracies still remain!


Deming et al. Program (Cycles 18 & 19)• Large collaboration

focused on hot giant exoplanets

• Sample of 16 objects• A number of planets may have

upper-atmosphere temperature inversions or high C/O ratios

• We started with several interesting (and outlying) cases:

• WASP-12: Very hot, first possible carbon-rich exoplanet, but results now in dispute

• WASP-17: Ultra-low density, retrograde orbit

• WASP-19: Shortest-period planet known (P ~ 19 hr) but no temperature inversion

• WASP-33: Very hot and massive, orbiting an A-type star, possibly carbon-rich

CoRoT-1 b

CoRoT-2 bHAT-P-7 bHAT-P-12 b

HAT-P-13 b

HD189733 bHD209458 bTrES-2 bTrES-3 bTrES-4 bWASP-4 bWASP-12 b

WASP-17 bWASP-18 bWASP-19 bXO-1 bWASP-33 b

List of Observed Planets

WASP-19

WASP-12

WASP-17

WASP-4

WASP-33

TransitsEclipses

Exoplanet Transit SpectroscopyFebruary 7, 2014Transit Spectra Analysis:

Systematics Removal Through Self-Calibration1. We used the divide-oot

method (Berta et al. 2012) to fit the band-integrated light curve

2. We subtracted the model from the raw light curve to obtain the residual systematic variation; additional trends due to spectral drift were also measured

3. We created a model for each wavelength bin, with a scaling parameter for each possible systematic trend in the data and an overall visit-long slope

WASP-12

WASP-17

WASP-19

WASP-17


• Primary Result: Amplitude of water absorption band is lower than expected (based on previous Spitzer obs.)

• Due to either:1.An unexplained haze layer

that increases the continuum opacity below a certain altitude

2.Less water due to non-solar abundances(T ~ 2500K)

(T ~ 2900K)

(T ~ 2000K)


1.A2.23.Cooler planets

seem to show well-defined spectral features, while hotter planets are ambiguous…

NEED MORE PLANETS and MORE SPECTRAL

COVERAGE

• Primary Result: Amplitude of water absorption band is lower than expected (based on previous Spitzer obs.)

• Due to either:1.An unexplained haze layer

that increases the continuum opacity below a certain altitude

2.Less water due to non-solar abundances

(T ~ 2000K)

(T ~ 1800K)

(T ~ 1700K)


Eclipse Spectra Analysis:• We again used the divide-oot

method to fit the band-integrated light curve,

• WASP-33 presents additional complications due to Delta Scuti oscillations in the parent star

• Band-integrated eclipse depths are much more uncertain than the transit measurements due to the low eclipse-to-noise ratio

• WASP-4 is especially problematic due to very little temporal coverage during eclipse


Tplan ~ 2200K

• WASP-4 Preliminary Result: WFC3 data appear to match up with the thermal-inversion atmosphere model from Beerer et al. 2011; however, a blackbody seems to be an even better fit

(T ~ 2500K)

(T ~ 2900K)

• The spectrum seems to show a slight peak at 1.4 microns, indicative of a possible strong inversion

• However, this model does not match the Spitzer data well

• A blackbody with Tplan = 2200 K provides an excellent fit to all existing data


• WASP-12 Preliminary Result: WFC3 data appear to support a carbon-rich model, showing no sign of the expected deep absorption band.

• However, as noted in Crossfield et al. 2012, correcting the Spitzer data for the nearby companions leads to an isothermal interpretation


• WASP-33 Preliminary Result: WFC3 data strongly support a model with no thermal inversion, and models that are carbon-rich fit better

• Further modeling is required to determine whether we can break degeneracies between temperature and composition


• JWST will provide sensitivity gains of more than an order of magnitude

• We are preparing to adapt our WFC3 analysis pipeline to JWST, based on current instrument models by M. Clampin & D. Lindler

Simulated Hot Super-Earth(Teq ~ 500K) around anM-star at 30 pc

SimulatedHabitableSuper-Earth(Teq ~ 300K)around an M-star at 20 pc

H2OAbs. H2O

Abs.

CO2

Abs.

Deming et al. 2009

The Future of Space-Based Characterization:JWST (of course)

JWST/NIRSPEC Simulations• For hot

Jupiters, the real test lies in which instruments and filters to use in order to MOST EFFICIENTLY constrain the atmospheric parameters

JWST Wavelength Coverage & Resolution

H2OCH4

H2O

H2O

COCO2

CO

CH4

HCN

C2H2 CO


JWST NIRSPEC Simulator1. Begins with In-

transit and Out-of-transit model

2. Maps onto pixel space

3. Convolves with PSF, multiplies by PRF

4. Add noise sources Zodiacal and

stray light Flat field errors Poisson and read

noise Spacecraft jitter

and drift

Images from Don Lindler, results from Batalha et al. (JWST White Paper)

14 pc, V = 154.5 pc

H2O & CH4

M-type host star4 MEarth planet25 transits


Pre-JWST Characterization: Low-Cost NIR Spectroscopy from a Balloon?

• Ultra-long duration (ULD) balloon platforms offer the potential for long-term, stable monitoring of transiting planets above almost all telluric contamination– As low as 1 - 2% of an equally-capable space mission

• Test flight using the Wallops Arc Second Pointer (WASP) gondola system planned for September 2014– Use of existing and off-the-shelf parts will allow us to benchmark the current

limits for stability and thermal control


Conclusions• The WFC3 instrument on HST has now been

validated as a reliable platform for high-precision exoplanet transit observations

• Observations of Hot Jupiters are revealing unexpected mysteries– Hazes and/or aerosols may be common, but vary with

planet properties

– Thermal emission measurements suggest blackbody emission at NIR wavelengths may be ubiquitous; unclear if this is due to thermal or compositional factors, and why it appears so uniform

• Increased S/N and larger wavelength coverage (combining Spitzer, HST and ground) will be necessary to grapple with these questions– JWST will clearly change the landscape dramatically, but

observing time will be precious, so we must pre-select targets for follow-up


Questions?

Avi M. Mandell NASA GSFC Collaborators :

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