Looking for atmospheric signatures of the exoplanet Qatar-1b
Carolina von Essen1 , Sergio A. Cellone2 , Simon Albrecht1
& Stefan Dreizler3
1: Stellar Astrophysics Centre, Århus, Dinamarca
2: IALP (CONICET-UNLP) and FCAG (UNLP)
3 Institut für Astrophysik, Georg-August-Universität Göttingen, Alemania
15 años de ciencia con Gemini en Argentina
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Planetario de La Plata, 1-5/jun/2015
Motivation
The formation and composition of a planetary atmosphere
depends mainly on:
• the evolutionary history of the planet
• its distance to the host star
• the position in the proto-planetary disk at which the planet was
formed
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Motivation
The formation and composition of a planetary atmosphere
depends mainly on:
• the evolutionary history of the planet
• its distance to the host star
• the position in the proto-planetary disk at which the planet was
formed
Studies of exoplanet atmospheres:
→
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probe exoplanet formation and evolution
Transit spectroscopy
Basic layout
Geometry of transit
spectroscopy:
the photons from the star are
filtered through the atmosphere
of the planet
(Tinetti et al. 2013, A&AR, 21, 63)
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Transit spectroscopy
Some previous results
Detected elements and molecules:
Na in HD 209458b (Charbonneau et al. 2002, ApJ, 568, 377; Sing et
al. 2008a, ApJ, 686, 658; 2008b, ApJ, 686, 667, with HST; Arribas et al.
2006, PASP, 118, 21, with WHT);
in HD 189733b (Redfield et al.
2008, ApJ, 673, L87)
K in X0-2b (Sing et al. 2011, A&A, 527, A73)
H2 O in HD 189733b (Deming et al. 2013, ApJ, 774, 95)
CH4 in HD 189733b (Swain et al. 2008, Nature 452, 329)
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Transit spectroscopy
Methodology
Most favourable conditions
• relatively bright host star
• large transit signal
• low planetary surface gravity
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Transit spectroscopy
Methodology
Most favourable conditions
• relatively bright host star
• large transit signal
• low planetary surface gravity
Also, in the particular case of low-resolution transmission
spectroscopy
• adequate reference stars within the field of view
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The target: Qatar-1b
Physical and geometrical characteristics
host star
ST
mass
RS
distance
V
K3V
0.85 M 0.82 R
∼ 200 pc
12.8 mag
planet
RP
1.16RJ
a
' 0.023 AU
T
∼ 1.42 d
i
83.47◦
surf. gravity
20 m/s2
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The target: Qatar-1b
Physical and geometrical characteristics
host star
ST
mass
RS
distance
V
K3V
0.85 M 0.82 R
∼ 200 pc
12.8 mag
planet
RP
1.16RJ
a
' 0.023 AU
T
∼ 1.42 d
i
83.47◦
surf. gravity
20 m/s2
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←− hot Jupiter
(Tsup & 1400 K)
The target: Qatar-1b
Observational conditions
100
QATAR−1
HD189733
HD209458
HATP−32
WASP−12
WASP−17
WASP−19
XO−2
Surface gravity (m/s2)
80
60
40
20
×
× ×
0
0.01
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0.015
0.02
0.025
Transit depth ([RP/Rs]2)
×
×
0.03
Observational setup
program:
instrument
wavelength coverage:
CCD read mode:
CCD binning:
slitlet size:
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GN-2014B-Q-47 (PI: Cellone)
GMOS-N (MOS mode) + B600 grating
∼ 500 →∼ 750 nm
(centered at the Na feature at 589 nm)
fast
4×2
∼ 30 (long) × 15 (width) arcsec
Observational strategy
Preimage and mask
←− Qatar 1
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Observational strategy
Spectra
←− Qatar 1
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Observational strategy
• 75 frames × 150 s integration each
• taken on September 2, 2014, between 08:10:32.7 UT and
12:03:50.0 UT:
◦ 20 before transit
◦ 35 during transit
◦ 20 after transit
• 1.43 ≤ airmass ≤ 2.06
• six field stars of similar brightness as Qatar-1A as reference
→
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differential spectro-photometry (Bean et al. 2010, Nature, 468, 669)
Data reduction
Gemini-IRAF standard tasks:
• overscan subtraction
• bias subtraction
• flat-fielding
• wavelength calibration (Cu-Ar)
• extraction of spectra:
◦ apertures: 1, 2, 3, 5, 8, 10, 15 ×hFWHMi
(hFWHMi ' 2 binned pix ≡ 0.6 arcsec)
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White light curve analysis
Selection of best aperture and reference star
White light curves were constructed (for each aperture) by:
• integrating fluxes between 550 and 750 nm
• dividing Qatar-1 / reference star (different combinations)
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White light curve analysis
Selection of best aperture and reference star
White light curves were constructed (for each aperture) by:
• integrating fluxes between 550 and 750 nm
• dividing Qatar-1 / reference star (different combinations)
Looked for minimum scatter in:
• off-transit data points
• on-transit data points after least-squares transit fit
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White light-curve analysis
Results:
best aperture: r = 2 × hFWHMi = 1.2 arcsec
best reference stars: RS2 (shown in blue) and RS1 (green)
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White light-curve analysis
Transit fitting
• transit model (Mandel & Agol 2002, ApJ, 580, L171):
a/RS : normalized sma
i: orbital inclination
RP /RS : planet radius / star radius ratio
T0 mid-transit time
• “detrending” function:
◦ airmass (cubic)
◦ seeing (linear)
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White light-curve analysis
Transit fitting
detrending function
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White light curve analysis
Results
1
Normalized flux
0.995
0.99
0.985
0.98
Residuals
0.975
1.002
1
0.998
-0.04
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-0.02
0
0.02
Orbital phase
0.04
-0.04
-0.02
0
0.02
Orbital phase
0.04
White light-curve analysis
Results
Parameter
a/RS
i [deg]
RP /RS
T0 − 2456092 [JD]
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This work RS1
6.424 ± 0.077
84.51 ± 0.18
0.1467 ± 0.0008
0.93881 ± 0.00006
This work RS2
6.594 ± 0.098
84.86 ± 0.21
0.1433 ± 0.0008
0.93892 ± 0.00006
White light-curve analysis
Results
Parameter
a/RS
i [deg]
RP /RS
P [days]
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von Essen et al. (2013)
6.42 ± 0.10
84.52 ± 0.24
0.1435 ± 0.0008
1.4200246 ± 0.0000004
Maciejewski et al. (2015)
6.319+0.070
−0.068
84.26+0.17
−0.16
0.14591+0.00076
−0.00078
1.42002406 ± 0.00000021
Results
(so far . . . )
White light-curves with excellent S/N have been obtained for
a transit of Qatar-1b
To be done . . .
• construction of transit light-curves in several (up to 29) different
spectral ranges (each one ∼ 15 → 20 nm wide)
• look for changes in RP /RS between different wavelength
ranges, consistent with an Na absorption feature in the planet’s
atmosphere
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¡Muchas gracias!
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