J/AJ/160/230 WASP-31b and host star radius compared with IMACS (McGruder+, 2020)
ACCESS: confirmation of no potassium in the atmosphere of WASP-31b.
McGruder C.D., Lopez-Morales M., Espinoza N., Rackham B.V., Apai D.,
Jordan A., Osip D.J., Alam M.K., Bixel A., Fortney J.J., Henry G.W.,
Kirk J., Lewis N.K., Rodler F., Weaver I.C.
<Astron. J., 160, 230 (2020)>
=2020AJ....160..230M 2020AJ....160..230M
ADC_Keywords: Exoplanets; Stars, diameters; Spectra, optical
Keywords: Exoplanet atmospheres ; Observational astronomy ; Exoplanets ;
Hot Jupiters ; Spectroscopy
Abstract:
We present a new optical (400-950nm) transmission spectrum of the hot
Jupiter WASP-31b (M=0.48MJup; R=1.54RJup; P=3.41days), obtained by
combining four transit observations. These transits were observed with
IMACS on the Magellan Baade Telescope at Las Campanas Observatory as
part of the ACCESS project. We investigate the presence of
clouds/hazes in the upper atmosphere of this planet, as well as the
contribution of stellar activity on the observed features. In
addition, we search for absorption features of the alkali elements NaI
and KI, with particular focus on KI, for which there have been two
previously published disagreeing results. Observations with Hubble
Space Telescope (HST)/STIS detected KI, whereas ground-based low- and
high- resolution observations did not. We use equilibrium and
nonequilibrium chemistry retrievals to explore the planetary and
stellar parameter space of the system with our optical data combined
with existing near-IR observations. Our best-fit model is that with a
scattering slope consistent with a Rayleigh slope
(α=5.3-3.1+2.9), high-altitude clouds at a log cloud top
pressure of -3.6-2.1+2.7bars, and possible muted H2O features. We
find that our observations support other ground-based claims of no KI.
Clouds are likely why signals like H2O are extremely muted and Na or K
cannot be detected. We then juxtapose our Magellan/IMACS transmission
spectrum with existing VLT/FORS2, HST/WFC3, HST/STIS, and Spitzer
observations to further constrain the optical-to-infrared atmospheric
features of the planet. We find that a steeper scattering slope
(α=8.3±1.5) is anchored by STIS wavelengths blueward of
400nm and only the original STIS observations show significant
potassium signal.
Description:
We observed four transits of WASP-31b on UT dates UT130226, UT130425,
UT140222, and UT190314 (UTYYMMDD) with namori Magellan Areal Camera
and Spectrograph (IMACS) on the 6.5m Baade Magellan Telescope at Las
Campanas Observatory in Chile. See details of observations in table 2.
Objects:
--------------------------------------------------------
RA (2000) DE Designation(s) (Period)
--------------------------------------------------------
11 17 45.36 -19 03 17.2 WASP-31 = WASP-31
11 17 45.36 -19 03 17.2 WASP-31b = WASP-31b (P=3.41d)
--------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 63 4 Observing Log for WASP-31b Data Sets from
Magellan/IMACS
table6.dat 107 36 Magellan/IMACS optical transmission spectrum
(planet radius/star radius,p) for each of our
four transit epochs
table7.dat 44 30 Combined transmission spectrum (planet radius/star
radius) for each of our four transit epochs
--------------------------------------------------------------------------------
See also:
J/A+A/531/A60 : WASP-31b photometry and radial velocities (Anderson+, 2011)
J/ApJ/736/12 : Transit light curves of GJ1214 (Berta+, 2011)
J/MNRAS/419/2233 : HD 80606 transits (Colon+, 2012)
J/A+A/564/A125 : AGN Torus model comparison of AGN in CDFS (Buchner+, 2014)
J/ApJ/791/55 : HD 189733b in transit light curve (McCullough+, 2014)
J/MNRAS/446/2428 : WASP-31b:HST/Spitzer transmission spectra (Sing+, 2015)
J/AJ/152/204 : HARPS-N radial velocities of HD 179070 (Lopez-Morales+,2016)
J/AJ/153/191 : Transiting planet GJ 1132 (Southworth+, 2017)
J/A+A/616/A145 : GTC transit light curves of WASP-127b (Chen+, 2018)
J/A+A/614/A35 : Differential photometry of GJ1214 (Mallonn+, 2018)
J/A+A/624/A62 : HAT-P-32b differential photometry time serie (Mallonn+,2019)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 I4 yr Obs.Y [2013/2019] Observation year
6- 8 A3 "month" Obs.M Observation month
10- 11 I2 d Obs.D Observation day
13- 17 A5 "h:m" Obs.T-b Time of observation, begin
19- 23 A5 "h:m" Obs.T-e Time of observation, end
25- 28 F4.2 --- AirMmin [1.02] Minimum airmass
30- 33 F4.2 --- AirMmax [1.3/1.5] Maximum airmass
35- 36 I2 s Texp [27/60] Exposure time
38- 39 I2 s Texpmax [36]? Maximum exposurer time
41- 42 I2 s Read [26/31] Readout time
44- 46 I3 --- Frames [168/363] Frames
48- 50 A3 --- Bin Binning
52- 54 A3 --- Cam Camera
56- 58 I3 --- Rmin [295/739] Minimum resolution
60- 63 I4 --- Rmax [822/1233] Maximum resolution
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.3 nm lambdamin [401/847] Lower bound of wavelength range for
given bin
9- 15 F7.3 nm lambdamax [416/964] Upper bound of wavelength range for
given bin
17- 22 F6.4 --- RpRs1 [0.11/0.17]? Radius of planet of Radius of
star for transit UT130226 (1)
24- 30 F7.4 --- E_RpRs1 [0.002/0.02]? Upper bound of 1-sigma RpRs
uncertainty for transit UT130226
32- 38 F7.4 --- e_RpRs1 [-0.009/-0.002]? Lower bound of 1-sigma RpRs
uncertainty for transit UT130226
40- 45 F6.4 --- RpRs2 [0.12/0.14]? Radius of planet of Radius over
star for transit UT130425 (1)
47- 53 F7.4 --- E_RpRs2 [0.001/0.005]? Upper bound of 1-sigma RpRs
uncertainty for transit UT130425
55- 61 F7.4 --- e_RpRs2 [-0.005/-0.001]? Lower bound of 1-sigma RpRs
uncertainty for transit UT130425
63- 68 F6.4 --- RpRs3 [0.12/0.14]? Radius of planet of Radius over
star for transit UT140222 (1)
70- 76 F7.4 --- E_RpRs3 [0.001/0.007]? Upper bound of 1-sigma RpRs
uncertainty for transit UT140222
78- 84 F7.4 --- e_RpRs3 [-0.008/-0.001]? Lower bound of 1-sigma RpRs
uncertainty for transit UT140222
86- 91 F6.4 --- RpRs4 [0.11/0.14]? Radius of planet of Radius over
star for transit UT190314 (1)
93- 99 F7.4 --- E_RpRs4 [0.001/0.008]? Upper bound of 1-sigma RpRs
uncertainty for transit UT190314
101-107 F7.4 --- e_RpRs4 [-0.02/-0.001]? Lower bound of 1-sigma RpRs
uncertainty for transit UT190314
--------------------------------------------------------------------------------
Note (1): UT130226,UT130425, UT140222, and UT190314, respectively. The data
were produced implementing the reduction and detrending processes
discussed in Section 3. These depths do not include the offsets for
combining each spectra. Gaps in the spectra (see Figure 1, prevented a
few bins from exactly overlapping in wavelength space. Those bins were
still weighted averaged together (x and y direction), with the resulting
bin composing of the full wavelength width of all bins. In this table,
each bin for the combined transmission spectrum is separated by a
vertical line.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 F7.3 nm lambdamin [401/847] Upper bound of wavelength range for
given bin
9- 15 F7.3 nm lambdamax [416/964] Lower bound of wavelength range for
given bin
17- 23 F7.3 nm lambda [409/899] Mean wavelength for given bin
25- 30 F6.4 --- RpRs [0.12/0.14] Radius of planet over Radius of star
for combined spectra (1)
32- 37 F6.4 --- RpRsmin Minimum value for RpRs
39- 44 F6.4 --- RpRsmax Maximum value for RpRs
--------------------------------------------------------------------------------
Note (1): Combined transmission spectrum from transit epochs UT130425,
UT140222, and UT190314. The spectra were combined following the
procedure outlined in Section 4.1. In the retrieval analysis, because
the retrievals do not take asymmetric wavelength errors,the wavelength
range of the few overlapping bins were re-centered based on the weighted
mean wavelength of the bin.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 25-Jan-2021