J/AJ/159/239 Transmission Spectroscopy Metric of exoplanets (Guo+, 2020)
Updated parameters and a new transmission spectrum of HD 97658b.
Guo X., Crossfield I.J.M., Dragomir D., Kosiarek M.R., Lothringer J.,
Mikal-Evans T., Rosenthal L., Benneke B., Knutson H.A., Dalba P.A.,
Kempton E.M.R., Henry G.W., McCullough P.R., Barman T., Blunt S.,
Chontos A., Fortney J., Fulton B.J., Hirsch L., Howard A.W., Isaacson H.,
Matthews J., Mocnik T., Morley C., Petigura E.A., Weiss L.M.
<Astron. J., 159, 239 (2020)>
=2020AJ....159..239G 2020AJ....159..239G
ADC_Keywords: Exoplanets; Spectra, infrared; Radial velocities;
Stars, diameters; Photometry, infrared; Effective temperatures
Keywords: Transit photometry ; Hubble Space Telescope ; Exoplanet atmospheres ;
Radial velocity
Abstract:
Recent years have seen increasing interest in the characterization of
sub-Neptune-sized planets because of their prevalence in the Galaxy,
contrasted with their absence in our solar system. HD97658 is one of
the brightest stars hosting a planet of this kind, and we present the
transmission spectrum of this planet by combining four Hubble Space
Telescope transits, 12 Spitzer/IRAC transits, and eight
Microvariability and Oscillations of Stars Telescope (MOST) transits
of this system. Our transmission spectrum has a higher signal-to-noise
ratio than those from previous works, and the result suggests that the
slight increase in transit depth from wavelength 1.1-1.7µm reported
in previous works on the transmission spectrum of this planet is
likely systematic. Nonetheless, our atmospheric modeling results are
inconclusive, as no model provides an excellent match to our data.
Nonetheless, we find that atmospheres with high C/O ratios (C/O~>0.8)
and metallicities of ~>100 solar metallicity are favored. We combine
the mid-transit times from all of the new Spitzer and MOST
observations and obtain an updated orbital period of
P=9.489295±0.000005, with a best-fit transit time center at
T0=2456361.80690±0.00038(BJD). No transit timing variations are
found in this system. We also present new measurements of the stellar
rotation period (34±2days) and stellar activity cycle (9.6yr) of
the host star HD97658. Finally, we calculate and rank the Transmission
Spectroscopy Metric of all confirmed planets cooler than 1000K and
with sizes between 1R⊕ and 4R⊕. We find that at least a
third of small planets cooler than 1000K can be well characterized
using James Webb Space Telescope, and of those, HD97658b is ranked
fifth, meaning that it remains a high-priority target for atmospheric
characterization.
Description:
Based on Wide Field Camera 3 (WFC3) observations during two Hubble
Space Telescope (HST) visits in 2013-December-19 and 2014-January-7
(HST program 13501, PI:Knutson) the first transmission spectrum of
HD97658b from 1.1 to 1.7µm was rerported.
Other observations were conducted on 2016-April-20 and 2017-January-31
under the HST program 13665 (PI:Benneke) the Space Telescope Imaging
Spectrograph (STIS) using the G750L grism (0.524-1.027µm).
Six transits were observed with the The Infrared Array Camera (IRAC)
3.6µm channel, and five transits were observed with the 4.5µm
channel from 2014-July to 2016-April under Spitzer program 11131. Each
transit was observed with 0.08s exposure per frame and approximately
0.13s per frame cadence.
Microvariability and Oscillation of Stars (MOST) is a microsatellite
carrying a 15cm optical telescope that acquires light through a
broadband filter spanning the visible wavelengths from 350 to 700nm.
It is in a Sun-synchronous polar orbit with a period of 101.4minutes,
which allows it to monitor stars in a Continuous Viewing Zone (CVZ)
without interruption for up to 8weeks. The CVZ covers a declination
range of +36deg>δ>-18deg. HD97658 was observed by MOST in Direct
Imaging mode, in which defocused images of the stars were projected
directly onto the CCD. The exposure times were all 1.5s, and the
observations were stacked on board the satellite in groups of 21 for a
total integration time of 31.5s per data point.
Since 1997 January, we have collected 553 radial velocity measurements
with the High Resolution Echelle Spectrometer (HIRES) on the Keck I
Telescope on Maunakea and 215 measurements with the Levy spectrograph
on the Automated Planet Finder at Lick Observatory (APF). The HIRES
data were often taken in sets of three due to the short ∼2min
exposures to mitigate the effects of stellar oscillations; this was
not necessary for the APF due to the smaller aperture and longer
exposure times (∼10-20min exposures).
Objects:
-------------------------------------------------------------------
RA (ICRS) DE Designation(s) (Period)
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11 14 33.16 +25 42 37.4 HD97658 = HD 97658 (P=9.49)
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table6.dat 37 767 Radial velocities of HD97658
table11.dat 67 1404 Transmission Spectroscopy Metric of confirmed
planets with R⊕<Rplanet<4R⊕,
and cooler than 1000K
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/A+A/503/601 : HD17156 transit photometry & radial velocities (Barbieri+,2009)
J/A+A/520/A66 : CoRoT-8b light and RV curves (Borde+, 2010)
J/ApJ/725/875 : Chromospheric activity for CPS stars (Isaacson+, 2010)
J/A+A/529/A75 : Limb-darkening coefficients (Claret+, 2011)
J/ApJ/747/35 : HST/WFC3 transit observation of GJ1214b (Berta+, 2012)
J/ApJ/772/L2 : Keck/HIRES radial velocities for HD 97658 (Dragomir+, 2013)
J/ApJ/786/2 : Spitzer photometric time series of HD 97658 (Van Grootel+,2014)
J/AJ/150/169 : Radial velocities of HD 6434 (Hinkel+, 2015)
J/ApJ/848/34 : CATalog of Stellar Unified Properties (Hinkel+, 2017)
J/AJ/153/191 : Transiting planet GJ 1132 (Southworth+, 2017)
J/AJ/155/66 : Stroemgren photometric observations GJ436b (Lothringer+, 2018)
J/A+A/631/A90 : K2-138 HARPS radial velocities (Lopez+, 2019)
J/AJ/157/33 : Radial velocity exploration of σ Eridani (Mawet+, 2019)
J/AJ/157/192 : Radial velocities and transit times for KOI 4 (Chontos+, 2019)
Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d BJD [2450463/2458560] Barycentric Julian Date,
TDB system
15- 20 F6.2 m/s RVel [-20.58/14.62] Radial Velocity
22- 25 F4.2 m/s e_RVel [0.91/7.78] Uncertainty in RVel
27- 31 F5.3 --- SHK [0.149/0.379] Stellar activity indicator, Calcium
H & K lines (1)
33- 37 A5 --- Inst Instrument used (2)
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Note (1): Isaacson & Fischer, 2010, J/ApJ/725/875.
Note (2): Instruments as follows:
APF = Automated Planet Finder at Lick Observatory (214 occurrences)
HIRES = High Resolution Echelle Spectrometer on the Keck I Telescope
in Maunakea (553 occurrences)
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Byte-by-byte Description of file: table11.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Name Planet name
18- 21 F4.2 Rsun Rstar [0.12/2.94] Stellar radius
23- 26 I4 K Teff [2559/7070] Stellar effective temperature
28- 33 F6.3 mag Jmag [3.981/14.858] J band magnitude
35- 38 F4.2 Rgeo Rplanet [1.04/3.96] Planet radius
40- 46 F7.2 Mgeo Mplanet [0.64/5995] Planet mass
48- 50 I3 K Teq [173/999] Equilibrium planet temperature
52- 61 F10.6 d Per [0.46/638] Planet orbital period
63- 67 F5.1 --- TSM [0/630] Transmission Spectroscopy Metric (1)
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Note (1): The transmission spectroscopy metric (TSM) of each planet, as
in Kempton+ (2018PASP..130k4401K 2018PASP..130k4401K), is defined to approximate an S/N of
one scale height in transmission spectra when observed with the Near
Infrared Imager and Slitless Spectrograph (NIRISS) instrument on James
Webb Space Telescope (JWST) for 10hr; therefore, it is proportional to
RpH/R*2xF, where H=kTeq/µg is the atmospheric scale height,
Rp is the planet radius, R* is the stellar radius, and F is the
stellar flux received on the detectors. See Section 6.2.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 16-Jun-2020