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Updated Parameters and a New Transmission Spectrum of HD 97658b

Guo, Xueying and Crossfield, Ian J. M. and Dragomir, Diana and Kosiarek, Molly R. and Lothringer, Joshua and Mikal-Evans, Thomas and Rosenthal, Lee and Benneke, Björn and Knutson, Heather A. and Dalba, Paul A. and Kempton, Eliza M. R. and Henry, Gregory W. and McCullough, P. R. and Barman, Travis and Blunt, Sarah and Chontos, Ashley and Fortney, Jonathan and Fulton, Benjamin J. and Hirsch, Lea and Howard, Andrew W. and Isaacson, Howard and Matthews, Jaymie and Močnik, Teo and Morley, Caroline and Petigura, Erik A. and Weiss, Lauren M. (2020) Updated Parameters and a New Transmission Spectrum of HD 97658b. Astronomical Journal, 159 (5). Art. No. 239. ISSN 1538-3881. doi:10.3847/1538-3881/ab8815.

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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. HD 97658 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 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 1.1–1.7 μm 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 ± 2 days) and stellar activity cycle (9.6 yr) of the host star HD 97658. Finally, we calculate and rank the Transmission Spectroscopy Metric of all confirmed planets cooler than 1000 K and with sizes between 1 R⊕ and 4 R⊕. We find that at least a third of small planets cooler than 1000 K can be well characterized using James Webb Space Telescope, and of those, HD 97658b is ranked fifth, meaning that it remains a high-priority target for atmospheric characterization.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Crossfield, Ian J. M.0000-0002-1835-1891
Dragomir, Diana0000-0003-2313-467X
Kosiarek, Molly R.0000-0002-6115-4359
Lothringer, Joshua0000-0003-3667-8633
Mikal-Evans, Thomas0000-0001-5442-1300
Rosenthal, Lee0000-0001-8391-5182
Benneke, Björn0000-0001-5578-1498
Knutson, Heather A.0000-0002-0822-3095
Dalba, Paul A.0000-0002-4297-5506
Kempton, Eliza M. R.0000-0002-1337-9051
Henry, Gregory W.0000-0003-4155-8513
McCullough, P. R.0000-0001-9165-9799
Barman, Travis0000-0002-7129-3002
Blunt, Sarah0000-0002-3199-2888
Chontos, Ashley0000-0003-1125-2564
Fortney, Jonathan0000-0002-9843-4354
Fulton, Benjamin J.0000-0003-3504-5316
Hirsch, Lea0000-0001-8058-7443
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Matthews, Jaymie0000-0002-4461-080X
Močnik, Teo0000-0003-4603-556X
Morley, Caroline0000-0002-4404-0456
Petigura, Erik A.0000-0003-0967-2893
Weiss, Lauren M.0000-0002-3725-3058
Additional Information:© 2020 The American Astronomical Society. Received 2019 November 15; revised 2020 March 8; accepted 2020 April 1; published 2020 April 28. We acknowledge support for this analysis by NASA through grants under the HST-GO-13665 program. I.J.M.C. acknowledges support from the NSF through grant AST-1824644 and through NASA and STScI through funding for program GO-13665. D.D. acknowledges support provided by NASA through Hubble Fellowship grant HSTHF2-51372.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. M.R.K. acknowledges support from the NSF Graduate Research Fellowship, grant No. DGE 1339067. G.W.H. acknowledges long-term support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence program. A.W.H. acknowledges NSF grant AST-1517655. Software Usage: BAsic Transit Model cAlculatioN (BATMAN) (Kreidberg 2015); Celerite (Foreman-Mackey et al. 2017); EXOFASTv2 (Eastman 2017); RadVel (Fulton & Petigura 2017); PLATON (Zhang et al. 2019); PANDEXO (Batalha et al. 2017).
Group:Astronomy Department
Funding AgencyGrant Number
NASA Hubble FellowshipHST-HF2-51372.001- A
NSF Graduate Research FellowshipDGE-1339067
Tennessee State UniversityUNSPECIFIED
State of Tennessee Centers of Excellence programUNSPECIFIED
Subject Keywords:Transit photometry ; Hubble Space Telescope ; Exoplanet atmospheres ; Radial velocity
Issue or Number:5
Classification Code:Unified Astronomy Thesaurus concepts: Transit photometry (1709); Hubble Space Telescope (761); Exoplanet atmospheres (487); Radial velocity (1332)
Record Number:CaltechAUTHORS:20200420-100331561
Persistent URL:
Official Citation:Xueying Guo et al 2020 AJ 159 239
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102646
Deposited By: Tony Diaz
Deposited On:20 Apr 2020 17:22
Last Modified:16 Nov 2021 18:14

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