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dc.contributor.authorLothringer, Joshua D.
dc.contributor.authorBenneke, Björn
dc.contributor.authorCrossfield, Ian J. M.
dc.contributor.authorHenry, G.
dc.contributor.authorMorley, Caroline V.
dc.contributor.authorDragomir, Diana
dc.contributor.authorBarman, Travis S.
dc.contributor.authorKnutson, Heather
dc.contributor.authorKempton, Eliza
dc.contributor.authorFortney, Jonathan J.
dc.contributor.authorMcCullough, Peter
dc.contributor.authorHoward, Andrew W.
dc.date.accessioned2018-02-12T15:40:24Z
dc.date.available2018-02-12T15:40:24Z
dc.date.issued2018-01-17
dc.identifier.citationAn HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436b 2018, 155 (2):66 The Astronomical Journalen
dc.identifier.issn1538-3881
dc.identifier.doi10.3847/1538-3881/aaa008
dc.identifier.urihttp://hdl.handle.net/10150/626526
dc.description.abstractGJ 436b is a prime target for understanding warm Neptune exoplanet atmospheres and a target for multiple James Webb Space Telescope (JWST) Guaranteed Time Observation programs. Here, we report the first space-based optical transmission spectrum of the planet using two Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) transit observations from 0.53 to 1.03 mu m. We find no evidence for alkali absorption features, nor evidence of a scattering slope longward of 0.53 mu m. The spectrum is indicative of moderate to high metallicity (similar to 100-1000x solar), while moderate-metallicity scenarios (similar to 100x. solar) require aerosol opacity. The optical spectrum also rules out some highly scattering haze models. We find an increase in transit depth around 0.8 mu m in the transmission spectra of three different sub-Jovian exoplanets (GJ 436b, HAT-P-26b, and GJ 1214b). While most of the data come from STIS, data from three other instruments may indicate this is not an instrumental effect. Only the transit spectrum of GJ 1214b is well fit by a model with stellar plages on the photosphere of the host star. Our photometric monitoring of the host star reveals a stellar rotation rate of 44.1 days and an activity cycle of 7.4 years. Intriguingly, GJ 436 does not become redder as it gets dimmer, which is expected if star spots were dominating the variability. These insights into the nature of the GJ 436 system help refine our expectations for future observations in the era of JWST, whose higher precision and broader wavelength coverage will shed light on the composition and structure of GJ 436b's atmosphere.
dc.description.sponsorshipNASA [NAS 5-26555]; NASA from Space Telescope Science Institute [HST-GO-13308, HST-GO-13665]; NSF; Tennessee State University; State of Tennessee through Centers of Excellence Programen
dc.language.isoenen
dc.publisherIOP PUBLISHING LTDen
dc.relation.urlhttp://stacks.iop.org/1538-3881/155/i=2/a=66?key=crossref.32dea01f31a240a9054b4098c94d15c0en
dc.rights© 2018. The American Astronomical Society. All rights reserved.en
dc.subjectplanetary systemsen
dc.subjectplanets and satellites: atmospheresen
dc.subjectplanets and satellites: individual (GJ 436b)en
dc.subjectstars: individual (GJ 436)en
dc.subjecttechniques: spectroscopicen
dc.titleAn HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436ben
dc.typeArticleen
dc.contributor.departmentUniv Arizona, Lunar & Planetary Laben
dc.identifier.journalThe Astronomical Journalen
dc.description.collectioninformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.en
dc.eprint.versionFinal published versionen
refterms.dateFOA2018-08-15T00:57:46Z
html.description.abstractGJ 436b is a prime target for understanding warm Neptune exoplanet atmospheres and a target for multiple James Webb Space Telescope (JWST) Guaranteed Time Observation programs. Here, we report the first space-based optical transmission spectrum of the planet using two Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) transit observations from 0.53 to 1.03 mu m. We find no evidence for alkali absorption features, nor evidence of a scattering slope longward of 0.53 mu m. The spectrum is indicative of moderate to high metallicity (similar to 100-1000x solar), while moderate-metallicity scenarios (similar to 100x. solar) require aerosol opacity. The optical spectrum also rules out some highly scattering haze models. We find an increase in transit depth around 0.8 mu m in the transmission spectra of three different sub-Jovian exoplanets (GJ 436b, HAT-P-26b, and GJ 1214b). While most of the data come from STIS, data from three other instruments may indicate this is not an instrumental effect. Only the transit spectrum of GJ 1214b is well fit by a model with stellar plages on the photosphere of the host star. Our photometric monitoring of the host star reveals a stellar rotation rate of 44.1 days and an activity cycle of 7.4 years. Intriguingly, GJ 436 does not become redder as it gets dimmer, which is expected if star spots were dominating the variability. These insights into the nature of the GJ 436 system help refine our expectations for future observations in the era of JWST, whose higher precision and broader wavelength coverage will shed light on the composition and structure of GJ 436b's atmosphere.


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