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Title: A Decade of H α Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere

Abstract

HD 189733 b is one of the most well studied exoplanets due to its large transit depth and host star brightness. The focus on this object has produced a number of high-cadence transit observations using high-resolution optical spectrographs. Here we present an analysis of seven full H α transits of HD 189733 b using HARPS on the 3.6 meter La Silla telescope and HIRES on Keck I, taken over the course of nine years from 2006 to 2015. H α transmission signals are analyzed as a function of the stellar activity level, as measured using the normalized core flux of the Ca ii H and K lines. We find strong variations in the strength of the H α transmission spectrum from epoch to epoch. However, there is no clear trend between the Ca ii core emission and the strength of the in-transit H α signal, although the transit showing the largest absorption value also occurs when the star is the most active. We present simulations of the in-transit contrast effect and find that the planet must consistently transit active latitudes with very strong facular and plage emission regions in order to reproduce the observed line strengths. We also investigate themore » measured velocity centroids with models of planetary rotation and show that the small line profile velocities could be due to large velocities in the upper atmosphere of the planet. Overall, we find it more likely that the measured H α signals arise in the extended planetary atmosphere, although a better understanding of active region emission for active stars such as HD 189733 is needed.« less

Authors:
;  [1];  [2]
  1. Wesleyan University, Astronomy Department, Van Vleck Observatory, 96 Foss Hill Drive, Middletown, CT 06459 (United States)
  2. University of Nebraska-Kearney, Department of Physics and Astronomy, 24011 11th Avenue, Kearney, NE 68849 (United States)
Publication Date:
OSTI Identifier:
22663696
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 153; Journal Issue: 5; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; ABSORPTION SPECTRA; ACTIVITY LEVELS; BRIGHTNESS; METERS; PLAGES; PLANETARY ATMOSPHERES; PLANETS; ROTATION; SATELLITE ATMOSPHERES; SATELLITES; STARS; TELESCOPES; VARIATIONS

Citation Formats

Cauley, P. Wilson, Redfield, Seth, and Jensen, Adam G., E-mail: pcauley@wesleyan.edu. A Decade of H α Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA6A15.
Cauley, P. Wilson, Redfield, Seth, & Jensen, Adam G., E-mail: pcauley@wesleyan.edu. A Decade of H α Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere. United States. doi:10.3847/1538-3881/AA6A15.
Cauley, P. Wilson, Redfield, Seth, and Jensen, Adam G., E-mail: pcauley@wesleyan.edu. Mon . "A Decade of H α Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere". United States. doi:10.3847/1538-3881/AA6A15.
@article{osti_22663696,
title = {A Decade of H α Transits for HD 189733 b: Stellar Activity versus Absorption in the Extended Atmosphere},
author = {Cauley, P. Wilson and Redfield, Seth and Jensen, Adam G., E-mail: pcauley@wesleyan.edu},
abstractNote = {HD 189733 b is one of the most well studied exoplanets due to its large transit depth and host star brightness. The focus on this object has produced a number of high-cadence transit observations using high-resolution optical spectrographs. Here we present an analysis of seven full H α transits of HD 189733 b using HARPS on the 3.6 meter La Silla telescope and HIRES on Keck I, taken over the course of nine years from 2006 to 2015. H α transmission signals are analyzed as a function of the stellar activity level, as measured using the normalized core flux of the Ca ii H and K lines. We find strong variations in the strength of the H α transmission spectrum from epoch to epoch. However, there is no clear trend between the Ca ii core emission and the strength of the in-transit H α signal, although the transit showing the largest absorption value also occurs when the star is the most active. We present simulations of the in-transit contrast effect and find that the planet must consistently transit active latitudes with very strong facular and plage emission regions in order to reproduce the observed line strengths. We also investigate the measured velocity centroids with models of planetary rotation and show that the small line profile velocities could be due to large velocities in the upper atmosphere of the planet. Overall, we find it more likely that the measured H α signals arise in the extended planetary atmosphere, although a better understanding of active region emission for active stars such as HD 189733 is needed.},
doi = {10.3847/1538-3881/AA6A15},
journal = {Astronomical Journal (Online)},
number = 5,
volume = 153,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}