The Near-infrared Transmission Spectra of TRAPPIST-1 Planets b, c, d, e, f, and g and Stellar Contamination in Multi-epoch Transit Spectra

Zhanbo Zhang, Yifan Zhou, Benjamin V. Rackham, Daniel Apai

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

The seven approximately Earth-sized transiting planets in the TRAPPIST-1 system provide a unique opportunity to explore habitable- and nonhabitable-zone small planets within the same system. Its habitable-zone exoplanets - due to their favorable transit depths - are also worlds for which atmospheric transmission spectroscopy is within reach with the Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). We present here an independent reduction and analysis of two HST Wide Field Camera 3 (WFC3) near-infrared transit spectroscopy data sets for six planets (b through g). Utilizing our physically motivated detector charge-trap correction and a custom cosmic-ray correction routine, we confirm the general shape of the transmission spectra presented by de Wit et al. Our data reduction approach leads to a 25% increase in the usable data and reduces the risk of confusing astrophysical brightness variations (e.g., flares) with instrumental systematics. No prominent absorption features are detected in any individual planet's transmission spectra; by contrast, the combined spectrum of the planets shows a suggestive decrease around 1.4 μm similar to an inverted water absorption feature. Including transit depths from K2, the SPECULOOS-South Observatory, and Spitzer, we find that the complete transmission spectrum is fully consistent with stellar contamination owing to the transit light source effect. These spectra demonstrate how stellar contamination can overwhelm planetary absorption features in low-resolution exoplanet transit spectra obtained by HST and JWST and also highlight the challenges in combining multi-epoch observations for planets around rapidly rotating spotted stars.

Original languageEnglish (US)
Article number178
JournalAstronomical Journal
Volume156
Issue number4
DOIs
StatePublished - Oct 1 2018

Fingerprint

transit
planets
near infrared
contamination
planet
time measurement
Hubble Space Telescope
James Webb Space Telescope
extrasolar planets
spectroscopy
data reduction
cosmic ray
flares
cosmic rays
observatories
astrophysics
light sources
brightness
observatory
cameras

Keywords

  • planets and satellites: atmospheres
  • planets and satellites: individual (TRAPPIST-1)
  • planets and satellites: terrestrial planets
  • stars: late-type
  • techniques: spectroscopic

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

The Near-infrared Transmission Spectra of TRAPPIST-1 Planets b, c, d, e, f, and g and Stellar Contamination in Multi-epoch Transit Spectra. / Zhang, Zhanbo; Zhou, Yifan; Rackham, Benjamin V.; Apai, Daniel.

In: Astronomical Journal, Vol. 156, No. 4, 178, 01.10.2018.

Research output: Contribution to journalArticle

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