Time-resolved image polarimetry of TRAPPIST-1 during planetary transits. (9th January 2019)

• Record Type: Journal Article
• Authors: Miles-Páez, P A; Zapatero Osorio, M R; Pallé, E; Metchev, S A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 484:Number 1(2019)
• Page Start: L38
• Page End: L42
• Publication Date: 2019-01-09
• Subjects: polarization -- stars: atmospheres -- stars: individual: TRAPPIST-1 -- stars: late-type -- stars: low-mass; Astronomy -- Research -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnrasl/slz001
• Languages: English
• ISSNs: 1745-3933

Abstract

ABSTRACT: We obtained linear polarization photometry ( J -band) and low-resolution spectroscopy ( ZJ -bands) of TRAPPIST-1, which is a planetary system formed by an M8-type low-mass star and seven temperate, Earth-sized planets. The photopolarimetric monitoring campaign covered 6.5 h of continuous observations including one full transit of planet TRAPPIST-1d and partial transits of TRAPPIST-1b and e. The spectrophotometric data and the photometric light curve obtained over epochs with no planetary transits indicate that the low-mass star has very low level of linear polarization compatible with a null value. However, the 'in transit' observations reveal an enhanced linear polarization signal with peak values of$p^* = 0.1\, {{\ \rm per\ cent}}$ with a confidence level of 3σ, particularly for the full transit of TRAPPIST-1d, thus confirming that the atmosphere of the M8-type star is very likely dusty. Additional observations probing different atmospheric states of TRAPPIST-1 are needed to confirm our findings, as the polarimetric signals involved are low. If confirmed, polarization observations of transiting planetary systems with central ultracool dwarfs can become a powerful tool for the characterization of the atmospheres of the host dwarfs and the validation of transiting planet candidates that cannot be corroborated by any other method.