High-resolution Transmission Spectroscopy of Ultrahot Jupiter WASP–33b with NEID

Abstract

We report an attempt to detect molecular and atomic species in the atmosphere of the ultrahot Jupiter WASP-33b using the high-resolution echelle spectrograph NEID with a wavelength coverage of 380–930 nm. By analyzing the transmission spectrum of WASP-33b using the line-by-line technique and the cross-correlation technique, we confirm previous detection of Hα, Hβ, Hγ, and Ca ii infrared triplets. We find no evidence for a significant day-to-night wind in WASP-33b, taking into account the effects of stellar pulsations using a relatively novel Gaussian process method and poorly constrained systemic velocity measurements. We also detect the previously reported pretransit absorption signal, which may be a pulsation mode induced by the planet. Combined with previous CARMENES and HARPS-N observations, we report the nondetection of TiO, Ti i, and V i in the transmission spectrum, while they were already detected in the dayside atmosphere of WASP-33b. This implies a difference in the chemical compositions and abundances between the dayside and terminator atmospheres of WASP-33b and certainly requires further improvements in the sensitivity of the detection methods.

Evidence for Nightside Water Emission Found in Transit of Ultra-hot Jupiter WASP-33 b

“…Previous optical transmission spectroscopy to detect atoms and ions in WASP-33 b showed no significant circulation patterns (Yan et al 2021;Yang et al 2024), consistent with the results here. However, due to the strong influence of stellar pulsations, caution should be taken when claiming species detection from the transmission spectrum of WASP-33 b (Borsa et al 2021;Cauley et al 2021;Yan et al 2021;Yang et al 2024).…”

“…Previous optical transmission spectroscopy to detect atoms and ions in WASP-33 b showed no significant circulation patterns (Yan et al 2021;Yang et al 2024), consistent with the results here. However, due to the strong influence of stellar pulsations, caution should be taken when claiming species detection from the transmission spectrum of WASP-33 b (Borsa et al 2021;Cauley et al 2021;Yan et al 2021;Yang et al 2024). Fortunately, H 2 O will not be present in WASP-33 b's host star due to the extremely high effective temperatures of A-type stars, so the effect of pulsations on the detection of H 2 O emission signals from WASP-33 b should be negligible.…”

“…Tan et al (2024) recently suggested that the formation of a nightside thermal inversion layer is possible when considering H 2 -H dissociation and recombination in planets with equilibrium temperatures above 2600 K and the absence of radiative cooling due to the lack of nightside coolants (e.g., TiO and VO). TiO has been detected on the dayside of WASP-33 b by emission spectroscopy (Cont et al 2021), but not on the terminator by transmission spectroscopy (Yang et al 2024). This implies that the condensation of TiO occurs on the terminator/nightside, which could then be circulated to the dayside to restore the gas phase.…”

“…The GIANO-B spectrograph has a high resolution of R ∼ 50,000 and covers the wavelength range from 0.95 to 2.45 μm. The basic method of high-resolution spectral data reduction follows Guilluy et al (2019), Giacobbe et al (2021), Yan et al (2022b), andYang et al (2024). We used SYSREM (Tamuz et al 2005) to remove telluric contamination and stellar spectral lines to obtain the final order-by-order spectral matrices for subsequent cross-correlation analyses (see Appendix B for the detailed data-reduction process).…”

“…We adopt the method detailed by Yan et al (2022b) and Yang et al (2024) to perform the subsequent spectral data reduction. To correct for outliers that are unlikely to be caused by the observed source, we flagged the pixels that were greater than 5 standard deviations from the flux values of the smoothed spectrum produced by a median filter with a window size of 9 pixels for each order.…”