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Spinning out of focus: The challenge of rotational line broadening in exoplanet reflection spectroscopy

Fuente: arXiv

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Bibliographic Details
Main Authors:	Winterhalder, T. O., Molaverdikhani, K., Cont, D., Yan, F., Nagel, E., Kaminski, A., Nortmann, L., Amado, P. J., Béjar, V. J. S., Bergond, G., Caballero, J. A., Czesla, S., Henning, Th., Morello, G., Montes, D., Palle, E., Quirrenbach, A., Reiners, A., Ribas, I., Schweitzer, A.
Format:	Preprint
Published:	2026
Subjects:	Earth and Planetary Astrophysics
Online Access:	Acceder al recurso
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_version_	1866918505724510208
author	Winterhalder, T. O. Molaverdikhani, K. Cont, D. Yan, F. Nagel, E. Kaminski, A. Nortmann, L. Amado, P. J. Béjar, V. J. S. Bergond, G. Caballero, J. A. Czesla, S. Henning, Th. Morello, G. Montes, D. Palle, E. Quirrenbach, A. Reiners, A. Ribas, I. Schweitzer, A.
author_facet	Winterhalder, T. O. Molaverdikhani, K. Cont, D. Yan, F. Nagel, E. Kaminski, A. Nortmann, L. Amado, P. J. Béjar, V. J. S. Bergond, G. Caballero, J. A. Czesla, S. Henning, Th. Morello, G. Montes, D. Palle, E. Quirrenbach, A. Reiners, A. Ribas, I. Schweitzer, A.
contents	Detecting light reflected off the dayside of an exoplanet in high-resolution spectroscopic data has proved to be a notoriously difficult endeavour. Despite several attempts, the faint signal has yet to be detected. We present a new effort at finding reflection signatures and show how a strong rotational broadening of the reflected spectrum can complicate this objective. We introduce a new figure of merit that quantifies the favourability of different systems for a reflection study, the reflection spectroscopy metric. Applying this metric, we identify the KELT-9 system, which features a highly misaligned, rapidly rotating host star, as the target for a case study based on a spectroscopic time series obtained by CARMENES. We also perform an injection-recovery test to determine the detectability of the signal in our data and demonstrate its sensitivity to rotational line broadening. The search for a genuine reflection signal in our data resulted in a non-detection. The injection-recovery test puts this finding into context by revealing the critical importance of taking rotational broadening into account when dealing with systems featuring rapidly rotating stars and large spin-orbit misalignments. The case study presented here underscores the need to incorporate stellar rotation and spin-orbit misalignment into assessments of a given planet's favourability to reflection studies.
format	Preprint
id	arxiv_https___arxiv_org_abs_2605_16491
institution	arXiv
publishDate	2026
record_format	arxiv
spellingShingle	Spinning out of focus: The challenge of rotational line broadening in exoplanet reflection spectroscopy Winterhalder, T. O. Molaverdikhani, K. Cont, D. Yan, F. Nagel, E. Kaminski, A. Nortmann, L. Amado, P. J. Béjar, V. J. S. Bergond, G. Caballero, J. A. Czesla, S. Henning, Th. Morello, G. Montes, D. Palle, E. Quirrenbach, A. Reiners, A. Ribas, I. Schweitzer, A. Earth and Planetary Astrophysics Detecting light reflected off the dayside of an exoplanet in high-resolution spectroscopic data has proved to be a notoriously difficult endeavour. Despite several attempts, the faint signal has yet to be detected. We present a new effort at finding reflection signatures and show how a strong rotational broadening of the reflected spectrum can complicate this objective. We introduce a new figure of merit that quantifies the favourability of different systems for a reflection study, the reflection spectroscopy metric. Applying this metric, we identify the KELT-9 system, which features a highly misaligned, rapidly rotating host star, as the target for a case study based on a spectroscopic time series obtained by CARMENES. We also perform an injection-recovery test to determine the detectability of the signal in our data and demonstrate its sensitivity to rotational line broadening. The search for a genuine reflection signal in our data resulted in a non-detection. The injection-recovery test puts this finding into context by revealing the critical importance of taking rotational broadening into account when dealing with systems featuring rapidly rotating stars and large spin-orbit misalignments. The case study presented here underscores the need to incorporate stellar rotation and spin-orbit misalignment into assessments of a given planet's favourability to reflection studies.
title	Spinning out of focus: The challenge of rotational line broadening in exoplanet reflection spectroscopy
topic	Earth and Planetary Astrophysics
url	https://arxiv.org/abs/2605.16491