Follow-up of three exocomet-host candidates

¹ Observatorio Astronómico Nacional (OAN-IGN), C/ Alfonso XII 3, 28014 Madrid, Spain
² Facultad de Ciencias Físicas, Pl. de Ciencias 1, Universidad Complutense de Madrid, 28040, Madrid, Spain
³ European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁴ Centro de Astrobiología (CAB), CSIC-INTA, ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁵ STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
⁶ Department of Astronomy and Steward Observatory, University of Arizona, 393 N Cherry Ave., Tucson, AZ 85721-0065, USA
⁷ Large Binocular Telescope Observatory, University of Arizona, 933 N Cherry Ave., Tucson, AZ 85721-0065, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 28 October 2025
Accepted: 19 January 2026

Abstract

Context. Exocomets are small bodies that evaporate when they approach their host star. They can be detected based on the variability of non-photospheric features using spectroscopy and/or asymmetric transits in time-series photometry. Over the past four decades, about 30 systems have exhibited such variations and have therefore been classified as exocomet host stars. However, some recent publications have pointed out mechanisms that might mimic exocometary features. Therefore, careful monitoring is needed to confirm the origin of the observed variability.

Aims. In this paper, we aim to investigate the exocomet nature of the non-photospheric variable features observed in the exocomet candidate stars HD 36546, HD 42111, and HD 85905. All of them have shown some degree of variability, particularly in their Ca II K line.

Methods. We analysed the non-photospheric Ca II K line features from high-resolution spectra obtained using new NOT/FIES and Mercator/HERMES, along with some additional archival spectra of the target stars. The variability was quantified through the changes in the equivalent widths of those features, which are assumed to be of circumstellar origin. The column densities were also estimated for each variable feature.

Results. Strong variability was found for HD 85905, consistent with a potential link to exocometary activity. However, the binarity of the system, which we confirmed through interferometric VLTI/PIONIER observations, complicates the interpretation of these signatures and prevents us from drawing definitive conclusions. The remaining two sources do not show any significant variability, but due to the sporadic nature of the exocometary events, we cannot discard the exocomet hypothesis. Further monitoring of the stars will be necessary to carry out a robust determination of the variability patterns and timescales that would completely rule out other scenarios.