A long-running watch of Rho Leo has found a persistent rhythm in the star's motion. The first-moment signal, which tracks a spectral line's centroid or radial velocity, repeated every 16.46 ± 0.08 days and had an amplitude of 3.94 ± 0.19 kilometres per second. The authors say the pattern is most consistent with non-radial pulsations, a repeating motion that is not simply the whole star expanding and contracting, although their analysis leaves a companion as a possible explanation.
The central question is what drives Rho Leo's long-term changes: something intrinsic to the star, or variability linked to a possible companion. This is a single-target time series, so the result is about which explanation best fits these observations, not a causal test or a measure of how common either explanation is. The authors do not settle whether the 16.46-day signal is exclusively pulsational.
A long record of line measurements
The main record comprised 3,492 spectra collected on 163 nights between 21 January 2014 and 1 June 2025. The researchers examined line-profile moments, measurements that describe a spectral line's strength, central shift or radial velocity, width and asymmetry.
To find repeating timescales, they used generalized Lomb-Scargle periodograms and iterative pre-whitening to characterize the overall frequency content. A weighted wavelet Z-transform was used to track how the signals changed over time. The analysis set a global false-alarm threshold of 0.1%, using analytic Baluev estimation and 5,000 bootstrap resamplings.
Across the main observing record, the approximately 16-day variability persisted over the full baseline. It was strongest in the line centroid, weaker in line asymmetry, and not apparent in line width. That uneven pattern across the line measures is one reason the authors considered a pulsational origin.
The same rhythm appears elsewhere
Analysis of the SONG Si III 4552 line recovered the same dominant period, about 16.4 days, as the main record. Shorter signals of about 10.8 days and 7 days appeared only during a brief interval rather than across the full record.
The line's centroid and asymmetry were moderately correlated, not tightly locked: Pearson r was 0.446, Spearman ρ was 0.436, and the linear-regression R2 was 0.2. In plain terms, the two measures shared some variation but did not move as a single clean signal.
Brightness data tell a less certain story
TESS photometry added a second, less certain timescale. The combined analysis reported a period of 33.01 ± 1.43 days and a brightness amplitude of 0.118 ± 0.003 magnitudes. The data set contained about 52,000 two-minute measurements covering 760 days.
That roughly 33-day result is sensitive to the reduction procedure. It was not recovered in the analysis of two consecutive sectors, so the exact dominant photometric period is not robustly determined.
The leading explanation remains provisional
Taken together, the recurring 16.46-day velocity signal, its weaker asymmetry signature and the approximately 33-day photometric modulation led the authors to favor long-term non-radial pulsations as the main explanation for Rho Leo's variability. They still leave binarity as a possible alternative.
The study does not show that Rho Leo has no companion, or that the 16.46-day signal is exclusively pulsational. With binarity still possible and the shorter signals confined to a brief interval, the authors point to longer, more uniformly sampled observations as the way to separate orbital motion from pulsation.
The document is an arXiv version 1 preprint dated 28 August 2026. It reports support from Estonian Research Council grants TT8, TARISTU24-TK3, IUT-40 and PRG 2159; the KosEST project and EU Regional Development Fund; EU Horizon Europe grant 101079231; UKRI grant 10051045; and Horizon 2020 Marie Skłodowska-Curie grant 823734.
Paper data and sources
Original title: A decade of radial-velocity monitoring of rho Leo: moment analysis and periodic variability
Authors: V. A. Checha, A. Aret, I. Kolka et al.
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-28
DOI: Not available
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