2026A&A...706A.179A

Context. Quantifying stellar parameters and magnetic activity for cool stars in double-lined spectroscopic binaries (SB2s) is not straightforward, as both stars contribute to the observed composite spectra and are likely variable. Disentangled component spectra allow a detailed analysis of the magnetic activity of the primary component.
Aims. We aim to separate the spectra of the two stellar components of the HR 7275 SB2 system. We also aim to obtain a more accurate orbital solution by correcting the observed radial velocities (RV) from activity perturbations of the spotted primary (“RV jitter”) and to derive a surface image of this component.
Methods. We obtained time-series high- and ultra-high resolution optical spectra and applied two different disentangling methods. We modeled radial velocity (RV) residuals using three-sine function fits and modeled the spectral-line profile of the primary with the Doppler imaging code iMAP. We measured magnetic fields for the primary based on least-squares deconvolved Stokes-V line profiles, and determined chromospheric emission from the line cores of CaIIH&K, CaIIIRT8542 Å, and Balmer Hα. We first applied our disentangling technique, which allowed us to determine the properties of the system more accurately before performing these analyses.
Results. The Doppler image of the primary shows two large cool spots that cover approximately 20% of the visible hemisphere, plus three smaller spots each still covering approximately 13% in size. Between May-June 2022, HR 7275a exhibited an impressive spottedness of roughly 40% of its entire surface. The RV is modulated by the rotation of the primary, with maximum amplitudes of 320 m s^–1 and 650 m s^–1 for two different modulation behaviors during the 250 d of our observations. This jitter is primarily caused by the varying asymmetries of the apparent disk brightness due to the cool spots. Its removal results in roughly ten times higher precision of the orbital elements. Our snapshot magnetic-field measurements reveal phase-dependent (large-scale) surface fields between +0.6±2.0 G at phase 0.1 and -15.2±2.7 G at phase 0.6, indicating a complex magnetic morphology related to the location of the photospheric spots. We also obtain a logarithmic lithium abundance of 0.58±0.1 for HR7275a, indicating considerable mixing, and 0.16_–0.63^+0.23 for HR7275b, which is an extremely low value.