A photospheric and chromospheric activity analysis of the quiescent retrograde-planet host $\nu$ Octantis A

Abstract

The single-lined spectroscopic binary $\nu$ Octantis provided evidence of the first conjectured circumstellar planet demanding an orbit retrograde to the stellar orbits. The planet-like behaviour is now based on 1437 radial velocities (RVs) acquired from 2001 to 2013. $\nu$ Oct's semimajor axis is only 2.6 AU with the candidate planet orbiting $\nu$ Oct A about midway between. These details seriously challenge our understanding of planet formation and our decisive modelling of orbit reconfiguration and stability scenarios. However, all non-planetary explanations are also inconsistent with numerous qualitative and quantitative tests including previous spectroscopic studies of bisectors and line-depth ratios, photometry from Hipparcos and the more recent space missions TESS and GAIA (whose increased parallax classifies $\nu$ Oct A closer still to a subgiant ~ K1 IV). We conducted the first large survey of $\nu$ Oct A's chromosphere: 198 Ca II H-line and 1160 H $\alpha$ indices using spectra from a previous RV campaign (2009-2013). We also acquired 135 spectra (2018-2020) primarily used for additional line-depth ratios, which are extremely sensitive to the photosphere's temperature. We found no significant RV-correlated variability. Our line-depth ratios indicate temperature variations of only $\pm$ 4 K, as achieved previously. Our atypical Ca II analysis models the indices in terms of S/N and includes covariance significantly in their errors. The H $\alpha$ indices have a quasi-periodic variability which we demonstrate is due to telluric lines. Our new evidence provides further multiple arguments realistically only in favor of the planet.

14 pages, 16 figures, 2 tables, accepted 2021 January 7

References in corpus (13)

• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Spectrum radial velocity analyser (SERVAL). High-precision radial velocities and two alternative spectral indicators
• Stellar activity of planetary host star HD 189733
• A Giant Planet Candidate Transiting a White Dwarf
• Fluxes in Hαand Ca II H and K for a sample of Southern stars
• Orbital Stability of Circumstellar Planets in Binary Systems
• The Reversibility Error Method (REM): a new, dynamical fast indicator for planetary dynamics
• On the survival of resonant and non-resonant planetary systems in star clusters
• Frequency of Planets in Binaries
• Precise radial velocities of giant stars. XII. Evidence against the proposed planet Aldebaran b
• Precise radial velocities of giant stars IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system
• An ablating super-Earth in an eccentric binary from the Dispersed Matter Planet Project
• Activity and telluric contamination in HARPS observations of Alpha Centauri B

Cited by in corpus (2)

• Multiplicity of stars with planets in the solar neighbourhood
• Constraining the orbit of the retrograde planet in the $\nu$ Octantis system