Stellar Cartography

The Pan-Pacific Planet Search — IX. A Menagerie Of Companions Orbiting Evolved Stars

By Keith Cowing

Status Report

astro-ph.EP

June 4, 2026

Filed under Anglo-Australian Telescope, Asteroseismology, astro-ph.EP, brown dwarf, exoplanet, HD 114899, HD 126105 b, HD 159743, HD 205577B, Hipparcos, Hipparcos-Gaia, Pan-Pacific Planet Search, radial-velocity, Spectrograph, Spectroscopy, stellar cartogaphy, TESS

The Pan-Pacific Planet Search — IX. A Menagerie Of Companions Orbiting Evolved Stars — Joint RV and Hipparcos-Gaia astrometry model for HD 205577. (Top) all RV data, including Gaia mean RVs, and best-fit RV model. (Bottom left) proper motion in right ascension and best-fit astrometric model. (Bottom right) proper motion in declination and best-fit astrometric model. In each panel the dark lines represent the best-fit model, while the light lines are drawn randomly from the posteriors. Though the orbit of HD 205577 B is not well-constrained by the data, the joint model returns a unique solution with 𝑃 = 4100+800 −180 days, a high eccentricity of 0.68+0.10 −0.16, and a true mass for the companion of 77+11 −9 𝑀J that straddles the Hydrogen-burning limit. — astro-ph.EP

We present resolutions as to the nature of six speculative candidate companions proposed in the final data release of the Pan-Pacific Planet Search, a 6-year radial-velocity survey of 164 southern evolved stars using the now-decommissioned UCLES spectrograph on the 3.9m Anglo-Australian Telescope.

New radial-velocity observations, TESS asteroseismology, and Hipparcos-Gaia astrometry are incorporated to refine the companion and host-star parameters. We confirm that HD 126105b is a giant planet (P=524.0±2.9 d, m sin i=1.67+0.19−0.17M_Jup), and that HD 205577B is a massive, eccentric brown dwarf (P∼11.2 yr, m=77+11−9M_Jup, e=0.68).

HD 115066B and HD 121156B are low-mass stellar companions, while HD 114899 and HD 159743 are shown to be unadorned by any detectable companions whatsoever. This demonstrates the utility of astrometric information to help overcome the temporal limitations of incomplete radial-velocity data sets and elucidate the true nature of suspected companion bodies.

Robert A. Wittenmyer, Alexander Venner, Tyler Fairnington, George Zhou, Duncan J. Wright, Evan Curtin, Timothy R. Bedding, Courtney L. Crawford, Yaguang Li, Dennis Stello, Marc Hon, Daniel Huber, Frank Grundahl, M. Skakke Fredslund, Pere L. Palle, Tianjun Gan, Jonathan Horner, John Kielkopf, Stephen R. Kane, Peter Plavchan, Avi Shporer, C.G. Tinney, Hui Zhang, Matthew W. Mengel, Jack Okumura

Comments: Accepted for publication in MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2606.00787 [astro-ph.EP] (or arXiv:2606.00787v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2606.00787
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Submission history
From: Robert Wittenmyer
[v1] Sat, 30 May 2026 16:08:51 UTC (2,200 KB)
https://arxiv.org/abs/2606.00787
Astrobiology, Astronomy, exoplanet,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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