[Paper Review] Probing long-period companions to planetary hosts. VLT and CFHT near infrared coronographic imaging surveys

G. Chauvin, A.‐M. Lagrange+6 more|ArXiv.org|Jun 7, 2006

Stellar, planetary, and galactic studies54 references57 citations

TL;DR

This study conducts deep near-infrared coronographic imaging with adaptive optics on the VLT and CFHT to search for long-period stellar and substellar companions around 26 radial velocity-detected planetary hosts. It identifies two new bound companions—HD 1237 B (a likely M dwarf at 70 AU) and HD 27442 B (a probable white dwarf at 240 AU), with orbital motion confirmed for HD 1237 B, while HD 27442 B is inferred from photometric consistency with white dwarf models.

ABSTRACT

We present the results of a deep imaging survey of stars surrounded by planets detected with the radial velocity technique. The purpose is to search for and to characterize long-period stellar and substellar companions. The sample contains a total of 26 stars, among which 6 exhibit additional radial velocity drifts. We used NACO, at the ESO Very Large Telescope, and PUEO-KIR, at the Candian French Hawaiian Telescope, to conduct a near-infrared coronographic survey with adaptive optics of the faint circumstellar environment of the planetary hosts. The domain investigated ranges between 0.1 to 15" (i.e. about 3 to 500 AU, according to the mean distance of the sample). The survey is sensitive to companions within the stellar and the substellar domains, depending on the distance to the central stars and on the star properties. The images of 14 stars do not reveal any companions once the field objects are removed. 8 stars have close potential companions that need to be re-observed within 1-2 years to check for physical companionship. 4 stars are surrounded by faint objects which are confirmed or very probable companions. The companion to HD13445 (Gliese 86) is already known. The HD196885 star is a new close visual binary system with a high probability of being bound. The 2 newly discovered companions, HD1237 B and HD27442 B, share common proper motions with the central stars. Orbital motion is detected for HD1237 B. HD1237 B is likely a low-mass M star, located at 70 AU (projected distance) from the primary. HD27442 B is most probably a white dwarf companion located at about 240 AU (projected distance).

Motivation & Objective

• To search for long-period stellar and substellar companions around stars hosting planets detected via radial velocity (RV) techniques.
• To characterize the multiplicity properties of planetary hosts beyond the inner system, particularly in the 3–500 AU range.
• To investigate whether massive companions or white dwarfs could explain observed RV drifts or influence planetary system dynamics.
• To improve understanding of the formation and evolution of extrasolar planets and brown dwarfs by extending observational constraints to longer periods and lower masses.
• To test the hypothesis that the 'brown dwarf desert' extends to larger separations by probing the substellar and stellar companion population at wider orbits.

Proposed method

• Conducted deep near-infrared coronographic imaging using NACO at the VLT and PUEO-KIR at CFHT with adaptive optics to suppress stellar glare.
• Targeted 26 planetary hosts with known RV-confirmed planets, covering distances from 10.9 to 68.5 pc.
• Investigated a spatial domain between 0.1" and 15" (3–500 AU), depending on distance, to detect faint companions.
• Used photometric and astrometric consistency across multiple epochs to distinguish physical companions from background field objects.
• Applied evolutionary models (e.g., Bergeron et al. 2001) to interpret the photometry of candidate companions.
• Performed radial velocity trend analysis on stars with unexplained RV drifts to assess potential unseen companions.

Experimental results

Research questions

• RQ1 Do long-period stellar or substellar companions exist around known planetary hosts, particularly at separations beyond 100 AU?
• RQ2 Can the observed radial velocity drifts in some systems be explained by the presence of distant, unseen companions?
• RQ3 Are white dwarfs common as distant companions to stars hosting planets, and what does this imply for binary evolution?
• RQ4 Do the orbital motions of newly detected companions confirm their physical association with the primary stars?
• RQ5 What is the frequency and mass distribution of companions in the 30–150 M_Jup range at wide separations?

Key findings

• HD 1237 B is confirmed as a physical companion with detected orbital motion, located at a projected separation of 70 AU and likely a low-mass M dwarf.
• HD 27442 B is most likely a white dwarf companion at a projected distance of 240 AU, with photometry consistent with evolutionary models for hydrogen- and helium-rich white dwarfs.
• The companion to HD 13445 (Gl 86) is a known white dwarf at ~20 AU, and its orbital motion is confirmed, making it a benchmark system for wide binary planetary systems.
• Eight stars show faint companion candidates requiring follow-up; these are likely background objects or require confirmation via proper motion monitoring.
• No companions were detected around six stars (HD 28185, HD 92788, HD 95128, HD 106252, HD 186427, HD 217107), despite RV trends in some, suggesting possible distant or low-mass companions.
• The system HD 196885 hosts a high-probability bound stellar companion candidate, with a low likelihood of being a background object.