[Paper Review] The multiplicity of exoplanet host stars - New low-mass stellar companions of the exoplanet host stars HD125612 and HD212301

M. Mugrauer, R. Neuhäuser|ArXiv.org|Dec 13, 2008

Stellar, planetary, and galactic studies37 references52 citations

TL;DR

This study identifies two new low-mass stellar companions to exoplanet host stars HD 125612 and HD 212301 using near-infrared direct imaging with SofI/NTT at the La Silla Observatory. The companions—HD 125612 B (M4 dwarf, 0.18 M☉, 4750 AU projected separation) and HD 212301 B (M3 dwarf, 0.35 M☉, 230 AU projected separation)—are confirmed as co-moving through astrometric analysis of multi-epoch data, increasing the known count of exoplanet host multiple systems to 43 and confirming a multiplicity rate of at least 17% among exoplanet hosts.

ABSTRACT

Aims: We present new results from our ongoing multiplicity study of exoplanet host stars, carried out with SofI/NTT. We provide the most recent list of confirmed binary and triple star systems that harbor exoplanets. Methods: We use direct imaging to identify wide stellar and substellar companions as co-moving objects to the observed exoplanet host stars, whose masses and spectral types are determined with follow-up photometry and spectroscopy. Results: We found two new co-moving companions of the exoplanet host stars HD125612 and HD212301. HD125612B is a wide M4 dwarf (0.18 Msun) companion of the exoplanet host star HD125612, located about 1.5 arcmin (~4750 AU of projected separation) south-east of its primary. In contrast, HD212301B is a close M3 dwarf (0.35 Msun), which is found about 4.4 arcsec (~230 AU of projected separation) north-west of its primary. Conclusions: The binaries HD125612AB and HD212301AB are new members in the continuously growing list of exoplanet host star systems of which 43 are presently known. Hence, the multiplicity rate of exoplanet host stars is about 17%. Based on observations obtained on La Silla in ESO programs 079.C-0099(A), 080.C-0312(A)

Motivation & Objective

• To identify wide stellar and substellar companions to exoplanet host stars using direct imaging.
• To determine the multiplicity rate of exoplanet host stars by identifying co-moving companions through multi-epoch astrometry.
• To assess orbital stability and detectability limits for additional companions in known binary systems.
• To contribute to the growing catalog of confirmed exoplanet host multiple star systems.
• To investigate the impact of stellar multiplicity on planet formation and orbital evolution.

Proposed method

• Conducted direct near-infrared imaging with SofI/NTT at the La Silla Observatory to detect wide companions to exoplanet host stars.
• Performed astrometric calibration using the 2MASS point source catalogue to determine precise source positions.
• Compared multi-epoch images (SofI 2007/2008 and 2MASS 1998) to measure proper motions and confirm co-moving companions.
• Used follow-up photometry and spectroscopy to estimate the masses and spectral types of detected companions.
• Applied evolutionary models (Baraffe et al. 1998) to estimate detection limits and constrain companion masses.
• Evaluated orbital stability using Holman & Murray (1999) criteria to define the long-term stable zone for additional companions.

Experimental results

Research questions

• RQ1 What is the multiplicity rate of exoplanet host stars, and how many are confirmed as multiple systems?
• RQ2 Are newly detected companions to HD 125612 and HD 212301 co-moving with their primary stars?
• RQ3 What are the physical properties (mass, spectral type, separation) of the newly identified companions?
• RQ4 What are the detection limits and stability constraints for additional companions in the HD 125612 and HD 212301 systems?
• RQ5 How do these findings contribute to understanding the role of stellar multiplicity in planet formation?

Key findings

• HD 125612 B is a co-moving M4 dwarf companion with a projected separation of approximately 4750 AU and a mass of 0.18 M☉.
• HD 212301 B is a co-moving M3 dwarf companion at a projected separation of about 230 AU and a mass of 0.35 M☉.
• The multiplicity rate of exoplanet host stars is confirmed to be at least 17%, based on 43 confirmed multiple systems among 250 known exoplanet hosts.
• The long-term stable zone for additional companions in the HD 125612 AB system extends up to approximately 650 AU (12.4 arcsec), while in the HD 212301 AB system it is limited to about 38 AU (0.7 arcsec).
• No additional companions were detected within the stable zones or beyond the 2MASS detection limit (15.1 mag, S/N=10) beyond 20 arcsec (~1060 AU) from either primary star.
• The study confirms that both HD 125612 AB and HD 212301 AB are new members of the growing list of exoplanet host multiple star systems.