A Survey of Stellar Families: Multiplicity of Solar-Type Stars (1007.0414v1)

Abstract: We present the results of a comprehensive assessment of companions to solar-type stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog with {\pi} > 40 mas, {\sigma}_{\pi}/{\pi} < 0.05, 0.5 < B - V < 1.0 (~ F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the CHARA Array, (2) close companions with speckle interferometry, and (3) wide proper motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs. The overall observed fractions of single, double, triple, and higher order systems are 56% \pm 2%, 33% \pm 2%, 8% \pm 1%, and 3% \pm 1%, respectively, counting all confirmed stellar and brown dwarf companions. Our completeness analysis indicates that only a few undiscovered companions remain in this well-studied sample, implying that the majority (54% \pm 2%) of solar-type stars are single, in contrast to the results of prior multiplicity studies. The orbital-period distribution of companions is unimodal and roughly log-normal with a peak of about 300 years. The period-eccentricity relation shows a roughly flat distribution beyond the expected circularization for periods below 12 days. The mass-ratio distribution shows a preference for like-mass pairs, which occur more frequently in relatively close pairs. The fraction of planet hosts among single, binary, and multiple systems are statistically indistinguishable, suggesting that planets are as likely to form around single stars as they are around components of binary or multiple systems with sufficiently wide separations.

• The paper refines solar-type star multiplicity fractions using comprehensive methods including interferometry and radial velocity monitoring.
• Period distributions reveal a log-normal pattern centered around 300 years with a preference for near-equal-mass companions.
• Findings indicate metallicity and age influence multiplicity, with lower companion rates in older stars and increased likelihood for stars with low [Fe/H].

Analysis of the Multiplicity of Solar-Type Stars

The paper presents an in-depth analysis of the multiplicity of solar-type stars within 25 parsecs using data from the Hipparcos catalog. It thoroughly evaluates stellar companions to solar analogs (spectral types F6–K3), providing an updated understanding of binary and higher-order systems compared to previous surveys, notably Duquennoy & Mayor (1991, DM91). The diverse methods employed for this paper, including long-baseline interferometry, speckle interferometry, and radial velocity monitoring, are comprehensive and cover a significant spectrum of detection space, ensuring high completeness.

Key Findings

1. Multiplicity Fractions: The paper finds that approximately 54% ± 2% of solar-type stars exist in solitude, challenging prior expectations of stellar multiplicity (which asserted most stars have companions). Only 33% are part of binary systems, while another 11% exist in triple or higher-order formations.
2. Period and Mass Ratio Distributions: The orbital period distribution is unimodal and log-normal, centering around 300 years, representing a longer median period than previous estimates, which underscores the paper's depth and thoroughness in capturing wide-separation binaries. Moreover, the mass ratio distribution shows a preference for like-mass pairs, especially at shorter periods, which was not detailed in earlier studies.
3. Stellar Companions and Metallicity: There appears to be an intriguing trend where stars with [Fe/H] < −0.3 exhibit a higher likelihood of having companions, deviating from past trends suggesting multiplicity might lessen with lower metallicity.
4. Eccentricity Observations: The paper observes flat eccentricity distributions beyond a circularization period of ~12 days. Systems with periods below this threshold show expected circularity, with only a few exceptions, which might be affected by mechanisms like the Kozai-Lidov oscillations in triple systems.
5. Age and Star System Dynamics: The survey aligns older, less active stars with lower multiplicity incidence, highlighting that dynamical evolution may strip systems of companions over time, possibly as a result of dynamical interactions.
6. Planet Formation: Planet formation appears equally feasible around single stars and those with wide companions, expanding the known viable environments for planet formation and suggesting that tight binaries are more prone to disrupting protoplanetary disks.

Implications

This research reframes our understanding of the prevalence of multiplicity among solar-type stars, showing a significant number exist as single stars, contrary to expectations from previous decades. By using a range of methods, each covering unique sections of the companion detection spectrum, the authors establish new benchmarks in which companion completeness is well-attested. Their results have far-reaching implications on models of stellar formation, adjustments needed for binary population synthesis, and the understanding of habitable environments considering stellar interactions and the availability of stable planet-hosting zones.

Future Directions

Based on the comprehensive survey and findings, further research could focus on longer orbital empirical characterization of large separation pairs and probing of potential dark or massive companions in binaries with high mass ratios. Furthermore, advancing definitions and constraints on the brown dwarf desert, indicated yet unresolved in this paper, remains promising. New missions with GAIA-level precision could refine these multiplicity fractions further and provide more definitive answers on companion dynamics and evolution across various stellar ages and environments.

This work not only advances our cataloging of nearby solar-type stars but also encourages the recalibration of predicted multiplicity rates of analogous stars in other galactic regions under varying metallicity and environmental conditions.