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Published March 2009 | Published
Journal Article Open

The Palomar/Keck Adaptive Optics Survey of Young Solar Analogs: Evidence for a Universal Companion Mass Function


We present results from an adaptive optics survey for substellar and stellar companions to Sun-like stars. The survey targeted 266 F5-K5 stars in the 3 Myr-3 Gyr age range with distances of 10-190 pc. Results from the survey include the discovery of two brown dwarf companions (HD 49197B and HD 203030B), 24 new stellar binaries, and a triple system. We infer that the frequency of 0.012-0.072 M_☉ brown dwarfs in 28-1590 AU orbits around young solar analogs is 3.2^(+3.1)_(–2.7%) (2σ limits). The result demonstrates that the deficiency of substellar companions at wide orbital separations from Sun-like stars is less pronounced than in the radial velocity "brown dwarf desert." We infer that the mass distribution of companions in 28-1590 AU orbits around solar-mass stars follows a continuous dN/dM_(2)∝ M^(–0.4)_2 relation over the 0.01-1.0 M_☉ secondary mass range. While this functional form is similar to that for isolated objects less than 0.1 M_☉ , over the entire 0.01-1.0 M_☉ range, the mass functions of companions and of isolated objects differ significantly. Based on this conclusion and on similar results from other direct imaging and radial velocity companion surveys in the literature, we argue that the companion mass function follows the same universal form over the entire range between 0 and 1590 AU in orbital semimajor axis and ≈ 0.01-20 M_☉ in companion mass. In this context, the relative dearth of substellar versus stellar secondaries at all orbital separations arises naturally from the inferred form of the companion mass function.

Additional Information

© 2009. The American Astronomical Society. Received 2008 January 25; accepted 2008 September 25; published 2009 February 20. We thank R. Dekany, M. Troy, and M. Britton for sharing with us their expertise on the Palomar AO system, R. Burress and J. Hickey for assistance with PHARO, R. Campbell, P. Amico, and D. Le Mignant for their guidance with using Keck AO, K. Matthews and D. Thompson for help with NIRC2, and our telescope operators at the Palomar Hale and Keck II telescopes. We are also grateful to K. Matthews for loaning us a pinhole mask for the astrometric calibration of PHARO, and to both R. Dekany and K. Matthews for key insights into the design of the calibration experiment. Use of the FEPS Team database has proven invaluable throughout the course of our survey.We thank J. Carpenter for building and maintaining the database. For the target selection, age-dating, and determination of distances to the FEPS sample stars, we acknowledge the tremendous amount of work performed by E. Mamajek. This publication makes use of data products from the 2MASS, funded by the NASA and the NSF. The authors also wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain ofMauna Kea we are privileged to be guests. Support for S.A.M. was provided by NASA through the Spitzer Legacy Program under contract 1407 and through the Spitzer Fellowship Program under award 1273192. Research for this paper was also supported by the NASA/Origins R&A program.

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