Type of Document Dissertation Author Raghavan, Deepak Author's Email Address raghavan@chara.gsu.edu URN etd-04212009-165714 Title A Survey of Stellar Families: Multiplicity of Solar-type Stars Degree Ph.D. Department Physics and Astronomy Advisory Committee
Advisor Name Title Harold A. McAlister Committee Chair A. G. Unil Perera Committee Member Brian D. Mason Committee Member David W. Latham Committee Member Douglas R. Gies Committee Member Russel J. White Committee Member Todd J. Henry Committee Member Keywords
- Radial Velocity
- Survey
- Brown dwarfs
- Exoplanet systems
- Solar neighborhood
- Solar-type stars
- Binary stars
- Stellar multiplicity
- Long baseline interferometry
Date of Defense 2009-04-02 Availability unrestricted Abstract I present the results of a comprehensive assessment of companions to 454 solar-type starswithin 25 pc. New observational aspects of this work include surveys for (1) very close
companions with long-baseline interferometry at the Center for High Angular Resolution
Astronomy (CHARA) Array, (2) close companions with speckle interferometry, and (3) wide
proper motion companions identified by blinking multi-epoch archival images. I have also
obtained and included unpublished results from extensive radial velocity monitoring programs.
The many sources utilized enable a thorough evaluation of stellar and brown dwarf
companions.
The results presented here include eight new companion discoveries, four of which are
wide common proper motion pairs discovered by blinking archival images, and four more
are from the spectroscopic data. The overall observed fractions of single, double, triple, and higher order systems are 57%±3%, 33%±2%, 8%±1%, and 3%±1%, respectively, counting
all stellar and brown dwarf companions. The incompleteness analysis indicates that only a
few undiscovered companions remain in this well-studied sample, showing that a majority
of the solar-type stars are single.
Bluer, more massive stars are more likely to have companions than redder, less massive
ones. I confirm earlier expectations that more active stars are more likely to have companions.
A preliminary, but important indication is that brown dwarfs, like planets, prefer stars with
higher metallicity, tentatively suggesting that brown dwarfs may form like planets when they
are companions to stars.
The period distribution is unimodal and roughly Gaussian with peak and median values
of about 300 years. The period-eccentricity relation shows a roughly flat distribution beyond
the circularization limit of about 12 days. The mass-ratio distribution shows a clear
discontinuity near a value of one, indicating a preference for twins, which are not confined
to short orbital periods, suggesting that stars form by multiple formation mechanisms. The
ratio 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 at sufficiently wide separations.
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