Very Low Mass Binaries Archive

This page last updated on Friday, August 18, 2006.

This Archive contains an uptodate list of all the stellar binary systems with total estimated mass < 0.2 M_solar known in the literature. It targets both theorists and observers interested in understanding the empirical data of this subject. In most cases binary parameters are extracted directly from refereed journals referenced in the Table. Additional background information can be found in:

Not Alone: Tracing the Origins of Very Low Mass Stars and Brown Dwarfs Through Multiplicity Studies (Burgasser, A. J., Reid, I. N., Siegler, N., Close, L., Allen, P., Lowrance, P., Gizis, J. 2006, chapter in Protostars and Planets V) (Download in postscript, PDF)

Relevant figures and figure captions: Mass Ratio Distribution, Separation Distribution, Spectral Type Combination Distribution.

Please send suggestions, corrections, and updates to nsiegler at I'm in the process of providing more complete references. If this table has been useful in your research, we suggest an acknowledgment of the form "This publication has made use of the VLM Binaries Archive maintained by Nick Siegler at

Columns In The Table:

Notes: dash: not measured or not reported; semicolon as suffix: estimated value (eg L:)

  1. "name" : name of the more massive component in the binary
  2. "rho (AU)" : projected separation (AU). It is the product of the measured angular separation in arcsec (column 4 / 1000) and distance in parsecs (column 6) unless astrometric constraints known (column 9)
  3. "rho_error (AU)" : projected separation uncertainty (AU). Uncertainties of the measured angular separation (column 5 / 1000) and distance (column 7) taken in quadrature.
  4. "rho (mas)" : angular separation (mas); SB2: double-lined spectroscopic binaries
  5. "rho_error (mas)" : angular separation uncertainty (mas); NG: uncertainty not given by authors
  6. "dist (pc)" : distance (pc) (typically photometric or spectra-photometric derived distances, trig parallax if column 8 = Y)
  7. "dist_error (pc)" : distance uncertainty (pc)
  8. "plx (Y/N)" : measured trigonometric parallax: Y/N
  9. "sma (Y/N)" : measured semimajor axis: Y/N (a Y may also include a constrained orbital period)
  10. "SpT A" : estimated spectral type component A (Unless spectra was obtained from the resolved binary components, a Y in column 11, component A is estimated from an empirical absolute magnitude relation chosen by the authors; delta magnitude is applied to obtain component B's spectral type. Absolute magnitude of the primary is estimated from A's color. Uncertainties are typically +/- 1.5 SpT.
  11. "SpT B" : estimated spectral type component B
  12. "SpT region (O/I)" : optical (O) or infrared (I) spectral classification; if both are available, optical is reported
  13. "resolv. sp. (Y/N)" : actual spectra obtained of the resolved members: Y/N
  14. "mass A (Msun)" : estimate of primary mass (solar masses); taken as the best estimate of the reported mass range. Except for the few cases where dynamical masses are measured or constrained (column 9 = Y), masses are estimated through the use of evolutionary models requiring age and distance estimates. There may be large uncertainties associated with these estimated masses mainly due to the unceratinties of these parameters (reported mass uncertainties are typically < 0.02 solar mass). Mass models are typically insensitive to ages > 1 Gyr.
  15. "mass B (Msun)" : estimate of secondary mass (solar masses); taken as the center of the reported mass range with uncertainties typically < 0.02 solar masses.
  16. "q" : q ratio
  17. "P (yr)" : period (yr). Calculated by Kepler's 3rd Law and a statistical scaling of the measured angular separation by 1.26 (Fischer & Marcy 1991) unless period measured or constrained by authors (column 9 = Y).
  18. "age (Myr)" : estimated age (Myr); central of range reported. Field star ages are not quantified here (dash) but can be considered to span the range of solar neighborhood common ages (0.6-7.5 Gyr).
  19. "location" : name of association or cluster, otherwise "field".
  20. "bin. ref." : binary reference
  21. "SpT ref." : spectral type reference of the integrated binary or if column 9 = Y of the resolved binary
  22. "dist. ref." : distance reference
  23. "comments" : comments