Observed polarization of brown dwarfs suggests low surface gravity

Sujan Sengupta, Mark S. Marley

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Light scattering by atmospheric dust particles is responsible for the polarization observed in some L dwarfs. Whether this polarization arises from an inhomogeneous distribution of dust across the disk or an oblate shape induced by rotation remains unclear. Here, we argue that the latter case is plausible and, for many L dwarfs, the more likely one. Furthermore, evolutionary models of mature field L dwarfs predict surface gravities ranging from about 200 to 2500 m s-2 (corresponding to masses of ∼15-70 MJupiter). Yet comparison of observed spectra to available synthetic spectra often does not permit more precise determination of the surface gravity of individual field L dwarfs, leading to important uncertainties in their properties. Since rotationally induced non-sphericity, which gives rise to non-zero disk-integrated polarization, is more pronounced at lower gravities, polarization is a promising low gravity indicator. Here, we combine a rigorous multiple scattering analysis with a self-consistent cloudy atmospheric model and observationally inferred rotational velocities and find that the observed optical polarization can be explained if the surface gravity of the polarized objects is about 300 m s-2 or less, potentially providing a new method for constraining L dwarf masses.

Original languageEnglish (US)
Pages (from-to)L142-L146
JournalAstrophysical Journal Letters
Issue number2 PART 2
StatePublished - Oct 20 2010
Externally publishedYes


  • Brown dwarfs
  • Polarization
  • Scattering
  • Stars: atmospheres
  • Stars: low-mass

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Observed polarization of brown dwarfs suggests low surface gravity'. Together they form a unique fingerprint.

Cite this