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Astrostatistics , and Brown Dwarfs

Astrostatistics , and Brown Dwarfs. Chris Koen , Dept. Statistics, University of the Western Cape. The GMC mass distribution in M33, as determined from radio flux measurements. HartRAO observations of G12.89+0.49. HartRAO observations of G12.89+0.49: detail. What are brown dwarfs?.

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Astrostatistics , and Brown Dwarfs

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  1. Astrostatistics, and Brown Dwarfs Chris Koen, Dept. Statistics, University of the Western Cape

  2. The GMC mass distribution in M33, as determined from radio flux measurements

  3. HartRAO observations of G12.89+0.49

  4. HartRAO observations of G12.89+0.49: detail

  5. What are brown dwarfs? • Stars : stable fusion of Hydrogen, M>70 • Planets: no nuclear reactions, M<13 • Intermediate objects with can sustain burning of Deuterium

  6. A few properties • Radius ~ 0.1 R₀ • Surface temperature < 3000 K • Luminosity ~ 10⁻⁴ L₀ • Central temperature ~ 10⁶ K • Deuterium burning lifetime a few Myr • Spectral classes M, L, T

  7. A conventional Hertzsprung-Russell diagram

  8. The ultracool bottom end of the HR diagram

  9. The Sun; M, L, T dwarfs; the planet Jupiter

  10. “Only a few hundred stellar radio sources are now known” (SKA website). • Because of their low temperatures and small radii, radiation levels of brown dwarfs are lower than those of stars.

  11. Nonetheless, radio emission has been detected from a few late M (i.e. spectral types M7-M9) and L dwarfs. • The emission is non-thermal, i.e. it is due to the action of magnetic fields.

  12. What do astronomers hope to learn from the radio emission of brown dwarfs? • Only direct access to magnetic fields • Field configuration

  13. Extent of the study to data • About 90 objects have been studied (more than 500 L and T dwarfs known) • Only 9 detections • Quiescent , flaring and burst emission have been seen • Quiescent emission not always at the same level • Mostly single frequency

  14. Quiescent radio emission from UCDs Name Spectral type Flux (microJy) LHS3003 M7 270±40 2M1048-3956 M8 140±40 TVLM513-46 M8.5 190±15 LSR1835+3259 M8.5 525±15 LP944-20 M9 74±13 BRI0021-0214 M9.5 83±18 2M0746+2000 L0.5 286±24 2M0523-1403 L2.5 231±14 2M0036+1821 L3.5 134±16

  15. Flaring radio emission from UCDs Name Spectral type Flux (microJy) 2M1048-3956 M8 (29.6±1)X10⁴ TVLM513-46 M8.5 980±40 LP944-20 M9 2600±200 2M0036+1821 L3.5 720±40

  16. DENIS 1048-3956 flaring emission at 4.80(gray) and 8.64 GHz (black)

  17. 8.44 GHz observations of TVLM 513-46546

  18. 8.44 GHz observations of 2M0036+2000

  19. Acknowledgments Comparison of the sun, MLT dwarfs, and Jupiter: Dr. Robert Hurt of the Infrared Processing and Analysis Center First HR diagram: Wikipedia Second HR diagram : Space Telescope Science Institute Maser data: Dr. SharmilaGoedhart TVLM 513-46546: Hallinan et al. (ApJ 663, L25; 2007) 2M0036+2000: Hallinan et al. (ApJ 684, 644; 2008) Denis 1048-3956: Burgasser & Putman (ApJ 626, 486; 2005)

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