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?

• Stars : stable fusion of Hydrogen, M>70

• Planets: no nuclear reactions, M<13

• Intermediate objects with can sustain burning of Deuterium

JM

JM

JJ MMM 7013

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

A conventional Hertzsprung-Russell diagram

The ultracool bottom end of the HR diagram

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

• “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.

• 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.

What do astronomers hope to learn from the radio emission of brown dwarfs?

• Only direct access to magnetic fields

• Field configuration

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

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±182M0746+2000 L0.5 286±24 2M0523-1403 L2.5 231±14 2M0036+1821 L3.5 134±16

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±2002M0036+1821 L3.5 720±40

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

8.44 GHz observations of TVLM 513-46546

8.44 GHz observations of 2M0036+2000

Acknowledgments

Comparison of the sun, MLT dwarfs, and Jupiter: Dr. Robert Hurt of the Infrared Processing and Analysis Center

First HR diagram: WikipediaSecond HR diagram : Space Telescope Science Institute

Maser data: Dr. Sharmila GoedhartTVLM 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)