Coronal X-ray emission from an intermediate-age brown dwarf

Astrophysics, abstract
astro-ph/0304231

From: Yohko Tsuboi <tsuboi@ieyasu.phys.chuo-u.ac.jp>

Date: Sat, 12 Apr 2003 08:18:00 GMT   (63kb)

Authors:
Yohko Tsuboi,
Yoshitomo Maeda,
Eric D. Feigelson,
Gordon P. Garmire,
George Chartas,
Koji Mori,
Steven H. Pravdo

Journal-ref: 2003, Apj 587, L51

We report the X-ray detection of the brown dwarf (BD) companion TWA 5B in a
$simeq 12$ Myr old pre-main sequence binary system. We clearly resolve the
faint companion (35 photons) separated from the X-ray luminous primary by 2
arcsec in a {it Chandra} ACIS image. TWA 5B shows a soft X-ray spectrum with a
low plasma temperature of only 0.3 keV and a constant flux during the 3 hour
observation, of which the characteristics are commonly seen in the solar
corona. The X-ray luminosity is 4$ imes10^{27}$ erg s$^{-1}$ (0.1–10 keV
band) or $log L_X/L_{bol} = -3.4$.

Comparing these properties to both younger and older BDs, we discuss the
evolution of the X-ray emission in BDs. During their first few Myr, they
exhibit high levels of X-ray activity as seen in higher mass pre-main sequence
stars. The level in TWA 5B is still high at $t simeq 12$ Myr in $log
L_X/L_{bol}$ while $kT$ has already substantially cooled.

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