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Astron. Astrophys. 345, L55-L57 (1999)

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6. X-ray luminosity

The inferred spectral type M5 places this object into a range of spectral classes where chromospheric activity is present in about half of all M dwarfs (see e.g. Hawley, Gizis & Reid 1996). Schmitt, Fleming & Giampapa (1995) presented a complete X-ray survey of all known M and K stars in the immediate solar vicinity (distances less than 7 pc). They found that the observed X-ray luminosity function of K and M dwarfs spans almost four orders of magnitude ([FORMULA]). However, the stars with [FORMULA] do not seem to exceed X-ray luminosities of [FORMULA] ergs s-1. With an ROSAT All Sky Survey (see e.g. Belloni, Hasinger & Izzo 1994) count rate of 0.0669 s-1 and X-ray hardness ratio of -0.49 and the estimated distance of 12 pc for APMPM J0237-5928 = 1RXS J023630.5-592827, we determine [FORMULA] using the conversion factor CF given in Schmitt, Fleming & Giampapa (1995). This is a relatively large [FORMULA] value, but still below the observed limit for late-type M dwarfs mentioned by Schmitt, Fleming & Giampapa (1995).

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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