Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21724218s&link_type=abstract
American Astronomical Society, AAS Meeting #217, #242.18; Bulletin of the American Astronomical Society, Vol. 43, 2011
Astronomy and Astrophysics
Astronomy
Scientific paper
For a long time ultracool dwarfs (stellar objects with spectral types later than M7) were not thought to display any of the characteristics associated with the presence and action of strong magnetic fields, but surprisingly, recent observations have demonstrated the continuation of chromospheric and coronal indicators into this regime. The radio and X-ray behavior of ultracool dwarfs in particular show strikingly different behaviors when compared to what is seen in higher mass stars: objects detected at X-ray wavelengths show the decline of plasma heating with effective temperature but with examples of flare-like behavior which suggest some continuation in behavior from early-mid M dwarf stars. Radio detections of ultracool dwarfs are characterized by variability which occurs on timescales associated with the rotation period, and the dominant emission mechanism may switch from the incoherent gyrosynchrotron seen on earlier M stars to a coherent maser process. There is a discontinuity between radio-detected ultracool dwarfs (which tend to be X-ray weak or undetected) and X-ray detected ultracool dwarfs, which tend to be radio weak or undetected. The young brown dwarf binary LP 349-25 is a peculiar radio emitter due to its lack of radio variability on both long and short timescales. The lack of rotational modulation presents difficulties for the generation of radio emission in strong large scale magnetic fields. To further investigate the conditions of LP349-25, we present simultaneous radio and x-ray observations of LP349-25. Initial analysis of the data shows that the radio emission continues to be constant and that LP349-25 additionally shows quiescent x-ray emission. This allows us to place additional constraints on the mechanism for radio emission in LP349-25 and explore the conditions which cause disparate high energy behaviors in ultracool dwarfs.
Hawley Suzanne L.
Ngoc P.
Osten Rachel Ann
Reid Neil
Schmidt Sarah J.
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