Deep infrared imaging and spectroscopy of the nearby late M-dwarf DENIS-P J104814-395606

R. Neuhäuser, E. W. Guenther, J. Alves, N. Grosso, Ch. Leinert, Th. Ratzka, Th. Ott, M. Mugrauer, F. Comerón, A. Brandner, W. Eckart

We obtained deep H- and K-band images of DENIS-P J104814-395606 using

SofI and the speckle camera SHARP-I at the ESO-3.5m-NTT as well as QUIRC

at the Mauna Kea 2.2m telescope between December 2000 and June 2001. The

target was recently discovered as nearby M9-dwarf among DENIS sources

(Delfosse et al. 2001). We detect parallactic motion on our images and

determine the distance to be 4.6 +/- 0.3 pc, more precise than

previously known. From the available colors, the distance, and the

spectral type, we conclude from theoretical models that the star has a

mass of ~ 0.075 to 0.09 Msun and an age of ~ 1 to 2 Gyrs.

We also obtained H- and K-band spectra of this star with ISAAC at the

VLT. A faint companion candidate is detected 6'' NNW of the

star, which is 6.4 +/- 0.5 mag fainter in H. However, according to

another image taken several month later, the companion candidate is not

co-moving with the M9-dwarf. Instead, it is a non-moving background

object. Limits for undetected companion candidates are such that we can

exclude any stellar companions outside of ~ 0.25'' (1 AU),

any brown dwarf companions (above the deuterium burning mass limit)

outside of ~ 2'' (9 AU), and also any companion down to ~

40 M_jup with >= 0.15'' (0.7 AU) separation, all

calculated for an age of 2 Gyrs. Our observations show that direct

imaging of sub-stellar companions near the deuterium burning mass limit

in orbit around nearby ultra-cool dwarfs is possible, even with

separations that are smaller than the semi-major axis of the outermost

planet in our solar system, namely a few tens of AU.

Department of Astrophysics
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Thüringer Landessternwarte Tautenburg, Universität zu Köln, European Southern Observatory (Germany), Max-Planck-Institut für extraterrestrische Physik, Max-Planck-Institut für Astronomie
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