Infrared imaging and spectroscopy of companion candidates near the young stars HD 199143 and HD 358623 in Capricornius

We present JHK images of the young (~20 Myrs) nearby (~48 pc) stars HD 199143 and HD 358623 to search for (sub-)stellar companions around them. The images were obtained in JHK with the speckle camera SHARP-I in July 2001 and in H with SofI in Dec 2000, July 2001, and Dec 2001, all at the ESO 3.5m NTT. We present a companion candidate with a 2 arc sec offset being almost 2 mag fainter than HD 358623 with proper motion consistent with the known proper motion of the primary star HD 358623 A. Then, we obtained a spectrum in the H-band (with SofI at the NTT) of this companion showing that it has spectral type M1-3, consistent with being a companion of HD 358623 A (K7-M0). Also, a companion candidate with a 1 arcsecond offset being 2 mag fainter than HD 199143 is detected. The JHK colors of this candidate are consistent with a spectral type M0-2. We determine the ages and masses of all four objects from theoretical tracks and isochrones, all four stars appear to be co-eval with ~20 Myrs. Our limits for additional detectable but undetected companions are such that we would have detected all stellar companions with separations > 0.5 arc sec (24 AU at 48 pc).