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

¹ MPI für extraterrestrische Physik, Giessenbachstraße 1, 85740 Garching, Germany
² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
³ I. Physikalisches Institut, Universität zu Köln, Germany

Corresponding author: R. Neuhäuser, rne@mpe.mpg.de

Received: 14 May 2002
Accepted: 4 September 2002

Abstract

We present JHK images of the young (~20 Myrs) nearby (~48 pc) stars HD 199143 and HD 358623 (van den Ancker et al. [CITE]) with high sensitivity and high dynamic range in order 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 the infrared imaging camera SofI in December 2000, July 2001, and December 2001, all at the ESO 3.5m NTT. We present a companion candidate with a 2 arcsec offset being almost 2 mag fainter than HD 358623 with proper motion (over one year baseline) consistent with the known proper motion of the primary star HD 358623 A and deviant from the assumption that it is a non-moving background object. Then, we obtained a spectrum in the H-band (with SofI at the NTT) of this companion showing that it has spectral type M2 (), consistent with its JHK colors (for negligible extinction) and with being a companion (i.e. at same age and distance) of HD 358623 A (K7-M0), given the magnitude difference. Also, a companion candidate with a 1 arcsec offset being 2 mag fainter than HD 199143 is detected, but clearly resolved from the primary only with SHARP-I, so that we have no proper motion information. Also, we could not obtain a spectrum with SofI due to the high dynamic range. The JHK colors of this candidates and the magnitude difference between primary (F8) and companion candidate are consistent with a spectral type M0-2. This companion candidate was predicted by van den Ancker et al. ([CITE]) to explain some unusual properties of the primary star HD 199143 A. 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. Both these companions were presented previously by Jayawardhana & Brandeker ([CITE]), but only with single-epoch images in J and K obtained in May 2001. Our limits for additional detectable but undetected companions are such that we would have detected all stellar companions with separations ≥ (24 AU at 48 pc).