2 Observations and data reduction

We observed the Gl 86 system with ESO's adaptive optics system ADONIS (Rousset & Beuzit 1999), mounted on the 3.6 m telescope on La Silla, Chile. The SHARP II+ near infrared camera was attached to the instrument and a pixel scale of 50 mas/pixel was used throughout all observations. In order to increase the sensitivity to detect any faint, closeby companion, the light of Gl 86 was suppressed by a pre-focal coronographic mask (Beuzit et al. 1997). For all observations a mask with a size of 1'' in diameter was chosen. Usually, we took cubes containing 60 images of Gl 86 with 6 s of integration time each. Sky emission was corrected by observing a position $1\hbox{$.^{\prime}$ }5$ north and south of Gl 86 immediately after the prime scientific target.

A brief observing log is given in Table 1.

For further data processing we got references of the Point-Spread-Function (PSF) by observing the star HD 13424 directly before or after each integration of Gl 86 (during the observations in September we observed an additional PSF reference star, namely HD 14112).

For the observing runs in November and December, the detector pixel scale and the absolute orientation of the camera were checked observing an astrometric reference field ($\theta$ Ori). The accuracy of the absolute field orientation is found better than $0.2 ^\circ$, fully consistent with systematic measurements taken over more than a year.

In general, the atmospheric conditions during our observations were good. Seeing conditions were always better than $1\hbox{$.^{\prime\prime}$ }2$ and in average around $0\hbox{$.^{\prime\prime}$ }8$. All observations were taken with an airmass of less than 1.5 except for the observations in December which were taken at an airmass of about 1.6. As photometric standard star we usually observed HR 0721. In the night of November 10, AS01 was observed as photometric standard star. The zero-points derived from the standard stars agree with the published values within 0.05 mag .

 

 

Table 1: Observing log for Gl 86. A coronographic mask with $1\hbox {$.^{\prime \prime }$ }$ in diameter was always used. For each filter setting, one data cube was acquired, except in the September night, when 5 independent measurements were performed

Date	filters used	remarks
08.09.2000	H	5 independent measurements
10.11.2000	J K
11.11.2000	J K $K_{\rm S}$
13.11.2000	$K_{\rm S}$
12.12.2000	CVF	$\lambda = 1.51, 1.57$ and $1.61~\mu$m