3 Companion candidates: Photometry

The companion candidates detected in J and K by JB01 in their May 2001 ADONIS images are also detected in our H-band SofI images in Dec. 2000 and Dec. 2001 and as well in JHK in our July 2001 SHARP-I images. We obtained the JHK magnitudes of the stars and companion candidates from the SHARP-I images (because the objects are best separated on those image, see Figs. 1 and 2) by normal aperture photometry with an aperture size just small enough to exclude the companion, compared to the flux standard HR 8278 (van der Bliek et al. 1996) observed in JHK immediately after the respective science target. Then, the magnitudes for the companion candidates are obtained from the background-subtracted flux ratio with their respective primary. The resulting photometric data are listed in Table 2.

3.1 HD 199143

We display the SHARP-I JHK images of HD 199143 and its close ( $1^{\prime \prime}$) companion candidate in Fig. 1 together with the Dec. 2000 SofI image, where the companion candidate (called HD 199143 B in JB01) was marginally detected.

   

Table 2: Photometry.

Object	J	H	K	AV	SpecType
HD 199143 A	6.2	6.0	6.0	$\le$0.1	F8 (1,2)
HD 199143 B	9.2	8.4	8.2	$\le$0.1	M0-2 (3)
HD 358623 A	8.0	7.3	7.2	$\le$0.1	K7-M0 (1,4)
HD 358623 B	9.7	9.0	8.8	$\le$0.1	M$2 \pm 1$ (5)

Magnitudes and absorptions from our data ($\pm 0.1$ mag). References for spectral types: (1) Simbad, (2) vdA00, (3) this work, from JHK photometry (Sect. 3.2), (4) Mathioudakis et al. (1995), (5) this work, from an H-band spectrum (Sect. 5).

Our data on HD 199143 A agree well with those in JB01, within our more conservative precision of $\pm$0.1 mag (as we observed less standards), while HD 199143 B is 0.3 mag brighter in our data than in JB01, possibly due to problems in JB01 with the subtraction of the bright background due to the PSF of HD 199143 A (R. Jayawardhana, priv. comm.).

The IR colors $J-H=0.2 \pm 0.1$ and $H-K=0.0 \pm 0.1$ mag (Table 2) for HD 199143 A are consistent with its spectral type F8 and its optical colors, for negligible foreground extinction. The companion candidate to HD 199143 is redder than the primary, either because it is less massive and/or more reddened, namely by either circumstellar material and/or other foreground extinction. In case of negligible absorption, as towards the primary, the JHK colors of the companion candidate would be consistent within the errors with a mid-K to mid-M type dwarf. If the companion candidate is at the same distance as the primary and also on the zero-age main-sequence, then its absolute JHK magnitudes are best consistent with an early M-type dwarf. Hence, our spectral type classification is M0-2.

3.2 HD 358623

HD 358623 and its close ( $2^{\prime \prime}$) companion candidate (called HD 358623 B in JB01) are shown in Fig. 2. The primary star and the companion candidate are also well separated and detected in our SofI images, so that we can obtain photometric and astrometric data from both the SofI and the SHARP-I images. In case of the SofI images, we used the faint HST standard stars S-361-D and S-754-C (Persson et al. 1998), and the data agree well with our SHARP-I H-band magnitudes. Our data on HD 358623 A and B also agree well with those in JB01. Hence, we have no indication of variability.

The IR colors $J-H=0.7 \pm 0.1$ and $H-K=0.1 \pm 0.1$ mag for HD 358623 A are consistent with its spectral type of K7-M0, for negligible extinction. There is no reddening observed in the near IR in these two stars, consistent with the spectral energy distribution shown in vdA01, where some moderate IR excess is seen only in the thermal IR.

The IR colors of the companion candidate HD 358623 B are very similar as for the primary HD 358623, but also consistent with any spectral type between mid-K and mid-M. Furthermore, the companion candidate is only slightly fainter (less than 2 mag) than the primary, so that it could be a slightly redder stellar secondary with slightly less mass and slightly later spectral type (early to mid-M). A spectral type M0-3 is most consistent with its absolute JHK-band magnitudes, when assuming that is has the same distance as HD 199143 A and that it is also located on the zero-age main-sequence. This classification will be refined by an H-band spectrum (Sect. 5).

Whether the two companion candidates are truely bound companions or (possibly reddened) background stars can be found out best by spectroscopy and proper motion.