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Astron. Astrophys. 360, L39-L42 (2000)

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2. The spectral type of CoD-33°7795 B

An optical spectrum of CoD-33°7795 B was obtained with the FOcal Reducer/low dispersion Spectrograph 2 (FORS2) at the European Southern Observatory (ESO) 8.2m telescope Kueyen, Unit Telescope 2 (UT2) of the Very Large Telescope (VLT). The 30 min exposure spectrum in the 6000 to 9000 Å range (R=680) using grism 300I and order separation filter OG590 was taken during a technical night on 23 Feb 2000. The [FORMULA] slit was positioned just on object B in E-W direction.

Standard data reduction was done with MIDAS. The final spectrum is shown in Fig. 1. The spectral type of CoD-33°7795 B is M8.5 to M9 according to different spectral indices (see also Kirkpatrick et al. 1991). The equivalent width of the H[FORMULA] emission is [FORMULA]Å, stronger than in old M8-M9 dwarfs. The Na I doublet line at 8183 and 8195Å is slightly weaker than in the standards, which is indicative of low gravity (Kirkpatrick et al. 1991). Both the strong H[FORMULA] emission and the weak Na absorption indicate a young age. The spectral resolution is too low to split the Na I doublet or to resolve the Li 6708Å line (next to the TiO 6713Å and Ca 6718Å lines).

[FIGURE] Fig. 1. Our optical spectrum of CoD[FORMULA] B compared with M8 dwarfs (average of LHS 2243, LHS 2397 A, LP 412-31, and vB 10) and M9 dwarfs (average of BRI 1222-1222, LHS 2065, LHS 2924, and TVLM 868-110639), showing that our object is M8.5 to M9 (comparison spectra from K. Luhman). Strong H[FORMULA] and weak Na indicate a young age

An H-band spectrum (R[FORMULA]) was obtained on 16 Apr 2000 with the Infrared Spectrograph and Array Camera (ISAAC) at the ESO 8.2m telescope Antu (VLT-UT1). The spectrum consists of 20 co-added 60s exposures through a [FORMULA] slit, aligned neither along the position angle of the pair nor perpendicular to it, but in between those two positions, so that the two objects are well separated and that the flux from the companion candidate is several times larger than the flux from the bright star.

After standard data reduction, we modelled and subtracted the flux of the bright star from the faint object's spectrum at each wavelength. Mainly due to the slope of the continuum (Fig. 2), CoD-33°7795 B has spectral type M8.5 to M9, consistent with the IHJK colors (L99 and W99). Recently, Schneider et al. (2000) presented an HST/STIS spectrum of CoD-33°7795 B, which is in good agreement with our results.

[FIGURE] Fig. 2. Our H-band spectrum of CoD[FORMULA] B compared with the M8 dwarfs LHS 2397 A and LP 771-21 as well as the M9 dwarf LHS 2065 (Delfosse et al. 1998) showing that our object is M8.5 to M9. Also plotted is CoD[FORMULA] A

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000