Astron. Astrophys. 330, 619-625 (1998)

2. Material

We have used the list of MK standards collected by Garcia (1989) and have sorted out all the stars of that list observed by Hipparcos. The selection by Garcia was based upon specific recommendation of W.W. Morgan. Since we are interested only in early type stars we have stopped at F5. Of the resulting stars we have selected those belonging to the Hipparcos survey (Turon et al., 1992) and from these -203 stars- we have retained only those with absolute magnitude errors 0.3 mag, which leaves us with 96 standards for the interval B0-F5. What is apparent from the latter condition is that high luminosity stars will be underrepresented. The stars were then scrutinized for companions and for interstellar extinction. The correction for binarity is no problem in the case of visual binaries. In the case of double lined spectroscopic binaries, the correction can be derived through the mass ratio and the mass luminosity relation. For spectroscopic single lined binaries we have used a uniform correction of 0.2 mag, which corresponds to a magnitude difference between components of 1.7 mag. This correction has also been applied when The Bright Star Catalogue (Hoffleit & Jaschek, 1982) states "SB" but no orbit exists. It is clear that more undetected binaries exist and that the average correction of 0.2 mag is a rough approximation. This introduces an unavoidable uncertainty in the absolute magnitudes of the order of one or two tenths, the stars being brighter than they should be in reality. As for interstellar extinction we have used the common procedure to take the colour excess in (B-V) for the estimation of the extinction. Fortunately, most of the stars have small colour excesses. Since the spectral type-(B-V) relation has an intrinsic width by itself, we have corrected the extinction only when the colour excess is larger than 0.03 mag. The cases in which corrections for binarity and color excess have been applied are marked in Table 1.

Table 1. Absolute magnitudes of the MK standards

Table 1. (continued)

Table 1. (continued)

© European Southern Observatory (ESO) 1998

Online publication: January 16, 1998
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