Before going into the analysis of the associated wave and the light curve of BH Vir itself, we have estimated the local interstellar extinction using the comparison stars.
HD 121935, (mv=9.67, F4 V) and HD 139643 (mv=9.44, G0 V), were
used as comparison stars. We checked their constancy every night. We found a
RMS dispersion for the 564 differential magnitudes measured of 0.012,
0.010, 0.015, 0.021, and 0.017
for V, (b-y), m1, c1 and 
respectively.
The standard value obtained for the comparison star, HD 121935, was
, 
, 
, 
,
and 
, for V, (b-y), m1, c1 and
respectively.
To estimate the local reddening we have followed a procedure similar to that described in Reglero et al. (1990). We obtained E(b-y)=0.031 and E(b-y)=0.021 for HD 121935 and HD 139643 respectively, with a mean value of E(b-y)=0.026. This value agrees well with the one calculated previously in Clement et al. (1993). The small apparent angular distance between the comparisons and BH Vir and their location at 208 and 106 pc behind and in front of BH Vir, suggests the same interstellar extinction for BH Vir itself. We have adopted the mean value as the reddening for BH Vir.
After correcting magnitudes and indices for reddening, radiative parameters
have been derived for both stars, using the well know
standard calibration procedure for F type stars given by Crawford
(1975). This method assumes the
index as a reddening free independent parameter. Effective
temperatures, 
, and visual surface brightness, 
, were
derived from the semiempirical calibrations of Saxner & Hammarback
(1985) and Moon (1985) respectively.
Both comparisons appear to be main sequence stars
with solar metal abundances and located at 208 and 106 pc respectively.
Their spectral types can be estimated, from the present photometric
calibrations, as F4 and G0 stars respectively. Their location in the HR
and photometric m1-(b-y)
and c1-(b-y) diagrams indicate a luminosity class V for both.
The derived physical quantities for the comparisons of BH Vir are listed in
Table 1 (click here). The errors on the table are the ones indicated for the
calibrations, and for the distance the error is obtained through error
propagation in the formula.
| name | Mv | | [Fe/H] | | d | Sp |
| HD 121935 | 3.1 | 3.83 | 0.1 | 6590 | 208 | F4 V |
| 3 | 3 | 2 | 60 | 27 | ||
| HD 139643 | 4.3 | 3.76 | -0.1 | 5914 | 106 | G0 V |
| 3 | 3 | 2 | 60 | 14 |