The parameters derived from the photometry are presented in Tables 2a and 2b. The
HD numbers, MK types and the reddening-corrected quantities (b-y)0, m0, c0 and
V0
together with the color excess E(b-y) are given in the first six columns. The absolute
magnitude Mv, the true distance moduli V0-Mv (for a normal extinction law (R=3.2)
and a
coefficient 0.74=E(b-y)/E(B-V)) and the distance r in parsecs are listed in the last three
columns.
It is well known that the color excess and absolute magnitude determination via
uvby
photometric quantities have to be done using different calibrations for the different spectral
and luminosity classes. For this reason, special attention was paid to the spectral classification
of the program stars. The MK spectral types used here were adopted after a rigorous
discussion with W. Buscombe (1994, private communication)
on the basis of his collection of MK classification data.
The color excesses for III, IV, V luminosity classes are obtained from the calibration given by Crawford (1978). The intrinsic colors of Kilkenny & Whittet (1985) are used for the early-type supergiants with values of c0 > -0.17 and the calibration of Crawford (1978) for values smaller than -0.17. For this calculation, a simple iteration procedure was adopted using [c1] as a first value of c0.
The absolute magnitude values for all stars are derived via . The
Balona &
Shobbrook (1984) calibration is used for luminosity classes III, IV, V. In this calibration, attempts are
made to correct the main uncertainties in the curve fitting method due to the width of the
main sequence and the evolution away from the main sequence of stars at the high-mass
end. The errors in the Mv values derived in this way are expected to be about 0.2 mag.
For the supergiants, the 
relation of
Zhang (1983) is applied. As is
shown in
Table IX of Zhang (1983), the standard deviation one should expect applying this calibration
is of the same order: 0.2 mag.
| HD | MK | Mv(Sp) |  |  | |
| s.e. | |||||
| 90273 | O7Vf | -4.9 | 0.5 | -5.63 | 0.73 |
| 91572 | O7Vf | -4.9 | 0.5 | -5.11 | 0.21 |
| 91598 | O9Ve | -4.4 | 0.6 | -5.28 | 0.88 |
| 92504 | O8Vn | -4.6 | 0.6 | -4.53 | -0.07 |
| 92850 | O9Ib | -6.1 | 0.8 | -5.53 | -0.57 |
| 93403 | O5IIIf | -6.1 | ... | -6.16 | 0.06 |
| 94024 | O8Vn | -4.6 | 0.6 | -5.91 | 1.31 |
| 94370 | O6IIIf | -5.7 | 0.3 | -5.54 | -0.16 |
| 94963 | O6Vf | -5.1 | 0.6 | -5.52 | 0.42 |
| 95589 | O7I | -6.5 | 0.5 | -6.08 | -0.48 |
| 96042 | O9.5Ve | -4.0 | 0.6 | -3.88 | -0.12 |
| 96264 | O6V | -5.1 | 0.6 | -4.95 | -0.15 |
| 96715 | O4Vf | -5.8 | 0.8 | -5.62 | -0.18 |
| 96946 | O7IIIf | -5.6 | 0.6 | -6.02 | 0.42 |
| 97166 | O7.5IIf | -5.0 | 0.4 | -5.52 | 0.52 |
| 97319 | O7.5V | -5.0 | ... | -4.83 | -0.12 |
| 97399 | O9V | -4.4 | 0.6 | -4.38 | -0.02 |
| 97434 | O7IIIn | -5.6 | 0.6 | -5.86 | 0.26 |
| 97597 | O8V | -4.6 | 0.6 | -3.99 | -0.61 |
| 97848 | O7.5II | -5.6 | 0.4 | -4.80 | -0.8 |
| 97913 | O9.5V | -4.0 | 0.6 | -5.42 | 1.42 |
| 99160 | O9III | -5.3 | 0.7 | -5.71 | 0.41 |
| 99546 | O7V | -4.9 | 0.5 | -4.88 | -0.02 |
| 305438 | O8V | -4.6 | 0.6 | -4.71 | 0.11 |
indices
for 24 O-type stars.
The differences are given in the last column
It is often questioned whether the distance determination via the values of H is
reliable
for O-type stars. There are 24 O-type stars in the sample. To compare the results
given by the Mv/(uvby) and Mv/Sp calibrations, we have calculated the
Mv values via
Mv/Sp calibrations of Conti et al. (1983) and have compared
them to the values derived via the Balona & Shobbrook (1984)
relation. The results can be seen in Table 3 (click here), where the HD numbers
and MK types are listed in the first two columns. The spectroscopic Mv
values with the corresponding errors, as given in Table 1 of Conti
et al. (1983) are shown in the third column. Note that this is the
standard deviation of the mean instead of the standard deviation used to
estimate the uncertainties concerning the other calibrations discussed here.
In the last two columns, the Mv(uvby) values obtained here
and the corresponding differences (Mv/Sp - Mv/(uvby))
are shown for each star. Taking into account the standard errors of the
calibrations, these determinations agree within their 1
errors. Only
three stars show larger differences which could be due to a wrong LC
determination. Deriving the absolute magnitude via H, one should
expect that emission in the stellar spectra would make the stars brighter.
To avoid this, for all stars with emissions indicated in their spectral
classifications, the absolute magnitudes are also estimated via the
spectral type - absolute magnitude calibration of Humphreys &
McElroy (1984) (for 
types) and Balona & Crampton
(1974) (for 
types). The results of these different types of estimation agree well within the errors.
For 14 stars in the fields of Car OB1 and Car OB2 which are earlier than B4-type
according to the PPM catalog but were not observed during this run, uvby
photometry is available in the literature. For these stars, we have also calculated the reddening-corrected quantities, color excesses, absolute magnitudes and the true distance moduli. These
data are shown in Table 4. The third and forth columns of this table contain the MK
classification and the sources of the photometric data.
Also not included in our sample are thirteen stars referred by
Humphreys (1978) to Car
OB1 and one star referred to Car OB2. For most of them, 
photometry is available
and the distances can be derived using a 
calibration. These stars are listed in
Table 5.
The photometric data and MK classifications are taken from the OB-star data base of
Reed
(1993) and the Mv values are calculated via the new calibration of
Reed & Beatty (1995).