Astron. Astrophys. 322, 730-746 (1997)

Appendix A: adding new calibrators

Here we provide formulae for calculating when new galaxies are added in the calibrator sample.

Following the results of a study on the type dependence of TF relation (Theureau et al. 1997), we assume that the relations of different Hubble types have a common slope. Type dependence is observed in the zero-point differences of the relations (M or ). Using the slope derived for the field sample we calibrate the zero-points,

In the equation above, n is the number of calibrators, all of them shifted to a common type () by

Equivalently, using the diameters:

and

When a new calibrator is added, we get a new value for simply by

or we can calculate

Hubble constant for the field sample is calculated from mean of logarithmic values (averaged over the unbiased 'plateau' sample):

When a new calibrator is introduced, and corresponding has been calculated, we get

giving

Correspondingly, for diameters:

In conclusion: when a new Cepheid distance is announced, the reader may substitute values of and from Table 3, and TF-parameters a and from section 5 to Eqs. (A.2) and (A.4). With thus obtained one gets a new value for (Eq. A.6).

© European Southern Observatory (ESO) 1997

Online publication: June 5, 1998

helpdesk.link@springer.de