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Novae and the H$_\circ$

The pioneering observations of the rates of decline and absolute magnitudes at maximum carried on, for a selection of Galactic novae, by McLaughlin (1945), were used to identify the so-called Maximum Magnitude vs. Rate of Decline (hereafter MMRD) relationship, which is the basic tool for the use of novae as distance indicators. The MMRD relationship acts in such a way that the brighter is a nova at maximum the faster is its rate of decline (see Fig. 1, from Della Valle and Livio 1995). In principle novae are very powerful distance indicators. They are very bright at maximum (achieving M $_B\geq
-10$), they are found in relatively dust-free environments, the MMRD relationship has a quite low intrinsic scatter and there exists a relatively good understanding of this relationship (Livio 1997). Della Valle and Livio (1996) by applying this relationship to a handful of novae belonging to the Virgo cluster they were able to set a value of H $_\circ \sim 70$ km/s Mpc. Our group is currently studying the possibility to detect novae in Fornax, with VLT (Della Valle and Gilmozzi 1998, Sorrento meeting). We note that the large field camera applied to LBT, will allow us to study novae in Coma cluster and to measure H$_\circ$ with an uncertainty of the order of 10% (this is due to the small ratio `peculiar motions/recession velocity', of the order of a few percent in the case of Coma and about 30

Finally - we note that the stacked frames (B, V and R) can be profitably used to study, in great deepness, the Globular Cluster Luminosity Function of the parent galaxies (which in turn will give an independent estimate of the distance) and the brightest blue and red stars.

By choosing the targets among the parent galaxies of `well-observed' SNeI-a, we shall obtain, for nothing, the calibration of the absolute magnitude at maximum of type Ia SNe, which is a cosmological key parameter of paramount importance (e.g. Perlmutter et al. 1998, Nature, 391).


next up previous contents
Next: Stellar populations Up: Extragalactic Novae Previous: Nova Rate
Guido Buscema
1999-01-29