Recently, new views of the current status of δ Scuti stars have been developed by Rodríguez & Breger (2001) who carried out an excellent review, listing 8 pre-main-sequence (PMS) δ Scuti candidates and examined the possibility of the existence of PMS δ Scuti variable stars. Here we discuss the nature of 4 stars from their list: 2 said to be members of NGC 2264 and 2 of NGC 6823.
Optical properties of hydrophobic silica aerogel SP-25 have been measured. These include: a seven point dispersion law nðl ¼ 266:2@514:5 nmÞ, absorbance, luminescence and other physical properties. The effect of chromatic dispersion on velocity resolution for an aerogel-based RICH counter was estimated. r
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