Among variable stars, $\delta$ Scuti are particularly interesting since they can pulsate in different evolutionary phases and are characterized by both radial and nonradial pulsation modes. Even if the majority of $\delta$ Scuti stars are in their Main Sequence (MS) or post-MS phases, there are growing evidences in the recent years about the presence of $\delta$ Scuti variables among stars which are still in their pre-MS phase (the so-called Herbig Ae-stars). Due to the small number of the known class members, the boundaries of Instability Strip are not well constrained. In this context, we present the preliminary results of a long term project to define these limits by enlarging the sample of PMS $\delta$ Scuti stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We derived the chemical abundances in the photosphere of $\delta$ Scuti, the prototype of the class of pulsating variables, from the analysis of a spectrum obtained at the Terskol Observatory 2-m telescope with a resolution $R=52000$ and $S/N=250$. VLT and IUE spectra were also used. The abundance pattern of $\delta$ Sct consists of 49 chemical elements. The abundances of Be, P, Ge, Nb, Mo, Ru, Er, Tb, Dy, Tm, Yb, Lu, Hf, Ta, Os, Pt, and Th were not investigated previously. The lines of third spectra of Pr and Nd also are investigated for the first time. The abundances of heavy elements show overabundances with respect to the Sun up to 1 dex. The abundance pattern of $\delta$ Sct is similar to that of the Am-Fm stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present preliminary results of a photometric multisite campaign on the $\delta$ Scuti-type Pre–Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 173 hour of observations over around 40 nights. Our current data permitted us to confirm the multiperiodic nature of this star and to determine at least 9 pulsational frequencies. A preliminary nonradial theoretical analysis seems to show that the star pulsates in a mixture of $l=0, 1, 2$ modes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Young A-type stars in the pre–main-sequence (PMS) evolutionary phase are particularly interesting objects since they cover the mass range ($\sim$1.5-4 $M_\odot$) which is most sensitive to the internal conditions inherited from the protostellar phase. In particular, they undergo a process of thermal relaxation from which they emerge as fully radiative objects contracting towards the Main Sequence. A-type stars also show intense surface activity (including winds, accretion, pulsations) whose origin is still not completely understood, and infrared excesses related to the presence of circumstellar disks and envelopes. Disks display significant evolution in the dust properties, likely signalling the occurrence of protoplanetary growth. Finally, A-type stars are generally found in multiple systems and small aggregates with lower mass companions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html