1. A review of Delta a studies of Galactic and Magellanic Clouds clusters

PINTADO, O.; NETOPIL, M.; PAUNZEN, E.

Cordoba

Congreso; Terceras Jornadas de Astrofísica Estelar; 2016

Observatorio Astronómico de Cordoba

We will review theachievements of the narrow band Δa system in Galactic clusters and theMagellanic Clouds.  The Δa photometric system  was originally introduced by Maitzen (1976,A\&A, 51, 223)to investigate the flux depression at 5200Å which is a keycharacteristic of classical chemically peculiar (CP) stars. It comprises ofthree narrow-band filters with FWHMs of about 100 Å .The a index samples thedepth of this flux depression by comparing the flux at the centre (5200 Å, g2)to the adjacent regions (5000 Å, g1 and 5500 Å, g3 or y). The final intrinsicpeculiarity index Δa is defined as the difference between the individual a -valuesand the a-values of non-peculiar stars of the same colour (spectral type). Ithas been shown that virtually all peculiar stars with magnetic fields havesignificant positive Δa values of up to +100 mmag, whereas Be/Ae and metal weakstars exhibit significantly negative ones. However, it can trace allpeculiarities in this wavelength region as, for example, peculiar bluehorizontal-branch and red giant-branch stars. Up to now, 91 Galactic openclusters and 3 Globular clusters were investigated and published in a series of23 papers. We will review the results of these joint efforts in more detail. We went one step furtherand started to survey the Magellanic Clouds within the Δa photometric system. Sincethen, we were able to complete this survey using the the 2.15m telescope atCASLEO as well as the Danish 1.54m and the MPG/ESO 2.2m telescope at La Silla.Here, we will present the already published as well as the the preliminaryresults of our survey in the Magellanic Clouds.