1. Armagh Observatory & Planetarium, College Hill, Armagh BT61 9DG, UK
2. Astrophysics Research Centre, School of Mathematics and Physics, Queens University, Belfast BT7 1NN, UK
3. Department of Mathematics, Physics and Electrical Engineering, Northumbria University, Newcastle Upon Tyne NE1 8ST, UK
4. Istituto Nazionale di Astrofisica (INAF), Osservatorio Astrofisica di Torino, Via Osservatorio, 20, I-10125 Pino Torinese (TO), Italy
5. INAF-Turin Astrophysical Observatory, Via Osservatorio 20, I-10025 Pino Torinese (TO), Italy
6. INAF-Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, I-80131 Napoli, Italy