Syed Zain, Sharifah Fetom, Nazhatulshima Ahmad, and Mohd Zambri Zainuddin. 2007. “Helium λ 4009.27 Ã… Phase Variation in Alpha Virginis”. Malaysian Journal of Science 26 (2):143-49. https://jupidi.um.edu.my/index.php/MJS/article/view/8082.