Agreed, it is very interesting. At a glance, I thought it was Dorje Shugden with the domed hat. But after careful scrutiny, it is indeed Pehar. The thangka is very elaborate and old but still beautiful. The artist did a very good job with the thangka as Buddha Shakyamuni is still clear and so is Guru Rinpoche. As for the longevity deities as stated by the curator of Rubin museum of Art, from the left of the thangka to the right, it is probably Green Tara, Namgyalma and White Tara.
When you have a really serious problem, such as a life-threatening disease, if you rely upon Tara, very commonly you will be freed from that problem; you will recover from that disease. If you eat poison, if you rely upon Tara, the poison will not harm you. -
http://www.insightstate.com/video/green-tara-mantra-om-tare-tuttare-ture-soha/The practice of Namgyälma removes obstacles to long life and brings powerful purification for all sentient beings. Even just reciting the Namgyälma mantra brings unimaginable benefit. Namgyälma pujas and practice help those with very severe disease. -
http://shop.fpmt.org/Practices-of-Namgyalma-_p_687.html“White Tara is particularly associated with healing, protecting and stabilizing your life-force.” Gelek Rimpoche -http://buddhaweekly.com/swift-healing-white-tara-rapid-path-long-life-merit-wisdom-health/
But, what is the significance of having all these deities in the same thangka as Pehar?