Why are stocks like BPCL and IOCL being referred to as fallen angels and how to trade these stocks?

Fallen angels are stocks where the debt has been downgraded from investment category to junk category. This has been driven by India's sovereign rating being downgraded. The six fallen angels in the oil and gas sector in India include stocks like Indian Oil Corporation, Hindustan Petroleum, Oil India, Petronet LNG, BPCL and ONGC. While their fundamental credit profile remains the same, the sovereign downgrade makes them potential for downgrades. Currently, such fallen angels have six from India out of the total 21 in the list. These 21 companies with significant downgrade potential have over $12.3 billion of outstanding bonds maturing in 2021.