Brihat Parashara Hora Shastra
एकराशियुतः केतुः सूर्यतुल्यः प्रजायते। अप्रकाशग्रहाश्चैते पापा दोषप्रदाः स्मृताः॥ ६४॥
By adding a Rāśi to UpaKetu, you get the original longitude of Sūrya. These are the Grahas, devoid of splendour, which are malefics by nature and cause affliction.
english translation
ekarAziyutaH ketuH sUryatulyaH prajAyate। aprakAzagrahAzcaite pApA doSapradAH smRtAH॥ 64॥
hk transliteration by Sanscript