Presidency University's head of physics Somak Raychaudhury announced on Thursday that he was leaving the institute to take up an "irresistible" offer, his exit from the College Street campus coming within a month of physicist Sabyasachi Bhattacharya quitting in a huff.

Seated next to vice-chancellor Anuradha Lohia at a news conference, Raychaudhury said: "It's not that I am leaving Presidency following any difference of opinion with the authorities.... I am leaving because I found the offer of director at the Inter University Centre of Astronomy and Astrophysics (IUCAA), Pune, a prestigious one."

Presidency has been counting its painful Ps since last month. First, Bhattacharya resigned as AJC Bose Distinguished Professor in Natural Sciences citing "lack of plurality". Around a fortnight ago, vice-chancellor Lohia stirred a debate about Presidency's failure to retain talent by saying that the physicist had quit because of a "pay disparity" with central institutes. Raychaudhury choosing prestige elsewhere over Presidency would hurt just as much.

"If I had got the offer (from the IUCAA) even two years ago, I would have left because this is an irresistible offer for anyone who works in the field of astrophysics," Raychaudhury said.

He had been teaching and researching astrophysics at the University of Birmingham in the UK before returning to Calcutta in 2012 to help shape his alma mater's quest for lost glory.

In May that year, the gold medallist from Presidency's Class of 1983 had told Metro: "I have joined Presidency in the hope that I will be able to contribute to my alma mater."

"This is a challenge I wanted to accept....I didn't come here expecting everything to be laid out on a platter. I want to shape these facilities, starting from scratch," Raychaudhury said.

While Bhattacharya left hardly nine months into his assignment, Raychaudhury not only stayed much longer but was also one of the faces of the resurgence that Presidency has been aiming for.

He had been made dean of sciences within a year of his appointment and also appointed one of the two chairpersons of the admissions committee.

Raychaudhury was in charge of introducing the GenEd programme at the undergraduate level. Several of the students Metro had spoken to during admissions last year said they had joined the physics honours programme at Presidency because Raychaudhury was the head of the department.

In contrast to what he said at the news conference, sources close to the physicist said he had felt the pangs of frustration over the past few months for not getting the credit he deserved. Raychaudhury denied being upset over anything.

At least 15 teachers have left Presidency over the past three years. The rate of attrition is a problem for any institute, especially at a time when academic institutions across the country are trying to scoop up talent.

"Acclaimed teachers are leaving Presidency. It should be cause for concern," said Debosruti Roychowdhury, Presidency's dean of students who took her release from the university on Thursday.

Vice-chancellor Lohia said Presidency would survive the attrition. "New teachers are joining. They are no less bright. Although we will miss Somak Raychaudhury, I have to say Presidency is going from strength to strength with each new recruitment."

She mentioned Pulak Ghosh, the IIM Bangalore professor who is to join as the first Infosys Foundation Chair Professor in Economics.