The CO(3-2) emission of the debris disc of the young A star 49 Ceti, known to be particularly gas rich, has been recently detected and measured using the ALMA interferometer. We study the observed line profile and comment on each of the possible contributions to its width. Line broadening is found to be dominated by Keplerian shear and an upper limit of km s−1 FWHM is placed on other possible contributions, including temperature, confirming the quietness of the gas contained in the disc and disfavouring models that would require relatively violent events to generate secondary gas. | Communications in Physics, Vol. 27, No. 2 (2017), pp. 107-119 DOI: PROFILE OF THE 12 CO(3-2) EMISSION LINE DETECTED FROM THE DEBRIS DISC OF 49 CETI PHAM THI TUYET NHUNG † , PHAM TUAN-ANH, DO THI HOAI, PHAM NGOC DIEP, NGUYEN THI PHUONG, NGUYEN THI THAO AND PIERRE DARRIULAT Department of Astrophysics, Vietnam National Satellite Center, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam † E-mail: pttnhung@ Received 28 March 2017 Accepted for publication 08 June 2017 Published 30 June 2017 Abstract. The CO(3-2) emission of the debris disc of the young A star 49 Ceti, known to be particularly gas rich, has been recently detected and measured using the ALMA interferometer. We study the observed line profile and comment on each of the possible contributions to its width. Line broadening is found to be dominated by Keplerian shear and an upper limit of km s−1 FWHM is placed on other possible contributions, including temperature, confirming the quietness of the gas contained in the disc and disfavouring models that would require relatively violent events to generate secondary gas. Keywords: circumstellar matter, debris disc, individual (49 Ceti). Classification numbers: , , , . I. INTRODUCTION The A star 49 Ceti is known to be surrounded by a debris disc that has been observed in infrared [1, 2] and optical [3] wavelengths as well as using the millimetre/sub-millimetre emission of carbon monoxide lines [4] and of various atomic species [2]. Carbon and oxygen have been detected close to the star from the absorption of its FUV emission [5]. The disc is known to be dusty and particularly gas rich in spite of being some 40 Myr old [6]. This peculiarity has raised the question of the origin of its gas and dust contents; arguments in favour of their being primordial as well as arguments of at least one of these being secondary have been presented. In particular, it
