First detection of AIF line emission towards M-type AGB stars

Journal article, 2022

The nucleosynthesis production of fluorine (F) is still a matter of debate. Asymptotic giant branch (AGB) stars are one of the main candidates for F production. However, their contribution to the total F budget is not fully known due to the lack of observations. In this paper, we report the detection of aluminium monofluoride (AlF) line emission, one of the two main carriers of F in the gas-phase in the outflow of evolved stars, towards five nearby oxygen-rich (M-type) AGB stars. We studied the Atacama large millimetre/submillimetre array (ALMA) observations of AlF (v = 0, J=4-3, 9-8, 10-9, and 15-14) and (v = 1, J=7-6) line emission towards o Ceti, and (v = 0, J= 7-6 and 15-14) lines towards R Leo. We also report a tentative detection of AlF (v = 0, J=7-6) line in IK Tau, (v = 0, J= 15-14) line towards R Dor, and (v = 0, J= 7-6 and J= 15-14) lines in W Hya. From spatially resolved observations, we estimated the A1F emitting region with a radius similar to 11R(*) for o Ceti and similar to 9R(*) for R Leo. From population diagram analysis, we report the AlF column densities of similar to 5.8 x 10(15) cm(-2) and similar to 3 x 10(15) cm(-2) for o Ceti and R Leo, respectively, within these regions. For o Ceti, we used the (CO)-O-18 (v = 0, J=3-2) observations to estimate the H2 column density of the emitting region. We found a fractional abundance of f(AlF/H2 )similar to (2.5 +/- 1.7) x 10(-8). This gives a lower limit on the F budget in o Ceti and is compatible with the solar F budget f(F/H2) = (5 +/- 2) x 10(-8). For R Leo, a fractional abundance f(AlF/H2) = (1.2 +/- 0.5) x 10(-8) is estimated. For other sources, we cannot precisely determine the emitting region based on the available data. Assuming an emitting region with a radius of similar to 11R(*) and the rotational temperatures derived for o Ceti and R Leo, we crudely approximated the AlF column density to be similar to(1.2-1.5) x 10(15) cm(-2) in W Hya, similar to(2.5-3.0) x 10(14) cm(-2) in R Dor, and similar to(0.6-1.0) x 10(16) cm(-2) in IK Tau. These result in fractional abundances within a range of f(AlF/H2) similar to (0.1-4) x 10(-8) in W Hya, R Dor, and IK Tau.