AlH lines in the blue spectrum of Proxima Centauri

Yakiv V. Pavlenko, Jonathan Tennyson, Sergei N. Yurchenko, Mirek R. Schmidt, Hugh R. A. Jones, Yuri Lyubchik, A. Suárez Mascareño

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The recently-computed ExoMol line lists for isotopologues of AlH are used to analyse the blue spectrum (4000-4500 {\AA}) of Proxima Cen (M5.5 V). Comparison of the observed and computed spectra enables the identification of a large number of 27AlH lines of the A1{\Pi} - X1{\Sigma}+ band system: the spectral range covering 1-0, 0-0 and 1-1 bands is dominated by clearly resolved AlH lines. We reveal the diffuse nature of transitions close to the dissociation limit which appears in the form of increasingly wider(up to 5 {\AA}) and shallower (up to the continuum confusion limit) AlH line profiles. The predicted wavelengths of AlH diffuse lines are systematically displaced. The effect broadening by pre-dissociation states on the line profiles is included by increasing the radiative damping rate by up to 5 orders of magnitude. We determine empirical values of damping rates for a number of the clean 0-0 Q-branch transitions by comparing the observed and synthetic stellar spectra. We find excellent agreement between our damping rates and lifetimes available in the literature. A comparison of 27Al1H ExoMol and REALH spectra shows that the observed spectrum is better described by the ExoMol line list. A search for 26Al1H lines in the Proxima Cen spectrum does not reveal any notable features; giving an upper limit of 27Al1H/26Al1H {>} 100.
Original languageEnglish
Pages (from-to)5655–5673
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Early online date15 Sept 2022
Publication statusPublished - 30 Nov 2022


  • astro-ph.SR


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