On the detection of CO and mass-loss of bulge OH/IR stars

• We report on the successful search forCO(2-1) and (3-2) emission associated with OH/IR stars in the Galactic bulge. We observed a sample of eight extremely red asymptotic giant branch stars with the Atacama Pathfinder EXperiment telescope and detected seven. The sources were selected at a sufficiently high galactic latitude to avoid interference by interstellar CO, which hampered previous studies of inner galaxy stars. To study the nature of our sample and the mass-loss, we constructed the spectral energy distribution (SEDs) from photometric data and Spitzer IRS spectroscopy. In a first step, we apply radiative transfer modelling to fit the SEDs and obtain luminosities and dust mass-loss rates (MLRs). Through dynamical modelling, we then retrieve the total MLR and the gas-to-dust ratios. We derived variability periods of our stars. The luminosities range between approximately 4000 and 5500 L⊙and periods are shorter than 700 d. The total MLR ranges between 10-5and 10-4M⊙yr-1. Comparison with evolutionary models shows that the progenitor mass ≈ 1.5 M⊙, similar to the bulge Miras of intermediate age (3 Gyr). The gas-to-dust ratios are between 100 and 400 and are similar to what is found for OH/IR stars in the galactic disc. One star, IRAS 17347-2319, has a very short period of approximately 300 d that may be decreasing further. It may belong to a class of Mira variables with a sudden change in period as observed in some Galactic objects. It would be the first example of an OH/IR star in this class and deserves further follow-up observations.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Meteorologi och atmosfärforskning (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Meteorology and Atmospheric Sciences (hsv//eng)

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

NATURVETENSKAP  -- Matematik -- Sannolikhetsteori och statistik (hsv//swe)

NATURAL SCIENCES  -- Mathematics -- Probability Theory and Statistics (hsv//eng)

Nyckelord

Stars: mass-loss

Stars: AGB and post-AGB

Radio lines: stars

Circumstellar matter

Galaxy: bulge

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