An early detection of blue luminescence by neutral PAHs in the direction of the yellow hypergiant HR 5171A?
Aims: We re-examined photometry (VBLUW, UBV, uvby) of the yellow hypergiant
Methods: We used two-colour diagrams based on atmosphere models, spectral energy distributions, and different extinctions and extinction laws, depending on the location of the supposed BL source: either in Gum48d on the background or in the envelope of HR 5171A.
Results: False L-excess sources, such as a hot companion, a nearby star, or some instrumental effect, could be excluded. Also, emission features from a hot chromosphere are not plausible. The fluxes of the L excess, recorded in the data sets of 1971, 1973, and 1977 varied (all in units of 10-10 Wm-2μm-1) between 1.4 to 21, depending on the location of the source. A flux near the low side of this range is preferred. Small brightness excesses in uv (uvby system) were present in 1979, but its connection with BL is doubtful. For the L fluxes we consider the lowest values as more realistic. The uncertainties are 20-30 %. Similar to other yellow hypergiants, HR 5171A showed powerful brightness outbursts, particularly in the 1970s. A release of stored H-ionization energy by atmospheric instabilities could create BL emitted by neutral PAHs.
Astronomy and Astrophysics
- Pub Date:
- November 2015
- ISM: molecules;
- HII regions;
- stars: variables: S Doradus;
- stars: individual: HR 5171A;
- Astrophysics - Solar and Stellar Astrophysics
- 7 pages, 2 figures, 5 tables, accepted for Astronomy &