The variable shell star HR 5999 : V. The spectral energy distribution.
Liseau, R.; Wamsteker, W.; The, P. S.; Tjin A Djie, H. R. E.; Viotti, R.; Cassatella, A.; Burger, M.; Fredga, K.; Bakker, R.; Bastiaansen, P. A.; Gahm, G.; Smyth, M. J.; Zeuge, W.
Abstract
From April to August 1978 an international campaign was organized to observe the variable shell star HR 5999 with different techniques. A study of part of the collected material yields the following results. The visual light variation follows the general pattern as found at earlier observations ; the star stays usually long around maximum brightness 7 = 6m.8 and reaches deep minima about one magnitude fainter. The polarization show that the percentage of linear polarization (of the order of 0.3%) is changing significantly during the brightness variation of the star. On the other hand, the position angle (about 23°) varies only little during the period of observation. A comparison of the spectral energy distribution, freed from foreground interstellar extinction, with that of a bright star of the same spectral type and luminosity class (A7 III) indicates
1) that the ultraviolet and visual energy absorbed by the dust shell around HR 5999 is about 25% of the total energy radiated by the star, 2) that this energy is reemitted as thermal energy by dust particles with a temperature of approximately 1400 K, 3) that there is a balance between the absorbed and reemitted energy, 4) that the extinction law in the ultraviolet is anomalous, such as also found in the infrared. Other physical properties of the stellar surface and the extended atmosphere are derived.