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Science Spotlight from this week's observations

Proposal ID = 12589
Principle Investigator =   Noel D. Richardson	- Georgia State University 
	  Research Foundation
Title = "The Current Ultraviolet Spectrum of S Doradus: As Hot as it Gets"
Time = May 11, 2012 21:21:55 - 23:55:04
Target = V-S-DOR


Luminous Blue Variables (LBVs) are the brightest and most massive stars; some being more than 100 times the mass of the sun and millions of times brighter. As implied by the name, LBVs are also variable in nature. They lie near the theoretical upper mass limits of stars, leading to large variations in luminosity as they try to find a balance between their own gravity, which is trying to hold the star together, and radiation pressure from their tremendous luminosity, which is trying to blow the star apart. During the outburst stage, much of the light is emitted by the material that has been ejected by the system, making it hard to study the underlying properties of the star itself. This proposal will observe the original LBV (S-Doradus) in the Large Magellanic Clouds (LMC) when it is at optical minimum, providing a better view of the central star. Some LBVs show evidence of rapid rotation, which may play an important role in the evolution of these enigmatic stars.

Paraphrasing from the abstract:

We propose to measure the ultraviolet flux of the prototype of the Luminous Blue Variables in the LMC, S Doradus, as it goes into the current optical minimum that corresponds to a maximum ultraviolet flux. During this time, the strength of the optical wind line H-alpha grows, with several high excitation emission lines emerging from the wind. In a similar state, the Galactic LBVs AG Carinae and HR Carinae have been found to show signs of rapid rotation. We aim to measure accurately the bolometric luminosity of this star at a visual minimum, examine the wind sensitive lines in the ultraviolet such as Si IV 1400, C IV 1550, and Mg II 2800, and determine a projected rotational velocity at this epoch. These observations can only be made with the echelle mode of HST/STIS, and they will help reveal the stellar and wind properties of one of the brightest stars in the Large Magellanic Cloud at an epoch when we view deep into its atmosphere.

You can find most of this information and more from the following webpage: by entering "12589" in the Prop. ID box.