Eddington Luminosity Limit and Characteristics of Eruptions

Eddington Luminosity Limit and Characteristics of Eruptions

by Tyler Alexander -
Number of replies: 1

Paper was dense.  Still doing some looking on light echoes, etc.  Hopefully will understand more from the Historic Transients paper.

Wondering if we could go into a bit more depth about light-echo analysis and how it is used, etc.  That is, how it works to visualize something from the 19th century as in this paper.  How does light produce an "echo"?

 Was also wondering about the Eddington Luminosity Limit.  What is this?

The paper mentions how the authors used cross-correlation with "G-type templates" to determine velocities - which I assume to be wind velocities.  First off, are the velocities actually wind velocities?  Second, how does one derive the G-type template?  That is, what models go into using it?

Lastly, wondering if we can talk about the eruptions.  I understand some of the causes are uncertain.  Wondering if we can explain a bit more about what we do know.  Seems strange, the luminosity would just 'randomly' increase.  What may cause this?

In reply to Tyler Alexander

Re: Eddington Luminosity Limit and Characteristics of Eruptions

by David Cohen -

Lots of good questions, Ty. We'll address them in class.

Some brief, superficial answers to a couple of questions to get the ball rolling:

Light echoes - if dust between us and a source of light (but not directly on a straight line between us - and in the case of eta Car, the dust is behind the star; see Fig. S1) scatters some of the light from the source, then it can reach us via a non-straight-line path (via two straight line segments) and so it will take longer for light to reach us. If the source of light is steady in time, this won't be so interesting, but if the source is variable, and specifically, if it has short periods of strong brightening (and then fading) those light pulses will show up later in the echo than in the direct source. So, that's sort of light someone shouting from a distance and you hear their shout and then you hear the echo some time later.

Eddington limit - the (theoretical) upper limit to the luminosity a self-gravitating object like a star can radiate before the force of the radiation on the matter in the object will exceed gravity and blow the object apart. If light having the capability to exert a force is surprising, recall that photons have momentum (E/c = h*nu/c) and that force is m*dv/dt or dp/dt, the time-derivative of momentum).