How was u_1 and u_2 star determined

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In summary, the system of equations represents the steady states of the system as $(0,0)$, $(1,0)$, and $(0,1)$. However, the book provides additional solutions for a steady state without explanation. These additional solutions are $\displaystyle u_1^* = \frac{1-a_{12}}{1-a_{12}a_{21}}$ and $\displaystyle u_2^* = \frac{1-a_{21}}{1-a_{12}a_{21}}$. These solutions are found by setting the derivatives of both equations to zero. The system of simultaneous equations for the steady state is $u_1+a_{12}u_2 = 1$
  • #1
Dustinsfl
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$$\begin{array}{lcl}
\frac{du_1}{d\tau} & = & (1-u_1-a_{12}u_2)\\
\frac{du_2}{d\tau} & = & (1-u_2-a_{21}u_1)
\end{array}
$$

The steady states for this system are $(0,0)$, $(1,0)$, and $(0,1)$.

But then the book says without explanation

$\displaystyle u_1^* = \frac{1-a_{12}}{1-a_{12}a_{21}}$

and

$\displaystyle u_2^* = \frac{1-a_{21}}{1-a_{12}a_{21}}$

Never mind solve the problem
 
Last edited:
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  • #2
dwsmith said:
$$\begin{array}{lcl}
\frac{du_1}{d\tau} & = & (1-u_1-a_{12}u_2)\\
\frac{du_2}{d\tau} & = & (1-u_2-a_{21}u_1)
\end{array}
$$

The steady states for this system are $(0,0)$, $(1,0)$, and $(0,1)$.

But then the book says without explanation

$\displaystyle u_1^* = \frac{1-a_{12}}{1-a_{12}a_{21}}$

and

$\displaystyle u_2^* = \frac{1-a_{21}}{1-a_{12}a_{21}}$

Never mind solve the problem

The are the solutions to the pair of equations for a steady state:

$$\begin{array}{lcl}
\frac{du_1}{d\tau} & = & 0\\
\frac{du_2}{d\tau} & = & 0
\end{array}
$$

Which is the system of simultaneous equations:

$$\begin{array}{lcl}
u_1+a_{12}u_2 & = & 1\\
u_2+a_{21}u_1 & = & 1
\end{array}
$$

Also, $(0,0)$, $(1,0)$, and $(0,1)$ are not in general the steady states of the system.

CB
 
Last edited:

FAQ: How was u_1 and u_2 star determined

How was the u1 and u2 star determined?

The u1 and u2 star were most likely determined through photometric observations and analysis. This involves measuring the brightness of the star at different wavelengths of light and using mathematical models to determine the temperature, size, and other characteristics of the star.

What is the significance of u1 and u2 in determining a star's properties?

The u1 and u2 parameters are important in determining a star's properties because they represent the limb darkening effect. This is the gradual decrease in brightness towards the edge of a star, which can provide information about the star's atmosphere and surface temperature.

Can u1 and u2 vary for different stars?

Yes, u1 and u2 can vary for different stars. The values of these parameters depend on the star's temperature, size, and other factors. Therefore, different stars will have different u1 and u2 values.

How accurate are the u1 and u2 values for a star?

The accuracy of the u1 and u2 values for a star depends on the quality of the observations and the analysis methods used. In general, these parameters can be determined with a high level of accuracy, but there may be some uncertainty due to factors such as instrumental errors or intrinsic variability of the star.

Are there any alternative methods for determining a star's properties besides u1 and u2?

Yes, there are other methods for determining a star's properties, such as spectroscopy, interferometry, and asteroseismology. Each of these techniques provides different types of information about a star, and they can be used in combination to obtain a more complete understanding of the star's properties.

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