sciolymom wrote:8. Star J is the primary yellow star shown below and Star K is the secondary red dwarf. The time between the
two blue lines on the light curve is 15.00 minutes and Star K is moving at 1770. km/s, what is the diameter
of Star J in km? [4]
sciolymom wrote:Star A and star B are T Tauri stars with same luminosity. Star A is 0.7 sm and has a radius 3x that of star B. What is the mass of star B?
The mass/luminosity/radius formulas I'm finding are comparing the star to the Sun. How do I answer this question comparing two other stars to each other? Also, any significance of them being T Tauri stars?
Also, separate question...what is the relationship between the time a star spends on the main sequence to the time it spends as a protostar? Or is there a mass relationship?
Thanks again...!
PatrickMcPherson wrote:So I've been looking at deriving these radial velocity equations. They seem to be very important, I feel like I understand the concepts (I've been doing it since my sophomore year and I'm a senior now) but I've always had issues wrapping my head around the math parts. I'm in AB calculus this year, so I've seen all of the elements when changing around this "center of mass frame of reference;" I've never liked the polar coordinate system, and I don't remember it very well. Also, there was a lot of implicit differentiation which can get (and was) very complicated, particularly in the problems demonstrated. I don't see how I could really solve these sorts of problems in a competitive time (my state test is 4 8 min sections if it is the same as the past two years). Do any of you have suggestions to help me grasp a more comprehensive understanding of how the equations operate with the systems (in the problems) at hand?
cifutielu wrote:Hey syo_astro, can you help me out?
I tried solving this problem:
Star G has a radius of 30. Rsun and an effective temperature of 3000. K. If the sun has a temperature of 5778 K,
what is the luminosity of Star G in solar luminosities?
And using the equation L = 4*pi*r^2*stefanboltzmanconstant*temperature^4, I ended up getting 2.79 * 10^25 watts. Therefore, I got .07 solar luminosities. However, the answer is 65 SL. What did I do wrong?
syo_astro wrote:cifutielu wrote:Hey syo_astro, can you help me out?
I tried solving this problem:
Star G has a radius of 30. Rsun and an effective temperature of 3000. K. If the sun has a temperature of 5778 K,
what is the luminosity of Star G in solar luminosities?
And using the equation L = 4*pi*r^2*stefanboltzmanconstant*temperature^4, I ended up getting 2.79 * 10^25 watts. Therefore, I got .07 solar luminosities. However, the answer is 65 SL. What did I do wrong?
Help you out to where (har har har aren't I funny?) .
Oh, I know star G! Actually I don't, but I love me a Stefan-Boltzmann Law question. I think you are forgetting a trick of proportionality you can perform with the Stefan-Boltzmann Law (and anything in astronomy or physics). I actually did this a few posts ago, so I'll get to the point here:
L/Lsun = (R/Rsun)^2 * (T/Tsun)^4. Note: if you were given pure mks units you would probably have an easier time just stick to mks, but this hints you towards solar units (it depends on whatever you have to multiply/convert the least, though you can mess up the stefan-boltzmann constant and whatnot...so usually stars are made easier by this).
L/Lsun = (30 Rsun)^2 * (3000 K / 5778 K * Tsun)^4 = 65.41 Lsun. Multiplication, so by sig figs it simply indeed becomes 65 solar luminosities.
I am fairly confused because http://www.wolframalpha.com/input/?i=5. ... minosities gets it...I tried messing around with the radius and temperature, but I couldn't find what you did precisely. I suspect it's either solar radius conversion or mistyping the Stefan Boltzmann constant. If you give full work I can try to check it (could just PM you by that point).
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