## Astronomy C

TheBalticSea
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### Re: Astronomy C

woops, will get back to u on that
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Flavorflav
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### Re: Astronomy C

crazy77 wrote:Ohhhh that kinda makes sense. So basically you can put the numbers they give you into L1 and L2 on your calculator, find the equation that best fits (for this I got cubic, does that sound right? r^2 was 1 so I just used that one), put the equation into Y1, graph it, and do second Trace value, put in the log of 3 (.477) and get -2.77 for the absolute magnitude and then use the equation from there? Does that sound right? If you wanna try the problem yourself, the numbers they gave were:

Log of period: Absolute Magnitude:
1 -4.0
.68 -3.6
1.6 -6.3
.5 -2.9

And yes they did give the apparent magnitude (15.3)
You method is wrong, but your answer is bizarrely close. You need to do what Baltic Sea already told you to do - look up the period on a chart and see what magnitude it corresponds with. If you really want to use you calculator, you can use the equation instead - that is, the cephied period-luminosity equation, not the equation that produces the light curve.
Last edited by Flavorflav on February 5th, 2011, 2:59 am, edited 1 time in total.

Flavorflav
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### Re: Astronomy C

smartkid222 wrote:Question:
A quasar's redshift is observed to be z= 3.65. Calculate the recessional velocity of the quasar, with respect to Earth?

Don't you just multiply z by c (the speed of light)?
Did you get this on a test? It is not simple to calculate, and depends on assumptions about the nature of spacetime, the angle of movement and the size the universe was when the light was emitted.

crazy77
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### Re: Astronomy C

Flavorflav wrote:
crazy77 wrote:Ohhhh that kinda makes sense. So basically you can put the numbers they give you into L1 and L2 on your calculator, find the equation that best fits (for this I got cubic, does that sound right? r^2 was 1 so I just used that one), put the equation into Y1, graph it, and do second Trace value, put in the log of 3 (.477) and get -2.77 for the absolute magnitude and then use the equation from there? Does that sound right? If you wanna try the problem yourself, the numbers they gave were:

Log of period: Absolute Magnitude:
1 -4.0
.68 -3.6
1.6 -6.3
.5 -2.9

And yes they did give the apparent magnitude (15.3)
You method is wrong, but your answer is bizarrely close. You need to do what Baltic Sea already told you to do - look up the period on a chart and see what magnitude it corresponds with. If you really want to use you calculator, you can use the equation instead - that is, the cephied period-luminosity equation, not the equation that produces the light curve.
But a chart wasn't given. Should we just have this in our binder? But also the period in the problem (about 3) isn't on the chart. Is there some other chart I should have? Which equation is the cepheid period-luminosity equation?

EastStroudsburg13
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### Re: Astronomy C

It would probably be a good idea to stick that chart in your binder just in case. That's what the binder is for, to put things in just in case you ahppen to need it. Since our team went to Athens, I was able to take the tests anyway, and the Astronomy test had a question about determining distance to a Cepheid. They gave the period but not the chart, so I'm going to print one out and put it in my binder if it shows up again.
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TheBalticSea
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### Re: Astronomy C

Sometimes they like to see that you can graph things, so they give you some Cepheid data and ask you to work out the relationship for yourself (magnitude is y-axis, log of period is x-axis). Also, because of hte "mechanism" that drives Cepheid variables, (take this with a grain of salt-- I'm no chemistry expert) is based on changing internal pressures, which causes changes in temperature, which causes ionization that changes the opacity of hte outer layers and this can vary with the materials which the stars are formed of. There are, in fact, two types of Cepheid variables including the common Population I stars and those which belong to Population II and have a different timescale for their variations. Hence, the equation mentioned by east stroudburg will *almost* always-- but not always-- work. And that is a very long winded explanation of why local callibration is a good idea.

Anyway! I saw there was a question about calculating distance based on recessional velocity (I think? maybe i remembered incorrectly).
If the typical wavelength of an object's spectrum is n and it's shifted so that the "new" wavelength is m , you calculate (n-m)/n and then multiply that by the speed of light to get the recessional velocity. From there, you use Hubble's recessional velocity-distance relation to get:
d = v/H
where d is distance (assuming you're using parsecs for distance and m/s for recessional velocity), v is, well, velocity, and H (usually denoted H sub naught) is Hubble's constant (most recently valued at around 70.4).
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wyu1229
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### Re: Astronomy C

Can anyone tell me how to do these two calculations?

A binary star produces the light curve and the radial velocity diagram shown below. Star A has a temperature of 17700 K and a radius of 5RSUN, while star B has a temperature of 11000 K and a radius of 1.5RSUN. The primary eclipse occurs every 3.85 days. The separation of the stars is 1.5E10 m. The extrema on the radial velocity graph are 250 km/s and -190 km/s for one curve; for the other, they are 93 km/s and -33 km/s. Use this information for numbers 39 – 52. (taken from 2007 PA exam).

1) Calculate the orbital velocity of Star A
2) Calculate the orbital velocity of Star B

2) 63 km/sec

If you want a link to the actual test, here it is: http://www.tufts.edu/as/wright_center/p ... C_exam.pdf

koumbare
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### Re: Astronomy C

Will we have to know parallax?
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smartkid222
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### Re: Astronomy C

koumbare wrote:Will we have to know parallax?
yes
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dreaminghigh
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### Re: Astronomy C

smartkid222 wrote:
koumbare wrote:Will we have to know parallax?
yes
Why do we have to know parallax? Isn't this year's topic galaxies?
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