Some Astro Q's

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Cesc

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Hi guys,

Im currently studying astrophysics in school and im finding it really interesting! However, I came across 2 questions that I found difficult and needed help with answering.

The given information is of a brightness vs time graph is given (in the shape much like a cepheid variable) for 50hrs. The brightness ranges from 7.8 to 7.0

Q1. Is this star an intrinsic variable or an extrinsic variable? Justify your answer.
I know the answer is pretty straightforward and simple an intrinsic variable but whats the best way to justify?

Q2. Using the Period-Luminosity relationships that is given, determine the distance of the star from Earth.
Now, upon working the period (which was 18hrs), i correlated that to absolute magnitude to get an answer of 0.35. My problem is I know im supposed to use the formula m-M=5log(d/10) but I don't know how to find m? (upon which after that, I will simply make d the subject)

I dont know if this is the right place to ask and im sorry if im taking much of your valuable time, but I hope you have the kindness to help me out

D

drwayne

Guest
This looks a lot like a "Help me with my homework" post, is this homework? It's best to be upfront about
that sort of thing.

Wayne

M

MeteorWayne

Guest
Yes, in general we don't like doing your homework for you, since we don't get the grades, and you don't learn anything if we do it for you.

The Other Wayne

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Cesc

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Hi,

I completely understand where you're coming from and just so you know, I dont want you (or anyone else) to do the homework for me cause in essence, I'll be sitting the exam and not you guys (and yes these questions are for homework). However, as you can see that Ive actually given these two questions a genuine attempt and shown my thought process (if I wanted you guys to do my homework I wouldve simply posed the question and asked for an answer). Also, since I live in the rural area, ive havent been fortunate enough to actually have a proper, formal teacher to help me out adequately and so thats why I thought I'd ask you guys.

Btw: I managed to solve Q2. Lately Ive been thinking...what evolution path path would a 7solar mass star take (i.e. would it end being a white dwarf or supergiant? and so forth), because in books 5 solar masses become white dwarfs whereas 10solar masses become supergiants.

Thanks heaps

S

Saiph

Guest
A few days late to the party, I know, but I'll throw in my two cents. Also, as these are homework questions I'll be a bit more vague than I normally am, but I'm also about a week late, so it certainly shouldn't be to harmful. These answers are the same sort I'd give out as a tutor.

Q1: Justifying whether it's an intrinsic or extrinsic variable... It depends on how the graph looks. If it's got a flat bottom (and top), it's one type, and if the graph shows multiple dips, one dip is almost always smaller than the other. If its curvy and sinusoidal, it's the other type. It's up to you to determine if the flat peaks, or curvy peaks is intrinsic or extrinsic, and why.

Q2: the little m in the magnitude equation is the apparent magnitude, which should be given to you as it is an observation (unless you know the distance already, then you can calculate it...).

Q3: You're a little confused here, as a star becoming a supergiant does not preclude it from becoming a white dwarf. A white dwarf is one of 3 possible end states of a star, while the red giant, or super giant phase is a stage the star goes through near the end of it's life.

But a 5 solar mass star ends up as a white dwarf, usually only becoming a red giant before doing so. 10 solar mass stars tend to swell to supergiant sizes before ending up as a neutron star.

Stars in between tend to end up as larger white dwarfs, or may tip over and turn into a neutron star, it gets a bit harder to define.

S

SpaceTas

Guest
Look up the meaning of intrinsic and extrinsic.
Check what type of variable it is (as Saiph says you may need to look at the light curve if you are not told its type), then find out what causes that type of star to vary.
Looks like you need practice is solving problems in a step by step manner
The only way to learn is practice.

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