Cephid Variables: Finding Distance from Parallax & Magnitude

  • Thread starter Thread starter Unto
  • Start date Start date
  • Tags Tags
    Variables
AI Thread Summary
The discussion focuses on calculating the distances of two Cepheid variable stars based on their parallax and magnitude differences. The first star's distance is determined to be 500 parsecs using its parallax of 0.002 arcseconds. The second star, being 20 magnitudes fainter, is inferred to be approximately 10,000 times further away, assuming both stars have the same absolute brightness due to their identical periods. The relationship between apparent magnitudes and distance is clarified through the distance modulus, and the importance of knowing the period to determine absolute magnitudes is emphasized. Overall, the conversation highlights the complexities of using parallax and magnitude in astrophysical calculations.
Unto
Messages
128
Reaction score
0
This one has me stumped:

A galactic Cephid variable has a parralax of 0.002 arcseconds. What is it's distance in parsecs? A second cephid variable with the same period is 20 magnitudes fainter. What is the distance to this second star?

-------

Now I worked out that the distance to the former is 500pc.

Then using a flux equation I learned in lectures, I gathered that since the difference in the maginuteds is 20, one of the the stars must be 1E8 times brighter. So if we denote the second star as flux 1, the first star has flux 1E8.

But how then would I work out the distance to the second star of flux 1?
 
Astronomy news on Phys.org
If a star is twice as bright it must be 4x nearer (since light spreads out in an inverse square)

The link between apparent magnitudes and distance is called the "distance modulus"
 
Thank you for your informative reply, but I don't want to jump into this just yet.

I have values (which are know exact but are representative) in fluxes. I understand that distances are usually correlated with luminosities and apparent magnitudes. Do I just jump the gun and say 'since this star is 1E8 times dimmer, it must be so-so further away?

And the question states that the two stars also have the same period, what does this tell me?

Is there anyway where I can get the magnitudes of the stars? I would be gratified for some more help as I really like astrophysics.
 
Unto said:
I have values (which are know exact but are representative) in fluxes. I understand that distances are usually correlated with luminosities and apparent magnitudes. Do I just jump the gun and say 'since this star is 1E8 times dimmer, it must be so-so further away?
Pretty much
You don't need to convert the magnitude to fluxes since the 'log' in the distance formula effectively does that. Since one star is 10^8 times fainter than it must be 10,000 times further away (assuming they are the same brightness)

And the question states that the two stars also have the same period, what does this tell me?
The period of a of a cepheid depends on it's absolute magnitude - so the same period means the same power.

Is there anyway where I can get the magnitudes of the stars?
If you have the period - yes there is a formula
 
Alas I was not given the period.

Thank you for your help.
 
Publication: Redox-driven mineral and organic associations in Jezero Crater, Mars Article: NASA Says Mars Rover Discovered Potential Biosignature Last Year Press conference The ~100 authors don't find a good way this could have formed without life, but also can't rule it out. Now that they have shared their findings with the larger community someone else might find an explanation - or maybe it was actually made by life.
TL;DR Summary: In 3 years, the Square Kilometre Array (SKA) telescope (or rather, a system of telescopes) should be put into operation. In case of failure to detect alien signals, it will further expand the radius of the so-called silence (or rather, radio silence) of the Universe. Is there any sense in this or is blissful ignorance better? In 3 years, the Square Kilometre Array (SKA) telescope (or rather, a system of telescopes) should be put into operation. In case of failure to detect...
This thread is dedicated to the beauty and awesomeness of our Universe. If you feel like it, please share video clips and photos (or nice animations) of space and objects in space in this thread. Your posts, clips and photos may by all means include scientific information; that does not make it less beautiful to me (n.b. the posts must of course comply with the PF guidelines, i.e. regarding science, only mainstream science is allowed, fringe/pseudoscience is not allowed). n.b. I start this...
Back
Top