2 replies to this topic

[Cotts]

Something I've wanted to ask for decades.

 

Using Delta Cephei as an example.  Observed magnitude range is 3.5 to 4.3.  Some online research comes up with the following information.  Absolute Magnitude -3.2 and luminosity 2000 times solar.

 

Here comes the rant.  The absolute magnitude is given as a single number whereas the magnitude changes by 0.8. 

Wouldn't the absolute magnitude also vary by 0.8??  And, believing I'm correct, does the -3.2 absolute magnitude refer to when the star is at maximum (giving an AbsMag range of -3.2 to -2.6), when the star is at minimum (giving an AbsMag range of -3.2 to -4.0 or is it a median value (giving an AbsMag range of -3.6 to -2.8).

 

No astronomy text I have ever read answers my question.  And I have wondered about this for decades.  

 

Dave.  

 

 

[triplemon]

Not every database is set up to provide ranges rather than single constant. And there is the visual versus photographic brightness.

 

Watch for "V band" or "Vmag" vs "UBV" or "Photographic": https://en.wikipedia..._colour_indices

So not surprising, the answer is "it depends".

[MisterDan]

Intrinsic luminosity and absolute magnitudes of Cepheid Type 1 variable stars:

https://en.wikipedia...nosity_relation

https://astrolab.awh...uk/cepheid.html

 

I'm just the messenger. 

 

Best wishes.

Dan