<p>I have some radio data (flux) in 1.4 GHZ and also distance data. I calculated the luminosity for this frequency. Here, i want to use power-law and/or blackbody relation to calculate possible luminosity values of the same sample at a 5GHZ.</p>
<p>I found the way: <span class="math-container">$$L_R=v*L_v= 5 GHz*L_5 = (5 GHz)*4*\pi*D^2*F_5$$</span></p>
<p>Here <span class="math-container">$$L_R$$</span> is luminosity at the observed frenquency. <span class="math-container">$$L_5,F_5$$</span> are the luminosity and flux density at 5GHz.</p>
<p>Btw, forgot to multiply the luminosity with 1.4GHZ while calculating  <span class="math-container">$$L_{1.4}$$</span> or (whatever you say) <span class="math-container">$$L_v, L_R$$</span></p>
<p>I suggest that the only thing that i need to do is multiplying the luminosity value with 5GHZ. Or need to divide by 5GHZ? Im confused here.</p>
<p>Correct me if I'm wrong</p>

CC BY-SA 4.0
2023-07-27T22:20:36.007Z
Look at the units of your variables
planetmaker
CC BY-SA 4.0
2023-07-28T21:13:17.047Z
What planetmaker is (for some reason only) hinting at is the idea of using [dimensional analysis](https://en.wikipedia.org/wiki/Dimensional_analysis). If you forget the numbers and just put the correct units in each place of an equation, it should also balance/agree. For example if we have to choose between F=ma and F=m/a the units give us the answer. (kg m / s^2) = (kg) x (m/s^2). Check the units for luminosity you are supposed to use (maybe watts, maybe unitless ratio to L☉) and the units for flux density. What happens when you work it through using dimensional analysis?
uhoh
CC BY-SA 4.0
2023-07-28T22:04:09.850Z
Okay i got the point. Actually i did this before. How ever my flux is in jansky and distance in cm, and the luminosity unit that i want is erg s^-1. So, i'm confused about where to put that Hz thing.
Ege Tunç
<radio-astronomy><radio><black-body>
How to calculate a part of a spectrum from another part of it?
Ege Tunç
# How to calculate a part of a spectrum from another part of it?

(Asked by: username_0 on 2023-07-27)

I have some radio data (flux) in 1.4 GHZ and also distance data. I calculated the luminosity for this frequency. Here, i want to use power-law and/or blackbody relation to calculate possible luminosity values of the same sample at a 5GHZ.

I found the way: $$L\_R=v\*L\_v= 5 GHz\*L\_5 = (5 GHz)\*4\*\pi\*D^2\*F\_5$$

Here $$L\_R$$ is luminosity at the observed frenquency. $$L\_5,F\_5$$ are the luminosity and flux density at 5GHz.

Btw, forgot to multiply the luminosity with 1.4GHZ while calculating $$L\_{1.4}$$ or (whatever you say) $$L\_v, L\_R$$

I suggest that the only thing that i need to do is multiplying the luminosity value with 5GHZ. Or need to divide by 5GHZ? Im confused here.

Correct me if I'm wrong

**Tags:** radio-astronomy, radio, black-body

> **Comments:**
> **username_1**: Look at the units of your variables  
> **username_2**: What username_1 is (for some reason only) hinting at is the idea of using [dimensional analysis](https://en.wikipedia.org/wiki/Dimensional_analysis). If you forget the numbers and just put the correct units in each place of an equation, it should also balance/agree. For example if we have to choose between F=ma and F=m/a the units give us the answer. (kg m / s^2) = (kg) x (m/s^2). Check the units for luminosity you are supposed to use (maybe watts, maybe unitless ratio to L☉) and the units for flux density. What happens when you work it through using dimensional analysis?  
> **username_0**: Okay i got the point. Actually i did this before. How ever my flux is in jansky and distance in cm, and the luminosity unit that i want is erg s^-1. So, i'm confused about where to put that Hz thing.  

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## 0 answers

