Is the Sun's luminosity in specific filters greater than its overall luminosity?

In summary, the conversation discusses the calculation of the Sun's luminosity in J, H, and K filters and the confusion surrounding the smaller absolute magnitudes in these filters compared to the bolometric absolute magnitude. The equation M2-M1 = -2.5 log (L2/L1) is mentioned, along with the possibility that the comparison is being made to Vega, which has a different spectral shape. The conversation ends with a request for clarification on the interpretation of these results.
  • #1
StarDweller
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I'm trying to calculate the luminosity of the sun in the infrared (J, H and K filters). According to http://mips.as.arizona.edu/~cnaw/sun.html, the absolute magnitudes of the Sun in each of these filters are

J: 3.64
H: 3.32
K: 3.28.

The absolute bolometric magnitude of the Sun is about 4.72. What I can't quite wrap my head around is this: how is it possible that the absolute magnitude in specific filters is smaller (as in brighter) than the bolometric absolute magnitude? Does this not mean that the luminosity of the Sun in each of these filters is greater than the bolometric luminosity? That is what the equation M2-M1 = -2.5 log (L2/L1) would seem to imply (though I'm not entirely sure if it's legal to have M1 as M_bol and M2 as M_J for instance; I'm fairly certain the filters have to be the same).

I'm sure it's just an interpretation error on my part. I understand that as a blackbody, to find the total luminosity the emission must be integrated over all wavelengths, but it doesn't make sense to me that the Sun would be brighter in one filter than in ALL filters. (Looking at the V magnitude as well this implies that the Sun is brighter in the IR than the visible but the peak of the blackbody distribution of the Sun is clearly in the visible.)

Any help is appreciated!
 
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  • #2
I believe they are comparing the brightness of the Sun to Vega. I'm not sure, but I think that Vega, being a higher temperature than the Sun, puts out more of it's energy in the higher energy wavelengths, like the UBV bands, than the lower energy bands, like the JHK. So when you compare the two perhaps the lower difference in the JHK bands is due to the different shape of the spectrums.
 

1. What is a Solar Absolute Magnitude?

Solar Absolute Magnitude is a measure of the intrinsic brightness of a star, specifically the Sun, at a standardized distance of 10 parsecs (32.6 light years) from Earth.

2. How is Solar Absolute Magnitude calculated?

Solar Absolute Magnitude is calculated by comparing the apparent magnitude of the Sun, as seen from Earth, to its distance from Earth. The formula is M = m - 5(log d - 1), where M is the absolute magnitude, m is the apparent magnitude, and d is the distance in parsecs.

3. Why is Solar Absolute Magnitude important?

Solar Absolute Magnitude is important because it allows astronomers to compare the true brightness of stars, regardless of their distance from Earth. This helps in understanding their properties and evolution.

4. What is the difference between Solar Absolute Magnitude and Solar Apparent Magnitude?

Solar Apparent Magnitude is the measure of the Sun's brightness as seen from Earth, while Solar Absolute Magnitude is the measure of its intrinsic brightness at a standardized distance. Apparent magnitude takes into account the distance between Earth and the Sun, while absolute magnitude does not.

5. How does Solar Absolute Magnitude vary for different stars?

The Solar Absolute Magnitude of stars can vary depending on their size, temperature, and distance from Earth. Smaller and cooler stars will have a lower absolute magnitude, while larger and hotter stars will have a higher absolute magnitude. Distance also plays a factor, with closer stars appearing brighter and having a lower absolute magnitude compared to more distant stars.

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