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I'm currently studying the star system of Gliese 570 and I´m trying to calculate the habitable zone of the component A from the luminosity value in relation of the Sun´s. I´ve read that the needed value of luminosity is the value of the bolometric luminosity (here 26%), but the calculations of the HZ that I found is about 0.40 AU, which seems to be calculated from the visual luminosity (about 16%).

So, the questions are: Which of these 2 values do I have to use to calculate the habitable zone? Does the stellar class of the star affect the selection of it?

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  • $\begingroup$ It might help to ask the following question: which parts of the EM spectrum are responsible for most of the heat? $\endgroup$ – probably_someone May 27 '17 at 18:01
  • $\begingroup$ Could you post your source for what you found at about .40 AU. There might be an explanation or it might be a questionable source. Loosely speaking, you should use the bolometric luminosity for estimates, but there's other factors like atmospheric reflectivity of longer-wavelength light and a fairly wide range of atmospheres with different heat capacity and greenhouse gas content. If nobody answers this I could cover the basics. Also a HZ should be a range, not a single number. $\endgroup$ – userLTK May 28 '17 at 11:50
  • $\begingroup$ I'm not expert enough to give an answer that this question deserves, but: I'm pretty sure that most references give stellar bolometric luminosity relative to the sun. The effective temperature of a planet is a function of this luminosity. semi-major axis and albedo. The habitable zone, of course, has been designated as where liquid water can exist on the surface of a planet, which depends on greenhouse, etc. Essentially, it is a range of effective temperatures determined by bolometric luminosity. $\endgroup$ – Jack R. Woods May 30 '17 at 2:44
  • $\begingroup$ As an aside, I am designing planetary systems for fun and a science fiction project. I find it easiest to use formula with all values relative to the Earth and the Sun (T(eff) of Earth is about 255K). I use a bond albedo for Earth of 0.3. $\endgroup$ – Jack R. Woods May 30 '17 at 2:57
  • $\begingroup$ stellar-database.com/Scripts/… $\endgroup$ – Eithne May 30 '17 at 16:11
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The number you need is the bolometric luminosity. This tells you how many Watts per square metre are incident upon the planet. That is true for the Sun and it is true for GL 570.

Beyond that, you will need to make assumptions about an atmosphere and an albedo if you are trying to calculate a realistic habitable zone. If you just assume the planet is like the Earth then using the same albedo value will probably do. But, because Gl 570 has a spectrum that peaks at 50% longer wavelengths than the Sun, then the albedo values at longer wavelengths are more important for a planet orbiting Gl 570. Whether that is bigger or smaller than the Earth would depend on exactly what sort of atmosphere/clouds/terrain were on the planet.

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