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I am interested in a sun-like star 138 light years away that is in the EUVE catalog. A table shows that a photon count of 2.6+/-0.5 photons per kilosecond at 100 angstroms has been detected for this star. I can not determine if this is high or not. I am even having a hard time finding what solar emission is at this wavelength so i can attempt the math to compare with the sun. Can somebody help me here?

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    $\begingroup$ A table? Where? The table must define a band in which the counts were measured. $\endgroup$
    – ProfRob
    May 3 '16 at 6:02
  • $\begingroup$ One photon every few minutes? Really? $\endgroup$
    – user11722
    May 4 '16 at 0:56
  • $\begingroup$ @nocomprende Yes, really. Quite typical for high energy detectors with very low background. $\endgroup$
    – ProfRob
    May 4 '16 at 11:22
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The EUVE catalog gives you a count-rate in a certain EUV band. To convert this into a flux, you need a flux conversion factor to go from counts per second to energy flux at the Earth per second. This conversion factor, also often known as an "ECF", depends on the intrinsic spectrum of the source and also how much absorption (known as the hydrogen column density) there is between Earth and the source. So there is no one answer that can be given. I Your best port of call is the PIMMS flux conversion tool, which has an EUVE module and can do these flux conversions for you if you know something about the spectrum and the absorption. I'd try it for you but I couldn't immediately see how to do it for EUVE, though it claims the information is there...

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If you're looking at Table 2 "EUVE Deep Survey" from the Second EUVE Source Catalog, the cheap way out would be to compare the star of interest to other stars of similar spectral type in that table, correcting for apparent magnitude. To compare to the Sun, part 4 "Flux Calibration" and Figure 3 "Deep-survey effective area vs. wavelength models" may help. Then you could apply a similar response function to the 5-20 nm band of a reference solar spectrum which includes extreme UV. I found a usable one in Table 2 of this book chapter.

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    $\begingroup$ I actually found my data thru SIMBAD at this source vizier.u-strasbg.fr/viz-bin/VizieR-S?EUVE%20J0706%2b22.6, but when looking at the 2EUVE catalog mentioned above, the record doesn't exist. Looking at other counts and given this fact, I think that I will just assume that the UV radiation of this star is not high enough to matter for my purposes. Thanks guys! $\endgroup$ May 9 '16 at 16:10

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