Thanks! i think I even understood most of that.The foreground star, 2MASS J07190568-1315389 is certainly a cool star that is much brighter at the longer wavelengths. So it would explain that.Would that also explain why the W-R star - which is not cool at all! - is so red, as well as the bright - foreground? - star in the lower right?
Well, that star, 2MASS J07181340-1315288 (Gaia DR3 3032940260440588544) appears to be very cool. No red band flux is available, but in the J band (1200 nm) it is about 16 times brighter than in the G band (464 nm). So the two red filters (H-a and S II) will pass a lot more light than the green filter (O III). I'm not sure what the final mapping used was, but looking at the histogram I'd guess that the blue and green channels are filled from the O III data and the red channel is filled from the H-a and S II data. Which would explain why the star is so red.
The W-R star, 2MASS J07182912-1313015 is brighter in the IR than the visible, which may have to do with the effects of dust. (Thermal dust emission is common in W-R nebulas; the presence of dust could cause reddening in optical wavelengths.) Its R and G flux is similar, but maybe twice as much R signal is present because that's coming from two filters, while the green is coming from just one. So much depends on the processing, and the final colors we get from narrowband data can be quite variable.
Statistics: Posted by johnnydeep — Tue Jan 09, 2024 7:41 pm — Replies 14 — Views 534