Simon de Visscher wrote:
As far as I understand you are comparing spectra having the same resolution, right? In our case we were just comparing the global shape of ALPY and echelle-made spectra. Beside the average resolution difference, I suspect that the resolution changes across the spectra, if not fully under control, may lead to fake peaks/dips where slopes are steepier. I mean, it would be easier to compare to ALPYs
Hi Simon,
That is why I suggested comparing with my ALPY 600 spectrum from 20191230 in the BAA database. That is very accurately flux calibrated and will be a direct comparison with your spectra. I have attached it as a zipped fits file.
The comparison of my ALPY spectrum with the MILES spectrum from 2000/2001 at slightly higher resolution than the ALPY is reliable I believe and shows a decrease in effective temperature of ~200-300K from the strength of the TiO bands ( ~1.5 points from say M2 to M3.5) That is also consistent with the results from my high resolution LHIRES spectrum and with the findings reported from 20191219 in ATel #13365 when the drop in brightness was less than it is now.
http://www.astronomerstelegram.org/?read=13365
The drop in temperature is enough to explain approximately half the drop in brightness but the radius may also have reduced due to the lower temperature so that might explain the total brightness drop seen. There is no sign of dust production in the spectrum as that would be expected to produce preferential dimming in the blue. I expect the brightness drop is just an exaggerated example of the normal pulsations but it will be interesting to see how low it goes.
The
Cheers
Robin