Messier 31 distance estimation based on Observation of Cepheids : 2.6 M light-yearsA total of 9 Cepheids within Messier 31 were surveyed over a period of 3 months from mid July to mid October 2023.
The position of the Cepheids are identified with the small red circles on the image of M31.
Their respective light curves were measured to determine the period and the Mean V magnitude.
Here is an example with the light curve obtained for V507.
The results are summarized in the following table :
Then by applying the following formula, the stars Absolute V Mag was estimated, resulting in the graph here below :
(* V mag vs Log10 P -1)
The following graph shows the 9 Cepheids light curves plotted together on a normalized x phase axis (from 0 to 2 Pi) and
normalized flux (from -1 to +1) on the y axis.
The correlation is quite good and the best fit clearly shows the light curve asymmetry (with a steeper increase and a flatter decrease).
From the apparent magnitudes and absolute magnitudes of the cepheids, the distances were determined.
The Galaxy distance was estimated using the average value of these distances : 2.6 Mega light-years with a standard deviation of 0.33 M l.yNotes :
1) stars V mag were estimated using Luminance exposures and comparing the cepheids with surrounding stars
2) the Luminance filter was calibrated against the V mag for stars of various B-V color index.
3) the cepheids color index was determined based on a published correlation and on the cepheid absolute magnitude
This slightly improved the quality of the light curves fit.
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