Some days ago, I made a (good) observation of Be star, from home, with Alpy 600 & C8 telescope. I'm in very poor conditions (urban lights, installed on my balcony...), but it worked fine (spectra are now in BeSS :>).
During this observation I did a very simple skill : take several spectra from reference stars, and build several times the instrumental response curve - normally I should get exactly the same result. ... I write this message, because it is not really the case, and I need your help to go further.
Here is exactly what I did.
- I selected two stars as reference, known to have no reddening issue (taken from LISA Pack documentation) : zet Ari and HD51104.
- For zet Ari, I took 2 spectra, with 1 hour difference. For the first one, the star was at 38° above the horizon, the second was at 49°. HD51104 was observed at 52°.
- In all cases, I observed roughly in the same direction - I do not think that there is any light pollution effect change to be taken into account.
- Because of the building heating and the poluted sky, I had an enormous seeing (more than 10 pixels FWHM), and I've an old mount which tracks hardly (I worked in autoguidig, however). All this is not good for the exposure time (I lose for sure a lot of efficiency), but it has the advantage to prevent any chromatic effect that I could have if I were is very good conditions.
To build the response curve of zet Ari (A1V, mag 4,8), I took a spectrum of HD000319 (Miles Library in ISIS database - there is no A1V in Pickles database).
For HD51104 (B8Vn, mag 5,9), I used the Pickles B8V spectrum.
For each spectrum (zetAri1, zetAri2, HD51104), I made the response curve using ISIS tools (response button, in the profile tab, then continuum calculation, by removing the balmer lines and smoothing the profle).
For zetAri2, I did the calculation two times at different moments, to see how consistent is my own contribution (buliding a response curve has some subjective effect). Here is the result :
- CompRepTetAri2a&b.png (4.83 KiB) Viewed 5301 times
Now, here is the comparison of both zet Ari spectra (1 and 2) :
- CompRepTetAri1&2.png (5.2 KiB) Viewed 5301 times
Now, here is my real problem. The picture below shows a comparison of the zet Ari (2nd observation) and HD51104. Spectra were not taken at the same moment - about 6 hours difference between observations - but stars were at the same elevation (49° vs 52°).
- CompRepTetAri-HD51104.png (5.48 KiB) Viewed 5301 times
And I have, of course, the question ; which one is the right one ?
I remind there are several differences between these observations :
- Not the same star (zet Ari - A1V, mag 4,8 and HD51104 - B8Vn, mag 5,9), but both are considered as reference stars (stable, no reddening...)
- Not the same catalog for theoritical spectrum (Miles a Pickles)
- Not the same time (19h30 vs 1h50), but same date and conditions (telescope, observer, direction of observation...)
My feeling is that main difference come from the catalog used for theoritical spectra - I know that the hardest problem is to find THE reference, to calibrate our data.
Note that for all my Be observations, I used zetAri1 observation to correct the response curve.
Friendly,
François
Any idea how I could go further ?