Choosing right reference star?

[Timo Kantola]

I gather the observation material for myself to get to the ahead training.
Tuesday-wednesday night may be clear here - so I've chosen 5 objects:

- CH Cyg M7IIIab+Be star (?) AAVSO Alert Notice 639
- M57
- HD178770 In Lyra, M6 star (I took a look and it look interesting, almost like CH Cyg)
- TYC 3590-277-1, B5 D ~ star (spectroscopic doublestar)
- M31 or M32 (just I want to see the spectrum of the galaxy).

I have tested my Alpy one short "night" 31.7.2018, and took some pics 12"F4 Newton without coma corrector (should it be used, I assume that less glass between object and CCD is better ???)

I did some training 1D spectras with Demetra. These do not have instrumental & atmospheric corrections because then things will become complicated (to me).. it looks like instrumental & atmospheric corrections is worth learning - well.

There is no spectral reference star chart / map anywhere? List of HD stars is not very neat.
Is there refstar list / constellation, Cassiopeia,Andromeda,Taurus..?

What is the criterion for good ref.star spectra to do instrumental & atmospheric corrections?
Hot A or B type star, with same mag.range (Demetra manual).
Somewhere read that it must be same spectral type, and it need to find in software reference spectrum catalog.

So what ref.star and how to find it for (not coordinates, but where did you dig it').
- CH Cyg
- M57
- HD178770
- TYC 3590-277-1
- M31

One stupid can ask more than ten wise men has time to respond!
Cheers!
Timo K.

[Francois Teyssier]

Hi Timo

What is the criterion for good ref.star spectra to do instrumental & atmospheric corrections?
Hot A or B type star, with same mag.range (Demetra manual).
Somewhere read that it must be same spectral type, and it need to find in software reference spectrum catalog.

Late type BV or eraly AV. why? very few absoprtion lines
Avoid special stars such as Emiision lines stars (often Be stars)
Choose a star with low interstellar reddening. E(B-V) < 0.05
The must not be too bright: the exposure must be > 20 sec without saturation (say max ADU < 50000)

This spreadsheet can help:
http://www.astronomie-amateur.fr/Docume ... inder.xlsm

Keep us informed
A good atmospheric response is very hard to obtained

All the best,
François

[Robin Leadbeater]

Hi Timo,

You definitely do not need the same spectral type as the star you are measuring. (How would you know what type it is before you measure it )
To get confidence in taking accurate spectra I recommend measuring a some stars with known spectra and comparing them with the published spectra (MILES stars for example) Here is an example of some tests I made using my ALPY

http://www.threehillsobservatory.co.uk/ ... 161105.pdf

(From this page on my website http://www.threehillsobservatory.co.uk/ ... opy_21.htm )

Cheers
Robin

[Timo Kantola]

Hi Francois and Robin!

This spreadsheet can help:
http://www.astronomie-amateur.fr/Docume ... inder.xlsm

Thanx for tips!
Is there older .xls spreadsheet, my Exell2000 refuses to open .xlsm

Hi Timo,
To get confidence in taking accurate spectra I recommend measuring a some stars with known spectra and comparing them with the published spectra (MILES stars for example)
Robin

This is great suggestion! Next clear must to do.

Last couple of weeks i beaten head against the wall with ISIS - made stupid mistakes and received poor results. Finally a few of days ago I think I got it. I still do not trust 100% the results. Robin's proposal is therefore more than welcome!

Some results so far:
HD181470 , my ref star.
HD213303, corected with HD181470 response profil . Actualy I thought using HD213303 for Mu Cephei, but Miles spectra for HD213303 look quite complex - is this Be star ? And my Alpy miss absorbtion line in 3934 Å.
Ch Cyg 2018-08-19 looks otherwise good but do blue end go right (?) Corected with HD181470 response profil .
P Cyg ...I'm not sure about this. Corected with same HD181470 response profil.
I have to do Robin's test!

Cheers!
Timo K.

[Robin Leadbeater]

HD213303, corected with HD181470 response profil . Actualy I thought using HD213303 for Mu Cephei, but Miles spectra for HD213303 look quite complex - is this Be star ? And my Alpy miss absorbtion line in 3934 Å.

The spectrum in MILES for this star (HD213307, not HD213303) certainly looks strange. The 3934A line is Ca K and should not be there in an A0 star. I wonder if the MILES spectrum is contaminated by nearby Del Cep ? The same star is in ELODIE 3.1 where the spectrum looks more sensible. I any case it looks like the MILES spectrum of this star should be avoided as a reference. (This is the second suspect spectrum to be found in MILES in the past few days which is worrying (The other is HD216916, reported on spectro-l)

Robin