alf Ari spectrum

Affiliation

Madrid Astronomical Association M1 (Spain) (AAM)

Mon, 01/06/2020 - 12:12

Hello.

I've submitted alf Ari spectrum for validation. In visualization page I see my obsrved spectrum superimposed to the standard star spectrum. They don't match at all, but I am wondering if that is the standard or I am mistaking the star.

alf Ari is a K2III type star. K2III spectrum is like in the attached pic. Even more, I checked alf Ari spectrum against a K2III spectrum of Miles db and it was OK.

I don't know what is going wrong.

Regards

File Upload

standard vs observed.JPG36.28 KB

K2III cfa_harvard_edu atlas.JPG24.59 KB

bpablo

Affiliation

American Association of Variable Star Observers (AAVSO)

Tue, 01/14/2020 - 21:15

Your Spectrum was accepted

Hello,

If you have not checked recently, your spectrum should have been accepted. The lack of visual match is misleading because they differ mainly in the continuum. This shape can depend on a lot of factors and not what is important to us. If you look closely the major lines occur at the right location and have roughly the right depth which is what we are looking for. Apologies for the late reply. Please let me know if you have any more questions.

Sincerely,
Bert Pablo
Staff Astronomer, AAVSO

Robin Leadbeater

Affiliation

British Astronomical Association, Variable Star Section (BAA-VSS)

Tue, 01/14/2020 - 23:47

rectification

Note the BeSS standard states that spectra should preferably not be rectified and if they are the appropriate flag should be set in the header. Rectification of low resolution spectra is frought with problems in any case as the true continuum is difficult to discern. For example as here which also demonstates the high precision to which relative flux calibration can be carried out.

https://www.aavso.org/comment/67947#comment-67947

Cheers

Robin

Robin Leadbeater

Affiliation

British Astronomical Association, Variable Star Section (BAA-VSS)

Tue, 01/14/2020 - 23:58

rectified reference spectrum

Your spectrum is flux calibrated ie corrected for instrument response and atmospheric extinction and so represents the true spectrum at the top of the atmosphere. The standard spectrum has been rectified ie the continuum shape has bee removed.

Cheers

Robin

Robin Leadbeater

Affiliation

British Astronomical Association, Variable Star Section (BAA-VSS)

Wed, 01/15/2020 - 00:05

interstellar extinction

Note though that the continuum shape of your star may still not match that of eg a Pickles standard or another star of the same spectral class due to interstellar reddening. You can see this for example if you compare the as measured MILES spectra in ISIS (ie not de-reddened) of the same spectral class but different interstellar reddening ie different E(B-V)

Cheers

Robin