Stellar reddening via Av calculation

[bruha]

Hello, please do somebody have some experiences with calculating of stellar reddening via interstellar extinction? I made some calculation based on apparent and absolute magnitudes and distances of brigthtness star but maximum Av which I got for Betelgeuse was 1.12 mag ( for its maximum apparent magnitude since it is variable star) and for Deneb 0.11 mag.
This results are in disagreement with Av presented in literature which reached values at least about 5-10 mag or more ( for example I found some equation Av (mag) = 2*d(kpc) for latitude b to 2 o and Av (mag) = 0.18/sin (b) for b over 10 o...
Thank you very much

 

[bruha]

Hello,
thank you. I can say that maybe , here is problem that is not clear if apparent and absolute magnitudes which I found posted on net are these calculated according to equation which neglected extinction or these which was real measured.

Thank you
T.Bruha