[Aavso-photometry] Newbie Question Re: AW Cyg

[Sal Giambruno]

Wolfgang,
   
  Thank you for the thorough explanation.  I hope I have understood it correctly. If I have, and as you summarize in the end, the most important thing to take away from this is that any particular measurement is expressed as and is completely dependent upon the spectral value of a star, which varies over time and whose various spectral magnitudes vary in relation to each other as well.
   
  In hindsight, I should have considered spectral value to be a factor.  I did not realize this immediately in large part because of my unfamiliarity with all the various notation used (e.g. "p" for photographic as a prefix to the magnitude parameter).
   
  This lesson will definitely serve as the basis for a more educated understanding and observation of variables well into the future.
   
  I must go now . . . I have much learning to do! :)
   
  Thank you once again.
   
  Sal Giambruno
   
  P.S.  I would also like to thank Michael Sallman at this time, who promptly responded to my question earlier, as I may have failed to cc "The List" when I responded to his original message.
  

Wolfgang Renz <w_renz at onlinehome.de> wrote:
  Hi Sal

AW Cyg is listed in the GCVS as SRB varying 11.0-14.5 p.
p means that these are (blue) photographic magnitude values.
AW Cyg is an orange carbon star (MKK C4,5(N3))

As the Johnson-Cousins magnitude system is A0-star calibrated,
the magnitude values of a stars that is significantly redder than
MKK A0 decreases numerically from B/pg over visual/V/pv to Rc
and to Ic bands by definition. E.g. Vega is of MKK type A0 and
has the same 0 mag values in all bands and therefore also 0 color
indices (in the past Vega was used as 0 point of the magnitudes
and color indices of the Johnson-Cousins photometric system).

The amplitudes are not the same in all bands either. E.g.
the RR Lyr stars have their maximum output in green, but
when they get brighter, they get a bit hotter too and therefore
emitt a bit more light in the B/pg band than when they are
in minimum light. Therefore the RR Lyr stars have their
maximum amplitude in the B/pg band. The amplitude
decreases in the U over the visual/V/pv to Rc and to Ic
bands. E.g. Mira stars might have an amplitude of more
than 6 mag in the visual when its less than 2 mag in the
IR LMN bands.

So one must always consider the band the mag values were
taken in AND the color of the star. There is usually no easy
way to exactly predict the mag values and amplitudes in the
other bands without knowing their MKK type and reddening,
their spectra or their color indices.

Clear skies
Wolfgang

--
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message -----
From: "Sal Giambruno" 
To: 
Sent: Thursday, October 04, 2007 4:18 AM
Subject: [Aavso-photometry] Newbie Question Re: AW Cyg

> Dear Fellow AAVSO Observers:
>
> Pardon my ignorance, and the basic nature of my forthcoming question, but
> I'm a newbie to the world of Variable Star Observing.
>
> Having said that, I was wondering why, when I look up the characteristics of
> AW Cyg in a star catalog, say, an AAVSO database or "The Sky," AW Cyg is
> described as a variable star with magnitude ranging 11.0 - 14.5, yet, an
> observation which I made recently correlates nicely with current and
> historical AAVSO observations and light curves which show the visual
> luminosity of AW Cyg varying in the vicinity of magnitude 8.8?
>
> There is obviously an error in my process or a gap in my understanding.
>
> I would be grateful if somebody could shed some light on this for me (no pun
> intended).
>
> Thank you,
> Sal Giambruno
> La Verne, California, USA