[Aavso-photometry] Reality Check - Basic Concepts

[Wolfgang Renz]

Hi David

> Consider the AAVSO light curve for V5558 Sgr (http://tinyurl.com/3bh74o) 
> Question #1: In general, do the data points in this light curve represent
> the results of observers who have been doing all-sky photometry and
> using standards such as Landolt, M67, etc?

No, usually not.
All-sky photometry is done by just a very few observers primarily for
creating sequences. All others do differential photometry.
Some might have derived the color transformation coefficients of their
setup and might observe standard fields to get the extinction coefficient
of the night .
But the far majority will just do simple plain untransformed differential
photometry with comp star mags taken from different sources.

For V5558 Sgr take a look at the LC:
<http://www.aavso.org/cgi-bin/newlcg.pl?name=V5558+SGR&lastdays=70&start=&stop=2454270&obscode=DKS&obstotals=on&type=png&width=800&height=600&style=points&mag1=7.5&mag2=10.5&grid=on&v=on&bband=on&r=on&iband=on&uband=on&j=on&h=on>
and the QLF:
<http://www.aavso.org/cgi-bin/newql.pl?name=1804-18&startdate=100&output=html>
Just 3 observers submitted obs up to now.
A single transformed BVRI set by DSI.
Some untransformed BVR sets by NMR using some kind of TYC mags.
Some untransformed V and BV sets by DKS that consistently use the 8.77 magV
comp and includes the 12.3 mag companion.

If one needs to get info on older data, one can get them via:
http://www.aavso.org/data/download/

> Are the values in this graph exactly as submitted by various observers,
> or have they been normalized in some way after they were submitted?

Usually as they were submitted.
Never normalized.
The AAVSO might correct obs if the mags of comp stars change,
but this has probably never been done (yet) except for special studies.

Clear skies
 Wolfgang

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