This web page is devoted to what the professionals have learned about "W Com" variability.  So far I've worked with data from just one published report:

    "The Optical Behaviour of ON 231 (W Comae) During and After the Great Outburst of Spring 1998," Tosti et al., Astronomy and Astrophysics, p. 395, 11, Nov, 2002.

(I'm a little confused about the data that I downloaded belonging to the above article, since the web page abstract refers to data for March 1997 to June 2001 but the associated data file has JD dates for 1994 to 1997.  For present purposes it doesn't matter, since we're just trying to get a "sense" for the kinds of variations W Com can exhibit.)

The measurements were made at five observatories in Italy.  It is important to assess the internal consistency of this large measurement set inorder to know how much credence to place in apparent brightenss changes.  I've done this by constructing a plot of "brightness difference" versus observation time difference.  Presumably measurements taken at the same time should agree, and the level of the agreement achieved can be seen from such a plot.

Figure 1.  Relation between brightness differene and time span. The dotted fit goes through the medians at time span intervals.  Only the V-magnitudes were used.

Based on this plot I conclude that a typical observation has an associated SE uncertainty of ~0.030 magnitude.  This is derived by dividing the measurement-to-measurement difference of 0.050 magnitude by SQRT(2).  Therefore, we can assign a SE of 0.030 magnitude for typical measurements.  The plot can also be used to state that typical month-to-month differences are ~0.3 magnitude.

Figure 2.  Sample of brightness versus date for the 1995 "W Com" observing season.  The "fitted" trace allows for the expected RMS scatter of 0.03 magnitudes.

This graph is for one season's obsrevations (5.9 months).  The impression I get from this plot is that W Com typically sustains a brightness trend for 20 to 50 days, then abruptly changes, sustaining a new trend (sometimes of oppsite sign).  Variations on shorter time scales might exist, if you accept the abundance of larger than 0.030 magnitude departures from the fitted trend lines.

The authors state in their abstract that their 1997 to 2001 data exhibits some hourly variations.
 
 
 
 

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This site opened:  June 19, 2003.  Last Update:  June 19, 2003