Re: Analyzing Data

[Patrick Wils <patrickwils@yahoo.com>]

--- Doug Welch <welch@physics.mcmaster.ca> wrote:
> 
> I suspect that a very successful minor modification to the
> WS statistic would be for it to calculate residuals from a
> given night's mean magnitude instead of a global mean magnitude.
> 
> On Sun, 4 Aug 2002, Tom Droege wrote:
> 
> > The answer is that they are there, one just has to look carefully
> with 
> > something better than WS.  OK, Doug has done a good job getting us
> a start, 
> > but something more is needed, I think.  We need a way to look at
> the data 
> > with WS over 1 and see what I can see if I look at it by eye.
> > 

I have been working on similar lines.  Besides the WS statistic, I look
at the value of Spearman's rank correlation coefficient (SRCC) for the
data within a night.  This measures basically whether magnitudes are
more or less randomly spread over a night, or whether e.g. bright and
faint mags tend to lie together.  The latter is an indication of
regular variation.
Short period variables have a large WS statistic and a highly
significant SRCC for all (or most) nights in V and I.

Some new short period variable stars in the July data set, found this
way (I have not checked all possible variables at this moment, I
haven't paid much attention to the WS < 4 range yet):
* GSC00380-00247, observed on 4 nights (WS=47): 2 clear minima and a
descending branch (4th night is too short, but shows a slight fading),
frequency 8.3 cycles/day ? (already featured in a "fresh meat" post
from Tom).
* NSV 7901 = GSC00395-01818, 3 nights (WS=15): one night no variability
(near maximum ?), one night fading, one night rising.  NSV gives type L
(slow irregular).
* GSC00396-00073, 4 nights (WS=13): 2 nights near maximum, a descending
branch + minimum, and a minimum + ascending branch. 
* HD 153586 = GSC00410-02004 (WS=12), 2 nights: an ascending and a
descending branch.
* GSC00410-02795, observed on 2 nights (WS=64): a descending branch and
a pronounced minimum.

At lower amplitudes (and lower WS), there is HIP 83986 = HD 155229 =
GSC00407-00415 (WS=4), with an ascending and descending branch.

In this way I also found the known variable V2377 Oph (WS=7) = HIP
85944 = HD 159356 = GSC00992-01402, 2 nights: an ascending and a
descending branch.

In contrast, for the Mira star SS Her (WS=70), the significance of SRCC
for the I mags is low on the two nights, indicating long term
variability.

Patrick




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