(cba:news) HO Delphini, Sensuous September Superhumper

[Joe Patterson]

Dear CBAers,                                           9/4 I think

What an interesting haul this morning.  Good thing there's no class to
prepare today.

I studied Tonny and Lasse's runs on HO Del.  Both show superhumps
exhibiting phase, amplitude, and periods in agreement, in my opinion.
They characterized the superhump amplitudes differently because Tonny
was using semi-amplitudes (maybe; correct me on this) or because the
shorter intergration times used by Lasse gives somewhat noisier data
and the eye is drawn to "the highest of the high" and "the lowest of
the low" as the points which define the amplitude range.  A more
reasonable definition of amplitude, for most purposes, uses the mean
amplitude, which smooths over these extremes.  (I think the latter is
the main reason, but I did want to clarify this semi- versus full-
amplitude issue.  Most people use "amplitude" to mean full amplitude
unless modified by "semi-".)

Haven't seen any other data yet.  From this 5.8 hour run I obtained a
period of 91.9+-1.8 min, in agreement with Tonny's estimate.  Formally
this error estimate is sufficient to beat down the 24-hr alias, but the
formal error estimate is often not too useful in these humpy-jumpy
stars.  Timings from other longitudes are really what's needed to nail
it down.  And a 3-4 day baseline is needed to give enough accuracy to
adequately define the superhump period excess.

Tonny and Lasse's data have 2 hours of overlap, enabling me to splice
them.  I notice that Tonny's differential measures give the same result
as Lasse's absolute numbers if it is assumed that they used the same
comp star with a "CBA-magnitude" of 12.66.  Probably they both used the
"12.8" GSC star (right?).  Anyway, the point I wanted to make is that
this is how I like to cross-calibrate the data.  Some of you have asked
that I supply "official" comp stars; and we sometimes do that, where we
are very concerned about accuracy or about wild variability (e.g. CR
Boo in most years).  But my preference is for after-the-fact
calibration, because:

* It's less authoritarian!
* Filterless operation with different CCDs gives quite different
  responses, and generally the assumption that the star's mean is the
  same is superior to assuming any such thing about the data itself.
* Because of different saturation levels, fields of view, and observing
  procedures, people have different preferred comp stars.
* We are period hunters, and some of our targets evolve rapidly.  If we
  were hunting rhinoceroses, I think no one would propose extensive
  debates on the color of the rhinoceros while it was in full charge.


I'll attach the spliced CBA-Low-Countries light curve (I condensed
Lasse's data by a factor of two so the integration times would be
comparable).

t(geo) versus delta mag (Var-Comp)

 329.3466      1.28
 329.3483      1.3
 329.35        1.3
 329.3518      1.32
 329.352       1.265
 329.3535      1.34
 329.3548      1.29
 329.3553      1.38
 329.357       1.38
 329.3576      1.335
 329.3587      1.36
 329.3605      1.33
 329.3622      1.40
 329.3631      1.38
 329.3659      1.43
 329.3726      1.35
 329.3743      1.35
 329.3761      1.36
 329.377       1.35
 329.3798      1.435
 329.3813      1.36
 329.3826      1.405
 329.383       1.35
 329.3848      1.4
 329.3868      1.365
 329.3882      1.37
 329.39        1.35
 329.3909      1.38
 329.3917      1.32
 329.3934      1.34
 329.3944      1.38
 329.3952      1.34
 329.3969      1.28
 329.3979      1.24
 329.4006      1.285
 329.4034      1.2
 329.4056      1.29
 329.4062      1.27
 329.409       1.29
 329.4108      1.29
 329.4118      1.27
 329.4125      1.31
 329.4143      1.31
 329.4152      1.28
 329.416       1.3
 329.4177      1.32
 329.4187      1.295
 329.4195      1.29
 329.4212      1.34
 329.4215      1.37
 329.4229      1.36
 329.4243      1.405
 329.4247      1.39
 329.427       1.41
 329.4298      1.475
 329.4326      1.33
 329.4354      1.395
 329.4368      1.39
 329.4395      1.4
 329.4423      1.4
 329.4451      1.4
 329.4472      1.39
 329.4559      1.33
 329.4611      1.26
 329.4628      1.28
 329.4646      1.25
 329.4681      1.3
 329.4733      1.32
 329.4767      1.33
 329.4785      1.3
 329.4802      1.32
 329.4854      1.32
 329.4872      1.33
 329.4889      1.34
 329.4906      1.32
 329.4924      1.34
 329.4941      1.4
 329.4958      1.39
 329.4976      1.4
 329.4993      1.39
 329.501       1.43
 329.5027      1.39
 329.5044      1.36
 329.5061      1.39
 329.5078      1.44
 329.5094      1.42
 329.5111      1.45
 329.5128      1.42
 329.5145      1.41
 329.5162      1.41
 329.5179      1.44
 329.5195      1.41
 329.5212      1.45
 329.5229      1.36
 329.5246      1.35
 329.5263      1.32
 329.528       1.32
 329.5297      1.32
 329.5314      1.27
 329.533       1.28
 329.5347      1.31
 329.5364      1.32
 329.5381      1.38
 329.5398      1.34
 329.5415      1.35
 329.5432      1.35
 329.5448      1.41
 329.5465      1.4
 329.5482      1.36
 329.5499      1.36
 329.5516      1.41
 329.5533      1.43
 329.555       1.44
 329.5568      1.4
 329.5585      1.36
 329.5602      1.41
 329.562       1.46
 329.5637      1.45
 329.5654      1.44
 329.5672      1.42
 329.5689      1.41
 329.5706      1.4
 329.5724      1.44


 Graph it up, it's a winner.