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[vsnet-ecl 341] Re: DE Dra confusion ?
Dear Kari,
Apparently I suffered from a "Senior Moment"! <G> I'm sorry for
the confusion. Cutting and pasting from several different e-mails,
each one about two different stars, did indeed result in my getting
some of your observations of DK Cam mixed in with the DE Dra
observations.
I've gone back over the postings I kept and taken out what I think
are the Hipparcos data. I've been assuming, perhaps incorrectly, that
the Hipparcos times are times at which Sebastian had discovered a
minimum. If they are not times of minimum, then my conclusions are,
of course, baseless.
Nevertheless, here is my revised comparison. If incorrect
observations are still included, please accept my apologies in advance
and ignore them. And if the "Hipparcos Minimum" times are not times
of minimum, then ignore the following table too! <G>
Predicted Minima Hipparcos Minimum Probable
Min I: Min II: Minimum
2448231.812 2448229.385 2448231.55 I
" " 8231.565 I
8316.582 8319.453 8317.112 I
8348.371 8351.242 8349.114 I
8438.439 8441.310 8438.858 I
The first two Hipparcos observations were taken from a posting by
Sebastian [vsnet-chat 4192] in which he attributed them to DE Dra.
The subject on the header was DK Cam, so perhaps those observations
are really of DK Cam.
My table of predicted times of minimum for the next month is
still valid because they depend only on the spectroscopic orbital
elements. I hope you have great weather and can report whether the
predictions are any good! <G>
The observations you reported of DE Dra in [vsnet-ecl 338] are all,
I've assumed, times of minimum. (By the way, why are two magnitudes
given for each time in the "observed mags" column? Did you observe
through filters?)
I've made a comparison of some of your observations, chosen more
or less at random; the two observations below marked with * are the
ones you identified as "deepest minima". The predicted minima are
from the spectrographic orbit (P=5.298111 days; JD Min I 244142.930;
JD Min II 2441145.811):
Observed times Min. I O-C Min. II O-C
JD JD (days) JD (days)
2451554.141 2451553.728 +0.413 2451556.599 -2.458
1554.325 " +0.597 " -2.274
1555.143 " +1.415 " -1.456
1752.406 1749.758 +2.648 1752.629 -0.223
1752.451 " " -0.178
1760.385* 1760.354 +0.031 1757.927 +2.458
1760.434 " +0.080 " +2.507
1776.317* 1776.219 +0.098 1773.822 +2.495
It looks like you observed Min. I on JD 2451760 and JD 2451776, and
Min II just starting on JD 2451752. Your observation on JD 2451555
is especially interesting and valuable because it occurs at very
nearly the spectroscopically predicted time of quadrature, so DE Dra
should have been very close to maximum then. Congratulations on
both counts!
The observations on JD 2451554 and 1555 are are also very useful
because they set limits on the duration of Min I. Min I cannot
have been shorter than about 0.6 day and could not have lasted longer
than about 1.3 or 1.4 days. The maximum length is far too long, and
a more reasonable assumption is that Min I probably lasts around
14-18 hours. That value can help when planning future observations.
A similar analysis of the rest of your observations could further
refine those estimates.
It would be very interesting to see a phase plot of the existing
visual observations against the 5-day period. If your observation
on JD 1760.385 is exactly at Min I, then its O-C implies that the
period should be shortened by 0.000015 days, to P=5.298096. However,
the observation was probably not made exactly at minimum (Mr. Murphy
is at it again!), so there really is no hard evidence for that
period.
If I may offer a word of caution: periodogram analysis doesn't
provide very meaningful results on small data sets which cover only a
limited time scale. False periods - "aliases" - can show up because
of a number of reasons. The period is already known for DE Dra - the
existing photometric and spectroscopic data rule out any period very
different from 5.298111 days.
Further observations, both photometric and spectroscopic, will
refine the period further. Well observed photometric minima are
definitely needed. My table of predicted minima and "guesstimate"
of Min. I duration can be used to plan observing to cover ingress
and egress, as well as the minima.
Good observing!
Cordially,
Thom Gandet
Kari Tikkanen wrote:
>
> >From: Thom Gandet <tgandet@mindspring.com>
> >Subject: DE Dra: Predicted Minima
>
> Hi!
>
> Thom said:
>
> > Kari Tikkanen reported observing minima, of unspecified magnitude,
> >at JD 2451996.43 and JD 2452013.5. The spectrographic orbit predicts
> >eclipses at JD 2451996.189 (Min. II), and at JD 2452014.510 (Min. I).
>
> You mixed stars.
> Those 2451996.43, 2452013.5 were my DK Cam minima
> not DE Dra minima.
>
> Also Your Hipparcos Minimum list mixes two star minima together.
> [...snip...]
> (Sorry, I should really have splitted my email to two different
> emails..)
--
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Thomas L. Gandet, Director
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