[Message Prev][Message Next][Thread Prev][Thread Next][Message Index][Thread Index]

[vsnet-chat 4281] Re: DE Dra confusion ?

Thom:
          In a hurry (a longer mail later or tomorrow...), There was a big
confussion: HIPPARCOS dates I provided were for observations made near the
times of eclipse predicted based on the GCVS ephemeris.
BUT the main point was THE OPPOSITE!!: that Hipparcos didn't catch any
eclipe at all!!!

So, there are no variability of any kind according to Hipparcos for DE
Draconis.
Which is very useful since we can rule out periods using these data.

Cheers and then I will come back.

Sebastian.



> 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..)
>
> --
> ************************************************************************
>                       Lizard Hollow Observatory
>                       Thomas L. Gandet, Director
>                             PO Box 77021
>                       Tucson, AZ 85703-7021  USA
> ************************************************************************


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://vsnet.grisoft.com).
Version: 6.0.249 / Virus Database: 122 - Release Date: 13/04/01

VSNET Home Page

Return to Daisaku Nogami

vsnet-adm@kusastro.kyoto-u.ac.jp