[vsnet-chat 3838] HIPPARCOS ECLIPSING BINARIES

["Sebastian Otero" <varsao@fullzero.com.ar>]

Thanks to all the folks that answered my message. I couldn't find published
articles on the stars mentioned.

I first got interested in Hipparcos EB's after reading Roger Sinnott's
articles in S&T last year. And now the delta Velorum thing made that
interest were reborn.
I started with the five EA's I mentioned in my previous e-mail because of
their southern location and rather large amplitude.
My surprise was to find that some of them had their periods sleeping -and
waiting to be awaken- in the data...

Using the accurate Hipparcos photometry I tried to put together the
different pieces of the light curves joining equal brightness points with my
test periods (that I found out just using a pocket calculator). This let me
reconstruct -by hand- rather complete light curves. With a ruler and a
pencil (drawing charts that cover only the eclipsing moment) I could find by
geometry the time of minimum and then check the period against all the
observations.
I love doing this, although some guys think that I'm wasting my time... My
concept of a "waste of time" is very different than theirs. This way I feel
I get to know the star as if it was a friend that is telling me all her
secrets. And in the process I learn a lot. Actually that's how I got the
delta Velorum period...

Let's analyse one by one.

For example, V366 Puppis doesn't even need to be looked at for
conmirmation!!! A short period and eclipses recorded far apart in time make
a very accurate period determination possible.
It turns out that the 39.1 day relation between eclipses mentioned in
Sinnott's december 1999 article is just random. With my method I got the
following elements:

V366 PUPPIS  -  HIP 35607 - HD 57897

JD 2448635.3668  +  2.4840258  x  E  min I
JD 2448636.9117  +  2.4840258  x  E  min II

Range:   I : V= 8.06 - 8.58
             II: V= 8.06 - 8.17

Primary eclipse lasts 0.11 days (2h 38m)
Secondary eclipse lasts 0.28 days (6h 43m) and occurs 1.545 days after
primary eclipse, that is at phase 0.622.
It stays under primary eclipse 4% of the period which is a typical duration.
If we take 39 days as a period, it would mean that only 0.28% of the period
is spent in eclipse... This figure is almost impossible (specially for a 0.5
mag. drop)

These are the next ten predicted eclipses (none of them visible from South
America):

JD 2451881.9872  Dec. 3, 11.40 UT
JD 2451884.4712  Dec. 5, 23.20 UT
JD 2451886.9552  Dec. 8, 10.55 UT
JD 2451889.4393  Dec.10, 22.35 UT
JD 2451891.9233  Dec.13, 10.10 UT
JD 2451894.4073  Dec.15, 21.45 UT
JD 2451896.8913  Dec.18, 09.25 UT
JD 2451899.3753  Dec.20, 21.00 UT
JD 2451901.8594  Dec.23, 08.40 UT
JD 2451904.3434  Dec.25, 20.15 UT


The case of V353 Hydrae is very interesting. In june 1999 S&T article, Roger
mentions that the star showed only one dramatic dip at the very end of 1991.
A first look at the light curve and we get the same impression. BUT there
are actually TWO consecutive eclipses recorded. In the folded 3 year light
curve, both minima look like one and may pass unnoticed.
For this star the period determination is not accurate because the eclipses
are so close that a small error could mean that predictions are off by as
much as a full day. So ANOTHER ECLIPSE OBSERVATION IS NEEDED.

V353 HYDRAE  -  HIP 69211  -  HD 123767

JD 2448608.459  + 7.555 (+/- 0.001) x E

Range:  V= 7.42 - 7.99:

Primary eclipse lasts 0.33 days (8 hours, 4% of the period again).
One single observation (V= 7.45) suggests that a secondary eclipse started
2.3 days after primary mideclipse. But it's just an speculation.
It's not possible to make an accurate prediction but observers should be
alert between:

JD 2451894.2 and JD 2451895.5
JD 2451901.8 and JD 2451903.1
JD 2451909.4 and JD 2451910.6
JD 2451916.9 and JD 2451918.2   ...and so on.

Just another detection and we'll have another accurate period. And we
shouldn't forget that it still exists the possibility of one of the recorded
eclipses being a secondary !!!


V362 Puppis is one of those hide-and-seek players. Two periods are possible:
ALMOST 10 or ALMOST 5 days. This way the eclipses can remain unseen for a
very long time!!

V362 PUPPIS  -  HIP 34659  - HD 55348

JD 2448825.264  + 4.98005 (or 9.9601) x E

Range:  V= 7.49 - 7.66

The eclipse lasts approximately 0.09 (or <0.16) days.
If the period is 4.98 days, we'll see next eclipses near:

JD 2451883.015  Dec..4, 12.20 UT
JD 2451887.995  Dec. 9, 11.50 UT
JD 2451892.975  Dec.14, 11.25 UT
JD 2451897.955  Dec.19, 10.55 UT
JD 2451902.935  Dec.24, 10.25 UT

If the period is 9.96 days, then there will be no eclipses on Dec. 9, 19 and
so on.
Minima can occur a little earlier or later.


WZ VOLANTIS  -  HIP 42841  - HD 75246

JD 2448716.13  +  452.55  x E

Range:  V= 8.28 - 8.53

Just two eclipses recorded at minimum, neither descending nor ascending
branchs, so few things can be said. The eclipse is longer than for the other
systems, so it is the period.
Of course, 452.55 can be a multiple of the true period. But the good news is
that whatever the actual value is, there will be an eclipse in the near
future:

JD 2451883.98.

So observers should be alert several days after and before December 5.


KV CANIS  MAJORIS  - HIP 32856  - HD 50118

Only one minimum near JD 2448353.45.

Range:  V= 7.16 - 7.40

This is the only star of the five that can't give us a clue on when to look
at it.


I'll keep analysing other stars and let you know.
Please, if someone knows Rogers e-mail addresss, I would like to send them
the news.

Thanks again to all, and good observing.

Sebastian Otero,
LIADA - Liga Iberoamericana De Astronomía.
Buenos Aires,
Argentina.


PS: I'll prepare charts and make them available later this week.

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