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AAVSO Special Notice #35

Eclipse of HD74057
(February 24, 2007)

Don Davies discovered a 7th magnitude eclipsing binary
(GSC 02484-00592, HD74057, VSX J084246.2+315145) in May, 2005,
announced on our discussion group (posting 5/27/2005),
and subsequently published in Peremennye Zvezdy:

The coordinates are
08:42:45.900 +31:51:41.00 J2000
and the approximate magnitude is V=7.18, with (B-V) = 0.56

By Davies' predictions, this star should undergo an eclipse
on March 3 UT, well-placed for northern hemisphere observers.
The period is about 31 days, and the eclipse length is about
5 hours.  The eclipse is centered at JD 2454162.7165
(about 05:11 UT on March 3).

This is an interesting system, containing two main-sequence
F/G stars, widely separated so that they are evolving
separately, yet very nearby (about 48 parsec), with a
highly eccentric orbit. It is also an X-ray source.

We request that PEP and CCD observers monitor this
object through its eclipse, obtaining data for a night
or two prior to the event, dense coverage during the eclipse,
and a few datapoints on nights after the eclipse.  The
eclipse depth is small enough (about 0.5mag) that visual
observations are not recommended.

We have added this new variable
to the Variable Star Plotter as VSX0842+31:
where any chart with 15arcmin or larger dimension will
show the two comparison stars towards the south.  The two
comparison stars are:
Star            RA (J2000) Dec        V   B-V
89 GSC 02484-00532  08:42:51.94 +31:43:19.4  8.86 0.69
96 GSC 02484-01314  08:43:00.88 +31:46:22.7  9.61 1.06

Use 0532 as the comparison and 1314 as the check star for
CCD and PEP work.  BVRcIc observations are welcome.  This
star is bright enough and the eclipse long enough that you
can take BVRI sets rather than having to stay in one filter
through the entire eclipse if you have multi-filter
capability.  We will let you know as soon as we have
better BVRcIc calibration for the comparison stars.
Arne Henden

AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484