[vsnet-chat 3708] del Vel : a note for observers using a diversity of equipment

[crawl@zoom.co.uk]

There appears to be some confusion re the multiplicity of delta Velorum,
and as this multiplicity _may_ also mean eclipses behave differently
dependant upon what instrumentation is being used, I'd better map out the
nature of this system.

All data is from the WDS2000 [Washington Double Star Catalog 2000], a
product of the USNO Astrometry Department [www.ad.usno.navy.mil]

TNG 1 is an Aa speckle pair having separations of 0.6" and 0.7" in PAs of
64 deg and 5 deg in 1978 and 1991 respectively.  Together star A and star a
compose the component A of Innes 10.

Innes 10 A-B were separated by 2.2" with PA 154 deg in 1953.

IMPORTANT : it will be noted that for the vast majority of equipment used,
from naked eye to pep photometry to CCD work that these three stars will
appear as one image.

So, some may find it interesting to note that it is impossible at this time
to say whether star A, star a or star B is actually undergoing the eclipse
events!!!!!!!!!

However, star B is estimated at visual magnitude 5.1, and thus would have
to undergo a deeper eclipse than the Aa pair to give an overall reduction
from around 1.9 to 2.3.  Incidently, star a is assumed to be approximately
1.3 magnitudes fainter than A.

I am not fully aware of the capabilities of pep photometry, and whether the
Aa pair can be measured separately from the B star given a 2.2 arcsec
separation.

The AaB system at sub 3 arcsec resolution comprises star A of HJ 4136 ACD.
C and D consist of a pair of visual magnitude 11.0 and 13.5 stars separated
by 6.3 arcsecs in a PA of 97 deg [for 1935], with C being 69.4 arcsecs from
A in PA 61 deg in 1913... ...thus these stars should not effect the
observations in any way.

None of these stars are capable of causing the eclipsing effect found by
Sebastian Otero.

[The Hipparcos astrometry for delta Velorum is 0.041 arcsecs, and given a
0.7" arcsec separation between A and a, a projected separation in AU can be
calculated, and if the orbit is assumed to be face on for convenience's
sake, Kepler's 3rd law should give a general idea of the orbital period
from this.  However, I'm not with my books at the moment, and can't
remember how to do this!  Anyone else tempted, feel free!  The figure is
apparently of the order of a few decades, which means none of the above
mentioned stars are liable themselves to be the eclipsing object in question]

John

JG, UK

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