seaman at noao.edu
Mon Jul 2 13:25:43 PDT 2007
On Jul 2, 2007, at 12:45 PM, Alasdair Allan wrote:
> Roy Williams wrote:
>> To turn that question around -- who will suffer if all the world's
>> exchange of light-curve data is based on MJD/HJD?
> Lots of people unless you meant to say TDB (a.k.a. BJD) rather than
> HJD. Nobody uses HJD anymore... ;)
Well, I chose to implement heliocentric cadencing in ICE in support
of the SONG asteroseismology experiment in 1996:
Given the same circumstances I would likely choose to do the same.
As I say in the paper:
"Note that the amplitude of the barycentric correction for the Solar
system is about 10 light seconds-about 1% of the heliocentric
correction. Jupiter contributes about half of the barycentric
leverage and Saturn most of the rest. At any given epoch the absolute
value of the barycentric effect may be significantly less than the
full 10s, depending on Saturn's position relative to Jupiter."
In fact, during the course of the observing season, the difference
between heliocentric and barycentric timings was small and varied
little. The benefit was that the algorithm governing the cadencing
(consider this an a priori time series on an even grid) was kept
simple enough that I could convince myself with paper and pencil that
I had implemented it properly. If precision had required it, the
small and nearly linear residual slope could have been reintroduced
during processing. The slight smearing of phase was understood up
front in the context of the particular experimental design.
That said, I agree that "BJD" is what we (VOEvent) should support.
Is it really true that nobody reports HJD anymore, however? Pointer
to guidelines for CBAT, MPC, ATEL, etc?
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