[Fwd: VOTimeSeries]

[Rob Seaman]

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:

	http://www.cv.nrao.edu/adass/adassVI/seamanr2.html

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?

Rob