Why are the 'Fixed Stars' so FIXED?

Henri Wilson wrote:

Anyway, put the numbers into your program and tell
me what you get and then we can discuss their
interpretation. Check the results for zero distance
first and make sure you get the right speed and phase.

Naturally for zero distance I get no brightness variation.
The observed velocity is in phase with the true velocity.

You should still get a very small variation due to the
conventional bunching you reminded me of at the top.

Not if the observer is at the orbit centre.

He isn't saying to put the observer at the orbit centre, he
is saying to locate the observer just in front of the light
source so that your program output shows the effect of the
initial bunching of the pulses due to the changing position
of the star, but not the bunching which occurs in transit.

At each iteration, the observer is at zero distance from
the source, but is treated as being motionless, as usual.
It is as if there were 30,000 observers round the orbit,
each motionless relative to the orbit centre, but placed
immediately in front of the source.

If your program is unable to do that, you should be able to
put the observer at the near side of the orbit. Apparently
you have simplified the program to treat an orbiting star
as a reciprocating point, oscillating back and forth in the
line of sight. Just place the observer at the near end of
the stroke.

I can't see the point.
There will be no opportunity for bunching and no brightness
variation. All I will see is conventional doppler frequency
variation using constant c.

There will be a small amount of bunching and brightness
variation from the advancing and retreating position of the
emitter, but basically you are right, what you see will be
very close to the conventional variation. That simulation
is like zeroing out a spring scale before weighing. Once
you have obtained results for the zero case, you can then go
on to look at differences between those initial (very small)
bunching and brightness changes, and the much larger changes
caused by bunching in transit.

George, I think you are refering to the pulses emitted by
the pulsar itself. These will be observed to have a cyclic
doppler shift.

The 'bunching of pulses' I refer to is not the same.

Are you saying that light pulses emitted by pulsars bunch
in a manner different from that of light pulses emitted by
other types of star?

Well basically no.... but it is the way they are handled
that matters. Pulsar pulses don't become any more intense
just because they 'bunch'. Nobody talks about the brightness
curve of a pulsar because the pulses are very constant.

What distinguishes pulsar light from other starlight is that
it is *not* constant. Is that a problem for your program?
The bunching process is the same, but your program is
designed to represent brightness changes in a continuous
stream of light, not in a chopped stream?

You said, 'The program assumes the star emits identical
pulses of light towards the observer at regular intervals
as it moves around its orbit...'

If it can handle pulses of light from a regular star, why
can't it handle pulses of light from a pulsar?

I use symbolic pulses from a star of constant brightness
emitted at equi-temporal points around the orbit. These
travel at varying c+cos(v) speeds towards a distant obsever.
The rate at which they arrive at the observer should then
simulate its brightness curve there.

So apply that to the pulsar.

There is no observed brightness variation reported
but that can probably only be taken to say any
variation is less than 1 mag, the existing single
measurements are no more accurate than that.

Most variations are around 1.5 mag or less.
...and yes, I don't have much faith in the accuracies of
many published figures.

Aside from dwarf novae, the only regularly-variable dwarf
stars I know of are ZZ Ceti variables. Wikipedia says:
"These non-radially pulsating stars have very short periods
of 0.5 to no more than 25 minutes with tiny fluctuations of
0.001 to 0.2 magnitudes."

there are millions of stars varying by 0.3 to 1.6 mags.
Cepheids (as they are broadly named) are the most interesting.

The star you asked for information about is a white dwarf.
I responded with relevant information about white dwarf
variability. We are not concerned at the moment with
other star types.

Leonard