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  #71  
Old August 13th 13, 10:20 AM posted to sci.astro.research
Steve Willner
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In article ,
Nicolaas Vroom writes:
When you remove all the stars above 0.4 mass the total mass left is
9,46 and the density is 1E-12. This are Red Dwarfs and Brown Dwarfs
and can be considered invisble baryonic matter.


Fair enough, except that at least the higher end of that mass range
would be detectable via lensing. One fly in the lensing ointment is
that measurements have been made only towards the LMC and the
Galactic center (unless I've missed other observations, which is
quite possible). If you can arrange for red dwarfs to occupy regions
other than these lines of sight and still explain the rotation
curves, you might get somewhere.

Regardless of lensing, if you want to explain rotation curves with
red dwarfs or similar objects, you have to postulate that they have a
different distribution than that of the visible stars. In
particular, you need more low-mass stars at large radii than expected
from the light distribution. That's possible, of course, but there's
no evidence for it. Galaxy colors don't change much with radius, for
example. Actually they become a little bluer at large radii because
of lower metallicity.

As I wrote earlier, I'm not sure all the parameter space is ruled
out, but it is shrinking.

Some comments on subsequent posts:

1) aside from rotation curves, there's a problem with spiral disk
instability. Putting mass in a halo rather than a disk stabilizes
the disk as well as solving the rotation curve problem. That doesn't
prove the halo explanation, but it makes it more attractive.

2) gravitational lensing can easily detect objects of half a solar
mass or larger. Smaller objects are more difficult, but observations
have improved. I'm not sure just where things stand now, but objects
more massive than some tenths of a solar mass cannot easily explain
the dark matter inferred for the Milky Way. (But see above about
"fly in the lensing ointment.")

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  #72  
Old August 13th 13, 10:20 AM posted to sci.astro.research
Steve Willner
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Default WIMPS?

In article ,
"Richard D. Saam" writes:
Deceleration (aP) as well as radiation power half_life
should then be on the order of 87.7/4 or 21.9 years


You've lost me there. Radiative deceleration should be proportional
to power (according to the equation you quoted earlier), which
decreases exponentially according to the half-life. I think you've
confused yourself by thinking about temperature.

These half_lives should be considered very accurate


Yes, half life is an intrinsic property of the Pu-238.

The point of the recent analysis was that the radiative model is
consistent with all known data, and there is no need for "new
physics" to explain the so-called Pioneer Anomaly. That doesn't
prove that no new physics exists, but it removes one piece of
evidence.

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  #73  
Old August 13th 13, 08:40 PM posted to sci.astro.research
Phillip Helbig---undress to reply
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In article , Steve Willner
writes:

One fly in the lensing ointment is
that measurements have been made only towards the LMC and the
Galactic center (unless I've missed other observations, which is
quite possible). If you can arrange for red dwarfs to occupy regions
other than these lines of sight and still explain the rotation
curves, you might get somewhere.


I'm pretty sure that there were observations of M31 looking for
microlensing effects.

For larger masses, one can rule them out because they would be visible
in QSO light curves. (Hawkins claims such a detection of dark matter,
but it doesn't stand up to a quantitative analysis.)
  #74  
Old August 27th 13, 08:55 AM posted to sci.astro.research
Richard D. Saam
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On 8/13/13 4:20 AM, Steve Willner wrote:
In article ,
"Richard D. Saam" writes:
Deceleration (aP) as well as radiation power half_life
should then be on the order of 87.7/4 or 21.9 years


You've lost me there. Radiative deceleration should be proportional
to power (according to the equation you quoted earlier), which
decreases exponentially according to the half-life.


but which half life are you indicating:
the RTG plutonium half life of 87.7 years
reflected in power equation
http://arxiv.org/abs/1204.2507v1 page 2
Qrtg(t) = 2^(-(t-t0)/87.74)*Qrtg(t0)
or the electrical half life of 87.7/4 or 21.9 years
http://arxiv.org/abs/1204.2507v1 table 1 data
Qelect(t) = 2^(-(t-t0)/21.9)*Qelect(t0)

The authors choose a subset
aP = n*Q/(pioneer mass *c)
of this more general equation
aP = F*stefan_constant*T^4*(4/(3*c))*pioneer area/pioneer mass
where n*Q = F*stefan_constant*T^4*(4/3)*pioneer asymmetric area

with two components
aP = nrtg*Qrtg/(pioneer mass *c) + nelect*Qelect/(pioneer mass *c)
with a well established finite element basis for
nelect*Qelect/(pioneer mass *c)
and
Qelect(t)=2^(-(t-t0)/21.9)*Qelect(t0)=Qelect(t0)*exp(-ln(2)(t-t0)/21.9)
but with no physical basis for
Qrtg(t) = 2^(-(t-t0)/87.74)*Qrtg(t0)= Qrtg(t0)*exp(-ln(2)(t-t0)/87.74)

The RTG component contribution to Pioneer deceleration (aPrtg) is
nrtg*Qrtg = F*stefan_constant*T^4*(4/3)*RTG_asymmetric_area

The RTG symmetrical design defines
RTG_asymmetric_area = 0 and therefore aPrtg = 0
Any RTG_asymmetric_area would be outside manufacturing tolerances
that perhaps or on the order of mm^2


These half_lives should be considered very accurate


Yes, half life is an intrinsic property of the Pu-238.

The point of the recent analysis was that the radiative model is
consistent with all known data, and there is no need for "new
physics" to explain the so-called Pioneer Anomaly. That doesn't
prove that no new physics exists, but it removes one piece of
evidence.


In
http://arxiv.org/abs/1204.2507v1
a detailed finite element radiative model
was applied to electrical power
with half life of 87.7/4 or 21.9 years
assuming the model daP/dt = -ln(2)(t-t0)/21.9.
The remaining aP 'constant with time' component
was modeled as daP/dt = -ln(2)(t-t0)/87.7
a modeling that can not be physically justified due to Pioneer design.
(A 87.7 year half life changes aP on the order of 20% over Pioneer life
for all intensive purposes represents a constant)
This 'constant with time' component on the order of 7E-8 cm/sec^2
cannot be linked to the internal physical nature of Pioneer
and can truly be considered the Pioneer anomaly
indicating a property of space through which the Pioneers travel.
This recent analysis
http://arxiv.org/abs/1204.2507v1
does not 'remove one piece of evidence'.
but unnecessarily stops investigation in this astrophysical area
at this important time
when 95 percent of the unknown universe is under investigation
as to identity
and all research avenues are needed as tools.

Richard D Saam
  #75  
Old August 30th 13, 07:34 AM posted to sci.astro.research
Steve Willner
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SW Radiative deceleration should be proportional to power

I was wrong about that. See below.

In article ,
"Richard D. Saam" writes:
but which half life are you indicating:
the RTG plutonium half life of 87.7 years
reflected in power equation
http://arxiv.org/abs/1204.2507v1 page 2
Qrtg(t) = 2^(-(t-t0)/87.74)*Qrtg(t0)
or the electrical half life of 87.7/4 or 21.9 years
http://arxiv.org/abs/1204.2507v1 table 1 data
Qelect(t) = 2^(-(t-t0)/21.9)*Qelect(t0)


In http://arxiv.org/abs/1204.2507v1
a detailed finite element radiative model
was applied to electrical power
with half life of 87.7/4 or 21.9 years


I don't see where you got that half life for electrical power, but it
may be right. The electrical efficiency decreases as the plutonium
decays and the RTGs cool off, so the electrical power generated drops
off faster than the total power of the plutonium.

As the OP wrote, the authors have a detaled thermal model, but in
essence there are two components: electrical power used in the
spacecraft itself and waste heat in the RTGs. The point -- that I
completely missed earlier -- is that these have entirely different
efficiencies (eta) for being turned into acceleration. The RTG waste
heat is emitted nearly uniformly in all directions, and its
efficiency for accelerating the spacecraft is only 1%. When powered
components inside the spacecraft generate waste heat, that heat is
directed predominantly away from the Sun (because of the geometry of
the spacecraft) and has a 41% efficiency for conversion into
electrical power. The net acceleration is the sum of these two.

The bottom line is that the calculated thermal acceleration is 80% of
the acceleration derived from the Doppler tracking data. However,
the error bars are larger than the 20% difference, so there is
currently no evidence of "new physics." (The RTG asymmetry is
uncertain because of unknown changes in the coating properties.
Making it just a bit bigger than 1% would give excellent agreement.)

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  #76  
Old August 31st 13, 07:00 AM posted to sci.astro.research
Richard D. Saam
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Posts: 240
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On 8/30/13 1:34 AM, Steve Willner wrote:

The bottom line is that the calculated thermal acceleration is 80% of
the acceleration derived from the Doppler tracking data. However,
the error bars are larger than the 20% difference, so there is
currently no evidence of "new physics." (The RTG asymmetry is
uncertain because of unknown changes in the coating properties.
Making it just a bit bigger than 1% would give excellent agreement.)

This presented logic is in a constant time frame.
'calculated thermal acceleration is 80%'
The RTG contribution is 1%
A more complete model would analyze
these deceleration contributions with time for a constant residual.
The much detailed finite element electrical contribution
fades faster with time (21.9 year half life)
(based on regression of http://arxiv.org/abs/1204.2507v1 table 1 data)
leaving the RTG contribution (87 year half life)
that can be considered constant in the measured Pioneer time frame.
No detailed finite element thermal RTG deceleration analysis was done in
http://arxiv.org/abs/1204.2507v1.
A prior RTG analysis in
http://arxiv.org/abs/gr-qc/0104064 page 32-33
reads in part:
"So, even though a complete thermal/physical model of
the spacecraft might be able to ascertain if there are any
other unsuspected heat systematics, we conclude that
this particular 'RTG' mechanism does not provide enough power
to explain the Pioneer anomaly"
That leaves a constant deceleration residual with time
with no on board mechanistic origin.

I won't say 'new physics' is required
but verification of known universal physics
(external to Pioneers)
is warranted to explain this constant deceleration residual.

Richard D Saam
  #77  
Old August 31st 13, 08:31 PM posted to sci.astro.research
Dan Riley
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Default WIMPS?

"Richard D. Saam" writes:
No detailed finite element thermal RTG deceleration analysis was done in
http://arxiv.org/abs/1204.2507v1.
A prior RTG analysis in
http://arxiv.org/abs/gr-qc/0104064 page 32-33
reads in part:
"So, even though a complete thermal/physical model of
the spacecraft might be able to ascertain if there are any
other unsuspected heat systematics, we conclude that
this particular 'RTG' mechanism does not provide enough power
to explain the Pioneer anomaly"


The "particular mechanism" of section VIII B is "anisotropic heat
reflection off of the back of the spacecraft high-gain antennae", a
mechanism that doesn't play any significant role in the 1204.2507
model--so that quote does not appear to be relevant.

1204.2507 accounts for the deceleration via approximately equal
contributions from differential emissivity of the RTGs and
non-isotropic radiative cooling from the electronics in the main body
of the spacecraft, which are covered in VIII C and VIII D
respectively. (I'll also note that, while the RTG portion of the
1204.2507 model isn't as detailed as it is for the main body of the
spacecraft, it is still considerably more developed than the arguments
in 0104064).

That leaves a constant deceleration residual with time
with no on board mechanistic origin.


It leaves a residual consistent with the mechanisms of 1204.2507 at
the one-sigma level. That doesn't exclude the possibility of an
unaccounted-for residual, but it also doesn't require one. To show
that something more is needed would require somehow reducing the
statistical and systematic uncertainties in 1204.2507.

-dan
  #78  
Old September 3rd 13, 07:36 AM posted to sci.astro.research
Eric Flesch
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On Sat, 31 Aug 13, "Richard D. Saam" wrote:
I won't say 'new physics' is required


Recently I posted an analysis of the Pioneer anomaly showing that its
scale is consistent with universal size, thusly:

At 20AU Pioneer was travelling 12500m/s. The anomalous sunward
acceleration was 9 x 10^-10 m/s^2. Therefore, per each second, the
distance travelled was 12500m, and the anomolous distance shortfall
was d=.5a = 4.5 x 10^-10m.

Thus the ratio of the shortfall to distance travelled is 3.6 x 10^-14.

Let's hypothesize that this anomaly is simply a function of distance.
Thus, 20AU / ratio = 3 x 10^9 km / 3.6 x 10^-14 = 8.33 x 10^22 km =
8.8 x 10^9 LY, which approximates the Einstein radius usually written
as 10^10 LY.

If this hypothesis is right, then the Pioneer anomaly would be
seen to be twice at 40AU as it was at 20AU.


Eric Flesch
  #79  
Old October 11th 13, 08:32 AM posted to sci.astro.research
Richard D. Saam
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On 9/4/13 1:28 AM, Richard D. Saam wrote:
[Mod. note: entire quoted article snipped -- mjh]
I have had to digitize the reported data.
Surely the data is available in textual format
for the scientific community.


As a follow-up
I have forwarded this Pioneer anomaly investigation logic to the authors
and director of JPL
No response.
The reported JPL Pioneer anomaly investigation
is a case of science by bureaucracy.
The Pioneer anomaly is not supposed to exist therefore it does not.

Richard D. Saam
 




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