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03/000
Cosmologic astrometry
Australian Government
Geoscience Australia
Yonsei University, Seoul
18 October 2010
ICRF1 → ICRF21995 → 2010
total number of objects 608 → 3414number of defining sources 212 →
295
formal error σ(0) = 60 µas → 7 µas
“inflated” error σ = 250 µas → 41 µas 22
02 )250()5.1( as 22
02 )40()5.1( as
Geoscience Australia
18 October 2010
40
60
Astrometry of stars (~2000 years)
↓ Astrometry of quasars
Geoscience Australia
18 October 2010
no structure huge variable structure
Instability of the ICRF sources (2201+315)
Variations of the 2201+315, RA
Year
2000 2001 2002 2003 2004 2005 2006
as
-2000
-1500
-1000
-500
0
500
1000
1500
Geoscience Australia
18 October 2010
Variations of the 2201+315, DEC
Year
2000 2001 2002 2003 2004 2005 2006
as
-2000
-1500
-1000
-500
0
500
1000
1500
Instability of ICRF sources ( 2201+315, in sky plane, 2001-2004)
as
-1000-50005001000
as
-1000
-500
0
500
1000
Daily dataApproximation
Geoscience Australia
18 October 2010
Kellermann et al. (2004)
Position angle of the brightest jet ~ 158ºGeodetic VLBI:
Position angle ~ 148º apparent proper motion ~ 0.6 mas/year
Change of position of a celestial object approximated
by linear trend
0t
Geoscience Australia
18 October 2010
Definition of proper motion
t
)()()( 00 tttt
2145+067
18 October 2010
RA, 2145+067
Year
1990 1995 2000 2005 2010
sec
-0.0002
-0.0001
0.0000
0.0001
0.0002
The apparent motions look random
The systematic has been searched since
(Gwinn, Eubanks et al. 1997; MacMillan 2003)
Geoscience Australia
18 October 2010
FK5 → ICRF2
1988 → 2010
position accuracy 0”.019= 19000 µas → 41 µas
apparent motion accuracy 700 µas/year → 10-100
µas/year
Geoscience Australia
18 October 2010
Assumption (1995)
“The reference radio sources have no measurable
proper motion [at the level of precision achieved by
1995]”
Geoscience Australia
18 October 2010
Possible reasons of the assumption violation
1. Secular aberration drift (Bastian, 1995; Sovers et al., 1998, Klioner,
2003)
18 October 2010
2. Hubble constant anisotropy (Kristian and Sachs, 1966)
3. Primordial gravitational waves (Kristian and Sachs, 1966; Pyne et al., 1996)
4. Motion of the Solar system with respect CMB
Kardashev (1986), Sovers et al (1998) <14 µas/year (Galaxy M81)
Directed towards the centre of Galaxy(RA= 270º, DE = -30º) a = V²/R
Geoscience Australia
18 October 2010
yearaskma /4sec/102 213
1. Centrifugal acceleration due to rotation of the Solar system
around the Galaxy center
Geoscience Australia
18 October 2010
1. Centrifugal acceleration due to rotation of the Solar system around the Galaxy center
Geoscience Australia
18 October 2010
1. Centrifugal acceleration due to rotation of the Solar system around the Galaxy center
V
a
V
a
cossinsinsincos
cossincos
321
21
aaa
aa
03
002
001
sin
cossin
coscos
aa
aa
aa
Geoscience Australia
18 October 2010
directonvectoronacceleratitheof
ofscoordinate),( 00 sourcetheof
ofscoordinate),(
1. Centrifugal acceleration due to rotation of the Solar system
Volatile!
2 и 3
18 October 2010
...]...)(2
1)(
)([
HueeEeuer
ehdt
de
Proper motion in the expanding Universe (Kristian and Sachs, 1966) “Observations in
cosmology”
2. The Hubble law
18 October 2010
The Earth
HrV
H - the Hubble constant
It is supposed to be isotropic for all directions on the sky
2. Hubble constant anisotropy
332211 ,, eee
reeeeeHV
2
22112
221133 cos2cos)(2
1sin))(
2
1(
cos2sin)(2
12211 ee
cossin2cos))(2
1cossin))(
2
1( 2211221133 eeeee
18 October 2010
- generalised Hubble expansion )(5.0 2211 eeH
332211 eee Heee 332211
rHV ),( HrV
00
18 October 2010
The Hubble law
00
Anisotropic Hubble
expansion and non-zero
systematic
2. Hubble constant anisotropy
3. Primordial gravitational waves
(Kristian and Sachs, 1966)
...]...)(2
1)(
)([
HueeEeuer
ehdt
de
18 October 2010
σ – “Shear”
ω - rotation
E – Electric-type gravitational waves
H – Magnetic-type gravitational waves
18 October 2010
Gwinn et al (1997) – power density of gravitational waves
2
),(
),(,22
0
2
10
3 mME
MEmGW a
H
yearasMpckmH /12sec102sec*/60 1180
3. Primordial gravitational waves
Only three reasons are considered
Geoscience Australia
18 October 2010
1. Dipole systematic2. Rotation (no physics yet)3. Gravitational waves and Hubble constant anisotropy
Proper motion model
18 October 2010
rotation
2
2,2,2,2,2
1
1,1,1
1
1,1,1 )(),(
m
Mm
Mm
Em
Em
m
Mm
Mm
m
Em
Em YaYaYaYa
Magnetic-type
Gravitational waves
Electric-type gravitational waves or Hubble constant anisotropy
dipole
Proper motion model
)cossin(1
)cossinsinsincos(1
)cossinsinsincos(1
)cossin(1
cos
21321
32121
caaa
c
caa
c
18 October 2010
dipole
rotation
~ 5000 24-hour sessions since 1980 ~ 6 million delays~ 3000 sources
Software CALC/SOLVE (S.Lambert, A.-M. Gontier; Paris Observatory)
Geoscience Australia
18 October 2010
Global solution
Proper motion model
)cossin(1
)cossinsinsincos(1
)cossinsinsincos(1
)cossin(1
cos
21321
32121
caaa
c
caa
c
18 October 2010
dipole rotation
0.16.1
8.05.5
7.06.0
3
2
1
a
a
a
7.07.0
9.06.0
9.05.1
3
2
1
Dipole effect in apparent proper motion
18 October 2010
α = 266º +/-8º
δ= -18º+/- 18º
A = 5.8 +/- 1.4 μas
Geoscience Australia
18 October 2010
Main results- Quadrupole systematic is marginal A = 3.5 +/- 0.9 μas
Energy density of primordial gravitational waves
20002.00031.0 hGW
Too much uncertainty!!!
- Galactocentric acceleration
213 sec/10)7.0(0.3 km
Geoscience Australia
18 October 2010
Dipole effect α = 266º +/-8º
δ = -18º+/- 18º
A = 5.8 +/- 1.4 μas
Main results
First direct identification of Galactocenrtic acceleration of the Solar system barycentre
Geoscience Australia
18 October 2010
Main results
Problems for ICRS definition
Assumption (1995)
“The reference radio sources have no measurable proper motion
[at the level of precision achieved by 1995]”
The secular acceleration drift (dipole effect) is not taken into account by the current ICRS definition/assumption
Question
18 October 2010
If proper motion are real, then the reference axes
are not fixed by the positions of the defining sources!
How to deal with the non-zero proper motion???
Conclusion
• Secular aberration drift has been found.
• Fundamental astrometry has a strong cosmologic component
• Geodetic VLBI is able to measure apparent motion of several
thousand reference radio sources and promote some fundamental
discoveries about the Universe
• Attract more resources (funds, grants, students) and public/media
attention
18 October 2010
Suggestion• Modify the IVS observational program to obtain about 3000 proper
motion by 2020 (instead of 700).
• This number increases very slowly, from ~500 in 2001 to ~700 in 2010.
Just because existing IVS observational programs target on the well-
known sources with long observational history. New sources are
observed rarely.
• To organize a dedicated astrometric program in the southern
hemisphere. New AuScope network + New Zealand dish + Asia-Pacific
network + Kokee.
18 October 2010