Kuhn - HMI Science Interests: Limb photometry and astrometry
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Transcript of Kuhn - HMI Science Interests: Limb photometry and astrometry
HMI Team 4/30/03
Kuhn - HMI Science Interests:Limb photometry and astrometry
• HMI, with 4Kx4K (or even 2Kx2K) pixel resolution will improve limb astrometry and photometry in some respects by over an order of magnitude
• HMI roll calibration and lessons learned from MDI thermal environment may do better than an order of magnitude improvement in some astrometric goals
HMI Team 4/30/03
Focus areas
• Limb Astrometry– rotational constraints through limb harmonics– secular radius variations– limb seismology (low frequency modes)
• Limb brightness– thermal magnetic diagnostics– limb seismology
HMI Team 4/30/03
Limb astrometry
dr
Angle of arrival fluctuations define dr
dI
Photometric gain uncertainty (flatfielding) defines dr
In practice limb isn’t knife edge, spacecraft pointing jitter is about 0.01 pixel,long term stability limitations are due to optics and thermal drifts [1px=2”]
mas 0.4r pixels limb 3000
mas 20 dr intensity rms 1%
HMI Team 4/30/03
Shape, rotation, and gravitational figure
(-1)
(10) (50)
HMI Team 4/30/03
Shape and gravitational potential
Coefficient l=2 (Uncertainty) l=4 (Uncertainty)density -5.87E-06 8.00E-08 6.16E-07 3.20E-08pressure -5.84E-06 5.93E-07observed -5.27E-06 3.80E-07 1.30E-06 5.10E-07J -2.22E-07 3.84E-09
HMI Team 4/30/03
Emilio et al.: No W measured -- limits only
c/yrmilliarcse 0.98.1 /
mas) 5 100 (vs.
cmilliarcse 321 ||
sec
dtdr
rcycleBush et al. 2002 sees different “temperature”trend after SoHO vacation.
HMI Team 4/30/03
Interpreting solar radius change
Log(W) Models
-4 -3 -2 -1 0
S&E ('79)
D&B ('80)
Gilliland ('84)
Spruit ('82)
II
rr
W
< 0.02
HMI Team 4/30/03
Oscillations: astrometry vs. Doppler measurements, random telegraph
2
2
2
2
2
2
0
20
2
2
24 ratios/n nt Displaceme
4 ratios/n Velocity
2/)2()(
/2
1
2)(
signal harmonic of amplitude velocity
noise telegraphof amplitude velocity
signal harmonic of period
s timeserieofduration
crossing zerobetween mean time
tP
tT
v
s
tT
v
s
PTsP
t
tvP
s
v
P
T
t
sig
noise
t=20
f=16
HMI Team 4/30/03
Astrometric advantages
on)(granulati10min t916.3006.
mode-r
hr-10
mode-g
hr-2
mode-p
min-5P
snrsnr
rv
r
HMI Team 4/30/03
P-mode limb oscillations
ti
tli
et
elt
),(),(
),(),( )(
P-mode 5min limbshape oscillations
15cm/s 10 microarcsec
dominates lk with b
)(cosP ),(Y
klm
lmlm
ikl
lkklmeb
r
HMI Team 4/30/03
G-modes in velocity and displacement
1600 days of MDI astrometry (l=6)
Appourchaux et al. (2000)
HMI Team 4/30/03
Low frequency oscillations
HMI Team 4/30/03
Another branch of the solar dispersion relation: r-modes
100m x 90,000km
HMI Team 4/30/03
Antishadows
HMI Team 4/30/03
Focus areas
• Limb Astrometry– rotational constraints through limb harmonics– secular radius variations– limb seismology (low frequency modes)
• Limb brightness– thermal magnetic diagnostics– limb seismology