Solar cycle variation in the peak asymmetry:

solar or artefact?

S. J. Jiménez-Reyes

IAC

13-sept-2004

Variation of peak asymmetry. It is real?

Our previous studies (Jiménez Reyes et al. 2003) uncovered a clear evidence for a systematic variation over the solar cycle. However, such conclusion ignores any potential contribution from the change in operating configuration through the GOLF lifetime.

Blue Red

Blue Red The convective overshoot in the photosphere makes the asymmetries less negative. It should be stronger in the blue period, when observations are sensitive to variations close to the base of the photosphere.

?

A one year modulation is visible due to the orbital velocity of the spacecraft.

This is what we can expect if the changes are due to the measurements make at different depths in the solar atmosphere.

Blue and red wing measurements

Blue Wing (mA)

D1: 129.7 Vmax109.8 Vmin

D2a: 155.9 136.0

D2b: 102.9 83.0

Variation of peak asymmetry. It is real?

Red Wing (mA)

D1: 82.5 Vmax102.5 Vmin

D2a: 108.8 128.7

D2b: 55.8 75.7

Given the annual variation of the line-of-sight velocity of the spacecrafts we should see a periodic modulation in the asymmetry variations. Indeed, this modulation should be of the order of height difference between both operating configurations. However, such height-dependent is not found.

Variation of peak asymmetry. How can we proceed?

Extent the observations of GOLF. Analyze the results obtained from both configuration

modes separately. Compare results obtained from time series with larger

length.

Perform a contemporaneous analysis of different datasets such as MDI, BiSON, etc.

Study a possible progressive intensity contamination of the velocity measurement (phase difference V-V).

Carry out a realistic simulation of the GOLF signal.

GOLF observations

2975 days:•Start: 1996 April 11•End: 2004 June 2•Duty cycle: 92%•Series of 100-days•Shifted 25 days•116 – 4 = 112 series•l=0, 1, 2 and 3•f=2.4 to 3.4 mHz

Blue BlueRed

Cycle 23

Note that in terms of level of solar activity,

there is not overlapping between blue and red-

wing periods.

Extraction of the mode parameters

2

22

x1

)1( P(x)

bbx

H /)-(2x o

Nigam & Kosovichev (1998)

This is a traditional peak fitting in the sense that the asymmetrical frequency shifts of the multiplet is

not taken into account.

Maximum heightFractional asymmetry

Width

Central frequency

Rotational splitting fixed to 400 nHz. Same linewidth for all the components of the multiplets. Fixed theoretical values for the instrumental sensitivity. Same peak asymmetry for both multiplets.

Frequency shift of low degree

Using this results it is possible to identify some of the main characteristics of the solar magnetic fields. Thus, differential analysis of the frequency shifts of different low-degree modes can provide information on the distribution of high-latitude fields.

Mean change in height and weight

The result found could be explained on the basis of

changes in damping affecting both the mode

with and the velocity power.

No long-term variations

Variation of peak asymmetry. It is real?

The new data confirms our previous results. We do not find any dramatic variation between both operating configuration modes.

0.60,3.06e-2

-0.02,9.40e-1

0.57,1.34e-3

-0.40, 1.74e-1

-0.38, 1.44e-1

-0.83,1.99e-8

0.77, 1.87e-03

0.84, 3.93e-05

0.92, 2.45e-12

ln,

lnh ,

lnb ,

ln,

-0.68,1.12e-2

-0.07,7.95e-1

-0.65,1.57e-4

Blue...

Red...

All...

Blue vs Red wing

Time series of 432d long

2975 days:•Start: 1996 May 5•Duty cyle: 87%•Series of 432-days•Shifted 216 days•14 series•l=0, 1, 2 and 3•f=1.8 to 3.7 mHz

Given the higher SNR, we have fitted an asymmetry parameter for each mode degree.

GOLF vs MDI. 100d and 432d

GOLF versus MDI. 100d and 432d

We can confirm an asymmetry variation of l=1,3 in both datasets although the peak-to-peak change does not agree. The higher sensitivity found for GOLF might arises from an additional contribution due to the observed depth in the solar atmosphere.

In principle, the variation of the asymmetry could be explained as part of a progressive intensity contamination of the velocity measurement. When Ic b

Let suppose first, that the long-term asymmetry variation is due to the observed depth in the solar atmosphere.

Can be explained the short-term variation as part of an intensity contamination?

We compute the phase difference between two simultaneous velocity measurements (GOLF-MDI)

Phase difference V-V

A clear phase difference of around 20º between both operating configurations is found, which coincides with initial estimations (Pallé et al. 1999). However, we did not find any trend of this parameter with time.

Variation of peak asymmetry. Summarize

CONFIRMED

CONFIRMED

CONFIRMED

PARTIALLYCONFIRMED

CONFIRMED

???????

Extent the observations of GOLF. Analize the results obtained from both

configuration modes separately. Compare results obtained from time

series with larger different length.

Perform a contemporaneous of different datasets such as MDI.

Study a possible progresive intensity contamination of the velocity measurement (phase difference V-V).

Carry out a realistic simulation of the GOLF signal.

Artificial data

The asymmetrical frequency shifts of the multiplets (l=2 and 3).

The window function (BiSON and GONG).

Possible systematic bias in the peak asymmetry determination.

Variation with the SNR of the power spectra.

Leakage from higher mode degrees, mainly from l=4 and 5.

Different issues need to take into account in the simulation:

What about l=4 and 5?

(l,m)=(2,0)

(l,m)=(2,2)

Artificial data

1. Empirical model of the p-mode parameters extracted from previousresults.

2. Empirical model of the p-mode parameter variations normalized to the Radio Flux changes.

3. Relative instrumental sensitivity up to l=5 (theoretical values)

4. Asymmetrical frequency shifts of the multiplets (l=2 and 3).

Artificial data. Results (i)

Artificial data. Results (ii)

Mean asymmetry Mean noise

The leakage from l=4 and 5 might affect the asymmetry determination of l=0,2 since the level of

noise cannot be estimated correctly.