P MODE TRAVEL TIME IN ACTIVE REGIONS USING TIME-DISTANCE METHOD

1
P MODE TRAVEL TIME IN ACTIVE REGIONS USING
TIME-DISTANCE METHOD
M. HADJARA(1) T.E. ABDELATIF(2)
CRAAG, Observatory of Algiers, BP 63 Bouzareah
16340, Algiers, Algeria. (1) massiniss1_at_yahoo.fr
(2) tabdelatif_at_yahoo.com
Time-Distance helioseismology measures directly
the travel times taken by acoustic waves which
propagate inside the sun between two separated
points from the solar surface (Duvall 1993). The
travel times contain a lot of information about
the internal proprieties of the sun like velocity
flows, sound speed,... (Giles 1999). In the
present work we calculate the P mode travel times
from the active regions using data from GONG.
We compute the p mode travel times in active
regions with time-distance helioseismology from
2004 October 31 GONG data these images ( 839x839
pixels size) contain one big and circular bipolar
sunspot about 3 diameter (F type), not far from
the centre of the image the sunspot 693. (The
duty of this day is to 71). Data treatment
steps Before using, our data must be
treated -The sun is a sphere, and all points on
the suns surface can be located by their
spherical coordinates. It is more convenient to
transform the solar region of interests to
Cartesian coordinate system for our studies. Each
image is transformed into sin(?)-f coordinates
using Postels projection (with Kholikovs code),
where ? and f are the latitude and longitude in a
spherical coordinate system the remapping. -In
order to keep tracking oscillations of specific
locations, the differential rotation rate of the
sun should be removed from the observations. The
used tracking rates here is the latitude
dependent Snodgrass rate (Snodgrass
1984). -Using the 3D FFT, we transform our three
dimensional datasets v(x,y,t) into V(kx,ky,?),
then we filtered it with a Gaussian filter of
FWHM2mHz centred at 3 mHz, and finally we do the
3D FFT inverse to obtain the three dimensional
datasets v(x,y,t) filtered. -We Compute
cross-correlations between some of average
regions around the sunspot for different
distances (?5 to 10) , for the ingoing and
outgoing times (? and ?-). -Finally, we extract
from the travel times from the CCF by fitting
with Gabor function.
Longitude (pixel)
Fig 1 From right to left the 04/10/31 image
from GONG, the same image after remapping (the
size of region is 55x75 in latitude and
longitude respectively), and finally the ring
diagram obtained for 512 minutes.
Before filtering
Before filtering
Fig 2 The signal in center of image and its FFT
before and after using the Gaussian filter, and
finally our image after remapping tracking and
filtering.
Fig 3 To right the k-nu diagram after filtering
obtained for 512 minutes, we can observe here the
ridges f (bottom) and p1 (top). To left the
acoustic power map for all time of our dataset (1
day).
Quiet sun
In this case, we have chosen to treat the
north-west suns region of 460x390 pixels sizes
(longitude x latitude) from the 04/01/10 GONG
data, we correlate along all the latitude, each
point with the mean of 45 circle part south
around this point, (for ?5 to 10) and we
obtain
-0.04
80
Actives regions
From the 04/10/31 GONG data, we correlate around
the sunspot 639 point with it opposite for
different angle (0 to 180), with ?5 to 10,
and we obtain
For 0
For 90
For 135
For 45
Duvall, T.L., Jr., et al., 1993, Nature,
362,430. Giles, P.M., December 1999,
Time-Distance Measurement of Large-Scale Flows in
the Solar Convection Zone. Kholikov, Sh.S.,
Burtseva, O.S., Serebryanskiy, A.V.,
Ehgamderdiev, Astronomy letters, 30-8, 2004.
Snodgrass H.B., 1984, Sol. Phys., 94., 13. Zhao,
J., Mars 2004, Inference of Solar Subsurface
Flows by Time-Distance Helioseismology GONG
http//gong.nso.edu/

• The travel times from active region (traveling
  the sunspot) is smaller than the travel times in
  the quiet sun (the sunspot is relatively cold
  then the quiet sun).
• The inversion with Fermats principle give us
  the internal proprieties of the sun (our future
  works).