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Adv. Space Res. Vol. 29, No. 10, pp. 1441-1444,2002 0 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved

Printed in Great Britain 0273-l 177/02 $22.00 + 0.00

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THE CALCIUM K-LINE PROFILES AS FUNCTION OF LATITUDE AND SOLAR CYCLE PHASE

JAGDEV SINGH

Indian Institute of Astrophysics,Bangalore -560034,1ndia.

ABSTRACT

We have monitored the Calcium K-line profiles on daily basis at all the latitudes while integrating the spectrum over the visible longitudes of the Sun by moving a N 340 mm solar image at a uniform speed in the E-W direction. The spectra were recorded at a dispersion of 9.34 mm/A on 35 mm Kodak 103-a0 film for the time interval of 1986-95. Now we obtain the spectra using 1K x 1K peltier cooled CCD Camera. We plan to use the data to study possible long term variation in chromospheric rotation rate, differential rotation rate, variation in background flux, and changes in polar regions with the phase of the solar cycle through various parameters of this line. 0 2002 COSPAR. Published by Elsevier

Science Ltd. All rights reserved.

INTRODUCTION I

One of the method to study the long term variability of the Sun is to monitor Ca+ K line profiles of the Sun as a star (White and Livingston, 1978). Skumanich et al. (1984) proposed a three component model of the solar cycle variability of the Calcium K emission using extent contrast and fractional area parameters for (1) cell, (2) network and (3) plage components and introduced an additional network component, ‘Active network’ in excess of quite Sun value. Comparison of Ca+K line data with space based irradiance measurements has shown the importance of sunspots and plage and network faculae as sources for solar cycle variability (Pap et al. 1991). Recently plage and enhanced network indices have been derived from Ca+ K spectroheliograms and filtergrams by Worden et a6 (1998) and Caccin et al (1998) to study the variation in these indices with the solar cycle phase and correlate these parameters with the VUV and UV irradiances. The observations of the sun as a star and various indices derived from the Ca+K filtergrams and spectroheliograms lack the information about the variation in quiet network flux. To determine if this variation exists, we started a program at Kodaikanal observatory on a daily basis in 1986 to monitor the CafK line profiles as a function of latitude and integrated over the visible longitudes. Also, the rotation modulation characteristic of the Ca+K line profile will permit us to study the variation in the rotation rate with the phase of solar cycle, if any and the chromospheric differential rotation. The basic purpose of this paper is to report the method of observations and type of data whic*h we have been taking since 1986 on a daily basis and to describe the plan of our study.

1441

1442 J. Singh

OBSERVATIONS AND DATA ANALYSIS

A 38 cm objective of 36.6 m focal length forms a 34 cm image of the Sun at the slit of the spectrograph. A Sunchart corresponding to the image size and heliographic latitude of disc centre ‘B’ on that day is made on a thick paper sheet with latitude lines at an interval of 10 degrees drawn on it. This is kept near the focal plane of the Sun’s image in such a way that N-S axis marked on Sunchart becomes parallel to the axis of rotation of image. To obtain the spectrum at a selected latitude and integrate over the 180 degree longitudes at that latitude, the image is moved in the E-W direction of the Sun along the given latitude line at a uniform speed with the help of second mirror of the coelostat. The spectra were recorded at 35 mm Kodak 103-a0 film till 1995. A set of 18 spectra have been obtained on a daily basis; at 17 different latitudes of the Sun with an interval of 10 degrees and the 18th spectrum of Sun as a star. These spectra are recorded using a 18.3m focus spectrograph with 600 lines per mm grating blazed at 2.5 micron in the first order. The spectrograph provided a dispersion of 9.34 mm/A in sixth order at Ca+ K wavelength. Two such typical profiles, one at a latitude of 80” N and other at equator are shown in Figure 1. All the profiles have been normalized at an intensity value of 13 percent at 3935.16A on the red wing of Ca+ K line (White and Suemoto, 1968).

0.18 I I I I

0.16 -

0.14 -

p: T

I I * i -

L: ir

0.06 -

0.04 4 I 3933

H2 I I

3934 3935 3936

Wavelength(A)

Fig.1 Ca+K line profiles obtained on Jan.1, 1986 at the solar equator and 80’ N and integrated over the 180” longitudes. The various K-line parameters are marked in standard K-line notation.

Calcium K-Line Profiles 1443

Now, we are recording the spectra using 1K x 1K peltier cooled CCD camera from Photometrics Co., Tucson, USA. To cover larger portion of the spectrum around the CafK line, we are making the observations in third order which provides a spectral resolution of about 20 m A.

RESULTS AND FUTURE STUDIES

We have computed K-index, Kr ,Kz and Wilson-Bappu widths and Kiv, K~v, KS, KP~ and K~R intensities for number of Ca+K line profiles taken in 1986. There is a considerable scatter in the intensity values on day to day basis but small variation in the values of widths. The scatter in intensity values may be partly real and partly because of photometric accuracy due to the use of film. The average values for 2-3 days of data reduce the scatter in intensity values. In Figure 2 we plot K1 and K2 widths for three days of data which show the variation of widths as a function of latitude. The figure shows a small increase of width at 105 compared with the values at equator and 10”N. We plan to use these data to study the followings.

- l-0( *a r F; O-7! .- 3

:- 0.5c

AZ ;; 0.50 .- 3 A! 0.25

I-

i-

I-

I-

C

I I I I I I I I I r 0 -31 DEC 1985

_r X -3 JAN1986 A -28JAN1986

I I 1 I I I I I I I 80 60 40 20 0 20 40 60 80 Li imt

North South Latitude

Fig.2 K1 and KX widths as function of latitude of the Sun.

(1) The sunspots ant1 related features give information only between 10 to 40 degree latitude belts whereas this method will yield information about the polar regions as well.

(2) We would get plagc: free profiles at all atitude belts during the different phases of the solar cycle, which wo~lltl make it possible to study the c:hmges in the active network as a

1444 J. Singh

function of the solar cycle.

(3) The power spectral analysis of the K-index (Singh and Livingstoql987) for different latitude belts would provide information on the chromospheric rotation as a function of latitude and hence it would help to establish the chromospheric differential rotation rate.

(4) Singh and Prabhu (1985) have shown from the analysis of plage areas that chromo- spheric rotation rate varies with time but the analysis is restricted to only few latitude belts due to the occurrence of plages in those latitudes. The analysis of the present data may yield the values of rotation rate with time in all latitudes and thus, would give a clue to the slow and fast rotating bands on the solar surface.

(5) The data will also be used to correlate K-index of the sun as a star with the various UV: VUV and irradiance in the visible wavelength region measured from space experiments.

ACKNOWLEDGEMENTS

I thank Dr.K.P.Raju for his help in preparing this manuscript.

REFERENCES

Caccin, B., I. Ermolli, M.Fofi and A.M.Sambuco, Variation of the chromospheric network with the Solar Cycle, Solar Phys, 177, 295 (1998).

Pap, J.M., J.London and G.J.Rottman, Variability of solar lyman alpha and total solar irradiance, A&on: Astrophys., 245, 648 (1991).

Singh, J. and W.C. Livingston, Sun as a Star: Rotation Rates from the Ca K -Index, SoEar Phys., 109, 387 (1987).

Singh, J. and T.P.Prabhu, Variation in Solar Rotation Rate Derived from Ca+ K Plage Areas, Solar Phys., 97, 203 (1985).

Skumanich, A., J.L.Lean, O.R.White and W.C.Livingston, The sun as a star: Three-component analysis of chromospheric variability in the calcium K line, Astrophys. J., 282, 776 (1984).

White, O.R. and W.C.Livingston, Solar Luminosity variation II. Behavior of calcium H and K at solar minimum and the onset of cycle 21, Astrophys. J., 226, 679

(1978). White, O.R. and ZSuemoto, A measurement of the solar H and K profiles,

Solar Phys.,3, 523 (1968). Worden, J.R., O.R.White and T.N.Woods, Plage and Enhanced Network Indices

Derived from Ca II K spectroheliograms, Solar Phys., 177, 255 (1998).