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Multi-Wavelength Investigations of Solar Activity
Proceedings IAU Symposium No. 223, 2004
A.V. Stepanov, E.E. Benevolenskaya & A.G. Kosovichev, eds.
c
2004 International Astronomical Union
DOI: 10.1017/S1743921304005423
The sensitivity of three lines to AR
V. Penza
1
,D.DelMoro
2
and B. Caccin
2∗
1
INAF - Osservatorio Astronomico di Roma, Via Frascati 33, I-00040, Monte Porzio Catone,
Rome, Italy email: penza@mporzio.astro.it
2
Dip. di Fisica, Universit´a “Tor Vergata”, Via della Ricerca Scientifica 1, I-00133, Rome, Italy
Abstract. We study the sensitivity to AR of three photospheric lines, comparing experimental
results, from THEMIS observations, with spectral synthesis, demonstrating the inappropriate-
ness of using these lines as indicators of quiet sun modifications, because their variations in the
active regions. We try to reconstruct the cyclic lines behavior.
1. Introduction
Faculae, network and sunspots explain almost all of Total Solar Irradiance (TSI) cyclic
variations (Krivova et al. 2003), but it is plausible the whole structure varies. Gray and
Livingston (1997, G&L henceforth) measured the depth (D) variation of three line (Fe I
537.958, C I 538.032 and Ti II 538.103 nm) to infer the background contribution to the
δ(TSI), but the observed lines behavior cannot be reproduced by a δ(T
eff
) alone (Caccin
et al. 2002). Here we show as the AR presence affects these lines, by comparing spectral
synthesis with experimental results. Additionally, we implement a simplified model to
reconstruct the cyclic lines trend.
2. Effects of bright active regions
The dataset was acquired at THEMIS (July 6 and 7, 2003) with IPM (Cavallini 1998).
Facular and quiet zones (FZ
n
and QZ) were defined via a threshold criterion on the Mg
I (518.740 nm) image, choosing three threshold values, obtaining three FZs. We obtained
D values via parametric fit of the averaged spectral positions, while the spectra synthesis
was computed via SPECTRUM (Gray 1994), using FAL models (Fontenla et al. 1999).
In Tab.1 we report the results (Penza et al. 2004 for details).
3. Lines during the Cycle (1978-1992): a simplified model
We reproduce the D trend by weighting model results with corresponding coverage
factors. Because we have no data about facular and network coverage for years 1978-
1992, we exploit the knowledge deriving from Cycle 23 (1996-2002), monitored by PSPT
in Rome (Penza et al. 2003). We used an unique activity index (MgII index, from www-
iup.physik.uni-bremen.de) and establish a (linear) relation between that one and fac-
ular, network and spot coverage (A
f
, A
n
, A
s
). By extending these relations, we es-
timate the unknown coverages. By comparing A
s
so obtained with the Rome archive
data (ftp.ngdc.noaa.gov) and the δ(TSI) produced by these A
i
with the PMOD/WRC
data (Fr¨olich & Lean 1998), we check the approach validity, obtaining a sufficient con-
fidence for the model reliability. Then, we reconstructed δ(D) through the formula:
D =
i
D
i
I
c
i
A
i
/
i
A
i
I
c
i
, where I
c
is the continuum and i indicates the different models.
We took: modC and modE for quiet sun and network, a Kurucz model (T
eff
=5200K)
[Kurucz 1994] for spot and alternatively modF and modH for facula (Fig.2).
4. Conclusions
The Fe I and Ti II lines are shallower in AR than in quiet zone; in other hand, these
lines are sensitivity to AR presence, then at least a part of δ(D) observed by G&L was
∗
We regret to note that Bruno Caccin passed away on June 19, 2004.
137
138 V. Penza et al.
Figure 1. Experimental line-depth differences QZ/F Z, compared with the models.
Figure 2. Line-depth from 1978 to 1992 compared with G&L data.
due to AR cyclic modulation. The C line, instead, does not present a monotonic trend. A
qualitative D reconstruction (only AR coverages varying) along the cycle, shows that ARs
could account for the Fe variation, but the C one seem to conceal another phenomenon.
Acknowledgements
The author thank Gray and Livingston for having provided unpublished data. THEMIS
is operated on Tenerife island by CNRS and CNR in the Spanish Observatorio del Teide
of the IAC. We thank data from the VIRGO Experiment on the cooperative ESA/NASA
Mission SoHO. Special thanks to the PSPT crew.
References
Caccin, B., Penza, V., Gomez, M.T. 2002 A&A 286, 286.
Cavallini, F. 1998 A&AS 125, 589.
Fontenla J., White O.R., Fox A.P., Avrett E.H. & Kurucz R.L. 1999 ApJ 518, 480.
Fr¨olich, C. & Lean, J. 1998 Geophys.Res.Let. 25, 4377.
Gray D.F., & Livingston, W.C., 1997 APJ 474, 802.
Gray, R.0. 1994 Astronomical Journal 107, 742.
Krivova, N.A., Solanki, S.K., Fligge, M.,Unruh, Y.C. 2003 A&A 399,L1.
Kurucz, R. L. 1994 CD-ROM No. 19.
Penza, V., Caccin, B., Ermolli, I., Centrone, M. & Gomez, M.T. 2003 ESA SP-535, pp.299.
Penza, V., Caccin, B., & Del Moro, D. 2004 submited.
