Spectroheliographic Observations in Madrid (1912 – 1917)

The Physics of Chromospheric Plasmas ASP Conference Series, Vol. 368, 2007 Petr Heinzel, Ivan Dorotoviˇc and Robert J. Rutten, eds.

J. M. Vaquero, M. C. Gallego, F. J. Acero and J. A. Garc´ıa Departamento de F´ısica, Universidad de Extremadura, Spain

Abstract. We have compiled information and data on solar spectroheliographic observations in Madrid during 1912–1917. We have created a database with information on 829 flocculi specifying heliographic position, dates of observation, angular velocity, and typology. We analyze the reliability of the data by reconstructing the butterfly diagram, active longitudes, and flocculi typology.

1. Introduction

The Madrid Astronomical Observatory was founded in the 18th century. Dur- ing the first years of the 20th century, this observatory made an active program of solar observations (sunspots, prominences, solar corona during eclipses, solar spectroscopy, etc.). In 1911, the observatory bought a spectroheliograph (As- carza 1912). The installation of this spectroheliograph was completed during the first months of 1912 (Ascarza & Tinoco 1915). In this work we provide some information about the spectroheliograph of the Observatory of Madrid, and aim to show the reliability of the data obtained from 1912 until 1917. Wwe have constructed a database of the flocculi observed in Madrid described in Section 2. In Section 3 some final comments are given. The spectrohelioscope of the Observatory of Madrid consisted of three fun- damental parts (Fig. 1). The first is a polar heliostate with two flat mirrors of 0.2 m diameter. The second is a lens of 0.25 m diameter and 6.8 m focal length. The third part is the spectrohelioscope, with two slits of 75 mm length, twin collimator and camera lenses of 0.1 m diameter and 2.18 m focal length, and a flint prism of 90 degrees and 20 cm height. The solar image has a diameter of 64 mm. A detailed description is given in Iniguez˜ & Ascarza (1911). At the end of 1910, the work on the installation of the spectroheliograph started. The pillars and the base to support and shelter the device were constructed. At the beginning of 1911 the installation of the instrument was started. The first photographs were obtained in June 1911. Nevertheless, until Decem- ber 1911 the observations were not begun regularly. The largest problems of the installation were related to the convective currents that formed near the spectroheliograph mount and its surroundings. The observing program consisted of photography of the Sun in the calcium K line and of analyzing the flocculi appearing on the photographs by calculating their heliographic positions and analyzing their aspect. 17 18 Vaquero et al.

Figure 1. The Madrid spectroheliograph installed in 1911.

2. Database

We have created a database with information on 829 ﬂocculi (heliographic position, dates of observation, angular velocity, and typology) from the spectroheliographic observations in Madrid during the years 1912-1917. This database is available by request to the authors.

3. Results

Figure 2 shows the butterfly diagram for the observed flocculi. During the years 1912 and 1913 one sees flocculi in very low latitudes, corresponding to solar cycle 15. In Fig. 2 flocculi appear also at high latitudes, getting down in latitude during the advance of solar cycle 16. Figure 3 shows a histogram of the number of flocculi with respect to their solar longitude. During 1912–1917 the maximum number of focculi occurred around longitude 180◦, the minimum around longitude 0◦. The observers in Madrid classified the flocculi according to condensation and intensity. For condensation they judged whether the flocculus was observed as a single, continuous, and compact surface or, on the contrary, whether the flocculus appeared fragmented, in several grouped areas, etc. With respect to condensation, they established the following categories: (cc) very condensed, (c) Spectroheliographic Observations in Madrid 19

Figure 2. Butterﬂy diagram for 829 ﬂocculi during 1912–1917.

Figure 3. Histogram of the number of ﬂocculi with respect to heliographical longitude during 1912–1917.

condensed, (s) subdivided, and (ss) very subdivided. With regard to the intensity of the ﬂocculi, the observers established the following categories: (f) strong intensity, (ﬀ) very strong intensity, (d) weak, and (dd) very weak. Figure 4 shows 20 Vaquero et al.

Figure 4. Distribution of ﬂoccular typology during 1912–1917 according to (left) their condensation and (right) their intensity.

the distribution of the diﬀerent typologies of ﬂocculi observed during 1912–1917. Flocculi with strong intensity and condensed are the most numerous.

4. Final Comments

In this work, we have tried to recover the observations carried out with the spectrohelioscope of the Observatory of Madrid during the beginning of the 20th century. So far we have processed the information from March, 1912 up to March, 1917. However, we have original observations until the year 1920. These observations can be useful to compare with observations of other spec- troheliographs of this epoch and to ﬁll gaps in the available time sequences of spectroheliographic observations during this decade. Acknowledgments. This research has made use of the Astrophysics Data System (NASA). Support from the Universidad de Extremadura is gratefully acknowledged.

References

Ascarza, F., & Tinoco, J. 1915, Asociacion Espanola˜ para el Progreso de las Ciencias, III, 155 I˜niguez, F., & Ascarza, F. 1911, Anuario del Observatorio de Madrid, 1912, 269 Ascarza, F. 1912, Anuario del Observatorio de Madrid, 1913, 441