We present here some preliminary results of observations performed with the spectro-polarimetric mode of the THEMIS telescope onactiv e regionNO AA 9125 on August 2000. We show the presence of high-velocity downflows located at the edge of a filament and stress on the non-stationary character of these flows. Flaring activities were also observed: we just present here some spectro-polarimetric

profiles of these regions, more accurate magnetic-field configuration determination being performed latter on

Aboudarham, J.

Briand, C.

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Briand, Carine

Aboudarham, Jean

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Multi-line spectro-polarimetry on active region NOAA 9125

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IL NUOVO CIMENTO Vol. 25 C, N. 5-6 Settembre-Dicembre 2002Multi-line spectro-polarimetry on active region NOAA 9125(∗)C. Briand(1)(2) and J. Aboudarham(2)(1) THEMIS - Via Lacte´a, E-38200 La Laguna, Tenerife, Spain(2) Observatoire de Paris, DASOP/UMR 8645 - Place J. Janssen, F-92195 Meudon, France(ricevuto il 10 Giugno 2002; approvato il 7 Agosto 2002)Summary. — We present here some preliminary results of observations performedwith the spectro-polarimetric mode of the THEMIS telescope on active region NOAA9125 on August 2000. We show the presence of high-velocity downflows locatedat the edge of a filament and stress on the non-stationary character of these flows.Flaring activities were also observed: we just present here some spectro-polarimetricprofiles of these regions, more accurate magnetic-field configuration determinationbeing performed latter on.PACS 96.60.-j – Solar physics.PACS 96.60.Qc – Sunspots, faculae, plages.PACS 01.30.Cc – Conference proceedings.1. – IntroductionAll the results presented here are based on observations performed with THEMIStelescope(1) during campaign 2000. The goal of the campaign was to study the emergenceand evolution of active regions. In this paper, we will present some preliminary resultsconcerning mainly flows in filaments and flares.Filaments are composed of a cold plasma embedded in a hot atmosphere, frozen inthe chromospheric magnetic field. They appear along neutral ligne separating regions ofopposite polarity. During the quiescent phase of the filament, only small upper motionsare noticed [1,2]. However, strong perturbations of the filament velocity map are usuallyseen during the activating phase, giving rise to flares [3, 4]. We report here some pre-liminary results on the presence of perturbating phase of some quiescent filaments. Thecorrelation between the appearance of strong up- and downflows and flares is still understudy.(∗) Paper presented at the International Meeting on THEMIS and the New Frontiers of SolarAtmosphere Dynamics, Rome, Italy, March 19-21, 2001.(1) Operated on the island of Tenerife by CNRS-CNR in the Spanish Observatorio del Teide ofthe Instituto de astrofisica de Canarias.c© Societa` Italiana di Fisica 741742 C. BRIAND and J. ABOUDARHAMFig. 1. – Magnetogram and Ca II intensity map of NOAA 9125 for the two wavelengths indicatedon the top of each image. The top right filament shows a sub-structure with an arch filamentshape (compare the two Ca II images) which is not seen in Hα line (not shown here). Alsoindicated the Solar North direction (S.N.) and the Sun Center direction (S.C.).Section 2 presents briefly the observations performed and the data reduction em-ployed. Section 3 presents the results obtained: in 3.1 the details on the high, non-stationary, downflows detected at the edges of filaments and in 3.2 some brief results onthe spectro-polarimetric measurements of the flaring region. Finally, sect. 4 provides theconclusions.Fig. 2. – Example of λ8542 Ca II profiles showing the peculiar absorption in the red wing. Aplasma falling down with a velocity of about 45 km s−1 seems to be superimposed to a quiet-Sunbackground (note that the Ca II core line is not shifted).MULTI-LINE SPECTRO-POLARIMETRY ON ACTIVE REGION NOAA 9125 743Fig. 3. – Longitudinal velocity maps obtained for Ca II core ±0.8 A˚, i.e. representing 28 km s−1(black being downwards motion), for three successive scans on the region. Strong velocity shearis noticeable at footpoints of the filaments. After almost complete disappearance of the strongdownflows (second map), it is once again present on the last map.2. – Observations and data reduction2.1. Instrumental configuration. – THEMIS is equipped with three different modesto performed polarimetric measurements (see THEMIS web page for their descriptionhttp://www.themis.iac.es). For these observations, we prefered the “Grid Method” asdescribed in [5]. The grid, located at the entrance of the polarimeter, selects differentfields of view of 16 arcsec width. The entrance slit of the spectrograph was 0.7 arcsecand three of these fields of view were recorded simultaneously on a single CCD camera.Three spectral lines were recorded simultaneously: the photospheric λ6302 Fe I, andthe two chromospheric λ6563 Hα and λ8542 Ca II.The region was scanned by steps of 0.7 arcsec. One scan of 91 × 85 arcsec, with thefour Stokes parameters recorded, took about 15 minutes.The region has been observed for 4 days (from August 11th to August 15th, 2000).The results we present here concerned mainly August 15th for which the seeing was thebest and activity was quite remarkable.Fig. 4. – Map of the whole active region as seen in Ca II (91×85 arcsec2). Fe I intensity contoursare overplotted. A large activity appears in the top sunspot. Another intense activity has beennoted close from the sunspot located on the lower right part of the image.744 C. BRIAND and J. ABOUDARHAMFig. 5. – Ca II Stokes I together with Fe I Stokes Q and V on the flaring region. Stokes Upresenting almost no signal is not presented here. The horizontal line on each spectra showswhere the profiles of fig. 6 have been extracted.2.2. Data reduction. – Data reduction is based on the well-known formulaIc =Ir − darkflat− dark ,(1a)where Ic stands for the corrected image, Ir for the raw image, flat for the flat-field imageand dark for the dark current image.The first step to obtain the flat field is to sum 100 images (acquired when the telescopewas moving). Spectral lines must be removed from the image before the flat field isapplied. Since spectral lines are slightly inclined and curved, it is necessary to firstapplying a bending correction to the spectral lines. Then, the mean spectral profile isextracted from this image and used to remove all spectral information from the averageimage. The flat-field image to be applied contains only defects from which the imagemust be corrected (fringes, dust,..., etc.).Dark current is obtained only by averaging 25 dark current images.The bending correction deduced from the flat-field image is applied to each individualdata of the scanning before eq. (1a) is applied.3. – Results3.1. Non-stationary longitudinal downflows in filaments . – At observing time, NOAA9125 was located at (E13, N21) that is very close from the solar meridian (µ = 0.96).Figure 1 shows the region as seen in Ca II at two different wavelengths together with themagnetogram obtained from iron line.Individual Hα and Ca II profiles reveal the presence of strong downflows: a Doppler-shifted profile is superimposed to a “quiet Sun” profile (cf. fig. 2). This suggests thepresence of plasma moving downwards in an almost static atmosphere (or moving hori-zontally, which cannot be detected here).All these profiles are correlated with the presence of filaments. Downflows at thefootpoints of quiescent filaments are well-known phenomena [6, 7, 1, 8]. Most of thepreceeding results were based on data with a moderate spectral resolution. The results wepresent here are based on spectroscopic data having a high spectral resolution (700000).This allows us to also identify fine velocity structures in the filament.MULTI-LINE SPECTRO-POLARIMETRY ON ACTIVE REGION NOAA 9125 745Fig. 6. – Profiles close from the flaring region. Magneto-optical effects are well seen on theStokes V parameters. Polarimetric precision on a single profile: 2 · 10−3 with an exposure timeof 300 ms.Figure 3 shows velocity maps of the region, at ±0.8 A˚ from the line core, underlyingvelocities of ±28 km s−1. Most of the flows present a symmetrical behavior with thepresence of a down- and an upflow. The most prominent feature is the strong (in valueand spatial extension) downflow associated with the filament of the middle left part ofthe image. If other noticeable flows are mainly concentrated at the filament footpoints,this one appears most likely at filaments edges. Velocities up to −45 km s−1 have beennoticed. This suggests a free-fall process.Data are not corrected for perspective effects. However, the region being close to thedisk center, their influence must be reduced. We cannot conclude yet on the presence ofacceleration of the flow, while falling down, even if the strongest downflows have been746 C. BRIAND and J. ABOUDARHAMdetected on the lower layers of the filaments. The time series we have allows us to pointout the non-stationary character of the downflow phenomenon. Figure 3 sketchs the flowsat three different times. It is evident that the strong downflow previously mentioned isnot always present (in black): very strong at 08h03, it almost completly disappears at08h18 and appears again at 08h32. Velocity field from Hα line shows the same behavior.It is noteworthy that the magnetic field (longitudinal or transversal) on the photospherebelow the filament should be very weak since no noticeable polarities appear on themagnetogram. An accurate determination of the magnetic-field configuration is howevernecessary and will be performed later on using inversion codes.These figures show that the presence of strong magnetic field in filamentary structureis not permanent during the lifetime of the structure but appears maybe recurrently.More specific observations on the subject are necessary with a better temporal resolution.A quick look at the data obtained latter on shows a complete transformation of thefilament. The whole data set must be reduced to check if any flare is present at or closeto the filament position, as suggested by Jiang et al. [3, 4].3.2. Flaring activity in a sunspot . – Many flares or sub-flares appear on the region.The most prominent one was located in one of the sunspots (cf. fig. 4). Figures 5 and 6show some example of Stokes spectra and profiles recorded during the flaring phase. Itis noteworthy that polarity in Stokes V and Q change appears in the sunspot, almost atthe maximum flare location.It lasted for at least half an hour. At first glance, we notice a diminution of thenegative polarity at photospheric level during the flare evolution (from the magnetogramsdeduced from the iron line—not shown here). A more accurate determination of themagnetic configuration will be performed latter on with an inversion code.4. – ConclusionsThe present set of data obtained with THEMIS telescope during the campaign 2000is very important to study the disturbance of filaments and the correlation with flareappearance. The accurate polarimetric measurements allow us to derive the magneticfield at photospheric levels. Some attempts will be done also to get the magnetic field atchromospheric level, at least where the magnetic field is strong enough.Another important item is to study the time evolution of the region over the 5 ob-serving days.REFERENCES[1] Schmieder B., Malherbe J. M., Poland A. I. and Simon G., Astron. Astrophys., 153(1985) 64.[2] Wang J., Shi Z. and Martin S. F., Solar Phys., 316 (1996) 201.[3] Jiang Y. and Wang J., Astron. Astrophys., 356 (2000) 1055.[4] Jiang Y. and Wang J., Astron. Astrophys., 367 (2001) 1022.[5] Semel M., Astron. Astrophys., 91 (1980) 369.[6] Mein P., Solar Phys., 54 (1977) 45.[7] Malherbe J. M., Schmieder B., Ribes E. and Mein P., Astron. Astrophys., 119 (1983)197.[8] Yoichiro H. and Hiroki K., Solar Phys., 124 (1989) 227.

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Multi-line spectro-polarimetry on active region NOAA 9125

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