1. THEMIS WORKING GROUP Third Themis Workshop Toulouse, 17 – 19 April, 2002

2. Missions Help for the organization of the Themis users Help for improving the communication between Themis users and Themis staff and bodies (Board of Directors, Scientific Council)

3. History The creation of such a group was a recommandation of the Scientific Council (February 2001). The organization and funding is under the responsability of the « Programme National Soleil-Terre » of INSU. The group was officially created in December 2001

4. Composition It is composed of 7 members, considered as representative of the different groups and laboratories which are implied in the scientific programs developed at Themis. J. Arnaud, G. Aulanier, V. Bommier, M. Faurobert, J.M. Malherbe, N. Meunier and F. Paletou. In agreement with the PNST, we wish to enlarge the group to Italian and Spanish representatives.

5. First activities Creation of a mailing list of users, on the basis of a voluntary subscription: cfu-themis@obs-nice.frthemis@obs-nice.fr Example of information spread through this mailing list:

6. Cher(e)s collegues, 1/ Vous trouverez une etude (a base de spectropolarimetrie) des plus interessantes presentee sur le site suivant : http://www.iac.es/gabinete/noticias/2002/m01d23i.htm, ref: Nature 415, p.403 (Jan. 24, 2002)http://www.iac.es/gabinete/noticias/2002/m01d23i.htm 2/ A noter la parution du livre « Astrophysical Spectropolarimetry » chez Cambridge Univ. Press (ISBN 0521809983).« Recent developments in theoretical astrophysics and astronomical instrumentation are leading an ever-growing number of astrophysicists to appreciate the enormous diagnostic potential offered by spectropolarimetry. The polarization of light will help scientists to understand the physics of many phenomena occurring in the Universe. This book contains the lectures delivered at the XII Canary Islands Winter School of Astrophysics on Astrophysical Spectropolarimetry. Written by eight prestigious astrophysics researchers, this timely volume will provide graduate students and researchers with an unprecedented introduction to the field. » ATTENTION, ENCORE QUELQUES JOURS POUR SOUMETTRE VOS DEMANDES DE TEMPS D'OBSERVATION A THEMIS ! Amicalement,

7. THEMIS QUESTIONNARY A questionnary was sent in March 2002 to the THEMIS users in order to collect their opinion about the possible improvements of the observing facilities at THEMIS.

8. LIST OF QUESTIONS I. TECHNICAL ISSUES: PRESENT LIMITATIONS AND EXPECTED IMPROVEMENTS 1. Polarimetry (MTR & MSDP) 2. Image Quality (all modes). Calibrations (polarization, spectrographs etc...) 4. Pointing and tracking 5. Detectors and data acquisiton (all modes) 6. Spectrographs simulator (to determine what sets of spectral lines can be observed simultaneously or not) 7. Users Interface (all modes) 8. Quick look routines (on site/all modes) II. ORGANISATION 1. Observing campaigns (which period(s)? duration? etc...) 2. Observing modes set- up 3. Scientific and technical support from THEMIS staff from a Users' Committee III. INFORMATIONS NEEDED BY THE OBSERVERS 1. Preparing the time allocation request 2. Preparing for the observing run 3. While observing at THEMIS 4. For processing (& archiving) the data IV. COMMUNICATION 1. Web pages 2. Users manuals 3. Technical & upgrade(s) status reports 4. Annual reports 5. Mission reports 6. Recommendations and decisions of THEMIS councils 7. Projects IV. PROSPECTIVE V. OTHER ISSUES

9. Summary of the answers DOCUMENTATION COMMUNICATION POINTING AND TRACKING CAMERAS (+ ACQUISITION) IMAGE QUALITY USERS INTERFACE DATA STORAGE

10. DOCUMENTATION TECHNICAL DOCUMENTATION All the users point out a lack of technical documentation on the instruments. Here are some examples of useful information missing: Calibration of analysor, spectrograph, cameras Some standards procedures for tunning and calibrations: spatial size of a pixel, co-spatiality of the 2 slits in F2 focus (MTR mode), dispersion and enlargement on the cameras, orientation of the beam shifter (MSDP mode) Definition and sign of the Stokes parameters Description of the users interface (up to date) SOFTWARE A software for the simulation of the spectropgraph should be available for the users in order to prepare the observation time requests (line compatibility and intensity levels) Quick look and pre-treatment softwares at Themis (for example to obtain quick maps of logitudinal velocities and magnetic fields)

11. COMMUNICATION All the users feel a lack of dialog between the users and the local team and with the councils of THEMIS. Suggestions A summary of the decisions or recommandations of the councils should appear on the Web page of THEMIS The dates and program of the meetings of the Councils should be put in advance of the Web. The prospective of the instrument should be discussed with the users in regular « Prospective Meetings », every three years for example. The technical staff should answer directly to the observers the questions they ask in their mission reports.

12. POINTING AND TRACKING All the users have encountered important problems with the pointing and guiding system (coordinates can be off by 40’’ and changing with time). This is a severe default which has to be fixed. Suggestions: Tracking locked on the solar limb or some solar structure

13. CAMERAS AND ACQUISITION Some cameras are not working properly (fluctuation of dark current, bright zones, etc…). An operation of renewing of the cameras should be planned. Suggestions: * Size of the cameras : bigger cameras are necessary. In MSDP mode: to allow recording the whole 4’ field of view of the telescope, In MTR mode, in order to get the 2 beams of 2’ on the same camera. * Acquisition rate : Higger acquisition rates are necessary. In MSDP mode: to study waves, instabilities, flares, etc… and to develop observing modes with short exposure times (speckle techniques or destretching) in order to improve the image quality. In MTR mode, the acquisition rate is presently limited to 1 image in 300 ms. A lot of time is lost for data acquisition for short time exposures. * Photometric accuracy : in MSDP and IPM mode the maximum number of photons per pixel is too low, this decreases the photometric accuracy. Cameras with physiccally larger pixels would be needed. * Sensitivity in the blue and in the near IR : Resonance polarization appears in the blue (in particular 800 nm) is important for its sensitivity to the Zeeman effect (active regions, prominences).

14. IMAGE QUALITY All the users have noticed a poor image quality for long exposure times. Adaptive Optics will not necessary be the best solution because it does work properly when the seeing is bad and it can correct images only on a small field. Suggestions: * It is first necessary to better understand where the images are degraded (in the atmosphere or inside the telescope?) * Before implementing a full OA system, a tip-tilt correction is the first necessary step. It would probably provide a significant improvement of the image quality (experience from other solar telescopes). * The development of speckle or destretching of image techniques is an alternative way for 2D modes such as MSDP and IPM. It requires high acquisition rates (see cameras) to take bursts of short exposure time images.

15. USERS INTERFACE It has been very much improved in 2001. Suggestions *The users manual should be put on the Web site of THEMIS, and in the users observing room. *Some instrumental calibration sequences should be included *The acquisition rate is too low for some programs where rapidly evolving phenomenons are studied. Is it possible to create the headers of the FITS file after the observation has been performed? *In order to save observing time, it should be possible to prepare the observing sequences in advance (one day before)

16. DATA STORAGE AND REDUCTIUON Request from BASS2000: Provide all the information for identifying the relevent calibration files. Data which cannot be calibrated are useless for the community. Request from the community: Some reduced « standard » data should be available for the international community at BASS2000. Well documented reduction procedures should be proposed too, for the scientists which are not familiar with the observations at THEMIS. Request from some observers: in order to allow fast rate observing or fast change of target, is it possible to create images in binary format instead of FITS format?

17. Most urgent needed improvements as seen by the users of the different observing modes

18. IPM MODE The instrument is not developed at THEMIS, the following requirements concern the environment provided at THEMIS *Tracking and pointing problems have to be fixed urgently *Image quality must be improved *Faster acquisition cadence would be useful

19. MSDP MODE *Simultaneous observations in 2 spectral lines *Tests with the new beam-shifter (for photospheric lines) *Faster acquisition rate (3 images /s instead of 1 image/s presently) *New grid for low-scattered-light polarization measurements

20. MTR MODE *Better control of the co-spatiality of the two beams in F2 is highly important for measuring meaningful polarization rates on spatially resolved structures *Locking of the coulisses for polarization measurements with the grid should be installed. *Interference fringes are formed in the quarter wave plates and not stable in time, they are not removed by the flat- field. They limit the polarimetric accuracy (see poster). The plates could be treated in order to reduce the fringes. *Larger cameras in order to get the two beams on the same camera without reducing the field of view. *Higher acquisition rate