TITLE: Study of the low frequency part of the Power Spectrum LEAD INVESTIGATOR: Alessandro Cacciani OTHER TEAM MEMBERS: E. Fossat, P. F. Moretti, J.M. Robillot, G. Severino (other researchers of Rome, Naples, Nice and Bordeaux are going to join this team) SOI Coordinator: R.Bogart SSSC Lead Programmer: J. Aloise ABSTRACT In the framework of a collaboration of the University of Rome, the Astronomical Observatory of Naples, the french network IRIS and the Astophysical Observatory of Bordeaux, an effort is being made to investigate all possible sources of noise (instrumental and solar) that make the low frequency part of the oscillatory spectrum ( p-modes below 2 mHz and g modes at lower frequencies) difficult to detect. The resources for this task are based on the availability of data analysis algorithms as well as a wide observational capability from the ground (both imaging and integrated disk for Doppler and magnetic field). The SOI data from the space are considered ideal, as far as the observing coverage and the absence of atmospheric noise are concerned, to step ahead toward the accomplishment of the proposed task of disentangle the various kind of solar, atmospheric and instrumental noises. INVESTIGATION PLAN: Recently the IRIS network has been implemented with additional MOFs (improved version, to be published, capable of producing simultaneous doppler and magnetic vector fields) that are being installed at the IRIS site in Tashkent and other two sites in California (Apple Valley + JPL). This new MOFs are small (no telscope) and are mounted in equatorial mounts. They are capable to detect Doppler and Magnetic fieds SIMULTANEOUSLY and very QUICKLY (that is, 4 frames at video rate are sufficient for one magnetogram as a difference of two dopplergrams , one for each circular polari- zation).The dopplergrams are obtained using the logarithmic difference log R - log B in order to avoid the time consuming computation of the ratio (B-R)/(B+R) (the logarithmic difference is found to produce a more linear doppler signal in comparison with the linear difference). The procedure is automatically repeated and the results accumulated in buffer memories at 16 bits. Two distinct hardware+software acquisition systems are used to accept and process the same video imput in parallel. The first is triggered by the modulator that alternates the Red and Blue wings of the MOF passband (DOPPLER). The second is triggered by the modulator that alternate the circular polari- zations of the incoming solar beam (MAGNETIC). This second modulator is driven at half the doppler frequency. This procedure is equivalent to the procedure illustrated at the Tenerife meeting (reference #1 ) with the IMPORTANT DIFFERENCE of minimizing the temporal changes caused by the seeing in the frames to be diffe- rentiated. This kind of seeing noise is clearly evident on the magnetograms presented at the Tenerife meeting and obtained at the Mt Wilson 60 foot solar tower, but is also present in the dopplergrams as large scale doppler inhomogeneities and small scale spurious doppler-like elements. So that the high spatial frequency pattern in the previous MOF dopplergrams may be mostly an artifact of the temporal lag between the Red and Blue frames. On the ground this noise arises mainly from the seeing distortion, but how much it is also given by other kind of changes in the time scale of the SOI filtergram acquisition can only be investigated by comparisons with higher temporal resolution data . It is well known that granules and supergranules are responsible for a substantial part of the solar noise and it is also well known that integrated disk measurements are better suited for very low l signals. However image resolution allows pixel by pixel intensity normalization and prograde/retrograde mode separation. Also, magnetic and other line profile changes that alter the doppler measurements can be taken into account. The AIM of this research proposal is to take advantage of our instrumental capabilities (IRIS + Bordeaux instrument + MOF, doppler & magnetic simultaneously, Sodium and Potassium lines) to produce a set of data that can be used to calibrate and clean the high resolution SOI dopplergrams whenever is possible. GOLF data are also available to us. The MOF stability and low noise performances are demonstarted in the reference #2 (collaboration with S.Tomczyk of HAO) where clean signals down to l=0 have been detected. Even better S/N level for l=0,1,2,3 is displayed in a presentation at the Asilomar meeting (reference # 3). We also mention here the ability of the MOF to produce a calibration image using the Stark effect (reference # 4). Among the data analysis capabilities, special mention deserve the work of the Observatory of Naples for the magnetic effects on Doppler (reference #5) and the IRIS software package. As the last step of our research plan we will use rebinned MDI doppler images, after carefull noise analysis and drift removal, in order to compare the low-l, low-fre- quency part of the Power Spectra from the ground and from the space . We are available to discuss collaborations with other investigation plans that may be overlapping with this proposal. One dopplergram and one magnetogram taken today ,Sept 26 1995 are available on IBIMAG.ROMA1.INFN.IT login : guest password: (space bar+ return) (once you are in, please type IDL then type MOF) WE CONSIDER THESE IMAGES IMPORTANT PICES OF OUR PROPOSAL! REFERENCES: 1- A.Cacciani et al. "Acquisition and Reduction Procedure for MOF Doppler-Magnetograms" in SEISMOLOGY OF THE SUN AND SUNLIKE STARS p. 185-188 ESA SP-286 2- S.Tomczyk et al. +A.Cacciani "An Instrument to Observe Low-Degree Solar Oscillations" Solar Physics 1995 3- A.Cacciani, P.F.Moretti, E.Smith "l=1 Rotational Splitting Detected from a 69 Day Observing Run ...." in Asilomar Meeting , April 1995 4- A.Cacciani, P.F.Moretti, et al. "The Stark Effect as a Calibration Tool in Helioseismology" Solar Physics, 144: 205 (1993) 5- C.Marmolino, M. Oliviero, L.A.Smaldone, G.Severino "Magnetic Noise Si- mulations in Velocity" in Asilomar Metting, April 1995