HOP 0138

abstract of observational proposal

Science case: An advantage of the unexplored Ti I 5644°A line is its high Stokes Q/I amplitude of ~0.3%. That is comparable to the 0.33% amplitude of the Na ID2 line, which has been already sucessfully used for low resolution scattering polarization observations by Stenflo et al. (2002) with a Lyot type filter (UBF). As the Ti I 5644°A line is formed in the deep photosphere and the Na ID2 line is formed in the high photosphere, we will be able to investigate the height dependence of the weak fields by employing these two lines. There is indirect evidence for spatial fluctuations of the turbulent fields at the granular level, with the strongest fields residing in the intergranular lanes. High resolution data observations of the mixed-polarity magnetic fields will help to fully characterize magnetic fields at (inter-)network scales and at granular scales.

We also intend to compare our results with simulations such as shown in V¨ogler & Sch¨ussler (2007). They propose the presence of local dynamo action by the granular overturning. There are no observations yet confirming this important process and height-dependant high resolution data will certainly be instrumental in uncovering the dynamics of these turbulent motions. We will collaborate with Alexander V¨ogler, currently part of the solar group at the Utrecht University, who will be able to clarify or modify the simulations when needed.

The Ti I lines have not been observed before but qualitatively analyzed by Manso Sainz & Landi Degl’Innocenti (2002), and we therefore have a theoretical framework available. The theoretical framework for the scattering polarization in the Na ID2 line, has been laid down by Trujillo Bueno et al. (2002).

Co-spatial observations with the Hinode instrument will be an invaluable addition to the measurements taken with IBIS. The magnetic maps obtained with the SP will allow us to determine the magnetic activity in the observed regions. The G band and Ca IIH images will enable us to identify faculae and the CN band scattering polarization can directly be compared to results for the weak turbulent fields obtained with IBIS.

remarks

Observation strategy: We will use IBIS in the the standard dual-beam configuration and cover several quiet sun areas at the solar limb targeting different magnetic field structures. We will also record magnetograms in the Fe 6302°A line. We are planning to obtain G band and Ca IIK images with a separate setup in addition, which will allow us to monitor the magnetic activity in the target region.

We will take co-spatial observations with the SOT (Solar Optical Telescope) on the Hinode satellite. The Spectro-Polarimeter will run in fast mode and we will record filtergrams in the G band and Ca IIH and full-Stokes scattering polarization data in the CN band. As the Hinode satellite has to be programmed well in advance, we will follow its positioning with the IBIS instrument. We applied for an observation run of 14 days at IBIS and indicated that we would like to observe in November 2009. As soon as we receive information on the actual allocated observation time we will be able to give more detail on the required observation dates for Hinode on which we would like to observe between 14:00 UT and 16:00 UT. Table 2 shows the observations requested from Hinode. A duration of 30 minutes per position is sufficient. We estimate the data volume without limb-factor correction for a single position to be about 75 Mbits for the G band and Ca IIH observations, 250 Mbits for the CN observations, and 75 Mbits for the SP map, totalling 400 Mbits per position. Since we will observe limb targets only, a fraction of the FOV will be off-limb, resulting in reduced
data volume.

We already gained experience with the data reduction processes involved in analyzing scattering polarization in the CN band and Na ID1 data with the Hinode Solar Optical Telescope (Snik et al. 2009). The results look promising and the combination of high spatial resolution ground based data and the additional magnetic mapping by Hinode make this a worthwhile project.