“ HINODE workshop” Zhanle Du & Huaning Wang 杜占乐 王华宁 中科院国家天文台 (NAOC) December 9, 2007 Problem of coronal temperature diagnostics 2007 年 12 月 8-10 日北京九华山庄

1.Divergences on coronal temperature and heating mechanism 2.Data 3.Filter ratio method 4.Improvements 5.Current state Outline

Accurate measurements on coronal temperature can check whether or not a model (heating mechanism) is in agreement with the real process in solar corona. The temperature of a coronal loop is uniform distribution ?( Lenz, et al. 1999,ApJ,517,L155 ； Aschwanden et al.2000,ApJ,541,1059. On EUV) or increase with height?( Rosner et al.1978,ApJ,220,643 ； chmelz et al, 2001,ApJ,556,896. On SXT) Where do the heating take place ？ top?( Reale,2002, ApJ,580,566 ) bottom?( Aschwanden,2001,ApJ,559,L171 ) uniform? ( Priest et al.1998 ) or random? These fundamental problems are unclear ( Patsourakos & Klimchuk, 2005 ， APJ, 628,1023 ). 1. Divergences on coronal temperature and heating mechanism

CDS （ Coronal Diagnostics Spectrometer ） on SOHO (Solar and Heliospheric Observatory): Å. EIT(EUV Imaging Telescope) on SOHO. 171 （ 1.0±0.7MK), 195(1.4±0.8MK), 284Å(2.1±1.2MK). TRACE (Transition Region and Coronal Exploer) NIS(normal incidence spectrometer), Å, Å 2. Data TRACE ： 173/195 angstrom (CHIANTI, EIT_TEMP)

The filter ratio method is one widely used in coronal temperature measurement. It is based on the hypothesis of isothermal equilibrium. For optically thin spectrum line, its intensity ： 3. Filter ratio method where A is elemental abundance, G(T) the contribution function, and P （ T ） is called response function. DEM (differential emission measure) is defined as ( Schmelz & Martens,2006,APJ,636,L49 ）： (ergs cm -2 s -1 sr -1 ) The emission measure is usually taken as constant for different lines 。

For the filter responses P(T) for 171, 195 and 284Å (top panel), a filter ratio: 3.1 filter ratio method It is multiple-valued (bottom panel), and thus could only be used to diagnose a particular monotonic interval, such as MK in corona (Weber et al., 2005,ApJ,636,L101 ； Noglik & Walsh, 2007, ApJ,655,1127 ). The measurement of the ratio for 195/171 is rather flat(0.81), which leads to an identical temperature:1.2MK!

The isothermal assumption required for the filter ratio technique did not match the differential emission measure curves from spectroscopic observations of the EUV emission from active Regions ( Cirtain et al ). It is valid only in some ranges ( Martens et al., 2002, ApJ, 577, L115 ). Stead heating model is often not consistent with observations ( Warren & Winebarger, 2007, APJ,666,1245; Serio et al, 1981,ApJ,243,288). The coronal loop is structured by multiple strands with multiple temperatures (Schmelz, et al. 2000, ApJ, 627, L81). The temperature deduced from filter ratio method is some weighted one, and maybe meaningless sometimes. 3.2 Isothermal assumption

There is a wide divergences on whether or not we should use the background subtraction technique to increase the signal/noise ratio. Necessary. ( Del Zanna & Mason,2003 、 Cirtain et al.2007 nunecessary. ( Schmelz et al. 2003,ApJ,599,604; 2007 AdSpR, 39,1497 ). The temperature in a loop is identical to that of the surroundings ( Schmelz et al ） ! 3.3 background subtraction

The temperatures are different for different line ratios(284/195 、 195/171)(1.8MK>1.2MK) （ Schmelz, et al.2003 ）. The radiation from high temperature is earlier than that from low one ： t 284 <t 195 <t 171 （ Warren et al. 2003, APJ, 593, 1174) ---which means that different lines come from different sites. Some authors have pointed out that the filter ratio method to determine loop temperature is inappropriate, and that temperature may be physically meaningless, ( Matens et al. 2002, ApJ,577,L115, Weber et al.,2005, ApJ, 635,L101; Chae et al, 2002, ApJ, 567,L159 ), --- including some other parameters such electron density. 3.4 Problems

Chae et al. ( 2002, ApJ,567,L159 ； Noglik & Walsh ， 2007 ) used two ratios to solely determine a certain temperature. 4.Improvements 4.1 color-color technique

With an adding relationship 4.2 Two temperature distribution model Four parameters, T C, T H, EM C,EM H, can be resolved (Zhang, et al. 1999, ApJ,527,977; Nitta & Yaji, 1997,ApJ,484,927), and thus determine the T C （ MK ） and T H ( MK ). Supposing a coronal loop is radiated from two temperature distribution, cold and thermal (T C, T H ).

Each coronal loop is composed of multiple finer strands with different temperatures: w=1.4Mm ( Aschwanden & Nightingale, 2005,ApJ,633,499 ； Cirtan, et al. 2007, ApJ, 655,598 ). Aschwanden, et al. (2007,ApJ,656,577) deduced some scale laws from monte- carlo similation. This model needs further improvements to relate tons the observations. 4.3 multiple strands

5.Current state 5.1 In use Some authors pointed out that the filter ratio method is questionable in determining the coronal loop temperature ( Matens et al. 2002, ApJ,577,L115, Schmelz et al. 2007, ApJ, 660,L157 ）， and continued to use it （ Warren & Winebarger, 2007, APJ, 666, 1245 ）. In fact, the temperatures are different for different positions in a coronal loop, the measured intensities for different lines come from different positions ( Klimchuk & Gary, APJ,2002, 448,925 ). The temperatures determined from line ratio method may deviated from the original isothermal hypothesis.

Coronal temperature diagnostics is very important either in theory or application. It is not yet clear about the temperature distribution in a coronal loop. It is now increasingly realized that a coronal loop is composed of multiple strands with different temperatures （ Reale & Peres, APJ 2000,528,L45;Testa et al ， APJ, 580, 1159 ）. It is only studied in theory or in simulation, and has not yet considered the detailed structures, e.g., the different positions, emission height, width etc. for different emission lines. Further improvements on coronal loop temperature should consider the fine structures, and elemental abundance, heating mechanism, dynamical process, and the topology…. 5.2 further improvements

Thanks!