Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://star.arm.ac.uk/preprints/2007/510.pdf Äàòà èçìåíåíèÿ: Thu Oct 11 12:57:28 2007 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 02:54:33 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 106

Jets or high velo city flows revealed in high-cadence sp ectrometer and imager co-observations?
M.S. Madjarska1 , J.G. Doyle2 , D. Innes1 and W. Curdt madjarska@mps.mpg.de ABSTRACT We rep ort on active region EUV dynamic events observed simultaneously at high-cadence with SUMER/SoHO and TRACE. Although the features app ear in the TRACE Fe ix/x 171 ° images as jets seen in pro jection on the solar A disk, the SUMER sp ectral line profiles suggest that the plasma has b een driven along a curved large scale magnetic structure, a pre-existing lo op. The SUMER observations were carried out in sp ectral lines covering a large temp erature range from 104 K to 106 K. The sp ectral analysis revealed that a sudden heating from an energy dep osition is followed by a high velo city plasma flow. The Doppler velo cities were found to b e in the range from 90 to 160 km s-1 . The heating pro cess has a duration which is b elow the SUMER exp osure time of 25 s while the lifetime of the events is from 5 to 15 min. The additional check on soft Xray Yohkoh images shows that the features most probably reach 3 MK (X-ray) temp eratures. The sp ectroscopic analysis showed no existence of cold material during the events. Subject headings: Sun: corona; Sun: transition region; line: profiles, metho ds: observational
1

1.

Intro duction

A large variety of jet-like phenomena are often observed in the solar atmosphere such as surges, spicules, sprays, Extreme-UltraViolet (EUV) and X-ray jets. X-ray jets (Shibata et al. 1992) were first identified in data obtained with the Soft X-ray Telescop e (SXT)
Max-Planck-Institut fur Sonnensystemforschung, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Ger¨ many
2 1

Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland


­2­ on Yohkoh (Tsuneta et al. 1991). They represent X-ray enhancements with an apparent collimated motion and were found to have a typical size of 5 â 103 ­ 4 â 105 km and an apparent velo city of 30 to 300 km s-1 . Their kinetic energy is estimated to b e 1025 ­ 1028 ergs. Most of the jets were asso ciated with small flares in large X-ray bright p oints or active regions. Shimo jo & Shibata (2000) derived the physical parameters of X-ray jets and found temp eratures from 3 to 8 MK (determined by using Yohkoh filter ratios) and densities of 0.7 ­ 4.0 â 109 cm-3 . It is strongly b elieved that they are pro duced by magnetic reconnection and represent the evap oration flow resulting from the reconnection heating. EUV jets were studied by Brekke (1999) in off-limb data from the Coronal Diagnostics Sp ectrometer (CDS) and the Extreme-ultraviolet Imaging Telescop e (EIT). From the CDS data it was found that the jet was emitting only at transition region temp eratures showing Doppler shifts in the O v 629.73 ° line up to -75 km s-1 . The event was also seen in the EIT A ° passband propagating with an apparent velo city of 180 km s-1 . The plasma Fe xii 195 A seemed to b e ejected along a large lo op ed magnetic structure. Jets were also analysed in on-disk data from the Transition Region And Coronal Explorer (TRACE) taken in the 171 ° A and 1216 ° passbands by Alexander & Fletcher (2000). In the 171 ° channel the ejected A A plasma was seen b oth in emission and absorption which suggests that simultaneously highly collimated hot and cold material was ejected along the magnetic field lines. An EUV jet from a new emerging active region (a large Bright Point) was analysed in simultaneous TRACE, EIT and CDS data by Lin et al. (2006). The authors found the plasma jet to emit in a wide temp erature range from 10 000 K (He i) to 2.5 MK (Fe xvi, the upp er temp erature limit of their observations). H surges are often asso ciated with EUV and X-ray emissions showing the co-existence of co ol (H ) and hot ejections of plasma (Jiang et al. 2007 and references therein). Only recently, however, have the spatial and temp oral relation of these emissions b een studied in detail (Jian et al. 2007) during surge events in a plage area of an active region. The authors A first observed the bright structures in TRACE 171 ° followed by the co oler H jet which they interpret as co oling of the hot plasma with a co oling time lasting ab out 6 ­ 15 min.

2.

Observations

The events discussed here o ccurred in the active region NOAA 8558 on 1999 June 2. No flares were registered during the events. Simultaneous Solar Ultraviolet Measurements of Emitted Radiation (SUMER) telescop e and TRACE observations were taken during several hours. The field-of-view (FOV) of the two instruments is shown in Figure 1. EIT Fe xii 195 ° A single images for some of the events are also available, as well as a few SXT images. In the


­3­ present letter only TRACE and SUMER data will b e shown. The SUMER sp ectrometer (Wilhelm et al. 1995, Lemaire et al. 1997) data were taken on 1999 June 2 starting at 09:17 UT and ending at 11:02 UT. A slit with a size of 0. 3 â 120 was used exp osing for 25 s p ointed at the plage area of the active region b etween two sunsp ots (Figure 1). Four sp ectral windows were telemetred, each with a size of 120 spatial â 50 sp ectral pixels. The sp ectral lines read out are shown in Table 1. At the start of the observations the sp ectrometer was p ointed at solar disk co ordinates xcen = -217 (at 09:17 UT) and ycen = 257 . Subsequently, the observations were comp ensated for the solar rotation. The sp ectral analysis was made in resp ect to a reference sp ectrum obtained by averaging over the entire dataset. The TRACE (Handy et al. 1999) data were obtained in the Fe ix/x 171 ° and 1600 ° A A passbands starting at 09:00 UT and finishing at 11:30 UT on June 2, 1999. The integration ° time was 2.9 s for the 171 ° passband and 0.3 s for 1600 ° The 171 A channel cadence A A. was 10 s which increased to 15 s when an image in the 1600 ° channel was taken. From A 09:18:38 UT until 09:32:28 UT only observations in the 1600 ° channel were taken. A The co-alignment of SUMER and TRACE observations (spatial resolution of 1.5 and 1 , resp ectively) was done by using SUMER raster observations, taken just b efore the time series in the Si ii 1260.44 ° line which falls in the transmitted O v 629.73 ° sp ectral A A window, and TRACE 1600 ° images. The SUMER raster was obtained with 5 s exp osure A time and 0.37 increment. The emission in the TRACE 1600 ° passband mainly comes from A continuum emission, C iv, C i, and Fe ii. Note that the SUMER times mark the b eginning of the exp osures, while the TRACE times the end of the exp osures.

3.

Features analysis: temp oral evolution, velo city and temp erature

We identified three events in the SUMER data which we will call further in the text EV1, EV2 and EV3. Only EV3 was fully co-registered by SUMER and TRACE. Figure 2 demonstrates through a sequence of difference images the app earance of EV3 as a jet-like event in the TRACE images. The difference images were obtained by substracting an image taken at 09:55:49 UT. The entire lifetime of EV1 and EV2 is only seen in the SUMER data, while TRACE registered only the fading phase of these features. ° EV1 started at 09:20:29 UT (12 min b efore the first TRACE 171 A image after the A observing gap, see Section 2) with a sudden increase in the emission of the Mg x 625 ° -1 line (Figure 3, left) coupled with a Doppler shift of up to 30 km s to the red. This increase is seen over-imp osed on the already relatively higher and red-shifted emission of


­4­ the Mg x min later, rapidly as the Mg x and just a 625 ° line due to a pre-existing feature (not discussed in this pap er). Around 2 A at 09:22:20 UT, the emission in O v 629 ° and N v 1238 ° started to increase A A well, reaching a maximum around 75 s (three exp osures) after the maximum in 625 ° line. A strong red-shift is seen in the O v 629 ° line (up to 110 km s-1 ) A A -1 ° line. few km s in the N v 1238 A

The detailed study on the line profiles revealed that the feature started with a sudden large radiance increase of the rest comp onent of the sp ectral lines and a red-shifted comp onent. This suggests that an energy dep osition to ok place followed by a collimated high velo city plasma flow. The heating pro cess and the initial acceleration had a duration b elow the exp osure time of 25 s. It to ok around 75 s for the three lines (Mg x, O V and Nv) to reach their maximum with the resp onse in O v 629 ° and N v 1238 ° coming approxiA A mately 75 s (three exp osures) later. That was followed by a further acceleration of the flow and simultaneous decrease of the emission at the rest comp onent in less than a minute. We clearly see the co oling of the event as a delay in the resp onse in O v 629 ° and N v 1238 ° A A (Figures 3 and 4). The feature had a stronger presence in the O v 629 ° and Mg x 625 ° A A ° lines and a mo dest resp onse in the N v 1238 A line with no signature at chromospheric temp eratures, indicating a high electron density (Doyle et al. 2006a). Its lifetime was around 10 min. The Doppler shifts in the O v 629 ° line are in the range from 90 to 160 km s-1 A derived from a double Gauss fit. EV 2 started 5 min after EV1 around 09:25:05 UT app earing along the SUMER slit just ab ove EV2. The maximum emission in the Mg x 625 ° line lasted during 3 exp osures and A the delay in the resp onse of the transition region lines was again around 2 min. The first TRACE 171 ° image at 09:32:28 UT revealed a jet-like event (see Figure 1, left). The time A of this image corresp onds to the decaying phase of the features seen in the SUMER data (Figure 3, left). In the SUMER data at the start of EV2, it was still p ossible to separate b oth features along the slit. During the decaying phase, however, the events app eared as a single feature along the SUMER slit, and that is how they were seen in the first TRACE image at 09:32:28 UT (see Figure 1, left). In Figure 4 the TRACE 171 ° image taken at 09:32:28 UT A and the time corresp onding SUMER sp ectral line profiles during the events (EV1 & EV2) are ° shown. The features app eared as a radiance increase of the rest comp onent of the O v 629 A line (Figure 3) and a strong red-shifted comp onent (Figure 4). The same is observed in the Mg x 625 ° line although the Doppler shift is smaller. No change in the emission of the A chromospheric lines (Table 1) was observed. The width of EV2 is around 3 derived from its pro jection along the SUMER slit. EV3 was registered during the observations starting at 09:59:52 UT with a width of 3 (Figure 1, right). The temp oral evolution of the amplitude of the radiance derived from


­5­ a single Gauss fit in all three sp ectral lines can b e seen in Figure 3 (right). In Figure 5 a TRACE 171 ° image and the time corresp onding SUMER line profiles during EV3 are A shown. The event showed the same temp oral b ehaviour as the events describ ed ab ove and had a duration of around 15 min. As for EV1 and EV2 no resp onse was found in the chromospheric emission. In order to find out with more precision whether cold plasma exist during the events we studied the ratio of the continuum emission of the SUMER first and second order radiation. ° The first order emission (1238 A) is ab ove the H Lyman limit, while the second order (629 ° is b elow. Second order emission will b e absorb ed by H i along the line-of-sight A) and the first order emission not (for details on the metho d see Innes et al. 2003). Therefore, the second- to first order ratio would show a decrease if cold material existed along the line-of-sight. The ratio did not show any changes which indicated that emission at low temp eratures was not present. During all three events brightenings were observed in SXT and EIT Fe xii 195 ° data. Such brightenings were often observed in SXT data and their A energetics is studied in detail by Shimizu (1995).

4.

Discussion

This letter presents, to our knowledge for the first time, EUV transient features in an active region identified and analysed in on-disk SUMER data and simultaneously obtained TRACE images. These instruments provide data at highest existing (1.5 and 1 ) spatial and 2 km s-1 sp ectral resolution (SUMER). Additionally, the combination of sp ectrometer and imager data obtained at high cadence (25 s and b elow) p ermitted the temp oral and spatial evolution, velo cities and esp ecially temp eratures of EUV active region transients to b e derived with the highest p ossible precision. Three dynamic events were studied in sp ectral lines covering a temp erature range from 104 to 106 K. All three features showed strong redshifted emission in the O v 629 ° and Mg x 625 ° lines suggesting high velo city flows which A A propagate in a direction away from the observer, i.e. towards the solar surface. Considering the magnetic fields structure of the active region field by the lo ops seen in TRACE 171 ° A, we suggest that the features although app earing with a jet-like structure in TRACE 171 ° images may rather represent a high velo city flow driven along a curved magnetic field, A most probably a pre-existing lo op. No signature of the events was found at chromospheric temp eratures. Both EIT/Fe xii 195 ° and Yohkoh/SXT showed brightenings in a pixel row A indicating the presence of a 1 to 3 MK plasma during the transients. The lower resolution of these instuments (6 ) in comparison to TRACE (1 ) do not p ermit the events to b e identified as jets. The resp onse in the transition region lines is delayed by around 2 min


­6­ in resp ect to the coronal line suggesting co oling of the events. In the future hydro dynamic numerical simulations (see for detail Doyle et al. 2006b) will b e p erformed with the results converted into observable quantities to b e then compared with the present data. We b elieve that the capabilities of the Hino de mission will bring a b etter understanding on these features and, more imp ortant, the physical mechanism b ehind them. The SUMER pro ject is financially supp orted by DLR, CNES, NASA, and PRODEX. Armagh Observatory's research is grant-aided by the N. Ireland Dept. of Culture, Arts & Leisure. Facilities:SUMER/SoHO, TRACE, Yohkoh/SXT, EIT/SoHO

REFERENCES Alexander, D. & Fletcher, L., 1999, Sol. Phys., 190, 167 Brekke, P., 1999, Sol. Phys., 190, 379 Doyle, J. G., Ishak, B., Madjarska, M. S., O'Shea, E. & Dzif´ akov´ E., 2006a, A&A, 451, ck a, L35 Doyle, J. G., Taroyan, Y., Ishak, B., Madjarska, M. S. & Bradshaw, S. J., 2006b, A&A, 452, 1075 Handy, B. N., Acton, L. W., Kankelb org, C. C., et al., 1999, Sol. Phys., 187, 229 Innes, D. E., McKenze, D. E. & Wang, T., 2003, Sol. Phys., 217, 247 Jiang, Y. C., Chen, H. D., Li, K. J., Shen, Y. D. & Yang, L. H., 2007, A&A, 469, 331 Lemaire, P., Wilhelm, K., Curdt, W., et al., 1997, Sol. Phys., 170. 105 Lin, Ch.-H., Banerjee, D., O'Shea, E. & Doyle, J. G., 2006, A&A, 450, 1181 Madjarska, M. S., Doyle, J. G., Ishak, B. & Curdt, W., 2007, A&A, to b e submitted Mazzotta, P., Mazzitelli, G., Colafrancesco, S. & Vittorio, N., 1998, A&AS, 133, 403 Shibata, K., Nozawa, S. & Matsumoto, R., 1992, PASJ, 44, 265 Shimo jo, M. & Shibata, K., 2000, ApJ, 542, 1100 Tsuneta, S., Acton, L., Bruner, M. et al., 1991, Sol. Phys., 136, 37


­7­ Wilhelm, K., Curdt, W., Marsch, E., et al.., 1995, Sol. Phys., 162, 189

A This preprint was prepared with the AAS L TEX macros v5.2.


­8­

Table 1: The observed sp ectral lines. Ion (° A) log(T) Nv 1238.82 5.3 Ci 1248.00 4.0 1248.88 Ci 1249.00 4.0 O iv/2 1249.24 5.2 Si x/2 1249.40 6.1 Ci 1249.41 4.0 Mg x/2 1249.90 6.1 O iv/2 1250.25 5.2 Si ii 1250.09 4.1 Si ii 1250.41 4.1 Ci 1250.42 4.0 S ii 1250.58 4.2 Si ii 1251.16 4.1 Ci 1251.17 4.0 O iv/2 1251.70 5.2 Si i 1258.78 4.1 S ii 1259.53 4.2 O v/2 1259.54 5.4 Si ii 1260.44 4.1

max

Comment

blend blend blend

blend

blend

blend

blend

Note: The expression /2 means that the spectral line was observed in second order. The comment `blend' means that the spectral line is blending a close by line. The line formation temperatures are taken from CHIANTI v5.0 using the Mazzota et al. (1998) ionization equilibrium.


­9­

Fig. 1.-- Colour table reversed TRACE Fe ix 171 ° images obtained on 1999 June 2. The A images are derotated to a reference time. The overplotted vertical line shows the SUMER slit p osition.


­ 10 ­

Fig. 2.-- TRACE 171 ° image sequence of EV3. The dimenstions of the images are 100 â A 50 and were taken approximately 50 s apart.


­ 11 ­

Fig. 3.-- Left: The p eak radiance (background substructed) averaged over 11 pixels along the SUMER slit obtained from a single Gauss fit during EV1 and EV2. The solid line corresp onds to the Mg x 625 ° line, dotted ­ O v 629 ° and dashed ­ N v 1238 ° The A A A. ° image taking (see vertical solid line shows the time of the restart of the TRACE 171 A Section 2). The shaded area marks the time p erio d during which another event app eared along the line-of-sight unrelated to the features discussed here (See for details Madjarska et al. 2007). Right: The p eak radiance (background substructed) averaged over 7 pixels along the SUMER slit during EV3. The linestyles have the same corresp ondence as in the left Figure.


­ 12 ­

Fig. 4.-- Left: TRACE 171 ° color table reversed image showing the first two events ­ EV1 A & EV2. The time of the image corresp onds to the vertical solid line on Figure 2, left. The vertical line marks the p osition of the SUMER slit, while the two horizontal lines outline the slit p osition which was analysed in the SUMER data. Right: The SUMER sp ectral line profiles at 09:32:06 UT. The dotted lines show the reference sp ectra.


­ 13 ­

Fig. 5.-- Left: TRACE 171 ° color table A image corresp onds to the vertical solid line p osition of the SUMER slit, while the two was analysed in the SUMER data. Right: dotted lines show the reference sp ectra.

reversed image showing EV3. The time of the on Figure 2, right. The vertical line marks the horizontal lines outline the slit p osition which The sp ectral line profiles at 10:01:16 UT. The