Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/masermeeting/web_papers/205_Zhou.pdf Дата изменения: Tue Apr 10 02:48:23 2007 Дата индексирования: Sun Dec 23 09:01:48 2007 Кодировка: Поисковые слова: planetary nebula

Possible CO clouds interacting with the SNRs G21.8-0.6 and G32.8-0.1
Jianjun Zhou1,3, Jarken Esimbek1 Xizheng Zhang2, Hongbo Zhang
1. National Astronomical Observatories/Urumqi Observatories, CAS, China 2. National Astronomical Observatories, CAS, China 3. Graduate School of Chinese Academy of Science

2

Abstract: OH 1720 MHz maser associated with the SNRs are one confident signature indicating SNR-molecular cloud interaction. We made the first CO(1-0) mapping to the SNRs G21.8-0.6 and G32.8-0.1, both of them are associated with OH 1720 MHz maser. Based on the morphological correspondence between the radio remnant and CO clouds, and the velocity and position agreement between the OH maser and CO clouds, we tentatively suggest that the clouds interacting with G21.8-0.6 and G32.8-0.1. However, the shock excited line broadenings was not found in coud F, and is not very strong in cloud F, we discussed the possible reasons. Introduction: Recently OH masers at 1720 MHz have been proven to be good signature of SNR-molecular cloud interaction. The excitation of OH 1720 MHz maser requires very dense gas ~105cm-3) with a temperature range of 50-125K. A C-type shock caused by the expanding SNR will create such conditions (Elitzur 1976; Wardle 1999; Lockett et al. 1999). This has been proven to be true by many molecular line observations to the SNRs associated with OH 1720 MHz masers (Koralesky et al. 1998; Reach & Rho 1998; Frail & Mitchell 1998; Reynoso et al. 2000). We performed the first CO(1-0) observations to the SNRs G21.8-0.6 and G32.8-0.1, they have been found to be associated with 1720 MHz OH maser. We hope to study the relation between the SNR and ambient CO clouds and search for the effects of SNR-molecular cloud interaction. Observation and results: Observations of the 12CO(1-0) line and its isotopes were performed with 13.7m telescope located in Delingha, Qinhai province of China, in April 2004. The sensitivity of the telescope is 0.26 K (rms) for an integration time of 60 seconds. The spectra of G21.8-0.6 and G32.8-0.1 are displayed in Fig1 and Fig2, Fig4 and Fig5 respectively. There is a dip in the spectra of G21.8-0.6 between 30 and 40 km s-1 (see Fig1 and Fig2), and seem to be evidence of self-absorption. However, careful examination of the off-spectra indicates that there is emission at the same velocities at the off-position. But the small dip appeared in the spectra of G32.8-0.1 between 0 and 10 km s-1 may be caused by self-absorption. If this is true, self-observation would be weak. 13 CO(1-0) emission of these two SNRs are very weak, and C18O(10) was not detected. The CO clouds around these two SNRs are displayed in Fig3 and Fig6, they are integrated over different velocity ranges. Discussion: Based on the analysis of position and velocity agreement between the OH maser and CO clouds , the morphological signature of the CO clouds and spectral line broadenings, we tentatively suggest that cloud C of G21.8-0.6 and cloud F of G32.8-0.1 may be related to the SNR physically (Fig3, Fig6). However, line broadenings is lack in the CO(1-0) spectra of G21.8-0.6 and is not very strong in G32.8-0.1 (see Fig1, Fig2, Fig4 and Fig5). Possible reason is that the shocked molecular gas may be highly excited and therefore weak in emission from the low-lying CO(1-0) transition (Wilner et al. 1998). The CO(1-0) spectra of G21.8-0.6 and G32.8-0.1 are complex, many blending features appear on it. This indicates that the confusion due to different velocity components along the line of sight may play an important role here and make it more difficult to discern such weak line broadenings. Our CO(1-0) observation results indicate that CO(1-0) is not appropriate for observe shock-excited molecular gas..
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