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4. Results

The results of the SiO maser observations are presented in Table 2 (click here), and spectra of the detected sources are shown in Fig. 1 (click here). The observations were made mainly in the SiO (v=1, J=2-1 and v=2, J=1-0) lines. Only a few selected sources were observed in the SiO (v=1, J=1-0) line. In total 28 sources were detected in SiO emission of which 13 are new detections. The detection rate for the v=2, J=1-0 line is 23% compared with 15% for the v=1, J=2-1 line, in agreement with the conclusion of Nyman et al. (1993a) that the v=1, J=2-1 line is relatively weak in objects with cool envelopes. A few objects, however, were detected in the J=2-1 line but not in the J=1-0 line, possibly due to the time variability of the SiO maser emission. Most of the detected objects are OH/IR stars. Only two objects classified as PPNe were detected (tex2html_wrap_inline2664 and tex2html_wrap_inline2666), and one, tex2html_wrap_inline2668, was tentatively detected. No SiO masers were found towards any of the PNe because most likely the SiO molecules will be photodissociated near their central stars.

  figure477  figure485
Figure 1: a) The SiO 43 GHz (v=1, J=1-0) and (v=2, J=1-0) spectra of the detected sources. The v=2 spectra are shown with solid lines, the v=1 spectra with dotted lines. b) The SiO 86 GHz (v=1, J=2-1) spectra of the detected sources. The velocity scale is given with respect to the local standard of rest

 figure491  figure497
Figure 1: b) continued

 

Source SiO v=1, J=1-0 SiO v=2, J=1-0 SiO v=1, J=2-1

Epoch rms peak Int. Epoch rms peak Int. Epoch rms peak Int.
01304+6211 *9344 0.4
03206+6521 *9343 0.4
03293+6010 *9344 0.4 2.6 2.9
04361+2547 8528 0.9
06319-0501 9251 1.4 9387 0.3
06530-0213 9251 1.3 8528 0.6
07027-7934 9251 1.6 9275 0.5
07131-0147 9251 1.1 8528 0.4
07180-1314 9252 1.9 9387 0.5 3.0 5.1
07399-1435 9253 2.1 5.1 9249 1.4 8.2 4.4 8528 0.5 5.0 6.4
07536-2830 9253 2.1 10.4 8.4 9251 1.3 9.6 3.4 9274 1.2 7.5 18.6
07559-5859 9251 1.8 9387 0.6
08005-2356 9253 2.1 9249 0.9 8528 0.6
08357-1013 9253 2.4 13.0 9.2 9251 1.6 11.6 8.3 9274 0.9 3.8 4.2
09371+1212 9253 2.2 9249 1.4 8723 0.8
09429-2148 9253 5.1 70.2 38.0 9251 2.6 55.0 21.1 9274 1.0 27.0 26.8
10197-5750 9253 1.8 9248 0.6 8723 0.5
10197-5750 9274 1.0
11385-5517 9253 1.2 9249 1.1 8723 0.5
11516-6201 9251 1.7 9274 0.9
12358-6323 9282 1.4
14086-0730 9253 2.3 18.7 9.7 9252 1.6 7.0 3.1 9387 0.8 10.0 13.0
14122-5947 9387 0.5
14341-6211 9282 1.1
15405-4945 9253 2.0 9247 *0.9 8527 0.6
16029-3041 9253 2.5 15.6 8.5 9249 2.2 41.0 11.9 8531 0.7 10.0 6.3
16086-5255 9282 1.1
16235-4832 9253 2.3 9251 2.1 8530 0.6
16342-3814 9253 2.0 9248 0.8 8527 0.5
16559-2957 9250 1.5 8527 0.8
16594-4656 9251 1.8 8911 0.5
17103-6302 9253 2.3 9247 *1.0 8530 0.6
17106-3046 9249 0.9 9275 1.2
17118-2952 9251 2.4 8723 0.7
17150-3224 9249 1.4 8911 0.8
17150-3754 9249 1.0 8530 0.6
17163-3907 9251 1.4 8530 0.6
17195-2710 9282 1.0
17207-2856 9249 0.9 8530 0.6
17221-3038 9249 1.2 8531 0.6
17233-2602 9282 1.0
17292-2727 9251 2.2 8786 0.7
17317-2743 9251 2.3 8786 0.8
17347-3139 9251 1.4 8531 0.6
17360-3012 9253 5.2 54.6 21.0 9250 2.7 39.8 19.2 8786 0.8 6.3 8.6
17371-2747 9253 1.7 9248 1.2 8527 0.5
17371(OH) 9252 1.2
17375-2759 9248 0.7 8531 0.5
17375(OH) 9252 1.3
17375-3000 9249 1.2 8533 0.6
Table 2: SiO maser observations. The epoch is given in JD+2440000, rms and peak intensity in Jy, and integrated intensities in units of tex2html_wrap_inline2686. Only the peak flux is given for tentatively detected sources. An asterisk(*) in front of the rms value of the SiO (v=2, J=1-0) observations indicate that the calibration is uncertain due to unstable weather. An asterisk (*) in front of the epoch of the SiO (2-1) observations indicate that they were made with the Onsala 20 m telescope

 

 

Source SiO v=1, J=1-0 SiO v=2, J=1-0 SiO v=1, J=2-1

Epoch rms peak Int. Epoch rms peak Int. Epoch rms peak Int.
17385-3332 9282 1.1
17393-2727 9249 1.4
17404-2713 9282 1.0
17411-3154 9253 4.1 108.1 33.6 9250 3.1 152.9 115.5 8786 0.7 20.0 27.3
17423-1755 9249 1.2 8530 0.5
17433-1750 9251 2.0 8531 0.5
17433-1750 9382 1.0
17443-2519 9250 1.3 8786 0.8
17443-2949 9249 1.3 8531 0.6
17459-3057 9250 2.1 8786 0.8 3.8 8.6
17484-1511 9251 1.9 8723 0.8
17505-3143 9253 2.6 6.6 1.4 9251 1.2 3.9 2.3 8563 1.0
17516-2526 9251 2.0 8723 0.8
17534+2603 8723 0.9
17565-2035 9252 1.7 8563 1.0
17579-3121 9249 1.0 9275 1.2
17580-3511 9248 1.5 8531 0.6
18016-2743 9382 1.0
18025-3906 9249 1.4 9282 1.0
18044-1947 9252 2.1 8533 0.8
18055-1833 9250 1.7 8533 0.7
18071-1727 9250 2.3 8533 0.8
18081-0338 9251 1.8 8563 1.1
18095+2704 *9338 0.4
18105-1935 9282 1.0
18107-0710 9253 3.0 5.5 9252 1.5 9.0 2.1 8563 1.2
18135-1456 9253 1.5 5.1 9247 0.7 8563 1.0
18135-1456 *9343 0.6
18161-1713 9252 1.7 8564 1.1
18167-1209 9249 1.5 8911 0.4
18176-1848 9253 2.2 17.2 9.8 9252 1.6 16.8 8.7 8564 1.1
18257-1000 9253 2.6 9251 1.6 27.7 14.2 8564 1.0
18276-1431 9253 1.6 9247 *1.0 8531 0.8
18276-1431 *9344 0.4
18281+2149 *9336 0.4
18298-2111 9251 1.8 8533 0.7
18303-0519 9252 2.1 8786 0.7
18310-2834 9252 1.2 8563 1.1
18314-2759 9251 1.4 8563 1.1
18340-0839 9251 1.9 8786 0.6 2.5 4.0
18348-0526 9253 2.3 44.5 11.8 9247 *5.8 67.5 21.1 8786 0.8
18437-0643 9253 2.0 5.5 9252 1.8 9.3 3.6 8533 0.9
18450-0148 9248 1.3 9275 1.0
18454+0250 9252 2.1 8563 1.1
18460-0254 9253 3.0 9251 1.7 26.9 12.2 9275 1.2
18479-2514 9251 1.2 8533 0.8
18491-0207 9249 1.6 8531 0.5
18526+0140 9990 0.4
18550+0130 9251 1.4 9275 1.2 5.3 20.1
18560+0638 9253 2.7 40.2 25.4 9252 3.1 73.3 56.7 9275 1.3
18596+0315 9253 1.9 9252 1.4 *9344 0.5
19010+0527 9251 1.9 9275 1.2
19010+0527 *9342 0.5
19067+0811 9253 3.6 18.6 11.0 9251 1.5 20.7 13.5 9276 1.2
19067+0811 *9342 0.8
Table 2: continued

 

Source SiO v=1, J=1-0 SiO v=2, J=1-0 SiO v=1, J=2-1

Epoch rms peak Int. Epoch rms peak Int. Epoch rms peak Int.
19075+0921 9251 2.0 9275 1.3
19075+0921 *9342 0.5
19114+0002 9251 2.0 8563 1.1
19127+1717 9251 1.3 8563 1.2
19127+1717 *9344 0.4
19134+2131 *9339 0.4
19161+2343 *9340 0.8
19178-2620 9253 2.4 19.5 13.4 9251 1.4 26.1 21.0 8533 0.8 16.3 17.5
19190+1102 9252 2.2 9275 1.2
19192+0922 9253 2.8 17.6 4.7 9252 1.7 19.9 5.2 9276 1.1 7.5 6.5
19219+0947 9248 1.4 8530 0.6
19244+1115 9248 1.8 8531 0.6
19283+1944 9253 3.1 10.1 2.1 9251 2.4 13.3 4.8 9276 1.2
19283+1944 *9342 0.8
19288+2923 *9339 0.6
19297+2300 *9342 0.6
19343+2926 *9336 0.3
19352+2030 9990 0.6
19511+3935 *9338 1.2
19566+3423 *9340 0.6
19576+2814 *9344 0.3
20043+2653 *9343 0.3 1.2 1.5
20272+3535 *9339 0.6
20406+2953 *9340 0.5
20491+4236 *9337 0.4 3.3 5.9
21206+5145 *9339 0.5
21554+6204 *9339 0.4
22036+5306 *9335 0.4
22177+5936 *9340 0.5
22480+6002 *9340 0.8 5.8 27.3
23321+6545 *9342 0.7
23541+7031 *9344 0.5
Table 2: continued

We will only discuss the detections and non-detections in a qualitative way, i.e., we will for instance not compare the relative intensities of the various transitions, since the data were taken at different epochs, in only one linear polarization, and for the SiO (v=2, J=1-0) transition a few sources were observed during unstable weather. Most of the PPNe and PNe were observed during good weather conditions, however, and we do not believe that we failed to make a detection because of the weather.

Apart from the tentative detection towards tex2html_wrap_inline2668, which is classified as a PPNe, SiO masers were found to be associated only with variable objects. Two of these are classified as PPNe (tex2html_wrap_inline2664 and tex2html_wrap_inline2666). The rest are OH/IR stars with the exception of two objects with uncertain classification (IRAS 08357-1013 and IRAS 16029-3041). The latter are however most likely OH/IR objects based on their double-peaked OH line profiles, the tex2html_wrap_inline3016 dust features, the single-peaked energy distributions, and the late-type (M) central stars. Their classification is uncertain because of the low value of the IRAS variability indices and the lack of monitoring observations reported in the literature. However, observations in the infrared and of the OH masers reported by various authors show variability both in the infrared and of the OH emission (e.g. Allen et al. 1977; Fouqué et al. 1992; te Lintel Hekkert et al. 1991; Le Squeren et al. 1979; Slootmaker et al. 1985).


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