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 ( and
), and one,
, 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.
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
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 |
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 |
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 |
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 , which is
classified as a PPNe, SiO masers were
found to be associated only with variable objects. Two of
these are classified as PPNe (
and
).
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
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).