2 Observations

Observations were made with the 100-m antenna at Effelsberg in December 1999. We used a cooled HEMT dual-channel receiver connected to only one sense of polarization, Left Circular Polarization (LCP). The system temperature was $\approx$60 K ( $T_{\rm mb}$) including ground pick up and sky noise. We used a position switching observing mode with the reference position offset by 600'' in longitude from the source position (the half-power beamwidth of the telescope at 6 GHz is 130''). The new auto-correlator AK90 was split into 2 bands of 20 MHz each thus allowing us to simultaneously observe the 2 main lines and the two satellites lines of the J= 5/2 state. There were 4096 channels per band giving a channel separation of 4.9 kHz and thus an effective spectral velocity resolution of 0.29 km s^-1. Proper functioning of the system was checked by observations of the strong 5 cm OH emission from the two compact HII regions W3(OH) and ON1 (see Table 1).

 

 

Table 1: Observations of the 6GHz OH maser transitions in AGB stars.

IRAS Source	Other Name	Type1	Observed Coordinates		Observed	Sensitivity2 (Jy)
			J2000.03		Velocity	(at 3$\sigma$)
			RA	Dec	Range, LSR	6 GHz
			h m s	$^\circ ~ '$ ''	(km s-1)	LCP
02232+6138	W3(OH)	UCHII	2:27:03.866	+61:52:24.82	-939/+998, (-45.0)	E
20081+3122	ON1	UCHII	20:10:09.073	+31:31:34.40	-894/1043, (+00.0)	E
00007+5524	Y Cas	Mira main	00:03:21.605	+55:40:48.21	-911/1026, (-17.0)	0.08
01037+1219	IRC+10011	OH/IR Moderate	01:06:25.965	+12:35:53.07	-886/1051, (+08.0)	0.07
02168-0312	OMI Cet	Mira main	02:19:20.679	-02:58:39.21	-848/1089, (+46.0)	0.06
02192+5821	S Per	SG	02:22:51.689	+58:35:11.76	-932/1005, (-38.0)	0.08
02251+5102	RR Per	Mira main	02:28:29.318	+51:16:17.60	-894/1043, (+00.0)	0.08
02420+1206	RU Ari	Mira sat	02:44:45.184	+12:19:08.15	-874/1063, (+20.0)	0.07
03206+6521	OH 138.0+7.2	OH/IR Moderate	03:25:08.552	+65:32:05.42	-931/1006, (-37.5)	0.08
03293+6010	OH 141.0+3.5	OH/IR Moderate	03:33:30.528	+60:20:09.10	-951/986, (-57.2)	0.07
03507+1115	IK Tau	Mira sat	03:53:28.983	+11:24:20.02	-861/1076, (+33.0)	0.05
05073+5248	NV Aur	OH/IR Moderate	05:11:19.747	+52:52:27.79	-891/1046, (+02.9)	0.08
05131+4530	RAFGL 712	OH/IR Moderate	05:16:47.103	+45:34:03.76	-926/1011, (-32.3)	0.09
05528+2010	U Ori	Mira sat	05:55:49.264	+20:10:30.77	-933/1004, (-39.5)	0.04
05559+7430	V Cam	Mira main	06:02:32.779	+74:30:27.26	-887/1050, (+06.5)	0.07
06297+4045	OH 174.7+13.5	OH/IR Moderate	06:33:14.921	+40:42:49.71	-910/1027, (-16.3)	0.08
06363+5954	U Lyn	Mira main	06:40:46.320	+59:52:00.23	-904/1033, (-10.0)	0.07
06500+0829	GX Mon	Mira sat	06:52:42.408	+08:25:23.33	-905/1032, (-11.0)	0.06
07209-2540	VY Cma	SG	07:22:58.17	-25:46:02.95	-872/1065, (+22.0)	0.07
07399-1435	OH231.8+4.2	PPN	07:42:16.738	-14:42:14.04	-878/1059, (+16.0)	0.06
07422+3054	AU Gem	Mira Main	07:45:27.590	+30:46:43.11	-890/1047, (+04.0)	0.04
07585-1242	U Pup	Mira sat	08:00:50.596	-12:50:31.88	-912/1025, (-18.0)	0.04
08005+2356		OH/IR Late	08:02:59.186	+23:45:33.23	-888/1049, (+05.7)	0.07
08357-1013	OH235.3+18.1	OH/IR Moderate	08:38:08.805	-10:24:16.95	-894/1043, (+00.0)	0.07
09425+3444	R Lmi	Mira main	09:45:34.314	+34:30:42.91	-894/1043, (+00.0)	0.14
09448+1139	R Leo	Mira main	09:47:33.446	+11:25:43.52	-893/1044, (+01.0)	0.05
10580-1803	R Crt	SR	11:00:33.822	-18:19:29.54	-884/1053, (+10.0)	0.05
12562+2324	T Com	Mira sat	12:58:38.600	+23:08:23.03	-879/1058, (+15.0)	0.07
13001+0527	RT Vir	SR	13:02:37.908	+05:11:08.56	-876/1061, (+18.0)	0.09
14247+0454	RS Vir	Mira sat	14:27:16.393	+04:40:40.38	-894/1043, (+00.0)	0.08
15193+3132	S Crb	Mira main	15:21:24.366	+31:22:02.05	-894/1043, (+00.0)	0.07
15255+1944	WX Ser	Mira sat	15:27:47.009	+19:34:02.33	-888/1049, (+06.0)	0.08
16235+1900	U Her	Mira main	16:25:47.411	+18:53:32.98	-907/1030, (-13.0)	0.05
18006-1734	GLMP 704	OH/IR Late	18:03:36.581	-17:34:00.59	-870/1067, (+23.9)	0.10
18071-1727	OH 12.8 +.9	OH/IR Late	18:10:05.813	-17:26:35.22	-868/1069, (+25.9)	0.09
18081-0338		OH/IR Thick	18:10:49.074	-03:38:14.46	-889/1049, (+05.6)	0.08
18100-1915	GLMP 740	OH/IR Thick	18:13:02.725	-19:14:20.42	-876/1061, (+17.6)	0.09
18107-0710		OH/IR Thick	18:13:29.720	-07:09:48.92	-876/1061, (+17.9)	0.08
18135-1456	OH 15.7 +.8	OH/IR Late	18:16:26.004	-14:55:13.43	-895/1042, (-01.1)	0.09

 

Table 1: continued.

IRAS Source	Other Name	Type1	Observed Coordinates		Observed	Sensitivity2 (Jy)
			J2000.03		Velocity	(at 3$\sigma$)
			RA	Dec	Range, LSR	6 GHz
			h m s	$^\circ$ ' ''	(km s-1)	LCP
18152-0919	OH 20.8 +3.1	OH/IR Thick	18:17:58.662	-09:18:42.44	-867/1070, (+26.7)	0.08
18198-1249	OH 18.3 +.4	OH/IR Late	18:22:43.046	-12:47:40.94	-846/1091, (+48.0)	0.10
18262-0735		OH/IR Thick	18:28:59.446	-07:33:25.44	-815/1122, (+78.9)	0.08
18268-1117	OH 20.4 -.3	OH/IR Thick	18:29:35.755	-11:15:53.97	-852/1085, (+41.8)	0.08
18266-1239	V435 Sct	OH/IR Thick	18:29:28.605	-12:37:40.55	-844/1093, (+50.0)	0.08
18348-0526	V437 Sct	OH/IR Thick	18:37:31.986	-05:23:59.35	-867/1070, (+27.2)	0.06
18432-0149	V1360 Aql	OH/IR Thick	18:45:52.691	-01:46:43.27	-828/1109, (+66.2)	0.08
18460-0254	V1362 Aql	OH/IR Late	18:48:40.999	-02:50:22.29	-795/1142, (+99.0)	0.09
18488-0107	V1363 Aql	OH/IR Late	18:51:25.772	-01:03:54.48	-818/1119, (+75.8)	0.08
18525+0210		OH/IR Thick	18:55:04.815	+02:14:41.21	-823/1113, (+70.2)	0.07
18549+0208	OH 35.6 -.3	OH/IR Thick	18:57:26.573	+02:12:11.24	-816/1121, (+77.9)	0.09
18560+0638	V1366 Aql	OH/IR Moderate	18:58:30.142	+06:42:55.91	-874/1063, (+19.7)	0.10
19039+0809	R Aql	Mira sat	19:06:22.196	+08:13:48.16	-846/1091, (+48.0)	0.09
19065+0832	OH 42.6 +.0	OH/IR Late	19:08:58.368	+08:37:47.08	-841/1096, (+53.1)	0.07
19071+0946	OH 43.8 +.5	OH/IR Thick	19:09:31.065	+09:51:54.41	-885/1052, (+09.1)	0.12
19161+2343		OH/IR Moderate	19:18:14.537	+23:49:26.23	-865/1072, (+28.6)	0.07
19219+0947	Vy 2-2	PN	19:24:22.078	+09:53:55.82	-956/981, (-44.3)	E/0.02
19244+1115	V1302 Aql	OH/IR Moderate	19:26:47.588	+11:21:14.77	-849/1088, (+45.0)	0.08
19343+2926	M1-92	PPN	19:36:16.768	+29:32:15.80	-894/1043, (+0.00)	0.24
19352+2030		OH/IR Thick	19:37:23.395	+20:39:21.86	-889/1048, (+05.0)	0.20
20043+2653	GLMP 972	OH/IR Thick	20:06:22.890	+27:02:11.23	-898/1039, (-04.6)	0.08
20047+1248	SY Aql	Mira sat	20:07:05.694	+12:57:07.39	-943/994, (-49.0)	0.08
NML Cyg		SG	20:46:25.941	+40:06:56.09	-894/1043, (+00.0)	0.02
20491+4236	OH 83.4 -.9	OH/IR Moderate	20:50:57.766	+42:48:04.31	-932/1005, (-38.4)	0.05
21554+6204	GLMP 1048	OH/IR Thick	21:56:58.184	+62:18:43.62	-914/1022, (-20.6)	0.06
22177+5936	NSV 25875	OH/IR Moderate	22:19:27.806	+59:51:21.74	-919/1017, (-25.6)	0.07
23041+1016	R Peg	Mira main	23:06:38.829	+10:32:37.94	-870/1067, (+24.0)	0.09
23558+5106	R Cas	Mira main	23:58:24.683	+51:23:18.18	-870/1067, (+24.0)	0.06

¹ UCHII: Ultra Compact HII region, SG: Supergiante, SR: Semi Regular, PN: Planetary Nebulae, PPN: Proto Planetary Nebulae.
² E = Emission; the upper limits correspond to 3$\sigma$.
³ B1950 coordinates processed to J2000 within GILDAS package.

Calibration of the data followed the procedure used in the 6 GHz survey of star-forming regions made by Baudry et al. (1997). OH spectra were calibrated in terms of the noise source coupled to one polarization channel and the flux density scale was determined by observations of NGC 7027 (Ott et al. 1994). The noise tube was calibrated in Jy assuming that the 6 GHz flux density of NGC 7027 was 5.9 Jy. We estimate that the flux density scale uncertainty is within 10%. All spectra were calibrated in terms of single polarization flux densities. This is one-half of the two polarization flux density. For possible 5 cm radio interference, we proceeded as in Baudry et al. (1997).

Our input catalog is listed in Table 1. It is based on 18 cm OH data. We selected sources which clearly exhibit the 1612 MHz satellite line and/or the 1665/1667 main lines. By these means we obtained targets with noticeable amounts of OH molecules and IR photons, that are not excessively distant in order to be detected.

Figure 2: Uncorrected IRAS colors from IRAS flux measurements available of the sources in our sample. (NML Cyg is not included as there is no IRAS measurement available.)

The sources are essentially OH Miras with thin or moderately thick envelopes, and thick OH/IR objects. Bright Miras with both satellite and main lines were selected, from the Sivagnanam et al. (1988) comprehensive OH survey of the 1-kpc solar neighborhood. Most of them are also known as 22 GHz water maser sources. From the David et al. (1993) Nançay survey of OH/IR objects, we retained bright 1612 MHz sources with detected 1667 MHz emission. Targets have been chosen in order to sample objects lying along the sequence drawn by evolved stars in the IRAS two-color diagram (see Fig. 2). They mostly belong to the AGB. This sequence of envelope thicknesses is thought to reflect various evolutionary stages, and a certain initial mass distribution. Given our selection criteria we favored the best candidate stars for showing OH maser emission i.e. the nearby OH/IR stars with high luminosity and large amounts of dust and infrared photons.

We also included in our survey a few typical Semi-Regular variables, Proto-Planetary Nebulae (PPN), and Planetary Nebulae (PN), that are thought to be linked to the same evolutionary tracks. We added some red Supergiants (SG). The latter are luminous massive stars that are not on the AGB, but which usually present somewhat similar circumstellar envelopes. In our input catalog are NML Cyg (SG) and Vy 2-2 (PN), for which tentative detections at 5 cm have been reported in the literature.