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SIL93 - Search for Hydroxyl in Southern Cold IRAS Sources

Short title: Silva et al. (1993)
Authors: Silva, A. M. Azcarate, I. N. Poppel, W. G. L. Likkel, L.
Journal: Astronomy and Astrophysics, Vol.275, NO.2/AUG(II), P. 510, 1993
Bibcode:

Abstract
We searched for OH in a sample of 53 objects selected from the IRAS Point Source Catalog. According to their color properties, the sources have the cool envelopes (temperature T_env &asymp 150-300 K) of objects in evolution between OH/IR stars and planetary nebulae (PN). The sources were chosen from within the southern sky with declinations (delta < - 30�. We sought the OH radical at the frequencies of 1612, 1665 and 1667 MHz with a 3O-m antenna at the Instituto Argentino de Radioastronomia (IAR). We found OH radiation in emission and/or absorption towards thirteen of the sources, among which are two known bipolar nebulae. Furthermore, we suggest the following identifications: two possible cloud sources with absorption in three OH lines and PN color at the positions of IRAS 16115 - 5044 and IRAS 16279-4757, respectively (new detections) four OH/IR stars with symmetric double peaked profiles and low variability, one of them a new detection (IRAS 17106-3046) a possible star in transition between oxygen to carbon-rich (IRAS 16279-4757, new detection) two OH/IR stars with high mass loss rates and variability (previously reported) in possible transition to bipolar nebulae and two new pre-PN candidates with very cold envelopes and irregular OH profiles (IRAS 17579 -3121 and 18025-3906). For IRAS 10197-5750 (Roberts 22) there is evidence of an uneven distribution of the matter surrounding the star. Its OH-variability was studied and a tentative light curve with a 7.2 yr period was constructed. Among the non-detections there are carbon star candidates and a few possible PN without the conditions needed for supporting maser operation. On the other hand there is no apparent difference in the color properties of non- detections and detections. We present evidence for radiative pumping of the 1612 maser line. The mean efficiency is <&epsil> = 0.13, assuming that the 35 mum line is the only pump line. Mass loss rates between 3 10^-6 and 5 10^-5 M_sun yr^-1 were estimated for the 10 objects detected with double peaked 1612 MHz lines. The importance of the mass loss process for understanding the evolutionary stage of the objects and its influence on OH line shapes is discussed.	Comments: Velocity resolution: 1.8 km/s Upper limit for non-detections: 2.4 Jy (3σ)

Abstract

We searched for OH in a sample of 53 objects selected from the IRAS Point Source Catalog. According to their color properties, the sources have the cool envelopes (temperature T_env &asymp 150-300 K) of objects in evolution between OH/IR stars and planetary nebulae (PN). The sources were chosen from within the southern sky with declinations (delta < - 30�. We sought the OH radical at the frequencies of 1612, 1665 and 1667 MHz with a 3O-m antenna at the Instituto Argentino de Radioastronomia (IAR). We found OH radiation in emission and/or absorption towards thirteen of the sources, among which are two known bipolar nebulae. Furthermore, we suggest the following identifications: two possible cloud sources with absorption in three OH lines and PN color at the positions of IRAS 16115 - 5044 and IRAS 16279-4757, respectively (new detections) four OH/IR stars with symmetric double peaked profiles and low variability, one of them a new detection (IRAS 17106-3046) a possible star in transition between oxygen to carbon-rich (IRAS 16279-4757, new detection) two OH/IR stars with high mass loss rates and variability (previously reported) in possible transition to bipolar nebulae and two new pre-PN candidates with very cold envelopes and irregular OH profiles (IRAS 17579 -3121 and 18025-3906). For IRAS 10197-5750 (Roberts 22) there is evidence of an uneven distribution of the matter surrounding the star. Its OH-variability was studied and a tentative light curve with a 7.2 yr period was constructed. Among the non-detections there are carbon star candidates and a few possible PN without the conditions needed for supporting maser operation. On the other hand there is no apparent difference in the color properties of non- detections and detections. We present evidence for radiative pumping of the 1612 maser line. The mean efficiency is <&epsil> = 0.13, assuming that the 35 mum line is the only pump line. Mass loss rates between 3 10^-6 and 5 10^-5 M_sun yr^-1 were estimated for the 10 objects detected with double peaked 1612 MHz lines. The importance of the mass loss process for understanding the evolutionary stage of the objects and its influence on OH line shapes is discussed.

Comments:
Velocity resolution: 1.8 km/s
Upper limit for non-detections: 2.4 Jy (3σ)

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Detection table from Silva et al. (1993)

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ID	Obs. RA	Obs. Dec	l	b	Group id	Source name	Frequency	V_range	V_peak	F_peak	List	Detection	Class	Dist. (parallax)	Ref.
	(J2000)	(J2000)	(deg.)	(deg.)			(MHz)	(km/s)	(km/s)	(Jy)		Yes/No		(kpc)
1	17 12 22.7	-42 25 11	345.0518	-1.8549	G345.052-1.855	IRAS 17088-4221	1612	30.0	-12.0	16.200	ENG15	+H₂O +OH	EVOLVED		SIL93
2	17 04 28.3	-38 44 23	347.1049	1.5480	G347.105+1.548	IRAS 17010-3840	1612	28.0	-7.0	8.500	ENG15	+OH +SiO	EVOLVED		SIL93
3	16 37 40	-38 20 17	344.0737	5.8466	G344.074+5.847	IRAS 16342-3814	1612	32.0	-17.0	7.100	ENG15	+H₂O +OH -SiO	EVOLVED		SIL93
4	16 14 2.5	-42 13 03	338.1225	6.4028	G338.123+6.403	IRAS 16105-4205	1612	25.0	-96.0	44.900	ENG15	-H₂O +OH	EVOLVED		SIL93
5	11 54 6.3	-62 18 42	296.3264	-0.1775	G296.326-0.177	IRAS 11516-6201	1612	23.0	9.0	3.000	ENG15	+OH	EVOLVED		SIL93
6	10 21 33.6	-58 05 41	284.1754	-0.7890	G284.177-0.790	IRAS 10197-5750	1612	42.0	-27.0	59.300	ENG15	+OH	EVOLVED		SIL93
7	17 13 51.6	-30 49 40	354.6239	4.7019	G354.624+4.701	IRAS 17106-3046	1612	25.0	-6.0	7.400	ENG15	-H₂O +OH	EVOLVED		SIL93
8	17 44 22.6	-31 55 39	357.3085	-1.3330	G357.309-1.333	IRAS 17411-3154	1612	37.0	-39.0	246.000	ENG15	-H₂O +OH +SiO	EVOLVED		SIL93
9	18 06 03	-39 05 57	353.2673	-8.7244	G353.267-8.724	IRAS 18025-3906	1612	27.0	-130.0	4.200	ENG15	+OH	EVOLVED		SIL93
10	10 21 33.6	-58 05 41	284.1754	-0.7890	G284.177-0.790	IRAS 10197-5750	1665	41.0	-26.0	75.400	ENG15	+OH	EVOLVED		SIL93
11	16 14 2.5	-42 13 03	338.1225	6.4028	G338.123+6.403	IRAS 16105-4205	1667	27.0	-98.0	3.500	ENG15	-H₂O +OH	EVOLVED		SIL93
12	16 37 40	-38 20 17	344.0737	5.8466	G344.074+5.847	IRAS 16342-3814	1665	62.0	19.0	0.600	ENG15	+H₂O +OH -SiO	EVOLVED		SIL93
	16 37 40	-38 20 17	344.0737	5.8466	G344.074+5.847	IRAS 16342-3814	1667	5.0	5.0	1.400	ENG15	+H₂O +OH -SiO	EVOLVED		SIL93
14	17 44 22.6	-31 55 39	357.3085	-1.3330	G357.309-1.333	IRAS 17411-3154	1667	37.0	-41.0	11.900	ENG15	-H₂O +OH +SiO	EVOLVED		SIL93
15	07 42 16.8	-14 42 52	231.8354	4.2195	G231.835+4.220	OH231.8+4.2	1667	19.0	19.0	15.900	ENG15	+H₂O -CH₃OH II +OH +SiO	EVOLVED		SIL93

Non-detection table from Silva et al. (1993)