1. EVN observations of OH maser burst in OH17.7-2.0
M. Szymczak
Torun Centre for Astronomy
collaborators:
A. Bartkiewicz (Torun Centre for Astronomy) E. Gerard (Paris Observatory)

2. Target characteristics
OH (IRAS )
central star earlier than K5, Te=4000 –104 K (Le Bertre 1987)
bimodal IR energy distribution
O-rich proto-planetary nebula (Kwok 1993)
small OH flux variations (Herman & Habing 1985)
non-variability or only slight variations at NIR (Le Bertre 1989)
no SiO masers (Nyman et al.1998)
disappearance of water maser in 1990 (Engels 1997)
ellipsoidal shape at 2.2m: 2.5x2arcsec, PA~20o
OH circumstellar shell of radius mas (Bains et al.2003)

3. Unusual outburst of ~73kms–1 feature at 1612MHz

4. Unusual outburst of ~73kms–1 feature at 1612MHz

5. Unusual outburst of ~73kms–1 feature at 1612MHz

6. Unusual outburst of ~73kms–1 feature at 1612MHz

7. Unusual outburst of ~73kms–1 feature at 1612MHz

8. Unusual outburst of ~73kms–1 feature at 1612MHz

9. Unusual outburst of ~73kms–1 feature at 1612MHz

10. Unusual outburst of ~73kms–1 feature at 1612MHz

11. Unusual outburst of ~73kms–1 feature at 1612MHz

12. Unusual outburst of ~73kms–1 feature at 1612MHz

13. Unusual outburst of ~73kms–1 feature at 1612MHz

14. Unusual outburst of ~73kms–1 feature at 1612MHz

15. Unusual outburst of ~73kms–1 feature at 1612MHz

16. Unusual outburst of ~73kms–1 feature at 1612MHz

17. Unusual outburst of ~73kms–1 feature at 1612MHz

18. Unusual outburst of ~73kms–1 feature at 1612MHz

19. Unusual outburst of ~73kms–1 feature at 1612MHz

20. Unusual outburst of ~73kms–1 feature at 1612MHz

21. Unusual outburst of ~73kms–1 feature at 1612MHz

22. Unusual outburst of ~73kms–1 feature at 1612MHz

23. Unusual outburst of ~73kms–1 feature at 1612MHz

24. Unusual outburst of ~73kms–1 feature at 1612MHz

25. Unusual outburst of ~73kms–1 feature at 1612MHz

26. Unusual outburst of ~73kms–1 feature at 1612MHz

27. Unusual outburst of ~73kms–1 feature at 1612MHz

28. Unusual outburst of ~73kms–1 feature at 1612MHz

29. Unusual outburst of ~73kms–1 feature at 1612MHz

30. Unusual outburst of ~73kms–1 feature at 1612MHz

31. Unusual outburst of ~73kms–1 feature at 1612MHz

32. Unusual outburst of ~73kms–1 feature at 1612MHz

33. Unusual outburst of ~73kms–1 feature at 1612MHz

34. Unusual outburst of ~73kms–1 feature at 1612MHz

35. Unusual outburst of ~73kms–1 feature at 1612MHz

36. Unusual outburst of ~73kms–1 feature at 1612MHz

37. Unusual outburst of ~73kms–1 feature at 1612MHz

38. Variations in the 1612MHz flux density of selected features

39. No variations in the 1665/1667MHz flux densities

40. Motivation of VLBI observations
where is an active region
to determine its properties
causes and mechanisms of the outburst
– a local enhancement of mass loss,
pump rate,
OH abundance,
– amplification of background continuum source
– magnetic beaming, overlap of Zeeman components
– interaction of a fast wind with remnant AGB shell

41. Observations 8 telescopes (Cm,Jb,Ef,Mc,On,Tr,Hh,Wb) of the EVN
2005 March 3 (1st epoch)
1612MHz OH line
phase-referencing observations
JIVE correlator, dual circular polzn
spectral resolution (0.5MHz/1024ch) ~0.09kms–1
beam 64 x 20mas, PA=8o
1s ~ 10mJy beam–1 for single circular polzn.
OH flux monitoring with the Nancay telescope

42. Comparison of the 1612 MHz spectra

43. Averaged channel maps 48.0/2 48.3/5 48.6/2 48.8/3 49.1/3 49.4/4 49.8/4
50.1/4
50.5/4
50.9/4
51.2/4
51.7/7
54.5/40
68.2/11
69.0/6
69.6/6
70.2/9
70.8/4
71.2/5
71.6/5
71.9/2
72.3/5
72.6/2
72.8/3
73.2/6
73.7/4
74.0/4
74.4/3
74.6/3
74.9/3

44. V = 47.96kms–1

45. V = 48.28kms–1

46. V = 48.60kms–1

47. V = 48.83kms–1

48. V = 49.10kms–1

49. V = 49.41kms–1

50. V = 49.77kms–1

51. V = 50.15kms–1

52. V = 50.50kms–1

53. V = 50.86kms–1

54. V = 51.23kms–1

55. V = 51.73kms–1

56. V = 54.46kms–1

57. V = 68.19kms–1

58. V = 68.96kms–1

59. V = 69.58kms–1

60. V = 70.18kms–1

61. V = 70.85kms–1

62. V = 71.18kms–1

63. V = 71.63kms–1

64. V = 71.95kms–1

65. V = 72.27kms–1

66. V = 72.59kms–1

67. V = 72.81kms–1

68. V = 73.22kms–1

69. V = 73.68kms–1

70. V = 74.04kms–1

71. V = 74.36kms–1

72. V = 74.63kms–1

73. V = 74.90kms–1

74. OH17.7-2.0 1612MHz blue-shifted emission 0 moment

75. OH17.7-2.0 1612MHz red-shifted emission 0 moment

76. Spot diagram outburst region 4 components of the maser emission:
– spherical shell
– biconical interaction region
– equatorial region
– stellar image
bipolar outflow with an axis at PA ~10o
outburst region is ~400mas to the S of the central star; cm for D=3.4kpc
outburst region

77. Expanding shell model OUTBURST stellar image V* = 61.6 kms-1
Vexp=13.8 kms-1
stellar image

78. Summary of results
two OH shells of radii ~250 and ~650mas ( and cm) were detected => episodic mass loss (time scale of 460years)
the bursting emission comes from two unresolved spots of Tb1011K located at cm from the central star
bipolar outflow; polar cavities oriented along PA ~10o and equatorial region at PA ~100o
stellar image due to amplification of background stellar photons

79. Conclusions strong support for the model of interacting stellar winds
interactions of bipolar outflow with the remnant shell quench the maser inside the biconical region and improve /induce the maser conditions at the biconical surface
the outburst appears to be a result of these interactions,
– the excitation of blobs in the remnant shell
VLBA polarimetric studies are required to explain a possible role of B field in this phenomenon
further EVN observations to monitor the outburst