Spatial and velocity coincidence of OH masers

1
Spatial and velocity coincidence of OH masers in
two star-forming regions, Cep A and W75N.
A. Niezurawska, M. Szymczak 1, R.J. Cohen and
A.M.S. Richards 2
1 Torun Centre for Astronomy, Poland 2 Jodrell
Bank Observatory, University of Manchester, UK
2
Cepheus A

• is a part of the Cepheus OB3 association (d725
  pc Blaauw et al. 1959)
• contains compact H II regions (e.g. Garay et al.
  1996 Torrelles et al. 1998)
• and OH and H2O maser sources (e.g. Cohen et al.
  1984 Argon et al. 2000)

W75N

• lies in the molecular cloud complex DR21-W75
  (d2 kpc
• Dickel et al. 1978)
• contains compact H II regions (e.g. Hunter et
  al. 1994 Torrelles et al. 1997)
• and OH and H2O maser sources (Baart et al. 1986
  Hutawarakorn et al. 2002)

Both sources showed 4765-MHz OH maser emission
(Szymczak et al. 2000).
3
Observations

• 5 or 6 antennas of MERLIN
• bandwidth 250-kHz (128 channels)
• phase referencing technique
• RMS noise few mJy beam-1
• Cep A
• January June 1999
• Freq. 4660-, 4750-, 4765-MHz and 1612-, 1665-,
  1667-
• and 1720-MHz
• W75N
• April 2000
• Freq. 4765-MHz

4

• Cep A
• 4.9-GHz continuum
• (Garay et al. 1996)
• masers
• - 22-GHz H2O
• (Torrelles et al. 1998)
• - 1665-MHz OH