Three Short Period Miras $-$ Z Aql, RZ Sco and R Cet: Water Maser Emission and its Implications

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Session 81 -- YSO's, Masers and Molecules
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[81.14] Three Short Period Miras $-$ Z Aql, RZ Sco and R Cet: Water Maser Emission and its Implications

I.R. Little-Marenin (Wellesley C), J.A. Mattei (AAVSO), R.R. Cadmus, Jr. (Grinnell C.)

We have monitored the 22 GHz water maser emission line from three short-period Miras since their detection in 1986/1987. These are: Z Aql (M3e; P=129 days; V(LSR)=8 km/sec), RZ Sco (M3e; P=160 days; V(LSR)=$-$163 km/sec) and R Cet (M4e; P=166 days; V(LSR)=31 km/sec). The water maser emission from all three stars is highly variable and varies in phase with the optical light curve. However, all three stars appear to show a phase lag of $0.3-0.4$ phase between the optical maximum and the maximum of the water maser emission. Water maser emission from Miras with periods $<$ 200 days is quite rare. Of the 58 short period Miras searched for water maser emission by us, only five were detected. Aside from the three mentioned above, we have also detected SV Pup (M5e; P=167 days, V(LSR)=29 km/sec) and S Sco (M3e; P=177 days; V(LSR)=174 km/sec). The detection rate of about 10\% for Miras with periods $<$ 200 days is low compared to the detection rate of about 30\% for Miras with periods $>$ 200 days. Analysis of the kinematics of Miras appears to indicate that the shorter period Miras are predominately pop II stars and are often observed as high velocity stars. Two out of the five stars (RZ Sco and S Sco) have Local Standard of Rest (LSR) velocities $>\mid160\mid$ km/sec. However, the other three have LSR velocities $<\mid 31\mid$ km/sec. Hence, it is not clear if lower metallicity in stars is the cause for the less likely production of maser emission in short period Miras. It has also been suggested that water maser emission is preferentially detected from bolometrically bright stars. However, neither R Cet nor RZ Sco are exceptionally bright (m(bol)=5.8 and 7.0) and these magnitudes are typical for Miras in this period range. The infrared colors of these short period Miras are also in line with the IR colors of the longer period Miras with water maser emission. Other implications of water maser emission associated with short-period Miras will be discussed.

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