Eleven nearby ( < 300 pc ) , short-period ( 50–130 days ) asymptotic giant branch ( AGB ) stars were observed in the CO J = ( 2 - 1 ) line .
Detections were made towards objects that have evidence for dust production ( K _ { s } - [ 22 ] { \lower - 1.2 pt \vbox { \hbox { \hbox to 0.0 pt { $ > $ } \lower 5.0 pt \vbox { % \hbox { $ \sim$ } } } } } 0.55 mag ; AK Hya , V744 Cen , RU Crt , \alpha Her ) .
Stars below this limit were not detected ( BQ Gem , \epsilon Oct , NU Pav , II Hya , CL Hyi , ET Vir , SX Pav ) . K _ { s } - [ 22 ] colour is found to trace mass-loss rate to well within an order of magnitude .
This confirms existing results , indicating a factor of 100 increase in AGB-star mass-loss rates at a pulsation period of \sim 60 days , similar to the known ‘ superwind ’ trigger at \sim 300 days .
Between \sim 60 and \sim 300 days , an approximately constant mass-loss rate and wind velocity of \sim 3.7 \times 10 ^ { -7 } M _ { \odot } yr ^ { -1 } and \sim 8 km s ^ { -1 } is found .
While this has not been corrected for observational biases , this rapid increase in mass-loss rate suggests a need to recalibrate the treatment of AGB mass loss in stellar evolution models .
The comparative lack of correlation between mass-loss rate and luminosity ( for L { \lower - 1.2 pt \vbox { \hbox { \hbox to 0.0 pt { $ < $ } \lower 5.0 pt \vbox { \hbox { $ \sim$ } } } % } } 6300 L _ { \odot } ) suggests that the mass-loss rates of low-luminosity AGB-star winds are set predominantly by pulsations , not radiation pressure on dust , which sets only the outflow velocity .
We predict that mass-loss rates from low-luminosity AGB stars , which exhibit optically thin winds , should be largely independent of metallicity , but may be strongly dependent on stellar mass .