Context : HCN is a major constituent of the circumstellar envelopes of carbon-rich evolved stars , and rotational lines from within its vibrationally excited states probe parts of these regions closest to the stellar surface .
A number of such lines are known to show maser action .
Historically , in one of them , the 177 GHz J = 2 \rightarrow 1 line in the l -doubled bending mode has been found to show relatively strong maser action , with results only published for a single object , the archetypical high-mass loss asymptotic giant branch ( AGB ) star IRC+10216 .

Aims : To examine how common 177 GHz HCN maser emission is , we conducted an exploratory survey for this line toward a select sample of carbon-rich asymptotic giant branch stars that are observable from the southern hemisphere .

Methods : We used the Atacama Pathfinder Experiment 12 meter submillimeter Telescope ( APEX ) equipped with a new receiver to simultaneously observe three J = 2 \rightarrow 1 HCN rotational transitions , the ( 0 , 1 ^ { { 1 } _ { c } } , 0 ) and ( 0 , 1 ^ { { 1 } _ { d } } , 0 ) l -doublet components , and the line from the ( 0 , 0 0 , 0 0 ) ground state .

Results : The ( 0 , 1 ^ { { 1 } _ { c } } , 0 ) maser line is detected toward 11 of 13 observed sources , which all show emission in the ( 0 , 0 0 , 0 0 ) transition .
In most of the sources , the peak intensity of the ( 0 , 1 ^ { { 1 } _ { c } } , 0 ) line rivals that of the ( 0 , 0 0 , 0 0 ) line ; in two sources , it is even stronger .
Except for the object with the highest mass-loss rate , IRC+10216 , the ( 0 , 1 ^ { { 1 } _ { c } } , 0 ) line covers a smaller velocity range than the ( 0 , 0 0 , 0 0 ) line .
The ( 0 , 1 ^ { { 1 } _ { d } } , 0 ) line , which is detected in four of the sources , is much weaker than the other two lines and covers a velocity range that is smaller yet , again except for IRC+10216 .
Compared to its first detection in 1989 , the profile of the ( 0 , 1 ^ { { 1 } _ { c } } , 0 ) line observed toward IRC+10216 looks very different , and we also appear to see variability in the ( 0 , 0 0 , 0 0 ) line profile ( at a much lower degree ) .
Our limited information on temporal variability , taken together with results for another HCN maser line from the literature , disfavors a strong correlation of maser and stellar continuum flux .

Conclusions : Maser emission in the 177 GHz J = 2 \rightarrow 1 ( 0 , 1 ^ { { 1 } _ { c } } , 0 ) transition of HCN appears to be common in carbon-rich AGB stars .
Like for other vibrationally excited HCN lines , our observations indicate that the origin of these lines is in the acceleration zone of the stellar outflow in which dust is forming .
For all the stars toward which we detect the maser line , the number of photons available at 7 and 14 \mu m , corresponding to transitions to vibrationally excited states possibly involved in its pumping , is found to be far greater than that of the maser photons , which makes radiative pumping feasible .
Other findings point to a collisional pumping scheme , however .