In a recent paper describing HST observations of Cepheids in the spiral galaxy NGC 4258 , Newman et al . ( 2001 ) report that the revised calibrations and methods for the Key Project on the Extragalactic Distance Scale yield that the true distance modulus of this galaxy is \mu _ { 0 , 4258 } = 29.40 \pm 0.09 mag , corresponding to a metric distance of 7.6 \pm 0.3 Mpc .
This Cepheid distance , which holds for 18.50 mag as the true distance modulus of the Large Magellanic Cloud ( LMC ) , is not significantly larger than 7.2 \pm 0.5 Mpc , the value determined by Herrnstein et al . ( 1999 ) from purely geometric considerations on the orbital motions of water maser sources .
However , if the metallicity difference \Delta [ O/H ] \sim 0.35 between NGC 4258 and LMC is taken into account , then the Key Project methods lead to a metallicity-corrected value of \mu _ { 0 , 4258 } = 29.47 \pm 0.09 mag , with \mu _ { 0 ,LMC } =18.50 mag , namely to a Cepheid distance of 7.8 \pm 0.3 Mpc which is 1.2 \sigma from the maser determination .
One might argue that these results are suggesting that a smaller distance to the LMC , \mu _ { 0 ,LMC } \sim 18.3 mag , should be used to calibrate the Cepheid brightness ( see , e.g. , Paczynski 1999 ) .
However , even though the well known controversy between short and long distance scale is far from being settled and current determinations of the LMC distance modulus are spanning \sim 0.4 mag , it seems that the various empirical methods converge on the value adopted by the Key Project ( see Carretta et al .
2000 ) .
In this paper we show that the metallicity correction on Cepheid distance determinations , as suggested by pulsation models with three different chemical abundances ( Y =0.25 , Z =0.004 ; Y =0.25 , Z =0.008 ; Y =0.28 , Z =0.02 ) , might provide the natural way of reaching a close agreement between Cepheid and maser distance to NGC 4258 for a wide variety of LMC distance determinations .
In fact , by adopting \mu _ { 0 ,LMC } = 18.50 \pm 0.10 mag we derive a Cepheid distance of 7.3 \pm 0.6 Mpc which is only 0.2 \sigma from the maser determination , while using \mu _ { 0 ,LMC } = 18.60 \pm 0.10 mag or 18.40 \pm 0.10 the Cepheid and maser distances are 0.8 \sigma and 0.4 \sigma , respectively , apart .