On the mass of moderately rotating strange stars in the MIT bag model and LMXBs

We compute the maximum mass of moderately rotating strange stars as a function of the strange quark mass, of the QCD coupling constant, ${\alpha }_c$, and of the bag constant (vacuum energy density), $B$, in the MIT bag model of quark matter with lowest order quark-gluon interactions. For a fixed value of $B$, the maximum stellar mass depends only weakly on ${\alpha }_c$, and is independent of this coupling in the limit of massless quarks. However, if it is the value of the chemical potential of quark matter at zero pressure which is held constant, for example at the value corresponding to the stability limit of nucleons against conversion to quark matter, the maximum mass of the strange star is higher by up to 25% for ${\alpha }_c=0.6$, than for non-interacting quarks, and this may be relevant in the discussion of kHz QPO sources. The maximum mass of a non-rotating strange star could be sufficiently high to allow an orbital frequency as low as 1.0 kHz in the marginally stable orbit. However, for all ${\alpha }_c<0.6$, the stellar mass cannot exceed $2.6M_{\odot }$ at any rotational period $\ge 1.6$ms.