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We investigate the characteristics of two newly discovered short-period,double-lined, massive binary systems, VFTS 450 (O9.7$\;$II--Ib$\,$+$\,$O7::)and VFTS 652 (B1$\;$Ib$\,+\,$O9:$\;$III:). We perform model-atmosphere analysesto characterise the photospheric properties of both members of each binary(denoting the `primary' as the spectroscopically more conspicuous component).Radial velocities and optical photometry are used to estimate the binary-systemparameters. We estimate $T_{\rm eff}=27$ kK, $\log{(g)}=2.9$ (cgs) for the VFTS450 primary spectrum (34kK, 3.6: for the secondary spectrum); and $T_{\rm eff}= 22$kK, $\log{(g)}=2.8$ for the VFTS 652 primary spectrum (35kK, 3.7: for thesecondary spectrum). Both primaries show surface nitrogen enrichments (of morethan 1 dex for VFTS 652), and probable moderate oxygen depletions relative toreference LMC abundances. We determine orbital periods of 6.89d and 8.59d forVFTS 450 and VFTS 652, respectively, and argue that the primaries must be closeto filling their Roche lobes. Supposing this to be the case, we estimatecomponent masses in the range $\sim$20--50M$_\odot$. The secondary spectra areassociated with the more massive components, suggesting that both systems arehigh-mass analogues of classical Algol systems, undergoing case-A masstransfer. Difficulties in reconciling the spectroscopic analyses with thelight-curves and with evolutionary considerations suggest that the secondaryspectra are contaminated by (or arise in) accretion disks.

The VLT-FLAMES Tarantula Survey. XXIII: two massive double-lined binaries in 30~Doradus