Using the 1.3m and 2.4m telescopes of the MDM Observatory, we identified the
close companions of two eclipsing millisecond radio pulsars discovered by the
Green Bank Telescope in searches of Fermi Gamma-ray Space Telescope sources,
and measured their light curves. PSR J1301+0833 is a black widow pulsar in a
6.5 hr orbit whose companion star is strongly heated on the side facing the
pulsar. It varies from R = 21.8 to R > 24 around the orbit. PSR J1628-3205 is a
"redback," a nearly Roche-lobe filling system in a 5.0 hr orbit whose optical
modulation in the range 19.0 < R < 19.4 is dominated by strong ellipsoidal
variations, indicating a large orbital inclination angle. PSR J1628-3205 also
shows evidence for a long-term variation of about 0.2 mag, and an asymmetric
temperature distribution possibly due to either off-center heating by the
pulsar wind, or large starspots. Modelling of its light curve restricts the
inclination angle to i > 55 degrees, the mass of the companion to 0.16 < M_c <
0.30 M_sun, and the effective temperature to 3560 < T_eff < 4670 K. As is the
case for several redbacks, the companion of PSR J1628-3205 is less dense and
hotter than a main-sequence star of the same mass.Comment: 9 pages, 5 figures, accepted for publication in Ap
