Orbital solution leading to an acceptable interpretation for the enigmatic gamma-ray binary HESS J0632+057

High-dispersion spectroscopic monitoring of HESS J0632+057 has been carried out over four orbital cycles in order to search for orbital modulation, covering the entire orbital phase. We have measured the radial velocity of the H alpha emission line with the method introduced by Shafter, Szkody, and Thorstensen (1986, ApJ, 308, 765), which has been successfully applied to some Be stars. The velocity is seen to increase much earlier than expected for the orbital period of 315 d, and much more steeply than expected at around apastron. The period of the H alpha modulation is found to be 308(-23)(+26) d. We have also analyzed Swift/XRT data from 2009 to 2015 to study the orbital modulation, selecting the data with good statistics (>= 30 counts). With additional two-year data to the previous works, the orbital period has been updated to 313(-8)(+11) d, which is consistent with the previous X-ray periods and the spectroscopic one. Previous XMM-Newton and Chandra observations prefer a period of 313 d. With the new period, assuming that H alpha velocities accurately trace the motion of the Be star, we have derived a new set of orbital parameters. In the new orbit, which is less eccentric (e similar or equal to 0.6), two outbursts occur: after apastron and just after periastron. Also, the column density in bright phase (4.7(-08)(+0.9) x 10(21) cm(-2)) is higher than in faint phase (2.2 +/- 0.5 x 10(21) cm(-2)). These facts suggest that outbursts occur when the compact object passes nearby/through the Be disk. The mass function implies that the mass of the compact object is less than 2.5 M-circle dot, assuming that the mass of the Be star is 13.2-18.2 M-circle dot (Aragona et al. 2010, ApJ, 724, 306), unless the inclination is extremely small. The photon index indicates that the spectra become softer when the system is bright. These suggest that the compact object is a pulsar.