Can the dust eclipses in WR 104 provide constraints on the system's inclination?

Abstract

When two massive stars orbit each other, their winds create a shock cone. In some cases, an evolved, carbon-rich Wolf-Rayet (WR) star's wind collides with that of an orbiting OB star, condensing into dust downstream. This dust is then seen as large spiral structures that eventually move into the interstellar medium. Among these colliding wind binaries, the archetype system WR104 has become an enigma. Aperture masking interferometry with Keck revealed an evolving face-on dust spiral with multiple rungs of dust visible from years of observations. In contrast to direct imagery, recent spectroscopic results implied that the orbit must have an inclination quite different from the face-on geometry. We examined the ASAS and ASAS-SN photometry to put further constraints on the geometry of the orbit. Through a phase-binning of the light curve, we find that the recent g-band light curve is brightest at a time when the OB star is in front of the WR star in our line of sight, with the lowest flux happening at the opposite conjunction. We fit the light curve with an illustrative model for scattering eclipses, which then allows us to infer an inclination of the system of $(41.8^{+13.0}_{-14.9})^\circ$. This inclination agrees with the recent spectroscopic orbit and presents challenges to previous interpretations of high-angular resolution images of the dust plume. We provide a qualitative geometric model for the dust plume to reconcile these results and show how WR104 can provide a means to study the properties of WR dust in detail.

Figures (6)

• Figure 1: The optical SED of WR 104 from 1987ApJS...65..459T normalized in the 4500-4600Å region along with scaled transmission curves for both the optical $g$- (dashed line) and $V$-bands (dotted line) overplotted. The SED from 1987ApJS...65..459T came with both blue and red observations which are shown in those respective colors.
• Figure 2: The $V-$ and $g$-band light curve of WR 104 observed by 2002PASJ...54L..51K, ASAS, and ASAS-SN. The expected "uneclipsed" light levels for each bandpass is shown as a dotted line ($V$) and a blue dashed line ($g$). In addition to the JD that is shown on the x-axis, we include the orbital phase relative to the ephemeris of Hill on the upper x-axis. Error bars are included, but are smaller than the points used for ASAS and ASAS-SN data. The errors from 2002PASJ...54L..51K were estimated at 0.2--0.3 in their analysis and we plot their data with 0.25 mag error bars.
• Figure 3: ASAS-SN $g$-band photometry phased to the ephemeris of Hill shown as points in the top panel. The colored lines each indicate the cycle-to-cycle variations in the observed flux. The bottom panel shows the mean in twenty phase bins as dark bold points, the median in each phase bin as a red diamond, along with the standard deviation of the data from the same bin.
• Figure 4: The results of the emcee sampler. Various fits are shown in red dotted lines. The most probable fit is shown in the thick blue line.
• Figure 5: The resulting plot showing the parameter space sampled and the most likely model parameters.