Unscrambling a Complex Young Stellar System

The top panel shows the spectrum of KH 15D during its "bright" phase, when the amount of direct starlight was greatest. The middle spectrum ("intermediate" phase) was taken when star B was just below the edge of the ring. Both spectra in the bottom panel were obtained during "faint" phases from two different cycles, when both stars were near periastron and the contribution from starlight was minimized. The spectrum from November has been offset by 1.5x10^-15 W m^-2 μm^-1 for comparison to the data from December.

Nicole Arulanantham of Wesleyan University (Middletown CT, USA) led a team that targeted the binary T Tauri system known as V582 Mon (KH 15D) with the Gemini Near-InfraRed Spectrograph (GNIRS) on Gemini North. Arulanantham et al. obtained data at three different orientations of the system’s two young stars – allowing the team to study a number of key aspects of this complicated system. These included; characterising the photosphere and magnetosphere of the companion star (B), exploring a jet of material associated with a bipolar outflow, and probing the scattering properties of the circumbinary ring. This led to the quantifying of an observed excess in near-infrared radiation that is likely the signature of a self-luminous hidden 10-Jupiter-mass protoplanet. While this unresolved planet displays the expected excess in infrared radiation, as well as a 2 micron spectral feature that may be due to methane or ammonia, other anticipated signs of these two compounds went undetected in the observations.

The team’s spectroscopic observations also revealed spectral features indicating a mixture of water and methane ice grains within the circumbinary ring where the frozen methane exists close enough to the primary stars that it must be shielded by dust from direct radiation.

In addition to determining that star B is an early-K type subgiant, the research revealed evidence that star B’s magnetosphere experienced variable helium I emission due to ongoing mass accretion. The team’s paper is accepted for publication in The Astrophysical Journal. The preprint is available here.