Optical and Radio Observations of the T Tauri Binary KH 15D (V582 Mon): Stellar Properties, Disk Mass Limit and Discovery of a CO Outflow

TL;DR

This study combines optical and radio observations of the KH 15D binary system, revealing the full emergence of Star B, constraining disk mass, and discovering a CO outflow aligned with optical polarization, advancing understanding of T Tauri star environments.

Contribution

First CCD-era measurement of Star B’s luminosity and color during emergence, and first high-sensitivity radio detection of a CO outflow in KH 15D, linking optical polarization with outflow orientation.

Findings

Star B fully emerges from the circumbinary ring during apastron.

Circumbinary disk mass is limited to less than 1.7 Jupiter masses.

Detected a CO outflow aligned with optical polarization and nearly orthogonal to the circumbinary ring.

Abstract

We present VRIJHK photometry of the KH 15D T Tauri binary system for the 2015/16 and 2016/17 observing seasons. For the first time in the modern (CCD) era we are seeing Star B fully emerge from behind the trailing edge of the precessing circumbinary ring during each apastron passage. We are, therefore, able to measure its luminosity and color. Decades of photometry on the system now allow us to infer the effective temperature, radius, mass and age of each binary component. We find our values to be in good agreement with previous studies, including archival photographic photometry from the era when both stars were fully visible, and they set the stage for a full model of the system that can be constructed once radial velocity measurements are available. We also present the first high sensitivity radio observations of the system, taken with ALMA and the SMA. The respective 2.0 and 0.88 mm observations provide an upper limit on the circumbinary (gas and dust) disk mass of 1.7 Jupiter masses and reveal an extended CO outflow which overlaps with the position, systemic velocity and orientation of the KH 15D system and is certainly associated with it. The low velocity, tight collimation, and extended nature of the emission suggest that the outflow is inclined nearly orthogonal to the line of sight, implying it is also orthogonal to the circumbinary ring. The position angle of the radio outflow also agrees precisely with the direction of polarization of the optical emission during the faint phase. A small offset between the optical image of the binary and the central line of the CO outflow remains as a puzzle and possible clue to the jet launching mechanism.