The TWA 3 Young Triple System: Orbits, Disks, Evolution

Abstract

We have characterized the spectroscopic orbit of the TWA 3A binary and provide preliminary families of probable solutions for the TWA 3A visual orbit, as well as for the wide TWA 3A-B orbit. TWA 3 is a hierarchical triple located at 34 pc in the ∼10 Myr old TW Hya association. The wide component separation is 1 55; the close pair was first identified as a possible binary almost 20 years ago. We initially identified the 35-day period orbital solution using high-resolution infrared spectroscopy that angularly resolved the A and B components. We then refined the preliminary orbit by combining the infrared data with a reanalysis of our high-resolution optical spectroscopy. The orbital period from the combined spectroscopic solution is ∼35 days, the eccentricity is ∼0.63, and the mass ratio is ∼0.84; although this high mass ratio would suggest that optical spectroscopy alone should be sufficient to identify the orbital solution, the presence of the tertiary B component likely introduced confusion in the blended optical spectra. Using millimeter imaging from the literature, we also estimate the inclinations of the stellar orbital planes with respect to the TWA 3A circumbinary disk inclination and find that all three planes are likely misaligned by at least ∼30°. The TWA 3A spectroscopic binary components have spectral types of M4.0 and M4.5; TWA 3B is an M3. We speculate that the system formed as a triple, is bound, and that its properties were shaped by dynamical interactions between the inclined orbits and disk.

On the diversity and statistical properties of protostellar discs

“…Evidence for misalignment is also starting to be found in both closer and younger multiple systems. The Class II triple system TWA 3 (Kellogg et al 2017) consists of a spectroscopic (35-day) binary with a circumbinary disc and a disc-less low-mass companion star at ≈ 50 au, with evidence that the disc and the orbits are misaligned by at least 30…”

Accretion Kinematics in the T Tauri Binary TWA 3A: Evidence for Preferential Accretion onto the TWA 3A Primary

“…References-(1) Kellogg et al (2017), (2) a The T peri value presented is 42 orbital periods prior to the value in Kellogg et al (2017), placing the earliest archival spectra at an orbital cycle of zero. The error is assumed to be the same.…”

“…Table 3 provides a list of the FEROS observation dates, their orbital cycles and phases, and select spectroscopic measurements. For a full description of these data we refer readers to Kellogg et al (2017). We note that due to the FEROS 2 fiber, these spectra also contain flux from TWA 3B.…”

“…In short, we find that the component flux ratio is recovered most readily by the template that provides the best radial-velocity precision for the primary star, determined from order-to-order measurement stability. Fortunately, this issue is somewhat mitigated by the small range in spectral types of the TWA 3 components (M3.0-M4.5; Kellogg et al 2017).…”

“…Blue, red and green points mark the primary (TWA 3Aa), secondary (TWA 3Ab), and tertiary (TWA 3B), respectively. The γ velocity (dotted line), orbital solution (dashed lines), and green band, representing the standard deviation of CfA RV measurements of TWA 3B, are from Kellogg et al (2017).…”