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Register a new userOrbital Motion, Variability, and Masses in the T Tauri Triple System
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We present results from adaptive optics imaging of the T Tauri triple system obtained at the Keck and Gemini Observatories in 2015-2019. We fit the orbital motion of T Tau Sb relative to Sa and model the astrometric motion of their center of mass relative to T Tau N. Using the distance measured by Gaia, we derived dynamical masses of M_Sa = 2.05 +/- 0.14 Msun and M_Sb = 0.43 +/- 0.06 Msun. The precision in the masses is expected to improve with continued observations that map the motion through a complete orbital period; this is particularly important as the system approaches periastron passage in 2023. Based on published properties and recent evolutionary tracks, we estimate a mass of ~ 2 Msun for T Tau N, suggesting that T Tau N is similar in mass to T Tau Sa. Narrow-band infrared photometry shows that T Tau N remained relatively constant between late 2017 and early 2019 with an average value of K = 5.54 +/- 0.07 mag. Using T Tau N to calibrate relative flux measurements since 2015, we found that T Tau Sa varied dramatically between 7.0 to 8.8 mag in the K-band over timescales of a few months, while T Tau Sb faded steadily from 8.5 to 11.1 mag in the K-band. Over the 27 year orbital period of the T Tau S binary, both components have shown 3-4 magnitudes of variability in the K-band, relative to T Tau N.
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We present a multi-wavelength analysis to reveal the nature of the enigmatic T Tauri triple star system. New optical and infrared measurements are coupled with archival X-ray, UV and mm datasets to show morphologies of disk material and outflow kinematics. A dark lane of obscuring material is seen in silhouette in several emission lines and in model-subtracted ALMA mm continuum dust residuals near the position of T Tau Sa+Sb, revealing the attenuating circumbinary ring around T Tau S. The flux variability of T Tau S is linked in part to the binary orbit; T Tau Sb brightens near orbital apastron as it emerges from behind circumbinary material. Outflow diagnostics confirm that T Tau N powers the blue-shifted western outflow, and the T Tau S binary drives the northwest-southeastern flow. Analysis of the southern outflow shows periodic arcs ejected from the T Tau system. Correlation of these arc locations and tangential kinematics with the orbit timing suggests that launch of the last four southern outflow ejections is contemporaneous with, and perhaps triggered by, the T Tau Sa+Sb binary periastron passage. We present a geometry of the T Tau triple that has the southern components foreground to T Tau N, obscured by a circumbinary ring, with mis-aligned disks and interacting outflows. Particularly, a wind from T Tauri Sa that is perpendicular to its circumstellar disk might interact with the circumbinary material, which may explain conflicting high contrast measurements of the system outflows in the literature. T Tauri is an important laboratory to understand early dynamical processes in young multiple systems. We discuss the historical and future characteristics of the system in this context.
We present new astrometric measurements of the components in the T Tauri system, and derive new orbits and masses. T Tauri was observed during the science verification time of the new extreme adaptive optics facility SPHERE at the VLT. We combine the new positions with recalibrated NACO-measurements and data from the literature. Model fits for the orbits of T Tau Sa and Sb around each other and around T Tau N yield orbital elements and individual masses of the stars Sa and Sb. Our new orbit for T Tau Sa/Sb is in good agreement with other recent results, which indicates that enough of the orbit has been observed for a reliable fit. The total mass of T Tau S is 2.65+/-0.11 Msun. The mass ratio M_Sb:M_Sa is 0.25+/-0.03, which yields individual masses of M_Sa = 2.12+/-0.10 Msun and M_Sb = 0.53+/-0.06 Msun. If our current knowledge of the orbital motions is used to compute the position of the southern radio source in the T Tauri system, then we find no evidence for the proposed dramatic change in its path.
We investigate the binary star T Tauri South, presenting the orbital parameters of the two components and their individual masses. We combined astrometric positions from the literature with previously unpublished VLT observations. Model fits yield the orbital elements of T Tau Sa and Sb. We use T Tau N as an astrometric reference to derive an estimate for the mass ratio of Sa and Sb. Although most of the orbital parameters are not well constrained, it is unlikely that T Tau Sb is on a highly elliptical orbit or escaping from the system. The total mass of T Tau S is rather well constrained to 3.0 +0.15/-0.24 M_sun. The mass ratio Sb:Sa is about 0.4, corresponding to individual masses of M_Sa = 2.1+/-0.2 M_sun and M_Sb = 0.8+/-0.1 M_sun. This confirms that the infrared companion in the T Tauri system is a pair of young stars obscured by circumstellar material.
T Tauri has long been the prototypical young pre-main-sequence star. However, it has now been decomposed into a triple system with a complex disk and outflow geometry. We aim to measure the brightness of all three components of the T Tauri system (T Tau N, T Tau Sa, T Tau Sb) in the mid-infrared in order to obtain photometry around the $sim 9.7~mu m$ silicate feature. This allows us to study their variability and to investigate the distribution of dust and the geometry of circumstellar and circumbinary disks in this complex system. We observe T Tauri with the VLT/VISIR-NEAR instrument. With kernel phase interferometry post-processing of the data, and using the astrometric positions of all three components from VLT/SPHERE, we measure the three components individual brightnesses (including the southern binary at an angular separation down to $sim 0.2~lambda/D$) and obtain their photometry. In order to validate our methods, we simulate and recover mock data of the T Tauri system using the observed reference point-spread function of HD 27639. We find that T Tau N is rather stable and shows weak silicate emission, while T Tau Sa is highly variable and shows prominent silicate absorption. T Tau Sb became significantly fainter compared to data from 2004 and 2006, suggesting increased extinction by dust. The precision of our photometry is limited by systematic errors, which is consistent with previous studies using kernel phase interferometry. Our results confirm the complex scenario of misaligned disks in the T Tauri system that had been observed previously, and they are in agreement with the recently observed dimming of T Tau Sb in the near-infrared. Our mid-infrared photometry supports the interpretation that T Tau Sb has moved behind the dense region of the Sa-Sb circumbinary disk on its tight orbit around Sa, therefore suffering increased extinction.
The immediate vicinity of T Tauri was observed with the new high-contrast imaging instrument SPHERE at the VLT to resolve remaining mysteries of the system, such as the putative small edge-on disk around T Tauri Sa, and the assignment of the complex outflow patterns to the individual stars. We used SPHERE IRDIS narrow-band classical imaging in Pa$beta$, Br$gamma$, and the $ u$ = 1-0 S(1) line of H$_2$, as well as in the nearby continua to obtain high spatial resolution and high contrast images over the NIR spectral range. Line maps were created by subtracting the nearby continuum. We also re--analyzed coronagraphic data taken with SPHEREs integral field spectrograph in $J$- and $H$-band with the goal to obtain a precise extinction estimate to T Tauri Sb, and to verify the recently reported claim of another stellar or substellar object in the system. A previously unknown coiling structure is observed southwest of the stars in reflected light, which points to the vicinity of T Tauri N. We map the circumbinary emission from T Tauri S in $J$- and $H$-band scattered light for the first time, showing a morphology which differs significantly from that observed in $K$-band. H$_2$ emission is found southwest of the stars, near the coiling structure. We also detect the H$_2$ emitting region T Tauri NW. The motion of T Tauri NW with respect to T Tauri N and S between previous images and our 2014 data, provides strong evidence that the Southeast-Northwest outflow triggering T Tauri NW is likely to be associated with T Tauri S. We further present accurate relative photometry of the stars, confirming that T Tauri Sa is brightening again. Our analysis rules out the presence of the recently proposed companion to T Tauri N with high confidence.
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