Lucky Imaging of the Multiple T Tauri System LkHα 262/LkHα 263


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Astronomers report high-spatial resolution, i' band imaging of the multiple T Tauri system LkHα 262/LkHα 263 obtained during the first commissioning period of the Adaptive Optics Lucky Imager (AOLI) at the William Herschel Telescope on September 24th and 25th, 2013. AOLI is a state-of-the-art instrument which combines two well-proven techniques for extremely high spatial resolution with ground-based telescopes: Lucky Imaging (LI) and Adaptive Optics (AO). Although the instrument was not yet complete, and was not operated in Adaptive-Optics mode, these observations demonstrate the high capabilities of the LI mode, yielding a FWHM for the best PSF of only 0.15 arcsec.

AOLI observed the multiple T Tauri system LkHα 262/LkHα 263. Astronomers obtained 4600 frames with an exposure time of 50 ms, giving a total on-source observation time of 230s. Using a standard LI algorithm, only 10% of the images were selected for building the final image.

Left: LkHα 262 (south) and LkHα 263 (north) image taken with LIRIS at the WHT in the 1.5 µ band (5 seconds integration time). Right: The same field as observed with AOLI. In this image, 10 per cent of 4600 individual 50 ms frames were selected for lucky imaging processing. Two components of LkHα263, A and B, are clearly resolved in the AOLI image. The dashed line indicates that the empty part of the field between LkHα 262 and 263 has been omitted. Scales in the four images are the same. Figure extracted from Velasco et al. (2016). Large format: PNG.

Velasco et al. (2016) find two resolved components, LkHα 263 A and B, at 0.41 arcsec separation, and marginal evidence for an unresolved binary or a disc in LkHα 262. The presence of discs in some of the components offers an interesting opportunity to investigate the formation and evolution of discs in the early stages of multiple very low-mass systems.

The AOLI data combined with previously available and newly obtained optical and infrared imaging show that the 3 components of LkHα 263 (A, B and double-disc) are co-moving, that there is orbital motion in the AB pair, and remarkably that LkHα 262/263 is a common proper-motion system with less than 1 mas/year relative motion. So this is likely a five-component gravitationally-bound system.

The AO system in AOLI is being commissioned at the WHT in 2016. The system includes a novel, low-order non-linear curvature wave-front sensor (WFS) together with a 241-actuator deformable mirror, a science array of four 1024×1024 EMCCDs, allowing a range of fields of view from 120×120 down to 36×36 arcseconds and a calibration subsystem.

Thanks to the revolutionary WFS, AOLI is able to use faint reference stars (I ∼ 16.5-17.5), and thus it can be used over a much wider part of the sky than with common Shack-Hartmann AO systems. Once AOLI is fully commissioned astronomers expect it will deliver images of only 0.04 arcsec FWHM, close to the diffraction limit of the WHT at the wavelength of the observations.

More information:

Velasco et al., 2016, "High spatial resolution optical imaging of the multiple T Tauri system LkHα 262/LkHα 263", MNRAS, doi: 10.1093/mnras/stw1071 [ arXiv ].
AOLI-related publications.