Laser Guide Star Adaptive Optics Integral Field Spectroscopy of a Tightly Collimated Bipolar Jet from the Herbig Ae star LkHa 233

TL;DR

This study uses high-resolution integral field spectroscopy with adaptive optics to analyze the collimated bipolar jet and circumstellar disk of the Herbig Ae star LkHa 233, revealing jet properties, disk inclination, and implications for stellar properties.

Contribution

First detailed high-resolution IR imaging of LkHa 233's jet and disk, providing insights into jet collimation, asymmetry, and disk orientation around a Herbig Ae star.

Findings

Jet is narrow with a 9-degree opening angle and ~100 km/s velocity.

Detected asymmetry between jet and counterjet, with the red-shifted jet being clumpier.

Estimated disk inclination at 65 degrees, affecting stellar luminosity and distance estimates.

Abstract

We have used the integral field spectrograph OSIRIS and laser guide star adaptive optics at Keck Observatory to obtain high angular resolution (0.06"), moderate spectral resolution (R ~ 3800) images of the bipolar jet from the Herbig Ae star LkHa 233, seen in near-IR [Fe II] emission at 1.600 & 1.644 microns. This jet is narrow and tightly collimated, with an opening angle of only 9 degrees, and has an average radial velocity of ~ 100 km/s. The jet and counterjet are asymmetric, with the red-shifted jet much clumpier than its counterpart at the angular resolution of our observations. The observed properties are in general similar to jets seen around T Tauri stars, though it has a relatively large mass flux of (1.2e-7 +- 0.3e-7) M_sun/year, near the high end of the observed mass flux range around T Tauri stars. We also spatially resolve an inclined circumstellar disk around LkHa 233, which obscures the star from direct view. By comparison with numerical radiative transfer disk models, we estimate the disk midplane to be inclined i = 65 +- 5 degrees relative to the plane of the sky. Since the star is seen only in scattered light at near-infrared wavelengths, we detect only a small fraction of its intrinsic flux. Because previous estimates of its stellar properties did not account for this, either LkHa 233 must be located closer than the previously believed, or its true luminosity must be greater than previously supposed, consistent with its being a ~4 M_sun star near the stellar birthline.