JWST Imaging of Earendel, the Extremely Magnified Star at Redshift $z=6.2$

Abstract

The gravitationally lensed star WHL0137-LS, nicknamed Earendel, was identified with a photometric redshift $z_{phot}=6.2\pm 0.1$ based on images taken with the Hubble Space Telescope. Here we present James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) images of Earendel in 8 filters spanning 0.8--5.0$\mu$m. In these higher resolution images, Earendel remains a single unresolved point source on the lensing critical curve, increasing the lower limit on the lensing magnification to $\mu >4000$ and restricting the source plane radius further to $r<0.02$ pc, or $\sim 4000$ AU. These new observations strengthen the conclusion that Earendel is best explained by an individual star or multiple star system, and support the previous photometric redshift estimate. Fitting grids of stellar spectra to our photometry yields a stellar temperature of $T_{\mathrm{eff}}\simeq 13000$--16000 K assuming the light is dominated by a single star. The delensed bolometric luminosity in this case ranges from $\log (L)=5.8$--6.6 $L_{\odot }$, which is in the range where one expects luminous blue variable stars. Follow-up observations, including JWST NIRSpec scheduled for late 2022, are needed to further unravel the nature of this object, which presents a unique opportunity to study massive stars in the first billion years of the universe.

Accepted to ApJL. Data products, lens models, and analysis code will be available online at https://cosmic-spring.github.io

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