分类： 天文学 >> 天文学 提交时间： 2023-02-19
Brian Welch
Dan Coe
Jose M. Diego
Adi Zitrin
Erik Zackrisson
Paola Dimauro
Yolanda Jimenez-Teja
Patrick Kelly
Guillaume Mahler
Masamune Oguri
F. X. Timmes
Rogier Windhorst
Michael Florian
S. E. DeMink
Roberto J. Avila
Jay Anderson
Larry Bradley
Keren Sharon
Anton Vikaeus
Stephan McCandliss
摘要： Galaxy clusters magnify background objects through strong gravitational lensing. Typical magnifications for lensed galaxies are factors of a few but can also be as high as tens or hundreds, stretching galaxies into giant arcs. Individual stars can attain even higher magnifications given fortuitous alignment with the lensing cluster. Recently, several individual stars at redshift $z \sim 1 - 1.5$ have been discovered, magnified by factors of thousands, temporarily boosted by microlensing. Here we report observations of a more distant and persistent magnified star at redshift $z_{\rm phot} = 6.2 \pm 0.1$, 900 Myr after the Big Bang. This star is magnified by a factor of thousands by the foreground galaxy cluster lens WHL0137--08 ($z = 0.566$), as estimated by four independent lens models. Unlike previous lensed stars, the magnification and observed brightness (AB mag 27.2) have remained roughly constant over 3.5 years of imaging and follow-up. The delensed absolute UV magnitude $M_{UV} = -10 \pm 2$ is consistent with a star of mass $M > 50 M_{\odot}$. Confirmation and spectral classification are forthcoming from approved observations with the James Webb Space Telescope
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Brian Welch
Dan Coe
Erik Zackrisson
S. E. de Mink
Swara Ravindranath
Jay Anderson
Gabriel Brammer
Larry Bradley
Jinmi Yoon
Patrick Kelly
Jose M. Diego
Rogier Windhorst
Adi Zitrin
Paola Dimauro
Yolanda Jimenez-Teja
Abdurro'uf
Mario Nonino
Ana Acebron
Felipe Andrade-Santos
Roberto J. Avila
摘要： 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.
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