Optical Spectra of MAXI J1820+070 with Keck

ATel #11425; Peter Garnavich and Colin Littlefield (Notre Dame)
on 16 Mar 2018; 02:41 UT
Credential Certification: Colin Littlefield (clittlef@alumni.nd.edu)

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We obtained spectra of the new X-ray transient MAXI J1820+070 (ATel #11399) with the Keck I telescope and LRIS spectrograph on March 15.6 (UT). The spectra have a resolution of 3 Ang and cover 3500 to 8000 Ang. The continuum dominates the light, but low-equivalent-width emission features are also seen. We confirm the presence of a broad, asymmetric H-alpha emission line (ATel #11424). We also detect broad H-beta, H-gamma, and H-delta absorption with emission lines in the center, characteristic of an accretion disk in outburst. He II 4686 (with EW = -1.7 Ang) is seen on top of the continuum. We also see deep Ca II interstellar absorption in the blue, suggesting significant extinction along the line-of-sight.

We thank Josh and Cynthia at the Keck Observatory for helping to obtain these observations.