SALT spectroscopy of the optical counterpart to MAXI J1803-289

ATel #14597; D. A. H. Buckley (South African Astronomical Observatory/University of Cape Town), J. Brink (UCT), P. A. Charles (University of Southampton), Daniel Groenewald (SAAO/SALT)
on 3 May 2021; 18:42 UT
Credential Certification: David Buckley (dibnob@saao.ac.za)

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On 2021 May 2, beginning at 22:56 UTC, we obtained two consecutive 1200 s exposures with the Robert Stobie Spectrograph on the Southern African Large Telescope (SALT) of the proposed optical counterpart of the new X-ray transient, MAXI J1803-289 (ATel #14587 and ATel #14588), reported by Gropp et al. (ATel #14591). The combined spectra cover the region 3500-7300Å, at a mean resolution of 5.7Å. We see emission features consistent with Bowen fluorescence and HeII 4686Å emission (both with E.W.s of about -3Å), plus an Hα P Cyg-like emission line with an E.W. of -5.5Å, with a prominent red peak shifted by 550 km/s. Weaker Hβ emission is also seen, again with a P Cyg-like profile in the first spectrum, but with a more double peaked structure in the second, where the blue and red peaks are separated by 1650 km/s. The spectrum is clearly consistent with that expected for a Low Mass X-ray Binary transient system and appears to exhibit variability over short timescales, deserving of more intensive followup observations.

The continuum rises to the red and absorption lines of CaII HK and strong NaD, plus the diffuse interstellar bands at 4430Å and 6285Å, are also present, consistent with a reddened source at a Galactic longitude and latitude of 1.5 and -4.3 degrees, respectively.

These observations were obtained under the SALT transient followup program.