Ground-based spectroscopic monitoring of the 2020 periastron in eta Carinae

ATel #13600; Felipe Navarete (IAG/USP), Augusto Damineli (IAG/USP), Noel Richardson (ERAU), Nour Ibrahim (ERAU), Bernard Heathcote (SASER), Giorgio Di Scala (SASER), Ken Harrison (SASER), Lidia Di Scala (SASER), Mark Johnston (SASER), Padric McGee (SASER/Adelaide Uni.), Paulo Cacella (SASER), Terry Bohlsen (SASER), Markus Rabus (LCOGT), Tim Brown (LCOGT)
on 30 Mar 2020; 16:17 UT
Credential Certification: Felipe Navarete (navarete@usp.br)

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Based on a high signal-to-noise and high plus intermediate resolution (R=100,000 and R>6,000) ground-based monitoring of eta Carinae periastron (ATEL #13508), we report the following results:

Representative lines of the extended primary's photosphere, (H-δ and SiIIλ6347A) indicate no significant changes as compared to the 2014.5 (Teodoro et al. 2016, ApJ 819, 131).
The HeIIλ4686A light curve, produced by the wind-wind collision and the borehole, exhibited an increase in the main peak (P2), similar to what was reported by Teodoro et al. (2016) for the 2014.5 periastron. Major changes occurred in the P3 peak, which was shifted to 9 days earlier (centered on JD=2458916.672) than expected.
Spectacular changes occurred in the narrow absorption features in the lines H-α (5 times fainter than in 2014.5) and NaD1λ5895.9A (equivalent width reached almost zero levels). These features are centered at RV= -150 km/s, probably in the Little Homunculus. Our guess is that this was caused by the dissipation of the natural coronagraph in front of eta Car, as described in Damineli et al. (2019, MNRAS, 484, 1325).
This strongly supports the scenario that the primary star is not evolving significantly in scales of decades, as opposed to dramatic changes in the circumstellar ejecta.

We encourage spectroscopic monitoring of these specific spectral lines over the next several months to quantify these expected variations, especially considering that all professional facilities are closed because of the COVID-19 pandemic. This work is sponsored by FAPESP Foundation under projects 2019/02029-2 (AD) and 2017/18191-8 (FN).