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The apparent eta Carinae's long-term evolution and the critical role played by the strengthening of P Cygni absorption lines

A. Damineli, D. J. Hillier, F. Navarete, A. F. J. Moffat, G. Weigelt, T. R. Gull, M. F. Corcoran, N. D. Richardson, T. P. Ho, T. I. Madura, D. Espinoza-Galeas, H. Hartman, P. Morris, C. S. Pickett, I. R. Stevens, C. M. P. Russell, K. Hamaguchi, F. J. Jablonski, M. Teodoro, P. McGee, P. Cacella, B. Heathcote, K. Harrison, M. Johnston, T. Bohlsen, G. Di Scala

Submitted on 2 November 2022

Abstract

Over the entire 20th century, Eta Carinae (\ec) has displayed a unique spectrum, which recently has been evolving towards that of a typical LBV. The two competing scenarios to explain such evolution are: (1) a dissipating occulter in front of a stable star or (2) a decreasing mass loss rate of the star. The first mechanism simultaneously explains why the central star appears to be secularly increasing its apparent brightness while its luminosity does not change; why the Homunculus' apparent brightness remains almost constant; and why the spectrum seen in direct light is becoming more similar to that reflected from the Homunculus (and which resembles a typical LBV). The second scenario does not account for these facts and predicts an increase in the terminal speed of the wind, contrary to observations. In this work, we present new data showing that the P Cygni absorption lines are secularly strengthening, which is not the expected behaviour for a decreasing wind-density scenario. CMFGEN modelling of the primary's wind with a small occulter in front agrees with observations. One could argue that invoking a dissipating coronagraphic occulter makes this object even more peculiar than it already appears to be. However, on the contrary, it solves the apparent contradictions between many observations. Moreover, by assigning the long-term behaviour to circumstellar causes and the periodic variations due to binarity, a star more stable after the 1900s than previously thought is revealed, contrary to the earlier paradigm of an unpredictable object.

Preprint

Comment: 17 pages, 12 figures, submitted to MNRAS

Subjects: Astrophysics - Solar and Stellar Astrophysics; Astrophysics - Astrophysics of Galaxies

URL: http://arxiv.org/abs/2211.01445