[en] The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf-Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014 when Star A (the LBV) eclipses Star B indicate that the fitted mass-loss rate and luminosity have reached the lowest values ever determined for such spectra: \dot{M} = 4.5 × 10[SUP]-5[/SUP]M_⊙ yr^{-1}, L = 1.7 × 10[SUP]6 [/SUP]L[SUB]⊙[/SUB]. In addition, the radius of the LBV's continuum-emitting region is similar to that derived from the eclipse light curves of the late 1970s. Hence, it appears to have attained a similar `low' state to that of the late 1970s. While a good fit to the emission spectrum is obtained using a CMFGEN model, there are discrepancies in the UV. In particular, the extent of the observed absorption profiles is ˜1000 km s[SUP]-1[/SUP] greater than predicted by the emission-line intensities. Further, HST UV observations obtained in 2016, when Star A is eclipsed by Star B, show unusual P Cygni profiles that are not easily explained. Surprisingly the 2016 emission-line spectrum is similar to that at the opposite eclipse obtained in 2014. The complex UV profiles are likely to arise as a consequence of the dynamics of the wind-wind collision and radiative braking, both of which will cause significant departures from spherical symmetry, and have a strong orbital phase dependence. However, other scenarios, such as intrinsically aspherical winds, cannot be ruled out.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Hillier, D. John ; Department of Physics and Astronomy & Pittsburgh Particle Physics, Astrophysics and Cosmology Center (PITT PACC), University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260, USA
Koenigsberger, Gloria; Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Ave. Universidad S/N, Cuernavaca, Morelos 62210, México
Nazé, Yaël ; Université de Liège - ULiège > Groupe d'astrophysique des hautes énergies (GAPHE)
Morrell, Nidia; Las Campanas Observatory, Carnegie Observatories, Colina El Pino, Casilla 601, La Serena, Chile
Barbá, Rodolfo H.; Departamento de Física y Astronomía, Av. Juan Cisternas 1200 Norte, Universidad de la Serena, La Serena, Chile
Gamen, Roberto; Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, and Instituto de Astrofísica de La Plata CCT La Plata, CONICET-UNLP, Paseo del Bosque S/N, B1900FWA La Plata, Argentina)
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