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The stability of the He II 4686 line emission across periastron passages in eta Carinae

ATel #6380; Mairan Teodoro (NASA/GSFC), Bernard Heathcote (SASER), Noel Richardson (U. of Montreal), Rodrigo Prates (LNA), Augusto Damineli (IAG/USP), Gabriel Hickel (Univ. Federal de Itajuba), Terry Bohlsen (SASER), Paul Luckas (SASER), Malcolm Locke (SASER), Felipe Navarete (IAG/USP), Julian West (SASER), Thiago A. Andrade (IAG/USP), Adriano M. Coimbra (LNA), Eduardo Fernandez-Lajus (Univ. Nacional de La Plata), Theodore Gull (NASA/GSFC), Francisco Jablonski (DAS/INPE), Michael F. Corcoran (NASA/GSFC-CRESST/USRA), Jose H. Groh (U. of Geneva), Kenji Hamaguchi (NASA/GSFC-CRESST/UMBC), Thomas Madura (NASA/GSFC/NPP), Lucas St-Jean (U. of Montreal), Gerd Weigelt (MPIfR)
on 11 Aug 2014; 12:36 UT
Credential Certification: Mairan Teodoro (mairan.teodoro@gmail.com)

Subjects: Optical, Binary, Star, Variables

Referred to by ATel #: 6408, 6464

Preliminary analysis of data from the international campaign to monitor eta Carinae through the 2014 event shows that, as expected, the equivalent width of the He II 4686 emission line has reached its minimum strength on JD=2456870.8 (August 01 2014). A comparative analysis of the current event with the other two well time-sampled past events (2003.5 and 2009.0; see Teodoro et al 2012, ApJ, 746(1), 73) indicates that the period derived from the He II 4686 is 2023.18 +/- 0.86 days, which is in excellent agreement with all of other measurements of the period employing different methods (e.g. radio, optical, and X-ray light curves, disappearance of the narrow components of He I lines). Comparison between recent ground based and STIS/HST data shows that the He II 4686 line emission is a point source within 0.1 arcsec. Thus, phase-locked changes in this line are produced within a region less than 230 AU (assuming a distance of 2350 pc) in radius around the binary system, and probably much smaller than that upper limit. The stability of the He II 4686 equivalent width variations with phase makes it unlikely that large changes in the primary mass-loss rate have occurred over the last 16.5 years (see Madura et al. 2013, MNRAS, 436(4), 3820–3855). The temporary recovering of the He II 4686 line strength has already started (within the expected time frame, as seen in past cycles), and we anticipate it to reach a local maximum between late August and early september. Shortly thereafter, the equivalent width is expected to weaken again reaching a basal level (less than 0.1 Angstrom) by early October, remaining at this low level until approach of the next periastron event in 2020. We encourage spectroscopic monitoring over the next several months to quantify these expected variations.

eta Car 2014 international campaign