Proposal #557

Project: The 2025.7 periastron passage of eta Carine
Author: Augusto Damineli, IAGUSP/Brazil

This star is a prototype of LBV stars and is an eccentric binary (p=2023d e=0.9) with wind-wind collision. It has been brightening in the last 4 orbital cycles, revealing an increasingly prominent peak in photometry and line intensity. This seems to be due to the decreasing extinction of an occulter intervening in our line-of-sight (Damineli et al. 2024, Gull et al. 2023). The exact behavior of the light-curve is not presently known, especially the evolution of the U-V color index. The dissipating occulter covers the so-called bore-hole (Madura & Owocki 2012) which is expected to be a very hot spot revealing the sub-photosphere of the primary star. In the long-term, the bore hole should change to bluer the color index, especially the U-V, which measures the Balmer jump.

Observational strategy

Our goal is to monitor the UBV magnitude of eta Car through the year 2025 at a cadence of:
-1 visit per week in 01/January to 30/June
-1 visit per day in 01/July to 30/September
-1 visit per week in 1/October to 31/December

Since the comparison in the field (HD303308) is ~4 magnitudes weaker, we need 100 images per filter per visit to be coadded to do not degrade the signal-to-noise of the target. The comparison star is at 1 arcmin North of the target.

Exposure time
texp=0.05 sec in Every filter (to be adjusted after the first visit)

Target magnitudes : V=4.0; B=4.6; U=4.0
RA= 10h 45m 03.6s
DEC= -59° 41′ 04.3″