American Association of Variable Star Observers (AAVSO)
Wed, 03/27/2019 - 01:22

Hi all,
Over the last month eta Carinae -which had been fading slowly from V= 4.3 to 4.5 over the last months, underwent a 0.15 mag. rapid brightening (which has been now followed by a 0.1 mag. fading).
Augusto Daminelli from Brazil, an active eta Car researcher says:

"Although I have already followed the correlation between V-magnitude and SiII absorption equivalent width, I was not expecting to see a correlated behavior at so small V-band variation. But, the correlation is there. The interpretation is not obvious but I hope to get there in the near future, on the basis of more data."

There are few observers contributing V data for eta Carinae. It is a very difficult object. Aperture photometry including all the Homunculus is the best choice, and even then each observer has a different zero point when it comes to eta Carinae so single datapoints from one observer won't help.
It would be great if several observers can provide a couple of points per week so their zero points can be adjusted and a consistent light curve be displayed.

I have a historical light curve of eta Carinae and I have adjusted it to the Auckland Photometry Group observations made during the last decades. Their zero point is almost 0.1 fainter than the observations made from La Plata over the last years (coverage now ended due to technical problems). And 0.05 mag. brighter than the observations by Giorgio Di Sala in our database. Giorgio's data are the most consistent and long-lasting coverage made recently. Maybe some others could join. Remember that high precision is required here because we are talking about 0.1 mag. variations.