AAVSO: American Association of Variable Star Observers

Proposal #212

Proposer (15617) Barber Observatory University of Illinois Springfield (jmart5@uis.edu) obscode: UIS01
Assigned To(3663) Dirk Terrell
Date SubmittedMay 21, 2021

Eta Carinae is the most massive and luminous star in our part of the Milky Way. It's Great Eruption in the 1840s is a prototype for supernova impostors. Over the last 250 years the star has been recovering from the Great Eruption. And now, for the first time since 1860 it has almost recovered to its historic pre-eruption brightness of V = 4.0. Ten years ago the it was more difficult to measure the brightness of the star without contamination from the surrounding bright nebula. But in the last decade it has steadily grown significantly brighter than the surrounding nebula. We need to keep watching this star. It is a popular visual target but for the last couple years it has not been regularly observed in V and B. Observer BLD has measured it regularly in TG, but not in a second filter to get color information.
I am proposing only B and V coverage because Eta is one of the brightness near-infrared objects in the sky and is likely to overwhelm it in R or I. I would be interested in getting filter-wheel grating spectra for it it that is an option. Eta's spectrum has some very broad emission features that will show variability even at low spectral resolution. The bright star monitors were made for a target like this and I am happy to take it on with my other targets for service observing. All photometry obtained from the BSMs will be immediately submitted to the IAD so anyone can use it.
For the minimum and maximum magnitude I have listed the star's 300 year min and max brightness. It is currently sitting at V ~ 4.4 and (B-V) ~ 0.5. Over the last decade, short term it can fluctuates about 0.1 mag over a few weeks. Over the last 20 years it has maintained a steady long term brightening trend at a rate of 0.03 mag/year for about the last 20 years. But it could do something exciting, which is why I want someone to be keeping an eye on it.

Target RA (H.HH) Dec (D.DD) Magnitude Telescope Observation Frequency Expiration Date Proprietary Term
Eta Car 10.750972 -59.68444 8.5–-2.0 BSM_Berry 1 Nov. 26, 2021 No


(4726) Kenneth Menzies — May 30, 2021, 6:04 p.m.

Committed to Berry

(15617) Barber Observatory University of Illinois Springfield — June 1, 2021, 1:42 p.m.

The first set of images obtained were out of focus. The prospects for using the grating images are not promising. But I'd like to give it one more shot with better focus to be certain.
Is there a place where I can get the dispersion per pixel information for the grating in BSM_Berry? Thank you.

(15617) Barber Observatory University of Illinois Springfield — June 2, 2021, 1:42 p.m.

The B and V images where in better focus last night but the grating images are still out of focus. Is it possible that the BSM is not re-focusing when it takes the grating exposure? This is a mistake I sometimes make myself. The grating has an effective thickness of zero. So while the filters may all be par-focal, the telescope needs to be refocused to have the images taken with the grating in focus.

(4726) Kenneth Menzies — June 3, 2021, 8:34 p.m.


I agree that the focus has not been good recently. It has normally been excellent! Some gremlin has snuck in here? Greg is working on it.

The grating is rarely used and the focus offset needs adjustment! Keep the faith, it will work? BTW, how is the exposure for this target in the grating? Can you make a guess whether we are close or way off?


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