[Deep Sky] Submission 142043 – Rolf Wahl Olsen

Please see https://www.rolfolsenastrophotography.com/Astrophotography/Light-Echoes-from-Eta-Carinae for full details of this project. This is the first amateur image of light echoes from the 19th-century Great Eruption of Eta Carinae. These light echoes have been detected by the Hubble Space Telescope and from large observatories such as the CTIO 4m telescope, but this is the first time that amateur images reveal these transient features. My other first amateur detection of light echoes from supernova SN1987a inspired me to try looking for the fainter echoes near Eta Carinae. What are Light Echoes? Light echoes occur when the initial flash from a bright source, like a supernova, is reflected back to us from a slightly different direction. Dust clouds in interstellar space reflect a portion of the outward-traveling light from the supernova, redirecting it towards Earth. These faint light echoes can be observed decades or centuries after the original flash. Swiss astronomer Fritz Zwicky, known for his contributions to supernovae, neutron stars, dark matter, and gravitational lenses, predicted the existence of light echoes as early as 1940. Together with Walter Baade, he coined the term 'supernova' in 1934 and proposed that faint echoes of historical supernovae could be visible long after the initial explosion. The Great Eruption was a significant brightening of the star Eta Carinae that occurred in phases during the mid-19th century. The light echoes are produced when the initial flash from the eruption is subsequently reflected off interstellar dust as light travels outward from the event. Direct light from the eruption was observed on Earth around 1840-50, and we then see light reflected from dust in interstellar space arriving later because it has travelled further to reach us. Methodology A sequence of three deep luminance images of the Southern part of the Carina Nebula (NGC3372) were taken over approximately a two year period. Difference analysis of the images reveal a faint extended light echo gradually progressing southwards in position angle 190.5 degrees, some 40 arcminutes from Eta Carinae near RA 10h 44m DEC -60° 20'. The light echo luminance structures were overlaid on a deep narrowband image of the area to provide colour and context. The animated sequence shows the progression of the echo over roughly a two year period, and a corresponding still image shows the colour coded echo features against the dramatic ethereal backdrop of the Eta Carinae nebula. Light Echo Geometry Most of the light echo features are somewhat diffuse but between February 2022 and March 2023 a couple of the brightest areas appear to move in sync approximately 16.7 arcseconds southwards. At Eta's distance of 7500 light years, this corresponds to an angular shift of 0.609 light years over 13 months (1.08 years) or a movement of 0.564 light years every year. Interestingly, when compared to my earlier measurement of the apparent superluminal speed of the light echo from SN 1987A, the echo from Eta Carinae appears much slower (sub-luminal). A conclusion is that the illumination is happening on the far side of a ellipsoid with Eta and Earth as the respective focal points, where in the case of SN 1987A the echo is arriving from points between us and the original source. Light Echo Acquisition details: Jan-Mar 2022, L 510m, total 8hrs 30mins @ -25C Mar-Apr 2023, L 695m, total 11hrs 35mins @ -25C Dec 2023, L 405m, total 6hrs 45mins @ -25C Nebula Acquisition details: Panel 1 (light echo): Apr-May 2023, Ha OIII: 345:510 mins, total 14 hours 15 mins @ -25C Panel 2: Feb-Mar 2022, Ha OIII: 270:360 mins, total 10 hours 30 mins @ -25C Panel 3 (Eta Carinae): Feb-Mar 2022, Ha OIII: 240:375 mins, total 10 hours 15 mins @ -25C Homunculus Nebula: L 122 x 0.4s, Ha 16 x 0.4s @ -25C Telescope: Homebuilt 12.5" f/4 Serrurier Truss Newtonian Camera: QSI 683wsg with Lodestar guider Filters: Astrodon 3nm Ha/OIII and LRGB E-Series Gen 2 Taken from my observatory in Auckland, New Zealand