After only five months since his first discovery, Australian amateur astronomer Rob Kaufman discovered yet another Nova! As its name suggests, the eruption took (is taking) place in the Lupus constellation, located within a 10° radius of several naked-eye stars, including η Normae, ε Lupi and μ Lupi, as well as the bright Globular cluster NGC 5927! Rob discovered the Nova on the night of June 3rd, 2018, when it was near peak brightness (visual magnitude of +9 mag)! Within the following day, photometric and low resolution spectroscopic observations were collected, suggesting that Rob’s transient was most to likely be a Nova. The suspicions were confirmed only a couple of days later based on high resolution spectroscopy.
Figure 1: Nova Lupi 2018 as imaged by Rob Kaufman soon after its discovery. Notice how the object seems to display a slight orange tint. The redder appearance of Novae is a reliable way of distinguishing them from other more commonly observed Cataclysmic variables, such as Dwarf novae. The latter usually display much bluer colours. The bright star near the lower limit of the image is HD 139559. (c) Rob Kaufman.
Rob Kaufman discovered the Nova during his holidays at White Cliffs, a small and isolated outback town deep within the Australian mainland, known for its prosperous opal mining during the 1890s and early 20th century. The poorly light-polluted sky makes it an ideal location for observations!
Rob has been a dedicated Nova hunter since 2010, but it was only last January that he made his first discovery, Nova Muscae 2018! I describe this Nova in an older blog post I wrote on January 28th, 2018: https://skyhuntblog.wordpress.com/2018/01/28/nova-muscae-2018-the-story/ ). His search method consists of imaging wide-field sections of the southern Milky Way (see figure 2), using a Canon DSLR (EOS 650D) together with a 55mm F/5.6 lens, as well as a Vixen Polarie monture for star tracking. He later blinks these images with earlier ones taken of the same field using Adobe Photoshop, with the hope of spotting new “stars” that don’t appear in his earlier images. These are indicative of bright transients, such as a Novae.
Figure 2: Stacked wide-field image centered on the Carina, Crux and Musca constellations. It was this image which enabled the discovery of Nova Musca 2018 on January 14th, 2018! (c) Rob Kaufman.
During his holidays on June 3rd, inbetween the presence of the full Moon, Rob imaged two wide-field sections, one centered on the Centaurus constellation, the other on Norma. Back inside, he compared his images with archival ones he took on May 20th. First he compared the one centered on Centaurus, finding no significative difference between the two. However, when comparing the one centered on Norma, he noticed a a potential candidate (see figure 3)! “Hmmm, I’ve got something here ” he told his partner once he noticed the object.
Rob explains that blinking objects are not uncommon to stumble upon during Nova hunting as many “impostors” may mimic the appearance of cataclysmic variables, at first glance. These “impostors” include Minor planets, periodic high-amplitude variable stars (Mira or Eclipsing Binaries for example), and even cosmic rays! The latter was ruled out, as the transient appeared in all the five exposures making up his image. Next he used the Guide planetarium program and the AAVSO/VSX catalog to try to identify the transient, but nothing showed up at the positions of the object. A search via the MPChecker revealed no known Minor planets at the location. Furthermore, he found that the object did not correspond to any known cataclysmic variable.
Figure 3: Cropped version of the original stacked wide-field discovery image of Nova Lupii 2018. The nova is clearly visible, despite not appearing any different from the surrounding field stars. (c) Rob Kaufman
“Excitement was growing as the realisation that this was a reportable object sunk in” Rob states. Unfortunaly however, the transient was too faint to be studied via his low resolution spectrometer, hence he could not confirm the nature of the object as being a true Nova. Nevertheless, the next step was to report the transient to the Central Bureau for Astronomical Telegrams (CBAT). Unfortunately again, he first encountered difficulties when trying to submit his report. “I carefully typed my report in the format required, taking great care with the spacings necessary, and hit the Submit button. And nothing happened!!” He continues by saying “A moment of panic, then I adjusted a few spacings, hit Submit again and a green banner saying “Report received” came up. Phew!”
He then proceeded by posting a notification of this object on the PACA_Transients facebook group, where people such as Patrick Schmeer (Germany) and Seiichiro Kiyota (Japan) took immediate action! Indeed, Seiichiro was the first to take a confirmation image the transient. He also provided a low resolution spectra, along with a Visible-NIR photometric magnitudes. Unfortunately the spectra was inconclusive, but the colours determined by photometry indicated a relatively “red” appearence, typical of Novae. It is possible that the spectra showed very weak Halpha emissions, but these were too close to the background noise level to be confirmed. Rob took a few more images of the transient under Moon light, stating that it appeared “pinkish under high-saturation” which was also a good sign! Notice how the reddish colour is also apparent in figure 1. During this time the transient was designated PNV J15384000-4744500.
High resolution spectra obtained by Fred Walter (Stony Brook University) via the SMARTS and SALT telescopes confirmed the transient to indeed be a true Nova, only two days after Rob first spotted it! More precisely, the spectra indicated the object to be an optically thick classical Fe-II type Nova near peak brightness, at the time of discovery. Swift observations failed to detect the Nova in X-Rays, but it does however appear obvious in the ultraviolet. The confirmation of the Nova lead it to be officially designated as Nova Lupi 2018! At the time of this post (June 13th, 2018), the Nova has a visual magnitude of about +10 according to AAVSO.
Private communication with Rob Kaufman, AAVSO VSX, AAVSO Light Curve, PACA_Transient facebook group, ATel #11681 and ATel #11693.