As of July 24 2020, there are more than 100 Nova Ret 2020 observations, most visual, with a handful of CCD submissions. Mine (visual) are shown in purple.
Most observers are from Brazil (10), then Bolivia and Australia (5 each), with one from Italy and South Africa.
The southerly declination of the target and comparison stars in Reticulum (almost -55o degrees) makes northern hemisphere observations difficult.
A linear fit shows an overall decline of around 0.17 magnitudes per day, but there’s a lot of spread in the data and novae are unpredictable.
MGAB-V207’s pre-brightening magnitude was 15.8 (Johnson V). Just before I wrote this, it was designated N Ret 2020 in VSX and the AAVSO International Database.
I observed the nova at around 5:30am this morning (July 17) in 7×50 binoculars. My estimate, based upon 4.95 and 5.45 visual magnitude comparison stars, was 5.2.
It may have been brighter but that was my best estimate, given the seeing quality at the time, and a lack of coffee. Having said that, I’m confident that it was reasonable.
At the time of my submission to AAVSO this morning, there were 6 observations, including mine. Andrew Pearce in WA submitted his second observation (brighter) soon after mine.
To get familiar with the field, I started with Stellarium:
and this AAVSO finder chart, which needs to be rotated by about 45 degrees anti-clockwise to match the Stellarium view:
In general, the sky was lovely this morning. After estimating the nova’s brightness, when the dawn became evident, I took this quick shot of a conjunction of the crescent Moon, Venus, and Aldebaran (alpha Tauri) low in the NE sky (1/5 sec, ISO 200, f 2.0, unprocessed) with our recently pruned walnut tree (thanks Karen!) visible at upper right:
Between the nova, satellites passing through my binocular field while observing it and the stars of Reticulum, a stray meteor, the Luna-Venus-Aldebaran conjunction, Orion rising in the east, and the general beauty of the sky, it was an uplifting start to the day.
I was again reminded that there is a hidden sky, waiting for all to see.
Variable stars and novae in particular, always reinforce to me the dynamic, constantly changing universe of which we are a small part. In what often feels like a dystopian world, especially in 2020, I find it oddly comforting that the Universe just keeps doing its thing, irrespective of us. Astronomy is a great way to get some perspective.
The semi-regular late-type variable supergiant star alpha Orionis, better known as Betelgeuse, pulsating with a period of around 420 days at a distance of 640 light years, one of the largest stars visible to the unaided eye and normally in the top 10 list of brightest stars in the sky, is currently undergoing a rapid dimming event.
If Betelgeuse was located at our sun’s position, it would engulf all the inner planets and extend out to the vicinity of Jupiter’s orbit.
When this star ends its life in a supernova explosion it will be visible in daytime and cast shadows at night.
There have been recent questions about the possibility of Betelguese going supernova (or having done so already) and whether the current dimming may be a sign of it.
ATel 13365 has this to say about the dimming event:
The current faintness of Betelgeuse appears to arise from the coincidence of the star being near the minimum light of the ~5.9-yr light-cycle as well as near, the deeper than usual, minimum of the ~425-d period.
It’s interesting to look at past observations of the star.
Here are the last 2 years of visual and Johnson V observations:
The last 5 years of observations:
The last 10 years of observations:
The last 25 years of observations:
In this and the next plot you can see the transition to image-based photometry about 50 years ago in the form of Johnson V data points.
The last 50 years of observations:
The last 100 years of observations:
It’s apparent that there have been similar dimming events over the last 100 years, e.g. in 1947, 1985 and other years.
It’s not obvious that the current dimming event is significantly more rapid than others that came before it, at least by looking at the slope of a linear fit of dimming events.
Alpha Orionis is a bright star, varying between around magnitude 0 and 1.3. It’s easily observable in the north-eastern late evening sky at the moment, along with comparison stars such as Aldebaran and Pollux.
You can create a finder chart via the AAVSO website. An easier way to get started is to see pages 2 and 3 and the chart on the last page of the AAVSO Citizen Sky southern “10 star” tutorial.
The submission of observations to the AAVSO is encouraged and there’s no need for binoculars or a telescope.
Receiving the Merit Award at Melbourne University from AAVSO Director, Stella Kafka, Dec 10 2019
Patrick Wills also received the AAVSO Merit Award this year for his work on the AAVSO Variable Star Index, a database that VStar also uses, including the web services Patrick has created.
An extremely modest number really, compared with other observers over a similar timeframe.
But still, somehow a nice milestone.
I’ve also submitted more than 100 DSLR photometry observations to AID. Again, not many in comparative terms.
The light curve shows the last ten years of visual and B band data along with the 169 (in purple) visual and DSLR eta Carinae observations I’ve made during that time. The red trend line shows the steady rise in eta Carinae’s brightness that has been going on for decades now.
Between VStar, work, and life in general, I don’t get a lot of time to observe these days, but I try to make each observation count.
For anyone following Strange Quarks, you will have noticed my preoccupation with other things in recent months.
Shortly after my last post I observed the nova again. Within 24 hours it has dropped by a full magnitude after peaking at 5.7, a little higher than my binocular estimate of 5.8 from last night.
My two observations are in purple, as usual, with the observation an hour ago under the cross-hairs.
A “happy snap” (with iPhone) of the sky over my backyard rooftop, with Luna peeping through cloud. The nova’s location is behind me from this vantage point.
After being away for a week and a cloudy sky on Sunday, I caught my first glimpse of Nova Carinae 2018 (ASASSN-18fv) in 7×50 binoculars minutes before the sky started clouding out.
I estimated it to be 5.8 (purple, at top right) at just after 11pm Adelaide time.
Note also the upward trend-line.
I had hoped to subsequently image the nova to carry out DSLR photometry for better accuracy but that didn’t pan out due to cloud.
At the time of submission to AAVSO the last observation before mine was 6.5, several hours earlier. Since then, others have submitted observations up to 5.9. So, I appear to have caught Nova Car 2018 on the rise and at its peak so far.
Nova Car 2018 or ASASSN-18fv was discovered by the ASAS Supernova network on March 21st and has so far reached around magnitude 6.5 from a progenitor magnitude of 19.9 within a couple of days.
Below is a Stellarium view of the location of ASASSN-18fv, very close to the 5.1 magnitude comparison star near the Eta Carina nebula and star, a variable whose brightness I often estimate.
A binocular finder chart with a slightly different orientation from the Stellarium screenshot is shown below:
AAVSO alert notice 613 for the nova in Circinus requests visual, DSLR, CCD and spectroscopic observations, with multiple observations each night if possible, in support of the Fermi Gamma-ray Space Telescope’s observations that are currently underway:
Target-of-opportunity observations requested by Dr. Mukai are taking place now through February 6 UT with the NASA Fermi Gamma-ray Space Telescope. To support these observations, observers are asked to make several observations per night.
I’m processing DSLR observations of the nova from last night and plan to continue observing over the next few nights. Its visual magnitude is currently at around 7.2.
In my last post on January 20 about Nova Mus 2018, I said that another southern nova had been discovered, this one by John Seach in the early hours of January 19 in the constellation of Circinus, near alpha and beta Centauri. That post also showed a Stellarium context screenshot and pointed to an AAVSO finder chart.
This nova has slowly been on the rise for the last several days from around magnitude 8.5 to 6.3 by January 27.
The following 15 second DSLR images I took on Jan 22, 23, 26 and 27 show the nova brightening over time:
If the images seem out of focus, that’s because they are. They were used for photometry rather than with the intention of being pretty; use of defocus is part of the procedure. See this talk I gave about DSLR photometry in 2015 for more detail. There’s some positional differences between frames, reflecting the difference in observation time from night to night.
The light curve below shows visual, Johnson V, and Tri-Color Green (DSLR) observations from January 19 to 28; mine are in purple. I’ve also submitted observations in blue and red bands.
This light curve doesn’t appear to show a simple linear increase, so it will be interesting to see where the rise stops.
The sky is largely clouded out tonight here in Adelaide at the end of a hot day (42° C), but I just caught a quick glimpse of the nova in 7×50 binoculars, but wasn’t able to check against comparison stars. It’s around the same magnitude as last night though. I’ll carry out more DSLR photometry as soon as I can.
In the meantime I have two more nights of Nova Mus 2018 (currently on the decline) DSLR images to process. I’ll write an update post for that nova too.
