Making sense of variable star observations

February 23, 2022

I recently gave a talk via ASSA@Home about making the connection between variable star observations (from the AAVSO International Database and Kepler mission) with the processes in the star systems themselves.

I gave examples of pulsating variables (Chi Cyg, RS Pup, RR Lyr, T Umi), an Algol type eclipsing binary (ASAS J035812+1629.7), the enigmatic luminous blue variable eta Car, and the recurrent nova RS Oph, showed videos linking light curves with stellar processes, inspected time series observations, created phase plots and carried out analyses such as period search and time-frequency analysis using VStar.

While not as polished and more ad hoc and exploratory than last year’s RS Oph recurrent nova eruption talk for ASSA, it was fun and seemed to be appreciated, despite less than best audio and video at times. It’s also not easy watching yourself give a talk. 🙂

A brief critique of the documentary 2040

February 20, 2022

The documentary 2040 (or visual diary as it has been referred to) does a good job of putting a positive outlook on the future by emphasising solutions, things that can be done to mitigate climate change, including but not limited to local solar electricity networks, kelp farms as a future protein source, and a move away from private car ownership toward more efficient transport systems.

I’m a father too, so I understand the film maker’s desire to put his young child (daughter in this case) at the centre of the story, imagining a better world for her early adult years and beyond.

2040 – official trailer

But, as uplifting and inspiring as 2040 is, it doesn’t go nearly far enough in my view.

What bothers me about the film is how anthropocentric it is. In what follows, I give examples of how its vision falls short. I may be accused by some of being overly critical of what is an otherwise heart-felt, genuine labour of love, but so be it.

There is a section in which a farmer is interviewed and there is talk of farming practices to improve the health of the soil, which is great. But the true costs of animal agriculture in terms of emissions (comparable to the whole transport sector) and animal welfare are not really addressed.

Near the end of the film, there is a self-congratulatory comment about how much less meat people will eat by 2040. We are already seeing a trend towards eating less meat and towards other protein alternatives.

Primary-school aged children were interviewed throughout. Their insights sometimes bordered on the profound and were often more wise than the adult utterances. The kid who talked about planting a seed and getting meat was on the money, if the rise of the lab grown meat industry is anything to go by, as was the girl who liked bacon but wasn’t sure she should eat it because of its source. These are the sorts of comments that get an uncomfortable “isn’t that cute” laugh from the audience, the members of whom may more-or-less dismiss the seriousness of the points being made.

There is a rushed and insipid comment by the film maker about the existence of some nice meat alternatives as supplements (not potential replacements), but no meaningful concession to the need for a totally plant based diet, just that we should be heading toward eating more plants: a no brainer since that’s what the latest Australian Dietary Guidelines have been telling us for almost a decade anyway!

At one point the future daughter asks her off-screen father “what were you thinking” regarding our generation’s shipping of fish long distance, as opposed to “what were you thinking” by engaging in the act of industrial scale fishing at all, with its attendant destruction of the ocean environment, species population decimation and untold suffering.

The film ends with a jubilant young generation having a party, but it’s a little too soon for much celebration it would seem to me, when there is no sign that any serious attempt to tackle speciesism (arguably, a barometer of our maturity as a species) has been made, and we are in 2040 likely still too narcissistic to think much beyond the end of our collective noses.

In short, 2040 is evolutionary, not revolutionary, and to be fair, that’s consistent with the film maker’s focus on what we can do in future derived from what approaches exist today.

But I think we should want to do even better than what is proposed by 2040, if we are not only going to mitigate the worst of effects of climate change for Australia and the world in general, but also to be able to look our future selves in the mirror and consider homo sapiens worthy of a place as anything like competent stewards of this planet.

Comet 2001/A1 Leonard

January 4, 2022
Dec 26, Canon 1100D, 100mm lens, piggybacked on Meade LX-90, ISO 200, f4, 90 secs

Comet Leonard has been putting on a show for us in the southern hemisphere since mid to late December 2021 and I’ve taken images with my modest equipment, a Canon 1100D with 100mm lens, and exposures of either a few seconds on a tripod or >= 30 second exposures with the camera piggybacked on my 20 year old (hard to believe) 8″ Schmidt-Cassegrain Meade LX-90.

These are all from my fairly light-polluted suburban home site, at least low in the western sky, so it’s a battle between gain (ISO), exposure time, f-stop.

Dec 25, Canon 1100D, 100mm lens, ISO 800, f2, 7 secs; a short satellite trail is evident at right

The following shows the comet’s movement with respect to reference stars over 6 days.

Comet’s path with respect to background stars (arrowed) from Dec 25 to Dec 30

I’ve been posting images to Facebook, Instagram, and Twitter mostly.

Michael Mattiazo’s Southern Comets page has some amazingly detailed images of the comet (look for Leonard in the left-hand side panel) taken with much better equipment and under darker skies.

Having just passed perihelion and with Luna encroaching on the night sky darkness, the days of good views of Comet Leonard are numbered. It’s been nice to have this over the holidays though.

I find that from time to time, I need events like this to reinvigorate my enthusiasm.

Bearing Witness

October 11, 2021

I wrote a post about Jehovah’s Witnesses in 2017, “Mr & Mrs JW: I have some questions…” If words are not enough to convince you of the problems with this organisation, you should watch the September 2021 Australian Broadcasting Corporation Four Corners episode: Bearing Witness.

source: ABC Four Corners

Waiting for U Sco: nearby gamma ray transient detected

September 29, 2021
The Fermi Gamma-ray Space Telescope (source: NASA)

Two days ago I wrote Waiting for U Sco. Today, here are a few excerpts from ATel #14941 (The Astronomer’s Telegram):

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has detected a new transient gamma-ray source, Fermi J1623-1752.

A possible counterpart to the LAT transient is the recurrent nova U Scorpii with position offset by 0.18 deg from the LAT position, thus just outside the 95% confidence error circle, but within the 99% confidence error circle. U Sco has a known recurrence interval of 10.3 years (Schaefer 2010, ApJS, 187, 275) prior to its outburst in January 2010, thus a new outburst from U Sco could be anticipated. The last observation of U Sco in the AAVSO lightcurve database was on 2021 Sep 19.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multi-wavelength observations, particularly optical follow-up of U Sco.

ATel #14941

I read about this in a post by Alexandre Amorim (Brazil) in the AAVSO novae forum. Robert Fidrich (Hungary) soon followed up with an iTelescope observation to say that there was no eruption visible.

Given that U Sco almost certainly had an outburst in its “seasonal gap” (unobservable due to position on the sky), probably in 2017, what this current gamma ray event means seems pretty uncertain.

I’ll continue imaging the U Sco region until it’s too low tonight (in between the clouds) and, consistent with my last post, whenever I can thereafter.

Waiting for U Sco

September 27, 2021

When the recurrent nova U Sco goes into outburst again, the image below shows where it will appear (see cross-hair style position marker), with the bright star Antares, and those bracketing it, shown for reference:

source: Stellarium

Zooming in shows two stars to the right of the nova position marker. Looking at previous outbursts, U Sco’s peak brightness should be somewhere between these two (around magnitude 7.5 to 8, so a binocular or small telescope object).

source: Stellarium

I’m taking images from my backyard of the U Sco region when I can. The image below (click it to enlarge) was taken on Sep 10 2021. I’ve taken a few since but want to step up the regularity. The red arrow shows where U Sco will appear and the green arrow shows the two stars pointed to above.

In any case, I won’t have the same cause to complain about missing the next outburst of U Sco that Leslie Peltier did about missing the T CrB outburst in 1946 (as related near the end of a recent talk I gave about RS Oph), given that my observing frequency is likely to be less and over a much shorter timeframe.

Addendum: Having said all this, given that there was almost certainly an unobserved eruption in the 2017 seasonal gap, as announced in a March 2019 AAVSO forum post, what does this imply for the prediction made by Brad Schaefer of 2020+/-0.7 in a paper published in June 2019? And yet, see the next post…

The Crab Nebula

September 25, 2021

We live only a few conscious decades, and we fret ourselves enough for several lifetimes.

(Christopher Hitchens)

I recently gave a 5 minute talk to a non-technical group about the Crab Nebula (M1, the first object in Charles Messier’s catalog) that related to a sense of wonder in Science. I thought the brief content was worth sharing here.

Chinese astronomers in 1054 witnessed a “guest star”, an explosion that gave rise to a remnant several light years wide called the Crab Nebula.

The object is several thousand light-years distant from earth, yet visible in a small telescope, although with nothing like the detail shown in the Hubble Space Telescope image of Figure 1!

Figure 1: The Crab Nebula, a Hubble Space Telescope image mosaic (source: NASA)

At the heart of the nebula is an object composed only of neutrons, a spoonful of which would weigh a billion tonnes, spinning 30 times per second, energising the nebula, wave-like rings expanding outward from the centre like ripples in a pond (Figure 2).

The original star ran out of the elements that had sustained its nuclear fusion for millions of years, its core collapsing then rebounding in a fraction of a second, ending as a supernova explosion.

Figure 2: The central region of the Crab Nebula (source: NASA)

The event synthesised elements heavier than iron that spread out into the space between the stars, to be incorporated into new stars and their planetary systems, some perhaps going on to develop life.

The iron in our blood, along with trace elements like zinc and iodine, come from such stars.

So, not only are we star-stuff, as Carl Sagan liked to say, but in fact we owe our existence to massive stars that burned bright and lived short lives (millions vs the billions of years our sun will last) then died, so that we could live for just a few decades.

RS Ophiuchi talk for The Astronomical Society of South Australia

September 4, 2021

A few days ago, on September 1 2021, I gave a short talk (15 minutes) to the Astronomical Society of South Australia about RS Ophiuchi and the 10 known recurrent novae more generally.

The talk starts at the 1 hour 7 minute 39 second mark (cued up here) in the YouTube video after the main speaker, Associate Professor Gary Hill, who gave a talk about observing astronomical phenomena with high energy neutrinos using a neutrino observatory he helped to construct in Antarctica. He was a hard act to follow.

On the subject of RS Ophiuchi, here is an updated visual light curve for September 4 2021 with my binocular observations in purple.

One thing I talked about was the most recent and the next predicted outbursts of recurrent novae. I neglected to add U Scorpii to the list which is predicted to go into outburst in the next year or two. Unlike T Corona Borealis which is likely to reach magnitude 2.5 or 3 sometime before 2026, U Sco will only be magnitude 7.5 or 8 at maximum (starting from around magnitude 18), fading by several magnitudes within a week.

RS Ophiuchi Decline Continues

August 16, 2021

The expected decline of the recurrent nova RS Oph continues, almost 3 magnitudes in 7 days. I’ve managed only 5 observations with a couple of cloudy nights between the last two. Luna at 60% illumination in nearby Scorpius tonight made estimating its magnitude (7.2) in 7×50 binoculars a little trickier tonight.

Recurrent Nova RS Ophiuchi Update

August 12, 2021

Since my Aug 9 observation of RS Oph, the AAVSO alert notice was published by Sara Beck: Alert Notice 752: Rare Outburst of Recurrent Nova RS Ophiuchi. My 4.5 visual estimate was listed there along with others from Australia, Brazil, the UK, the US, Belgium and Russia.

The next night was cloudy and wet, but there were enough clear periods tonight for another estimate, 5.7 visual, as shown below:

The last 2 years of RS Oph visual data (including photometry from CCDs, DSLRs)

The next two plots show more detail:

The last week of RS Oph visual data
The last few days of RS Oph visual data

I suggested in my last post that based upon previous outbursts, RS Oph will have reduced by 1 magnitude in 2 days, which it has done. A little more actually, from 4.4 on Aug 9 to 5.7 on Aug 11.

These objects are a reminder that we live in a violent, ever changing universe.