Object 111: RR Pictoris

Podcast release date: 13 November 2023

Right ascension: 06:35:36.1


Epoch: ICRS

Constellation: Pictor

Corresponding Earth location: Roughly 400 km from Antarctica in the Indian Ocean

The object for this episode is the star system RR Pictoris located at a distance of 1641 light years (503 pc) [1, 2] in the constellation Pictor. I thought about spending some time making fun of this constellation, but I previously mocked this constellation in Episode 61, so I recommend listening to that episode if you want my commentary about how stupid the constellation Pictor is.

Anyway, RR Pictoris is referred to as a classical nova. This is a car model that was manufactured by Chevrolet beginning in 1962, but the model would undergo several revisions, which included the introduction of the classical muscle car version in 1968 [3]... OK, that's about the classic Chevrolet Nova. A classic astronomical nova contains both a white dwarf and some sort of evolved star like a red giant that are in a close binary orbit with each other.

Both stars would have started out their lives as Sun-like stars powered by the fusion of hydrogen into helium in their cores. The star that is now the white dwarf would have been the first where its core filled up with helium, in which case it would have expanded to become a red giant, with the fusion of hydrogen into helium taking place in a shell around the helium core, and then more stuff would have happened, including the fusion of helium into carbon in the star's core. However, the star would have been too small for triggering the fusion of carbon into heavier elements, so what would have happened is that the star would have blown off its outer gas layers to form a planetary nebula, leaving just the carbon core.

The second star in the system is now at the stage where its core filled up with helium and it's evolved into something like a red giant. However, because that red giant is very close to the white dwarf that it's orbiting, the outer gas layers of the red giant, which consists mainly of hydrogen, end up getting gravitationally stripped away by the white dwarf and falling onto the white dwarf.

A nova occurs in these types of star systems when the gas falling onto the white dwarf is sufficiently high in density and/or temperature that it undergoes fusion, causing the star system to increase dramatically in brightness in an event called an outburst before slowly fading afterwards. This is exactly what astronomers saw happening in RR Pictoris in 1925. Today, this star system has a magnitude of about 12.5 [4]. For comparison, the brightest star system in the sky has a magnitude of -1.5 [5], and the faintest stars that can be seen without a telescope are between magnitudes of 5 and 6, so RR Pictoris doesn't really look that notable. In 1925, however, RR Pictoris reached a magnitude of 1.2 [6], which would have made it the brightest star in the constellation Pictoris. It was one of the brightest novae ever seen as well as one of the closest to Earth [7]. It also would have remained the brightest star in the system for quite a while. 80 days after the nova outburst, the system faded to magnitude 2, and then 150 days after this event, the system faded to magnitude 3 [8].

Even though this one outburst took place about a hundred years ago (at the time of this recording), and the only data about the nova outburst comes from old photographic plates, astronomers have still spent a lot of time looking at this system to understand the aftermath of the nova explosion and to understand more about the system in general. This has included the analysis of filaments of gas ejected from the system [6]; calculations of the rate at which gas is falling into the white dwarf [9]; detailed measurements of periodic variability in the brightness of the system that look related to the stars' orbits around each other [10, 11]; and even the inference of the presence of a possible third dwarf star within the system [12]. Over what has been nearly a century, RR Pictoris has clearly continued to yield lots of exciting information about these types of star systems, and it will continue to be a popular target for astronomers to study in the upcoming centuries as well.


[1] Gaia Collaboration et al., The Gaia mission, 2016, Astronomy & Astrophysics, 595, A1

[2] Gaia Collaboration et al., Gaia Early Data Release 3: Summary of the contents and survey properties, 2020, arXiv e-prints, arXiv:2012.01533

[3] Gold, Aaron, The Chevrolet Nova: History, Generations, Specifications, 2022, MotorTrend

[4] Zacharias, N. et al., The Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4), 2013, Astronomical Journal, 145, 44

[5] Ducati, J. R., VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system., 2002, VizieR Online Data Catalog

[6] Williams, R. E. and Gallagher, J. S., Spectrophotometry of filaments surrounding nova RR Pictoris 1925., 1979, Astrophysical Journal, 228, 482

[7] Ramsay, Gavin et al., Distances of cataclysmic variables and related objects derived from Gaia Data Release 1, 2017, Astronomy & Astrophysics, 604, A107

[8] McLaughlin, Dean B., The Relation Between Absorption Velocity and Rate of Decline for Galactic Novae., 1940, Astrophysical Journal, 91, 369

[9] Sion, Edward M. et al., Far Ultraviolet Spectroscopy of Old Novae. II. RR Pic, V533 Her, and DI Lac, 2017, Astronomical Journal, 153, 109

[10] Ribeiro, Fabíola M. A. and Diaz, Marcos P., A Tomographic Study of the Classical Nova RR Pictoris, 2006, Publications of the Astronomical Society of the Pacific, 118, 84

[11] Fuentes-Morales, I. et al., Photometric long-term variations and superhump occurrence in the Classical Nova RR Pictoris, 2018, Monthly Notices of the Royal Astronomical Society, 474, 2493

[12] Vogt, N. et al., The Orbital Ephemeris of the Classical Nova RR Pictoris: Presence of a Third Body?, 2017, Publications of the Astronomical Society of the Pacific, 129, 014201


Podcast and Website: George J. Bendo

Music: Immersion by Sascha Ende

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