UT: Astronomers Find the Oldest Planetary Nebula

[bystander]

Astronomers Find the Oldest Planetary Nebula
Universe Today | 2022 Aug 31

Abell 39 is a good example of a planetary nebula, similar to the one discovered in M37. Credit: WIYN/NOAO/NSF

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Planetary nebulae are short-lived “leftovers” of sun-like stars. Most of these “star ghosts” only last—at most—about 25,000 years. Usually, their clouds of debris disperse so broadly that they fade out fairly quickly. However, there’s one that has lasted at least 70,000 years. That makes it a “grande dame” of planetary nebulae.

A team of astronomers led by members of the Laboratory for Space Research (LSR) and the Department of Physics at the University of Hong Kong spotted this rare celestial jewel in the open star cluster M37. It orbits in our galaxy in the same galactic arm as the Sun and contains about 1,500 solar masses. The object, called IPHASX J055226.2+323724, is the third known planetary nebula associated with an open cluster in our galaxy. So, how do astronomers know it’s so old?

A planetary nebula is a hot white dwarf star surrounded by a shell of material it ejected as it aged. In some planetary nebulae, the shell is roughly circular, while in others, it can be bi-polar-looking. The radiation from the star heats the nebula, which causes it to glow. The age of the expanding shell might seem tough to determine. Yet, there are ways. The team that discovered this object, led by HKU’s Quentin Parker, found it has a “kinematic age” of 70,000 years. That’s an estimate, but it’s a good one, based on how fast the nebula is expanding. The clues lie in the emission spectrum of light emitted from hot glowing gas in the expanding shell around the dying star. Those are “emission lines.”

The team also assumed the expansion speed has remained effectively the same since the beginning. Combining all that, you get the time elapsed since dying the star first ejected its outer layers. In this case, it comes to 70,000 years. By comparison, most “typical” planetary nebulae only last about 5,000 to 25,000 years. That’s a relatively quick time, compared to the life of the star, which could have been around hundreds of millions or billions of years. ...

Discovery of the Oldest Visible Planetary Nebula ...
Science Faculty | University of Hong Kong | 2022 Aug 26

The Planetary Nebula in the 500 Myr Old Open Cluster M37 ~ Vasiliki Fragkou et al

• Astrophysical Journal Letters 935(2):L35 (2022 Aug 20) DOI: 10.3847/2041-8213/ac88c1
  arXiv > astro-ph > arXiv:2208.06101 > 12 Aug 2022

[Ann]

I found this paper, The Planetary Nebula in the 500 Myr Old Open Cluster M37, hugely interesting!

First of all, the old planetary nebula in M37 is nothing like Abell 39. Abell 39 is almost perfectly spherical and greenish-blue from OIII emission. IPHASX J055226.2+323724 is bipolar, enormously large, exceedingly faint and reddish from hydrogen alpha and ionized nitrogen.

Abell 39. Image: WIYN/NOAO/NSF.

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Old planetary nebula IPHASX J055226.2+323724. Image: Laboratory for Space Research (LSR) and Department of Physics at The University of Hong Kong (HKU)

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I like the way the team identified the central star of the planetary.

The central star of planetary nebula IPHASX J055226.2+323724.

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Fragkou et al. wrote:

Based on Sloan Digital Sky Survey imagery (Gunn et al. 2006) we found the CSPN at R.A.: 05:52:26.18, decl.: 32:37:24.63 (J2000), almost exactly at the PN's geometric center (<10'' displacement) which is ∼7farcm2 across its major axis. This is also the only blue star within a 116'' radius from the PN's center, making it the only plausible CSPN candidate (see Figure 2).

I like the fact that the astronomers used the blue color of this star to identify it as the central star of the planetary nebula.

What I found most interesting, however, is the fact that the team estimated both the mass of the progenitor and the mass of the remnant white dwarf:


Central star initial mass ${2.78}_{-0.1}^{+0.12}$ M⊙
Central star final mass ${0.63}_{-0.04}^{+0.03}$ M⊙

So, okay. The initial mass of the central star was 2.78 solar masses, give or take a tenth of a solar mass. The final mass of the white dwarf it evolved into is 0.63 solar masses, give or take a few hundredth of a solar mass.

The initial mass of the central star was halfway between Vega and Regulus - well, a little closer to Vega - but it lost almost ¾ of its mass as it evolved through its red giant phase and then into a white dwarf.

The central star of another planetary, PHR 1315-6555, started out with 2.25 solar masses, and it lost a little less than ¾ of its mass, as it kept 0.58 solar masses. But a more massive central star of a planetary nebula, started out with some 5.58 solar masses and ended up with only 0.95 solar masses, so it lost almost ⅚ of its mass.

Evolution of a 'fat star' turning white dwarf?

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I find this hugely interesting!

Ann