Starship Asterisk*

Stellar Wind-Shaped Nebula RCW 58

Explanation: Imagine traveling to a star about 100 times as massive as our Sun, a million times more luminous, and with 30 times the surface temperature. Such stars exist, and some are known as Wolf Rayet (WR) stars, named after French astronomers Charles Wolf and Georges Rayet. The central star in this image is WR 40 which is located toward the constellation of Carina. Stars like WR 40 live fast and die young in comparison with the Sun. They quickly exhaust their core hydrogen supply, move on to fusing heavier core elements, and expand while ejecting their outer layers via high stellar winds. In this case, the central star WR 40 ejects the atmosphere at a speed of nearly 100 kilometers per second, and these outer layers have become the expanding oval-shaped nebula RCW 58.

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Captain Kirk to bridge, Kirk to bridge "we are not going to go through that thing, are we ?"

APOD Robot wrote:
The central star in this image is WR 40...

Warning! This is a bad site!

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Universe Guide wrote:
WR 40 is located in the Milky Way galaxy, and this is the galaxy that you reside in.

Fancy that. I have always wondered.

In case you're wondering, WR 40 is not located within the Solar System, and there is only one star in the Solar System, the Sun.

You don't say?

No one has visited WR 40, and we have no probes on a rendezvous with the star.

Ohh-kay.

All non-Rogue Stars, like planets, orbit around a central spot.

Say what?

Based on the star's spectral type of WN8 (SB1), There is no relationship between colour and size.

I feel enlightened.

WR 40 radius has been calculated as being 73.49 times bigger than the Sun. The Sun's radius is 695,800km, therefore, the star's radius is an estimated 51,134,342.km. If you need the star's diameter, you just need to multiply the radius by 2.

Are you sure the WR star's radius isn't 51,134,343 km? But thanks for the tip on how to calculate a star's diameter from its radius!

Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74.

Who said our Sun is an ordinary star?

WR 40 distance from Earth is 16308.17 light-years away from Earth or 5000 parsecs. If you want that in miles, it is about 95,869,621,952,191,753.094, based on 1 Ly = 5,878,625,373,183.61 miles.

Darn! Now I have to convert that into kilometers!

When you use the 2007 distance, WR 40 is roughly 375,023,932.219 Astronomical Units from the Earth/Sun give or take a few.

Thanks... I have always been wondering... ⇒

A note about the calculations, when I'm talking about years, I'm talking about non-leap years only (365 days).

Well, I just checked my calendar, and it appears that 2023 is not a leap year!

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Right. I guess I have just shown you what kind of a site that Universe Guide really is.
Now let's look at the really problematic claims of this site:

WR 40 radius has been calculated as being 73.49 times bigger than the Sun.

No.

Wolf-Rayet stars are not extremely large. That is because they lose such prodigious amounts of matter through their furious stellar winds. What remains of the star itself just gets smaller and smaller.

Wikipedia wrote about another WR star, WR 104, that its radius is 3.29 solar radii. If WR 40 is of a reasonably similar size, which seems likely to me, then Universe Guide exaggerated the size of WR 40 by some 20 times.

Here is another tidbit:

WR 40's effective temperature is 7,431 Kelvin which is hotter than our own Sun's effective temperature, which is 5,777 Kelvin.

No.

Unfortunately, I have never managed to make head or tails of what exactly is meant by "effective temperature". But if we drop the "effective" from "effective temperature" and just consider the straightforward temperature of the photosphere of the Sun and a typical WR star, then the Sun's temperature is indeed around 5,777 K, whereas the temperature of WR 140 is calculated to be 45,000 K. It seems likely to me that the temperature of WR 40 is similar.

So when Universe Guide claims that the temperature of WR 40 is 7,431 K, it is underestimating the temperature of this star by a factor of 6.

However, if the temperature of WR 40 really had been 7,431 K, then WR 40 would have been an F-type star. It would have been similar to Procyon, with a luminosity of 7 times solar from a distance of 11 light-years. Hello, Procyon my old friend, I've come to talk with you again! 🖐


So, no. There apparently exists no good information on WR 40 specifically, so if you want to know about this particular star, the best thing you can do is read Wikipedia info and other online info about other WR stars. And, to summarize:

APOD shouldn't use Universe Guide to find any specific information about WR 40 (such as temperature, size and luminosity). I wouldn't trust a word that Universe Guide says about these things.

Ann

I was wondering what the red clouds and blue halo indicate about the chemical composition of the nebula? I expect they are false colours to enhance the image, but it would be nice to know.

Thanks in advance of replies.

The Giant Lamprey of Space.

Ann wrote: ↑Wed Feb 08, 2023 7:30 am

APOD Robot wrote:
The central star in this image is WR 40...

Warning! This is a bad site!

Thank you! That site has now been de-linked on the main NASA APOD. - RJN

Eclectic Man wrote: ↑Wed Feb 08, 2023 1:04 pm I was wondering what the red clouds and blue halo indicate about the chemical composition of the nebula? I expect they are false colours to enhance the image, but it would be nice to know.

Thanks in advance of replies.

The red is hydrogen. The blue is oxygen. Both are approximately true color. (The oxygen emission is actually closer to green, but this is within the range of what we commonly see in astronomical image processing. It doesn't really push things into the realm of false color.)

Eclectic Man wrote: ↑Wed Feb 08, 2023 1:04 pm I was wondering what the red clouds and blue halo indicate about the chemical composition of the nebula? I expect they are false colours to enhance the image, but it would be nice to know.

Thanks in advance of replies.

I think the colors are "true". All the red nebulosity that we see in the APOD is almost certainly ionized hydrogen, emitting red Hα light at 656 nm, ███. The outermost blue clouds, by contrast, likely glow from ionized oxygen at 501 nm, ███. The OIII in the APOD is "on the blue side", because I expect OIII light to be less like the blue clouds in the APOD and more like the green rectangle I posted here, but in any case we should probably consider the blue clouds in the APOD to be glowing from OIII.

For comparison, let's look at the Vela supernova remnant:


Bear in mind that WR 40 is not a supernova remnant, so the gas clouds expelled from WR 40 are not slamming into the surrounding medium with the same force as the gas tendrils of the Vela supernova remnant. This affects the degree of ionization of these two nebulas.

Ann

Another Wolf-Rayet nebula NCG 6888 is heart-shaped. Mapping RCW 58 with the technology used to map the Crab Nebula might prove to be enlightening.

Or at least heart-warming prior to Valentines Day.

there are many radial threads that seem to have come from the star.
But I think I see two tangential protoberance tubes. Are they magnetic field loops?

...

The synopsis does not give distance and size. Are those unknown?

Uncle Jeff wrote: ↑Thu Feb 09, 2023 2:13 am The synopsis does not give distance and size. Are those unknown?

As for distance, Gaia gives a parallax for WR 40 of 0.3572 ± 0.017 milliarcseconds, which translates into an (approximate) distance of 9,000 light-years.

As for size, nothing is known, although it would be possible to calculate the size of the nebula by measuring its angular size on the sky, and then "translating" the apparent size of the nebula into the real size of it in view of its distance. But I don't know if the angular size of the nebula has been measured.

As for the size of the star itself, again nothing is known. But it will have shrunk prodigiously in size as it shed all the material that now makes up its surrounding nebula. It is probably still a few times bigger than the Sun.

The best way to understand WR 40, for lack of much information on the star itself and its nebula, is probably to compare it with other Wolf-Rayet stars.

WR 40 is a WC8 class of a Wolf Rayet star, and I found this info on WC8 stars in a table in the Wikipedia article about WR stars:

Temperature: 60,000 K. Radius: 6.3 solar. Mass: 18 times solar. Luminosity: 398,000 solar. Absolute magnitude: −5.32.

According to Wikipedia, another WR star, WR 124, is surrounded by a nebula of its own making, M1-67, which is calculated to be approximately 6 light-years across and is thought to be 20,000 years old.

But just because the nebula surrounding WR star 124 is some 6 light-years across, we can't just assume that the nebula surrounding WR 40 is the same size.

Ann

Ann wrote: ↑Thu Feb 09, 2023 4:53 am ...
WR 40 is a WC8 class of a Wolf Rayet star, and I found this info on WC8 stars in a table in the Wikipedia article about WR stars:

Temperature: 60,000 K. Radius: 6.3 solar. Mass: 18 times solar. Luminosity: 398,000 solar. Absolute magnitude: −5.32.
...

Ann, looks like your spectral type is not correct. Multiple links (2005 to present) state that WR 40 (HD 96548) has a WN8h spectral type (e.g. Simbad). In fact, WR 40 is considered to be the brightest WN star in the sky.

Temperature: 40,000 K, Radius: 22 solar, Mass: 39 solar, Luminosity: 1.3 million solar, Absolute magnitude: −7.2

I'm not sure why / how you decided on WC category.

alter-ego wrote: ↑Fri Feb 10, 2023 3:33 am

Ann wrote: ↑Thu Feb 09, 2023 4:53 am ...
WR 40 is a WC8 class of a Wolf Rayet star, and I found this info on WC8 stars in a table in the Wikipedia article about WR stars:

Temperature: 60,000 K. Radius: 6.3 solar. Mass: 18 times solar. Luminosity: 398,000 solar. Absolute magnitude: −5.32.
...

Ann, looks like your spectral type is not correct. Multiple links (2005 to present) state that WR 40 (HD 96548) has a WN8h spectral type (e.g. Simbad). In fact, WR 40 is considered to be the brightest WN star in the sky.

Temperature: 40,000 K, Radius: 22 solar, Mass: 39 solar, Luminosity: 1.3 million solar, Absolute magnitude: −7.2

I'm not sure why / how you decided on WC category.

Sorry, alter-ego. My mistake. I tend to think of Wolf-Rayet stars as WC stars, because most WR I have looked up with my software have been described as WC stars. I saw the number 8, and then somehow just thought that, yeah, WR 40 is a WC8 star.

The fact that WR 40 is a WN8h star means that it is so young that it is still fusing hydrogen to helium in its core, and it is a quite large and massive star too, because it hasn't yet lost so much of its mass. According to Wikipedia, WN8h stars have the following properties:

Temperature: 40,000 K. Radius: 22 solar. Mass: 39 solar. Luminosity: 1,300,000 solar. Absolute magnitude: −7.2.

So WR 40 is a cooler, a very much larger, a more massive and a much more luminous star than I gave it credit for. I'm very sorry about the incorrect info I gave on WR 40 in my other posts! And thank you so much for correcting me, alter-ego!

Please disregard what I said about the properties of WR 40 in my post just above alter-ego's one!

Ann