APOD: Shells and Arcs around Star CW Leonis (2023 Jul 17)

[johnnydeep]

Lots of VERY interesting background galaxies stealing the show, IMO, and conveniently arrayed all around it, like fireflies around a camp fire!

But a basic question: what does the "CW" mean in CW Leonis? What's the convention being followed here?

"CW" just means that this is a variable star in constellation Leo, and it is not the first variable star discovered in this constellation - far from it!

The first discovered variable star in a constellation gets the letter "R", followed by the constellation name in genitiv form. One example is R Corona Borealis. The next letter for a variable star in a constellation, after R is taken, is S, as in S Monocerotis. Then we have T, as in T Lyrae.

There are variable stars with designations beginning on U, V and W too, although I can't remember one beginning on Z.

After these letters are used up, variable stars get double-letter names, as in AE Aurigae. Even novas can get double-letter names like these, such as GK Persei.

Read about the naming of variable stars here.

Ann

Thank you Ann, and Chris for the Wikipedia link. Yes, the naming convention is indeed a mess! From Wikipedia:

The current naming system is:[1]

- Stars with existing Greek letter Bayer designations are not given new designations.
- Otherwise, start with the letter R and go through Z.
- Continue with RR...RZ, then use SS...SZ, TT...TZ and so on until ZZ.
- Use AA...AZ, BB...BZ, CC...CZ and so on until reaching QZ, omitting J in both the first and second positions.[2]
- Abandon the Latin script after 334 combinations of letters and start naming stars with V335, V336, and so on.
- The second letter is never nearer the beginning of the alphabet than the first, e.g., no star can be BA, CA, CB, DA and so on.

And this convention applies PER CONSTELLATION, right? The Wikipedia link didn't make that clear, but I suppose it has to be that way or else we'd quickly be into just the Vnnn designations by now!

[Ann]

Lots of VERY interesting background galaxies stealing the show, IMO, and conveniently arrayed all around it, like fireflies around a camp fire!

But a basic question: what does the "CW" mean in CW Leonis? What's the convention being followed here?

"CW" just means that this is a variable star in constellation Leo, and it is not the first variable star discovered in this constellation - far from it!

The first discovered variable star in a constellation gets the letter "R", followed by the constellation name in genitiv form. One example is R Corona Borealis. The next letter for a variable star in a constellation, after R is taken, is S, as in S Monocerotis. Then we have T, as in T Lyrae.

There are variable stars with designations beginning on U, V and W too, although I can't remember one beginning on Z.

After these letters are used up, variable stars get double-letter names, as in AE Aurigae. Even novas can get double-letter names like these, such as GK Persei.

Read about the naming of variable stars here.

Ann

Thank you Ann, and Chris for the Wikipedia link. Yes, the naming convention is indeed a mess! From Wikipedia:

The current naming system is:[1]

- Stars with existing Greek letter Bayer designations are not given new designations.
- Otherwise, start with the letter R and go through Z.
- Continue with RR...RZ, then use SS...SZ, TT...TZ and so on until ZZ.
- Use AA...AZ, BB...BZ, CC...CZ and so on until reaching QZ, omitting J in both the first and second positions.[2]
- Abandon the Latin script after 334 combinations of letters and start naming stars with V335, V336, and so on.
- The second letter is never nearer the beginning of the alphabet than the first, e.g., no star can be BA, CA, CB, DA and so on.

And this convention applies PER CONSTELLATION, right? The Wikipedia link didn't make that clear, but I suppose it has to be that way or else we'd quickly be into just the Vnnn designations by now!

That's right!

Light echo around V838 Monocerotis. In January 2002, a dull star in an obscure constellation suddenly became 600,000 times more luminous than our Sun, temporarily making it the brightest star in our Milky Way galaxy. Credit: NASA, ESA and H.E. Bond (STScI)

---

Wikipedia wrote:

V838 Monocerotis (Nova Monocerotis 2002) is a spectroscopic binary star system in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was one of the largest known stars for a short period following the outburst.[11] Originally believed to be a typical nova eruption, it was then identified as the first of a new class of eruptive variables known as luminous red novae. The reason for the outburst is still uncertain, but is thought to have been a merger of two stars within a triple system...

I guess that the name "V838 Monocerotis" means that all the "letter designations for variable stars in constellation Monoceros" (334 of them?) were already taken, and V 838 Monocerotis was the 838th non-letter and non-Bayer variable star discovered in the constellation of the Unicorn!

And that, mind you, was back in 2002!

Ann

[bystander]

...

Wikipedia wrote:

V838 Monocerotis (Nova Monocerotis 2002) is a spectroscopic binary star system in the constellation Monoceros about 19,000 light years (6 kpc) from the Sun. The previously unremarked star was observed in early 2002 experiencing a major outburst, and was one of the largest known stars for a short period following the outburst.[11] Originally believed to be a typical nova eruption, it was then identified as the first of a new class of eruptive variables known as luminous red novae. The reason for the outburst is still uncertain, but is thought to have been a merger of two stars within a triple system...

I guess that the name "V838 Monocerotis" means that all the "letter designations for variable stars in constellation Monoceros" (334 of them?) were already taken, and V 838 Monocerotis was the 838th non-letter and non-Bayer variable star discovered in the constellation of the Unicorn!

And that, mind you, was back in 2002!

Ann

Wikipedia wrote: ...

On January 6, 2002, an unknown star was seen to brighten in the constellation Monoceros, the Unicorn.[14]
Being a new variable star, it was designated V838 Monocerotis, the 838th variable star of Monoceros.