identical twins? ( APOD 19 Dec 2006)

[ipaqgeek]

http://antwrp.gsfc.nasa.gov/apod/ap061219.html

Zooming up on pismis24-1 you see 2 distinct stars.

Two questions here; the APOD article says 24-1 is made of at least 3 - but we only see two in the image above. Where is the 3rd, etc?

The other question is with regard to the 2 that are resolved in the above image ... they look to be identical in the distribution of light that is imaged. Of course stars are round, so is this shape an aberration of the hubble telescope lensing system or what?

[astro_uk]

The third star is probably too faint, or close in to one of the other stars to be resolved individually. Like the problem of spotting planets around other stars if the planet or smaller star is much fainter than the others it can be difficult to seperate from the brighter component. For things to be resolved on the HST they need to have an angular separation on the sky of at least 0.05 arcseconds, this is a best case for objects of equal brightness, the separation increases when one object is much brighter than the other (I think). So the third star is probably either very faint, or within perhaps 0.1" of one of the others.

Regarding the shape of the objects, any unresolved objects that are point sources (as stars essentially are due to their great distance) will form round objects on the detector, simply due to the optics of the system. The light gets spread into Airy discs which are related to the resolving power of the intrument.

[BMAONE23]

This:
We determine that Pismis 24-1 is composed of at least three objects, the resolved Pismis 24-1SW and the unresolved spectroscopic binary Pismis 24-1NE. The evolutionary zero-age masses of those two objects and that of the nearby Pismis 24-17 are all approximately 100 solar masses, very large but under the stellar upper mass limit.

is directly from the link:
http://adsabs.harvard.edu/cgi-bin/nph-b ... .ph.12012M

So apparently one is a binary. But I must agree that it is interesting that the images appear to be duplicates with resoect to how the light is imaged.

[jimsaruff]

what does 'evolutionary zero-age mean, precisely?

[Pete]

"Evolutionary zero-age" refers to when a star first begins fusing hydrogen in its core.

[jimsaruff]

Thank you, Pete.

Did the discussion on the proper use of the term 'evolution', on another thread, cause you to rethink it's use in astronomy?

I am just curious. Thanks again for your time.

Jim

[Pete]

Hi jimsaruff,

I read the evolution thread, and personally I'm fine with usage of the term in astronomy; as one poster (Qev?) pointed out in there, the term "evolution" predates its biological meaning, and can mean to change, develop, form, etc. Deeply ingrained astronomy terms like "stellar evolution" might as well stay in use.

Happy holidays, everyone!