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Unome wrote:For anyone who's curious, the two distance measurements for NGC 6357 appear to originate here (~1.7 kpc) and here (~2.6 kpc). I've yet to figure out which of these would be more likely to be accepted by event supervisors (or whether to vary my answer depending on the conditions).

I have 5,500 ly in my notes, so I'd do 1.7 kpc

Unome wrote:Question: Why do gamma ray images often have so much background noise? I would think that, being mostly the result of energetic rare events, they wouldn't be that common in the background.

Hm, nobody seemed to have responded yet...hoping to see others answer and discuss more.

Where'd you get the source for that? I don't know if *all* gamma ray images necessarily have high noise? Sorry that I always catch on generalizations . Nonetheless, you typically get SOME noise for any image. I know a common source of gamma rays on Earth, for example, would be cosmic rays.

Has anyone found a source for the Period-Luminosity relationship for type II Cepheids? I've looked and I can't really seem to find one.
Thanks!

syo_astro wrote:

Unome wrote:Question: Why do gamma ray images often have so much background noise? I would think that, being mostly the result of energetic rare events, they wouldn't be that common in the background.

Hm, nobody seemed to have responded yet...hoping to see others answer and discuss more.

Where'd you get the source for that? I don't know if *all* gamma ray images necessarily have high noise? Sorry that I always catch on generalizations . Nonetheless, you typically get SOME noise for any image. I know a common source of gamma rays on Earth, for example, would be cosmic rays.

I didn't say all, but for example this image - there seems to be a lot of background noise, though I can't tell whether that's just due to the scale being weird. It seems like gamma ray images are often rather fuzzy (though this applies to X-ray images as well in my experience).

PM2017 wrote:Has anyone found a source for the Period-Luminosity relationship for type II Cepheids? I've looked and I can't really seem to find one.
Thanks!

I believe it scales similarly, but at a generally lower luminosity.

I can't seem to find the apparent and absolute magnitude for the DSO RCW 103. Does anyone have an accurate value that they have found?

CaldwellBrownies wrote:I can't seem to find the apparent and absolute magnitude for the DSO RCW 103. Does anyone have an accurate value that they have found?

I'm not in Astronomy (as I'm still in Div. B, but I did RFTS), but from my findings, this is a magnetar, and these types of neutron stars would be emitting x-rays and gamma rays, so I don't believe that you could put anything for the magnitudes of this DSO. I'm not saying I'm right, however, but those are just my findings.

When a massive O/B star starts fusing Helium, why is there no "flash", similar to that in sun-like stars?

raxu wrote:When a massive O/B star starts fusing Helium, why is there no "flash", similar to that in sun-like stars?

I believe it has to do with the properties of the convection & radiation layers - Adi explained it once, but I can't remember.

Edit: Per Wikipedia and other sources, high-mass stars don't form a degenerate core until significantly higher temperatures, so they start fusing helium more smoothly rather than at once, since the degenerate core is what causes the flash.

Unome wrote:

PM2017 wrote:Has anyone found a source for the Period-Luminosity relationship for type II Cepheids? I've looked and I can't really seem to find one.
Thanks!

I believe it scales similarly, but at a generally lower luminosity.

According to Wikipedia, it's basically the same as type I except a type II is 1.6 magnitudes fainter than a type I Cepheid of the same period.

I'm a bit confused on how to find proper motion. My understanding is that you take the observed motion across the sky and divide that by however many years it was observed for, but that hasn't worked for me when I've tried those problems..

orangewhale wrote:

Unome wrote:

PM2017 wrote:Has anyone found a source for the Period-Luminosity relationship for type II Cepheids? I've looked and I can't really seem to find one.
Thanks!

I believe it scales similarly, but at a generally lower luminosity.

According to Wikipedia, it's basically the same as type I except a type II is 1.6 magnitudes fainter than a type I Cepheid of the same period.

I'm a bit confused on how to find proper motion. My understanding is that you take the observed motion across the sky and divide that by however many years it was observed for, but that hasn't worked for me when I've tried those problems..

Proper motion in terms of angle is just the angle divided by the time, exactly as you said. To find proper motion in units of distance per time, you'll need to know the distance and use the small angle approximation to determine the length of the angular proper motion (or if it's close enough, the approximation may not be very good and you'll have to use tangent of the angle).