Stars in M31

[Stonius (Markus)]

Possibly a silly question;

I've never spent much time on M31, given that it rarely coincides with auspicious observing opportunities, moon phases and my latitude. The other night it was perfectly positioned so I had a go. It would only have been 10 degrees or so above the horizon at culmination, so not much to go on.

I picked out the two satellite galaxies quite easily, and the inner dust lane after some more observation, and a bit of the extended nebulosity in the arms, but then something suprised me. In averted vision it seemed to have a certain 'graininess'. Is it possible to actually make out individual stars in the Andromeda Galaxy? Or am I just going nuts?

Cheers

-Markus

[RobF (Rob)]

Hi Markus

Probably not visually, unless some of the gurus here chime in. Its more likely you're seeing intervening stars from our galaxy.

Definitely possibly photographically - see here:
http://www.iceinspace.com.au/forum/s...ghlight=hubble

[Stonius (Markus)]

I think you must be right, Rob. I could ascribe the graininess to just barely resolved foreground stars, which photographs show clearly. I'll have to set up that USNO B1.0 catalogue to really see how many stars approaching mag 15 would have been on the edge of perception for me at the time. Otherwise, I have no idea what it was I was seeing; artifact or actual? :-)

Cheers

Markus

[Stonius (Markus)]

Then I came across this in Sky and Telescope;

Resolving Andromeda — How to See Stars 2.5 Million Light-Years Away

So maybe...?

[RobF (Rob)]

Very interesting Markus....

[Robh (Rob)]

Hi Markus,

I must admit I would have been dubious about any visual sighting of stars in M31 (apart from a bright nova). Mag 14.8 at 2.5 million light years (mentioned as the brightest star in the Sky & Tel article) corresponds to an absolute magnitude of about -9.62, which I guess would make it a blue hypergiant.

Bob King doesn't say at what altitude M31 was observed. I'm guessing it was probably fairly high in the sky. At 10 degrees altitude, I think seeing any of these stars would be unlikely or you would need a lot more aperture.

Don Pensack mentions about a half dozen of the stars superimposed on NGC 206 are in the Milky Way and are just “line of sight” stars. So, it would make it tough to say one way or the other.

Interesting post, thanks
Rob

[Stonius (Markus)]

Originally Posted by Robh

Hi Markus,

I must admit I would have been dubious about any visual sighting of stars in M31 (apart from a bright nova). Mag 14.8 at 2.5 million light years (mentioned as the brightest star in the Sky & Tel article) corresponds to an absolute magnitude of about -9.62, which I guess would make it a blue hypergiant.

Bob King doesn't say at what altitude M31 was observed. I'm guessing it was probably fairly high in the sky. At 10 degrees altitude, I think seeing any of these stars would be unlikely or you would need a lot more aperture.

Don Pensack mentions about a half dozen of the stars superimposed on NGC 206 are in the Milky Way and are just “line of sight” stars. So, it would make it tough to say one way or the other.

Interesting post, thanks
Rob

Yes, good point. You're probably right.
:-)

Markus

[Stonius (Markus)]

Well, I decided to do a little experiment.

Being not too great with maths, I used an online calculator for visual magnitude Vs Absoloute Magnitude Vs Distance (available here)

And combining what i learned on another thread here; the most luminous known star in the known universe is R136a1 in the LMC (actually, in the tarantula nebula). The Absoloute Mag of this star is supposedly -8.09. At the 50,000 parsecs distance of the LMC, that makes it a 12th VMag star, although if you calculate what it's mag should be using the above calculator, it should actually be 10.4 visually. Maybe there's some intervening gas and dust or something?

Anyway, that same star placed in M31, 780,000 kiloparsecs away would be 16.37 VMag. My scope has a theoretical limit of 15.7, so it seems like there's no way it could resolve stars in M31, even if it was full of R136a1 type monsters.

Hubble (the man, not the telescope) studied cepheid variable stars in M31 to establish that it was an independent galaxy much further away than the foreground stars, but I believe much of his work was photographic in nature. So yes, as was mentioned below, individual stars are possible to see photographically, but not visually - which rather casts into doubt the veracity of the article I mentioned below where there were supposed sightings of stars in the andromeda galaxy with amateur telescopes.

-Markus

[geolindon (Lindon)]

Hay Markus,

get one of these

http://www.obsessiontelescopes.com/t...s/25/index.php

- limiting mag 17,