Proxima Centauri - (shallow space)

[ChrisM]

I was inspired to find Proxima Centauri recently, as I had volunteered to make a presentation to the local astronomical society on the topic of our nearest stellar neighbours.

I took a 2 degree widefield picture and a narrow field 23 arc min picture too. Initially I couldn't find the star at all. The original 2 degree RAW image, taken through an f/5.2 refractor captured just shy of 20,000 stars, and the other photo captured about 4,500 stars. I finally tracked it down by finding a recognisable asterism on a published photo. Adding to my original confusion was the fact that the star had moved a considerable amount; it moves nearly 4 arc seconds per year.

Proxima Centauri is thought to orbit the Alpha Centauri A & B at a distance of around 13,000 AU, and is a small red dwarf flare star of magnitude 11, and about 1/7 the size of our Sun and 1/8 of its mass, giving it a specific gravity of about 56.

Wide field image 60 secs at ISO 1600
Narrow field image 60 secs at ISO 800
Both taken with a Nikon D7000.

Chris

[strongmanmike]

Well done Chris, one of those things I think many of us have thought about doing but never have so good on you....it is a somewhat inconsequential looking star huh?

Mike

[Lee]

I did that last weekend :) .... didn't think I'd gone deep enough, as the nova.astrometry.net site wouldn't ID what I thought was proxima as so - it has obviously shifted from J2000 coords.... I ended up confused, as I thought I must have it, given its magnitude....
My next little project is to try and get yearly pics of Barnard's Star....

[ChrisM]

Thanks Mike. Yes - poor little prox just gets lost in a sea of stars. That little project had been on my list for a while, so was very pleased to have identified it. Apparently, over 75% of main sequence stars are red dwarfs, so we don't see many of those normally.

Chris

[ChrisM]

So did you actually identify it Lee? Prox is about Mag 11, so you don't need to go very deep to find it. If you are not sure, post your image and I'll see if I can spot it. It was the star's movement over time that allowed me to confirm that I had indeed found it.

I would also like to find Barnards star, but am thinking that even at Mag 9.5 it could be difficult to find initially in Ophiuchus, although I guess that a couple of images taken a few months apart should show about 2 arc seconds of movement.

Chris

[madbadgalaxyman]

Mike, I do agree, Red Dwarf stars sure do look inconsequential......

The very faintest & lowest-mass individual Red Dwarf stars are about a million times less luminous than our own Sun!...... These 'vanishingly faint' little stars weigh in at about 0.08 solar masses each, which shows that these little 'stellar critters' do actually contain substantial mass....and this also implies that their tiny energy output is due to the inefficiency with which these small stars emit light.

I believe that Proxima Centauri has a visual absolute magnitude of 15.45 (I think!), as compared to a visual absolute magnitude of 4.82 for the Sun, which makes Proxima some 17,000 times less luminous than our Sun.

(at the other end of the scale, the most luminous stars have about a million times larger energy output than our own Sun)

The total range of stellar mass, from 0.08 solar mass stars through to 120 solar mass stars, is relatively small.
But the luminosity range of the stars in our Galaxy is much much larger!

Is the Sun, therefore, a "typical" star? Recent work shows that, in fact, the most numerous stars are about 0.3 solar masses each, so in fact the 'typical star' is a lot less massive and luminous than our Sun!
This is why people who study even the largest-scale structures in the universe have to worry about these tiny Red Dwarf stars; these extremely-numerous Very Faint stars can contribute a meaningful portion of the total mass of a Galaxy......

Best regards,
Robert

Madbadgalaxyman's comment of the day:
From the above simple arguments about stellar masses, it is easy to see that the 100 billion solar masses of stars in our Milky Way Galaxy are not made up of 100 Billion individual stars "like it says in the textbooks". The textbooks lie!

[Lee]

Yes, I took another look at my images last night, it's there, smack in middle of frame - I used a plate solve app to point the mount... I got confused when nova.astrometry.net wouldn't identify it....
I was shooting mono too, which made things harder....

Here is the plate solve from centre of frame - Tycho-2 9010-4949-1 is proxima.....

[ChrisM]

Lee, I believe that Proxima is the bright star at the top of your frame - dead centre.

Chris

[Lee]

Hope you don't mind, I cropped the centre from your pic, and plate solved it - same result as mine..... its a wanderer this one....

Calibration info for this frame-

Center (RA, Dec):(217.401, -62.676) Center (RA, hms):14h 29m 36.273s Center (Dec, dms):-62° 40' 33.458" Size:9.65 x 6.04 arcmin Radius:0.095 deg Pixel scale:1.11 arcsec/pixel Orientation:Up is 81.4 degrees E of N

[ChrisM]

No problems Lee. You've got me looking at SIMBAD after a long pause.

The star Tycho-2 9010-3645-1 is mag 12.45 (as seen towards the lower RH corner) and Prox is supposedly mag 11.05, so should be somewhat brighter. In both of the plate solves, there is actually nothing visible in the 4949-1 circle, so I'm thinking that something is not quite right with the plate solve. I haven't used that software myself. I'm still backing the star originally marked.

Chris

[Lee]

The plate solves are showing J2000 co-ords - is it just that Proxima is moving at a high rate?
To be honest I don't fully understand the differences between the epochs, and how the numbers relate to stars with high proper motion.... maybe someone who does know might chime in??

[ChrisM]

Lee, after a closer look at SIMBAD, it seems that the proper motion is taken into account. Prox is actually called V* V645 Cen (http://simbad.u-strasbg.fr/simbad/sim-id?Ident=%403379714&Name=V*%20V645%20Cen&submit=submit), and Tycho-2 9010-3645-1 is another star about 32 asecs away.
Chris

[kinetic]

Nice work Chris and Lee! :):thumbsup:
I've been doing some ProxCent. imaging of my own for about 3 years now
with a few combinations of FL and mirror size.
Lots of data compiled but it is quite a task to quantify it all.
One day I might get time to assemble an animation.
More recently I've done cooled CCD sets with an exact F.L. config
to make a 1 or 2 year animation run fluidly.
What I have noticed is that movement is TINY.....! :)

For example, here is a stack of frames from Jan to Apr this year, so
any movement should appear as a line and not a dot, compared to the
background stars. Also an animation showing 1 month movement.
See how P.Cent is just starting to blur......

PS, here are some others you could try:
http://en.wikipedia.org/wiki/File:Near-stars-past-future-en.svg

Steve

[ChrisM]

Thanks Steve. The movement is small but detectable. Maybe I'll wait another six months to grab another frame.
Chris