Is Proxima Cen the nearest star?

1. Jan 15, 2004

Nereid

Staff Emeritus
... beyond our solar system ...

A lot of attention is given to the latest discoveries in the far reaches of the universe - the cosmic background radiation, galaxy evolution in the first few billion years, distant supernovae which show the universe is expanding at an accelerated rate, ... - and rightly so.

So it's easy to overlook the fact that good research is being done much closer to home, and largely with much more modest equipment than the HST, the Kecks, or the VLTs.

RECONS (Research Consortium on Nearby Stars) aims "to understand the nature of the Sun's nearest stellar neighbors, both individually and as a population. Our goals are to discover missing'' members of the sample of stars within 10 parsecs (32.6 light years), and to characterize all stars within that distance limit. New members are found via astrometric, photometric, and spectroscopic techniques, or through companionship studies at small and large separations. Characterization includes photometry and spectroscopy at both optical and infrared wavelengths, as well as determinations of the luminosity function, mass function, and multiplicity fraction of the nearby stars."

They haven't found a star closer to the Sun than Proxima Cen ... yet. Will they?

Popular summary:
http://skyandtelescope.com/news/article_1154_1.asp

http://www.chara.gsu.edu/RECONS/ [Broken]

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2. Jan 15, 2004

marcus

Hi Nereid, I checked out the RECONS homepage by the link you gave
and especially the "NStars project" which was comparatively rich
in detail. They said their search radius was 25 parsecs and they had found some 2600 stars in that radius.

they said that these 2600 stars were in some 2000 systems which
was a little surprising because it means most of the stars are loners
Care to expound on that, Nereid?
Looking at bright stars my impression was more than half are in multiple-star systems----like at least binary.
But unless I misunderstood them, most of the stars in this nearby sample
are
1. solitary
2. small dim red-orange dwarves, less than a tenth the luminosity of the sun

3. Jan 16, 2004

Phobos

Staff Emeritus
It would have to be pretty darn dim!

4. Jan 16, 2004

Nereid

Staff Emeritus
A brown dwarf at 1 parsec (Prox is 1.3 parsecs distant) would have a visual magnitude ~15, or approx 50 times fainter than Proxima Cen ... that's pretty faint!

5. Jan 16, 2004

Nereid

Staff Emeritus
Some good illustrations of selection effects (etc). For example, the 10 pc sample has a higher proportion of objects in multiple systems than the 25 pc sample - is it significant?

Is the average star in the 10 pc sample fainter than that in the 25 pc sample (intrinsic, not apparent)? If so, is that statistically significant?

Without a doubt, red dwarfs are predominant type of star in our neighbourhood, and likely throughout the universe. Quiet, unassuming, long-lived (up to 1 trillion years?) ... a nice place to retire to?

It's not so much that we can't see a star with a 'visual magnitude' of 20 or more (the GEMS Hubble image went down to 24 or 25; the Hubble deep fields to 30), but that there are so many faint stars! How to tell which ~100 are the 'missing systems' within 10 pc, from among ~1 billion on the POSS II plates?

6. Apr 4, 2004

Andre

So, about red dwarfs and the closest possible star, any chance that Nemesis exists and will be discovered?

Richard Muller sees a correlation between the dating of mass extinctions and cratering activity on the moon with synchronious spikes every 26 million years. His Nemesis hypothesis assumes that the sun has a red dwarf twin, that passes by every 26 million years in a highly eccentric orbit. The cosmic debris associated with these passes created havoc on the moon and on Earth.

http://muller.lbl.gov/pages/lbl-nem.htm

http://muller.lbl.gov/papers/Lunar_impacts_Nemesis.pdf

So what do you think?

7. Apr 5, 2004

Nereid

Staff Emeritus
Nemesis - unlikely to be a red dwarf

If Muller's brightness estimates are accurate (~7 to 12, today; visual magnitude), I'd say Nemesis certainly doesn't exist at the top of that range (AFAIK, all stars with visual magnitude ~<8-9 have been studied), so any closer than 1pc would have already been discovered. At the fainter end, and if Nemesis were a brown dwarf, there's a small chance there's such a faint object just waiting to be discovered.

However, I'd be somewhat skeptical that an object could exist with an orbit such as Muller proposes.

8. Apr 5, 2004

Phobos

Staff Emeritus
[backpedall]
Just like I predicted....pretty darn dim.
[/backpedal]

9. Apr 5, 2004

Memnoch

Here's a stupid question but I'll ask anyway.
If a brown dwarf cools with age then wouldn't it become even more dim?

10. Apr 5, 2004

Mike2

I hear that there will be a shuttle mission soon with someone on board who will search for brown dwarfs.

11. Apr 6, 2004

Andre

That Nemesis orbit has been subject of a rather heavy dispute indeed. I seem to remember that Piet Hut had a hard time after that publication. Anyway, there is only one way to prove the hypethesis, find nemesis.

12. Apr 6, 2004

Staff Emeritus
BUt if you don't find it, the Nemesis fans will just say "Absence of evidence isn't evidence of absence!"

13. Apr 6, 2004

Andre

Right, but an unproven hypothesis is no theory, yet. Anyway, perhaps another mechanism would be the same as used for finding planets of other stars. If somebody could show that the sun is wobbling slightly in reference to the orbit in the galaxy, with a period of 26 MY, it could be rather convincing too.

14. Apr 12, 2004

Nereid

Staff Emeritus
Yes, it will. However, even the oldest brown dwarfs - which would be unlikely to be in the solar neighbourhood - won't have cooled enough to become invisible from Earth.

For those who are patient, by ~2015 the Nemesis question should be pretty firmly answered one way or the other, by the ESA's GAIA mission (be sure to spend some time reading the mission objectives and background science links).
http://www.spitzer.caltech.edu/index.shtml [Broken] will certainly find many a brown dwarf, though it wasn't launched by the Shuttle. Do you have further info Mike2?
In principle one could use this method. However, I suspect that even the back of a small envelope would be big enough to show that methods used by GAIA (or similar) would be a much more cost effective approach to detection.

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15. Apr 13, 2004

Andre

Impressive indeed, that Earth goddess. I think I may have seen some posters on that in http://astro.estec.esa.nl/GAIA/news_archive.html [Broken].

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