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Mungascr
2006-Jan-25, 04:24 PM
I remember reading something years ago when the first batch of extrasolar planets were being detected about the fourth nearest star to ours, the red dwarf Lalande 21185 having a planetary companion (or maybe more than one?) discovered orbiting it.

Later though and the texts (a few books I've seen -'Infinite Worlds' being one & a recent astronomy magazine another reference seen) have stated that Epsilon Eridani hosts the closest exoplanet system - but I am sure its further away. (10~12 light years for Eps-Eri. versus about 5~9 for Ll-21185 I think.)

So what happened to Lalande 21185's extrasolar planet finding?

Was it refuted? If so I haven't heard ..

Forgotten? Surely someone, besides me, would have picked up on that for the published sources I saw?

Been really fascinated by the extrasolar planetary area and following it fairly closely - perhaps the latest embargoed news is of one orbiting Alpha Centauri or Barnard's Star or Wolf 359 and thus making this moot but ..

What happened to Lalande-21185's exoplanet and if it exist isn't that the closest not Epsilon Eridani's one?

Anyone know?

BTW. Terminology-wise which is better : Extrasolar planet or exoplanet? Any prob. / difference with either?

ngc3314
2006-Jan-25, 06:22 PM
I remember reading something years ago when the first batch of extrasolar planets were being detected about the fourth nearest star to ours, the red dwarf Lalande 21185 having a planetary companion (or maybe more than one?) discovered orbiting it.

Later though and the texts (a few books I've seen -'Infinite Worlds' being one & a recent astronomy magazine another reference seen) have stated that Epsilon Eridani hosts the closest exoplanet system - but I am sure its further away. (10~12 light years for Eps-Eri. versus about 5~9 for Ll-21185 I think.)

So what happened to Lalande 21185's extrasolar planet finding?



First thing I learned on tracking thus down is that Lalande 21185 is often known as GJ 411.

The initial report of a planet was based on a very delicate analysis of the star's position over the years, done by George Gatewood, which suggested reflex orbital motion due to one or more companions. He found that such companions would usually appear more than 0.8 arcsecond from the M dwarf itself. Subsequent searches, using coronagraphs and multifilter techniques to reduce the scattered-light problems from the star, have yet to turn up any such companion, and the star's radial velocity is so constant that Geoff Marcy and company use it as the poster child for comparison giving "normal" M dwarf stability levels. Most folks seem to figure that this was one of an unfortunate series of marginal results from astrometry, because systematic effects at this very tiny level are hard enough to identify, much less fully remove. For example, you have to correct for the different mean wavelengths of the light reaching the detector from the M dwarf and reference star, because everywhere except the zenith, atmospheric refraction will affect the average position of light from each star differently in a way depending not only on its position but its color. van de Kamp (at Allegheny Observatory) got burned by this kind of thing in announcing a planet around Barnard's Star - the signal wound up mostly being caused by the telescope objective having been removed for cleaning and repolishing and replaced with a rotation back on the telescope tube.

joema
2006-Jan-25, 08:09 PM
...have stated that Epsilon Eridani hosts the closest exoplanet system...
This exoplanet search engine shows Epsilon Eridani as the closest currently known exoplanet, at 3.2 parsecs (10.44 light years). I don't know what the data source is, but it allows searching and sorting on many different criteria:

http://vo.obspm.fr/exoplanetes/encyclo/catalog-main.php?mdAff=output#tc

Romanus
2006-Jan-26, 04:28 PM
I also had high hopes for Lalande 21185, but the fact that we haven't heard anything else just yet leads me to believe that either confirmation is still not finished, or that the data were flawed--and probably the latter. Unfortunate; in spite of its limitations, I still believe high-resolution astrometry is the best planet-hunting technique out there, short of direct observation (including transits as the latter).

Planetwatcher
2006-Jan-30, 10:45 PM
I myself have wondered why we haven't heard more about Lalande 21185. It seemed at one time there was speculation of two possible planets. I'm still hoping myself.

I also heard of speculations of Barnard's Star having up to two small planets a number of years ago, but since the star has such large proper motion, it would be more difficult to detect planets using the traditional method.

But I wonder if the micro lensing technique might work for Barnard's star.

I also seem to remember an internet article a number of years ago claiming that Hubble may have detected a planetary transit across Alpha Centauri C, (the smallest and closest of the three) but never any follow up.

So the officially closest known exoplanet system is Epsilon Eridani, which is supposed to be where Spock will be from in about 300 years, with at least 3 closer but unconfirmed possibilities.

Mungascr
2006-Jan-31, 05:03 AM
Thanks for all that info. everyone.

Didn't know about Lalande 21185's alternate name. Wasn't Ll-21185 obscure enough or something! ;-)

A minor gripe : All these catalog no. "names" get a bit confusing and irritating for non-astonomers although they make logical sense and are useful enough to professionals I guess. Just be nice to have something more memorable that trips off the tongue a bit better ..

Doesn't sound promising for Ll21185-b does it? At best unconfirmed and at worst just a data glitch although I still think its likely there's something there orbiting the star just something too small and hard to find so that we haven't detected it yet.

I tend to think almost _all_ stars will turn out to have planets or asteroidal type bodies just because of the nature of stellar formation but then I don't know really and suchlike assumptions have often proved very dangerous and very wrong. We only really know what we find from observations and even that can be iffy, eg. the Barnard's Star case.

Hadn't heard anything about Proxima's planet - would be excellent if true. A case of 'No news is good news'? If only! ;-)

Thanks again.

astromark
2006-Jan-31, 09:38 AM
The no news idea might prove to be the best. As detection seems to require a osculation or eclipse. We just need to watch and wait. This could take a while. . . . or have I missed something here?

Kaptain K
2006-Feb-04, 11:41 AM
astromark,
You appear to feel it's OK to play "fast and loose" with spelling. e.g. Close enough is good enough. Whatever. If the moderators and owners don't mind, who am I to judge?
However, it sometimes results in (unintended??) humor. Just for grins, you might want to look up the definition of the word "osculation"!

Denis12
2006-Feb-04, 08:52 PM
Why are the possible planets found around a cool dwarfstar? And not around a star that is equal to the sun? If an earthlike planet orbits the so called lalande stars ,the orbit must be very close to the dwarfstar because the only place where you have warmth is very close to the dwarfstar. Can somebody explain this?

astromark
2006-Feb-05, 02:41 AM
Denis 12., I am not sure i understand your question. But that wont stop me adding my two pence worth... Its the heat range. To find a habitable environment the planet of a cooler dwarf brown star would need to be closer than that of a larger hotter star more like our sol. We need to be looking for smaller planets as we have found the bigger gas giants don't seem to have the environment that would support the kind of life we think we are looking for...