Subject:
|
Re: The "geography" of local space
|
Newsgroups:
|
lugnet.space
|
Date:
|
Mon, 22 Nov 1999 04:30:05 GMT
|
Viewed:
|
523 times
|
| |
|
|
"John J. Ladasky Jr." wrote:
> This thread just keeps going and going!
Hey, it's a good thread.
> > "John J. Ladasky Jr." wrote:
> >
> > > We don't know yet whether such planets actually exist! In recent years, you may
> > > have been hearing in the news that planets have been discovered orbiting other
> > > stars. ...
> >
> > Apparently they actually got occlusion readings from a near star in the
> > last week--by "near" I'm talking ~40pc. I can find the article and the
> > star name, but it's one of the HDs (that narrows it down to several hundred
> > thousand objects....;) ).
>
> Right. Lindsay is referring to HD 209458. Catchy name, huh? 8^)
Dangnab frickin' frackin' million-and-fifty-two catalogues...
> The Doppler shift research team that I mentioned in an earlier post predicted that HD
> 209458 has a planetary companion. The object is predicted to be about two-thirds the
> mass of Jupiter, and orbiting quite close to its parent star, with a period of only 3.5
> days. They have always forwarded their finds to a second research group that does
> astrometry -- very precise measurements of the *intensity* of stars. The Doppler
> measurements are done by color.
>
> Consider that, from our vantage point on Earth, we can see Mercury and Venus cross in
> front of our own Sun regularly. That is because our Sun and all of its planets are more
> or less in the same plane. When one of these planets makes a transit in front of the
> Sun, the amount of sunlight that reaches us is moderately reduced.
>
> The Doppler people have asked the astrometry people to attempt to confirm their
> predictions for every candidate planet that they have found. For this to work, the orbit
> of the extrasolar planet around its parent star must more or less intersect the Earth,
> analogous to the situation with our Sun and Mercury or Venus. Most systems are not so
> cooperative, but HD 209458 appears to be. At the exact time predicted by the Doppler
> team, the light from the parent star was observed to dim by about two percent, and then
> brighten again. The entire event took about two hours.
>
> If you have access to the standard USENET newsgroup hierarchy, you can surf over to
> sci.astro and read all about the HD 209458 announcement -- including a (modestly)
> critical thread started by Yours Truly...
Nice incitation effect there. It does seem that an intensity change of over 1.5% ought to be detectable again! Given (as you said) that a perfect lineup of their ecliptic to us is a real needle-in-a-haystack sort of thing, I'd say that
criticality is warranted.
Also, wouldn't you think that a planet of three Jupiter masses (almost certainly a gas giant) that circles a star in 3.5 days would be *very* malformed--vaguely teardrop-shaped if in tidal lock, perhaps even more flattened than Jupiter if not?
> [snip material on E Eridani's flareness/get to the companion stuff]
It's something that I remember from a while back--might be from the heady days of raw hypothesis. I haven't studied in any systematic manner in many years, I'm afraid.
> e Eri, a.k.a. HD 22049, a.k.a. HIP 16537, is on this list. They state confidently that
> the stars listed have no bodies orbiting them that are larger than three Jupiter masses.
Then I'll take that as definitive, but I wouldn't be surprised if something much less than 33.5 Jupiter masses is circling it.
> Now, how about 61 Cygni? For starters, it's a double star system. The two stars are
> spectral types K5 and K7. As I mentioned above, I placed my cutoff, somewhat arbitrarily perhaps, at spectral type K4.
>
> Synonyms for 61 Cygni A include HD 201091 and HIP 104214. This star is listed as a"variable of BY Draconis type." Now, I don't know the details about this type of
> variable star. Do you? However, the visual magnitude of 61 Cyg A was observed to vary from +5.16 to +5.85 by Hipparcos. Other variable measurements are references. This is nearly a two-fold variation in intensity. That didn't sound too
> hospitable to life to
> me.
I think the designation "BY Draconis type" simply means that it's like BY Draconis because it's (they're?) roughly the same spectral type (K7e?) as BY Draconis. Burnham's says "Elliptical Variable" for BY but doesn't give detailed notes of it as
a "type star."
I guess your arbitrary cutoff isn't so odd here--but I wonder if, bearing in mind the stability of the variability cycle, life couldn't adapt to changes in energy output--it would be a weird system of living, but not an impossible one. Were the
cycles variable, however, I'd be a lot less forgiving. :) The tidal-lock issue is harder to pass by, however. I think it could go either way--I've always been of the mind that planets' rotational motion will tend to decrease unless you whack
it at an angle with another marble (asteroid or planetoid); there's more drag closer in towards a star so tidal locking happens sooner.
> 61 Cygni B, a.k.a. HD 201092, a.k.a. HIP 104217, is much more stable in its output.
> However, it has a spectral type of K7, as I mentioned, so it wasn't included on my list.
> A K7 star is about 1/10 as bright as our own Sun, so a planet that would receive an
> equivalent amount of light as Earth would have to be located about 100 times closer >than the Earth is to the Sun. That's tidal-locking distance, I would guess.
Isn't there a bit of trivia (or urban legend?) that, devoid of environmental cues, the human body operates on a 25-26 hour cycle, hinting at a different speed of rotation at some seminal (pun perhaps intended) moment?
> I haven't been able to find references to the separation of 61 Cyg A and B, nor their
> orbital period, etc. These factors can only complicate the possibility of life or living
> in this system.
Agreed, but I've played with it anyhow, just to be argumentative. ;)
best,
Lindsay
---
Lindsay Frederick Braun
Department of History
Rutgers, the State University of New Jersey
|
|
Message has 1 Reply:
 | | Re: The "geography" of local space
|
| Greetings, Earthilings. (...) At least there's a pretty well-done on-line cross reference to the common catalogs now. Paul Baulch was kind enough start me down the road to finding this. I know that I mentioned it before, but here's the URL again for (...) (25 years ago, 23-Nov-99, to lugnet.space)
|
Message is in Reply To:
| | Re: The "geography" of local space
|
| This thread just keeps going and going! (...) Right. Lindsay is referring to HD 209458. Catchy name, huh? 8^) The Doppler shift research team that I mentioned in an earlier post predicted that HD 209458 has a planetary companion. The object is (...) (25 years ago, 20-Nov-99, to lugnet.space)
|
34 Messages in This Thread:
 
- Entire Thread on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
This Message and its Replies on One Page:
- Nested:
All | Brief | Compact | Dots
Linear:
All | Brief | Compact
|
|
|
|
