Alpha Centauri, the hunt for planets.

A well written article has appeared in Seed. In it, it is revealed that HARPS has been examining Alpha Centauri B since 2003.

http://seedmagazine.com/content/article/the_long_shot/

Quote :

Since 2003, Mayor and his team have used HARPS to search for planets around Alpha Centauri B. Last August, they began observing the star every available night in a strategy similar to Fischer’s.

Quote :

In a recent [HARPS] survey, the team showed that one-third of about 200 nearby Sun-like stars harbor rocky, terrestrial worlds several times more massive than Earth in short-period orbits. They’re called “super-Earths.”

“These objects aren’t exactly like our Earth, but they may very well be habitable,” Mayor said. “We’re discovering them everywhere we look.

Greg Laughlin goes more in depth in his post at oklo.org
http://oklo.org/?p=337

As there are threads on Corot and Kepler maybe we should start to keep one on Alpha Centauri???

http://oklo.org/

Greg has been a keen pusher on this theory and lately it seems to have caught on a bit more...

Let's hope to hear something later than sooner!

A post has already been started in the detection projects forum about this. I'll merge the two.

Greg Laughlin discusses the possibility of terrestrial planet formation at Alpha Centauri.

http://oklo.org/2009/08/22/keep-hope-alive/

Quote :

Payne, Wyatt and Thebault suggest that outward migration of planetary embryos in the Alpha Cen B protoplanetary disk can provide a mechanism for circumventing the problems associated with habitable planet formation in the binary environment. In the second paper (posted to astro-ph earlier this year) Xie and Zhou argue that a modest inclination between Alpha Cen A’s proptoplanetary disk and Alpha Cen B’s orbit can also tip the balance quite significantly in favor of terrestrial planet accretion around A (and with similar logic applying to planet formation around B).

According to this okly entry, it turns out HARPS is doing more like 25 radial velocity measurements a year on Alpha Centauri instead of 100.

Quote :

Since signal-to-noise increases as the root of the number of observations, this means that the minimum mass threshold for Alpha Cen Bb at any given time is approximately doubled relative to my estimates at the beginning of the Summer. Instead of arriving at 2.5 Earth masses in the habitable zone a bit more than a year from now, they’ll be at roughly 5 Earth masses.

Greg Laughlin wrote:

I would advocate two fully p-mode averaged velocities per night, 50 nights per year. I know that because Alpha Cen B is so bright, the duty cycle isn’t great. I know that there are a whole panoply of other interesting systems calling for time. It is indeed a gamble, but from the big-picture point of view, there’s a hugely nonlinear payoff in finding a potentially habitable planet around Alpha Centauri in comparison to any other star.

Greg's comment (#6) is very interesting

greg
August 31st, 2009 at 4:34 am
Hi Coolstar,
Debra Fischer (with Geoff Marcy as a collaborator) is indeed running a competing program on Alpha Cen from the southern hemisphere. From what I hear, it’s progressing quite well — I think it’s important though, for a discovery of this importance, to have two competing teams.
You can read the details in both the Seed article, as well as in the google translation of the FAZ article.
cheers,
Greg

Let us hope for more news later rather than sooner!

Sirius_Alpha wrote:

According to this okly entry, it turns out HARPS is doing more like 25 radial velocity measurements a year on Alpha Centauri instead of 100.

http://archive.eso.org/eso/eso_archive_main.html
Title "Searching for Earth analogs around nearby stars with HARPS"

From what I can tell, "Searching for Earth analogs around nearby stars with HARPS" was just a poster for an astronomy conference early last month.

Here's an interview with Debra Fischer on her CTIA 1.5 meter scope focused search on Alpha Centauri A and B for terrestrial planets inside the 2 AU dynamical limit.

http://marketsaw.blogspot.com/2009/10/eyes-on-alpha-centauri-hunt-for-pandora.html

Quote :

Michael: The Hubble recently directly imaged the first extrasolar planet...

Quote :

Prof. Fischer: That was around HR 8799...

Wasn't Fischer one of the people who made the press release about the discovery, with HST, of the planet orbiting Fomalhaut? Surely, that's what Michael is talking about.

Picture take http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=46020

Quote :

With the chosen strategy, for a quiet K V star like α Cen B, we would be able to detect planets with masses a few times the mass of Earth with an orbital period of 200-300 days, which corresponds to the habitable region of this type of stars. These estimates are still including HARPS instrumental limitations (with centring and guiding effects) and a contribution from photon noise. Improvements are then expected with more stable instruments as ESPRESSO and longer exposure times to better average the stellar oscillations.

http://www.astro.yale.edu/smarts/schedules/15m10A.txt
Planned to redouble the search for Alpha Centauri Debra Fischer in 2010?

For comparison
http://www.astro.yale.edu/smarts/schedules/sched15m2008b.txt
http://www.astro.yale.edu/smarts/schedules/sched15m2008b.txt
http://www.astro.yale.edu/smarts/schedules/sched15m2009a.txt
http://www.astro.yale.edu/smarts/schedules/sched15m2009b.txt

Planetesimal Accretion in Binary Systems: Could Planets Form Around Alpha Centauri B ?
http://arxiv.org/abs/1001.2614

Abstract wrote:

Stellar perturbations affect planet-formation in binary systems. Recent studies show that the planet- formation stage of mutual accretion of km-sized planetesimals is most sensitive to binary effects. In this paper, the condition for planetesimal accretion is investigated around  CenB, which is believed to be an ideal candidate for detection of an Earth-like planet in or near its habitable zone(0.5-0.9 AU). A simplified scaling method is developed to estimate the accretion timescale of the planetesimals em- bedded in a protoplanetary disk. Twenty-four cases with different binary inclinations(iB=0, 0.1o 1.0o, and 10o), gas densities(0.3,1,and 3 times of the Minimum Mass of Solar Nebula, MMSN hereafter), and with and without gas depletion, are simulated. We find: (1) re-phasing of planetesimals orbits is independent of gas depletion in  CenB, and it is significantly reached at 1 − 2 AU, leading to accretion-favorable conditions after the first  105 yrs, (2)the planetesimal collision timescale at 1-2 AU is estimated as: TB col  (1 + 100iB) × 103 yrs, where 0 < iB < 10o, (3)disks with gas densities of 0.3-1.0 MMSN and inclinations of 1o-10o with respect to the binary orbit, are found to be the favorable conditions in which planetesimals are likely to survive and grow up to planetary embryos, (4)even for the accretion-favorable conditions, accretion is significantly less efficient as compared to the single-star case, and the time taken by accretion of km-sized planetesimals into planetary embryos or cores would be at least several times of TB col, which is probably longer than the timescale of gas depletion in such a close binary system. In other words, our results suggest that formation of Earth-like planets through accretion of km-sized planetesimals is possible in  CenB, while formation of gaseous giant planets is not favorable.

Still hasn't been much study of delivering water to any terrestrial planets orbiting Alpha Centauri A or B. Could be a bunch of desert worlds even if they are in the HZ.

(I suspect any material falling in from any circumbinary disc would come in very fast, which is probably unfavourable to significant accretion)

I read somewhere that if Proxima is truly bound to the system (or at least was at the relavant time period), it could have dislodged Oort-cloud style comets inward toward the stars, providing volatiles after the planets formed.

In program search analogs of the Earth in 10 nearby stars similar to the Sun on HARSP selected in 85 semester (01.04.2010-01.10.2010) 45 nights, compared with 30 nights in 84 semester (01.10.2009-01.04.2010).

I wonder what that could mean? There are promising candidates or the program has entered the planned target time-consuming - 25% (1/4) of the available time HARSP to find analogues of the Earth in 10 nearby stars similar to the Sun?</SPAN>

I hope the mention of this program Geneva group did not violate the embargo? It is indeed shrouded in mystery, but at the same oklo.org about her mentioned.

List of stars this giant program located in the open access
http://www.eso.org/sci/observing/visas/gto/85/harps/p85_harps_upg-geneva.pdf

Yeah it's public knowledge that HARPS has been monitoring some nearby sun-like stars (like you said, mentioned at oklo). Maybe they're just increasing their observing in hopes of catching something. I don't know.

http://exoplanets.astro.psu.edu/workshop/presentation/2-e-Tokovinin-CHIRON.pdf

Quote :

3 m/s per spectrum
0.6 m/s in 1h
0.2 m/s in 1 night (B-A)

Since launched search in May-August 2008, it already has 2-2.5 years of observation!

Borislav wrote:

http://exoplanets.astro.psu.edu/workshop/presentation/2-e-Tokovinin-CHIRON.pdf

Quote :

3 m/s per spectrum
0.6 m/s in 1h
0.2 m/s in 1 night (B-A)

This is probably the instrumental noise. Total accuracy (along with the activity of the chromosphere stars) is given in the pictures:

alfa Cen A
rALL=3.15 ms-1
rBIN=0.86 ms-1
rINT=0.68 ms-1

alfa Cen В
rALL=3.00 ms-1
rBIN=1.18 ms-1
rINT=0.57 ms-1

date of observation is - April 14, 2010

Interesting article Geneva Group

http://arxiv.org/abs/1010.2616

Quote :

Applying 3 measurements per night of 10 minutes exposure each, 2 hours apart, seems to average out most efficiently the stellar noise considered. For quiet K1V stars as α Cen B, such a strategy allows us to detect planets of ∼ 3 times the mass of Earth with an orbital period of 200 days, corresponding to the habitable zone of the star.

In addition, there is talk about the future article on the system of three Neptune.

Quote :

A star like HD69830 (see Lovis et al. 2006, Lovis et al. 2010 in preparation for additional points) as been followed using an ideal calendar of 1 measurement per night on 10 consecutive nights per month and over more than 4 years.

Quote :

In order to check if the calendar we use is not too idealistic compared to a real one (see section 4.1), we compute the detection limits using the real calendar of one of the most followed star using HARPS, HD69830. This real calendar regroups a total of 157 nights over an observing span of 1615 days (Lovis et al. 2006, Lovis et al. 2010, in preparation). Figure 6 shows the difference in mass detection limits between the calendar used in this paper and the real one for HD69830. At 100 days of period, the detection limit for the 2 calendar are 2 and 2.5M⊕, respectively. This small increase of 25% is only due to the total number of night present in each calendar.

It is interesting in this new work on the refinement of the parameters of the three planets or the discoveries of new planets in the system?

I'm wondering if perhaps we will know, one way or another, what can be found at Alpha Centauri within another year...?