Alpha Centauri, the hunt for planets.

Maastrichian wrote:

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

I think after doubts about the Corot-7b, Glize-436c, Glize-581g such a discovery will be published only after a very thorough inspection. Probably it will be a joint publication of the three groups leading the search of planets in the Alpha Centauri system.

And if the planets at α Cen resemble those of Sol, they're below the detection limit for a while longer, too. At the moment, I see it as "the later, the better." A 1 M_e planet is going to be more exciting than a 2 M_e planet.

Exactly they can not afford for mistake not to be sure 100% of existence planet especially after cases gj 581 g,f and now gj 433 b,gj667Cb now distracted

Sirius_Alpha wrote:

And if the planets at α Cen resemble those of Sol, they're below the detection limit for a while longer, too. At the moment, I see it as "the later, the better." A 1 M_e planet is going to be more exciting than a 2 M_e planet.

That's definitely a point to bear in mind in all the excitement over finding various super-Earths (some of which are turning out to be less than secure). Finding an analogue of our own inner solar system is an extremely challenging task. At present the only system that looks vaguely like the inner planets of our solar system is PSR B1257+12: the other low-mass planetary systems (other than those detected via microlensing) contain worlds with extremely short orbital periods which indicate a history of significant migration that seems not to have occurred here.

(That does raise the question of what the formation of our solar system and the pulsar planet system had in common that was not shared by, say, HD 10180 or 55 Cancri...)

Paper about HARPS detection efficiency considering the specific case of α Cen B. Figure 9 suggests the current observing strategy being used by HARPS would be sensitive only to planets more massive than about 5-10 times the Earth's mass in the habitable zone. ESPRESSO following an optimal strategy (and at a somewhat lower assumed stellar activity) would be able to detect planets over 1-2 times the Earth's mass in the habitable zone.

Predictably, the detection capabilities are worst for periods close to 1 year.

There is going to be an exoplanet meeting on May 27, from 9:00 am to 5:30 pm EDT, with live webcast. In the agenda is an Alpha Centauri update from Debra Fischer.

Agenda (.pdf)
Webcast feed

I'm going to be pessimistic and guess this is going to be about detection limits rather than any announcement of planet candidates...

I don't think that's an unreasonable stance in the slightest. Given the lack of a major press release, I think it's a pretty sure one.

Until now , no news about detections on Alpha were good news. Now , with observation time accumulated , good algorithms , etc , failure to detect anything increasily amouts to say there is nothing there to detect

Let's keep the hope.

ciceron wrote:

failure to detect anything increasily amouts to say there is nothing there to detect.

If a clone of Mercury, Venus, Earth and Mars orbited α Cen A or B, we would not have detected them yet.
When the detection limits start pushing down toward Lunar-mass objects in the habitable zone, then maybe the idea that nothing is there to detect will seem more reasonable.

Well ,of course , we are not there yet, so there is some time to keep hope. Two to three years is the time margin i suspect is time to lose that hope.

That nothing has been detected thus far , is good news.

The Alpha Centauri update is no longer in the Agenda...

Natalie Batalha on follow up of Kepler candidates: 288 stars selected for followup this year / 75 only with high-precision RV.

Yes that was quite interesting, especially the bit about changing the strategy to take advantage of the multi-planet systems. Also the bit about the stars being noisier than expected, so maybe not so many Earth-size candidates unless the mission is extended.

From the recent paper about the HARPS search for Earth-like planets in the habitable zone, it looks like they've got a paper specifically dedicated to Alpha Centauri B coming out fairly soon. They do note that of the 10 candidates listed in the paper (one of which is Alpha Centauri B), three of them currently show evidence for planets (82 Eridani, HD 85512 and HD 192310), so I don't think we should expect a planetary detection for now...

The first comment on this Centauri Dreams post is quite interesting... the limits are coming down...

Debra Fischer to improve the precision of her search installing a new fiber scrambler on the 1.5 m telescope at CITO:

http://www.planetary.org/blogs/bruce-betts/planets-around-alpha.html

HARPS scores! Earth mass exoplanets in a 3.2 days orbit around Alpha Centauri B

http://www.science20.com/news_articles/discovery_earthmass_exoplanet_orbiting_alpha_centauri_b-95292

We've learned that small planets tend to come in packs, so probably the hunt has only started, with additional planets awaiting to be detected in the system.

Planetary Society blog includes Debra Fischer's response.

Apparently they're now matching the HARPS precision which is very good news, even aside from Alpha Centauri there's now capability to get independent confirmation of the various HARPS results.

Given the location it doesn't do much for the longitude coverage (as far as I can tell), which means they'll have similar gaps in the observation times due to having daylight at the same time.

Detectability of Earth-like Planets in Circumstellar Habitable Zones of Binary Star Systems with Sun-like Components
http://arxiv.org/abs/1212.4884

Main example used here is Alpha Centauri.

Finding habitable planets by astrometry is slightly easier for Alpha Centauri A than it is for B because of the wider orbit.

Unfortunately...

Quote :

Given the current observational facilities, enormous amounts of observing time would be required to achieve such precisions. If the α Centauri was a transiting system, however, a habitable planet could be detectable using current technologies. It seems that the detection of Earth-like planets in circumstellar habitable zones of binaries with Sun-like components via astrometry and radial velocity is still somewhat beyond our grasp, leaving photometry to be the only current option in this respect.

P.S. Oooh I've gone up a spectral type... how long until I get to supermassive black hole?

Debra Fischer Hunts for a Second Earth at Alpha Centauri
http://www.planetary.org/multimedia/planetary-radio/show/2013/20130128-debra-fischer-alpha-centauri-exoplanet-search.html

Highlights from the interview with Fischer.
Upgrades to CHIRON instrumentation in Jun 2012. Precision dramatically improved with fibre optics. Standing "toe-to-toe" with HARPS team. HARPS was $10M, CHIRON was < $1M. Able to measure RV stability over two weeks is less than or about 50 cm/s. 35 cm/s nightly stability. May not be able to do much better, limited by CCD performance. Spectral lines are 4 px across, measuring variation on the order of 1/10,000th of a pixel. Fischer's team will aim for confirming Alf Cen Bb in the Spring of 2013. Rocky planets tend to come in multiplets, so additional planets are likely.

Sirius_Alpha wrote:

Fischer's team will aim for confirming Alf Cen Bb in the Spring of 2013.

An indipendent confirmation of such a difficult detection will be great. On the other end we haven't seen so far any additional studies carried out on the HARPS dataset. So far no alternative analysis published confirming or rejecting the find. I wonder if it's a good or bad sign..

Implications of the spectroscopic abundances in α Centauri A and B
http://arxiv.org/abs/1304.0450

Quote :

...Given the trends seen when analyzing the refractory abundances [X/Fe] with condensation temperature, we find it possible that {\alpha} Centauri A may host a yet undiscovered planet.

From Sara Seager's facebook page.

Quote :

Moments ago the Hubble Space Telescope has turned to observe Alpha Centauri B, checking to see if the Earth-mass planet Alpha Cen B b might show transits. Brice-Olivier Demory is leading our team effort with Hubble, (and we are joined by another group who will independently analyze the same data.) Let's keep our fingers crossed that nature put a transiting Earth-mass planet around our nearest sun-like star. And, incidentally, we're in the Swiss Alps, on a trip also organized by Brice. The Hubble data will be in our hands couple of weeks from now and it will take another month or so to analyze the data. Hubble doesn't usually observe such a bright object!

Would be nice.I do not expect radius larger than 1.15 earth rather 0.95-1.What is transit probability?