Alpha Centauri, the hunt for planets.

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 30th January 2013, 6:21 pm

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.

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Re: Alpha Centauri, the hunt for planets.

Post by Galzi on 1st February 2013, 12:57 pm

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..

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 2nd April 2013, 7:16 pm

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

...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.

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 7th July 2013, 9:24 pm

From Sara Seager's facebook page.

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!

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Re: Alpha Centauri, the hunt for planets.

Post by tommi59 on 8th July 2013, 10:47 am

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

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Re: Alpha Centauri, the hunt for planets.

Post by Led_Zep on 8th July 2013, 4:15 pm

http://en.wikipedia.org/wiki/Alpha_Centauri_Bb

« …the chances of a transit of Alpha Centauri Bb being observable from Earth are estimated at between only 10 and 30%… »

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 8th July 2013, 7:48 pm

There's the geometric probability which can be pretty low and ignores the mass distribution of planets which skews the transit probability favourably toward low RV-mass planets -- see this paper), and furthermore if the planet is roughly coplanar with the star system (which is tilted somewhat edge-on), the odds increase dramatically.

I would not be as pessimistic as 10-30%... but 30% is still great odds.

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 15th October 2013, 12:05 pm

Alpha Centauri planet hunt update.
http://www.planetary.org/blogs/bruce-betts/20130828-alpha-centauri-planet-hunt.html
From Debra Fischer

In May, we observed Alpha Cen B almost every night. The new tip-tilt system brought more photons into the FINDS fiber - on single stars we measured an efficiency improvement of about 8%. Unfortunately, even with the improved guiding, the contamination from Alpha Cen A was significant on several of our nights when there was poor seeing. I've spoken with Xavier Dumusque on the Geneva team and they have similar results with the HARPS data. We are now revising our analysis code to see if we can model out this contamination. Fingers crossed, we'll have some results soon.

The search for true Earth analogs faces several challenges and one of them is identification and removal of signals on the surface of the star. Stars are boiling cauldrons of plasma threaded with magnetic fields. The photospheres of the stars have spots, flares, granulation, pulsations and other flows that are imprinted in the stellar spectrum and obscure tiny signals from small rocky worlds.

To understand these sources of stellar noise, we are using CHIRON on other stars, including Tau Ceti and Epsilon Eridani, two stars that Frank Drake observed with Project Ozma. Tau Ceti is a favorite of Doppler planet hunters because the stellar velocities are so constant... or are they? A recent analysis by Tuomi et al. suggests that low amplitude signals may be embedded in the data. We are now able to check that result.

Epsilon Eridani is a more challenging star with spots that mimic Doppler velocity signals. We are writing up our results for that star now - by luck, we caught the star during a stretch when it had large persistent spots; this data set is a training ground for my students who are writing computer algorithms to identify and de-correlate stellar noise from Doppler data.

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Re: Alpha Centauri, the hunt for planets.

Post by Led_Zep on 15th October 2013, 3:21 pm

Crying or Very sad 
It's not very good news...

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 19th March 2014, 7:37 pm

The Mt John University Observatory Search For Earth-mass Planets In The Habitable Zone Of Alpha Centauri
http://arxiv.org/abs/1403.4809

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Re: Alpha Centauri, the hunt for planets.

Post by Sirius_Alpha on 24th July 2014, 8:03 pm

Searching for Earth-mass planets around α Centauri: precise radial velocities from contaminated spectra
http://arxiv.org/abs/1407.6415

This work is part of an ongoing project which aims to detect terrestrial planets in our neighbouring star system α Centauri using the Doppler method. Owing to the small angular separation between the two components of the α Cen AB binary system, the observations will to some extent be contaminated with light coming from the other star. We are accurately determining the amount of contamination for every observation by measuring the relative strengths of the H-α and NaD lines. Furthermore, we have developed a modified version of a well established Doppler code that is modelling the observations using two stellar templates simultaneously. With this method we can significantly reduce the scatter of the radial velocity measurements due to spectral cross-contamination and hence increase our chances of detecting the tiny signature caused by potential Earth-mass planets. After correcting for the contamination we achieve radial velocity precision of ∼2.5ms −1 for a given night of observations. We have also applied this new Doppler code to four southern double-lined spectroscopic binary systems (HR159, HR913, HR7578, HD181958) and have successfully recovered radial velocities for both components simultaneously.

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Re: Alpha Centauri, the hunt for planets.

Post by Shellface on 24th July 2014, 8:17 pm

We are currently in the process of reducing all ∼47000 observations of the two stars with the method described above and expect that we can scrutinize the reality of the putative planet in a 3.24-d orbit around α Cen B once we have a full set of corrected RVs.
HYPE

(though, uh, good luck performing a proper analysis without activity indicators. Look at what Dumusque et al. had to trawl through!)

(Also, a first deep look into the RVs of the primary! HYPE)

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