Alpha Centauri, the hunt for planets.

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Re: Alpha Centauri, the hunt for planets.

Debra Fischer Hunts for a Second Earth at Alpha Centauri

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

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..

Galzi
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Re: Alpha Centauri, the hunt for planets.

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

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

tommi59
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Re: Alpha Centauri, the hunt for planets.

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%… »

Led_Zep
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Re: Alpha Centauri, the hunt for planets.

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

It's not very good news...

Led_Zep
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Re: Alpha Centauri, the hunt for planets.

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

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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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

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)

Shellface
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Re: Alpha Centauri, the hunt for planets.

Debra Fischer had an interview with Planetary Radio about the laser comb calibrator. Starts at around 8:00.

Alpha Centauri observations are currently on hold until 2016 due to their proximity.
EXPRESS is maybe two or three years from first light.

CHIRON comissioning. Reached half-metre per second precision, but new signals started appearing. Likely caused by motion of gas in the star. Two, almost three year dataset achieved for three stars with "exciting discoveries in astrophysics" including how to get higher precisions.

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Sirius_Alpha

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Re: Alpha Centauri, the hunt for planets.

http://blogs.scientificamerican.com/observations/2015/01/27/planet-hunters-bet-big-on-a-small-telescope-to-image-alien-earths/

According to Ruslan Belikov and Eduardo Bendek, two research scientists at NASA’s Ames Research Center in California, a 45-kilogram space telescope with a 30-to-45-centimeter mirror would be sufficient to deliver images of rocky planets in the habitable zones of either Alpha Centauri A or B. That’s smaller than some of the telescopes you can buy on Amazon.com, though you can’t purchase a planet-imaging space observatory off-the-shelf quite yet. Belikov, Bendek, and their collaborators call the concept ACESat – the Alpha Centauri Exoplanet Satellite – and have submitted it to NASA in response to the agency’s October 2014 call for proposals for Small Explorer missions, which have budgets capped at \$175 million. If selected, the mission would be ready to launch no later than the end of 2020

Led_Zep
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Re: Alpha Centauri, the hunt for planets.

« … a special-purpose space telescope with a mirror only 18 inches in diameter can, and it's being designed and built. It's called ACEsat (Alpha Centauri Exoplanet satellite), and is planned for launch before 2020... »

A link with a pdf (presentation)
http://pathways2015.sciencesconf.org/66590

Led_Zep
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Re: Alpha Centauri, the hunt for planets.

A group of papers on today's arXiv about imaging planets in the Alpha Centauri system...

Males et al. "Orbital Differential Imaging: A New High-Contrast Post-Processing Technique For Direct Imaging of Exoplanets"

Belikov et al. "How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope"

Bendek et al. "Space telescope design to directly image the habitable zone of Alpha Centauri"

Thomas et al. "A method to directly image exoplanets in multi-star systems such as Alpha-Centauri"

Lazarus
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Re: Alpha Centauri, the hunt for planets.

Let's just wait for some results. So far poor constraints on actual presence of inner planet but hints of a possible transiting second one...

Edasich
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Re: Alpha Centauri, the hunt for planets.

New orbit determination for the Alpha Centauri AB binary, that now seems to be in line with the asteroseimology results for the stellar masses. The parallax is consistent with the original version of the Hipparcos catalogue but not with the new revision.

Pourbaix & Boffin "Parallax and masses of α Centauri revisited"
http://arxiv.org/abs/1601.01636

Lazarus
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Re: Alpha Centauri, the hunt for planets.

Lazarus wrote:A group of papers on today's arXiv about imaging planets in the Alpha Centauri system...

Males et al. "Orbital Differential Imaging: A New High-Contrast Post-Processing Technique For Direct Imaging of Exoplanets"

Belikov et al. "How to Directly Image a Habitable Planet Around Alpha Centauri with a ~30-45cm Space Telescope"

Bendek et al. "Space telescope design to directly image the habitable zone of Alpha Centauri"

Thomas et al. "A method to directly image exoplanets in multi-star systems such as Alpha-Centauri"

How to Spy on Alpha Centauri and Other Binary Stars to Hunt Exoplanets

Led_Zep
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Re: Alpha Centauri, the hunt for planets.

In a fairly unrelated paper by Dumusque lies a notable note:

We note, however, that the 50 cm s-1 signal claimed as a planet at the time is probably an artifact that is due to sampling and the model used to mitigate stellar signals (Rajpaul et al. 2016)
(Seems the referred paper was not mentioned here, but it is quite important)

Since Dumusque was the lead author of the discovery paper for Alpha Cen Bb, It would seem that the HARPS team has changed footing. Certainly, this is no fault of theirs; this was the first attempt to deal with such complex data, and mistakes are very possible.

At this point, I would say it would be reasonable to no longer consider the 3.24-d planet as valid. It remains to be seen whether Alpha Centauri hosts any (detectable) planets, Proxima included.

Shellface
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Re: Alpha Centauri, the hunt for planets.

Nevertheless is need to establish period of putative transiting planet around star B

tommi59
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Re: Alpha Centauri, the hunt for planets.

Well at the time the Rajpaul et al. paper was published, the statements from Dumusque in the National Geographic news story indicated that they basically agreed with the findings.

Even the team that originally reported the planet agrees. “This is really good work,” said Xavier Dumusque of the Harvard-Smithsonian Center for Astrophysics. “We are not 100 percent sure, but probably the planet is not there.”

Lazarus
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Re: Alpha Centauri, the hunt for planets.

http://www.eso.org/public/unitedkingdom/announcements/ann16075/?lang

A rare opportunity for planet hunting in Alpha Centauri A predicted for 2028

« …One of the most exciting alignments predicted by this study is between the more massive star in the Alpha Centauri pair, named Alpha Centauri A, and a distant background star — probably a red giant — nicknamed S5. In May 2028, there is a strong chance that the light from S5 will create an Einstein ring around Alpha Centauri A, observable with ESO’s telescopes… »

Led_Zep
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Re: Alpha Centauri, the hunt for planets.

tommi59
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Re: Alpha Centauri, the hunt for planets.

http://www.eso.org/public/unitedkingdom/news/eso1702/

ESO press release :

VLT to Search for Planets in Alpha Centauri System
ESO Signs Agreement with Breakthrough Initiatives

Led_Zep
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