Proxima Centauri

The Pale Green Dot: A Method to Characterize Proxima Centauri b using Exo-Aurorae
https://arxiv.org/abs/1609.09075

The Space Weather of Proxima Centauri b
https://arxiv.org/abs/1609.09076

http://www.scientificamerican.com/article/how-to-see-proxima-b/

How to See Proxima b

(Scientific American.com)

Sirius_Alpha wrote:

No Conclusive Evidence for Transits of Proxima b in MOST photometry
http://arxiv.org/abs/1609.08718

Non-detection, but can't be sure it doesn't transit.

The flares look like they're going to be a real problem for this one, both in terms of unambiguously determining whether transits are occurring, and in terms of prospects for habitability.

Twitter :

Why not an ocean planet ?

https://arxiv.org/abs/1609.09757
Possible Internal Structures and Compositions of Proxima Centauri b

We should wait until transit is definitely confirmed or ruled out nevertheless ocean planet is in my opinion unlikely due to proximity to the host star

Another application of measuring Proxima's radial velocity: it now looks like it is a bound companion of the Alpha Centauri system with a high degree of probability, which is in contrast to previous results which used less precise radial velocity data.

Kervella & Thévenin "Proxima's orbit around Alpha Centauri"
https://arxiv.org/abs/1611.03495

Upper limits for Mass and Radius of objects around Proxima Cen from SPHERE/VLT
https://arxiv.org/abs/1611.10362

Doesn't look like this covers any parameter space that hasn't already been ruled out by other methods.

Proxima reloaded: Unravelling the stellar noise in radial velocities
https://arxiv.org/abs/1612.03786

Different analysis of data, recovery of Proxima Centauri b. No evidence for a second planet.

Lazarus wrote:

Another application of measuring Proxima's radial velocity: it now looks like it is a bound companion of the Alpha Centauri system with a high degree of probability, which is in contrast to previous results which used less precise radial velocity data.

Kervella & Thévenin "Proxima's orbit around Alpha Centauri"
https://arxiv.org/abs/1611.03495

http://www.eso.org/public/france/announcements/ann16089/

ESO press release :

Orbit of Proxima Centauri Determined After 100 Years
Strongest evidence yet that Proxima Centauri orbits Alpha Centauri pair

Ribas et al. "The full spectral radiative properties of Proxima Centauri"
https://arxiv.org/abs/1704.08449

There appears to be a ~20% excess in the 3–30μm region of the spectrum, interpreted as evidence of warm dust in the system. Proxima b currently receives about 60 times the XUV flux that Earth does, and may have lost between 0.5 and 2 Earth oceans of water before Proxima's luminosity decreased sufficiently for it to enter the habitable zone. If the water loss mechanism continued for the lifetime of the planet, the total loss (assuming an infinite reservoir) would be 15–25 Earth oceans.

https://reddots.space/proxima-centauri-harps-data-release-1/

Live from La Silla !!!

An update on Proxima Centauri planet seach efforts.
https://reddots.space/proxima-harps-data-release-2-and-more/

Quote :

Data on Proxima remains tricky to interpret. When all datasets are combined together, the signal of Proxima b remains strong and growing in significance, but the new data alone shows only weak evidence of it. This is within the expectation for such a small signal, and the not-so ideal sampling caused by the first weeks of bad weather.

Quote :

More mysterious is the nature of the longer term signal. Non-random variability remains beyond reasonable doubt, but four candidate periods are equally favoured. Once one of these second signals is added to the model, not much is left on the data.

http://www.eso.org/public/images/potw1737a/

ESO : "is Proxima c hiding in this graph?"

Feng & Jones "Was Proxima captured by alpha Centauri A and B?"
https://arxiv.org/abs/1709.03560

Based on dynamics, it seems that there is a fairly decent chance that Proxima is not an original member of the Alpha Centauri system. There is also evidence that Proxima has a lower metallicity than Alpha Centauri AB, which would also seem to support the capture hypothesis.

Today from Twitter :

ALMA Discovery of Dust Belts Around Proxima Centauri
https://arxiv.org/abs/1711.00578

Quote :

Proxima Centauri, the star closest to our Sun, is known to host at least one terrestrial planet candidate in a temperate orbit. Here we report the ALMA detection of the star at 1.3 mm wavelength and the discovery of a belt of dust orbiting around it at distances ranging between 1 and 4 au, approximately. Given the low luminosity of the Proxima Centauri star, we estimate a characteristic temperature of about 40 K for this dust, which might constitute the dust component of a small-scale analog to our solar system Kuiper belt. The estimated total mass, including dust and bodies up to 50 km in size, is of the order of 0.01 Earth masses, which is similar to that of the solar Kuiper belt. Our data also show a hint of warmer dust closer to the star. We also find signs of two additional features that might be associated with the Proxima Centauri system, which, however, still require further observations to be confirmed: an outer extremely cold (about 10 K) belt around the star at about 30 au, whose orbital plane is tilted about 45 degrees with respect to the plane of the sky; and additionally, we marginally detect a compact 1.3 mm emission source at a projected distance of about 1.2 arcsec from the star, whose nature is still unknown.

Very interesting bit at the end.

"Finally, an exciting alternative scenario is that the source traces a ring of dust surrounding an as yet undiscovered giant planet orbiting at a (projected) distance of 1.6 au (orbital period & 5.8 yr). By analogy with the rings of Saturn we expect a power-law distribution with an index of −3.5 and a maximum particle size of 5-10 m (Zebker et al. 1985; Brilliantov et al. 2015), resulting in a total mass of ∼ 10−5 M⊕ for such a planetary ring. Theoretical arguments (Charnoz et al. 2017) suggest that evolved planetary rings have a mass ∼ 10−7 times the mass of the planet. Thus, under this scenario, we would expect a planet of mass ∼ 100 M⊕, the mass of Saturn, to account for the observed 1.3 mm emission. No clear RV signal that would indicate such a planet is present in the data of the long-term monitoring of the star. Further observations are being undertaken to confirm, or rule out this intriguing possibility. At any rate, our study shows that ALMA provides already the necessary sensitivity and resolution to detect rings around exoplanets in alpha Centauri, and perhaps in other nearby stars"

Interesting stuff. Assuming the 30 AU belt is real and the system is coplanar, that would give a true mass of Proxima b of around 1.8 Earth masses.

Proxima being unveiled month by month, great updates. And more has yet to come.

Is the "unknow source" the candidate of HARPS Survey ? (see Red dot campaign)
EDIT : no !
https://reddots.space/harps-data-release-3-independent-analyzes-more/

Press release on ESO with a more artistic rendering of the system.

So Proxima turns out much "dustier" than expected.

A Q&A on the Proxima Centauri disk that has some information on the Red Dots campaign.
http://www.astronomy.com/news/2017/11/proxima-rings

Quote :

Q: Out of curiosity, aside from the second radial velocity signature at Proxima, how are the RedDot searches at Barnard’s Star and Ross 154 going?

A: We have a lot of data on Barnard’s Star and Ross 154. The thing I can say at this point is that this answer is very complicated. There’s data from four or five other instruments that we are combining all together. We should be able to report what we found there within a few months, but at this point we can’t really tell because the data set is complicated. We’re still discussing and trying to build a consensus on what is there.

Q: At Ross 154 or Barnard’s star or both?

A: If we find something around Barnard’s star, we will be reporting it big time as well, because that will be a wonderful thing because it’s nearby and we’d expect to do follow-up studies of all sorts.

As discussed in the Exoplanets and Planet Formation Meeting thread.

Searching for the Transit of the Earth--mass exoplanet Proxima~Centauri~b in Antarctica: Preliminary Result
https://arxiv.org/abs/1711.07018

Quote :

Proxima~Centauri is known as the closest star from the Sun. Recently, radial velocity observations revealed the existence of an Earth--mass planet around it. With an orbital period of ∼11 days, the surface of Proxima Centauri b is temperate and might be habitable. We took a photometric monitoring campaign to search for its transit, using the Bright Star Survey Telescope at the Zhongshan Station in Antarctica. A transit--like signal appearing on September 8th, 2016, is identified tentatively. Its midtime, TC=2,457,640.1990±0.0017~HJD, is consistent with the predicted ephemeris based on RV orbit in a 1σ confidence interval. Time--correlated noise is pronounced in the light curve of Proxima Centauri, affecting detection of transits. We develop a technique, in a Gaussian process framework, to gauge the statistical significance of potential transit detection. The tentative transit signal reported here, has a confidence level of 2.5σ. Further detection of its periodic signals is necessary to confirm the planetary transit of Proxima Centauri b. We plan to monitor Proxima Centauri in next Polar night at Dome A in Antarctica, taking the advantage of continuous darkness. \citet{Kipping17} reported two tentative transit--like signals of Proxima Centauri b, observed by the Microvariability and Oscillation of Stars space Telescope in 2014 and 2015, respectively. The midtransit time of our detection is 138 minutes later than that predicted by their transit ephemeris. If all the signals are real transits, the misalignment of the epochs plausibly suggests transit timing variations of Proxima Centauri b induced by an outer planet in this system.

https://arxiv.org/abs/1712.04483

A Candidate Transit Event around Proxima Centauri

We present a single candidate transit event around Proxima Centauri, found during a blind transit search using a robotic 30\,cm telescope at Las Campanas Observatory. The event lasted 1 hour, with an estimated depth of 5\,mmag, and is inconsistent with the transit window predicted for the recently discovered planet b. We modeled the lightcurve under the assumption that the event was caused by a transiting exoplanet, and our model predicts the planet has a radius R∼1R earth . We encourage continued monitoring of Proxima to elucidate the origin of this event