Proxima Centauri

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Re: Proxima Centauri

Post by Sirius_Alpha on 13th February 2018, 9:31 pm

A Multi-Year Search For Transits Of Proxima Centauri. I: Light Curves Corresponding To Published Ephemerides
https://arxiv.org/abs/1802.04284

Proxima Centauri has become the subject of intense study since the radial-velocity discovery by Anglada-Escud\'e et al. 2016 of a planet orbiting this nearby M-dwarf every ~ 11.2 days. If Proxima Centauri b transits its host star, independent confirmation of its existence is possible, and its mass and radius can be measured in units of the stellar host mass and radius. To date, there have been three independent claims of possible transit-like event detections in light curve observations obtained by the MOST satellite (in 2014-15), the BSST telescope in Antarctica (in 2016), and the Las Campanas Observatory (in 2016). The claimed possible detections are tentative, due in part to the variability intrinsic to the host star, and in the case of the ground-based observations, also due to the limited duration of the light curve observations. Here, we present preliminary results from an extensive photometric monitoring campaign of Proxima Centauri, using telescopes around the globe and spanning from 2006 to 2017, comprising a total of 329 observations. Considering our data that coincide directly and/or phased with the previously published tentative transit detections, we are unable to independently verify those claims. We do, however, verify the previously reported ubiquitous and complex variability of the host star. We discuss possible interpretations of the data in light of the previous claims, and we discuss future analyses of these data that could more definitively verify or refute the presence of transits associated with the radial-velocity discovered planet.

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Re: Proxima Centauri

Post by Sirius_Alpha on 25th February 2018, 9:30 pm

Whelp, ... there go the debris disks.

Detection of a Millimeter Flare From Proxima Centauri
https://arxiv.org/abs/1802.08257

We present new analyses of ALMA 12-m and ACA observations at 233 GHz (1.3 mm) of the Proxima Centauri system with sensitivities of 9.5 and 47 μJy beam−1, respectively, taken from 2017 January 21 through 2017 April 25. These analyses reveal that the star underwent a significant flaring event during one of the ACA observations on 2017 March 24. The complete event lasted for approximately 1 minute and reached a peak flux density of 1004 mJy, nearly a factor of 1000 brighter than the star's quiescent emission. At the flare peak, the continuum emission is characterized by a steeply falling spectral index with frequency, Fν∝να with α=−1.770.45, and a lower limit on the fractional linear polarization of |Q/I|=0.190.02. Since the ACA observations do not show any quiescent excess emission, we conclude that there is no need to invoke the presence of a dust belt at 1−4 AU. We also posit that the slight excess flux density of 1019 μJy observed in the 12-m observations compared to the photospheric flux density of 744 μJy extrapolated from infrared wavelengths may be due to coronal heating from continual smaller flares, as is seen for AU Mic, another nearby, well-studied, M dwarf flare star. If this is true, then the need for warm dust at ∼0.4 AU is also removed.

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Re: Proxima Centauri

Post by Lazarus on 26th February 2018, 4:52 pm

Ouch. And it's plausible the ~30 AU belt is due to background sources as well. On the upside, that might make transits a (slightly) more realistic possibility.
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Re: Proxima Centauri

Post by Sirius_Alpha on 8th April 2018, 8:38 pm

The First Naked-Eye Superflare Detected from Proxima Centauri
https://arxiv.org/abs/1804.02001

Proxima b is a terrestrial-mass planet in the habitable-zone of Proxima Centauri. Proxima Centauri's high stellar activity however casts doubt on the habitability of Proxima b: sufficiently bright and frequent flares and any associated proton events may destroy the planet's ozone layer, allowing lethal levels of UV flux to reach its surface. In March 2016, the Evryscope observed the first naked-eye-visible superflare detected from Proxima Centauri. Proxima increased in brightness by a factor of ~68 during the superflare and released a bolometric energy of 10^33.5 erg, ~10X larger than any previously-detected flare from Proxima. Over the last two years the Evryscope has recorded 23 other large Proxima flares ranging in bolometric energy from 10^30.6 erg to 10^32.4 erg; coupling those rates with the single superflare detection, we predict at least five superflares occur each year. Simultaneous high-resolution HARPS spectroscopy during the Evryscope superflare constrains the superflare's UV spectrum and any associated coronal mass ejections. We use these results and the Evryscope flare rates to model the photochemical effects of NOx atmospheric species generated by particle events from this extreme stellar activity, and show that the repeated flaring is sufficient to reduce the ozone of an Earth-like atmosphere by 90% within five years. We estimate complete depletion occurs within several hundred kyr. The UV light produced by the Evryscope superflare therefore reached the surface with ~100X the intensity required to kill simple UV-hardy microorganisms, suggesting that life would struggle to survive in the areas of Proxima b exposed to these flares.

Well that's unfortunate.

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Re: Proxima Centauri

Post by Lazarus on 9th April 2018, 3:09 pm

Well, this kind of thing probably goes some way to explain why we find ourselves orbiting a G-type star instead of the far more common M-dwarfs.

Hopefully whatever's at Proxima has factor nine billion sunblock.
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Re: Proxima Centauri

Post by Lazarus on 5th July 2018, 3:22 pm

Mass of Proxima Centauri as determined by microlensing is 0.150+0.062-0.051 solar masses, which would increase the minimum mass of Proxima b to 1.56+0.064-0.053 Earth masses. The candidate transit signal does not appear to have been caused by a background eclipsing binary.

Zurlo et al. "The gravitational mass of Proxima Centauri measured with SPHERE from a microlensing event"
https://arxiv.org/abs/1807.01318
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Re: Proxima Centauri

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