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View Full Version : Epsilon Indi, getting more complicated with each passing year



Roger E. Moore
2018-Aug-01, 05:48 PM
https://en.wikipedia.org/wiki/Stars_and_planetary_systems_in_fiction#Epsilon_Ind i

Epsilon Indi, like tau Ceti, has long been a reliable fixture in science fiction, given its similarity to Sol and its nearness to Earth. Star Trek, Space: Above and Beyond, Halo, and Larry Niven's Known Space have all included it in their settings. It is worth noting that in Niven's 1973 novel Protector, epsilon Indi has a gas giant named Godzilla.

Here is the latest news on the real epsilon Indi, which [drum roll] is now confirmed to have a Jupiter-like gas giant, plus two co-orbiting brown dwarfs that orbit the main star itself--a complicated system if there ever was one. Other planets are NOT ruled out.

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https://arxiv.org/abs/1807.09880

Dynamical Masses of Eps Ind B and C: Two Massive Brown Dwarfs at the Edge of the Stellar-Substellar Boundary

Dieterich, Sergio B.; Weinberger, Alycia J.; Boss, Alan P.; Henry, Todd J.; Jao, Wei-Chun; Gagne, Jonathan; Astraatmadja, Tri L.; Thompson, Maggie A.; Anglada-Escude, Guillem
07/2018

We report individual dynamical masses for the brown dwarfs Epsilon Indi B and C, which have spectral types of T1.5 and T6, respectively, measured from astrometric orbit mapping. Our measurements are based on a joint analysis of astrometric data from the Carnegie Astrometric Planet Search and the Cerro Tololo Inter-American Observatory Parallax Investigation as well as archival high resolution imaging, and use a Markov Chain Monte Carlo method. We find dynamical masses of 75.0 +-0.82 Mjup for the T1.5 B component and 70.1 +-0.68 Mjup for the T6 C component. These masses are surprisingly high for substellar objects and challenge our understanding of substellar structure and evolution. We discuss several evolutionary scenarios proposed in the literature and find that while none of them can provide conclusive explanations for the high substellar masses, evolutionary models incorporating lower atmospheric opacities come closer to approximating our results. We discuss the details of our astrometric model, its algorithm implementation, and how we determine parameter values via Markov Chain Monte Carlo Bayesian inference.

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https://arxiv.org/abs/1803.08163

Detection of the closest Jovian exoplanet in the Epsilon Indi triple system

Feng, Fabo; Tuomi, Mikko; Jones, Hugh R. A.
03/2018

We confirm the trend in the radial velocity data for Epsilon Indi A suggesting a long-period planetary companion and find significant curvature is present, sufficient to quantify Epsilon Indi Ab as a cold Jupiter with a minimum mass of 2.71 -0.44/+2.19 Mjupiter on a nearly circular orbit with a semi-major axis of 12.82 -0.71/+4.18 au and an orbital period of 52.62 -4.12/+27.70 yr. We also identify other significant signals in the radial velocity data. We investigate a variety of spectral diagnostics and interpret these signals as arising from activity-induced radial velocity variations. In particular, the 2500 and 278 d signals are caused by magnetic cycles. While a planetary signal might be present in the 17.8 d signal, the origin of 17.8 and 11 d signals are most easily interpreted as arising in the rotation of the star with a period of about 35 d. We find that traditional activity indicators have a variety of sensitivities. In particular, the sodium lines and CaHK index are sensitive to all activity-induced signals. The line bisector measurement is sensitive to stellar rotation signal while H$\alpha$ is sensitive to the secondary magnetic cycle. In general, because of their different sensitivities these activity indicators introduce extra noise if included in the noise model whereas differential RVs provide a robust proxy to remove wavelength-dependent noise efficiently. Based on these analyses, we propose an activity diagnostics procedure for the detection of low amplitude signals in high precision radial velocity data. Thus the Epsilon Indi system comprises of at least Epsilon Indi A, Ab as well as a long period brown dwarf binary Ba and Bb; so it provides a benchmark case for our understanding of the formation of gas giants and brown dwarfs.

Roger E. Moore
2018-Oct-06, 08:19 PM
https://www.sciencedaily.com/releases/2018/09/180917101301.htm

Recent "Science Daily" article that elaborates on one of the papers above. The masses of the two epsilon Indi brown dwarfs are so high that the discovery challenges the division between brown dwarf and hydrogen-burning stars.