# Thread: Epsilon Indi, getting more complicated with each passing year

1. ## Epsilon Indi, getting more complicated with each passing year

https://en.wikipedia.org/wiki/Stars_...n#Epsilon_Indi

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.

2. https://www.sciencedaily.com/release...0917101301.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.

3. Did we get a message from epsilon Indi? No, but we might have passed through its shock wave.

https://arxiv.org/abs/2010.02826

The TeV Cosmic Ray Bump: a Message from Epsilon Indi Star?

Mikhail A. Malkov, Igor V. Moskalenko

A recently observed TV bump in the cosmic ray (CR) spectrum, comprising two consecutive breaks, is likely caused by a stellar bow shock. It reaccelerates preexisting CRs, and they diffuse to the Sun along the magnetic field lines. They drive turbulence that self-controls the diffusion and forms the bump. ... There are at least two passing stars in this range: the binary Scholz's Star at 6.8 pc, and a triplet Epsilon Indi at 3.6 pc. Based on their current positions and velocities, we speculate that our Sun is in the wake of the Scholz's star, while the spectral bump is transmitted by the Epsilon Indi. Given the proximity of this star, the bump appearance may change in a relatively short time.

4. The K Dwarf Advantage for Biosignatures on Directly Imaged Exoplanets (Giada N. Arney).

Oxygen and methane are considered to be the canonical biosignatures of modern Earth, and the simultaneous detection of these gases in a planetary atmosphere is an especially strong biosignature. However, these gases may be challenging to detect together in the planetary atmospheres because photochemical oxygen radicals destroy methane. Previous work has shown that the photochemical lifetime of methane in oxygenated atmospheres is longer around M dwarfs, but M dwarf planet habitability may be hindered by extreme stellar activity and evolution. Here, we use a 1-D photochemical-climate model to show that K dwarf stars also offer a longer photochemical lifetime of methane in the presence of oxygen compared to G dwarfs. For example, we show that a planet orbiting a K6V star can support about an order of magnitude more methane in its atmosphere compared to an equivalent planet orbiting a G2V star. In the reflected light spectra of worlds orbiting K dwarf stars, strong oxygen and methane features could be observed at visible and near-infrared wavelengths. Because K dwarfs are dimmer than G dwarfs, they offer a better planet-star contrast ratio, enhancing the signal-to-noise (SNR) possible in a given observation. For instance, a 50 hour observation of a planet at 7 pc with a 15-m telescope yields SNR = 9.2 near 1 um for a planet orbiting a solar-type G2V star, and SNR = 20 for the same planet orbiting a K6V star. In particular, nearby mid-late K dwarfs such as 61 Cyg A/B, Epsilon Indi, Groombridge 1618, and HD 156026 may be excellent targets for future biosignature searches.

https://arxiv.org/abs/2001.10458