AU Mic - Rumors of planets

rumours rumours rumours... (ExSS4)
Great discover around another young star !!!


P.S
https://en.wikipedia.org/wiki/AU_Microscopii

A forthcoming planet around AU Mic was mentioned in the DS Tuc Ab discovery paper.

"Rumors" speak of 2 planets detected by TESS and Spitzer; RV measurements for one of the two…

https://twitter.com/FringeDoctor/status/1163485470308872194

Well the DS Tuc Ab paper referred to "Plavchan et al. submitted", so...

Hello AU Mic b, a Neptune-sized planet in an 8-day orbit. There's also a single-transit candidate.

NASA press release: "NASA’s TESS, Spitzer Missions Discover a World Orbiting a Unique Young Star"*
Plavchan et al. (2020) "A planet within the debris disk around the pre-main-sequence star AU Microscopii"
Twitter thread from Peter Plavchan here.

* incidentally this kind of title bugs me a little, better wording would be something like "astronomers discover world using data from NASA's TESS, Spitzer missions" - it's not like there weren't actual humans involved...

Wow, quite a few papers on arXiv.

Papers on AU Mic on arXiv tonight.

Limits on the Spin-Orbit Angle and Atmospheric Escape for the 22 Myr-old Planet AU Mic b
https://arxiv.org/abs/2006.13243

A planet within the debris disk around the pre-main-sequence star AU Microscopii
https://arxiv.org/abs/2006.13248

Magnetism and spin-orbit alignment in the young planetary system AU Mic
https://arxiv.org/abs/2006.13269

The dichotomy of atmospheric escape in AU Mic b
https://arxiv.org/abs/2006.13606

Transmission spectroscopy and Rossiter-McLaughlin measurements of the young Neptune orbiting AU Mic
https://arxiv.org/abs/2006.13609

The Youngest Planet to Have a Spin-Orbit Alignment Measurement AU Mic b
https://arxiv.org/abs/2006.13675

And now a stab at a mass measurement.

Investigating the young AU~Mic system with SPIRou: large-scale stellar magnetic field and close-in planet mass
https://arxiv.org/abs/2011.13357

Quote :

with an estimated mass of 17.1+4.7−4.5 M_E* and a bulk density of 1.3±0.4 g/cm−3, inducing a RV signature of semi-amplitude K=8.5+2.3−2.2 m/s in the spectrum of its host star

(* corrected typo)

Led_Zep wrote:

"Rumors" speak of 2 planets detected by TESS and Spitzer; RV measurements for one of the two…

https://twitter.com/FringeDoctor/status/1163485470308872194

Welcome AU Mic c, with "c" for "Christmas"...  

New constraints on the planetary system around the young active star AU Mic. Two transiting warm Neptunes near mean-motion resonance

Quote :

AU Mic is a young, active star around which a transiting planet has been recently detected. Here we report an analysis of its TESS light curve where we model the quasi-periodic rotational modulation by starspots simultaneously to the flaring activity and planetary transits. We measured a flare occurrence rate of 6.35 flares-per-day for flares with amplitudes in the range 0.06%<fmax<1.5% of the star flux. We employ a Bayesian MCMC analysis to model the five transits of AU Mic b observed by TESS, improving the constraints on the planetary parameters. The measured planet-to-star radius ratio of 0.05345+0.00014−0.00015 implies a physical radius of 4.38±0.18 M⊕ and a planet density of 1.1±0.3 g\,cm−3, confirming that AU Mic b is a Neptune-size moderately inflated planet. Whereas a single feature possibly due to a second planet was previously reported in the former TESS data, we report the detection of two additional transit-like events in the new TESS observations of July 2020. This represents substantial evidence for a second planet (AU Mic c) in the system. We analyzed its three available transits and obtained an orbital period of 18.858991±0.000010 d and a planetary radius of 3.51±0.16 R⊕, which defines AU Mic c as a warm Neptune-size planet with an expected mass in the range 1.7 M⊕<Mc<27.7 M⊕. The two planets in the AU Mic system are in near 9:4 mean-motion resonance. We show that this configuration is dynamically stable and should produce TTV. Our non-detection of significant TTV in AU Mic b suggests an upper limit to the mass of AU Mic c of <7 M⊕. Being a young multi-planet system with at least two transiting planets, AU Mic becomes a key system for the study of atmospheres of infant planets as well as of planet-planet and planet-disk dynamics at the early stages of planetary evolution.

I guess there are much more hidden planets coming soon.

TTVs for AU Mic and a new planet candidate

Transit Timing Variations for AU Microscopii b & c

Quote :

We explore the transit timing variations (TTVs) of the young (22 Myr) nearby AU Mic planetary system. For AU Mic b, we introduce three Spitzer (4.5 μm) transits, five TESS transits, 11 LCO transits, one PEST transit, one Brierfield transit, and two transit timing measurements from Rossiter-McLaughlin observations; for \aumic c, we introduce three \tess Cycle transits. We present two independent TTV analyses. First, we use EXOFASTv2 to jointly model the Spitzer and ground-based transits and to obtain the midpoint transit times. We then construct an O-C diagram and model the TTVs with Exo-Striker. Second, we reproduce our results with an independent photodynamical analysis. We recover a TTV mass for AU Mic c of 10.8+2.3−2.2 ME. We compare the TTV-derived constraints to a recent radial-velocity (RV) mass determination. We also observe excess TTVs that do not appear to be consistent with the dynamical interactions of b and c alone, and do not appear to be due to spots or flares. Thus, we present a hypothetical non-transiting "middle-d" candidate exoplanet that is consistent with the observed TTVs, the candidate RV signal, and would establish the AU Mic system as a compact resonant multi-planet chain in a 4:6:9 period commensurability. These results demonstrate that the AU Mic planetary system is dynamically interacting producing detectable TTVs, and the implied orbital dynamics may inform the formation mechanisms for this young system. We recommend future RV and TTV observations of AU Mic b and c to further constrain the masses and to confirm the existence of possible additional planet(s).

Revised mass measurements for both planets of AU Mic

One year of AU Mic with HARPS: I - measuring the masses of the two transiting planets

Quote :

The system of two transiting Neptune-sized planets around the bright, young M-dwarf AU Mic provides a unique opportunity to test models of planet formation, early evolution, and star-planet interaction. However, the intense magnetic activity of the host star makes measuring the masses of the planets via the radial velocity (RV) method very challenging. We report on a 1-year, intensive monitoring campaign of the system using 91 observations with the HARPS spectrograph, allowing for detailed modelling of the ∼600ms−1 peak-to-peak activity-induced RV variations. We used a multidimensional Gaussian Process framework to model these and the planetary signals simultaneously. We detect the latter with semi-amplitudes of Kb=5.8±2.5ms−1 and Kc=8.5±2.5ms−1, respectively. The resulting mass estimates, Mb=11.7±5.0M⊕ and Mc=22.2±6.7M⊕, suggest that planet b might be less dense, and planet c considerably denser than previously thought. These results are in tension with the current standard models of core-accretion. They suggest that both planets accreted a H/He envelope that is smaller than expected, and the trend between the two planets' envelope fractions is the opposite of what is predicted by theory.

Edasich wrote:

TTVs for AU Mic and a new planet candidate

Here's a great twitter thread by Hugh Osborn showing how the CHEOPS TTV's aren't consistent with the Wittrock et al model. Their third planet candidate may not exist (it would have made the system really crammed), but perhaps there's still a third planet somewhere in system.
https://twitter.com/exohugh/status/1493167486950424579

Another paper on AU Mic d TTV's.

Validating AU Microscopii d with Transit Timing Variations
https://arxiv.org/abs/2302.04922

Welcome to AU Mic e

The magnetic field and multiple planets of the young dwarf AU Mic

Quote :

In this paper we present an analysis of near-infrared spectropolarimetric and velocimetric data of the young M dwarf AU Mic, collected with SPIRou at the Canada-France-Hawaii telescope from 2019 to 2022, mostly within the SPIRou Legacy Survey. With these data, we study the large- and small-scale magnetic field of AU Mic, detected through the unpolarized and circularly-polarized Zeeman signatures of spectral lines. We find that both are modulated with the stellar rotation period (4.86 d), and evolve on a timescale of months under differential rotation and intrinsic variability. The small-scale field, estimated from the broadening of spectral lines, reaches 2.61±0.05 kG. The large-scale field, inferred with Zeeman-Doppler imaging from Least-Squares Deconvolved profiles of circularly-polarized and unpolarized spectral lines, is mostly poloidal and axisymmetric, with an average intensity of 550±30 G. We also find that surface differential rotation, as derived from the large-scale field, is ≃30% weaker than that of the Sun. We detect the radial velocity (RV) signatures of transiting planets b and c, although dwarfed by activity, and put an upper limit on that of candidate planet d, putatively causing the transit-timing variations of b and c. We also report the detection of the RV signature of a new candidate planet (e) orbiting further out with a period of 33.39 ± 0.10 d, i.e., near the 4:1 resonance with b. The RV signature of e is detected at 6.5 σ while those of b and c show up at ≃ 4 σ, yielding masses of 10.2^+3.9_-2.7 and 14.2^+4.8_-3.5 Earth masses for b and c, and a minimum mass of 35.2^+6.7_-5.4 Earth masses for e.