---
title: 'HD 143811 AB b: Circumbinary Planet Imaging'
url: https://www.emergentmind.com/topics/hd-143811-ab-b
type: topic
---

# HD 143811 AB b: Circumbinary Planet Imaging

HD 143811 AB b is a directly imaged, young, planetary-mass companion orbiting the close double-lined spectroscopic binary HD 143811 AB, itself a member of the Scorpius–Centaurus (Sco-Cen) star-forming region. This object represents a benchmark system for empirical characterization of planet formation and dynamical evolution in circumbinary environments, due to its rare status as a directly imaged planet orbiting a compact spectroscopic binary at moderate separation [2509.06729, 2509.06009, 2509.06727].

## 1. Host System: HD 143811 AB

HD 143811 AB is a well-characterized double-lined spectroscopic binary (SB2) comprising two solar-type stars:
- Primary: $M_A = 1.30^{+0.03}_{-0.05}\ M_\odot$, $T_{\rm eff,A} = 6439 \pm 132$ K,
- Secondary: $M_B = 1.15^{+0.03}_{-0.04}\ M_\odot$, $T_{\rm eff,B} = 5900 \pm 157$ K,
- Metallicity: $[M/H] = -0.18 \pm 0.10$,
- Orbital period: $P = 18.59098 \pm 0.00007$ days,
- Eccentricity: $e = 0.4935 \pm 0.0013$,
- Semimajor axis: $a = 0.1854^{+0.0014}_{-0.0024}$ au,
- Inclination: $i_{AB} = 22.9^{+0.3}_{-0.2}^\circ$ (with retrograde mirror solution $156.1^{+0.2}_{-0.3}^\circ$).

The system's age, adopted from Sco-Cen subgroup studies, is $13 \pm 4$ Myr, and the distance is $136.9 \pm 0.4$ pc. Both components exhibit lithium absorption indicative of youth, with no strong chromospheric emission [2509.06727].

## 2. Discovery and Observational Confirmation

HD 143811 AB b was first identified via direct imaging by the Gemini Planet Imager (GPI) in 2016, confirmed at subsequent epochs with GPI (2019), Keck/NIRC2 ($L'$-band, 2022), and SPHERE/IRDIS ($H_{23}$ dual-band, 2025). These multi-instrument detections leveraged advanced high-contrast post-processing (e.g., PACO, ADI) to achieve sensitivity at separations $<0.5"$, crucial for circumbinary planet discovery [2509.06009, 2509.06729].

Key astrometric measurements:
| Epoch                     | Instrument        | Separation [mas]      | Position angle [deg]   |
|---------------------------|-------------------|-----------------------|------------------------|
| 2016-04-30                | GPI ($H$)         | $427.8 \pm 3.0$       | $11.79 \pm 0.46$       |
| 2019-08-10/11             | GPI ($H$)         | $427.3 \pm 3.3$       | $16.29 \pm 0.38$       |
| 2022-06-10                | NIRC2 ($L'$)      | $421 \pm 9$           | $18.7 \pm 1.2$         |
| 2025-07-24                | SPHERE ($H_{23}$) | $431.1 \pm 0.63$      | $21.71 \pm 0.09$       |

All epochs yield a projected separation $\sim 430$ mas ($\approx 60$ au), directly confirming the companion. A common proper motion analysis rejects the background hypothesis at $>20\sigma$; the companion’s motion is consistent with a bound orbit rather than a stationary background object [2509.06729, 2509.06009].

## 3. Orbital Architecture and Dynamical Configuration

Orbital parameters were derived via OFTI (“Orbits for the Impatient”) as implemented in orbitize! v3, incorporating astrometry, system mass ($2.44$–$2.46~M_\odot$), and Gaia parallax. The resulting solution:
- Semimajor axis: $a = 64^{+32}_{-14}$ au [2509.06729], $63^{+30}_{-12}$ au [2509.06009],
- Eccentricity: $e = 0.23^{+0.24}_{-0.16}$ [2509.06729], $0.19 \pm 0.12$ [2509.06009],
- Inclination: $i = 38 \pm 16^\circ$ [2509.06729], $37^{+11}_{-12}~^\circ$ [2509.06009],
- Period: $P = 330^{+280}_{-100}$ yr [2509.06729], $319^{+248}_{-86}$ yr [2509.06009].

The orbit is moderately inclined, near-circular, and stable relative to the tight inner binary ($a_{\rm bin}/a_{\rm p} \sim 0.003$). Current data permit coplanarity but lack full 3D constraint on the mutual inclination; both the planet's and binary's node angles are poorly determined. Future astrometric and interferometric monitoring is required to resolve the orbital architecture definitively [2509.06727].

## 4. Photometric and Spectroscopic Characterization

The planetary companion's photometry and spectroscopy were derived from multi-band imaging and H-band spectroscopy:
- GPI $H$-band spectrum ($1.50-1.80$ $\mu$m, $R\sim40$, SNR up to 7.7),
- Keck/NIRC2 $L'$-band ($M_{L'} = 10.87 \pm 0.32$),
- SPHERE/IRDIS $H_{23}$ ($H2 = 14.31 \pm 0.10$, $H3 = 13.85 \pm 0.10$),
- Non-detection in SPHERE/IFS ($J > 21.34$).

Observed colors ($H_{GPI} - L'_{NIRC2} = 3.3 \pm 0.4$; $J-H2 > 1.4$) and spectra are consistent with a cool, planetary-mass object. The flux calibration models the host as an unresolved binary, with negligible flux error propagation ($<0.2\%$ in $H$-band) [2509.06009, 2509.06729].

Spectral comparison utilized both PHOENIX stellar templates and Exo-REM/HADES exoplanet atmosphere models. The data strongly favor cool Exo-REM-like atmospheres with thick cloud cover and vertical mixing, disfavouring stellar spectral templates, notably with the addition of $L'$ data [2509.06729, 2509.06009].

## 5. Physical Properties and Atmospheric Modeling

Atmospheric fits yield:
- Effective temperature: $T_{\rm eff} = 1042^{+178}_{-132}$ K (Exo-REM, [2509.06729]), $T_{\rm int} = 1000 \pm 30$ K (HADES, [2509.06009]),
- Bolometric luminosity: $L = 3.3^{+0.8}_{-0.6} \times 10^{-5}\ L_\odot$ (Stefan–Boltzmann consistent),
- Planetary mass: $M = 5.6 \pm 1.1~M_{\rm Jup}$ (hot-start models, [2509.06729]), $6.1^{+0.7}_{-0.9}~M_{\rm Jup}$ (HADES, [2509.06009]),
- Radius: $R = 1.41 \pm 0.03\ R_{\rm Jup}$ (evolution models, [2509.06729]), $1.4 \pm 0.1~R_{\rm Jup}$ (HADES, [2509.06009]),
- Metallicity: $[{\rm Fe/H}] = 0.1^{+0.8}_{-0.4}$,
- Sedimentation parameter: $f_{\rm sed} = 2.8^{+1.1}_{-0.8}$,
- Vertical mixing: $\log K_{zz} = 9.0^{+1.2}_{-1.5}$.

The companion is interpreted as a young, self-luminous, and likely cloudy planetary-mass object. Atmospheric fits indicate the presence of vertical mixing and potential chemical disequilibrium. The physical parameters are constrained assuming a $13\pm4$ Myr age and hot-start entropy initial conditions; core mass remains weakly constrained [2509.06729, 2509.06009].

## 6. Scientific Significance, Formation, and Future Prospects

HD 143811 AB b is one of a select group of directly imaged circumbinary planets and is unique at its moderate ($\sim 60$ au) separation from a tight ($a\sim0.19$ au), eccentric spectroscopic binary. This configuration provides a critical test for planet formation theories in multiple-star environments. The low-to-moderate eccentricity and separation are compatible with in situ formation by core accretion or disk instability, but post-formation migration or scattering remain possible. The system's architecture, notably the large planet-binary separation ratio, ensures dynamical stability [2509.06729, 2509.06009, 2509.06727].

HD 143811 AB b joins a small cohort (HD 106906 b, b Cen b, WISPIT 1bc) of planets imaged in orbit around close binaries, but it occupies a previously underrepresented parameter regime. As both host binary and planet are sufficiently bright and well separated, the system is considered a prime candidate for:
- Continued high-precision astrometry,
- Interferometric monitoring (VLTI/GRAVITY),
- Spectral and photometric surveys with JWST and ELTs for atmosphere/composition studies,
- Further dynamical modeling to constrain mutual inclination and formation pathway.

A plausible implication is that discovery and further characterization of such systems will clarify the incidence and migration/formation histories of circumbinary planets in contrast to those around single stars, and constrain the conditions under which massive planets survive or form in multi-stellar disks [2509.06729, 2509.06009, 2509.06727].

## 7. Summary Table: System and Planet Properties

| Parameter                      | HD 143811 AB         | HD 143811 AB b              |
|---------------------------------|----------------------|-----------------------------|
| Type                            | SB2, F+G            | Directly imaged planet      |
| $M_A$ ($M_\odot$)               | $1.30^{+0.03}_{-0.05}$ | —                        |
| $M_B$ ($M_\odot$)               | $1.15^{+0.03}_{-0.04}$ | —                        |
| [M/H]                           | $-0.18 \pm 0.10$     | $0.1^{+0.8}_{-0.4}$         |
| $P_{\rm bin}$ (days)            | $18.59098 \pm 0.00007$ | —                        |
| $e_{\rm bin}$                   | $0.4935 \pm 0.0013$  | —                           |
| $a_{\rm bin}$ (au)              | $0.1854^{+0.0014}_{-0.0024}$ | —                 |
| $a_{\rm p}$ (au)                | —                   | $64^{+32}_{-14}$            |
| $e_{\rm p}$                     | —                   | $0.23^{+0.24}_{-0.16}$      |
| $i_{\rm p}$ (deg)               | —                   | $38 \pm 16$                 |
| $M_{\rm p}$ ($M_{\rm Jup}$)     | —                   | $5.6 \pm 1.1$ / $6.1^{+0.7}_{-0.9}$ |
| $T_{\rm eff,p}$ (K)             | —                   | $1042^{+178}_{-132}$ / $1000\pm30$   |
| $L_{\rm p}$ ($L_\odot$)         | —                   | $3.3^{+0.8}_{-0.6} \times 10^{-5}$ |
| Age (Myr)                       | $13 \pm 4$           | $13 \pm 4$                  |
| Distance (pc)                   | $136.9 \pm 0.4$      | $136.9 \pm 0.4$             |

All planet parameters reference [2509.06729] and [2509.06009]; host binary parameters are from [2509.06727].

## References

- [2509.06729] HD 143811 AB b: A Directly Imaged Planet Orbiting a Spectroscopic Binary in Sco-Cen
- [2509.06009] GPI+SPHERE detection of a 6.1 $M_{\rm Jup}$ circumbinary planet around HD 143811
- [2509.06727] Characterization of the Host Binary of the Directly Imaged Exoplanet HD 143811 AB b

Source: https://www.emergentmind.com/topics/hd-143811-ab-b