---
title: 'TOI-6692 b: Eccentric Giant Exoplanet Characterization'
url: https://www.emergentmind.com/topics/toi-6692-b
type: topic
---

# TOI-6692 b: Eccentric Giant Exoplanet Characterization

TOI-6692 b is a transiting giant exoplanet discovered via a single transit in TESS photometry and characterized through extensive radial velocity (RV) and ground-based photometric follow-up [2601.16357]. It is notable for its moderate eccentricity, secure mass and radius determination at an orbital period exceeding 100 days, and evidence for an outer companion inferred from a long-term RV drift. The multi-modal discovery and subsequent characterization workflows exemplify best practices for confirming long-period single-transit TESS candidates.

## 1. Discovery Workflow and Observational Timeline

TOI-6692 b (TIC 324609409) was initially identified as a candidate by citizen-science teams—the Visual Survey Group and Planet Hunters TESS—as a community TESS Object of Interest (cTOI) in October 2021, later promoted to TOI-6692 in October 2023. TESS observed the target in Sectors 27 (600s cadence) and 39, 66, 67, 93, 94 (120s cadence), with only a single transit event (depth ≈ 6 ppt; duration ≈ 11 h) recorded in Sector 39. The single-transit nature precluded a SPOC pipeline TOI designation at the time. 

The period was subsequently constrained using multi-instrument RV monitoring:
- Planet Finder Spectrograph (PFS, Magellan II 6.5m): 45 spectra (2022 May–2024 Jun; R ≈ 115,000)
- CHIRON (CTIO 1.5m): 31 spectra (2021 Sep–2022 Sep; R ≈ 80,000)
- FEROS (MPG 2.2m): 6 spectra (2023 Aug–2024 Jun; R ≈ 48,000)
- CORALIE (Euler 1.2m): 7 spectra (2024 Apr–Jul; R ≈ 60,000)

A total of 89 RVs revealed a 130-day Keplerian signal and a persistent long-term linear drift. Ground-based photometric follow-up was performed using the LCOGT network: twelve consecutive nights on six 1m telescopes at CTIO, SAAO, SSO with SINISTRO cameras in Sloan i′. While ingress and egress of the ∼11 hr transit were not captured, a 5–6 ppt in-transit signal was detected on 2025 May 24 UT, permitting a refined orbital period determination.

## 2. Fundamental Physical and Orbital Parameters

Fitting combined data with the EXOFASTv2 suite (incorporating TESS photometry, multi-instrument RVs, Gaia parallax, broadband SED, and spectroscopic priors), the following system parameters were derived:

| Parameter          | Value                                                       | Uncertainty/Notes                |
|--------------------|------------------------------------------------------------|----------------------------------|
| Orbital period     | $P = 131.125 \pm 0.012$ days (updated global fit)          | Previous: $130.57^{+0.42}_{-0.40}$ days |
| Transit epoch      | $T_0 = 2459378.4174 \pm 0.0022$ BJD_TDB                    |                                  |
| Transit duration   | $T_{14} = 11.06 \pm 0.24$ hours                            |                                  |
| Eccentricity       | $e = 0.537 \pm 0.010$                                      |                                  |
| Arg. of Periastron | $\omega_p = -16.6^{+7.9}_{-7.7}$ degrees                   |                                  |
| Planet mass        | $M_p = 0.62^{+0.080}_{-0.070} M_J$                         |                                  |
| Planet radius      | $R_p = 1.04 \pm 0.05 R_J$                                  |                                  |
| Bulk density       | $\rho_p \simeq 0.73$ g cm$^{-3}$                           | Computed: $0.62 M_J / 1.04^3 R_J$|
| Semi-major axis    | $a = 0.512^{+0.014}_{-0.012}$ AU                           |                                  |
| RV semi-amplitude  | $K = 28.5^{+3.2}_{-2.7}$ m s$^{-1}$                        |                                  |
| RV drift           | $\dot{\gamma} = -0.0280^{+0.0046}_{-0.0045}$ m s$^{-1}$ day$^{-1}$ |                      |

These metrics place TOI-6692 b within the regime of moderately inflated giant planets on eccentric orbits at intermediate periods.

## 3. Radial Velocity and Transit Characterization Equations

Standard equations quantifying the system's dynamics were employed:

- **Radial velocity semi-amplitude:**
  $$
  K = \left(\frac{2\pi G}{P}\right)^{1/3} \frac{M_p \sin i}{(M_* + M_p)^{2/3}} \cdot \frac{1}{\sqrt{1-e^2}}
  $$
  where $K$ is the RV semi-amplitude, $P$ the period, $M_p$ the planet’s mass, $M_*$ the stellar mass, $e$ the orbital eccentricity.

- **Transit duration (assuming circular chord):**
  $$
  T_{14} = \frac{P}{\pi} \arcsin\left[\frac{\sqrt{(R_* + R_p)^2 - (a \cos i)^2}}{a}\right]
  $$
  where $T_{14}$ is the total transit duration, $R_*$ the stellar radius, $R_p$ the planetary radius, $a$ the semi-major axis, and $i$ the inclination.

These relations were central to the EXOFASTv2 global fits used to infer system architecture.

## 4. Eccentricity and Migration Histories

The measured eccentricity ($e \approx 0.54$) is significant but falls distinctly below the $e \gtrsim 0.8$ regime characteristic of high-eccentricity tidal migrators (e.g., HD 80606 b). Instead, planet-planet scattering models such as those discussed by Petrovich (2014) predict $e \leq 0.8$ for runaway encounters, fully consistent with TOI-6692 b’s observed eccentricity. This suggests an evolutionary scenario involving dynamical interactions and subsequent weak tidal damping rather than recent high-e migration.

A plausible implication is that TOI-6692 b presents a valuable testbed for constraining intermediate-eccentricity migration mechanisms and the population outcomes of scattering events at moderate orbital periods.

## 5. Ephemeris Refinement and Prospects for Future Monitoring

The initial single TESS transit left an approximate $\pm$4.6 day uncertainty on the orbital period. The multi-night LCOGT in-transit detection in 2025 narrowed this to $\pm$0.012 day, yielding an updated ephemeris:
- Next transit windows can be scheduled with $<$20 min timing uncertainty.

Such precise period refinement enables targeted capture of full ingress/egress in future campaigns. Ongoing and proposed monitoring via ground- and space-based observatories (including LCOGT and CHEOPS) will permit detailed transit curve characterization and transmission spectroscopy (TSM $\simeq$ 23), supporting atmospheric and interior structure inference.

## 6. Long-Term Radial Velocity Trends and Outer Companion Constraints

A persistent linear RV slope ($\dot{\gamma} \sim -0.028$ m s$^{-1}$ day$^{-1}$ across $\sim$800 days) signals the gravitational influence of an outer companion. Speckle imaging with Zorro/Gemini-South excludes stellar companions brighter than $\Delta$mag $\leq$ 6 at separations 0.1–1.2″ (30–376 AU), imposing an upper mass limit $<$400 $M_J$ for resolved objects at $>$20 AU.

Interior to $\sim$20 AU, RV residuals constrain $M \sin i$ versus $a$. Continued RV monitoring is needed to establish the outer companion’s orbital period and mass, a plausible implication being the presence of low-mass substellar or planetary companions influencing TOI-6692 b’s long-term dynamical evolution.

## 7. Significance within TESS and Exoplanet Population Context

TOI-6692 b is one of the few single-transit TESS candidates at $P > 100$ days for which a secure mass, radius, and eccentricity have been measured. Its confirmation highlights the efficacy and necessity of coordinated citizen-science identification, high-cadence RV monitoring, and multi-night ground-based photometry for constraining ephemerides and system parameters in cases of limited transit coverage. The night-to-night stability demonstrated by LCOGT and similar facilities proves crucial for refining long-period single-transit planet discoveries.

For population studies, TOI-6692 b enters an exclusive regime, providing empirical leverage on late-stage migration channels and the architectures of giant planet systems beyond 1 AU [2601.16357].

Source: https://www.emergentmind.com/topics/toi-6692-b