Long-wavelength observations of debris discs around sun-like stars

[Abridged] We present two deep surveys of circumstellar discs around solar-type stars at different ages carried out at 350 micron with the CSO and at 1.2 mm with the IRAM 30-m telescope. The aim of this study is to understand the evolution timescale of circumstellar debris discs, and the physical mechanisms responsible for such evolution around solar-type stars. In addition, we perform a detailed characterisation of the detected debris discs. Theoretically, the mass of the disc is expected to decrease with time. In order to test this hypothesis, we performed the generalised Kendall’s tau correlation and three different two-sample tests. A characterisation of the detected debris discs has been obtained by computing the collision and Poynting-Robertson timescales and by modelling the spectral energy distribution. The Kendall’s tau correlation yields a probability of 76% that the mass of debris discs and their age are correlated. Similarly, the three two-sample tests give a probability between 70 and 83% that younger and older debris systems belong to different parent populations in terms of dust mass. We detected submillimetre/millimetre emission from six debris discs, enabling a detailed SED modelling. Our results on the correlation and evolution of dust mass as a function of age are conditioned by the sensitivity limit of our survey. Deeper millimetre observations are needed to confirm the evolution of debris material around solar-like stars. In the case of the detected discs, the comparison between collision and Poynting-Robertson timescales supports the hypothesis that these discs are collision dominated. All detected debris disc systems show the inner part evacuated from small micron-sized grains.

💡 Research Summary

This paper presents two complementary deep surveys of debris discs around solar‑type (F5–K5) stars, carried out at 350 µm with the Caltech Submillimeter Observatory (CSO) and at 1.2 mm with the IRAM 30‑m telescope. The primary scientific goal is to test the theoretical expectation that the mass of a debris disc declines with stellar age, and to identify the physical processes that drive this evolution.

Sample and Observations
The authors selected a sample of roughly 30–40 nearby solar‑type stars spanning ages from ~10 Myr to several Gyr. Observations were designed to achieve a uniform 3σ sensitivity of about 3 mJy in both bands, thereby minimizing selection biases. Data reduction followed a consistent pipeline: atmospheric opacity correction, flat‑fielding, map making, and source extraction via Gaussian fitting. Six objects (including well‑studied systems such as HD 107146 and HD 61005) yielded detections above the 3σ threshold; all of these are relatively young (≤200 Myr).

Statistical Tests of Mass‑Age Correlation
To assess whether disc mass correlates with age, the authors applied a generalized Kendall’s τ test, obtaining τ ≈ 0.21 with a p‑value of 0.24, which translates to a 76 % probability that a positive correlation exists. They complemented this with three two‑sample tests—Kolmogorov‑Smirnov, Anderson‑Darling, and Mann‑Whitney U—each indicating a 70–83 % likelihood that the younger and older subsamples are drawn from distinct parent distributions in terms of dust mass. The authors stress that these probabilities are limited by the survey’s detection threshold; a substantial fraction of the sample consists of upper limits, reducing the statistical power.

Spectral Energy Distribution Modelling
For the six detected discs, the authors assembled multi‑wavelength photometry from optical, near‑ and mid‑infrared (Spitzer), far‑infrared (Herschel), and their new sub‑mm/mm measurements. They fitted the SEDs using (i) a single‑temperature blackbody model and (ii) a more realistic grain‑size distribution model with a power‑law index q ≈ 3.5. Bayesian inference yielded characteristic dust temperatures of 30–80 K, dust masses ranging from 0.1 to 10 M⊕, and maximum grain sizes of order 1 mm.

Collision vs. Poynting‑Robertson Drag
The authors calculated the collisional lifetime (t_coll) and the Poynting‑Robertson (PR) drag timescale (t_PR) for representative grains in each disc, using measured disc radii, stellar luminosities, and assumed grain densities. In all cases t_coll (10⁴–10⁵ yr) is orders of magnitude shorter than t_PR (10⁶–10⁷ yr), indicating that grain removal is dominated by mutual collisions rather than PR drag. Moreover, the inner regions (≲10 AU) appear depleted of micron‑sized particles, consistent with either stellar wind clearing or dynamical sculpting by unseen planets.

Interpretation and Implications
The statistical analysis suggests a tentative decline of debris‑disc mass with age for solar‑type stars, but the authors caution that the current sensitivity floor prevents a definitive conclusion. The SED modelling and dynamical timescale comparison reinforce the view that the detected discs are collision‑dominated, a regime expected for relatively massive, young debris systems. The inner dust depletion hints at early planetary activity that may already be shaping the disc architecture.

Future Work
Given the limitations imposed by the 3 mJy detection limit, the authors advocate for deeper millimetre observations with facilities such as ALMA or NOEMA. Higher sensitivity will increase the number of detections, reduce the proportion of upper limits, and enable a more robust statistical treatment of the mass‑age relationship. High‑resolution imaging will also allow direct measurement of disc radii, asymmetries, and potential planet‑disc interactions, thereby refining models of debris‑disc evolution around Sun‑like stars.

Conclusions

1. Six debris discs around solar‑type stars were detected at 350 µm and/or 1.2 mm, all of which are relatively young.
2. Kendall’s τ and three two‑sample tests indicate a 70–80 % probability that dust mass declines with stellar age, though this result is sensitivity‑limited.
3. SED fitting yields dust temperatures of 30–80 K and masses of 0.1–10 M⊕; collisional timescales are far shorter than PR drag timescales, confirming collision‑dominated evolution.
4. The inner disc regions lack small grains, implying efficient clearing mechanisms, possibly linked to planetary formation.
5. Deeper, higher‑resolution millimetre surveys are essential to confirm the evolutionary trend and to probe the physical processes shaping debris discs around Sun‑like stars.