Evolution of Brown Dwarf Disks: A<i>Spitzer</i>Survey in Upper Scorpius
Bibliographic record
Abstract
We have carried out a Spitzer survey for brown dwarf disks in the ~5 Myr old Upper Scorpius (UpSco) star-forming region, using IRS spectroscopy from 8 to 12 μm and MIPS photometry at 24 μm. Our sample consists of 35 confirmed very low mass members of UpSco. Thirteen objects in this sample show clear excess flux at 24 μm, explained by dust emission from a circum-substellar disk. The spectral energy distributions (SEDs) of the remaining objects are consistent with pure photospheric emission. Objects without excess emission have either no disks or disks with inner opacity holes of at least ~5 AU radii. Our disk frequency of 37% ± 9% is higher than what has been derived previously for K0-M5 stars in the same region (1.8 σ confidence level), suggesting a mass-dependent disk lifetime in UpSco. The clear distinction between objects with and without disks, as well as the lack of transition objects, shows that disk dissipation inside 5 AU occurs rapidly, probably on timescales of ≲10 5 yr. For the objects with disks, most SEDs are uniformly flat, with flux levels of a few mJy, well modeled as emission from dusty disks affected by dust settling to the midplane. The silicate feature around 10 μm is either absent or weak in our SEDs, arguing for a lack of hot, small dust grains. Compared with younger objects in Taurus, brown dwarf disks in UpSco show less flaring. These results clearly demonstrate that we see disks in an advanced evolutionary state. Dust settling and grain growth are ubiquituous in circum-substellar disks at ages of 5 Myr, arguing for planet-forming processes in brown dwarf disks.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".