Testing the fragmentation limit in the Upper Sco association★
Bibliographic record
Abstract
We present the results of a deep (J∼ 21 at 5σ) infrared photometric survey of a 0.95-deg2 area in the central region of the Upper Sco association. The photometric observations consist of a deep Y+J-band image obtained with the Wide Field Camera on the United Kingdom Infra-Red Telescope (UKIRT) with part coverage in Z complemented by the methane ON and OFF imaging survey conducted with the Wide-field InfraRed Camera on the Canada–France–Hawaii Telescope. We have selected five potential T-type objects belonging to the Upper Sco association on the basis of their blue methane colours and their J− CH4 off colours. We have also identified a sample of seven to eight Upper Sco member candidates bridging the gap between known cluster M types and our new T-type candidates. These candidates were selected based on their positions in various colour–magnitude diagrams, and they follow the sequence of known Upper Sco members identified in the UKIRT Infrared Deep Sky Survey Galactic Clusters Survey. We present additional membership constraints using proper motion estimates from the multiple epochs available with us. We also present optical and near-infrared spectra obtained with the X-Shooter spectrograph on the Very Large Telescope for five L-type candidates covering the 0.6–2.5 m wavelength range, none of which is confirmed as a young brown dwarf. We discuss the lack of detection of new candidate members as well as the possible turn-down in the Upper Sco mass function as we are approaching the fragmentation limit.
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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 | 0.001 | 0.008 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
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".