SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS (SONYC): THE BOTTOM OF THE INITIAL MASS FUNCTION IN NGC 1333
Bibliographic record
Abstract
SONYC—Substellar Objects in Nearby Young Clusters—is a survey program to investigate the frequency and properties of substellar objects with masses down to a few times that of Jupiter in nearby star-forming regions. Here, we present the first results from SONYC observations of NGC 1333, a ∼1 Myr old cluster in the Perseus star-forming complex. We have carried out extremely deep optical and near-infrared imaging in four bands ( i ', z ', J , K ) using Subaru Prime Focus Camera and Multi-Object InfraRed Camera and Spectrograph (MOIRCS) instruments at the Subaru telescope. The survey covers 0.25 deg 2 and reaches completeness limits of 24.7 mag in the i ' band and 20.8 mag in the J band. We select 196 candidates with colors as expected for young, very low mass objects. Follow-up multi-object spectroscopy with MOIRCS is presented for 53 objects. We confirm 19 objects as likely brown dwarfs (BDs) in NGC 1333, seven of them previously known. Nine additional objects are classified as possible stellar cluster members, likely with early to mid M spectral types. The confirmed objects are strongly clustered around the peak in the gas distribution and the core of the cluster of known stellar members. For 11 of them, we confirm the presence of disks based on Spitzer /Infrared Array Camera photometry. The effective temperatures for the BD sample range from 2500 K to 3000 K, which translates to masses of ∼0.015–0.1 M ☉ , based on model evolutionary tracks. For comparison, the completeness limit of our survey translates to mass limits of 0.004 M ☉ for A V ≲ 5 mag or 0.008 M ☉ for A V ≲ 10 mag. Compared with other star-forming regions, NGC 1333 shows an overabundance of BDs relative to low-mass stars, by a factor of 2–5. On the other hand, NGC 1333 has a deficit of planetary-mass objects: based on the surveys in σ Orionis, the Orion Nebula Cluster and Chamaeleon I, the expected number of planetary-mass objects in NGC 1333 is 8–10, but we find none. It is plausible that our survey has detected the minimum mass limit for star formation in this particular cluster, at around 0.012–0.02 M ☉ . If confirmed, our findings point to significant regional/environmental differences in the number of BDs and the minimum mass of the initial mass function.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 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".