The distance and neutral environment of the massive stellar cluster Westerlund 1
Bibliographic record
Abstract
Context.In spite of a large number of recent publications about the massive stellar cluster Westerlund 1, its distance from the Sun remains uncertain with values as low as 1.1 kpc, but largely between 4 and 5 kpc.Aims.The goal of this study is to determine a distance to Westerlund 1 independent of the characteristics of the stellar population and to study its neutral environment, using observations of atomic hydrogen.Methods.The H i observations are taken from the Southern Galactic Plane Survey to study H i absorption in the direction of the H ii region created by the members of Westerlund 1 and to investigate its environment as observed in the H i line emission.A Galactic rotation curve was derived using the recently revised values for the Galactic centre distance of R = 7.6 kpc, and the velocity of the Sun around the Galactic centre of Θ = 214 km s -1 .This rotation curve successfully predicts the location of the Tangent point gas and the velocity of the Sagittarius Arm outside the solar circle on the far side of the Galaxy to within 4 km s -1 .Compared to the typically used values of R = 8.5 kpc and Θ = 220 km s -1 this reduces kinematically determined distances by more than 10%.Results.The newly determined rotation model leads us to derive a distance of 3.9 ± 0.7 kpc to Westerlund 1, consistent with a location in the Scutum-Crux Arm.Included in this estimate is a very careful investigation of possible sources of error for the Galactic rotation curve.We also report on small expanding H i features around the cluster with a maximum dynamic age of 600 000 years and a larger bubble which has a minimum dynamic age of 2.5 million years.Additionally we re-calculated the kinematic distances to nearby H ii regions and supernova remnants based on our new Galaxic rotation curve.Conclusions.We propose that in the early stages of the development of Wd 1 a large interstellar bubble of diameter about 50 pc was created by the cluster members.This bubble has a dynamic age similar to the age of the cluster.Small expanding bubbles, with dynamical ages ∼0.6 Myr are found around Wd 1, which we suggest consist of recombined material lost by cluster members through their winds.
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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 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| 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".