Mission Overview

JWST Resolved Stellar Populations Early Release Science ("JWSTSTARS")


Primary Investigator: Daniel R. Weisz

HLSP AuthorsDaniel R. Weisz

Released: 2024-02-15

Updated: 2024-02-15

Primary Reference(s): Weisz et al. 2023, Weisz et al. 2024

DOI: 10.17909/cn6n-xg90

Citations: See ADS statistics

Read Me

Source Data:

Left: The color-image of the NIRCam observation of star-forming dwarf galaxy WLM.  Select zoom-ins are shown to highlight JWST’s ability to resolve its stellar populations.  Right: The NIRCam F090W-F150W color-magnitude diagram of WLM.  This ERS program includes similar NIRCam and NIRISS data for globular cluster M92, ultra-faint dwarf galaxy Draco II, and star-forming dwarf galaxy WLM.


The JWST Resolved Stellar Population Early Release Science (ERS) Program obtained NIRCam and NIRISS imaging of 3 resolved stellar targets in the Local Group: globular cluster M92, ultra-faint dwarf galaxy Draco II, and star-forming dwarf galaxy WLM. NIRCam was the primary instrument and observed each target in 4 filters: M92 (F090W, F150W, F277W, F444W), Draco II (F090W, F150W, F360M, F480M), WLM (F090W, F150W, F250M, F430M). NIRISS was used in parallel and obtained imaging in 2 filters (F090W, F150W). The 3rd exposure of M92, for both NIRCam and NIRISS, is not included in the analysis as it suffered from excess astrometric jitter and cannot produce adequate photometry. See Weisz et al. 2024 for more details.

Using this imaging data, the ERS team developed JWST NIRCam and NIRISS modules for DOLPHOT, a crowded field stellar photometry package widely used in nearby galaxies. This data release includes the full, multiband photometric catalogs produced by DOLPHOT for each field and the id2 drizzled reference images used for astrometrically aligning images for each target. The NIRISS field for Draco II did not contain prominent member stars, and the photometric catalog is not included in this data release.  

The FITS images used for this data release have the following JWST pipeline versioning information: CAL_VER=1.11.4, CRDS_VER=11.17.2, and CRDS_CTX=jwst_p1147.pmap.

Data Products

Data file naming convention:



  • <inst> is the instrument used, either "nircam" or "niriss"
  • <target> is the target name; one of "draco", "m92", or "wlm"
  • <filter> is the filter used; "f150w" for drizzled images, and combination filters from "f090w", "f150w", "f250m", "f277w", "f360m", "f430m", "f444w", "f480m" for catalogs
  • <prodType> is the data product type; "phot" or "i2d"

Data file types:

_i2d.fits Drizzled images of the target that was used as a reference image for the DOLPHOT reduction
_phot.fits Full-stack 4-band (NIRCAM) photometry or 2-band (NIRISS) tables for each field in the program

Catalog Description

The photometric catalogs are stored as binary fits tables.  The catalogs were constructed as described in Weisz et al. 2024 .  The photometric reductions were performed using the DOLPHOT (Dolphin 2000, 2016) stellar photometry package using the .cal files provided by the JWST pipeline, with pipeline versioning references above and stored in the fits headers.

The columns in each fits file are summarized below and are also contained in the headers of each fits file.

We have not applied any culling criteria to these catalogs.  Weisz et al. 2024  and Warfield et al. (2023) provide suggestions for culling criteria that are applicable to the short wavelength NIRCam data.  However, given the multiband nature of the data and a wide range of possible science use cases, users are encouraged to explore catalog culling criteria tailored to their science case.

Column Description
Number Object number in the catalog
RA ICRS Right Ascension of the source in decimal degrees, aligned to Gaia DR3
DEC ICRS Declination of the source in decimal degrees, aligned to Gaia DR3
X X value of the pixel position on the reference drizzled image
Y Y value of the pixel position on the reference drizzled image
OBJECT TYPE Object type (1=bright star, 2=faint, 3=elongated, 4=hot pixel, 5=extended)
These are followed by 8 columns for each filter, described in detail in the DOLPHOT documentation
[filter name]_VEGA Magnitude for the source, Vega system; Null values are indicated by 99.999
[filter name]_ERR Uncertainty in magnitude (Poisson noise only); Null values are indicated by 9.999 
[filter name]_CHI Goodness-of-fit to the PSF
[filter name]_SNR Signal-to-noise ratio of the measurement
[filter name]_SHARP Sharpness of the source
[filter name]_ROUND Roundness of the source
[filter name]_CROWD Crowding of the source (the difference that subtracting neighbors has on the measured magnitude of the source)
[filter name]_FLAG  DOLPHOT quality flag


Data Access

Both the image observations and the catalogs are available in the MAST Portal and astroquery. Set the 'Provenance Name' filter to JWSTSTARS in the Portal Advanced Search to match all observations. Each catalog is organized as the member product of each reference image observation. They can be downloaded with their reference image as a bundle or individually retrieved by selecting in the download basket. The observations can also be retrieved programmatically using the astroquery.mast module. The code example below retrieves all products.

from astroquery.mast import Observations
all_obs = Observations.query_criteria(provenance_name="jwststars")
data_products = Observations.get_product_list(all_obs)
  • A web-based interface for cross-mission searches of data at MAST or the Virtual Observatory
  • Search for and retrieve JWSTSTARS data products programmatically.


Please remember to cite the appropriate paper(s) below and the DOI if you use these data in a published work. 

Note: These HLSP data products are licensed for use under CC BY 4.0.