AC02
Measure starlight in a crowded sky
A telescope turns each star into a patch of light. Follow the photons into pixels, learn to separate overlapping stars, and repeat a measurement on actual TESS data. Begin with the story, then work through the two measurement chapters before opening the data tutorial.
L1
Did the star really fade?
Follow a circle around a star to see how blurred images, background and neighboring light change a brightness measurement.
L1
From one photoelectron to an aperture of pixels
Build a photon-counting model, aperture correction and signal-to-noise estimate, including the background that remains after subtraction.
L2
One pixel can contain light from two stars
Derive a weighted two-star fit from a two-pixel example, then test blending, uncertainty and injection recovery.
L3
Extract TESS brightness from twelve pixels
Re-run aperture photometry on frozen measured TIC 25155310 Sector 1 pixels, keeping quality flags, background and failure examples.
L4
Read the residuals in deblending and difference images
Read ZOGY, scarlet and version-pinned Rubin documentation to distinguish source separation, image differences and detections.
Sources and calculation scope
- MAST, Read and Display A TESS Target Pixel File
Target TIC 25155310, Sector 1, FITS columns and aperture bit 2. The frozen tutorial subset is extracted from this named product.
- TESS Science Data Products Description, Revision F (2020)
Section 4.2.2, Table 8: FLUX is already background-subtracted; FLUX_BKG and FLUX_BKG_ERR preserve the removed estimate. Table 32 describes quality flags.
- Photutils 3.1.1, Aperture photometry
Fractional aperture weighting, background subtraction and error propagation. The browser uses its own documented midpoint area quadrature.
- Photutils 3.1.1, PSF photometry
Source grouping, fitted fluxes and the role of an accurate point-spread function. The teaching fit fixes both centroids and the Gaussian width.
- Zackay, Ofek & Gal-Yam (2016), Proper image subtraction, arXiv:1601.02655v2
Read sections III.1, III.3, III.6, IV.1 and VIII.1–VIII.4; compare the difference image with its detection score. The guide reads the method, not a reproduced survey pipeline.
- Melchior et al. (2018), scarlet, arXiv:1802.10157v2
Section 2 and figure 1: multiband components, morphology constraints and residuals. Read alongside the authors’ documentation.
- scarlet authors, Core Concepts
Components, observations and PSF convolution in the authors’ implementation; accessed 2026-10-28.
- Rubin Science Pipelines w_2026_41, ip_diffim overview
Version-pinned subtraction tasks and Alard–Lupton kernel matching; prevents equating a historical paper with every current pipeline.