FISTAR(1)

💖 NAME 💖

fistar — detecting and characterizing point-like sources.

That's the whole vibe, bestie: it finds star-like blobs in your astronomical images and tells you everything about them. It lives in section 1 of the manual, the User Commands one, so it's a program you just run from the shell. Periodt. 💅

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✨ SYNOPSIS ✨

fistar [options] <input> [-o|--output <output>]

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🦋 DESCRIPTION 🦋

okay so the main character job of this program is to detect and extract sources — like, star-like objects — out of astronomical images. And it does it in three big steps, no skips:

1. First, pixel groups get derived that possibly belong to the sources. These preliminary detections are called source "candidates". (The original page spells it "callad", and honestly? iconic. we love a typo moment. 🙈)
2. Second, those candidates get modelled with some sort of analytic model function, so you can derive way more precise centroid coordinates and shape parameters.
3. Last step: extract the point-spread function (PSF) for the image, based on the detected and modelled sources.

Basically: the input must be an astronomical image, and the output is the list of detected and extracted sources plus all their respective characteristics. That's it, that's the serve. 👑

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🌸 OPTIONS 🌸

🎀 General options 🎀

• -h, --help — gives general summary about the command line options.
• --long-help, --help-long — gives a detailed list of command line options.
• --wiki-help, --help-wiki, --mediawiki-help, --help-mediawiki — gives a detailed list of command line options in Mediawiki format.
• --version, --version-short, --short-version — gives some version information about the program.
• -i, --input <image file> — name of input file from which the sources are extracted.
• -o, --output <data file> — name of the data file where the list of the extracted sources and their respective characteristics are written.

🔥 Basic source detection and characterization options 🔥

• -t, --threshold <threshold> — detection peak threshold, in ADUs.
• -f, --flux-threshold <flux threshold> — detection flux threshold, in ADUs.
• --algorithm <algorithm> — source cadidate extraction algorithm. It can be "uplink" (default) or "parabolapeak".
• -p, --prominence <prominence> — critical relative prominence parameter used in the "uplink" algorithm. The default is to use no prominence based pixel grouping.
• -r, --shrink <shrink factor> — shrink factor applied before star candidate detection. The image is shrunk by this specific factor, and after the detection, the candidate coordinates are multiplied by this value.
• --only-candidates — do not involve any analitic model funcion during the derivation of the centroid coordinates and shape parameters, but derive these from some sort of simple pixel statistics.
• --model <model>[order=<order>] — analytic model function used in the second stage of source extraction. This can be "gauss" (symmetic Gaussian profile), "elliptic" (assymetic Gaussian profile) and "deviated" (Gaussian profile multiplied by a polynomial up to the specified order).
• --iterations symmetric=<n>,general=<n> — the number of Levenberg-Marquardt iterations during the analytic model fit. The fit is done in two substeps: first the symmetric profile parameters are derived only, which step is followed by the fit for all of the shape parameters.
• -s, --sort {x|y|peak|fwhm|amp|flux|noise|s/n} — sort the output list of extracted sources by X or Y coordinate, peak flux (no background level subtracted), profile FWHM, peak intensity (background level is subtracted), total flux, noise level or signal-to-noise ratio; respectively.
• --mag-flux <mag>,<flux> — magnitude - flux conversion level. The specified magnitude will be equivalent to the specified flux level.
• -M, --input-mask <image file> — input mask file to co-add to the mask of the input image. Useful for marking pixels to be excluded from source extraction process beyond the ones which are previously marked in the input image.
• -F, --format <format> — comma separated list of format tags, for formatting the output list of extracted sources. Each row represents an extracted source, while the format specified here defines the quantities listed in each row of the output file. See "Format tags" for more details.

🌈 Format tags 🌈

these are the little building blocks you drop into --format, bestie. each one is a quantity that'll show up in a row of your output file:

• id — an unique identifier for the source (an integer number, in fact).
• ix — integer X coordinate for the centroid pixel.
• iy — integer Y coordinate for the centroid pixel.
• x — centroid X coordinate in native coordinate convention.
• y — centroid Y coordinate in native coordinate convention.
• bg — background level.
• amp — peak amplitude.
• S — Gaussian momenum for the stellar profile (S=1/sigma^2).
• D — plus-shaped momentum for the stellar profile.
• K — cross-shaped momentum for the stellar profile.
• sigma — sigma parameter for the stellar profile (FWHM is roughly 2.35 * sigma).
• delta — delta (plus-shaped deviance) parameter for the stellar profile.
• kappa — kappa (cross-shaped deviance) parameter for the stellar profile.
• fwhm — full width at half magnitude (FWHM) of the stellar profile.
• ellip — ellipticity of the stellar profile.
• pa — position angle of the stellar profile.
• flux — total flux of the source.
• nosie — noise level of the source. (yes, it's spelled nosie in the source of truth. not me, not my fault, keep it as-is. 💀)
• s/n — signal-to-noise ratio of the detection.
• magnitude — brightness of the source in magnitudes (see also --mag-flux).
• cx — candidate centroid X coordinate (derived from pixel flux statistics).
• cy — candidate centroid Y coordinate (derived from pixel flux statistics).
• cbg — background level for the source candidate.
• camp — peak amplitude of the source candidate.
• cmax — maximum intensity on the source cadidate.
• cs — Gaussian momenum for the source cadidate, derived from pixel flux statistics.
• cd — plus-shaped momentum for the source cadidate, derived from pixel flux statistics.
• ck — cross-shaped momentum for the source cadidate, derived from pixel flux statistics.
• npix — number of pixels assigned to the detetcted source.

🧚 Obtaining the point-spread function (PSF) 🧚

• --psf <parameters> — comma-separated list of parameters related to the PSF fitting:
  • grid=<grid> — subgrid size for the PSF.
  • halfsize=<half size> — half-size of the PSF stamp; the full size of the stamp will always be 2*<half size>+1 and the PSF itself is centered at the center of the central pixel.
  • order=<order> — order of spatial variations in the PSF.
  • symmetrize — symmetrize the resulting PSF (i.e. fit a symmetric PSF instead of a normal one).
  • spline — use a spline interpolation during the determination of the PSF.
• --output-psf <output PSF FITS file> — name of the output file where the PSF is saved in FITS format. The PSF is stored in a 3 dimensional (a.k.a. "data cube") structure where the z-axis is for the various polynomial coefficients describing the spatially varied PSF.

💜 Alternate sources for object candidates 💜

• -C, --input-cadidates <cadidate list file> — name of input cadidate list file. If such a file is defined in the command line, the cadidates are not searched by the build-in algorithms. Instead, the centroids are read from this file and the pixels for each object are defined within a certain radius from this centroid (see -r|--cadidate-radius also). The role of this option is twofold. First, it is suitable if only some of the sources have to be modelled with an analytic function; second, PSF determination can be done only a previously cleaned list of sources, in the case when there might be contaminating sources too.
• -r, --candidate-radius <radius> — this option defines a distance, where pixels within this are assigned to the candidate.
• --col-xy <colx>,<coly> — column indices for X and Y centroid coordinates.

🫠 tiny heads up, bestie: the original page really does hand -r to two different options — --shrink up above and --candidate-radius right here. Not me inventing drama, that's just literally what it says. iykyk.

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😭 REPORTING BUGS 😭

Report bugs to <apal@szofi.net>, see also https://fitsh.net/.

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👑 COPYRIGHT 👑

Copyright © 1996, 2002, 2004-2008, 2010-2016, 2018-2020; Pal, Andras <apal@szofi.net>

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and that's a wrap on fistar(1), bestie! this page is from fistar 0.9.4 (2021.01.24), dated January 2021 — go detect some stars, you absolute icon 💖✨🎀