Siril pour les scientifiques

Depuis des années Siril est un outils puissant pour les astronomes amateurs. Avec la possibilité de produire de courbes de lumière, rechercher dans des catalogues en lignes, réaliser des opérations sur une séquence d'images, et bien plus depuis les récent ajouts, il est devenu un bon outil pour de l'analyse scientifique. Cette page est un guide rapide pour les scientifiques qui veulent en apprendre plus rapidement sur Siril, sous forme d'un FAQ.

Comment Siril peut-il m'aider dans mes recherches ?

Siril's default file format is FITS files, containing either a single image or several (see the FITS cubes question below). Siril has always been developed with data accuracy in mind. Displaying an image can be done in various ways without destroying input data.

Siril has many tools that can help scientific observations: star detection, elaborate plate solving, registration of an image sequence using stars or using astrometric solutions, aperture photometry with magnitude calibration using catalogues, automated light curve creation, object lookup from online catalogues (stars, galaxies, solar system objects). Many of those operations can be done from the GUI or from text inputs (commands or scripts), some operations produce comma-separated values (CSV) files for results, some can produce graphs directly in Siril.

Quelle version de Siril dois-je installer ?

Siril follows an even/odd versioning system, e.g. 1.2.x was a stable series whereas 1.3.x was a development series. For scientific use it is recommended to install the latest version of the latest stable series: download links can be found at siril.org. Beta versions, those distributed on the website, can also be considered quite stable for general use.

Comment puis-je contacter les développeurs ?

The official forum is on pixls.us. If you want to contact us privately you can send us a direct message there or on gitlab. Our email addresses can also be found in the AUTHORS file. If you speak French you can find us on Astrosurf or Webastro. Feel free to reach out if you have specific needs for your research.

Quelle est la précision des résultats de Siril ?

Many algorithms in Siril rely on peer-reviewed published algorithms which can be found in the documentation page of the features. We are testing Siril often, sometimes comparing results with other tools, but we don't have the resources to have a automated tests on all pieces of the software, so data comes with no warranty. We know some things could be improved, for example error computation on magnitudes, which depend on camera gain, not always available in the FITS header.

Les données d'astrométrie sont aussi fiable que les autres et prend en charge la convention WCS FITS.

Comment citer Siril ?

Si vous utilisez Siril dans vos recherches, veuillez citer :

Richard, C., et al. (2024). Siril: An Advanced Tool for Astronomical Image Processing. Journal of Open Source Software, 9(102), 7242. https://doi.org/10.21105/joss.07242

Format BibTeX :

@article{Richard2024,
  title={Siril: An Advanced Tool for Astronomical Image Processing},
  author={Richard, Cyril and others},
  journal={Journal of Open Source Software},
  volume={9},
  number={102},
  pages={7242},
  year={2024},
  publisher={The Open Journal},
  doi={10.21105/joss.07242}
}

Comment puis-je ouvrir des cubes FITS avec Siril ?

FITS cubes come in two shapes for Siril:

  • those that contain several images of the same size and format, we call those FITS sequences or fitseq for short, and use them as an alternate file representation of image sequences;

  • those that contain several images of changing properties, or even tables and other data formats. Siril will only read image data, but is able to work on each image of such FITS cubes if an option is enabled in settings (named Allow FITS cubes to have images of different sizes in FITS Options). Most sequence operations will not be available on this kind of file.

Siril can also extract images from FITS cubes to individual FITS files or to other formats if needed.

How do I measure FWHM in an image?

Siril peut vous donner la FWHM d'une seule étoile si vous tracez une sélection autour de celle-ci dans l'interface graphique, puis cliquez avec le bouton droit et sélectionnez PSF, ou pour les étoiles dans une zone de l'image ou l'image entière. Vous pouvez également utiliser le bouton quick PSF dans la barre d'outils principale.

More generally: open your image and open the Dynamic PSF tool (from the Tools menu). From there clicking on the first button will start the star detection, within the selected area if you drew one. Clicking on the Sigma icon will give mean values for all detected stars. See also the next question.

How do I use star detection (source extraction)?

Siril's source extractor can be found in the GUI in the Dynamic PSF tool, it is also available as the findstar command. It is normally only able to detect stars and will struggle if two stars are too close from each other, or if stars have asymmetrical or very non-Gaussian shapes, but there are many settings that you could adjust to your needs, including brightness, amplitude, roundness thresholds or star shape (Gaussian or Moffat).

The GUI will display the found stars by clicking on the button on the left of the lower bar, giving quick feedback on the detection settings. The GUI and the command can produce a CSV file that can then be used to check extracted sources in an image or in a sequence of images (command only).

The list of stars can be sorted by property, clicking on a row will highlight the star in the image.

Quels sont les outils d’astrométrie disponibles ?

Siril has now a very high quality astrometric solver (plate solver) and tools that interact with the astrometric solution. All is based on the FITS WCS convention and on WCSLIB. Here is a list of tools related to astrometry:

  • Plate solving with local Gaia DR3 catalogue extract or with remote full Gaia DR3, PPMXL or APASS.

  • Display stars from the catalogue on image, to have a visual feedback of the accuracy of the astrometric solution, using the conesearch command.

  • Query online catalogues for an object using its name and the image time.

  • Get centroid equatorial J2000 coordinates for any detected object.

  • Show a mark on image for user provided J2000 coordinates (show command).

  • Align images on the celestial grid, possibly creating a mosaic (an image bigger than the original).

  • Correct for geometrical aberration of images, using a master correction image based on astrometry.

Peut-il traiter les objets du système solaire ?

Siril can query IMCCE services to find a solar system object coordinates and display the expected position on images. It can also display the known solar system objects in an image. Observer location will be required for those uses and can be configured with MPC codes in the settings. See the annotations documentation page.

Soon, Siril will be able to do synthetic tracking of known solar system objects, making them appear on stacking if they are too faint to be seen on single exposures.

But Siril is not made to process closeup view of planets with multi-point stacking like other tools such as PlanetarySystemStacker (PSS) does.

Siril peut-il fonctionner avec des spectre ?

Siril was not designed to handle spectrometry data. An Profil d'intensité tool that shows the graph of pixel intensities can be used for preview of a spectrum. FITS tables are not displayed in any way.

Siril peut-il remplacer IRAF ?

Certaines fonctionnalités seront absentes, mais beaucoup seront beaucoup plus faciles à utiliser avec Siril. Nous n'avons pas encore de liste.

Siril est développé depuis 2012 et nous n'avons pas l'intention d'arrêter de sitôt. Il compte 3 développeurs actifs et des milliers d'utilisateurs amateurs.