Аннотации

Annotations are glyphs displayed on top of images to depict the presence of known sky objects, like galaxies, bright stars and so on. They come from catalogues but can only be displayed on images for which we know which part of the sky they represent, images that have been plate solved and contain the world coordinate system (WCS) information in their header, so only FITS or Astro-TIFF files.

Вид полностью аннотированного изображения

Plate solving, can be done within Siril in the Image Information ‣ Image Plate Solver... entry, or using external tools like astrometry.net or ASTAP.

Кнопки для аннотаций

When a plate solved image is loaded in Siril, you can see the sky coordinates for the pixel under the mouse pointer displayed at the bottom right corner and the buttons related to annotations become available. The first button toggles on or off object annotations, the second the celestial grid and the compass.

Виды каталогов

Siril comes with a predefined list of catalogues for annotations:

• Каталог Мессье (М)

• Новый общий каталог (NGC)

• Index Catalogue (IC)

• Lynds Catalogue of Dark Nebulae (LdN)

• Sharpless Catalogue (Sh2)

• Star Catalogue (3661 of the brightest stars)

В дополнение могут быть использованы 2 пользовательских каталога:

• Пользовательский каталог объектов глубокого космоса

• Пользовательский каталог объектов Солнечной системы

Управление каталогами

Both these catalogues can be enabled/disabled for display in the Preferences menu ‣ Astrometry tab.

A slider on the right side, allows you to easily navigate across the catalogue list.

Catalogue management in Preferences/Astrometry

The two user defined catalogues can also be purged (ie deleted) via the appropriate buttons.

The user catalogues (DSO, SSO or extra catalogues) are stored in the user settings directory and can be easily modified.

Their location depends on the operating system:

• for Unix-based OS they will be in ~/.config/siril/catalogue

• on Windows they are in %LOCALAPPDATA%\siril\catalogue.

The position of the compass on the image can be adjusted from the preferences too.

These annotation catalogues are for display purposes only. They are not used in astrometry or photometry tools, contrary to the star catalogues like NOMAD, which can now be installed locally too.

Local Catalogue (NOMAD) setup

Поиск нового объекта

When the name of an object in the image is known (if not, see the Inverse Search section), it is possible to add it to annotations:

• with the image loaded and plate solved, type Ctrl + Shift + / or Search in the pop-up menu (right click).

A small search dialog will appear. In it, object names can be entered, then pressing Enter will send an online request to SIMBAD (for a star of Deep Sky Object) to get the coordinates of an object with such a name. If found, and not already in any catalogue, the object will be added to the Deep Sky user Catalogue.

The items of this catalogue are displayed in ORANGE while the objects from the predefined catalogues are displayed in GREEN.

Deep sky objects from user and predefined catalogues

From Siril version 1.2, we can now search for solar system objects too, using the Miriade ephemcc service. This is done by prefixing the name of the object to be searched by some keyword representing the type of object: a: for asteroids, c: for comets, p: for planets. Since they are moving objects, they can be added several times, and the request is done for the date of observation of the currently loaded image. The date is associated to the name in the user Solar System Catalogue. The items of this catalogue are displayed in YELLOW.

Examples of valid inputs (not case sensitive):

• HD 86574 or HD86574 are both valid for this star

• c:67p or c:C/2017 T2 are valid forms for comets

• a:1 and a:ceres are both valid for (1) Ceres

• a:2000 BY4 is valid for 103516 2000 BY4

• p:4 or p:mars for Mars

Filling a Solar System user Catalogue: which SSO is in this field?

To answer the question Is there any solar system object in my image?, a special function does a request to an online server of the IMCCE too (SkyBoT) and displays the results in the console and in the image.

• with the image loaded and plate solved, right click/Solar System Objects, or in the command line you can use the solsys function.

It displays in RED all the Solar System objects in the field of view (if any are known and found of course). Objects magnitudes and equatorial coordinates for the image date are printed in the console.

These red annotations will be erased as soon as the Show Objects names button is toggled.

Result of a Search Solar System process

However, you may want to save any particular item in the User Solar System Objects Catalogue. It can be done by using the Search command for a solar system object as previously described.

This way, the saved item is diplayed in YELLOW and will be displayed in any image that has this field of view by enabling the annotations.

View with predefined/DSO/SSO

Примечание

Newly discovered objects, or some fast moving objects, will have their position misaligned with the image. This is often the case for comets for example, which can be an arcminute off. This happens because the orbital parameters of the object are not very well known or that they have not been updated recently in the system. If you are looking for an alternate computation of the coordinates of the known objects of the field, you might query manually the JPL Small Body identification tool.

The inverse search: what is this object?

Especially useful for photometry works, it is possible to identify a star or other objects in the image by drawing a selection around them, right clicking to bring up the context menu, and selecting the PSF entry. This will open the PSF window, and if it’s a star it will display the Gaussian fit parameters, but it will also display a Web link at the bottom left of the window: opening it will bring you to the SIMBAD page for the coordinates of the object and in many cases will give you the name of the object. SIMBAD doesn’t have all known objects, but the coordinates from the page can still be used as a starting point to look for the object in other online catalogues, for example Gaia DR3 (VizieR).

Дополнительные каталоги

Sometimes, users create their own catalogues, we can try to link them here to help everybody. They are user catalogues, so installing them requires either replacing the current user catalogue, or by manually merging their lines into a new file.

Список известных пользовательских каталогов:

• Variable stars, extracted from GCVS 5.1, discussed here in French, (file link).