Source Catalog File Formats¶
Mirage accepts 7 different types of ascii source catalogs, all of which can be generated using Mirage’s catalog generation functionality. These include:
- Point sources
- Galaxies (2d Sersic profiles)
- Extended targets
- Non-sidereal source
- Moving point sources
- Moving Sersic sources
- Moving extended sources
For information on the optional hdf5 catalog that can be used when simulating WFSS data, see the WFSS simulation page.
The type of source catalog(s) you need depends on the scene you are simulating. The table below shows the possible catalogs for sidereal and non-sidereal observations. For sidereal observations, the point source, galaxy, and extended source catalogs can be used to create static sources in the scene. The three types of moving target catalogs can be used to create sources that trail across the field of view during the observation. For non-sidereal observations, the non-sidereal source catalog is used to create a static source in the scene. This is the non-sidereal target which JWST is tracking. The other types of catalogs can then all be used to create trailed sources. In this case, the inverse of the non-sidereal source’s velocity is applied to all targets in the other catalogs. In this way, Mirage will create trailed background stars and galaxies, as well as trailed non-sidereal targets that have velocities other than that of the main target.
|Type of observation||Static source catalogs||Trailed (moving) source catalogs|
Common formatting details¶
Mirage scans the top 4 lines of each catalog for certain phrases that can be used to characterize the inputs. These phrases are used to specify the units of source locations or velocities, as well as the magnitude system to use. Multiple phrases can be used in a single catalog, but only one phrase per line is allowed. Examples are shown in the catalogs below.
The locations of sources can be specified in RA, Dec or in (x,y) pixel locations on the detector. If you wish to provide positions in units of (x, y) detector pixels, then the string ‘position_pixels’ must be added after the # in one of the top 4 lines of the file.
RA and Dec values can be given in decimal degrees, colon-separated values (HH:MM:SS and DD:MM:SS), or in more conventional string formats, but all sources in a given catalog must have the same format:
Mirage uses AB magnitudes as the default for input sources. However, you can change the magnitude system by specifying an alternative in one of the top 4 lines. The three acceptible options are vegamag, stmag, and abmag. All sources in a given catalog must be in the same magnitude system.
For moving targets (both those that are moving across the field of view, as well as non-sidereal targets), the default unit for velocity is arcseconds per hour. If you wish to instead use pixels per hour, then velocity_pixels must be added to one of the 4 top lines of the catalog.
Point sources are specified using a catalog that includes the locations of the sources in RA and Dec (or x,y pixel locations on the detector) and the corresponding magnitudes through the filter specified by the user. Currently the simulator supports the use of ABMAG [Oke, 1983]_, STMAG [Stone, 1996]_ , and VEGAMAG () systems, with ABMAG as the default.
An example point source catalog is shown below with the positions given in RA and Dec.
# # # # abmag # # Magnitudes are converted from input flux densities. x_or_RA y_or_Dec nircam_f200w_magnitude 53.0886395 -27.8399952 20.0 53.0985009 -27.8398137 19.2
Mirage looks for the exact column names shown above when reading point source catalogs. Changing these column names will cause the simulator to fail when attempting to read in the file.
Galaxies (aka 2D Sersic profiles)¶
Below is an example of a galaxy source catalog. In this case, galaxy positions are given in RA, Dec decimal degrees, and the half light radii are in units of arcseconds. The half light radius can also be specified in units of pixels. In that case, you must add radius_pixels after the # in one of the top four lines.
Position angle values are defined as degrees east of north.
The simulator software looks for the exact column names shown below when reading these catalogs. Changing these column names will cause the simulator to fail when attempting to read in the file.
# # # # abmag # # Magnitudes are converted from input flux densities. x_or_RA y_or_Dec radius ellipticity pos_angle sersic_index niriss_f200w_magnitude 53.05 -27.83 0.17 0.46 104.35 3.3 18.06 53.10 -27.83 0.73 0.01 195.50 2.7 16.86
The extended object catalog lists files containing stamp images to be added to the seed image. For example, a source such as a nebula or spiral galaxy that cannot be simulated via a 2-dimensional Sersic profile can be added by placing an image of the source in a fits file. Mirage will then read in, scale, and add this image to the seed image.
It is assumed that the fits file contains an array in the 1st (rather than 0th) extension. The array can be any size. If it is larger than the field of view of the simulated data, then it is cropped by placing the center of the extended stamp image at the specified x,y or RA, Dec location on the detector, and cropping any areas that fall outside of the detector.
Each row of this catalog contains the name of a FITS file containing the image to use, along with the RA, Dec (or x,y) position of the source, the position angle to use, and the source’s magnitude. The position angle is the angle in degrees counter clockwise to rotate the as-read-in image before adding it to the simulated scene. For stamp images where it may not make sense to specify a magnitude (such as a galaxy cluster), it is possible to specify ‘None’ as the magnitude. In this case the code assumes that the data contained in the fits file is in units of ADU per second, and will not rescale the data before adding to the seed image. However, the user can also adjust the signal rate of all extended sources through the use of the extendedScale field in the input yaml file. This is a multiplicative factor to apply to the data in the fits file prior to adding the source to the seed image.
# # # # # Columns 1 and 2 can be either x,y positions on the detector aperture (e.g. # 0,0 is lower left corner of the full frame of the subarray used for the # output) or RA,Dec location of the center of the source. If they are x,y # positions, make the top line of the file '# position_pixel' # # # x_or_RA y_or_Dec pos_angle nircam_f200w_magnitude filename 359.65 0.0006 20 16.000 ring_nebula.fits
This catalog is used when creating non-sidereal simulated exposures. In this case, all targets other than the non-sidereal target will then trail through the field of view during the observation. This mode is meant to simulate observations of solar system targets with non-sidereal velocities. This catalog should contain only one entry, with RA, Dec or x, y position, as well as velocity values (arcsec/hour or pixels/hour) and object magnitude.
# # # # abmag # # radius can also be in units of pixels or arcseconds. Put 'radius_pixels' at top of file # to specify radii in pixels. # position angle is given in degrees counterclockwise. # An "object" value containing 'point' will be interpreted as a point source. # Anything containing "sersic" will create a 2D sersic profile. # Any other value will be interpreted as an extended source. # x_or_RA_velocity is the proper motion of the target in units of arcsec (or pixels) per hour # Y_or_Dec_velocity is the proper motion of the target in units of arcsec (or pixels) per hour # if the units are pixels per hour, include 'velocity pixels' in line 2 above. object x_or_RA y_or_Dec x_or_RA_velocity y_or_Dec_velocity nircam_f200w_magnitude pointSource 53.101 -27.801 2103840. 0.0 17.
Moving Point Sources¶
The moving point source catalog contains a list of point sources to move through the field of view during the integration. Similar to the static point source catalog, the position of each object (at the beginning of the integration) in RA, Dec or x,y must be provided, along with the object’s magnitude in the filter used for the simulation. In addition, the velocity of the object must be specified. This is done in units of delta RA, delta Dec (arcsec/hour), or delta x, delta y (pixels/hour). ‘velocity_pixels’ must be placed in one of the top 4 lines of the file if the provided velocities are in units of pixels per hour rather than arcseconds per hour.
Below is an example catalog:
# #abmag # # # List of point sources to create as moving targets (KBOs, asteroids, etc) # position can be x,y or RA,Dec. If x,y, put the phrase 'position_pixels' in one # of the top 4 lines of the file. # Velocity can be in units of pix/hour or arcsec/hour. # If using pix/hour, place 'velocity_pixels' in the second line of the file. # Note that if using velocities of pix/hour, the results will not be # strictly correct because in reality distortion will cause object's # velocities to vary in pixels/hour. Velocities in arcsec/hour will be # constant. x_or_RA y_or_Dec nircam_f200w_magnitude x_or_RA_velocity y_or_Dec_velocity 53.0985 -27.8015 14 180 180
Moving 2D Sersic Objects¶
This option may be useful for simulating moving moons around a primary target that is being tracked. Similar to the static galaxy inputs, each moving target in this catalog must have an initial position in RA, Dec or x,y specified, along with a radius in arcseconds or pixels, ellipticity, position angle, Sersic index, and magnitude. In addition, velocities in the RA, Dec or x,y directions must be specified in units of arcseconds or pixels per hour.
# # # #abmag # Columns 1 and 2 can be either x,y positions on the detector aperture (e.g. # 0,0 is lower left corner of the full frame of the subarray used for the # output) or RA,Dec location of the center of the source. If they are x,y # positions, make the top line of the file '# position_pixels' # # radius is the half-light radius in pixels or arcseconds. If in pixels # make the second line of the file '# radius_pixels # # pos_angle is the position angle of the semimajor axis, in degrees. # 0 causes the semi-major axis to be horizontal. x_or_RA y_or_Dec radius ellipticity pos_angle sersic_index nircam_f200w_magnitude x_or_RA_velocity y_or_Dec_velocity 354.765 0.00064 1.0 0.25 20 2.0 16.000 -0.5 -0.02
Moving Extended Sources¶
Similar to the catalog of static extended targets, this catalog contains a fits filename for each source containing the stamp image to use for the object, along with an initial position in RA, Dec or x,y, the object’s magnitude, and position angle (of the array as read in from the fits file). In addition, velocities in the RA, Dec (arcsec/hour) or x,y directions (pixels/hour) must be specified.
# # # #abmag # List of stamp image files to read in and use to create moving targets. # This is the method to use in order to create moving targets of # extended sources, like planets, moons, etc. # position can be x,y or RA,Dec. Velocity can be in units of pix/hour or arcsec/hour. # If using pix/hour, place 'velocity_pixels' in one of the top 4 lines. # Note that if using velocities of pix/hour, the results will not be # strictly correct because in reality distortion will cause object's # velocities to vary in pixels/sec. Velocities in arcsec/hour will be # constant. filename x_or_RA y_or_Dec nircam_f200w_magnitude pos_angle x_or_RA_velocity y_or_Dec_velocity ring_nebula.fits 0.007 0.003 12.0 0.0 -0.5 -0.02