|
| 1 | +# FITS source list formats |
| 2 | + |
| 3 | +There are three supported fits file formats: |
| 4 | +- LoBES: used in LoBES catalogue <https://doi.org/10.1017/pasa.2021.50> |
| 5 | +- Jack: extended LoBES format for Jack Line's sourcelist repository, <https://github.com/JLBLine/srclists/>. |
| 6 | +- Gleam: used in GLEAM-X pipeline <https://github.com/GLEAM-X/GLEAM-X-pipeline/tree/master/models> |
| 7 | + |
| 8 | +These formats differ mostly in the names of columns, and component and flux types |
| 9 | +supported. *LoBES* fits files support point, and Gaussian components with list, |
| 10 | +power law and curved power law flux density models. *Jack* fits files extend the |
| 11 | +LoBES format with an additional table for shapelet coefficients. *Gleam* fits are |
| 12 | +similar to LoBES fits, but with different column names, and combine power law and |
| 13 | +curved power law flux density models into a just two columns. |
| 14 | + |
| 15 | +More info from [woden docs](https://woden.readthedocs.io/en/latest/operating_principles/skymodel.html) |
| 16 | + |
| 17 | +## Source posititons |
| 18 | + |
| 19 | +Coordinates are right ascension (RA) and declination, both with units of degrees |
| 20 | +in the J2000 epoch. All frequencies are in Hz and all flux densities are in Jy. |
| 21 | + |
| 22 | +Jack and LoBES fits formats use the columns `RA` and `DEC` for source positions, |
| 23 | +while Gleam fits files use `RAJ2000` and `DEJ2000`. |
| 24 | + |
| 25 | +## Component types |
| 26 | + |
| 27 | +Jack and LoBES fits formats use the column `COMP_TYPE` for component types: |
| 28 | +- `P` for point |
| 29 | +- `G` for Gaussian |
| 30 | +- `S` for shapelet (Jack only) |
| 31 | + |
| 32 | +Jack and LoBES fits formats use the columns `MAJOR_DC`, `MINOR_DC` and `PA_DC` |
| 33 | +for Gaussian component sizes and position angles (in degrees), while Gleam |
| 34 | +fits files use `a`, `b` (arcseconds) and `pa` (degrees). |
| 35 | + |
| 36 | +In an image space where RA increases from right to left (i.e. bigger RA |
| 37 | +values are on the left), position angles rotate counter clockwise. A |
| 38 | +position angle of 0 has the major axis aligned with the declination axis. |
| 39 | + |
| 40 | +## Flux density models |
| 41 | + |
| 42 | +Jack and LoBES fits formats use the column `MOD_TYPE` for flux density types: |
| 43 | +- `pl` for power law |
| 44 | +- `cpl` for curved power law |
| 45 | +- `nan` for lists |
| 46 | + |
| 47 | +Jack and LoBES fits formats use the columns `NORM_COMP_PL` and `ALPHA_PL` for |
| 48 | +power law flux density normalisation and spectral index; and `NORM_COMP_CPL`, |
| 49 | +`ALPHA_CPL` and `CURVE_CPL` for curved power law flux density normalisation, |
| 50 | +while Gleam fits files use `S_200`, `alpha` and `beta`. |
| 51 | + |
| 52 | +A reference frequency of 200MHz is assumed in all fits files. |
| 53 | + |
| 54 | +Jack and LoBES fits formats use the columns `INT_FLXnnn` for integrated flux |
| 55 | +densities in Jy at frequencies `nnn` MHz, while Gleam fits files use only `s_200`. |
| 56 | +These columns are used to construct flux lists if power law information is |
| 57 | +missing, or `MOD_TYPE` is `nan`. |
| 58 | + |
| 59 | +Only Stokes I can be specified in fits sourcelists, Stokes Q, U and V are |
| 60 | +assumed to have values of 0. |
| 61 | + |
| 62 | +## Examples |
| 63 | + |
| 64 | +Example Python code to display these files is in the [examples |
| 65 | +directory](https://github.com/MWATelescope/mwa_hyperdrive/tree/main/examples). |
| 66 | + |
| 67 | +e.g. `python examples/read_fits_srclist.py test_files/jack.fits` |
| 68 | + |
| 69 | +| UNQ_SOURCE_ID | NAME | RA | DEC | INT_FLX100 | INT_FLX150 | INT_FLX200 | MAJOR_DC | MINOR_DC | PA_DC | MOD_TYPE | COMP_TYPE | NORM_COMP_PL | ALPHA_PL | NORM_COMP_CPL | ALPHA_CPL | CURVE_CPL | |
| 70 | +|-----------------|---------------|------|-------|--------------|--------------|--------------|------------|------------|---------|------------|-------------|----------------|------------|-----------------|-------------|-------------| |
| 71 | +| point-list | point-list_C0 | 0 | 1 | 3 | 2 | 1 | 0 | 0 | 0 | nan | P | 1 | 0 | 0 | 0 | 0 | |
| 72 | +| point-pl | point-pl_C0 | 1 | 2 | 3.5 | 2.5 | 2 | 0 | 0 | 0 | pl | P | 2 | -0.8 | 0 | 0 | 0 | |
| 73 | +| point-cpl | point-cpl_C0 | 3 | 4 | 5.6 | 3.8 | 3 | 0 | 0 | 0 | cpl | P | 0 | 0 | 3 | -0.9 | 0.2 | |
| 74 | +| gauss-list | gauss-list_C0 | 0 | 1 | 3 | 2 | 1 | 20 | 10 | 75 | nan | G | 1 | 0 | 0 | 0 | 0 | |
| 75 | +| gauss-pl | gauss-pl_C0 | 1 | 2 | 3.5 | 2.5 | 2 | 20 | 10 | 75 | pl | G | 2 | -0.8 | 0 | 0 | 0 | |
| 76 | +| gauss-cpl | gauss-cpl_C0 | 3 | 4 | 5.6 | 3.8 | 3 | 20 | 10 | 75 | cpl | G | 0 | 0 | 3 | -0.9 | 0.2 | |
| 77 | +| shape-pl | shape-pl_C0 | 1 | 2 | 3.5 | 2.5 | 2 | 20 | 10 | 75 | pl | S | 2 | -0.8 | 0 | 0 | 0 | |
| 78 | +| shape-pl | shape-pl_C1 | 1 | 2 | 3.5 | 2.5 | 2 | 20 | 10 | 75 | pl | S | 2 | -0.8 | 0 | 0 | 0 | |
| 79 | + |
| 80 | +| NAME | N1 | N2 | COEFF | |
| 81 | +|-------------|------|------|---------| |
| 82 | +| shape-pl_C0 | 0 | 0 | 0.9 | |
| 83 | +| shape-pl_C0 | 0 | 1 | 0.2 | |
| 84 | +| shape-pl_C0 | 1 | 0 | -0.2 | |
| 85 | +| shape-pl_C1 | 0 | 0 | 0.8 | |
| 86 | + |
| 87 | +e.g. `python examples/read_fits_srclist.py test_files/gleam.fits` |
| 88 | + |
| 89 | +| Name | RAJ2000 | DEJ2000 | S_200 | alpha | beta | a | b | pa | |
| 90 | +|-----------|-----------|-----------|---------|---------|--------|-------|-------|------| |
| 91 | +| point-pl | 1 | 2 | 2 | -0.8 | 0 | 0 | 0 | 0 | |
| 92 | +| point-cpl | 3 | 4 | 3 | -0.9 | 0.2 | 0 | 0 | 0 | |
| 93 | +| gauss-pl | 1 | 2 | 2 | -0.8 | 0 | 72000 | 36000 | 75 | |
| 94 | +| gauss-cpl | 3 | 4 | 3 | -0.9 | 0.2 | 72000 | 36000 | 75 | |
| 95 | + |
| 96 | +these are both equivalent to the following YAML file (ignoring shapelets and |
| 97 | +lists for the gleam example): |
| 98 | + |
| 99 | +```yaml |
| 100 | +point-list: |
| 101 | +- ra: 0.0 |
| 102 | + dec: 1.0 |
| 103 | + comp_type: point |
| 104 | + flux_type: |
| 105 | + list: |
| 106 | + - freq: 100000000.0 |
| 107 | + i: 3.0 |
| 108 | + - freq: 150000000.0 |
| 109 | + i: 2.0 |
| 110 | + - freq: 200000000.0 |
| 111 | + i: 1.0 |
| 112 | +point-pl: |
| 113 | +- ra: 1.0 |
| 114 | + dec: 2.0 |
| 115 | + comp_type: point |
| 116 | + flux_type: |
| 117 | + power_law: |
| 118 | + si: -0.8 |
| 119 | + fd: |
| 120 | + freq: 200000000.0 |
| 121 | + i: 2.0 |
| 122 | +point-cpl: |
| 123 | +- ra: 3.0000000000000004 |
| 124 | + dec: 4.0 |
| 125 | + comp_type: point |
| 126 | + flux_type: |
| 127 | + curved_power_law: |
| 128 | + si: -0.9 |
| 129 | + fd: |
| 130 | + freq: 200000000.0 |
| 131 | + i: 3.0 |
| 132 | + q: 0.2 |
| 133 | +gauss-list: |
| 134 | +- ra: 0.0 |
| 135 | + dec: 1.0 |
| 136 | + comp_type: |
| 137 | + gaussian: |
| 138 | + maj: 72000.0 |
| 139 | + min: 36000.0 |
| 140 | + pa: 75.0 |
| 141 | + flux_type: |
| 142 | + list: |
| 143 | + - freq: 100000000.0 |
| 144 | + i: 3.0 |
| 145 | + - freq: 150000000.0 |
| 146 | + i: 2.0 |
| 147 | + - freq: 200000000.0 |
| 148 | + i: 1.0 |
| 149 | +gauss-pl: |
| 150 | +- ra: 1.0 |
| 151 | + dec: 2.0 |
| 152 | + comp_type: |
| 153 | + gaussian: |
| 154 | + maj: 72000.0 |
| 155 | + min: 36000.0 |
| 156 | + pa: 75.0 |
| 157 | + flux_type: |
| 158 | + power_law: |
| 159 | + si: -0.8 |
| 160 | + fd: |
| 161 | + freq: 200000000.0 |
| 162 | + i: 2.0 |
| 163 | +gauss-cpl: |
| 164 | +- ra: 3.0000000000000004 |
| 165 | + dec: 4.0 |
| 166 | + comp_type: |
| 167 | + gaussian: |
| 168 | + maj: 72000.0 |
| 169 | + min: 36000.0 |
| 170 | + pa: 75.0 |
| 171 | + flux_type: |
| 172 | + curved_power_law: |
| 173 | + si: -0.9 |
| 174 | + fd: |
| 175 | + freq: 200000000.0 |
| 176 | + i: 3.0 |
| 177 | + q: 0.2 |
| 178 | +shape-pl: |
| 179 | +- ra: 1.0 |
| 180 | + dec: 2.0 |
| 181 | + comp_type: |
| 182 | + shapelet: |
| 183 | + maj: 72000.0 |
| 184 | + min: 36000.0 |
| 185 | + pa: 75.0 |
| 186 | + coeffs: |
| 187 | + - n1: 0 |
| 188 | + n2: 0 |
| 189 | + value: 0.9 |
| 190 | + - n1: 0 |
| 191 | + n2: 1 |
| 192 | + value: 0.2 |
| 193 | + - n1: 1 |
| 194 | + n2: 0 |
| 195 | + value: -0.2 |
| 196 | + flux_type: |
| 197 | + power_law: |
| 198 | + si: -0.8 |
| 199 | + fd: |
| 200 | + freq: 200000000.0 |
| 201 | + i: 2.0 |
| 202 | +- ra: 1.0 |
| 203 | + dec: 2.0 |
| 204 | + comp_type: |
| 205 | + shapelet: |
| 206 | + maj: 72000.0 |
| 207 | + min: 36000.0 |
| 208 | + pa: 75.0 |
| 209 | + coeffs: |
| 210 | + - n1: 0 |
| 211 | + n2: 0 |
| 212 | + value: 0.8 |
| 213 | + flux_type: |
| 214 | + power_law: |
| 215 | + si: -0.8 |
| 216 | + fd: |
| 217 | + freq: 200000000.0 |
| 218 | + i: 2.0 |
| 219 | +``` |
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