Module to read user input from files and create standardized input for orbitize
Reads data from any file for use in orbitize readable by
astropy.io.ascii.read(), including csv format. See the astropy docs.
There are two ways to provide input data to orbitize.
The first way is to provide astrometric measurements, shown with the following example.
Example of an orbitize-readable .csv input file:
epoch,object,raoff,raoff_err,decoff,decoff_err,radec_corr,sep,sep_err,pa,pa_err,rv,rv_err 1234,1,0.010,0.005,0.50,0.05,0.025,,,,,, 1235,1,,,,,,1.0,0.005,89.0,0.1,, 1236,1,,,,,,1.0,0.005,89.3,0.3,, 1237,0,,,,,,,,,,10,0.1
Each row must have
epoch(in MJD=JD-2400000.5) and
object. Objects are numbered with integers, where the primary/central object is
0. If you have, for example, one RV measurement of a star and three astrometric measurements of an orbiting planet, you should put
objectcolumn for the RV point, and
1in the columns for the astrometric measurements.
Each line must also have at least one of the following sets of valid measurements:
RA and DEC offsets [mas], or
sep [mas] and PA [degrees East of NCP], or
RV measurement [km/s]
Columns with no data can be omitted (e.g. if only separation and PA are given, the raoff, deoff, and rv columns can be excluded).
If more than one valid set is given (e.g. RV measurement and astrometric measurement taken at the same epoch),
read_file()will generate a separate output row for each valid set.
For RA/Dec and Sep/PA, you can also specify a correlation term. This is useful when your error ellipse is tilted with respect to the RA/Dec or Sep/PA. The correlation term is the Pearson correlation coefficient (ρ), which corresponds to the normalized off diagonal term of the covariance matrix. Let’s define the covariance matrix as
C = [[C_11, C_12], [C_12, C_22]]. Here C_11 = quant1_err^2 and C_22 = quant2_err^2 and C_12 is the off diagonal term. Then
ρ = C_12/(sqrt(C_11)sqrt(C_22)). Essentially it is the covariance normalized by the variance. As such, -1 ≤ ρ ≤ 1. You can specify either as radec_corr or seppa_corr. By definition, both are dimensionless, but one will correspond to RA/Dec and the other to Sep/PA. An example of real world data that reports correlations is this GRAVITY paper where table 2 reports the correlation values and figure 4 shows how the error ellipses are tilted.
Alternatively, you can also supply a data file with the columns already corresponding to the orbitize format (see the example in description of what this method returns). This may be useful if you are wanting to use the output of the write_orbitize_input method.
RV measurements of objects that are not the primary should be relative to the barycenter RV. For example, if the barycenter has a RV of 20 +/- 1 km/s, and you’ve measured an absolute RV for the secondary of 15 +/- 2 km/s, you should input an RV of -5.0 +/- 2.2 for object 1.
When providing data with columns in the orbitize format, there should be no empty cells. As in the example below, when quant2 is not applicable, the cell should contain nan.
filename (str or astropy.table.Table) – Input filename or the actual table object
Table containing orbitize-readable input for given object. For the example input above:
epoch object quant1 quant1_err quant2 quant2_err quant12_corr quant_type float64 int float64 float64 float64 float64 float64 str5 ------- ------ ------- ---------- ------- ---------- ------------ ---------- 1234.0 1 0.01 0.005 0.5 0.05 0.025 radec 1235.0 1 1.0 0.005 89.0 0.1 nan seppa 1236.0 1 1.0 0.005 89.3 0.3 nan seppa 1237.0 0 10.0 0.1 nan nan nan rv
quant_typeis one of “radec”, “seppa”, or “rv”.
quant_typeis “radec” or “seppa”, the units of quant are mas and degrees, if
quant_typeis “rv”, the units of quant are km/s
- Return type
Written: Henry Ngo, 2018
Updated: Vighnesh Nagpal, Jason Wang (2020-2021)
- orbitize.read_input.write_orbitize_input(table, output_filename, file_type='csv')
Writes orbitize-readable input as an ASCII file
table (astropy.Table) – Table containing orbitize-readable input for given object, as generated by the read functions in this module.
output_filename (str) – csv file to write to
file_type (str) –
Any valid write format for astropy.io.ascii. See the astropy docs. Defaults to csv.
(written) Henry Ngo, 2018