Fitting unresolved binaries

Starting from v1.3.0, MADYS provides a straightforward way to derive the parameters of both components of an unresolved binary system. Given the ubiquity of short-period binaries and the biases these systems introduce in any effort dealing with the age and mass distribution of a stellar sample, this feature of the program will be beneficial to a large variety of statistical studies focused on directly imaged exoplanets or on the stars themselves.

Given the limited information used by MADYS to derive stellar parameters, no attempt is made to leave the secondary-to-primary ratio as a free parameter; instead, the user can specify either a secondary-to-primary mass ratio (through the keyword secondary_q) or a magnitude difference (through the keyword secondary_contrast) in a suitable band when running the SampleObject.get_params() method.

Let’s suppose that a SampleObject instance is creating containing a list of two stars.

example_object = madys.SampleObject(file, id_type='DR3', verbose=0, ext_map='leike')

Using a scalar value for secondary_q will apply the given mass ratio to all the objects:

result = example_object.get_params('bhac15', secondary_q=0.7)

Using an array with same length as the object list will instead apply a different q to every system:

result = example_object.get_params('bhac15', secondary_q=np.array([0.7, 0.5]))

Every other optional keyword in SampleObject.get_params() can be used as in the general, single-star model (see here). In particular, we suggest providing any available age constraint to increase the precision of the final results.

Note

Unlike secondary_q, secondary_contrast must be specified as a one-key dictionary with key name equal to the name of the filter where the magnitude difference is measured. The dictionary value works exactly in the same way as a secondary_q value.

Note

Please have also a look here for information about the available filters. Check beforehand that the filter of interest is available for the theoretical model you wish to use.

Note

When providing an array for a list of star, use a value of np.inf (for a contrast) or 0 (for a mass ratio) to tell MADYS that the corresponding element should be treated as a single star.