Quickstart

SPLAT is best used in the ipython or jupyter notebook; all of the necessary data is included in the github install, so you shouldn't need to be online to run anything unless you are using proprietary data (these are not distributed with the package) or the web interface.

All of the routines in SPLAT are organized into packages:

  • splat.core: core functionalities, including index measurement, database access and classification

  • splat.citations: biblographic/bibtex routines

  • splat.database: access the spectral and source databases, as well as online resources through astroquery

  • splat.empirical: empirical conversion relations

  • splat.evolve: access to evolutionary models and population synthesis routines

  • splat.model: access to spectral models and model-fitting routines

  • splat.photometry: spectrophotometry routines

  • splat.plot: plotting and visualization routines

  • splat.utilities: additional routines for general analysis

  • splat.web: SPLAT's web interface

To access routines, you should first import the appropriate package.

Most routines also have help docstrings that can be accessed by appending a question mark to the end of the function call:

>>> splat.getSpectrum?

Accessing Spectra

The best way to read in a spectrum from the SPLAT library is to use getSpectrum()

>>> import splat
>>> splist = splat.getSpectrum(shortname='0415-0935')
>>> splist = splat.getSpectrum(young=True)
>>> splist = splat.getSpectrum(spt=['M7','L5'],jmag=[14.,99.])
>>> splist = splat.getSpectrum(lucky=True)

The last case returns a randome spectrum. In each case, splist is a list of Spectrum class objects, which is the container of various aspects of the spectrum and its source properties. For example, selecting the first spectrum,

>>> sp = splist[0]

will extract that object, which contains many parameters and intrinsic functions. For example, sp.wave contains the wavelengths of this spectrum, sp.flux the flux values, and sp.noise the flux uncertainties. `sp.info()`_ will print out a set of information about the spectrum either set by your or contained in the SPLAT database. Read more about the Spectrum on the Spectrum class help page.

You can also search more generally for sources in the SPLAT database using `searchLibrary()`_:

>>> s = splat.searchLibrary(subdwarf=True)
>>> print(s)

This will print out a pandas dataFrame table with the relevant source and spectral information.

You can also read in your own spectrum by passing a filename directly to the Spectrum class object:

>>> sp = splat.Spectrum(filename='PATH_TO/myspectrum.fits')

Note that this file (fits or ascii) must conform to the standard of the SPL data: the first column is wavelength in microns, second column flux in f_lambda units, third column (optional) is flux uncertainty. You can preset the units for wavelength and flux density with optional keywords and using the astropy units package:

>>> import astropy.units as u
>>> sp = splat.Spectrum(filename='PATH_TO/myspectrum.fits',wunit=u.Angstrom,funit=u.erg/u.cm/u.cm/u.sec/u.Angstrom)

Manipulating Spectral Data

Spectral data can be manipulated in many ways using routines intrinsic to the Spectrum class object. For example, you can normalize or scale the spectrum using these respective functions:

>>> sp = splat.getSpectrum(shortname='0415-0935')[0]
>>> sp.normalize()                                              # normalizes the spectral flux by dividing out overall maximum
>>> sp.normalize(range=[1.1,1.3])               # divide by maximum in wavelength range 1.1-1.4 micron
>>> sp.scale(5.0)                                               # scale the spectral flux by a factor of 5.0

To flux calibrate the spectrum, use the object's built in fluxCalibrate() method:

>>> sp.fluxCalibrate(14.0, '2MASS J')   # flux calibrate to 2MASS J = 14.0

Spectra can be added and subtracted from each other with simple addition and subtraction

>>> sp1 = splat.getSpectrum(shortname='0415-0935')[0]
>>> sp2 = splat.getSpectrum(shortname='0559-1404')[0]
>>> sp3 = sp1+sp2       # sum
>>> sp4 = sp1-sp2               # difference

To display the spectrum, use the Spectrum object's plot() function or plotSpectrum()

>>> sp.plot()
>>> from splat.plot import plotSpectrum
>>> plotSpectrum(sp)

which will pop up a window displaying flux vs. wavelength. You can save this display by adding a filename:

>>> sp.plot(sp,file='spectrum.png')

You can also compare multiple spectra:

>>> sp1 = splat.getSpectrum(shortname='0415-0935')[0]
>>> sp2 = splat.getSpectrum(shortname='1217-0311')[0]
>>> from splat.plot import plotSpectrum
>>> plotSpectrum(sp1,sp2,colors=['black','red'])

You can add several extras to this to label features, plot uncertainties, indicate telluric absorption regions, make multi-panel and multi-page plots of lists of spectra, etc. Be sure to look through the SPLAT plotting subpackage for more details.

SPLAT can analyze and compare an arbitrary number of spectra.

>>> sp = splat.getSpectrum(shortname='0415-0935')[0]
>>> value, error = splat.measureIndex(sp,[1.14,1.165],[1.21,1.235],method='integrate')
>>> indices = splat.measureIndexSet(sp,set='testi')

The last line returns a dictionary, whose value,error pair can be accessed by the name of the index:

>>> print(indices['sH2O-J'])            # returns value, error

>>> sp = splat.getSpectrum(young=True, lucky=True)[0]
>>> splat.classifyGravity(sp,verbose=True)

This returns (depending on the source returned):

>>> Gravity Classification:
>>>   SpT = L1.0
>>>   VO-z: 1.193+/-0.018 => 1.0
>>>   FeH-z: 1.096+/-0.026 => 2.0
>>>   H-cont: 0.973+/-0.010 => 2.0
>>>   KI-J: 1.044+/-0.008 => 2.0
>>>   Gravity Class = VL-G

>>> sp = splat.getSpectrum(shortname='0415-0935')[0]
>>> spt,unc = splat.classifyByStandard(sp,spt=['T5','T9'])
>>> spt,unc = splat.classifyByIndex(sp,set='burgasser')
>>> bestMatches = splat.classifyByTemplate(sp,spt=['T6','T8'],nbest=5)

The last line returns a dictionary containing the best 5 template matches to the Spectrum sp. Note that comparing to the large template library of SPLAT can take a long time to run; currently you have to set force=True to run more than 100 templates. (then go get a coffee!)

>>> from splat.model import loadModel     # loads in model reading package
>>> sp = splat.getSpectrum(shortname='0415-0935')[0]
>>> mdl = loadModel(teff=700,logg=5.0)  # BTSettl08 model by default
>>> chi,scale = splat.compareSpectra(sp,mdl,plot=True,file='comparison.pdf')

Notice in the last line, the keyword plot allows you to visualize the comparison, which can be saved as a file

The available spectral models are

>>> import splat.model as spmodel
>>> sp = splat.getSpectrum(shortname='0415-0935')[0]
>>> results = spmodel.modelFitGrid(sp,teff_range=[1200,2500],model='Saumon',file='fit1507')
>>> results = spmodel.modelFitMCMC(sp,initial_guess=[900,5.0,0.0],nsamples=1000)
>>> results = spmodel.modelFitEMCEE(sp,t0=900,g0=5.0,nwalkers=50,nsamples=500,output='basefilename')

The output of each of these is a dictionary containing the best fit model parameters, average fit model parameters, and visualization plots. Refer to the API for these for more details.

All of these routines have many options worth exploring, and which are (partially) documented in the following pages. If there are other capabilities you need, please suggest them, or note it in the "Issues" link on our github site

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