MANUAL

3_FSPS_manual

User Manual:

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Manual for FSPS v3.1July 15, 20181. OverviewThe collection of fortran routines contained in this package allows the user to compute simple stellar pop-ulations (SSPs) for a variety of IMFs and metallicities, and for a variety of assumptions regarding themorphology of the horizontal branch, the blue straggler population, the post–AGB phase, and the locationin the HR diagram of the TP-AGB phase. A variety of simple and flexible prescriptions for attenuationby dust are also included, as are dust emission models based on the Draine & Li 2007 dust models. Fromthese SSPs the user may then generate composite stellar populations (CSPs) for a variety of star formationhistories (SFHs) and dust attenuation prescriptions. Outputs include the spectra and magnitudes of theSSPs and CSPs at arbitrary redshift. In addition to these fortran routines a collection of IDL routines areprovided that allow easy manipulation of the output.The user is strongly encouraged to read Conroy et al. 2009 for an overview of stellar population synthesis(SPS) and for details regarding this collection of routines. As of v2.0, this code has been extensively calibratedagainst a suite of observational data (for details see Conroy & Gunn 2010). The code package is a in essencea highly flexible SPS code and has therefore come to be called FSPS.The rest of this manual is organized as follows. In §1 we briefly discuss the overall philosophy of the codestructure and highlight the main features. In §2 we present the routines, how they are used, and provide theuser with a basic program that demonstrates the use of the routines. §3 discusses the IDL routines providedto read and manipulate the outputs from the fortran package. §4 discusses a variety of questions (ok, onlyone) the user may have.For a description of revisions since the initial release of the code, see the file REVISION HISTORY inthe doc directory. Installation instructions are also provided in that directory.1.1 Downloading the codeAs of v2.5, FSPS is now distributed via github: github.com/cconroy20/fsps (the googlecode SVN repos-itory is no longer supported). The code can be checked out with standard github commands. Emails willbe sent to the mailing list whenever new versions become available (this is one reason why it is essential forusers of this code to be on the mailing list).1.2 Environment variablesAs mentioned on the webpage, you will need to set an environment variable called SPS HOME that pointsto the root SPS directory (i.e. the directory that contains the src,OUTPUTS, etc. directories)1.3 Inclusion of TP-AGB spectraThe TP-AGB empirical spectral library does not extend past the rest-frame K-band and so in previousversions the integrated spectra were not reliable beyond λ≈2.4µm. Up to v2.2 the empirical TP-AGBspectra were extrapolated with the BaSeL library for models at the same Teff and the lowest surface gravitiesavailable in the BaSeL library. As of v2.3, the TP-AGB spectra are extrapolated blueward with simpler linearslopes (as advocated in Lancon & Wood 2002). The spectra of the carbon stars are now extrapolated redwardwith the Aringer et al. 2009 synthetic carbon star spectral library. The spectra of the oxygen-rich TP-AGBstars are now extrapolated with the latest version of the PHOENIX stellar spectral library (the BT-SETTLlibrary).1.4 UnitsThis code produces two types of files. The first are spectral files (*.spec). The spectra are in units ofL⊙/Hz, i.e. they are fν. Integrating over frequency generates the bolometric luminosity of the spectrum.Wavelengths are in angstroms in vacuum, and the wavelength array for the stellar libraries can be found inthe files BaSeL3.1/basel.lambda and MILES/miles.lambda. The full wavelength array is also now printedin the first line in the *.spec files. The second type of file contains magnitudes in a variety of filters. Themagnitude zero point (i.e., AB or Vega) is set by the variable compute vega mags described below. Both of1
these output files contain information on the age, mass, bolometric luminosity, and star formation rate. Allof these quantities are in the log (base-10), with units of years, M⊙,L⊙, and M⊙yr−1, respectively.1.5 Redshift EffectsThe code allows the user to specify a redshift (see Section 3.1.2 below). As of v2.4, specifying a non-zeroredshift affects both the computed magnitudes and spectra. There are two qualitatively different options forredshifting. See the parameter redshift colors below for more details. As of v2.5 the returned magnitudesinclude both the relevant (1 + z) factors and the distance modulus. Also as of v2.5, IGM absorption viaMadau (1995) can be turned on and will attenuate the spectrum (and mags). This feature is enabled onlyfor non-zero redshifts.1.6 FiltersThe current release contains 105 filters. The filter names can be found in the file FILTER LIST in the datadirectory. The actual filter definitions are in the file allfilters.dat in the same directory. The transmissionprofiles in this file include atmospheric absorption and are in units of relative response per photon (as opposedfor example to relative response per unit power). The filters are normalized internally within the code. Theoutput magnitudes are listed in the filter order displayed in the FILTER LIST file. The user is cautioned touse whenever possible the exact filter transmission curve appropriate for the data being considered. Thereis, for example, no such thing as THE B−band filter. Differences of a few hundredths of a magnitude arecommon between different definitions of a given filter such as B.1.7 Computation of magnitudesThe AB magnitude through a filter b,mb, is defined according to the following formuale:hfνib=RRbγfνd ln νR(ν/νb)βRbγd ln ν(1)mb=−2.5log10(hfνib)−48.60 (2)where fνis the spectrum and Rbγis the relative response per photon of the filter. The factor (ν/νb)βinthe demoninator of Equation 1 may surprise those used to working with optical photometry. Indeed, forUV, optical, and near-IR photometry, one usually adopts β= 0 (e.g., for the GALEX, SDSS, and 2MASSsurveys). However, IR photometry typically assumes a different calibration. For example, the IRAS,SpitzerIRAC, and Herschel PACS and SPIRE magnitudes are frequently quoted assuming β= 1 while the SpitzerMIPS filters adopt β= 2 (i.e., a 104K blackbody). The parameter νbis the central wavelength of the filter.The motivation underlying this convention is that for sources with an intrinsic spectral slope β, thebandpass-convolved flux quoted at frequency νbwill be precisely the flux at that frequency. For example,observing a 104K blackbody through the MIPS filters with the above calibration will return a flux density atthe central frequency of the filter that is precisely the true flux at νb. In the end, this is merely a convention,but one that must be handled carefully when comparing data to models. See the routine sps setup.f90 forimplementation.1.8 Interpretation of the ∆Land ∆TparametersAs described below, the user may modify the bolometric luminosity and effective temperature of the TP-AGB phase by applying overall shifts in log(Lbol) and log(Teff ) via the parameters ∆Land ∆T. In previousversions, these parameters were with respect to the default Padova model calculations circa 2008. As of v2.0,these parameters represent shifts with respect to the best-fit values found in Conroy & Gunn 2010. In otherwords, leaving these values set to 0.0 means that the user adopts the calibrations described in Section 3.1.3in Conroy & Gunn 2010.As of v2.5 these default settings of these parameters have been redefined in order to agree with the LFsof AGB stars in the LMC; see Villaume et al. 2014 for details.2

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