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XSPEC fit of XSTAR model
Two component XSTAR model fit to the 800 ks Chandra HETG observation of NGC 3783. Model fit performed in xspec11 using the warmabs analytic model.
XSPEC fit of XSTAR model
XSTAR model fit to the HST/COS combined emission and absorption line spectrum of Mrk 290. Top panel: data and model fit; lower panels: emission and absorption model components (Zhang et al. 2014).

What is XSTAR?
XSTAR is a computer program for calculating the physical conditions and emission spectra of photoionized gases.

How Do I Get XSTAR?
Xstar is avaible in several different ways.

  • The XSTAR package is now integrated and distributed with the HEASARC's standard HEADAS package, so if your facility has this package installed then you already have access to xstar.

  • XSTAR is also available as a standalone package. The standalone XSTAR (or the full HEADAS), is available in either source or binary versions and it can be downloaded from here .

  • Check the revisions section of the manual for recent bug fixes. The most recent version with fixes included is the current develop version .

  • The release version of xstar is now available on hera. To use it, you must install fv and set up your environment to use it (fv is part of the standard heasoft software distribution or it can be installed standalone), and type 'fv -r xstar'. Input parameters are specified by prompting or else on the command line. Currently the output is buffered in large blocks, rather than printing each line of output as processing progresses. Thus it may appear that nothing is happening for a while until the buffer fills and is sent to your screen. It's also possible to start up the xstar task in hera, and then retrieve the results later, without having to keep the command window open. One would need to specify all the parameters directly on the command line, and also add a "-nowait " flag. For example: "fv -r -nowait me@milkyway.gsfc.nasa.gov xstar cfrac=1. temperature=400. ..." You will then receive an email message when the job is finished, with instructions on how to retrieve the output.

  • A utility has been created for extracting atomic data and rates from the xstar database. This utility is a standalone fortran program, which calls many of the xstar routines, and returns the rate (forward and reverse) and raw atomic data for a single type of rate for a single ion. It can be found here

  • An analytic model for calculating warm absorber and emitter spectra within xspec is available. This has the advantage that it avoids the intrinsic approximations associated with use of tables for absorption with variable abundances treated as multiplicative parameters, and the intrinsic clumsiness of the use of tables. It also allows the use of arbitrary spectral resolution, not limited by the internal xstar spectral resolution. To use it, download the tarfile, unzip and untar in your user area, and follow the installation instructions contained in the README. This includes the analogous routine which simulates the absorption (and emission) by a gas in coronal equilibrium. Scattered emission can be modeled using the 'windabs' model. These routines are still in the testing phase, so please send reports of bugs and problems.

    The develop version of warmabs, is here. It must be used with population files constructed with the develop version of xstar.

  • A version of xstar which allows for parallel computation of a grid of models has been developed by Michael Noble of MIT. pvm_xstar fosters parallel execution of XSTAR over large, time-consuming sets of parameters.

  • A php tool for making the xstinitable.par file needed by xstar2xspec is provided by D. Maitra of the University of Michigan here. This is a GUI form which produces the file in ascii. No error checking is provided.

    Online Documentation
    XSTAR documentation is included as part of the standard source distribution and is also viewable online or can be downloaded as a PostScript file or HTML.

    Related Files
    Sample xstar output from optically thin photoionized model, alpha=1 power law, line emissivities
    Sample xstar output from optically thin photoionized model, alpha=1 power law, line opacities
    Sample xstar output from optically thin photoionized model, alpha=1 power law, RRC emissivities
    Sample xstar output from optically thin photoionized model, alpha=1 power law, RRC opacities
    Sample XSPEC table models
    Line list.

    Line finding list.

    Level list.

    Subroutine xstar
    Postscript plots of atomic rates(42 Mbytes).
    An ascii version of the xstar database (28 Mbytes).

    The xstar database sorted according to process. (16 Mbytes).

    Sample output: Lexington H II region.

    Sample inputs.

    Atomic data.

    UADB, a comprehensive database for atomic data..

    Platforms Currently Supported
    XSTAR requires a standard Fortran 77 compiler. It has been tested on the following systems:
    • Mac OS X
    • Linux (both x86 & PPC)

  • For questions and comments about XSTAR, contact Tim Kallman or use the Feedback form