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1. n command line option p nthreads command line option C command line option V 5 f 5 h 5 n 5 p nthreads 5 5 5 5 5 5 212. so the distance can be given as 100 pc for example If the source is located at a cosmological distance this parameter is the luminosity distance integer img i gt unit required The unit of the image This variable can take values between 0 and 4 0 for Kelvin 1 for Jansky per pixel 2 for SI units and 3 for Solar luminosity per pixel The value 4 is a special option that will create an optical depth image cube dimensionless string img i gt filename required This variable is the name of the FITS file It has no default value double img i gt phi optional Phi is an optional geometric parameter Like theta it should be given in radians between 0 and 27 Phi is the rotation angle of the model x y plane around the z axis If the model is view face on so that the line of sight coincides with the z axis phi corresponds to the position angle on the sky The default value is 0 double img i gt source_vel optional The source velocity is an optional parameter that gives the spectra a velocity offset This parameter is useful when comparing the model to an astronomical source with a known relative velocity integer img i gt nchan semi optional nchan is the number of velocity channels in a spectral image cube See the note below for additional information double img i gt velres semi optional The velocity resolution of the spectral dimension
3. 1 9 else temperature 0 temp 1 x0 r temp 0 x0 temp 1 x0 1 temp 1 x0 temp 0 x0 1 temp 0 x0 void abundance double x double y double z double x abundance abundance 0 1 e 9 void doppler double x double y double z double xdoppler xdoppler 200 void velocity double x double y double z double xvel double R phi r theta R sqrt x x y y zZ Z theta atan2 sqrt x xt y y Z phi atan2 y x r sqrt 2 6 67e 11 1 989e30 R vel 0 rx sin theta cos phi vel 1 rx sin theta sin phi vel 2 rx co0s theta 1 5 Output from LIME Besides the FITS images which are the main output LIME produces other output that can be used not only for diagnostics but also science results This chapter describes the various output files and how to work with them 1 5 1 The grid Once the Delaunay grid has been created by LIME a VTK file with the grid and grid properties are written 1f the parameter par gt gridfile is set see chapter 2 The VTK Visualization Tool Kit format is a formatted ascii file that are used to handle geometrical objects in our case an unstructured grid VTK files can be read by several visualization software packages In particular we advocate the use of paraview http www paraview org which is an open source program available for several platforms The grid file contains the x y z coordinate of each grid point as well as a reference to th
4. beam profile In this case model and data is compared in frequency space in which case the model image needs to be Fourier transformed or in image space in which case the model should be sampled with the u v spacing from the dataset and 18 Chapter 1 LIME user manual LIME Documentation Release inverted and cleaned using the same process as the observed data has gone through When Fourier transforming the model image one should be careful to avoid aliasing effects that are caused by the regularity of the pixel grid Such effects are model dependent and difficult to prevent entirely On the other hand comparing the model to interferometric data in image space is dangerous as well because of the non uniqueness of the de convolved image Both convolution and Fourier transforming can be done using the MIRIAD tasks convolve and fft after converting the FITS file into MIRIAD format using the MIRIAD task fits Both convolution and Fourier transformation can be done in IDL or Python 1 6 2 Plotting the model The LIME data cubes can be visualized in numerous ways both in one and two dimensions One dimensional plots include the spectrum of a single pixel and the brightness profile along either spatial direction a a specific frequency or summed over a range of frequencies The two dimensional contour plots are images when done in the plane spanned by the two spatial axis and position velocity PV diagrams when done in the frequency and any
5. convolved with a beam profile that corresponds to the instrument beam at the frequency in question Before convolving am image it is important to make sure that the image is larger that the beam size and that the beam is resolved by the pixels pixel size lt lt beam size The reason that the image needs to be bigger that the beam is to avoid artificial edge effects at the corners of the image This is not very important if only the spectrum toward the center of the image is of interest but if the image is being used as a model of a single dish map edge effects become important In general it is recommended that the image is made large enough that the emission has dropped sufficiently close to zero at the edges of the image If the beam size is small it may be an issue that the beam is not sufficiently resolved by pixels This is important to make sure that structures that are picked up by the telescope beam is sufficiently sampled by the ray tracer in LIME In general it is a good idea to calculate the image in a considerably higher resolution than what is needed because artifacts in the image that are due to the randomness of the grid are then smoothed out In order to compare a convolved model spectrum to a single observed spectrum toward the source center the spectrum at the center pixel should be used without additional averaging of pixels When comparing model images to interferometric observations there is no need to convolve the image with a
6. dat i e co or co dat moldatfile is an array so multiple data files can be used for a single LIME run There is no default value string par gt dust optional Path to a dust opacity table This table should be a two column ascii file with wavelength in the first column and opacity in the second column Currently LIME uses the same tables as RATRAN from Ossenkopf and Henning 1994 and so the wavelength should be given in microns 1e 6 meters and the opacity in cm2 g This is the only place in LIME where SI units are not used The moldatfile and dust parameters are optional in the sense that at least one of them or both should be set There is no default value A future version of LIME will allow spatial variance of the dust opacities so that opacities can be given as function of x y and z string par gt outputfile optional This is the file name of the output file that contains the level populations If this parameter is not set LIME will not output the populations There is no default value string par gt binoutputfile optional This is the file name of the output file that contains the grid populations and molecular data in binary format This file is used to restart LIME with previously calculated populations Once the populations have been calculated and the binoutputfile has been written LIME can re ray trace for a different set of image parameters without re calculating the po
7. memory for the grid and the molecular data based on the parameter settings in the model file All user defined settings are checked for sanity and in case there are inconsistencies LIME will abort with an error message It then goes on to generate the grid unless a predefined grid is provided by picking and evaluating random points until enough points have been chosen to form the grid The grid is then iteratively smoothed to avoid oddly shaped Delaunay triangles Because the grid needs to be re triangulated at each iteration the smoothing process may take a while After smoothing a number of grid properties e g velocity splines are pre calculated for later use and the grid is written to file When the grid is ready LIME decides whether to calculate populations or not depending on the user s choice of output images and LTE options see chapter 2 If one or more non LTE line images are asked for LIME will proceed to calculate the level populations This too is an iterative process where the radiation field and the populations are recalculated repeatedly The radiation field is obtained by propagating photons through the grid a fix number for each grid point and using the resulting radiation field the code enters a minor iteration loop where a set of linear equations determining the statistical equilibrium are iterated upon in order to converge upon a set of populations This is done for each grid point in turn Once all the grid points has g
8. LIME Line Modeling Engine is an excitation and radiation transfer code that can be used to predict line and contin uum radiation from an astronomical source model The code uses unstructured 3D Delaunay grids for photon transport and accelerated Lambda Iteration for population calculations LIME was developed for the purpose of predicting the emission signature of low mass young stellar objects including molecular envelopes and protoplanetary disks In principle the method should work for similar environments such as giant molecular clouds atmospheres around evolved stars high mass stars molecular outflows etc As opposed to most other line radiation transfer codes which are constrained by cylindrical or spherical symmetry LIME being a 3D code does not impose any such geometrical constraints The main limitation therefore to what can be done with LIME is the availability of input models LIME is distributed under a Gnu General Public License Any publication that contains results obtained with the LIME code should cite the publication Brinch amp Hogerheijde A amp A 523 A25 2010 1 1 3 Development history The initial LIME code was written by Christian Brinch between 2006 and 2010 with version 1 0 appearing in early 2010 LIME derives from the radiation transfer code RATRAN developed by Michiel R Hogerheijde and Floris van der Tak Hogerhijde amp van der Tak 2000 although after several rewrites the shared codebase is very smal
9. LIME Documentation Release Christian Brinch August 21 2015 Contents 1 LIME user manual 3 Ll Introduchom 2 225 4 2 Seba e di AO ee ee A 3 1 2 Command line options setacea oY RA Ee A E SR ROE AE Re A AR 5 1 35 Sete Up models s cti eet Ph ee deehGc be thant eee eed rs 6 14 Modeltuncuons ss ee goes eG bape RE REDE A EERE BA E SES OSs 10 15 Output from LIME e re ea beak bb bea ee be e eee ee Be ae 17 1 6 POSt processiM s s os e a A A we Be See ee ee he a ee a 18 1 7 Ideasdor LIME 2 0 oe oe a eh ee eG AE A hee ee Se al Gee DA e 19 1 3 Appendix Bibliography ss sarosa mmt a a OR ES Re RE Re 19 LIME Documentation Release Contents Contents 1 LIME Documentation Release 2 Contents CHAPTER 1 LIME user manual 1 1 Introduction 1 1 1 Disclaimer We the authors and maintainers of LIME do not guarantee that results given by LIME are correct nor can we be held responsible for erroneous results We do not claim that LIME is perfect or free of bugs and therefore the user should always take utmost care when drawing scientific conclusions based on results obtained with LIME Itis very important that the user performs tests and sanity checks whenever working with the LIME code to make sure that the results are reasonable and reliable In particular care needs to be taken when extending the runtime parameters into regimes for which the code was not designed 1 1 2 The LIME code
10. ar tool The information in the population file allows the user to plot projections and slices of the model properties including the populations This is the best way to directly compare the LIME model and the result of the excitation calculation with the results obtained by other codes One particularly interesting property to plot is the excitation temperature Du Qu AE exp m g kp Tex which is obtained from the level populations u and 1 refers to the upper and lower level and g are the statistical weights Calculating the excitation temperature is the best way to check for masering in the model since the excitation temperature turns negative in the case of population inversion If and only if the gas is in local thermodynamic equi librium LTE the excitation temperature equals the kinetic temperature so plotting the ratio of kinetic gas temperature to the excitation temperature gives a measure of the deviation from LTE 1 5 3 Images Image cubes are the main output from LIME LIME produces model images in the FITS file format only 1 6 Post processing In order to make direct comparisons between LIME models and observations some kind of post processing of the images will be needed in almost all cases In this chapter we will give some hints and tricks to how this can be done using readily available software packages 1 6 1 Convolution In order to compare LIME results to single dish observations the image cube needs to be
11. basic settings such as number of grid points model radius input and output filenames etc Some of these parameters always need to be set by the user while others are optional with preset default values There is an exception to this rule namely when restarting LIME with previously calculated populations In that case none of the non optional parameters are required double par gt radius required This value sets the outer radius of the computational domain It should be set large enough to cover the entire spatial extend of the model In particular if a cylindrical input model is used e g the input file for the RATRAN code one should not use the radius of the cylinder but rather the distance from the center to the corner of the r z plane double par gt minScale required minScale is the smallest scales sampled by the code Structures smaller than minScale will not be sampled properly If one uses spherical sampling see below this number can also be though upon as the inner edge of the grid This number should not be set smaller than needed because an undesirable large number of grid point will end up near the center of the model integer par gt pIntensity required This number is the number of model grid points The more grid points that are used the longer the code will take to run Too few points however will cause the model to be under sampled with the risk of getting wrong results Usef
12. broutine for the doppler velocity systemic velocity dust temperature and abundance are similar using the appropriate keywords to identify the column in the RATRAN mdl file Since RATRAN uses molecular density and not abundance the abundance function should read void abundance double x double y double z double x abundance abundance 0 ratranInput model md1 nh x y z ratranInput model md1 nm x y Z 4q Obviously it is possible to mix RATRAN input that is using different mdl files for the different functions All parameters in model c still need to be set ie par gt radius even though this information is contained in the RATRAN header If the RATRAN grid is not logarithmically spaced it may be advantageous to set par gt sampling 1 1 4 Model functions 15 LIME Documentation Release 1 4 12 Example model file Here follows the model c file that can be found in the example directory in the LimePackage This model describes a simple spherical envelope of HCO gas The temperature is also one dimensional but provided as a table of value The additional code in the temperature subroutine interpolates the values of the table A constant molecular abundance and Doppler b parameter is used The velocity field is described by a free fall on radial trajectories toward a central mass of one Solar mass This example will produce a single image of the HCO J 4 3 line in the approximate distance of the Taur
13. e amount of memory gt 1 GB but less will do as well LIME can be run in multi threaded parallel mode if several CPUs are available It is also possible to run several instances of LIME simultaneously on a multi processor machine with enough memory 1 1 6 Setting up LIME LIME is compiled at run time so there is no need to make any kind of pre installation of the code The only require ment for the code to run is that the path to lime script is in the PATH environment variable Note Starting with LIME 1 5 sourcing the sourceme bash or sourceme bash depending on your SHELL type is not needed anymore 1 1 7 Running LIME Once the PATH variable is set LIME can be run from the command line bash lime model c where model c is the file containing the model this file can have any name This will cause the code to be compiled and the terminal window should change and display the progress of the calculations After completion the user is prompted to press a key which will bring the terminal window back It is possible to run LIME in silent mode that is without any output in the terminal window This is done by setting the silent flag to 1 the default setting is 0 in the file LimePackage src lime h LIME also accepts several command line options 4 Chapter 1 LIME user manual LIME Documentation Release 1 1 8 The inner workings of LIME The first thing that happens after compilation is that LIME allocates
14. e neighbors of each grid point From this information the Delaunay triangulation can be reconstructed The file also holds three scalar fields and a vector field for the H2 density temperature molecular density and the velocity field Other properties could be written out as well but that will require the user to edit the write_VTK_unstructured_Points function in grid c Inspecting the grid using paraview can be a useful way to make sure that the model indeed behaves as expected It makes for impressive visualizations that can be included in presentations However paraview does a poor job when it comes to publication quality plots 1 5 Output from LIME 17 LIME Documentation Release 1 5 2 Populations The level populations are written out in a separate file if LIME is set up to calculate the level populations that is if at least one molecular data file is defined in model c and if the parameter par gt outputfile is set Currently LIME can only write out populations from the first molecule par gt moldatfile 0 The populations output file contains the x y and z coordinates for each grid point as well as the H2 density temperature and molecular density besides the level populations Contrary to the grid file it does not however contain information about the neighbors of the grid points and therefore the Delaunay triangulation cannot be reconstructed from this file unless the points are re triangulated with qhull or a simil
15. el c file If this function is left out LIME defaults to a dust to gas ratio of 100 everywhere This number only has an effect if the continuum is included in the calculations void gasIIdust double x double y double z double xgtd xgtd x y Z 1 4 8 Other settings A number of additional settings can be found in the file LimePackage src lime h These settings should in general not be changed by the user unless there is an explicit need to do so A few of them however could be useful to some users The keyword silent which is by default set to zero can be set to one This will cause LIME to run completely silent with no output to the screen at all This can be useful for running LIME in batch mode in the background Another number that might be of interest is NITERATIONS by default set to 16 This is the number of major iteration loops LIME will go through before ray tracing If the user is happy with the signal to noise achieved after fewer iterations this number can be lowered accordingly Obviously a higher number will cause LIME to go through more iterations which may be needed for models with slow convergence 1 4 9 Advanced setup Standard use of LIME requires the user to formulate the model in the model functions described above as either an analytical expression or a look up table of values As input models increase in complexity however analytical descriptions may no longer be possible and with model dimens
16. g the specified number of threads Serial operation is the default 1 3 3 Images LIME can output a number of images per run The information about each image is contained in a structure array called img The images defined in the image array can be either line or continuum images or both All definitions of an image may be changed between images 1 e distance resolution inclination etc so that a number of images with varying source distance or image resolution can be made in one go In the following i should be replaced by the image number 0 1 2 8 Chapter 1 LIME user manual LIME Documentation Release integer img i gt pxls required This is the number of pixels per spatial dimensions of the FITS file The total amount of pixels in the image is thus the square of this number double img i gt imgres required The image resolution or size of each pixel This number is given in arc seconds The image field of view is therefore pxls x imgres double img i gt theta required Theta is the viewing angle the angle between the model z axis and the ray tracers line of sight This number is given in radians not degrees so that a face on view of models where this term is applicable is 0 and edge on view is 7 2 double img il gt distance required The source distance in meters LIME knows the conversion between parsec AU and meters
17. hat kind of image is produced line or continuum Only certain combinations are permitted however some of them have to be set LIME decides to make a continuum image 1f the parameter nchan is left unset This will result in a single channel continuum image In nchan is unset the only other parameter which is allowed to be set is freq which however has to be set In addition the parameter par gt dust needs to be set as well otherwise LIME will produce an error In order to produce a line image cube either the parameter nchan velres and trans or nchan freq and bandwidth should be set Any other combination will produce an error For line images at least one moldatfile should be provided and optionally a dust opacity table as well 1 4 Model functions The second part of the model c file contains the actual model description This is provided as seven sub routines density molecular abundance temperature systematic velocities random velocities magnetic field and gas to dust ratio The user only needs to provide the functions that are relevant to a particular model e g for continuum images only the user need not include the abundance function or any of the ve locity functions The magnetic field function needs only be included for continuum polarization images 1 4 1 Density Z The density subroutine contains a user defined description of the 3D density profile of the collision partner s void density doub
18. ionality higher than one look up tables become difficult to manage within the model c functions In the following we will explain how to use complex numerical models and pre gridded models as input for LIME 1 4 10 Using numerical input models Numerical input model can roughly be divided into two groups those where the model properties are described as cell averages and those where the model properties are described at cell nodes see figure In either case LIME will send a coordinate to the model functions and expect a value back It is the up to the user to write an interface that will look up the appropriate return value In the simplest case where the numerical model is described as cell averaged values the user needs to loop through the cells and find the cell in which the LIME point falls and return the value of that particular cell In the case where the model is described on cell nodes the user must loop through the nodes to find the node which lies closest to the LIME point and return that node value This approach obviously limits the LIME model smoothness to the input model resolution since all LIME points which falls with an input model grid cell or within a certain distance from a grid node gets the same value One way to get around this is to interpolate in the input grid which in principle can be done in either case although this may be highly non trivial if the model is described on unstructured grid nodes or 1 4 Model func
19. l The photon transport method is a direct implementation of the SimpleX algorithm Ritzerveld amp Icke 2006 Subsequent to the creation of the package by Christian Brinch contributors to LIME have included e Tuomas Lunttila LIME Documentation Release e S bastien Maret e Marco Padovani e Anika Schmiedeke e lan Stewart e Mathieu Westphal 1 1 4 Obtaining LIME The LIME code can be obtained from gitHub at https github com lime rt lime The available files include the source code this documentation and an example model The documentation can be read on line at https readthedocs org projects lime 1 1 5 Requirements LIME runs on any platform with an ANSI C compiler Most modern operating systems are equipped with the GNU gcc compiler but if it is not already present it can be obtained from the GNU website http www gnu org Furthermore LIME needs a number of libraries to be present including ncurses GNU scientific Library GSL cfitsio and qhull Please refer to the README file within the LimePackage for details on how to obtain and install these libraries on various systems Although it is not strictly needed for LIME to run it is useful to have some kind of software that can process FITS files DL CASA MIRIAD etc in order to be able to extract science results from the model images There are no specific hardware requirements for LIME to run A fast computer is recommended gt 2 GHz with a reasonabl
20. le x double y double z double xdensity density 0 f x y z density 1 f x y z density n f x y z LIME can deal with an unlim ited number 10 Chapter 1 LIME user manua LIME Documentation Release of collision partners n However LIME will produce an error if more density pro files are given in the density subroutine than there are collision part ners listed in the molecular data file In most cases a single density profile will suffice The density is a number density that 1s the number of collision partners per unit volume in cubic me ters not cubic centimeters Please note that the cur rent version of LIME always takes the abundance relative to the first collision partner This is potentially a problem if the first collision partner is not the total H2 density and the user will have to correct for this in the abundances see below 1 4 2 Molecular abundance The abundance subroutine contains descriptions of the molecular abundance profiles of the input model The number of abundance profiles should match exactly the number of molecular data files defined in par gt moldatfile void abundance double x double y double z double x abundance abundance 0 f x y z abundance 1 f x y Z abundance n f x y Z The abundance is the fractional abundance with respect to the primary collision partner density 0 s
21. n retained for purposes of backward compatibility In practice there is little obvious difference between the outputs from O versus 2 The default value is now sampling 2 double par gt tcmb optional This parameter is the temperature of the cosmic microwave background This parameter defaults to 2 725K which is the value at zero redshift i e the solar neighborhood One should make sure to set this parameter properly when calculating models at a redshift larger than zero TCMB 2 725 1 z K It should be noted that even though LIME can now take the change in CMB temperature with increasing z into account it does not yet take cosmological effects into account when ray tracing such as stretching of the frequencies when using Jansky as unit This is currently under development string par gt moldatfile i optional Path to the i th molecular data file Molecular data files contains the energy states Einstein coefficients and collisional rates which are needed by LIME to solve the excitation These files need to conform to the standard of the LAMDA database http www strw leidenuniv nl moldata Data files can be downloaded from the LAMDA database but from LIME version 1 23 LIME can also download these files automatically If a data file name is give that cannot be found locally LIME will try and download the file instead When downloading data files the filename can be give both with and without the surname
22. o that the molec ular density of the first species is given by abundance 0 x density 0 The abundances are dimensionless 1 4 Model functions 11 LIME Documentation Release 1 4 3 Temperature The temperature subroutine contains the descriptions of the gas and optionally the dust temperature void temperature double x double y double z double xtemperature temperature 0 f x y z temperature 1 f x y z The entry 0 in the temperature array is the kinetic gas temperature This value is required for LIME to run The entry 1 is the optional dust temperature Both are in Kelvin If there is no explicit dust temperature given in the temperature subroutine LIME will assume that the dust temperature equals the gas temperature 1 4 4 Random velocities This subroutine contains a scalar field which describes the velocity dispersion of the random motions of the gas This number is the Doppler b parameter which is the 1 e half width of the line profile The doppler subroutines differs from the other model subroutines in the sense that the return type is a scalar and not an array The doppler b parameter should be given in m s void doppler double x double y double z double xdoppler xdoppler f x y z Because the return type is a scalar the asterisk in front of the variable name needs to be present doppler 0 does not work 1 4 5 Velocity field The velocity field
23. of the FITS file the width of a velocity channel This number is given in m s See the note below for additional information integer img i gt trans semi optional The transition number when ray tracing line images This number refers to the transition number in the molecular data files Contrary to the numbers in the data files trans is zero index meaning that the first transition is labeled 0 the second transition 1 and so on For linear rotor molecules without fine structure transition in their data files CO CS HCN etc the trans parameter is identified by the lower level of the transition For example for CO J 1 0 the trans label would be zero and for CO J 6 5 the trans label would be 5 For molecules with a complex level configuration e g H20 the user needs to refer to the datafile to find the correct label for a given transition See the note below for additional information 1 3 Setting up models 9 LIME Documentation Release double img il gt freg semi optional Center frequency of the spectral axis in Hz This parameter can be used for both line and continuum images See the note below for additional information double img il gt bandwidth semi optional With of the spectral axis in Hz See the note below for additional information 1 3 4 Note on semi optional image parameters The above parameters listed as semi optional determine w
24. olumns using proper C syntax as arrays and putting them in a header file that can be included in model c int size numer_of lines_in model file double model_x size xl x2 xn double model_y sizel y1 y2 vn double model_z size z1 z2 zn double model_density size densityl density2 densityn The pseudocode example from above now reads density x y z mindist very_large_number for i from 0 to size by 1 calculate distance from x y z to model_x i model_y i model_z i dist if dist lt mindist then mindist dist bestdensity model_densiy i return bestdensity 1 4 11 RATRAN models as input for LIME It is possible to use existing 1D or 2D model files from the RATRAN code in LIME This is done with ratranInput subroutine The mdl file has to comply with the RATRAN standard and the header everything above the sign of the file needs to be intact The functions in model c look like this void density double x double y double z double xdensity density 0 ratranInput model mdl1 nh x y z xle6 and void teperature double x double y double z double xtemperature temperature 0 ratranInput model mdl te x y z for the density and temperature respectively Notice that the density is multiplied by le6 to convert the cgs units from RATRAN into LIMEs SI units The calls to the su
25. one of the spatial axis When plotting images it is often useful to sum over a range of frequencies This results in what is know as moment maps These can be made to any order but zero and first moments are most often used The nth moment is defined as Hn z y J v Visual I z Y z dv Sometimes the first moment and also higher order moments is normalized by the zero moment 1 7 Ideas for LIME 2 0 In the following we list a number of new features which are being considered for the next major release of LIME Users should feel free to contact the maintainers with suggestions improvements new functionalities or bugs needing to be fixed e Line polarization e Visibility output e Tau images e User defined function based grid sample weights e Basecol Vamdc support e etc 1 8 Appendix Bibliography e Brinch amp Hogerheijde A amp A 523 A25 2010 see also http www nbi dk brinch lime php e Hogerheijde amp van der Tak A amp A 362 697 2000 e Ritzerveld amp Icke PhysRevE 74 26704 2006 e Ossenkopf amp Henning A amp A 291 943 1994 e Kernighan amp Ritchie The C Programming Language 2nd ed Prentice Hall 1988 ISBN 13 978 0131103627 e Padovani et al A amp A 543 A16 2012 1 7 Ideas for LIME 2 0 19 LIME Documentation Release 20 Chapter 1 LIME user manual Index Symbols V command line option f command line option h command line option
26. otten new populations the process is repeated When the solution has converged the code will ray trace the model to obtain an image Ray tracing is done for each user defined image in turn At the end of the ray tracing FITS files will be written to the disk at the code will clean up the memory and terminate 1 2 Command line options Note Starting with LIME 1 5 command line options can be used to change LIME default behavior without editing the source code LIME accepts several command line options V Display version information h Display help message f Use fast exponential computation When this option is set LIME uses a lookup table replacement for the exponential function which however due to cunning use of the properties of the function returns a value with full floating point precision indeed with better precision than that for much of the range Use of this option reduces the run time by 25 n Turn off ncurses messages This is useful when running LIME in a non interactive way p nthreads Run in parallel mode with nthreads The default a single thread i e serial execution Note The number of threads may also be set with the par gt nThreads parameter 1 2 Command line options 5 LIME Documentation Release 1 3 Setting up models 1 3 1 The model file All basic setup of a model is done in a single file which we refer to as model c although it may be given any name Model c is a
27. pulations There is no default value 1 3 Setting up models 7 LIME Documentation Release string par gt restart optional This is the file name of a binoutputfile that will be used to restart LIME If this parameter is set all other parameter statements except par gt antialias see below will be ignored and can safely be left out of the model file There is no default value string par gt gridfile optional This is the file name of the output file that contains the grid If this parameter is not set LIME will not output the grid The grid file is written out as a VTK file This is a formatted ascii file that can be read with a number of 3D visualizing tools Visualization Tool Kit Paraview and others There is no default value string par gt pregrid optional A file containing an ascii table with predefined grid point positions If this option is used LIME will not generate its own grid but rather use the grid defined in this file The file needs to contain all physical properties of the grid points 1 e density temperature abundance velocity etc There is no default value integer par gt lte_only optional If set LIME performs an LTE calculation Useful for quick checks The default lte_only 0 i e full non LTE calculation integer par gt blend optional If set LIME takes line blending into account however only if the
28. re are any overlapping lines among the transitions found in the moldatfile s LIME will print a message on screen if it finds overlapping lines Switching line blending on will slow the code down considerably in particular if there is more than one molecular data file The default is blend 0 no line blending integer par gt antialias optional If set LIME will anti alias the output image anti alias can take the value of any positive integer with the value 1 default being no anti aliasing Greater values correspond to stronger anti aliasing LIME uses stochastic super sampling anti aliasing This is very effective in minimizing artifacts in the image but 1t also slows down the ray tracer by a factor equal to the value of antialias This parameter is the only one that will not be ignored in case par gt restart is set integer par gt polarization optional If set LIME will calculate the polarized continuum emission This parameter only has an effect if LIME is set up to do a continuum calculation only The resulting image cube will have three channels containing the Stokes I Q and U In order for the polarization to work a magnetic field needs to be defined see below When polarization is switched on LIME is identical to the DustPol code Padovani et al 2012 integer par gt nThreads optional If set LIME will perform the most time consuming sections of its calculations in parallel usin
29. s the name suggests C source code which is compiled together with LIME at runtime and therefore it must conform to the ansi C standard Setting up a model however requires only little knowledge of the C programming language For an in depth introduction to C the user is referred to The C Programming Language 2nd ed by Kernighan and Ritchie and otherwise numerous tutorials and introductions can be found on the Internet The file lime_cs pdf contained in the LimePackage directory is a quick reference for setting up models for LIME Please not that all physical numbers in model c should be given in Sl units In most common cases everything about a model should be described within model c However model c can be set up as a wrapper that will call other files containing parts of the model or even call external codes or subroutines Examples of such usage are given below in the section Advanced setup model c should always begin with the following inclusion include lime h to make model c aware of the global LIME variable structures Other header files may be included in model c if needed with the possible need of modifying the Makefile accordingly Following the preprocessor commands the main model function should appear void input inputPars image This function should contain the parameter and image settings 1 3 2 Parameters A structure named par is defined in lime h This structure contains all
30. st of a table of values for instance as when using the output of another code as input for LIME the idea is look up the input grid point or cell which is closest to the LIME grid point in question or for cell based tables the cell in which the LIME point falls The way to deal with this is to make a column formatted ascii file with the input model x_1 y 1 z_l density_1 temperature_1 any_other_stuff_1 X2 ye 2 2 2 density_2 temperature_2 any_other_stuff_2 xn yn zon density_n temperature_n any_other_stuff_n The idea is to find the i th entry in that list where minimum x_i x 2 y_i y 2 z_i z 2 is true or in other words which entry in the list lies closest to a given LIME point x y z One way to solve this would be as follows example in pseudocode density x y z mindist very_large_number open model_input_file read while not end of file l read_one_line x_i y_i z_i density_i calculate distance from x y z to x_i y_i z_i dist if dist lt mindist then mindist dist bestdensity density_i close file return bestdensity and similarly for the temperature and other properties This is potentially a slow process opening and closing a file for every grid point To speed up the process it is useful to make the model columns available as arrays in model c 14 Chapter 1 LIME user manual LIME Documentation Release This can be done by formatting the c
31. subroutine contains the systematic velocity field of the gas The return type of this subroutine is a three component vector with components for the x y and z axis void velocity double x double y double z double xvelocity velocity 0 f x y z velocity 1 f x y z velocity 2 f x y z In the current version of LIME splines are calculated based on the information in the velocity field function and therefore this function is only called once Hence it need not be as optimized as in previous versions of LIME It is now feasible to use look up tables for the velocity field as well LIME will use a forth order polynomial to approximate the line of sight velocity field component In case the par pregrid option is set LIME will use linear interpolation between grid points 1 4 6 Magnetic field The magnetic field subroutine contains a description of the magnetic field The return type of this subroutine is a three component vector with components for the x y and z axis The magnetic field only has an effect for continuum polarization calulations that is if par gt polarization is set 12 Chapter 1 LIME user manual LIME Documentation Release void magfield double x double y double z double B B O f x y z B 1 f x y z B 2 f x y z 1 4 7 Gas to dust ratio Finally the gas to dust ratio is an optional function which the user can choose to include in the mod
32. tions 13 LIME Documentation Release is of a dimensionality greater than one An example of linear interpolation in a one dimensional table can be found in the example model c file below In the special case where the input model is described on unstructured grid nodes e g Smoothed Particle Hydro dynamics simulations the input grid can be used directly in LIME This requires the user to set the par gt pregrid parameter If the user is more comfortable writing code in the FORTRAN language it is possible to use the model subroutines as wrappers to call FORTRAN functions which then carries out any necessary calculations and return the values to model c This can be done the following way void density double x double y double z double density fortransub_ amp x amp y Z amp density 0 UBROUTINE fortransub x y z temp OUBLE x y z temp emp f x y Z ETUR D Hw orouomn In order for this to work the file containing the FORTRAN function needs to be compiled by a FORTRAN compiler and the resulting object file needs to be linked with LIME This only works if the linking is also done with the FORTRAN compiler so some modification to the Makefile is needed Notice that the underscore after the name of the FORTRAN subroutine in the C function call has to be present Please note that the example above is untested and may need modification in order to work If the input model file consi
33. ul numbers are between a few thousands up to about one hundred thousand integer par gt sinkPoints required 6 Chapter 1 LIME user manual LIME Documentation Release The sinkPoints are grid points that are distributed randomly at par gt radius forming the surface of the model As a photon from within the model reaches a sink point it is said to escape and is not traced any longer The number of sink points is a user defined quantity since the exact number may affect the resulting image as well as the running time of the code One should choose a number that gives a surface density large enough not to cause artifacts in the image and low enough not to slow down the gridding too much Since this is model dependent a global best value cannot be given but a useful range is between a few thousands and about ten thousand integer par gt sampling optional The sampling parameter takes value 0 1 or 2 sampling 0 is used for uniform sampling in Log radius which is useful for models with a central condensation i e envelopes disks whereas sampling 1 is uniform sampling in x y and z The latter is useful for models with no central condensation molecular clouds galaxies slab geometries The value sampling 2 was added because the routine for 0 was found not to generate grid points with exact spherical rotational symmetry The 2 setting implements this now properly sampling 0 has however bee
34. us star forming region using Kelvins as the unit include lime h void input inputPars x par par gt radius par gt minScale par gt pIntensity par gt sinkPoints par gt dust Jen par gt moldatfile 0 par gt outputfile par gt binoutputfile image img 2000xAU 0 5xAU 4000 3000 a_thin_e6 tab hcot xpol dat populations pop restart pop par gt gridfile grid vtk img 0 nchan 60 img 0 velres 500 img 0 trans 37 img 0 pxls 100 img 0 imgres 0 1 img 0 theta 0 0 img 0 distance 140xPC img 0 source_vel 0 img 0 unit 0 img 0 filenam image0 fits void density double x double y double z double xdensity double r r sqrt x xty y zx zZ density 0 1 5e6xp void temperature doubl int i k x0 0 double r double temp 2 10 2 0e13 5 0e13 44 777 31 037 X y r sqrt x xty y zx zZ if r gt temp 0 0 amp amp for 1 0 1 lt 9 1 if r gt temp 0 i if r lt temp 0 0 ow r 300 AU 1 5 1le6 double y double z double xtemperature 8 0e13 1 1e14 1 4e14 1 7e14 2 0e14 2 3e14 2 6e14 2 9e14 25 718 22 642 20 560 19 023 17 826 16 857 16 050 15 364 r lt temp 0 9 amp amp r lt temp 0 i 1 x0 i temperature 0 temp 1 0 16 Chapter 1 LIME user manual LIME Documentation Release else if r gt temp 0 9 temperature 0 temp
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