#include <LyaOptions.hpp>

Inheritance diagram for LyaOptions:

Public Types
enum class	LyaAccelerationScheme : int { None , Constant , Variable }

Public Member Functions
bool	includeHubbleFlow () const

LyaAccelerationScheme	lyaAccelerationScheme () const

double	lyaAccelerationStrength () const

Public Member Functions inherited from SimulationItem
template<class T >
T *	find (bool setup=true) const

template<class T >
T *	interface (int levels=-999999, bool setup=true) const

virtual string	itemName () const

void	setup ()

string	typeAndName () const

Public Member Functions inherited from Item
	Item (const Item &)=delete

virtual	~Item ()

void	addChild (Item *child)

const vector< Item * > &	children () const

virtual void	clearItemListProperty (const PropertyDef *property)

void	destroyChild (Item *child)

virtual bool	getBoolProperty (const PropertyDef *property) const

virtual vector< double >	getDoubleListProperty (const PropertyDef *property) const

virtual double	getDoubleProperty (const PropertyDef *property) const

virtual string	getEnumProperty (const PropertyDef *property) const

virtual int	getIntProperty (const PropertyDef *property) const

virtual vector< Item * >	getItemListProperty (const PropertyDef *property) const

virtual Item *	getItemProperty (const PropertyDef *property) const

virtual string	getStringProperty (const PropertyDef *property) const

int	getUtilityProperty (string name) const

virtual void	insertIntoItemListProperty (const PropertyDef property, int index, Item item)

Item &	operator= (const Item &)=delete

Item *	parent () const

virtual void	removeFromItemListProperty (const PropertyDef *property, int index)

virtual void	setBoolProperty (const PropertyDef *property, bool value)

virtual void	setDoubleListProperty (const PropertyDef *property, vector< double > value)

virtual void	setDoubleProperty (const PropertyDef *property, double value)

virtual void	setEnumProperty (const PropertyDef *property, string value)

virtual void	setIntProperty (const PropertyDef *property, int value)

virtual void	setItemProperty (const PropertyDef property, Item item)

virtual void	setStringProperty (const PropertyDef *property, string value)

void	setUtilityProperty (string name, int value)

virtual string	type () const

Protected Member Functions
	LyaOptions ()

Protected Member Functions inherited from SimulationItem
	SimulationItem ()

virtual bool	offersInterface (const std::type_info &interfaceTypeInfo) const

virtual void	setupSelfAfter ()

virtual void	setupSelfBefore ()

Protected Member Functions inherited from Item
	Item ()

Private Types
using	BaseType = SimulationItem

using	ItemType = LyaOptions

Private Attributes
bool	_includeHubbleFlow

LyaAccelerationScheme	_lyaAccelerationScheme

double	_lyaAccelerationStrength

Friends
class	ItemRegistry

Detailed Description

The LyaOptions class simply offers a number of configuration options related to the treatment of Lyman-alpha line transfer, if this is enabled in the simulation.

Member Enumeration Documentation

◆ LyaAccelerationScheme

enum class LyaOptions::LyaAccelerationScheme : int

strong

The enumeration type indicating the supported Lyman-alpha acceleration schemes.

In a high-optical-depth medium, the number of scatterings for photon packets near the Lyman-alpha line is so high, and the corresponding free path lengths so short, that the Monte Carlo photon cycle becomes prohibitively slow. The core-skipping acceleration mechanism, first introduced by Ahn et al. 2002 (ApJ, 567:922-930) and used by many authors since, forces the wavelength of some photon packets from the core of the Lyman-alpha line into the wings of the line. This dramatically reduces the scattering cross section, allowing the photon packet to escape. More specifically, all photon packets with a dimensionless frequency $x$ smaller than a given critical value $x_{c r i t}$ are treated this way.

SKIRT implements three variations of the core-skipping acceleration scheme:

None: no acceleration is performed, corresponding to $x_{c r i t} = 0$ . This can be useful for models with low optical depths, or to produce reference results for models with medium optical depths. For models with high optical depths, the run times will be prohibitively long.
Constant: acceleration with a constant critical value given by $x_{c r i t} = 3 s$ , where $s$ is the acceleration strength configured by the user. This option can be useful when the optical depth is fairly constant throughout the model, as is the case with many benchmark models.
Variable: acceleration with a variable critical value that depends on the local gas temperature and density. Specifically, the critical value is determined as
$x_{c r i t} = s {(\frac{n_{H}}{T})}^{1 / 6},$
where $s$ is the acceleration strength configured by the user and $n_{H}$ is the neutral hydrogen number density (in $m^{- 3}$ ) and $T$ the gas temperature (in K) in the spatial cell hosting the scattering event. The rationale behind this formula is discussed below. This variable mechanism is applicable for most models, and is preferred for models with a broad dynamic range in optical depths.

For both the constant and variable schemes, the user can configure the acceleration strength $s$ , with a default value of unity. Larger values will decrease run time and accuracy; smaller values will increase run time and accuracy.

Rationale for the variable scheme

The approximate analytical solutions for the Lyman-alpha spectrum emerging from a static slab or sphere (Neufeld 1990, Dijkstra et al. 2006) depend on the product $a τ_{0}$ , where $a$ is the Voigt parameter and $τ_{0}$ is the optical depth at the Lyman-alpha line center. Inspired by this result, many authors proposed acceleration schemes where $x_{c r i t}$ is determined as a function of this product. For example, Smith et al. 2015 (MNRAS, 449, 4336-4362) used a critical value proportional to $(a τ_{0})^{1 / 3}$ .

However, calculating the optical depth requires selecting a path length. This has forced these schemes to depend on either a local scale (such as the size of the current spatial cell) or a global scale (such as the domain size). Both options seem undesirable, as they lead to a dependency on non-physical parameters (the resolution of the discretization or the portion of the physical world included in the model). Interestingly, Smith et al. 2015 (MNRAS, 449, 4336-4362) noted that one could use the Jeans length as a physically motivated length scale. Expressing the Jeans length as well as the other quantities in $(a τ_{0})^{1 / 3}$ as a function of the local gas properties leads to $x_{c r i t} \propto (n_{H} / T)^{1 / 6}$ . With the gas properties expressed in SI units, experiments with benchmark models show that a proportionality factor of order unity is appropriate.

None : "no acceleration" .

Constant : "acceleration scheme with a constant critical value" .

Variable : "acceleration scheme depending on local gas temperature and density" .

Constructor & Destructor Documentation

◆ LyaOptions()

LyaOptions::LyaOptions ( )

inlineprotected

Default constructor for concrete Item subclass LyaOptions : "a set of options related to Lyman-alpha line transfer" .

Member Function Documentation

◆ includeHubbleFlow()

LyaOptions::includeHubbleFlow ( ) const

inline

This function returns the value of the discoverable Boolean property includeHubbleFlow : "include the Doppler shift caused by the expansion of the universe" .

The default value for this property is given by the conditional value expression "false" .

This property is displayed only if the Boolean expression "Level2" evaluates to true after replacing the names by true or false depending on their presence.

◆ lyaAccelerationScheme()

LyaOptions::lyaAccelerationScheme ( ) const

inline

This function returns the value of the discoverable LyaAccelerationScheme enumeration property lyaAccelerationScheme : "the Lyman-alpha line transfer acceleration scheme" .

The default value for this property is given by the conditional value expression "Variable" .

This property is displayed only if the Boolean expression "Level2" evaluates to true after replacing the names by true or false depending on their presence.

◆ lyaAccelerationStrength()

LyaOptions::lyaAccelerationStrength ( ) const

inline

This function returns the value of the discoverable double property lyaAccelerationStrength : "the acceleration strength; higher is faster but less accurate" .

The minimum value for this property is "]0" .

The maximum value for this property is "10]" .

The default value for this property is given by the conditional value expression "1" .

This property is relevant only if the Boolean expression "lyaAccelerationSchemeConstant|lyaAccelerationSchemeVariable" evaluates to true after replacing the names by true or false depending on their presence.

This property is displayed only if the Boolean expression "Level2" evaluates to true after replacing the names by true or false depending on their presence.

The documentation for this class was generated from the following file:

LyaOptions.hpp

Public Types

Public Member Functions

Protected Member Functions

Private Types

Private Attributes

Friends

Detailed Description

Member Enumeration Documentation

◆ LyaAccelerationScheme

Constructor & Destructor Documentation

◆ LyaOptions()

Member Function Documentation

◆ includeHubbleFlow()

◆ lyaAccelerationScheme()

◆ lyaAccelerationStrength()