# Equivalent width

## How do you find the equivalent width?

To compare strengths of absorption lines, equivalent widths are used. The equivalent width of an absorption line is a measure of the area of the absorption line. The width of a rectangle with a height equal to that of the continuum that has the same area of the absorption line is the equivalent width.

## Can equivalent width be negative?

The equivalent width is the width of the spectral continuum that has the same area as the line. Values are negative for emission lines, positive for absorption lines.

## How do you measure the width of a spectral line?

It is found by forming a rectangle with a height equal to that of continuum emission, and finding the width such that the area of the rectangle is equal to the area in the spectral line. It is a measure of the strength of spectral features that is primarily used in astronomy.

## What is equivalent width in astronomy?

Equivalent Width (W) is defined as the section of a surface counted between the level of the continuum, normalized to unity, and reference zero, having a surface identical to the profile of line (see figure below).

## How is line width related to pressure?

According to eqn [9], the linewidth is proportional principally to the air density, and therefore to the pressure, hence the term ‘pressure broadening.

## What is natural line width?

The line width ΔνL is also called natural line width and is connected with the decay time τ which is also known as natural life time. Typical values of ΔνL for single and undisturbed molecules that perform transitions within the visible range of the electromagnetic spectrum are between one and 10 Megahertz. Fig.

## How does natural line width?

The natural linewidth arises because excited states have a finite lifetime. Collisions randomize the phase of the emitted radiation. If frequent enough they (effectively) shorten the lifetime further.

## Can width be negative CSS?

According to the CSS 2.1 specifications, negative values for width are illegal, so you may be on thin ice with this.

## Can CSS height be negative width?

Negative values are not allowed. It specifies the height of an element using the length units such as px, cm, pt, etc. Negative values are not allowed.

## Can there be a negative length?

No such thing negative lengths, maybe squares can described by negative coordinates but alas they still have positive side length.

## User Guide

This width converter and conversion scale can be used to convert any measurement of width from one unit of width to another.

## Conversion Factors

The following units and associated conversion factors in metres (SI units for width) are used by this width converter:

## equivalent width

A measure of the strength of a spectral line. The line profile of an absorption line, for example, shows a dip below the continuum level, and the equivalent width is calculated as the area of the dip divided by the height of the continuum.

## equivalent width

A measure of the total absorption of radiant energy as indicated by an absorption line or absorption band.

## What is equivalent width?

Equivalent Width (W) is defined as the section of a surface counted between the level of the continuum, normalized to unity, and reference zero, having a surface identical to the profile of line (see figure below). The equivalent width is thus measured in wavelength unit (in angstroms for example). Sometimes the normalized equivalent width W l is used, which is the equivalent width W divided by the wavelength of the line, which is useful to compare the shape of lines located at different wavelengths.

## What is the width of the circumstellar emission curve?

The measured equivalent width is here of 0.49 angstroms.

## What is FWHM in math?

Full Width at Half Maximum ( FWHM) is the width measured at half level between the continuum and the peak of the line . The FWHM is expressed either in wavelength unit or in speed unit when the objective is to measure expansion or disk speeds (if FWHM is in unit of wavelength, the width in km/sec is given by c . FWHM /l, with c is the speed of the light = 3.10 5 km/s). Example, suppose that the FWHM is of 2A at 6563A, the equivalent resolved velocity is about 90 km/s.

## Can you subtract a photospheric profile before equivalent width?

For the situation of a weak emission feature into an absorption photospheric line it is useful to subtract this photospheric profile before equivalent width calculation. We use the following empirical formulae for fitting the photospheric profile P ( l) (see J. Chauville & all, A&A, 378, 861-882, 2001):