<p>When you place a spectrograph slit on a source, the spectrum recorded can be thought of as lots of images of the slit at different wavelengths.</p>

<p>Ordinarily, you would sum up this spectrum along the direction of the slit images to give you a one dimensional spectrum. If however, you leave the image as recorded, then you have a two dimensional spectrum - intensity as a function of wavelength along one axis and as a function of position along the slit in the other.</p>

<p>Two dimensional spectra are used when we expect the spectrum to vary with position along the slit. Examples might include a spectrum recorded across a galaxy, or a spectrum of a binary star with the slit placed across both components.</p>

<p>An example is shown below. The inset image shows a broad-band image of V458 Vul - a classical nova that is surrounded by (not visible) shells of ionised material. The authors of this <a href="http://www.vgoranskij.net/v458/v458atel2.htm" rel="nofollow noreferrer">particular study</a> lined up a spectrograph slit as shown in the inset and then obtained the two two-dimensional spectra shown in the main image. What you have to imagine is that each position on the slit produces a horizontal spectrum at a vertical position that corresponds to its position on the slit. Therefore we see a bright spectrum across the middle corresponding to the central source, but there are then "knots" of emission at particular wavelengths that are some distance away from the central star.</p>

<p><a href="https://i.sstatic.net/BZTkR.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/BZTkR.jpg" alt="A two dimensional spectrum"></a></p>

<p>Slitless two dimensional spectroscopy is also possible using integral field spectrographs. Fibers record spectra over a two dimensional area. This can also be referred to as two dimensional spectroscopy.</p>

CC BY-SA 3.0
2016-12-05T08:02:36.253Z
It would be nice if you put some graphs to explain more clearly. Thanks a lot.
A.Bbom
CC BY-SA 3.0
2016-12-07T13:40:15.240Z
I understand now, thank you for spending your precious time on my simple question. Thanks again.
A.Bbom
CC BY-SA 3.0
2016-12-05T07:30:22.183Z
2016-12-05T16:40:13.033Z
2016-12-05T16:40:13.033Z
ProfRob
<p>mostly, we use the one-dimensional spectrum. But sometimes we use two-dimensional spectrum, what's the differences between them?</p>

CC BY-SA 3.0
2016-12-06T07:11:51.783Z
check out the one at Keck that I use, the documentation might prove more helpful than any else. https://www2.keck.hawaii.edu/inst/hires/
LaserYeti
CC BY-SA 3.0
2016-12-07T15:16:14.840Z
No problem `thumbsup`
LaserYeti
<spectroscopy><spectra>
What's the differences between one-dimensional spectrum and two-dimensional spectrum?
A.Bbom
# What's the differences between one-dimensional spectrum and two-dimensional spectrum?

(Asked by: username_0 on 2016-12-05)

mostly, we use the one-dimensional spectrum. But sometimes we use two-dimensional spectrum, what's the differences between them?

**Tags:** spectroscopy, spectra
> **Comments:**
> **username_1**: check out the one at Keck that I use, the documentation might prove more helpful than any else. https://www2.keck.hawaii.edu/inst/hires/  
> **username_1**: No problem `thumbsup`  

---

## 1 answers

### Answer by username_2 on 2016-12-05. Score: 4 | Accepted answer

When you place a spectrograph slit on a source, the spectrum recorded can be thought of as lots of images of the slit at different wavelengths.

Ordinarily, you would sum up this spectrum along the direction of the slit images to give you a one dimensional spectrum. If however, you leave the image as recorded, then you have a two dimensional spectrum - intensity as a function of wavelength along one axis and as a function of position along the slit in the other.

Two dimensional spectra are used when we expect the spectrum to vary with position along the slit. Examples might include a spectrum recorded across a galaxy, or a spectrum of a binary star with the slit placed across both components.

An example is shown below. The inset image shows a broad-band image of V458 Vul - a classical nova that is surrounded by (not visible) shells of ionised material. The authors of this [particular study](http://www.vgoranskij.net/v458/v458atel2.htm) lined up a spectrograph slit as shown in the inset and then obtained the two two-dimensional spectra shown in the main image. What you have to imagine is that each position on the slit produces a horizontal spectrum at a vertical position that corresponds to its position on the slit. Therefore we see a bright spectrum across the middle corresponding to the central source, but there are then "knots" of emission at particular wavelengths that are some distance away from the central star.

[![A two dimensional spectrum](https://i.sstatic.net/BZTkR.jpg)](https://i.sstatic.net/BZTkR.jpg)

Slitless two dimensional spectroscopy is also possible using integral field spectrographs. Fibers record spectra over a two dimensional area. This can also be referred to as two dimensional spectroscopy.

> **Comments:**
> **username_0**: It would be nice if you put some graphs to explain more clearly. Thanks a lot.  
> **username_0**: I understand now, thank you for spending your precious time on my simple question. Thanks again.  

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