<p>Hi I am analysing slitless spectrograph of type A9 star Canopus. Here is as sample of the spectrograph.
<a href="https://i.sstatic.net/ZnkOFUmS.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ZnkOFUmS.png" alt="2D nd array of debayered spectrum" /></a></p>
<p>I basically did a simple summing up of the columns and added the data (as a simple spectrum co- adder)</p>
<p><a href="https://i.sstatic.net/Umu7yk8E.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/Umu7yk8E.png" alt="Spectrograph of Canopus with y-axis Intensity x-axis Wavelength in Angstroms" /></a></p>
<p>Now I understand the calibration requires the pixel position of the zeroth order(known)
and a well-known feature (in this case the Balmer series)
However, given the poor resolution. I am unable to make out which trough corresponds to which absorption line.</p>
<p>Any advice or expert opinion is highly appreciated.</p>
<p>Thanks!</p>
<p><strong>Edit</strong> I have attached the remaining spectrographs of Stars we observed(please ignore the graph legend (I dont wanna(long time) recompile my code to edit)</p>
<p><strong>Nusakan(Beta Coronae Borealis)</strong>
<a href="https://i.sstatic.net/E4ovNW1Z.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/E4ovNW1Z.png" alt="enter image description here" /></a></p>
<p><strong>Spica</strong>
<a href="https://i.sstatic.net/oJXFMCcA.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/oJXFMCcA.png" alt="enter image description here" /></a></p>
<p><strong>Antares</strong> (spelling!!)
<a href="https://i.sstatic.net/kt5qKxb8.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/kt5qKxb8.png" alt="enter image description here" /></a></p>
<p>This was done with the calibration coefficient obtained from Canopus.</p>
<p>I really appreciate the help from yall, and really apologise for the stupid mistakes (like spelling Axis labelling wrongly). But
<strong>Does the spectrographs look correct?</strong>
I only have one reference from Antares and it seems like the Telluric oxygen line matches the sample spectrograph at wavelength 7200++ Angstrom</p>

CC BY-SA 4.0
2024-04-14T09:57:01.330Z
Please label your axes.  I'd expect "green" to be around 500nm,  but it seems to be at about 1300 (somethings?) So I don't really know what we are looking at, nor what the extremely strong emission line at about "400" is supposed to represent, perhaps that's some sort of calibration, and not part of the spectrum, perhaps this isn't "light" and we're looking at something else altogether.
James K
CC BY-SA 4.0
2024-04-14T22:42:12.940Z
There are three ways to I can think of to get an approximate wavelength calibration for your x axis. 1) identify a spectral feature from your stellar spectrum (which seems difficult as you don't have anything clear here) 2) use a separate source with a much, much stronger spectral feature (like sodium or mercury lamp line or a known laser line) 3) estimate it by getting the distance in along the focal plane and the known dispersion of the grating.  You might be able to improve the resolution by taking more time to focus. For intensity calibration, use a blackbody source (old style light bulb)
uhoh
CC BY-SA 4.0
2024-04-14T22:43:28.637Z
I think those lumpy features might be due to the use of a color CCD camera with three separate color filters. A monochrome (black-and-white) camera will give you a less lumpy spectral response.
uhoh
CC BY-SA 4.0
2024-04-15T06:52:56.140Z
Now I don't understand. The top plot is in pixels, but the spectrum now appears to be wavelength calibrated. If it's wavelength calibrated, then the Balmer lines are of course at their usual wavelengths.
ProfRob
CC BY-SA 4.0
2024-04-15T06:54:38.187Z
Hi @JamesK I apologise, the prior spectrograph was in Pixels, I forgot to do the conversion. My Lecturer provided the conversion formula as $\lambda(x) = d \sin[ \arctan(\frac{x - x_0)}{S} )] $ where x_0 := the pixel position of the zeroth order and S is the calibration coefficient. I have basically obtained the Calibration coefficient by assuming that the most significant "trough"  is H_alpha . The calculation showed a linear relationship between pixels to wavelength.
likely_fail_2202 T_T
CC BY-SA 4.0
2024-04-15T06:58:57.967Z
Hi @uhoh really appreciate the feedback! Unfortunately I live in the City with alot of light pollution, as part of our project we travelled to the rural area to make the spectrographs, Unfortunately the guide also did not instruct us to use calibration lamps. It just told us to capture a prominent type A star and guess the absorption line. However Our calibration star Sirius data was messed up.. I only have Canopus (A9) , Spica, nusakan , and Antares. data.
likely_fail_2202 T_T
CC BY-SA 4.0
2024-04-15T07:03:25.813Z
@uhoh On the topic of CCD Cameras, we used the QHY5III462C Camera , with the SA-100 Star analyser, Celestron Nexstar 5SE. I did the conversion using the aforementioned conversion formula, and it returned a linear relationship. Even based on the Diffraction grating equation.
likely_fail_2202 T_T
CC BY-SA 4.0
2024-04-15T07:04:22.963Z
@ProfRob Thank you for the response, the conversion turned out to be linear so there was no adjustment of the spectrum just translation to the appropriate wavelengths
likely_fail_2202 T_T
CC BY-SA 4.0
2024-04-15T10:05:58.660Z
@likely_fail_2202T_T wow you put a lot of work into this, thanks for such a detailed reply!
uhoh
<spectroscopy>
How to identify Hydrogen lines of slitless spectrograph of Type A9 star
likely_fail_2202 T_T
# How to identify Hydrogen lines of slitless spectrograph of Type A9 star

(Asked by: username_0 on 2024-04-14)

Hi I am analysing slitless spectrograph of type A9 star Canopus. Here is as sample of the spectrograph.
[![2D nd array of debayered spectrum](https://i.sstatic.net/ZnkOFUmS.png)](https://i.sstatic.net/ZnkOFUmS.png)

I basically did a simple summing up of the columns and added the data (as a simple spectrum co- adder)

[![Spectrograph of Canopus with y-axis Intensity x-axis Wavelength in Angstroms](https://i.sstatic.net/Umu7yk8E.png)](https://i.sstatic.net/Umu7yk8E.png)

Now I understand the calibration requires the pixel position of the zeroth order(known)
and a well-known feature (in this case the Balmer series)
However, given the poor resolution. I am unable to make out which trough corresponds to which absorption line.

Any advice or expert opinion is highly appreciated.

Thanks!

**Edit** I have attached the remaining spectrographs of Stars we observed(please ignore the graph legend (I dont wanna(long time) recompile my code to edit)

**Nusakan(Beta Coronae Borealis)**
[![enter image description here](https://i.sstatic.net/E4ovNW1Z.png)](https://i.sstatic.net/E4ovNW1Z.png)

**Spica**
[![enter image description here](https://i.sstatic.net/oJXFMCcA.png)](https://i.sstatic.net/oJXFMCcA.png)

**Antares** (spelling!!)
[![enter image description here](https://i.sstatic.net/kt5qKxb8.png)](https://i.sstatic.net/kt5qKxb8.png)

This was done with the calibration coefficient obtained from Canopus.

I really appreciate the help from yall, and really apologise for the stupid mistakes (like spelling Axis labelling wrongly). But
**Does the spectrographs look correct?**
I only have one reference from Antares and it seems like the Telluric oxygen line matches the sample spectrograph at wavelength 7200++ Angstrom

**Tags:** spectroscopy
> **Comments:**
> **username_1**: Please label your axes.  I'd expect "green" to be around 500nm,  but it seems to be at about 1300 (somethings?) So I don't really know what we are looking at, nor what the extremely strong emission line at about "400" is supposed to represent, perhaps that's some sort of calibration, and not part of the spectrum, perhaps this isn't "light" and we're looking at something else altogether.  
> **username_2**: There are three ways to I can think of to get an approximate wavelength calibration for your x axis. 1) identify a spectral feature from your stellar spectrum (which seems difficult as you don't have anything clear here) 2) use a separate source with a much, much stronger spectral feature (like sodium or mercury lamp line or a known laser line) 3) estimate it by getting the distance in along the focal plane and the known dispersion of the grating.  You might be able to improve the resolution by taking more time to focus. For intensity calibration, use a blackbody source (old style light bulb)  
> **username_2**: I think those lumpy features might be due to the use of a color CCD camera with three separate color filters. A monochrome (black-and-white) camera will give you a less lumpy spectral response.  
> **username_3**: Now I don't understand. The top plot is in pixels, but the spectrum now appears to be wavelength calibrated. If it's wavelength calibrated, then the Balmer lines are of course at their usual wavelengths.  
> **username_0**: Hi @JamesK I apologise, the prior spectrograph was in Pixels, I forgot to do the conversion. My Lecturer provided the conversion formula as $\lambda(x) = d \sin[ \arctan(\frac{x - x_0)}{S} )] $ where x_0 := the pixel position of the zeroth order and S is the calibration coefficient. I have basically obtained the Calibration coefficient by assuming that the most significant "trough"  is H_alpha . The calculation showed a linear relationship between pixels to wavelength.  
> **username_0**: Hi @uhoh really appreciate the feedback! Unfortunately I live in the City with alot of light pollution, as part of our project we travelled to the rural area to make the spectrographs, Unfortunately the guide also did not instruct us to use calibration lamps. It just told us to capture a prominent type A star and guess the absorption line. However Our calibration star Sirius data was messed up.. I only have Canopus (A9) , Spica, nusakan , and Antares. data.  
> **username_0**: @uhoh On the topic of CCD Cameras, we used the QHY5III462C Camera , with the SA-100 Star analyser, Celestron Nexstar 5SE. I did the conversion using the aforementioned conversion formula, and it returned a linear relationship. Even based on the Diffraction grating equation.  
> **username_0**: @ProfRob Thank you for the response, the conversion turned out to be linear so there was no adjustment of the spectrum just translation to the appropriate wavelengths  
> **username_2**: @likely_fail_2202T_T wow you put a lot of work into this, thanks for such a detailed reply!  

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## 0 answers

