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Hello,

Just wanted to show an other simple method in order to calibrate low resolution spectra with the Neon lmap available with LISA and LHIRES3.

- First of all, take a short (typically 0.3 s) exposure spectrum of the lamp in order to get red Neon lines;
- Take a long exposure (typically 15 s, be aware with remanance!) to get blue lines;
- Merged 2d spectrum with the background unified (red edge of long exposure was set to 0, see Juanary SpcAudace release):


You get the best of the two worlds!

Then, the lines profiles with identified main lines is made for you:


(Figure updated on 2012/01/29)

I recommand you to select widespreaded lines in order not to favour the red edge or blue edge.

- The following lines seem working fine for a deg 3 polynom:
4065.65, 4348.06, 5400.56, 5852.49, 6402.25, 7032.41 and 7245.17
Which lead to a rms of 0.6 A where the dispersion is here 2.57 A/pixel, so an accuracy of 1/5 pixel.
- With a deg 4 polynome and the following lines:
4065.65, 4348.06, 4710.06, 5400.56, 5852.49, 6402.25, 7032.41, 7245.17, 6143.06, 6678.28 and 6929.47,
the following dispersion law was found: Lambda=3917.50781533+2.43491203042*(x-1)+0.000230671871345*(x-1)^2+-1.61973682859e-07*(x-1)^3+4.63971559225e-11*(x-1)^4 with RMS=0.293443870835,
So a linear law described by: 3917.50781533+2.56720166243*(x-1).

Enjoy,

Benji

Hi Benji,

Thanks a lot for that simple way for getting the blue side.

Will try it next time I am in the Observatory

Nice work Benjamin. I hope repeated long neon exposures are not harmful for the acquisition camera... Also I am afraid we still lack calibration wavelengths between 4348 and 5341Angstroems. This may hamper the accuracy of a high degree (>3) calibration polynomial.
Patrick Lailly

Patrick,

You're right, with a deg 4 polynom, you may also ty using 4710 blended Neon line.
I improved calibration by finding that blue lines were blended.
Note the updated calibrated lines profile.

Benji

Benji wrote:Hello,

- With a deg 4 polynome and the following lines:
4065.65, 4348.06, 4710.06, 5400.56, 5852.49, 6402.25, 7032.41, 7245.17, 6143.06, 6678.28 and 6929.47,

Benji

I tried to calibrate my low resolution spectra using these lines but the result shows an inaccuracy of about 5 Angstroems in the blue. Did someone check that the neon lamp that equips the Lisa shows the mentioned wavelengths?
Patrick Lailly

After carrying out a detailed analysis of the lines shown by the neon calibration lamp between 3900 and 4300 A, I made extensive experiments to reduce the inaccuracy mentioned above and I conclude that the attractive approach suggested by Benji seems hopeless. We cannot avoid using the Balmer lines of a reference star for an accurate calibration.
Patrick Lailly

Hi,

Finally I was able to test the calibration proposed by Benji.

I made 10 Neon images with 5 seconds and 10 images with 300s and then stitched them together. Then I analized it and the result is quite good from my point of view as I compared with an equation I use made on Vega.

If I have the opportunity I will test the calibration method on various stars.

Below you can see both results.

Integrated Neon calibration lamp in my LISA spectrograph with 35µm slit.
Vega calibration

Hi Rainer,

The resolution of your spectrum looks very good.
Which slit did you use ?
Could you send us the .dat file ?

All the best

François Teyssier

Hi Francois,

Which spectrum do you refer to ? Combined Neon ? If yes please download from this link

http://astroforo.net/astro/rspec/LISA/N ... s02762.dat

and here the combined Neon image *.fit file

http://astroforo.net/astro/rspec/LISA/N ... s-0300.tif

I used the 35µm slit.

regards Rainer

Hi Rainer,

I think there's a problem.
Your lines don't match with the theorical ArI lines given by VSpec.

I took a 120 sec spectrum of the neon lamp. Divided by its "continuum". Wavelenght calibrated (ISIS)

Your spectrum : black
Mine : blue
ArI : orange
NeI : cyan
Neon lines near 5400 match correctly

I'am taking another spectrum, 600 secondes exposure in order to get the weak lines.
I'll keep you informed

All the best

François