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Hi Peter,
I think you are using a slitless Star Analyser, in which case I wonder if small tracking errors could be the cause. If the star moves or gradually drifts, then so would the spectrum and that would blur the final stacked spectrum. It does appear that the star at the zero order position just below 50 pixels in your first plot is located at a slightly different position between the stack and the single image.
Another check you can do is to compare the first and last image in the stack, or a selection of images in the stack.
I think there are several ways to align individual spectrum images before combining them in a final spectrum, either pre or post extracting the spectrum from the image, though I’ve never done this myself. That could potentially be used to fix tracking errors after the event. Though in general the better the tracking the better the results.
Cheers,
Andy
That is a major accomplishment Andrew! To both build an echelle spectrograph as well as create the processing pipeline. I look forward to seeing your future results with this impressive instrument.
Andy
Looks fantastic Tony! Ready in time for the long Winter nights. All we need now is plenty of clear skies.
Cheers,
Andy
It is worth noting that all the spectroscopy software packages I have used do sky background subtraction. It is one of the standard processing steps when you usually select regions above and below the spectrum.
Hi Peter,
Nice you are starting to get results. You can pick out the strong hydrogen absorption lines of this A-type star, from right to left H-alpha, H-beta and H-gamma are clearly visible with a hint of H-delta at about 4100 Angstroms. You also have an atmospheric telluric band just short of 6900 Angstroms.
Best wishes,
Andy
Hi Alun,
That is a nice set of results showing different H-alpha profiles.
While Vega has a very simple spectrum, I do like it as it is such a great illustration of the luminosity class, which in the case of Vega is a V for dwarf. As the star has a smaller radius, so the surface pressure is higher, leading to pressure broadening of the spectral lines.
Once you get used to doing darks and flats then you will find them a doddle. Particularly with the Lhires III inbuilt flat lamp.
Cheers,
Andy
Hi Peter,
The neon bulb would have to be placed in front of the slit.
Typically you either have the neon lamp inside the spectrograph in front of the slit, or outside of the telescope so the light goes through the telescope optics and then the spectrograph. The advantage of having it shine down the telescope is you do not have to worry about the lamp position too much. If it is inside the spectrograph, then as I understand it the neon lamp must be carefully positioned so that the light follows the same path as the light coming from the telescope. Otherwise a shift in position of the lamp would cause an apparent but unreal shift in wavelength.
Though there were no light leaks, was the room completely dark or was there an opportunity for other light to pass into the spectrograph optics? Alternatively someone may have a spectrum of a similar lamp, in which case they may know if it also has a broad spectrum component.
Best wishes,
Andy
Hi Peter,
Interesting project.
At a guess I would say that you have a light leak as a neon bulb should only generate discrete emission lines, no continuum. It is possible that there is a problem with the neon bulb, but I think a light leak is more likely.
You could try taking 2 exposures of the same length, one with the neon bulb turned on, and the other with it turned off.
The other effects that can cause an offset are dark current and bias offset, but they should be roughly uniform, not showing the hump you seen in your spectrum.
Cheers,
Andy
Hi Jack,
You can measure the resolution using BASS, as per section 9a of the BASS tutorial I wrote (I think you have already done this):
You can also create a .png, .jpg or .bmp of your spectrum graph at any time by selecting:
Chart -> Save Chart to file
These will be small compared to the original fits file.
Best wishes,
Andy
There are a couple of other factors which will change how the chart looks.
First it will depend on which filter, filters or unfiltered were used when acquiring the image. I suspect the AAVSO chart is showing magnitudes for a V filter, so you would expect similar results when using a V filter on your camera. However, unfiltered or RGB would cause the stars to appear at different relative brightness. For example very red stars will typically appear much brighter in an unfiltered image.
The other factor is variable stars. You will occasionally come across other stars in your field which vary in magnitude by a sufficient degree to look different. Indeed great care has to be taken when producing charts for variable star measurement, to ensure that non of the comparison stars are themselves variable.
Nice image by the way 🙂
Best wishes,
Andy
Congratulations on the new magazine Ernst. Great to have another spectroscopy publication!
Eric, you can try translating it with Google Translate. Type ‘Translate’ into Google. Follow the link and upload the document. Then select German to English. You’ll find you need to switch back and forth between the Google translation and the pdf as the table and figures are missing from the translation.
Best wishes,
Andy
Hi Matt,
First of all welcome to the BAA 🙂
Robin has already given you some excellent advice on spectral typing so I won’t bother adding any more.
I own an Lhires III and I find it an excellent spectrograph. It took me several months of practice to get to know it well and tweak its performance, but I was able to get good spectra of bright stars very quickly. While a star analyser is great to start off with, as well as always being a good tool for fainter targets, there are some things that will be easier with the Lhires III. For example wavelength calibration, flat fielding and simply having a slit removes the potential problem of nearby stars contaminating a slitless spectrum. Though of course you do need a good mount to be able to position the star onto the slit and to hold it there accurately.
Best wishes,
Andy
I am completely with you there Gary! 🙂
I think it is an interesting enigma but the evidence does not support any kind of intelligence. It could be an opportunity to help solve the puzzle using science, putting a stop to the unfounded speculation which has dominated some of the press.
Cheers,
Andy
Hi Paul,
That is a very useful webpage, thanks for sharing.
Though I usually do spectroscopy, this is not the right kind of target for my setup. So I’m hoping to take a look at it though my Dobsonian instead.
Cheers,
Andy
Hi Ernst,
An interesting paper and a good demonstration of what can be achieved with the high resolution spectrographs that are now available to the amateur community.
Best wishes,
Andy
Hi Michael,
That is a very thorough analysis! Hopefully Bill or someone with knowledge of meteor spectroscopy will comment on your spectrum. It certainly looks good but I cannot comment on the line identification.
Cheers,
Andy
