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You should see Filey where we were on holiday for a few days last week. They have fitted all the lamps and strings of lights along the prom seen here
http://www.geograph.org.uk/photo/833144
with the bluest LED light bulbs I have ever seen. (Hundreds of them. They looked almost purple, like mercury discharge lamps. A shame as just off the front they have a few warm white LEDs ) We stayed in a hotel on the front and the rooms were lit with this eerie light and the seagulls seemed to be awake all night.
Robin
Is there an established method of determining the rated effective temperature of these LED lights? (They are a long way from being black bodies or even the spectral energy distribution of the sun)
Robin
Hi Tony,
The CAOS group site is a good source for design ideas
https://spectroscopy.wordpress.com/fibres/
but the tough bit is sourcing/making a mirror with the end of the (typically 50um) fibre embedded in it. I think most amateur built fibre fed spectrographs have ended up using the Shelyak guide head
https://www.shelyak.com/produit/pf0008-f-6-50%C2%B5m-injection-unit/?lang=en
Cheers
Robin
I see the author of AIP4WIN is jointly presenting a poster paper at the BAA/AAVSO meeting this weekend. Not sure if he is attending in person though
Robin
I see the VSS are already investigating possibilities, There are two papers on potential pro-amateur cooperation concerning exoplanets in the variable star meeting on the Sunday
11.00 – 11.50 Dr Guillem Anglada Escude (Queen Mary, University of London) Red Dots Initiative: science and opportunities in finding planets around the nearest red-dwarfs
11.50 – 12.10 Lukasz Wyrzykowski (University of Warsaw) How to find planets and black holes with microlensing events
Hello Jack
What limitations are you trying to overcome compared with the Lodestar ? If you are looking to guide on the faintest stars, the 314 will probably go a bit fainter with a few seconds exposure. (I tried a Lodestar with my ALPY 200 but returned it as my old cooled 16ic-s would guide on fainter stars) On bright stars though you might have to use the cropped frame feature to get a decent update speed. Also what main camera are you using ? I dont think for example you can fit two 314 sized cameras side by side on the LHIRES. Anyway since you have both why not try them and let us know which works best?
Cheers
Robin
Peter Somogyi has published a spectrum taken with an ALPY. It confirms reports of an almost featureless blue spectrum but does not shed any more light on this puzzling object
Reports are it is now showing spectral features of a 1c-BL supernova. There is an HCT spectrum (rectified to remove the blue continuum) linked from David Bishop’s page
http://www.rochesterastronomy.org/sn2018/sn2018cow.html
but the features are not as obvious yet compared with this one for example I called as a 1c-BL last year
https://wis-tns.weizmann.ac.il/object/2017ixv
Robin
Yes the ATK 414 is one of the best for low dispersion ripples but sadly one of the worst for high dispersion ripples seen with the LHIRES at the highest resolution (unlike its predecessor the 314 which is good at both low and high dispersion.) Unfortunately none of this is known until one tries to use them for spectroscopy. The low dispersion ripples are all but eliminated by using a flat but the high dispersion ripples can be really tough to remove.
Cheers
Robin
I have been keeping an eye on development with this one too. The reported spectra is blue and featureless which would be consistent with it being a CV. I think the speculation about it possibly being an SN comes from the fact that it is coincident in position with the galaxy and is within the brightness range expected for an SN at this distance (though the latest measurement at mag 13.8 would put it towards the top end for an SN at this distance I think.) The problem at the moment is, because the spectrum is currently featureless and there are confusing spectral features from the galaxy there is no definitive redshift measurement yet which would conclusively prove if it is a foreground object.
Robin
Hi John,
The ripples come from the camera sensor. See my comment here
https://britastro.org/comment/4916#comment-4916
When you take a flat with a slit spectrograph, you are effectively taking a spectrum of the flat lamp. The ripples are from the wavelength response of the camera. These are also imprinted on the star spectrum of course so when you divide the star spectrum image by the flat they cancel out along with any other flat defects.
The ripples are caused by interference in the light, between different layers in the sensor (an etalon effect) and their spacing and severity varies from sensor to sensor. (Similar but much finer fringes are seen in high resolution spectra where they are caused by interference due to internal reflections in the sensor cover glass)
Cheers
Robin
The attached paper describes the mechanism which produces these ripples in CCD sensors (page7-11) The same effect is also seen in CMOS sensors.
Robin
Hi Jack,
The two Na D lines are from the two different spin levels. (3s to 3p1/2 and 3p3/2 in absorption) There probably is Zeeman splitting of the lines as well but this will be very small in the solar magnetic field.
Cheers
Robin
As Andy says, BeSS standard practise is to leave the telluric lines in when submitting to the database. When analysing spectra though you will want to remove them and it is quite possible for amateurs to do this.
For high resolution spectra where the individual lines are visible it is quite straightforward using a standard template for O2 and H2O lines which is scaled to fit the magnitude of the lines. Some software eg ISIS Visual spec have this function built in.
For low resolution spectra it is more difficult as the lines blend into broad bands. The same technique can be used though by producing your own low resolution template. This is done by taking spectra of a hot star at two different air masses. If you divide one by the other, the result is the extra atmospheric absorption due to the additional atmosphere. This can then be used as a template to remove the telluric bands. You can see a simple example of using a low resolution template in this poster paper
(This technique of measuring stars at different air masses is used by professionals (and sometimes by amateurs) to correct for all atmospheric effects including extinction rather than trying to match the air mass of reference star as is commonly used by amateurs. Correction for extinction (rather than just the telluric bands) using this technique though needs photometric skies so the atmospheric conditions do not change between the two measurements at different air masses.
Cheers
Robin
Note though that the instrument response for a slit spectrograph is only smooth provided a flat has been used otherwise it will have ripples from the camera response.(A good reason for always using a flat). Even then I find that my ALPY instrument response has a kink in it which I believe is quite common. (a combination of the flat lamp and atmospheric extinction curves) You can see it in my MILES star report here for example.
https://britastro.org/sites/default/files/attachments/ALPY600_MILES_tests_20161105.pdf
from this thread
https://britastro.org/node/8153
The acid test to see if your instrument response is correct is to rerun the reduction on the reference star using the instrument response. The result (except for any resolution differences) should perfectly match the reference spectrum (other than the telluric bands)
Cheers
Robin
To mark the occasion I though I would take a spectrum. It looks similar to others found in the literature from the 1980-90s
https://britastro.org/node/14188
Robin
So sad news. It was seeing what Maurice was doing in spectroscopy over 20 years ago that got me and many others into the field. The supernova spectroscopy work I am doing is a direct result of his measurements then and the prophecy he made when president that one day amateurs would be able to confirm and classify supernovae spectroscopically, which he lived to see fulfilled. He was an important champion of spectroscopy, encouraging me and others personally and helping to build the popularity it has today. He will be sadly missed by that community internationally.
Robin
I dug out my before and after grism alignment images (spectrum of the sky). The spectrum is horizontal as seen by the lines generated by dust specks on the slit.
Hi Nick,
My ALPY (one from the first production batch) somehow came with the grism significantly skewed so I fixed it with Francois Cochard’s guidance. (Also I have a habit of taking everything apart to “see how it works” ! ) If it is only slightly skewed then I would not worry about it. The main reason for correcting the slant/smile is so that any lines in the sky background subtract correctly. In ISIS you select a strong lamp or sky line and it automatically measures the slant and curvature and corrects for it. I expect Demetra does something similar.
Spectroscopically I “grew up” with ISIS so I know most of its quirks well and knowing Christian Buil, I had confidence that it would give good reliable results. I was down as a beta tester of Demetra but to be honest there was no pressure for me to change over, particularly as (at least at the time. I have not kept up with its development) it was not as comprehensive and flexible as ISIS so I never really got into it. Similarly with BASS which I have never used.
Robin
