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Everything posted by robin_astro
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Calibrating a LowSpec3.0 Spectrum of Alpha UMa
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
It is more common to mount them in a circle to give even illumination independent of the orientation relative to the direction of the slit. A nice setup suggested by Christian Buil with his StarEx is to feed optical fibres to small clips round the edge. The obstruction is small and they can be left mounted without significantly disturbing the telescope throughput. They can even be switched on during the exposure to superimpose lines on the spectra giving very high precision calibration for example where flexure might be an issue during long exposures. https://groups.io/g/Solex-project/topic/88905429 (In French but the photos tell the story and Google etc translates well if you need more information) Cheers Robin -
Supernova discovered in M101 tonight
robin_astro replied to robin_astro's topic in Celestial Events Heads Up
There is a excellent piece on this supernova in the "Science in Action" radio programme on the BBC World Service. Astronomers , both amateur and professional tanking enthusiastically about the discovery and what they know about it so far. Some great Science and even a live observing session on the radio 🙂 https://www.bbc.co.uk/sounds/play/w3ct4sc9 They talk about the way the early spectroscopy shows the interaction of the explosion with the surrounding circumstellar material. Here is an animation of my measurements showing that early interaction during the first week Cheers Robin -
Calibrating a LowSpec3.0 Spectrum of Alpha UMa
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
Provided the actual width of the line is significantly narrower than the resolution then yes this works but Ha alpha can be wide particularly in some stars eg like in Vega so you really need a line which is known to be very narrow. Try measuring the width in some of the narrow metal lines in your spectrum and see if this gives a higher resolution or sky lines (natural or from light pollution) or from narrow lines in the calibration lamp provided it illuminates the spectrograph well (Note a single small lamp at the telescope aperture will not work for this as it like a very high focal ratio pinhole camera and gives a perfect in focus image even when you are out of focus! If doing this using neons arrange 3 or 4 of them round the aperture edge) Cheers Robin -
Calibrating a LowSpec3.0 Spectrum of Alpha UMa
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
If you are looking specifically around H alpha at high resolution a simple neon lamp will do the job. Point the telescope at a bright A or B star and look for H alpha which will be obvious as there will be no other strong lines near it. Then when you have it centred take a neon lamp as a refence and identify the lines from for example Christian Buil's website here http://www.astrosurf.com/buil/us/spe2/hresol4.htm Cheers Robin -
Supernova discovered in M101 tonight
robin_astro replied to robin_astro's topic in Celestial Events Heads Up
The supernova is clearly there in your first image. It was discovered on Friday ~17:00 UTC but there are pre discovery images found so far which show it back to Thursday evening (UTC) see https://www.wis-tns.org/astronotes/astronote/2023-125 Apologies if I have already asked you about this image on Cloudy Nights (I get confused with the different names) but what is the date and time on the first image ? (These images are potentially important scientifically to constrain the exact time of the explosion) Thanks Robin -
supernova in M101 any pre discovery images ?
robin_astro replied to robin_astro's topic in Imaging - Deep Sky
On TNS currently latest non detection 2023-05-18 10:17:15 (UTC) (ATLAS) earliest detection 2023-05-19 03:41:35 (UTC) (Stephen Limeburner) https://www.wis-tns.org/object/2023ixf The gap is closing ! Can anyone narrow the time of explosion down further ? Robin -
supernova in M101 any pre discovery images ?
robin_astro replied to robin_astro's topic in Imaging - Deep Sky
Looking at Nick James' image on the BAA forum I would say it is located in the blank space in the middle of that horseshoe of stars https://britastro.org/forums/topic/supernova-in-m101#post-617411 Cheers Robin -
Supernova discovered in M101 tonight
robin_astro replied to robin_astro's topic in Celestial Events Heads Up
Latest measurement 2023 May 20.4517UT by Robert Fidrich on VSNet-alert puts it already at mag 13. Being a type II, it probably wont get as bright as type 1a 2011fe in M101 did though which reached mag 10 Cheers Robin -
ZTF report a 10 hours pre-discovery detection at mag 15.9 (g) 2023-05-19 07:45:07 and a negative (fainter than 21.3) 2023-5-16 19:35:38.00 https://www.wis-tns.org/astronotes/astronote/2023-120 so any deep images taken between those dates could be of interest Here is a link to the discovery image Cheers Robin
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Koichi Itagaki has discovered a supernova in M101 tonight. https://www.wis-tns.org/object/2023ixf mag 14.9 at discovery, it has been confirmed and classified spectroscopically as SN 2023ixf, a type II (core collapse) supernova Robin
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The photons have this energy on average but individual photons will have a spread of energy values even for photons repeatedly emitted from a single isolated atom, dependent on the lifetime of the excited state such that ∆E∆t ≈ h/2π. This is seen observationally as a broadening of the spectral line. This is an example of the fundamental uncertainty inherent in our quantum world. Robin
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Fraunhoffer lines, which way round are these?
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
I am quite old school. My scope is linked to Cartes du Ciel. I use the finder (with a webcam strapped to the eyepiece) to find bright stars and then centre them in the spectrograph mirror slit guider (I don't have a guidescope on the telescope) and align on them. I then star hop to the target using fainter stars using CdC and the guider image, syncing as necessary as I go . For crowded fields I download and overlay a DSS image to CdC so I can match what I see in the spectrograph guider and identify the target. (I usually then take a shot of the guider image as a record that I took the right target) Very occasionally If I get completely lost I may resort to taking a deeper guider image and plate solving it but that is rare. Cheers Robin -
Fraunhoffer lines, which way round are these?
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
This was taken in colour with a Toucam pro webcam and 85 frames stitched to together. The first spectrum I took with my newly constructed LHIRES kit back in 2006. -
Fraunhoffer lines, which way round are these?
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
Here is a recent much better one by Olivier Masse https://oliviermasse.fr/solex/20230502_solex_spectre_complet_5000.png from this thread on the Solex forum https://groups.io/g/Solex-project/topic/colorisation_spectre_complet/98665300 -
Fraunhoffer lines, which way round are these?
robin_astro replied to SteveBz's topic in Radio Astronomy and Spectroscopy
Here is mine with a LHIRES (much reduced) Unfortunately I lost the full size version. http://www.threehillsobservatory.co.uk/astro/spectra_28.htm I suggest moving to the red until you see the very distinct Oxygen telluric band pattern (at the end of my spectrum) and then work back from there. H alpha is broad and strong, the Na D lines are distinct but some of the weaker lines round there are telluric water lines so dont always show clearly. The Mg triplet should also be clear. At the violet end you should see two broad strong Calcium H J lines before the sensitivity of the camera runs out Cheers Robin -
You can compute the theoretical energy but if you measure it you find a spread of values. This is seen for example in the natural broadening of spectral lines. The lines from transitions with a short lifetime are broader in agreement with HUP Cheers Robin
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Here are some examples just posted on the solex/starex forum of some spectra at both high and low resolution with a StarEx and an f5 Newtonian so quite demanding for the spectrograph optics. The results look good even down to below 3800A in the UV and up to 9500A in the IR https://groups.io/g/Solex-project/topic/un_session_au_newton_200f5/98516943 Robin
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If you are relatively new to spectroscopy and are looking for a home build I would go for the StarEx. The optical kit for it from Shelyak uses specially designed lenses which perform better in the blue than standard off the shelf achromats and it is a good match for the f8 RC8. The UVEX is more an advanced design for experienced observers, particularly if looking for the best performance in the UV but it is tricky to get working well. Cheers Robin
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That is a good and interesting question. This was one of his earliest spectrograph designs and in that case he just used standard SLR camera lenses which have many elements to correct for various aberrations, important for making good sharp images across the field at low focal ratios rather than specifically for spectroscopy. You can use simpler (smaller and lighter) achromats in spectrographs eg the StarEx, LowSpec, LHIRES all use achromats but they do have drawbacks such as not working well at low focal ratios and suffer from chromatic aberration, particularly noticeable as a shift of focus at the blue end of the spectrum. The ALPY also uses achromats and works well down to f4 but they are specially designed lenses that Christian designed to minimise chromatism in the particular application. There are commercial designs that use multi-element camera lenses like Shelyak's LISA and eShel (A good sharp image over a wide field is particularly important in echelle spectrograph designs) but even there chromatism at the blue end can be problem even with high quality camera lenses. Spectroscopy is a severe test for chromatism and most professional spectrographs use all reflective optics. Shelyak's UVEX is an example of this but they are difficult to design and align to be free of other aberrations. Cheers Robin
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Watched it here in Cumbria for about half an hour when the the skies cleared. Cloudy to the north now though. Lumix LF1 30sec
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Owl Nebula ..and a seriously deep-sky Quasar !!
robin_astro replied to Craney's topic in Imaging - Deep Sky
It is indeed remarkable what can be observed with modest equipment thanks to modern sensor technology. With the addition of a relatively simple spectrograph it is even possible to verify the redshift of these and even more distant objects. Here are some quasars at 4.3-4.5 redshift (over 12 billion years light travel time) https://britastro.org/observations/observation.php?id=20210411_134753_85f4b3ebf4faaefe Cheers Robin -
Help with spectral analysis of Sirius
robin_astro replied to GabrieleRiquena's topic in Radio Astronomy and Spectroscopy
There are many very high resolution spectra downloadable from the ESPaDOns spectrograph in the polarbase archive http://polarbase.irap.omp.eu/ eg but again the flux calibration is suspect as there are some differences in the continuum shape between spectra and problems with overlapping echelle orders so probably only the normalised spectra are reliable Robin