robin_astro

Yes the spectra of most "normal" stars look pretty boring with the Star Analyser but the more unusual stars make the best targets for the Star Analyser and are the most interesting astrophysically. Those with strong features, particularly emission lines . This one of a recurrent nova for example https://www.cloudynights.com/topic/674213-recurrent-nova-v3890-sgr-erupts-again/?p=9624439 or planetary nebulae, Wolf Rayet stars and Luminous blue variables like P Cygni, recorded here with a Star Analyser with a very small 55 mm aperture https://www.cloudynights.com/topic/677560-grab-and-go-spectroscopy/ Robin

Hi Louise, Here is a quick result using Visual Spec from your jpg image. It is quite a bit less noisy so I suspect the noise in your spectrum may well be an artifact caused by rotating the spectrum in software which the jpg has smoothed out. Cheers Robin

Hi Louise Nice result. Rather noisy though, particularly for a 60x2 sec stack on such a bright target. The noise looks like it may be pixel artifacts which are sometimes seen with short focal length systems where the star size is very small. (a pixel to pixel sawtooth) Did you have to rotate the spectrum to get it horizontal? Rotation can introduce this sort of effect so taking care to get the spectrum horizontal helps The difference between A0v and A2v is very small but if you want to be spot on you could average the two Pickles references to produce an A1v (Not worth it though!). Vega is usually considered to be A0v but precise spectral classification is an inexact science. You can see the various classifications in the literature for many stars in Brian Skiff's huge catalogue here. http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk The position of the maximum in the raw profile depends on the spectral response of grating plus the particular camera so is not consistent between different setups even for the same star. Cheers Robin

Focus on the zero order star first then tweak the focus a bit to best see the spectrum features. As an alternative to main sequence A stars (Like Delta Cas for example) stars with a bright H alpha emission line can be easier to focus on, like Gamma Cas or P Cygni. Look for a bright dot in the spectrum towards the red end. As here for Gamma Cas for example http://www.threehillsobservatory.co.uk/astro/spectra_12.htm Cheers Robin

Also binning could give an under sampled image with such a short focal length which can give processing problems with spectra (artifacts) so I would recommend running unbinned

You can get RSpec to do a lot in real time but personally for best results I would first use the real time feature of RSpec using an avi to get the best focus on a brightish main sequence A star which would also be your reference calibration star and then capture a series of subs of both reference and target using Sharp Cap which you then preprocess off line before passing back to your favourite spectrum processing program which could be RSpec or another program. The subs can be an avi for bright targets, which are then dark subtracted, aligned, selected for sharpness and stacked like planetary imaging to produce a 16 bit fits image or longer exposure full bit depth subs up to how long you can track for with faint targets, like in deep sky imaging, The objective is to produce the best (well, not over, exposed, low noise, sharp) image of the spectrum you can to pass to the spectrum processing program. Cheers Robin

From my website here http://www.threehillsobservatory.co.uk/astro/spectroscopy_17.htm The annoying design of the Canon lenses means the grating rotates as you focus but an empty rotating filter cell from a cheap set of polarising filters https://uk.telescope.com/catalog/product.jsp?productId=109834 completes the setup, making it easy to rotate the SA (glue the rotating filter cell into the hole in the lens cap and screw the SA into that) Clip on lens caps work best but it can be difficult to find ones where the clip mechanism does not prevent a large enough hole for the SA Robin

Hi Peje, Wow, lots of chatter and advice on here since I last looked, not all of it correct unfortunately. As the designer of the Star Analyser which I developed in 2004 and the source of the equations used in the RSpec calculator and the advice given there, I think it might be best if you contact me off list and I can give you the best advice Cheers Robin

About the Star Analyser, yes but don't ask me to solve Brexit 😉. Yes there are other software packages around like Visual Spec which RSpec is based on, BASSS and ISIS but my advice would be to not get too bogged down with the processing side initially and just look at a few interesting stars. One of my favourite Star Analyser images is this one by Christian Buil from his website here http://astrosurf.com/buil/staranalyser/obs.htm Even without any processing there is a huge amount of astrophysics revealed in that one image. What equipment do you plan to use? (The ATIK428EX on your equipment list for example is an excellent camera for spectroscopy. I use one on my ALPY faint object spectrograph) EDIT: that plus your 200mm f4 Newtonian would work really well with an SA100 Cheers Robin

Thanks Andrew,Chris, The latest one 19qcg was particularly marginal being so near the core and in bright moonlight. Here is the image off the spectrograph guider (20x10s). ( I guided using the brighter star to the right of the core, calculating the offset needed to place the nova on the slit) and the raw unprocessed spectrum (16x10min). The nova spectrum is the thin line above the overexposed galaxy core. The background spectrum is a combination of galaxy, moonlight, air glow and light pollution

Meanwhile with the LHIRES spectrograph, for the past month I have been following a number of Be stars in the field of the TESS satellite at H alpha and He6678A at a resolving power of R=5500 contributing to a Pro Am study trying to correlate star activity with disc formation. Although there have not been too many clear nights they only take 30min-1 hour each so it is possible to knock off half a dozen in an evening. The graphic shows the results for selection of different Be stars at H alpha. The one in red currently has no circumstellar disc so just shows the normal absorption line of a B star. Where a disc is present the emission from the disc is superimposed on the absorption and if the disc is strong enough this completely dominates. Whether the emission is single or double peaked depends on the orientation of the rotating disc relative to us. When viewed pole on there is no Doppler broadening from the rotation so we just see a single narrow line. When viewed side on we see two peaks from the two sides of the disc rotating towards and away from us. Robin

For a few years now I have been using a modified ALPY spectrograph to confirm and classify supernovae spectroscopically http://www.threehillsobservatory.co.uk/astro/spectroscopy_20.htm but over the past year I have also been trying my hand at novae in M31. The brightest are typically around mag 16 so similar to the supernovae I have been measuring but because the lines are narrower (due to the lower velocities involved) they need higher resolution to resolve them well so I have been using the ALPY 600 spectrograph in its standard configuration. They turned out to be tough targets for the standard ALPY and the “light pollution” from the galaxy itself does not help so the spectra are very noisy. It is just possible to though pick out the relevant features and as far as I am aware, these may be the only spectra of M31 novae taken using amateur equipment. Cheers Robin

I must admit I found the notes rather confusing. Perhaps they work better with the presentation material. Anyway I have added some comments clarifications (in red) Cheers Robin Practical Spectroscopy K M Harrison_revisedRL.pdf

Hi Ken, I can't find any there in the current campaigns and no publications as co-author. http://saser.wholemeal.co.nz/ Just one in the BeSS database from 2017. I try as far as possible to give practical examples from my own observations when explaining particular issues to beginners.

Just to clarify, statements like "Never touch the surface of a grating – death is imminent" "Yeah don't touch the grating, breath on it try and wipe it or otherwise anyway misuse it. " Do not apply to the Star Analyser gratings as the surface is protected. The instructions for cleaning can be found in the user manual Cheers Robin

Hi Whirlwind, I find the best advice is given by people who are already producing good data. It is difficult putting forum nicknames to actual people though. Are you active in amateur spectroscopy? What equipment do you have and do you have any results to show? I've known Ken (Merlin) for a long time but I have yet to persuade him to actually publish any of his spectra 😉 Cheers Robin

My contributions to BAA workshops in 2008 and 2015 are also available on my website http://www.threehillsobservatory.co.uk/astro/spectroscopy_10.htm One day perhaps I will get round to adding some notes to the 2015 ones but if you have any questions on them, ask away ! Robin

Yes this particular content was deliberately left open to encourage wider interest in spectroscopy. For the past few years the BAA has been supporting members interested in spectroscopy through assisted purchase of spectrographs and running a series of workshops. It also hosts a spectroscopic database for the wider amateur community complementing its variable star database https://britastro.org/specdb/ where spectra of any object meeting the required quality standard are welcome (4791 spectra at current count) Cheers Robin

The highlighted star is HD172380 at Mag 7.3 so 800x fainter than Vega (The Star Analyser is very sensitive !) it is catalogued as spectral class M4iii. With this information we can make a quick rough and ready calibration of the spectrum image (Here using Visual Spec, other software is available 😉 ) The dispersion is~7.8A/pixel The blue spectrum is from the image and the red spectrum is a standard M4iii spectrum from the Pickles library of spectra. Note the broad molecular bands mainly from TiO which can form in this star's cool atmosphere

Hi Helen, Good to see you here too ! Yep way over exposed. Aim for an exposure more like the star highlighted here (a cool star showing nice molecular bands) As I mentioned on the Staranalyser forum, aim for under exposure rather than over initially as it is easier to see the features (Note how the well exposed unblazed spectrum on the left more clearly shows the features.) Even here the correct, blazed spectrum is over exposed as Ken's spectrum profile shows, though this might be due stretching the image to produce the jpeg?) Cheers Robin

If looking to make useful scientific observations you might also find these presentations made at a BAA workshop of interest https://www.britastro.org/downloads/15701 Amateurs are already contributing to real science and have been increasingly so over the past 15-20 years. The ARAS forum for example is very active in this area http://www.spectro-aras.com/forum/ Cheers Robin

Interestingly Claudio Balcon in Italy built a similar imaging/spectroscopy setup using an SA100 where he can introduce the grating and an adjustable slit. It included an off axis guider. Like the ALPY200, he has used it in slit mode to spectroscopically confirm and classify a couple of supernovae. Cheers Robin

Hi Andrew, A very nice evolution of the junk box spectrograph. http://www.threehillsobservatory.co.uk/astro/spectroscopy_19.htm Here's to catching some flares ! Robin

You can see typical transits on the TRESCA website (a project looking for variations in transit timing for known transiting exoplanets) http://var2.astro.cz/EN/tresca/index.php?lang=en The typical 1 sigma residual per point in the recent measurements looks to be an impressive 2-5 mmag. Based on this it would probably be just possible to detect a known transit at 0.1% but whether a transit of this depth could be pulled out of a several month long data series where the period and timing is unknown is I would say debatable

This could be checked by prospective observers by measuring a known non variable over an extended period