robin_astro

Have you bagged a Uranus spectrum yet? Well placed in the early evening, about the same brightness as 63 And. It should appear pretty much star like in your short focal length Newt so give a sharp spectrum showing nice Methane bands. G0v star 29 Ari is conveniently nearby too at the moment and similar enough to the G2v solar spectrum so if you take that as well and divide one by the other (no need to correct for response) you should get the reflectance spectrum of Uranus direct without the contamination from the solar spectrum features. Cheers Robin

You also need to watch what gain you run with some of these CMOS cameras if you are stacking a lot of short subs. You can generally get away with more shorter subs with CMOS compared with CCD as the read noise is lower but if you look at the specs for this camera the read noise suddenly shoots up to a poor figure at lower gain settings https://www.firstlightoptics.com/user/products/large/zwo_asi294mc_read_noise.jpg Robin

A quick search suggests naturally produced atmospheric I2 may impact ozone levels though eg https://www.pnas.org/content/114/38/10053 Robin

Correct. Spectra of so called telluric standard stars are recorded to correct spectra of the target for atmospheric absorption. (Absorption lines from the interstellar medium are also imprinted on spectra) You probably would not want to be observing directly through a cloud of Iodine though. Molecular Iodine has a lot of lines in the visible spectrum, so much so that Iodine cells are used to calibrate high resolution spectrographs. You might have difficulty "seeing the wood for the trees" ! http://spiff.rit.edu/classes/resceu/lectures/radial_vel/iodine_spec.png Cheers Robin

The reference given at the foot of the article appears to an unrelated paper. Here is the original paper https://www.nature.com/articles/s41467-021-26920-6

Arcturus perhaps ? Bright, orange almost directly West (rather than SW for Ophiuchus) after dark currently. Low in the sky so twinkling due to the thickness of atmosphere we are looking through Cheers Robin

This spectrum (taken using the C11 and ALPY600 spectrograph) is of magnitude 15 star IRAS 00500+6713 in Cassiopeia. It is believed to be the result of a merger between two white dwarfs, kept from complete collapse by a powerful magnetic field and may be the stellar remnant of the supernova seen by Chinese astronomers in 1181. It is a star of extremes with a temperature of 200,000 K and 16,000 km/s winds. More about this star and references on my BAA page here https://britastro.org/observations/observation.php?id=20210930_153458_144e8bbb0f30f495 Cheers Robin

Nice capture but note that AT objects are not necessarily supernovae (in fact most probably are not). To be confirmed as a supernova it needs to have spectrum taken. In this case it turns out to be a Cataclysmic Variable (a dwarf nova) in outburst in our own galaxy. You can see the classification on the Transient Name Server (where AT numbers are generated and where, if they do turn out to be supernovae, the name is changed to SN yyyyabc , the point at which it officially becomes a supernova https://www.wis-tns.org/object/2021yaf Cheers Robin

The same wiggles are also seen in the Telluric H2O lines from our own atmosphere so cannot be solar in origin. See the comparison with a high resolution annotated professional spectrum Cheers Robin

Hi Ken, What's causing emission peaks round the sharp absorption lines ? Is this some sort of sharpening/compression artifact? Or a diffraction effect off the edge of a very narrow slit perhaps? Robin

Some school lab diffraction gratings are not too bad. The Star Analyser started out as one of those. (All gratings you can buy are replicas from a master, that has nothing to do with the quality) The simplest thing you can try is put it in front of a DSLR camera and image some stars with it. It will turn the stars into smeared out spectra. Like this on my website using a Star Analyser but use a shorter focal length lens with your grating perhaps around 20-30mm otherwise the spectrum will be too long and faint. (test it by pointing at a bright street light first before trying on stars) http://www.threehillsobservatory.co.uk/astro/spectroscopy_11.htm http://www.threehillsobservatory.co.uk/astro/spectroscopy_17.htm It will work on the brightest stars but how well it works on fainter stars though will depend on the efficiency of the grating. If you look through it by eye at a point light source, you will see some light which goes straight through and several spectra either side of that. If it is a good grating one spectrum will be brighter than the others. Something like this on Christian Buil's website. http://www.astrosurf.com/buil/us/stage/session0/img2.jpg All the other light except in that spectrum is wasted light so the more light is in one of the spectra the better If you want to try something more sophisticated to mount on a telescope here is a simple design also from Christian Buil which would work with your 600 l/mm transmission grating. Use it without the slit so it is simple to use as you don't have the problem of putting the star on the slit and guiding it there. http://www.astrosurf.com/buil/us/loris/loris.htm Here it uses a 300 l/mm grating. For 600l/mm you would need to double the angle. Cheers Robin

Steve, If you want to see a binary in action in "real time" with the Star Analyser an eclipsing binary like U Cep is a good target. Here by Mike Harlow with an objective prism but the Star Analyser should also show the changes in the spectrum well https://britastro.org/node/19199 Cheers Robin

Careful focusing on the specific region of interest and choosing targets at high elevation and nights with better seeing can help but I think that is pretty typical for the Star Analyser used in the conventional way. I use other spectrographs for high resolution work. There are examples using the Star Analyser with combinations of wedge prisms at very high dispersions to get high resolution but these are either objective grating setups (ie mounted in front of the telescope/camera lens) or are high focal ratio setups which reduce the aberrations that the converging beam produces. but these are tricky to use and calibrate compared with the standard Star Analyser setup or conventional slit spectrographs. See the experiments by Uwe Zurmuhl for example in "Spektrum" editions 51 and 55 https://spektroskopie.vdsastro.de/journal-30.html Resolution is not the only parameter in spectroscopy. You can go much fainter at low resolution and there are lots of interesting targets for the simple Star Analyser including WR stars, bright novae and supernovae and even quasars. I would say attempting to see the difference between two almost identical spectral types (6,7 Lyr) which will only show the subtlest of differences is not the best place to start though. Perhaps try Albireo instead. The hotter star A8v star would make a good calibration standard and is interesting as it is also a Be star. (Can you detect any H alpha emission line?) and the cooler K2ii star will have strong metal lines so would be a good test of how much you can resolve the features) Cheers Robin

6 Lyr is also one of the stars in the MILES catalogue of stars (referenced on my web page on flux calibration.) Here it is in the database included with ISIS software.

Yes 6Lyr definitely is a known binary with a close secondary (The orbital period is just 4.3 days) but the secondary is not seen in the spectrum, most likely because it is much fainter. We know it is a binary because the lines in the spectrum from the primary move back and forth on a 4.3 day period. This is known as a single line spectroscopic binary. See the wikipedia page for the reference to the 1910 paper Cheers Robin

No not noise (The SNR is given as 320 which is very high.) If you zoom in you can see the details of the lines. The spectrum is not particularly complex. Even a normal F0v star will show lots of metal lines though they become stronger at lower temperatures eg in G an K spectral types. Here is an F0iv star from UVES POP, another source of very high resolution spectra https://www.eso.org/sci/php/tools/uvespop/bin/readspectra.cgi?wave_LO=3060&wave_HI=10000&out_FORMAT=gif&star_ID=19319&sa=Plot Amateurs are capable of high resolution spectra on bright objects like this though. For example take a look at recent spectra by Joan Guarro Flo in the BAA database using an echelle spectrograph built by him from a design by Tim Lester, another amateur. eg here is symbiotic star CQ Dra https://britastro.org/specdb/data_graph.php?obs_id=10258 again, zoom in to see the detail Cheers Robin

There is an extremely high resolution professional spectrum of 6 Lyr in the ELODIE archive http://atlas.obs-hp.fr/elodie/fE.cgi?ob=objname,dataset,imanum&c=o&o=6 lyr Cheers Robin

I am not sure the 6 Lyr binary companion is even visible in the spectrum. According to the wikipedia page it is a single line spectroscopic binary, ie it was discovered to be a binary from the periodic doppler shift in the lines in the primary star spectrum. A literature search though might throw more recent light on this. It is very unlikely you will be able to untangle the components in a low resolution star Analyser spectrum though

From the classification in SIMBAD. I see it even has its own wikipedia page https://en.wikipedia.org/wiki/Zeta1_Lyrae Your signal/noise is already very high so longer exposures will not give you any more detail. You can already see the characteristics of a hot star eg F0 in your spectrum but you need a higher resolution spectrograph to do detailed spectroscopic classification. Your Star Analyser setup is not suitable for this sort of work. Robin

They may well be but I stand by my original statement, unless you have proof of orbital motion. SIMBAD describes zet Lyr as a double or multiple star

If you are interested generally in the sort of research work amateurs are doing in spectroscopy then I can recommend browsing the ARAS forum. This is mostly with equipment more sophisticated than the Star Analyser though https://www.spectro-aras.com/forum/ For a wide ranging overview of everything spectroscopic from an amateur perspective explore Christian Buil's website http://www.astrosurf.com/buil/index.html A good source of amateur spectra is the BAA database https://britastro.org/specdb/ and there are a number of other spectroscopy related resources on the BAA website here https://britastro.org/node/19378 A good overview of an interesting range of targets for low resolution spectroscopy, many accessible with the Star Analyser is Francois Teyssier's "Low resolution spectroscopy observer's guide" from this page http://www.astronomie-amateur.fr/ Cheers Robin

If you follow the references in Skiff's catalogue you will find how the classification was made. In some cases you might find a spectrum but in general the classification just follows from the features seen in the spectrum. Also you can do general research on a particular star by following up the references found by looking it up directly in SIMBAD eg https://simbad.u-strasbg.fr/simbad/sim-id?Ident=6+Lyr Gray and Corbally "Stellar Spectral Classification" is the "bible" on how to do spectral classification but more accessible for amateurs is perhaps Richard Walker's excellent "Spectral Atlas for Amateur Astronomers" A set of spectra of "normal" stars though can be found in the Pickles library found in the various software, which is why I suggested overlaying some on your spectra to see if you can find the best match 7 Lyr should be a good match to F0v 6 Lyr is odd though. This is because it is an Am star. https://en.wikipedia.org/wiki/Am_star The classification kA5hF0VmF3 means it looks like an A5 star based on the strength of the Ca II K line but F0V based on the strength of the Balmer lines and F3 based on the strength of other metal lines. At your resolution I expect it will look like an F0v so similar to 7Lyr with similar strength Balmer lines. Spectroscopic classification is not a big area of interest for amateurs though as it has mostly already been done. Most amateur research work in spectroscopy is on stars that are unusual in some way or vary in interesting ways. Cheers Robin

Note that while zeta Lyr is visually a double star it is not necessarily a binary pair. To be a binary the two have to be gravitationally bound ie in orbit round each other Robin

7 Lyr is straightforward. It is an F0v star, a main sequence star hotter than the sun (G2v) but cooler than Vega (A0v) for example. Its spectrum is dominated by strong Hydrogen Balmer lines. You could try overlaying the F0v spectrum from the Pickles library 6 Lyr is much more complex, it is a binary so a mix of spectral types and at least one of the components has an unusual metal composition which further confuses the classification (ie the spectral classification is different depending on which lines you look at) so is classified for example as kA5hF0VmF3 To see these features though you would need a much higher resolution spectrograph than the Star Analyser and overall, Hydrogen Balmer lines again dominate your spectrum. To see the published classifications for a particular star I can suggest Brian Skiff's huge Catalogue of Stellar Spectral Classifications" http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/mk Note though that it is only possible to make an approximate spectra classification at the resolution of these spectra. To do this accurately needs higher resolution and some specialist knowledge Cheers Robin

I suggest scaling them so that the intensity is 1 at the same wavelength which makes them easier to compare independent of their brightness. (550nm is commonly chosen).