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I see cropping the spectrum to remove the bad edges is mentioned in the ISIS tutorial ~ 2/3 the way down. I think you have just missed that step
“Tip: The response profile changes shape very rapidly near the edges and it may not accurately represent the response in these regions as the signal there is almost zero. It is a good idea to crop the useful part before smoothing the spectrum. Use the “Cut” tool for this operation. The smoothing will then be easier and the results better. Here is the smoothing result under these conditions:”
Cheers
RobinHi Jonathan,
Firstly congratulations on getting as far as you have with ISIS. Although it is very powerful, particularly for producing research grade spectra from more advanced spectrographs than the Star Analyser, it can be tough to master and most people use different software with the SA like Visual Spec, RSpec, BASS project which can be easier to use with the SA. (I tend to use mixture of VisualSpec and ISIS, mainly because that was what was around then). I think you actually are ok though with what you have done and I suspect the flat line is just because the resulting spectrum has some really high and low values at the edges outside the wavelength range where there is good data and ISIS has autoscaled to include them. If you rescale manually or crop the bad edges (using the crop tool in the profile display) hopefully you should be able to see the result.
There are also some other resources on the website here that you might find useful
https://britastro.org/section_information_/equipment-and-techniques-section-overview/spectroscopy
David Boyd’s “Scientific analysis of amateur spectra” at the top is an excellent overview of the whole subject.
Particularly for the Star Analyser, my slides for the tutorial “Low Resolution Slitless Spectroscopy” downloadable here
https://britastro.org/document_folder/baa-document-store/past-talks/spectroscopy-workshop-at-the-nlo-oct-2015
Also the document on my website here specifically tackles the subject of response correction (flux calibration)
http://www.threehillsobservatory.co.uk/astro/Relative_flux_calibration_20221222.pdfCheers
RobinThe earlier Baader filters were conventional multilayered coloured glass filters which would explain the interference rings, with I believe a dielectric coating to block IR leaks (I have an old V filter from a different supplier which has delaminated on the edge.) The RGB and latest BVRI filters from Baader (and others) are now a single thickness of dielectric coated glass
Cheers
RobinI’ve just been reading in The Darkness Manifesto by Johan Eklof about how the craze for floodlighting churches in Sweden significantly affected bat populations. (In the space of ten years half of the church roosts were lost with two species now on the red list.) Apparently turning off the lights before midnight helped to some degree
Currently reading my Christmas present “The Darkness Manifesto” by Swedish Biologist Johan Eklof. Light pollution is having serious affects on the natural world (including humans) which reach well beyond us not being able to see the stars.
It seems from this survey RW Cep is dimming by ~ the same amount in Ic and V
http://kws.cetus-net.org/~maehara/VSdata.py
which is significantly different to the Betelgeuse event.
(Thanks to “VY Canis Majoris” on Cloudy Nights for the heads up on this)
https://www.cloudynights.com/topic/854288-rw-cephei-great-dimming/?p=12378723Cheers
RobinA high resolution spectrum (R=15000) taken tonight shows H alpha to be in emission
https://britastro.org/specdb/data_graph.php?obs_id=13128
There are a number of publicly available archived high resolution spectra taken with the ELODIE spectrograph at Observatoire Haute Provence between 1998 and 2005. None of these show H alpha in emission so this may be unique to this dimming.
Plots of the ELODIE spectra and comparisons with my spectra at both low and high resolution can be seen here on my website
http://www.threehillsobservatory.co.uk/astro/RW_Cep/rwcep_elodie_archive_THO_2022-12-19_lowres.png
http://www.threehillsobservatory.co.uk/astro/RW_Cep/rwcep_elodie_archive_THO_2022-12-19_Halpha.png
Is there any professional interest in these observations ? If so who should I be talking to for guidance on what specifically I should be focussing on (resolution, specific regions/lines)
Cheers
RobinI suspect the M2 classification may have come from the colour index which would match an M star without reddening but the lack of molecular bands in the spectrum immediately shows we are dealing with a hotter star here (significantly hotter than Betelgeuse)
Cheers
RobinHere is a spectrum tonight (R=1000 using an ALPY 600 with a narrower than usual 10um slit)
https://britastro.org/specdb/data_graph.php?obs_id=13110
It is very red but clearly heavily reddened by interstellar or circumstellar dustVSX suggests a very wide range of spectrum classifications ranging from G to M2 but Keenan suggests K2i in his 1989 catalogue.
https://articles.adsabs.harvard.edu/pdf/1989ApJS…71..245K
Using the B,V brightness values in SIMBAD, this would imply for a K2i star an E(B-V) = 0.99. Dereddening my spectrum by this amount indeed gives a good match to the Pickles standard for K2i both in terms of the continuum shape and more importantly in the spectral line details (My spectrum is a slightly higher resolution which would explain the higher apparent intensity of the lines in my spectrum)
https://britastro.org/specdb/view_image.php?obs_id=13110Cheers
Robin
EDIT- trying to get the link working.. and failing đ cut and paste it if you need toSome (PEP) photometry in the IR might be interesting. Betelgeuse hardly faded at all in H and J. There is no history for RW Cep in those bands in the AAVSO database though. Does anyone in the BAA have this capability ?
Where does manipulation start though ? For example I would venture to suggest almost every deep sky, comet and planetary image in the gallery has had undocumented processing which affects the scientific value (non linear stretch, sharpening, noise reduction star elimination etc etc). As a science based organisation though contributors should welcome challenge and be able to supply the raw data if required. (With the new website there doesn’t appear to be any simple way to make contact with other members any more though)
Cheers
RobinSo, if youâre trying to fix a broken link, you can generally find the page youâre looking for by changing the broken link into the canonical form and seeing where it redirects to in the new site.
Thanks! Link now points directly at the destination
Cheers
RobinIt has now been imaged by HST and resolved into four lensed components
https://www.wis-tns.org/sites/default/files/astronotes_files/1052/note_color_wide.jpg
from
https://www.wis-tns.org/astronotes/astronote/2022-196Cheers
RobinThis is also my experience. I don’t think these satellite maps are showing the true picture. They are measuring the light escaping into space. (If all the light did that we would have dark skies!) What we need to know is the light which is scattered back which depends on the wavelength and the factors Gianni mentioned. A shift in the spectrum of the light pollution from a predominantly orange to blue at the same light intensity would increase the scattering reducing what the satellite sees but making the skies brighter when viewed from the ground.
Also some LED lights which look like they are full cut off are just flat LED panels with a very wide pattern and no attempt to contain the beam. I have a neighbour a couple of hundred metres away with a very bright one of these. It is directed almost straight down so should be ok but it still overspills into my garden.
Robin
A comparison of the spectrum this maximum with that by Miguel Rodriguez at a more typical maximum is in the latest BAA VSSC
https://britastro.org/vss/VSSC193.pdf
page 16It has now faded to visual magnitude ~7, a brightness more like that typically seen at maximum. The temperature from the TiO bands in the spectrum spectrum has dropped to that more typically seen at maximum, though the intensity of the Balmer emission remains high. Attached is a comparison between my most recent spectrum and that of Miguel Rodriguez taken at the 2020 maximum.
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This reply was modified 2 years, 7 months ago by . Reason: sp
Attachments:
Finally caught it tonight
40×20 sec clearAttachments:
The ZTF cutouts on the alerce site are useful. There is a faint something (the parent galaxy ?) at the coordinates in the template but this is clearly brighter with the SN (about the same brightness as two other stars in the same string on 25th)
(The clouds rolled in here as dusk fell)
Robin
Attachments:
Align and stack programs like Siril for example
https://siril.org/
can output a series of fits images as avi which can then be converted to animated gifs using various on line toolsCheers
RobinSince the point spread function of each of these stars would be expected to be similar, is it possible to use some kind of psf fitting technique to separate the flux from each component instead of aperture photometry ?
They are obviously having fun combing these images. Here they have found what is left of SN 2013ej in M74
https://www.wis-tns.org/astronotes/astronote/2022-147
which reached mag 12 back in August 2013 seen here in Damian Peach’s image.
http://www.damianpeach.com/deepsky/m74sne_2013_08_05dp.jpg -
This reply was modified 2 years, 7 months ago by
