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Sorry this is a historical observation from the Digitized Sky Survey plates
Have just been looking at where this field is so I can take a quick look with the spectrograph guider from time to time. Impressed by how bright (and blue) it appears in the DSS image
>That is why I was careful to state that the dynamic range can be improved by a factor of NxN for N-fold post-binning, and not the signal to noise ratio. Sometimes the dynamic range is particularly important, such as when trying to detect extremely low contrast objects for instance.
Indeed and this is a limitation of in camera binning where unlike post binning, you cannot see the individual pixel counts, so to be sure of not having any individual saturated pixels you have to limit the total counts in a super-pixel to the full well depth of an individual pixel.(Well I suppose one could perhaps assume a gaussian distribution of brightnesses in the star image and allow a higher maximum count per super-pixel which would bring some dynamic range benefit.)
The in camera binned exposure could be split into NxN shorter sub-exposures to match the post binned dynamic range without risking saturation but that then returns you to the same read noise contribution as for post binning. In camera binning can be advantageous though for weak signals in a dark background where the read noise contribution can be significant (in spectroscopy at low SNR for example.)
I think you mean oversampled ie there are more than 2 pixels per star FWHM. (Why do you consider 1.7 arcsec pixel optimum? What is your actual best seeing?)
Undersampling is to be avoided for science applications but the effect of the additional read noise on signal/noise ratio due to oversampling (this is the only disadvantage I know of) depends on the observation. Playing with Michael Richmond’s calculator for example entering actual numbers for different cameras and observing conditions will give you an idea of the significance for photometry.
http://spiff.rit.edu/richmond/signal.shtml
Note with CCD cameras (not CMOS), in camera binning (as opposed to post binning) reduces the read noise as there is only one dose per binned super- pixel, though CMOS cameras generally have lower read noise
Cheers
Robin
Could a short term solution be for the submitter to have the option to disable plate solving where it is obviously incorrect or otherwise inappropriate
Cheers
Robin
Living near the wettest place in England, dewing is ever present hazard for me but with this specific ATIK camera model which I have been running for many years the only time I have had a dewing problem has been when water got into an SCT when it got rained on making the air inside the telescope particularly humid. The dew then was on the outside of the camera window and drying out the telescope solved the problem. If this is a reoccurring problem (eg with an open tube telescope) this is where a specific dew heater for the camera could help. The other possibility though is dewing internal to the camera, either on the inside of the camera window or on the sensor cover glass (this can actually be frost if the sensor is cooled,as here). In the ATIK cameras, this is prevented by making the chamber in front of the sensor hermetically sealed and the air kept dry by a desiccant tablet. If the dewing is on the inside it is because the air in the chamber has become wet (either over time or because the seal has failed) In this case opening the chamber in a warm dry environment, introducing dry air and recharging the desiccant as ATIK recommend will solve the problem, though the solution may be temporary if the chamber is leaky.
Cheers
Robin
The ability to upload multiple images against an observing report rather than having to construct a composite image would be useful eg
https://britastro.org/node/23284
Robin
It could be the desiccant tablet needs changing. This is easy on the later ATIK cameras but you have to take the back off the 314 to get to it. I have not yet had to do it but have this page bookmarked in case I do
https://forums.atik-cameras.com/index.php?topic=571.0
Cheers
Robin
Yes it is real. I also see it in a Star Analyser spectrum I took a couple of days ago. It is a blend of several lines ~4500-4600A unresolved at the Star Analyser resolution Here it is overlaid on a spectrum from David Boyd in the BAA database (red)
(It looks quite intense relative to H gamma because H lines are narrow compared with the Star Analyser resolution so are reduced in height)
Cheers
Robin
V-I is a ratio though so should be independent of the actual flux under some scenarios eg partial obscuration by a completely opaque medium or by one which semi-transparent but absorbs equally at all wavelengths. We can therefore rule out these scenarios based on this. I agree though for scenarios where there is an additive effect eg starspots (or like your flares) the absolute magnitudes need to be considered to separate out the two components. Fortunately there is plenty of V mag data and the spectra cover the full passband so the spectra could be converted to absolute magnitude
The amateur spectroscopic monitoring was very extensive and as far as I know remains untapped by professionals. It would be interesting to know how our data fits the various models.
Cheers
Robin
I mean for identification (ie shorthand to identify the line in question) not for stating the measured wavelength. (I can measure that to a precision of up to 0.01A). In papers on astrophysics you only need to say for example Na 5890, Na 5896, He 6678, DIB 6613 etc for the reader to know the line you are talking about. That’s what I meant by avoiding the ugly decimal point.
nm I can cope with (though the need to include a decimal point when defining well known lines is ugly). It is the use of Janskys for flux in optical spectra instead of the traditional (but definitely not SI) erg/cm2/sec/Angstrom that really throws me when I see it as being based on frequency, it completely changes the shape of the spectrum.
Actually I debated that briefly. The wavelength range in the images is approximate as the dispersion is non linear and it is a crop and I could not be bothered to work out the exact wavelengths to the nearest Angstrom. I used nm as 10 Angstrom was close enough 🙂
This relatively modern paper sums it up (I did not realise before that some of these lines do not always track the dust or even each other)
When I first saw it I expected it to be atomic in origin because it looks so narrow (Think NaD or K 7699 interstellar lines) but I found no matches. Apparently it is probably (I should say possibly, nothing seems very clear from the literature I have found) formed by a high molecular weight PAH molecule but exactly which one is not clear. It is fascinating that something that is seen in so many spectra and has been known about for many decades is still a mystery
Cheers
Robin
Perfect ! Thanks David. (I had tried underlining but that did not work so did not explore further.) I have changed my recent post. I think Bold, Italic looks quite good 🙂
Cheers
Robin
