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Robin,
M85 is getting low in a bright sky but this is an image from a few minutes ago showing the SN. It doesn’t seem much brighter (Astrometrica gives 17.5 unfiltered using Gaia DR2 G and an unfiltered KAF-6303 CCD).
David, so you follow in illustrious footsteps! Chelmsford has Calver of course. A more recent connection but not an orbital dynamicist.
The cost of these photometric filters is pretty eye-watering compared to the bog-standard LRGB filters that people use for imaging. As Robin says it is necessary to calibrate the transformation coefficients for any particular sensor in any case and you then need to image in multiple bands so you can apply those coefficients. It may not be perfect but could you use imaging RGB filters and transform them to something close to the standard photometric bands? I know that people use DSLRs for variable work and do something similar with the Bayer RGB pixels. I’ve certainly found that the green pixels of my ASI294 match Gaia G quite nicely and I use a neat tool called rawtran which transforms the RGB into other photometric bands. It seems to work pretty well with reference to APASS photometry.
Is there something special about spectroscopy that would mean that scaling darks was a normal thing to do? Unlike flats, darks are really easy to obtain so I don’t really understand why you wouldn’t just take a set of darks corresponding to the exposure/temperature that you use for images.
Regarding amp glow I have a ZWO ASI294MC which uses the Sony IMX294. The amp glow in darks is a bit spectacular (see attached for a 120s example at -10C) but it calibrates out completely. I rarely go beyond 120s since stacking algorithms work much better if they have lots of frames to stack and the read-out noise and dead time of these cameras is negligible.
I don’t see any reason why CMOS should be any different to CCD if you are careful not to saturate either the individual subs or the final stack and the images are calibrated accurately. Due to much lower read noise and much faster readout times CMOS tends to be used with shorter exposures so the smaller well depth and reduced bit depth (12 or 14 bits rather than 16 bits) are not really relevant. If the standard deviation of the noise in each image exceeds a few LSBs than the quantization is not relevant anyway whichever technology you are using. A key thing if you stack images before measuring them is to use mean rather than sum and ouput the resulting FITS as float rather than int to avoid saturation and quantization effects.
CMOS and CCD have the same problems as far as calibration is concerned (flats, darks etc) and in terms of aligning wavelength sensitivity with standards (filters etc) but otherwise they are pretty similar. CMOS has many other advantages so it won’t be long before CCD detectors are only available for very specialist applications.
I had to wait until it was almost daylight for it to clear my house roof but here it is. I’ll need to dig out my nova patrol films from 1989 to see the last time I got it this bright.
THE ASTRONOMER Electronic Circular No 138 1988 Mar 26 14.32UT.
Telecom Gold 72:MAG60138
Ed:Guy M Hurst, 16, Westminster Close, Kempshott Rise, Basingstoke,
Hants, RG22 4PP, England. Telephone:(0256)471074.Int:+44256471074
Telex:265871(MONREF G) Quote”72:MAG60138 ATT G.HURST”in FIRST line.
——————————————————————-
TAV0226+39 = VAR OBJ IN AND
M.Mobberley and G.Hurst report confirmation of the new object
announced on E137. Available magnitude estimates (some re-reduced):
1988 Feb 12.802UT,(11.5pv M.Mobberley 85mmFL f2 Tri-X
Mar 15.835UT,( 9.0pv N.James 55mmFL
1988 Mar 21.900UT, 10.0pv D.McAdam 305mmFL f4 K2415
21.913UT, 10.0pv D.McAdam 305mmFL f4 K2415
25.844UT, 10.8pv M.Mobberley 0.36-m f5 refl. Tri-X
25.844UT, 10.6v G.Hurst 0.44-m refl.
N.James, Chelmsford, reports the object is not present on patrol
photos with the following limiting magnitudes:
1986 Dec 6, 10; 1987 Feb 20, 10; Oct 17, 11; Nov 14, 11;
1988 Jan 20, 11; Feb 12, 11.
G.Hurst reports a revised position from analysis of the discovery
photos:
RA 02h26.3m DEC +39 50′(1950)
There is no candidate on Atlas Stellarum to an approx limiting
magnitude of 13.8B. (1969 Aug 9).
Preliminary sequence:
Comp RA(1950) DEC(1950) mv Source
A 02 27.6 +39 57 6.8 CSI
B 02 26.3 +39 47 8.7 M34 Transfer
C 02 25.7 +39 39 9.3 do.
D 02 25.9 +39 39 10.2 do.
E 02 25.6 +39 43 10.6 do.
F 02 26.2 +39 47 10.8 do.
G 02 26.3 +39 49 11.2 do.
The discovery has been communicated to the Central Bureau by telex
and as yet, no independent results have been announced.
Guy M HurstI’m sure Guy won’t mind me posting this here. This is from my archive as downloaded using a 1200 baud modem…
THE ASTRONOMER Electronic Circular No 137 1988 Mar 24 19.04UT.
Telecom Gold 72:MAG60138
Ed:Guy M Hurst, 16, Westminster Close, Kempshott Rise, Basingstoke,
Hants, RG22 4PP, England. Telephone:(0256)471074.Int:+44256471074
Telex:265871(MONREF G) Quote”72:MAG60138 ATT G.HURST”in FIRST line.
——————————————————————-
VARIABLE OBJECT IN AND= Q1988/18
D.McAdam, Telford, reports his discovery of a variable object in
And. The stellar object, of mag approx 10.5pv is present on two
photos taken on 1988 Mar 21 at 21.36UT and 21.55UT for the UK
Nova/Supernova Patrol. The position is:
RA 02h26.5m DEC +39 50′(1950)
The object was not present on photos of Jan 22 and to date no
variable or asteroid candidate has been found.
Observers with a clear sky tonight are urgently requested to check
the field and report their findings by e-mail using ‘EXPRESS’.
Guy M HurstI remember Dave from the old TA days. A great guy. I chased up a few of his suspects back in the late 80s. I remember discussing the TA/VSS computer archive with him when computers weren’t quite what they are today.
I’ll have a go at getting some images from here tomorrow morning but it will have to wait until the sky is quite bright.
Ditto for me. I haven’t refocused mine for years (3.8mm, f/0.8). My main problem is spiders. Now that planes are mostly gone they are a major source of false triggers on my cams. I have a brush on a long pole for dealing with them but they don’t stay away for long.
Did you mean the Circulars (at the link provided by Martin) or the e-bulletins? The e-bulletins were archived somewhere but I can’t find them on this site.
I agree. It was an inspired idea from Andy and Dominic to get these going. They have been really popular and I hope that we can continue them in some form even when things get back to normalish.
I’m just resurrecting this thread since it started with a post from me on May 2nd tentatively predicting a nice comet for around about now but with, hopefully, sufficient caveats that members wouldn’t be disappointed if it fizzled. The first post in the thread included a chart for May 20 and this morning I managed to get an image here which matches the field if not the splendour. C/2020 F8 is probably somewhere between mag 6 and 7 at the moment and it is certainly not an easy object but it is there and if you are up early it is worth searching out. It goes under the pole at midnight on May 26 and from then on it will be better in the evening but it is now fading. Images received will appear in the Comet Section archive here.
Eric has provided me with his data. The geometry is not very favourable since our stations are too close together but here is the ground track. It was out over the English Channel off the north coast of France.
