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I put some LCG graphs of the status of CCD observations into two PowerPoint slides, in particular for V-filter observations. First slide is an overview for the last 70 days (U-B-V-I-R), second focusses on last night (V only). Last night's (Oct.21-22) brightening has been observed by a number of observers. Nice!
Cheers,
Helmar (AHM)
P.S.: Gary's mini campaign for ensemble measurements paid off...?
Excellent light curve. Great slides. Shows the power of the collaboration/ mini campaign.
I have to admit sheepishly, that last night, I reduce and posted my V results, was pretty disscusted with discovering another "Systematic". So I went to bed.
Reduced the I data from last night, expecting to see the same "Systematic", but no, it was different. I then reduced the B data, and it matched the V data. Posted it and took a look, and whoa and behold, LDJ has V data with the same "Systematic". This could be science. Now there are 5 observers with supporting data, including AHM, SRIC, LDJ, EEY, and WGR. BTW; SRIC just emailed me this morning and reported that his light curve was using 1 comp, the 125, and he is now going back and reducing using the 4 star Ensemble, 121, 105, 125, and 122, as I suspect most of the other data has been done. Can't Wait.
Can't contribute directly to this because of the very unsettled weather we're having, right now, in the UK. But the light curve suggests a three day standstill, with today, a resumption of the decline.
Looking at the V339 Del V-band light curve, it looks like there's a "standstill" around the previous full moon (September 20-24) as well. Could we be seeing some affect due to the bright sky?
it looks like there's a "standstill" around the previous full moon (September 20-24) as well. Could we be seeing some affect due to the bright sky?
[/quote]
While this may be more suitable for CCD discussions, I always wonder how bright backgrounds might affect the automated data reductions that most CCD'ers use? For visual observers who have sufficient experience, the background can be properly discounted by using good comps very closely bracketing the variable. But for CCD, wouldn't it depend on many operational details, such as size of apertures, what part of the response curve/linearity you are working on, what specifically the software does in regards to subracting the background, etc? Are new "flats" specifically done for bright backgrounds? A lot of these specifics may be out of the hands of the operator using the common software, and thus potentially result in errors due to the automated algorithms employed?
Bright backgrounds only affect the signal/noise of an image, as there is more noise in the background when the sky is bright. So for faint objects, the background soon dominates the noise/error and they become difficult to measure. For something as bright as V339 Del, a bright background from the moon is not a problem. In this case, the full moon in October was at RA 1:44, Dec +11, and so over 75 degrees from the nova field, and even when the moon crossed RA 20 at first quarter, it was at Dec -14, so again not close to the nova field.
Even for twilight flats themselves, the full moon is always low on the horizon and doesn't affect the gradients across your image.
I think we must go elsewhere for an understanding of any monthly pattern in the standstills.
Bright backgrounds only affect the signal/noise of an image, as there is more noise in the background when the sky is bright....
Even for twilight flats themselves, the full moon is always low on the horizon and doesn't affect the gradients across your image.
I think we must go elsewhere for an understanding of any monthly pattern in the standstills.
[/quote]
Arne, This may be generally so, but maybe we need to look for more subtle effects of bright moonlight? For example, even if the moon is 75 degs away, I have noticed much more severe background degradation, if the atmosphere isn't perfectly clear. Dust/smoke/air pollution/haze, water vapor can greatly diffuse the star's image into a large diameter, and scatter the background light much more than under perfect conditions. If the FWHM of the star is the size of a planet, wouldn't you need to compensate for that in the aperture? I have used HL Cma as an example to visually test the effects of atmospheric scatter, and it can be very severe, even from a -1 magnitude star, the haze can cover maybe a moon's width from the source. So, a full moon at -11 can have devastating effects on background over a large distance, if the atmosphere is poor.
It might be useful for some CCD'ers to experiment with taking a flat of the bright sky just prior to exposing on the variable, and see if it makes any difference from the twilight flat?
This is my first post, but I've been following this dicussion with great interest. These forums are a great way for a beginner at variable star photometry to learn the ropes.
I've been making observations of Nova Del sporadically for the last month, trying the various stacking techniques and ensemble sets being suggested here. I've been happy that my novice observations are not hugely discrepant with those of other observers. In some cases they were, and I wenbt back and checked why (for instance as the nova faded and I lengthened my exposures I managed to saturate the 80 comp star, and had to redo the reducation and resubmit). All good learning experience. And I figured that reporting these data was better than nothing, given my Australian time zone means the nova is often otherwise unobserved at this time.
I was disappointed that my observations on 20 October were quite a lot fainter than others, who were reporting a brightening. I had it at pretty much bang on V Mag 11 I rechecked my reduction and extinction calculations which seemed fine.
However I just realised that I had been observing V339 Del low to the north of Canberra through pretty intense bushfire haze (the whole state of NSW is on fire at the moment, it seems). The moon was blood red that night. Given that the comp stars are quite a lot redder than the nova, could this bushfire haze explain why my observations were so discrepant that night? Those more experienced than I might be able to give a confident answer to this question.
if the full moon has a significant effect on CCD derived magnitudes of Nova Del it should have similar effect on other variables so light curves of these should show the same luna month features. Is there any evidence of this? Cheers,
That's what I'm seeing. Observed it tonight and thought it was only slightly fainter (0.1 magnitude) than 5 nights ago.
I put some LCG graphs of the status of CCD observations into two PowerPoint slides, in particular for V-filter observations. First slide is an overview for the last 70 days (U-B-V-I-R), second focusses on last night (V only). Last night's (Oct.21-22) brightening has been observed by a number of observers. Nice!
Cheers,
Helmar (AHM)
P.S.: Gary's mini campaign for ensemble measurements paid off...?
Hello Helmar
Excellent light curve. Great slides. Shows the power of the collaboration/ mini campaign.
I have to admit sheepishly, that last night, I reduce and posted my V results, was pretty disscusted with discovering another "Systematic". So I went to bed.
Reduced the I data from last night, expecting to see the same "Systematic", but no, it was different. I then reduced the B data, and it matched the V data. Posted it and took a look, and whoa and behold, LDJ has V data with the same "Systematic". This could be science. Now there are 5 observers with supporting data, including AHM, SRIC, LDJ, EEY, and WGR. BTW; SRIC just emailed me this morning and reported that his light curve was using 1 comp, the 125, and he is now going back and reducing using the 4 star Ensemble, 121, 105, 125, and 122, as I suspect most of the other data has been done. Can't Wait.
Great work by all the observers on this one.
Gary
WGR
Can't contribute directly to this because of the very unsettled weather we're having, right now, in the UK. But the light curve suggests a three day standstill, with today, a resumption of the decline.
Looking at the V339 Del V-band light curve, it looks like there's a "standstill" around the previous full moon (September 20-24) as well. Could we be seeing some affect due to the bright sky?
-Emery (EEY)
[quote=emeryerdelyi]
it looks like there's a "standstill" around the previous full moon (September 20-24) as well. Could we be seeing some affect due to the bright sky?
[/quote]
While this may be more suitable for CCD discussions, I always wonder how bright backgrounds might affect the automated data reductions that most CCD'ers use? For visual observers who have sufficient experience, the background can be properly discounted by using good comps very closely bracketing the variable. But for CCD, wouldn't it depend on many operational details, such as size of apertures, what part of the response curve/linearity you are working on, what specifically the software does in regards to subracting the background, etc? Are new "flats" specifically done for bright backgrounds? A lot of these specifics may be out of the hands of the operator using the common software, and thus potentially result in errors due to the automated algorithms employed?
Mike LMK
Hi Mike,
Bright backgrounds only affect the signal/noise of an image, as there is more noise in the background when the sky is bright. So for faint objects, the background soon dominates the noise/error and they become difficult to measure. For something as bright as V339 Del, a bright background from the moon is not a problem. In this case, the full moon in October was at RA 1:44, Dec +11, and so over 75 degrees from the nova field, and even when the moon crossed RA 20 at first quarter, it was at Dec -14, so again not close to the nova field.
Even for twilight flats themselves, the full moon is always low on the horizon and doesn't affect the gradients across your image.
I think we must go elsewhere for an understanding of any monthly pattern in the standstills.
Arne
[quote=HQA]
Bright backgrounds only affect the signal/noise of an image, as there is more noise in the background when the sky is bright....
Even for twilight flats themselves, the full moon is always low on the horizon and doesn't affect the gradients across your image.
I think we must go elsewhere for an understanding of any monthly pattern in the standstills.
[/quote]
Arne, This may be generally so, but maybe we need to look for more subtle effects of bright moonlight? For example, even if the moon is 75 degs away, I have noticed much more severe background degradation, if the atmosphere isn't perfectly clear. Dust/smoke/air pollution/haze, water vapor can greatly diffuse the star's image into a large diameter, and scatter the background light much more than under perfect conditions. If the FWHM of the star is the size of a planet, wouldn't you need to compensate for that in the aperture? I have used HL Cma as an example to visually test the effects of atmospheric scatter, and it can be very severe, even from a -1 magnitude star, the haze can cover maybe a moon's width from the source. So, a full moon at -11 can have devastating effects on background over a large distance, if the atmosphere is poor.
It might be useful for some CCD'ers to experiment with taking a flat of the bright sky just prior to exposing on the variable, and see if it makes any difference from the twilight flat?
Mike LMK
This is my first post, but I've been following this dicussion with great interest. These forums are a great way for a beginner at variable star photometry to learn the ropes.
I've been making observations of Nova Del sporadically for the last month, trying the various stacking techniques and ensemble sets being suggested here. I've been happy that my novice observations are not hugely discrepant with those of other observers. In some cases they were, and I wenbt back and checked why (for instance as the nova faded and I lengthened my exposures I managed to saturate the 80 comp star, and had to redo the reducation and resubmit). All good learning experience. And I figured that reporting these data was better than nothing, given my Australian time zone means the nova is often otherwise unobserved at this time.
I was disappointed that my observations on 20 October were quite a lot fainter than others, who were reporting a brightening. I had it at pretty much bang on V Mag 11 I rechecked my reduction and extinction calculations which seemed fine.
However I just realised that I had been observing V339 Del low to the north of Canberra through pretty intense bushfire haze (the whole state of NSW is on fire at the moment, it seems). The moon was blood red that night. Given that the comp stars are quite a lot redder than the nova, could this bushfire haze explain why my observations were so discrepant that night? Those more experienced than I might be able to give a confident answer to this question.
Cheers
Jonathan
Hi All,
if the full moon has a significant effect on CCD derived magnitudes of Nova Del it should have similar effect on other variables so light curves of these should show the same luna month features. Is there any evidence of this? Cheers,
Mark