On October 6, 1923 renowned astronomer Edwin Hubble discovered a pulsating star in the Andromeda Galaxy which quickly led to the revolutionary discovery that M31 is a galaxy unto itself 2.5 million light-years away, and not a gaseous cloud of stars within our own Milky Way...
I've begun the process of capturing data points in an effort to construct the star's light curve. I was hoping to use my lowly 71mm f/5.9 refractor and Bortle 5 skies but alas it is not feasible according to my calculations. At minimum light (magnitude 19.8) the required integration time would take days to complete.
I turned to Pier 12 for help, an RC Optical Systems (RCOS) 12.5-inch Ritchey-Cretien. Last night I grabbed a one-hour time slot and captured 12x 5-minute subs. According to my calculations the 60-minute stack would have yielded a good signal-to-noise ratio. Unfortunately M31 was not high enough in the sky to yield that kind of quality so I discarded 10 of the 12 subs, and stacked the remaining two for a total integration time of only 10 minutes.
The screenshot below is from a program called AstroImageJ (AIJ). I use it for all photometry and exoplanet work. There is one green bulls-eye and two red ones. The red "apertures" are known constant brightness comparison stars: C2 is magnitude 15.522 and C3 is magnitude 16.01. The green aperture I placed on top of Edwin Hubble's variable star. You can see from the screenshot that AIJ calculated the magnitude as 19.168. Just now I looked at an ephemeris and see that the magnitude was expected to be around 19.2. So it works!
This is pretty amazing considering only 10 minutes integration time but the sad part is the accuracy is not very good. AIJ computed the error to be 0.155 magnitudes. Well, I wouldn't say that is unusable but I know I can do better. What's worse is that the star at minimum light of 19.8 may not even be detectable with only 10 minutes integration time. Thankfully, M31 grows higher in the sky with each passing night so it is increasingly possible to obtain better quality data. The first frame of last night's data was captured at only 34 degrees above the horizon, and the last frame at 46 degrees. The frame quality increased as time went on.
Brian
I've begun the process of capturing data points in an effort to construct the star's light curve. I was hoping to use my lowly 71mm f/5.9 refractor and Bortle 5 skies but alas it is not feasible according to my calculations. At minimum light (magnitude 19.8) the required integration time would take days to complete.
I turned to Pier 12 for help, an RC Optical Systems (RCOS) 12.5-inch Ritchey-Cretien. Last night I grabbed a one-hour time slot and captured 12x 5-minute subs. According to my calculations the 60-minute stack would have yielded a good signal-to-noise ratio. Unfortunately M31 was not high enough in the sky to yield that kind of quality so I discarded 10 of the 12 subs, and stacked the remaining two for a total integration time of only 10 minutes.
The screenshot below is from a program called AstroImageJ (AIJ). I use it for all photometry and exoplanet work. There is one green bulls-eye and two red ones. The red "apertures" are known constant brightness comparison stars: C2 is magnitude 15.522 and C3 is magnitude 16.01. The green aperture I placed on top of Edwin Hubble's variable star. You can see from the screenshot that AIJ calculated the magnitude as 19.168. Just now I looked at an ephemeris and see that the magnitude was expected to be around 19.2. So it works!
This is pretty amazing considering only 10 minutes integration time but the sad part is the accuracy is not very good. AIJ computed the error to be 0.155 magnitudes. Well, I wouldn't say that is unusable but I know I can do better. What's worse is that the star at minimum light of 19.8 may not even be detectable with only 10 minutes integration time. Thankfully, M31 grows higher in the sky with each passing night so it is increasingly possible to obtain better quality data. The first frame of last night's data was captured at only 34 degrees above the horizon, and the last frame at 46 degrees. The frame quality increased as time went on.
Brian
Morning Brian
just do you know, we can state a min imaging elevation in our software so it wont image until say 40d for example
whilst you cannot specify this in the booking form, as I know its a science thing where this stuff matters just message me and when filling out the image acquisition page I can tick a few extra boxes
hth
steve
just do you know, we can state a min imaging elevation in our software so it wont image until say 40d for example
whilst you cannot specify this in the booking form, as I know its a science thing where this stuff matters just message me and when filling out the image acquisition page I can tick a few extra boxes
hth
steve
Please ignore my dylexia wherever possible, just be thankful I can control my Tourettes ;)
Things to do, so little time!
Steve
Roboscopes Tea Boy
Thanks, Steve, I might take you up on that!
Here is a good comparison of what can be accomplished given enough integration time. This is the work of Robert Gendler whose wonderful survey of globular clusters in M31 can be found here: http://robgendlerastropics.com/M31NMmosaicglobs.html
He says he used an RCOS 20-inch Ritchey-Cretien but gives no further details.
Brian
Here is a good comparison of what can be accomplished given enough integration time. This is the work of Robert Gendler whose wonderful survey of globular clusters in M31 can be found here: http://robgendlerastropics.com/M31NMmosaicglobs.html
He says he used an RCOS 20-inch Ritchey-Cretien but gives no further details.
Brian
Awesome
Ok so Mr Gendler used a very expensive big scope by amateur standards but none the less is still very impressive what we can acheive with ground based telescopes like this that are way smaller than what Scientists get to use
Just let me know as I said Brian the offer is there...
Ok so Mr Gendler used a very expensive big scope by amateur standards but none the less is still very impressive what we can acheive with ground based telescopes like this that are way smaller than what Scientists get to use
Just let me know as I said Brian the offer is there...
Please ignore my dylexia wherever possible, just be thankful I can control my Tourettes ;)
Things to do, so little time!
Steve
Roboscopes Tea Boy
One thing I failed to take into consideration when calculating signal-to-noise ratio is that the star is embedded within dust. (Notice in Robert Gendler's image that there are dozens of nearby stars that are just above the detection threshold. Those stars are more deeply embedded but may be just as intrinsically bright as the variable star but because their light is diminished by the dust they are barely detected.)
Of the many levers I can pull in my SNR calculator there is one that addresses this case most directly: Sky Brightness. Currently I have sky brightness set to Bortle 2 but that would only apply to stars against dark space. Since it is not then I will bump up sky brightness to Bortle 3 or perhaps 4. That should give me more realistic estimates of SNR when evaluating other scopes.
Brian
Of the many levers I can pull in my SNR calculator there is one that addresses this case most directly: Sky Brightness. Currently I have sky brightness set to Bortle 2 but that would only apply to stars against dark space. Since it is not then I will bump up sky brightness to Bortle 3 or perhaps 4. That should give me more realistic estimates of SNR when evaluating other scopes.
Brian
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