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Whirlwind

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About Whirlwind

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    Star Forming

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    Leicester
  1. Whirlwind

    Detecting exoplanet

    You should be able to increase the exposure time then (I'm assuming it was perfect conditions, no high cloud etc). However, it will reduce the sampling of the transit (especially the ingress and egress). You would be able to bin data points if you left it at 30s as well if you needed to so I'd probably leave it at this.
  2. Whirlwind

    Detecting exoplanet

    Is that the median value across the aperture or is it the highest pixel value? It is the highest pixel value that is important and it is this that needs to be less than about 35000
  3. Whirlwind

    Detecting exoplanet

    I haven't used Itelescope so am not sure what software you are given access to. I am assuming a lot is hidden behind a web interface to stop people messing with settings. As such it really depends on whether you get an active display or not that you can put an aperture over. It will still be 16 bit converter though although the maximum well depth will be greater than 100,000 I'm assuming it will report back only 65536 maximum levels (2^16). So you want roughly half of this value in any one pixel on average, it will swing below this and above this during you observations and it will change steadily because of the airmass change (pointing altitude). Looking at the spectral type (K2V) you'll probably want to use the V filter (not the B or I). If you can't see the output flux live then you should email itelescope and see whether they have any test exposures of varying exposures for the telescope using this filter. This way you'll get a good idea of what exposure you might need. If you are unsure on the night it is best to err on shorter exposures. You can always bin short exposures to increase your signal to noise. If you loose flux due non-linearity/bleeding then you can't recover this.
  4. Have you had a look at the videos/DVDs from the same person? I found these useful to allow you to see how things work initially.
  5. Whirlwind

    Detecting exoplanet

    You might not need to guide as long as the tracking can keep the object on the roughly the same pixels over the three hours and there isn't a drift. It is a paramount so I would be hopeful. It also has a large pixel scale (4.4") so any residual PE should be less important. To put it into context this setup used a 115mm refractor:- http://var2.astro.cz/EN/tresca/transit-detail.php?id=1514312910 It is a much less sensitive CCD as well and still observed the transit using 60 seconds exposures. So on the T5 with approx 3 times the aperture (after taking into account the central obstruction) and a CCD that is close to twice as sensitive I would The full well depth is greater but you still only want to reach that to about 50% in any one particular exposure. Otherwise sudden improvements in seeing, high cloud can result in pixels reaching non-pixel regimes and blooming. My best guess would be that you won't need anything more than 30s and even that might be too much.... At these length exposures you shouldn't really need guiding as long as the mount is working properly.
  6. Whirlwind

    Detecting exoplanet

    OK, well you could use the T5 instead. That should get you some more time. The transit appears to be just short of two hours which means you need 3 hrs minimum really (30 mins before and after the transit). Here is an example using a C8. The T5 is a 10" (likely in better conditions). http://var2.astro.cz/EN/tresca/transit-detail.php?id=1382798470
  7. Whirlwind

    Detecting exoplanet

    I would suggest that if you've never undertaken transit photometry before then I would stay well away from these telescopes to start with otherwise you might find it's an expensive waste of money. Even someone that knew what they were doing from a transit photometry perspective (bur didn't know the telescopes) would likely need 30 minutes just to find the settings that they would need. If you have your own equipment then try using this first. WASP exoplanets were all found using camera lenses. If you have even some modest equipment like a C8 and a DSLR then you should be able to capture these from your own home. Once you are comfortable with this methodology and you want to advance then you can start to think of using the semi-professional set ups. You can even practice with some variable stars first (there are examples on this forum). Oh and there is a database here that will give you transit times:- http://var2.astro.cz/ETD/index.php
  8. It was for the setting circles. Back before anything was electronic those numbered dials allowed you to move straight to the target of interest with nothing more than a sky atlas. Then you only then have to turn one of the rods to keep it on track. As rightly noted though many of the cheap Eq mounts were very wobbly and not really suitable for the telescopes placed on them. Obviously now the Altaz options are a lot more advanced and I get the impression that 'star hopping' is more common to find a target.
  9. Whirlwind

    SX-694 CCD clean and re-gas?

    Yes, you need to purge the chamber of air. Otherwise when you cool the camera you can risk water vapour condensing onto the CCD itself. Unless you have a clean room you can use, it is likely that by opening up the camera to the air this will risk more dust getting onto the CCD than the benefit of removing the dust you already have. You can use this tool to give you an idea of the location of the dust:- http://www.ccdware.com/resources/dust.cfm
  10. I'm not sure the seal is good enough as it stands to purge the environment. The casing would probably need some significant changes to be able to effectively purge the atmosphere. The dome is designed to be easily replaceable if it is scratched etc.
  11. I have the same camera, but don't get the same issue. The outside will fog over after rain but not form condensation inside the way yours does (and its cleared after about an hour). I leave my heater on permanently. I would agree that it is likely a ventilation issue. Regardless of how well you screw on the dome you won't have a perfect seal. As such humidity will leach inside. The lack of air flow will trap air generally however. What happens is this - the dome is exposed to daylight. It acts as a greenhouse so the air inside warms up (even the dew heater can cause this slightly). The dome is being cooled by the air outside and you will probably find it is 10C or more difference in the direct sunlight. The dew heater is designed to keep the dome temperature slightly above the outside radiative temperature on a clear night. So you have warm air inside, which holds more moisture. The outside air cools the dome. The dome is hence cooler than the inside ambient air and hence when the water molecules hit the dome they lose energy. This will cause moisture to condense on the inside of the dome. The reason for ventilation is that it means the air is the same temperature inside and outside. The dome is therefore the same temperature. Moisture will hence no longer condense onto the inside of the dome (indeed the dew heater keeps it slightly warmer) to help prevent this.
  12. Whirlwind

    Weird Noise

    I think you might be misunderstanding what dithering is there to do. At a basic level there are two types of noise that need to be considered. 1) There is a type of fixed noise which may be better described as known errors on the camera. These are things like hot pixels, cold pixels and so forth, bad columns and so forth. These stay in the same location all the time. Darks and bias can partially correct for these but they can accrue charge in a non-linear way which means even with dark/bias correction they can still partially exist (this is particularly relevant for non temperature controlled cameras). If your tracking is so accurate that the points will always fall on the same point in your image then when you combine them it will reinforce this artefact and you will end up with little bright or dark spots over the image. 2) There is random noise. This comes from that it is statistically impossible to measure something at the highest levels of precision. If as an example the flux arriving at a pixel is 300 counts then when you image the object you would find that the you get a range of values with greater frequency towards the actual value. So over five images you may get the following values 295, 298,299, 301, 308. This is called random or gaussian noise. It is impossible to predict the exact value you will measure from image to image. However, it is random and follows a gaussian statistical variation. As such because some values will be lower and some higher you can median or mean (average) combine such data and the result will trend to the 'real' value of 300. The more images you take the more you can average out these random fluctuations. Hence this is why you take multiple images and stack them. When you process the data you exaggerate this effect as you are trying to pull out the slight variations to the signal (for example in a nebula) that might be very similar to the level of random noise you get. Hence with too few images averaged then what is real and what is noise becomes confused. This is what causes the mottling effect. The more images you take the more you can average out the background noise and the more certain you are as to what is data and what isn't. Hence when people refer to images being overdone, overcooked this is what is happening. The details have been over processed to the point that the noise is being processed not 'real' signal. So why dithering? Well dithering is a random jump of your camera close to the target of interest. It makes no difference to random noise because it is not based on a specific location. Wherever you point your camera you will get random noise. On the other hand the fixed point noise (like hot pixels) are tied to specific pixels, columns and so forth. As such they will move about your image when your slightly shift (dither) the telescope. Most software when it combines data will reject any that are hugely discrepant from the average data in your image when tied to a fixed position through star alignment. So suppose you had a hot pixel that had been dithered once at a specific sky position. You may get something in counts like this:- 300, 299, 306, 295, 301, 2000. The software will recognise the last value as discrepant and then ignore that data for that specific pixel and reject it. If you don't dither you would get something like:- 1999, 1998, 2003, 2007 2003, 2000. Hence the software won't recognise that this is a hot pixel but consider it a real value and include it on your image. What you end up with is an image that has scattered single pixel bright spots because of this type of fixed noise. As such when noted above that your image looks like dithering is working it is because there doesn't appear to be any single pixels that are overly bright for their location. The noise you are looking at is random noise which can't be fixed by dithering, only by taking more images and you can never get rid of it completely. So it becomes a balance as to how much time you want to spend on an object and how much processing you can get away with before the remaining noise becomes distracting.
  13. Whirlwind

    Starlight Express SXVF-M8C buy used?

    It will be a smaller FOV than 700D and is quite narrow. Try running it through Astronomy Tools. It has small pixels though so should give you a decent image scale. It should be a decent camera if you can live with the rectangular FOV. Probably better for smaller galaxy work (e.g. M51) rather than larger nebula (e.g. M42)
  14. Whirlwind

    Telescope vs Airport security

    I tend to find that they are more concerned with the clock drives (like the Star Adventurer) than the glass itself. I can see the point in this to some extent. However I think in the main you'll tend to find people are more suspicious with what they don't know. Flying back from La Palma in the canary's is likely to be easier because they will have simply come across telescopes more often.
  15. Whirlwind

    Strange vignetting/internal reflections

    I would suggest this might be a specific issue with the STF and the reducer. From the images of the camera it has a plastic shield in front that is only slightly larger than CCD itself. In addition it looks like the CCD is set quite far back from this plastic cover plate. Add in a 'fast' light cone and what I would suggest is that light is being diffracted off the plastic cover plate onto the CCD. So I would agree that it is probably a knife edge effect. To confirm what I would do is rotate the camera solely relative to everything else (including the filter wheel). If the same pattern stays then it has to be from the camera itself.
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