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Detect exoplanets by yourself with the cheapest equipment

alberto91

By alberto91
in Imaging - Deep Sky

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alberto91

alberto91

Posted
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Hi guys,

I detected my first exoplanet (hd 189733 b) and made a video about it showing step by step how I did it. I thought it could be useful for the people interested in the topic or already starting with transit photometry.

The star has an apparent magnitude of 7.7 and the exoplanet produces a drop of 2.8% during almost 2 hours.

I used a tele-photo lens (the Pentacon 135 mm f 2.8 ), a CMOS camera (ZWO ASI 120 MM) and an equatorial mount (Skywatcher EQ3-2)

I also have a dual-axis motor drive, but a simple one that only controls the right ascension would be enough.

I bought most of the items second-hand from Ebay and I spent around 300 euros.

To set up the tele-photo lens and the camera I have a couple of guide rings and in order to focus the tele-photo lens, I have to separate it 33 mm from the camera by using for example 2 M42 extension rings, one of them 28 mm long and the other one 5 mm.

Now, the steps to detect the exoplanet are the following:

  1. Find out when is the exoplanet going to transit the star with the Exoplanet Transit Database.
  2. With a program called SharpCap, take for example 5-second exposures with a gain of 1 for 3 hours.
  3. Once the transit has finished, with a program called ‘AstroImageJ’ open all the images, select the target star and for example a couple of reference stars, and perform multi-aperture photometry to detect the light curve.

I think it is better explained with a video: https://www.youtube.com/watch?list=PL3RiFKfZj3pv1ZqpFxuZinoGtUGEOankw&v=XHCppdWYs6w

 

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gorann

gorann

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Interesting!

To be sure that you are not only measuring changes in your atmosphere that affects the brightness of the star that you interpret as an exoplanet passing (especially when it only involves a 2 % drop in brightness) it would be more convincing to do several measurements during transist and between transits and compare these.

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Stub Mandrel

Stub Mandrel

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15 hours ago, gorann said:

Interesting!

To be sure that you are not only measuring changes in your atmosphere that affects the brightness of the star that you interpret as an exoplanet passing (especially when it only involves a 2 % drop in brightness) it would be more convincing to do several measurements during transist and between transits and compare these.

Isn't that why you use a selection of nearby reference stars?

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alberto91

alberto91

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On 15/10/2018 at 17:26, PaulM said:

Brilliant and great video :)

How would you go about finding out good candidate stars to do this on, shortish transit with a detectable dip in brightness?

Thanks everybody for the kind words! I really appreciate them :)

And thanks for the tips!

Yes, I would go for the brightest stars and the dippest drops in brightness.

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michael8554

michael8554

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Made a start tonight by testing my setup on WASP-33b, aka HD 15082 in Andromeda.

The next transit is on the 22nd at 21:40, lasts about 160 minutes.

Using my 200mm FL guidescope and ZWO ASI 120 MM. which gives 82 x 62 arcmins FOV.

I did a Goto Almach, centred, SYNCH'd, then GoTo'd the target - spot on when comparing with the 15 x 15 arcmins Digitized Sky Survey image on the ETD site.

I've only used SharpCap briefly for Solar, so which combination of exposure and Gain should I use to be sure the stars aren't saturated, which I assume is crucial if a dip is going to be detected?

I used the "Highlight Over Exposed" FX, but even on 1 second exposure and 50% gain it was still showing red on the target star, but when I checked the recordings later it measured only 217 (out of 255) on the 5 second/100% Gain images?

Having now had time to read the User Manual I see there's a histogram I hadn't spotted, and a box I can put around the target star   ?

Will try the AStroImageJ software tomorrow.

Michael

 

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alberto91

alberto91

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15 hours ago, michael8554 said:

Made a start tonight by testing my setup on WASP-33b, aka HD 15082 in Andromeda.

The next transit is on the 22nd at 21:40, lasts about 160 minutes.

Using my 200mm FL guidescope and ZWO ASI 120 MM. which gives 82 x 62 arcmins FOV.

I did a Goto Almach, centred, SYNCH'd, then GoTo'd the target - spot on when comparing with the 15 x 15 arcmins Digitized Sky Survey image on the ETD site.

I've only used SharpCap briefly for Solar, so which combination of exposure and Gain should I use to be sure the stars aren't saturated, which I assume is crucial if a dip is going to be detected?

I used the "Highlight Over Exposed" FX, but even on 1 second exposure and 50% gain it was still showing red on the target star, but when I checked the recordings later it measured only 217 (out of 255) on the 5 second/100% Gain images?

Having now had time to read the User Manual I see there's a histogram I hadn't spotted, and a box I can put around the target star   ?

Will try the AStroImageJ software tomorrow.

Michael

 

Great target !

mm yes, I guess it is a matter of try/fail to find the right exposure/gain to avoid over saturation

I checked the ETD and saw that wasp 33 is 8.3 magnitude and 1.5 % dip so...

I would increase the exposure a bit, to for example 10, and greatly reduce the gain, to for example, 3

I'm sure the experts in the forum can give you better advices !

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michael8554

michael8554

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I misinterpreted Alberto's Sharpcap gain setting of 1 to be 100, so no wonder my test files were saturated !

Part 2 of setting up was AstroImageJ.

On running it prompted to find javaw.exe

This was in system32, but the AstroImage browser would only show the folders in system32, and none of the many files not in folders, including javaw.exe.

Show hidden system files was already enabled.

In the end I put a copy of javaw.exe in the AstroImageJ folder, which worked.

Run AstroImage as an Administrator.

The first of the three star selection circles has to be just bigger than the star, not small enough to fit inside as I first thought.

The second and third must fall outside the star profile, they measure the background.

This is tricky because  WASP-33b has another star very close by.

I thought the prog wasn't working until I spotted the result graph was showing tiny blue spots, not the joined-up lines in Alberto's video - some setting I guess.

So tomorrow night 22nd it's All Sytems Go.........

I was running out of big galaxies and nebula to image, so this has come at a good time.

Michael

 

 

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Victor Boesen

Victor Boesen

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Just now, michael8554 said:

I misinterpreted Alberto's Sharpcap gain setting of 1 to be 100, so no wonder my test files were saturated !

Part 2 of setting up was AstroImageJ.

On running it prompted to find javaw.exe

This was in system32, but the AstroImage browser would only show the folders in system32, and none of the many files not in folders, including javaw.exe.

Show hidden system files was already enabled.

In the end I put a copy of javaw.exe in the AstroImageJ folder, which worked.

Run AstroImage as an Administrator.

The first of the three star selection circles has to be just bigger than the star, not small enough to fit inside as I first thought.

The second and third must fall outside the star profile, they measure the background.

This is tricky because  WASP-33b has another star very close by.

I thought the prog wasn't working until I spotted the result graph was showing tiny blue spots, not the joined-up lines in Alberto's video - some setting I guess.

So tomorrow night 22nd it's All Sytems Go.........

Michael

 

 

Excited to hear about the outcome!! Good luck from here.

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Shibby

Shibby

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Nice work! Good to see you managed this with budget equipment. I've been trying my hand a photometry recently, although I haven't posted anything on SGL. (Photometry normally goes in this forum though: https://stargazerslounge.com/forum/52-observing-and-imaging-double-and-variable-stars/ )

On 15/10/2018 at 16:26, PaulM said:

How would you go about finding out good candidate stars to do this on, shortish transit with a detectable dip in brightness?

I've been using this transit finder: https://astro.swarthmore.edu/transits.cgi

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michael8554

michael8554

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Last night was not without its trials.

Started to image 10 minutes before the transit, with 5 second exposures every 2 minutes.

Except SharpCap wouldn't go into record.

And refused to shut down, Ctrl-Alt-Del took forever to take effect.

So I got very few frames of the normal brightness before the transit.

The results don't show any sign of a dip as far as I can tell.

But early days, steep learning curve etc,  Kepler-447b, WASP-135b, Kepler-785b, Kepler 76b etc  all beckon....,,,

Michael

Measurements.jpg.6cf5e7aede5de944ffda7d42c7c207ee.jpg

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Shibby

Shibby

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On 23/10/2018 at 17:53, michael8554 said:

The results don't show any sign of a dip as far as I can tell.

Precise measurements can be very difficult. What magnitude of star were you imaging, and how deep is the dip you're looking for? For a mag 12 star, I settled on 120s exposures, so 5s seems a bit short if you're hoping for a good star profile? Also, how many reference stars are you using? The more the better, but it's best if they have similar colour profiles to your target.

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Whirlwind

Whirlwind

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On ‎23‎/‎10‎/‎2018 at 17:53, michael8554 said:

Last night was not without its trials.

Started to image 10 minutes before the transit, with 5 second exposures every 2 minutes.

Michael

 

This method isn't great really because you are dumping a lot of potential data.  What you want to do is take 5 second exposures continuously and then (if you want to) is bin the data into 2 minute sections (take a median of the values in each block).

This will median out issues related to seeing conditions and so forth.  The comparison stars are there to remove large long term trends (for example high cloud) but you still want as much data as possible.  Also always start at least 30 minutes before a transit as that will allow you to median more out of transit points.  Ten minutes (five data points) before is way too small really.

 

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michael8554

michael8554

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10 hours ago, Shibby said:

For a mag 12 star, I settled on 120s exposures, so 5s seems a bit short if you're hoping for a good star profile

WASP-33b is Mag 8.3, exposure was 5 seconds with gain 5, any higher saturated.

120s ? No chance !

But Whirlwind's suggestion to median stack gives a similar result ?

Michael 

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Whirlwind

Whirlwind

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1 hour ago, michael8554 said:

WASP-33b is Mag 8.3, exposure was 5 seconds with gain 5, any higher saturated.

120s ? No chance !

But Whirlwind's suggestion to median stack gives a similar result ?

Michael 

Hmmm, when you say 5 seconds almost saturated is that literally what you mean?  The flux in any individual pixel should never be more than about 50%-60% of your full well depth.  If you are at 80% or 90% not only are you at risk of being non-linear (regardless of what the paperwork says), but any sudden improvement in seeing can take individual pixels to the saturation limit.  Even professional astronomers with non-anti blooming cameras don't try and exceed 75% of the well depth as even these have non-linear effects.  At the depths of transits that's never a good thing.

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