12 replies to this topic

[CraigT82]

Hello,

 

This is my first exoplanet transit detection attempt. I used a 102mm ED doublet frac with an ASI533mc & UV/IR filter.

 

After getting some good advice on how to choose a target by Dr Paul Leyland over on BAA forum I chose HAT-P-32b, as it was a relatively deep transit of a mag 11.15 star, high in the sky and not crossing the meridian. 
 

All data processing done in AIJ. I used Patriot Astro’s tutorial on YouTube and Richard Lee’s workflow based guide to AIJ access at the BAA website to help me with the work in AIJ ( my IT skills are non existent and I often struggle with software - so I found it particularly difficult and wouldn’t be surprised if I got things wrong in AIJ). I also tried HOPS but couldn’t get it to work. 
 

Anyway here is the first of hopefully many light curves from me. It was immensely satisfying watching AIJ plot out those points for the first time and I dare say quite addictive! 

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[timmywampus]

that must be immensely satisfying to do on your own equipment.  i've listened to many interviews and blogs regarding exoplanet detection through transit and the odds just blow me away.  the remote star's ecliptic having to be oriented correctly toward us is the most amazing thing to me.  congratulations on the data aligning so well with model prediction, that is awesome!

[GaryShaw]

Nice first transit capture Craig. What caused the data gap during mid transit?

 

When/if you get around to reporting your observations, don’t neglect to include all the data labels, a few comp star data plots ( often a second light curve page) and, importantly, the systematics which go at the bottom of the main data plot and transit ‘fit’. The systematics include: Airmass, tot_C_cnts, Width_T1, X(FITS), Y(FITS) and SkyPixel_T1. These are all explained in Dennis Conti’s Guide to Exoplanet Observations which is the Gold Standard for AIJ observations, analysis and reporting to the NASA archive. 

Gary 

Edited by GaryShaw, 08 February 2025 - 11:37 AM.

[CraigT82]

that must be immensely satisfying to do on your own equipment.  i've listened to many interviews and blogs regarding exoplanet detection through transit and the odds just blow me away.  the remote star's ecliptic having to be oriented correctly toward us is the most amazing thing to me.  congratulations on the data aligning so well with model prediction, that is awesome!

Thanks for the comments. Coming from a more mainstream imaging background - where you at least have an idea if you have had a successful session by inspecting the subs as they come in - this was actually thrilling as I had absolutely no idea how successful I’d been until I hit enter after placing the apertures and watched the plot grow across the screen, hoping for that dip to appear!

[CraigT82]

Nice first transit capture Craig. What caused the data gap during mid transit?

 

When/if you get around to reporting your observations, don’t neglect to include all the data labels, a few comp star data plots ( often a second light curve page) and, importantly, the systematics which go at the bottom of the main data plot and transit ‘fit’. The systematics include: Airmass, tot_C_cnts, Width_T1, X(FITS), Y(FITS) and SkyPixel_T1. These are all explained in Dennis Conti’s Guide to Exoplanet Observations which is the Gold Standard for AIJ observations, analysis and reporting to the NASA archive. 

Gary 

Thanks Gary. The gap mid transit is passing cloud. Also the post egress captures were ruined by clouds too. I did have a look through Dennis’ guide a couple of weeks ago but I will have a closer look at it. 

[Xilman]

I am particularly impressed by seeing such a successful result coming from a 100mm aperture. Most people suggest that twice that is entry-level for the field of exoplanet transit observations.

 

Paul

[Xilman]

that must be immensely satisfying to do on your own equipment.  i've listened to many interviews and blogs regarding exoplanet detection through transit and the odds just blow me away.  the remote star's ecliptic having to be oriented correctly toward us is the most amazing thing to me.  congratulations on the data aligning so well with model prediction, that is awesome!

Actually, it should perhaps be more satisfying to see that the prediction is not perfect. The whole point of this kind of observation is to check the quality of the predictions. Any discrepancy between model and reality can be used to refine the orbital parameters and hence make more accurate predictions of future transits.

 

Paul

[Tapio]

You can do it even with DSLR and telephoto.

https://www.cloudyni...telephote-lens/

[GaryShaw]

Hi

There are several parameters to look at in order to gage the quality of an observation. These include:

 

- the RMS of the Fit Statistics: below 5.00 is decent, below 3 is preferred ( shown on AIJ Page Titled:  rel_flux _T1 which is not included above) 

- the transit ‘Depth’ compared to that shown in the current NASA archive (~23 I believe)

- a parameter called a/R* which is about 6.0 in the NASA archive ( also shown on AIJ Page Titled: rel_flux_T1 which is not included above)

 

Of the above, the first is the most common value reflecting the overall quality of the curve fit.

 

Although many of the more subtle parameters are difficult to get accurately with modest instruments and novice observation practices, very modest backyard gear can often contribute to the refinement of the exoplanet ephemera such as the mid- transit time in BJD TDB. If I had one photometric filter to use for such observations, it would be a Chroma or Baader (lower cost) V filter. Barring those, I’d go unfiltered rather than use a UV/IR cut filter. Unfiltered allows for the highest cadence which is valuable in accurate curve fitting.
 

Another very general guideline I would offer is to get as many images as quickly as you can, ie shortest exposure, so long as you can achieve an SNR at or close to 100. This is especially applicable to modest equipment when you’re going for accuracy on the mid-transit time Tc - assuming you capture the entire transit and at least 30 minutes before and after. 
Hope some of this helps.

Gary

Edited by GaryShaw, 09 February 2025 - 12:46 PM.

[GaryShaw]

Actually, it should perhaps be more satisfying to see that the prediction is not perfect. The whole point of this kind of observation is to check the quality of the predictions. Any discrepancy between model and reality can be used to refine the orbital parameters and hence make more accurate predictions of future transits.

 

Paul

Hi Paul

The above is quite correct when viewed in the context of the early stages of data acquisition on a relatively new target.  Once you work with targets, like Hat-P-32b, that have become extremely well documented and whose ephemera are well-established, you should expect that a good observation would yield data results very close to those in the NASA Archive.

Gary

[pvdv]

- a parameter called a/R* which is about 6.0 in the NASA archive ( also shown on AIJ Page Titled: rel_flux_T1 which is not included above)

Essentially the semi-major axis of the orbit of the planet. Direct application of Kepler's third law if the transit is nicely aligned. 
Or, in not so aligned cases, through the use of the "impact parameter" (reflects centers misalignment) which can be derived from the transit shape.
And as you said, that one is pretty well defined, so it is a good idea to see how close one gets to the known value to assess ones own work.

Further down the road and on less established transits one has to keep in mind that one assesses probability distributions for the independently measured parameters (corner plots to visualize) and that AIP's modeling will give you the most probable fit among possibly many (which is essentially why, now and then, the assumptions prove to be all wrong )  

[Xilman]

Hi Paul

The above is quite correct when viewed in the context of the early stages of data acquisition on a relatively new target.  Once you work with targets, like Hat-P-32b, that have become extremely well documented and whose ephemera are well-established, you should expect that a good observation would yield data results very close to those in the NASA Archive.

Gary

Yes but ...

 

 

The Exoclock project is targetting exoplanets with well-established ephemera, specifically to refine those ephemera. The reason: to enable predictions good to a very few minutes up to a decade ahead so that the ARIEL satellite can spend its limited observing time watching a transit rather than having to wait for (or worse, be too late for) a transit. A discrepancy of, say, two minutes now can easily grow to the best part of an hour by 2030.

 

https://www.exoclock.space/ and https://arielmission.space/ for more information.

 

Paul

[Xilman]

Yes but ...

Further, discrepancies between predicted and observed times are the smoking gun for TTVs --- transit timing variations --- which could well arise from the gravitational perturbations of other planets in the system. Those planets may only rarely, or never, transit the star and TTVs are the best way of detecting them and characterizing their orbits.