Exoplanet Kepler-191d

[AMcD]

This is the second of the exoplanet light curves I obtained this past week using my remote controlled ROR observatory and a QHY8 OSC with a Baader UBVRI photometric filter on a TS152 achromatic refractor.  The scope and imaging train is mounted on a Losmandy G11 and guided with PHD2.  The data was obtained on the night of 23 to 24 June 2022 and was captured using SGPro.  Unlike the previous curve I posted for Kepler-1566b, and whilst the data is still very messy, the data for this observation produced a light curve in both AstroImage J and NASA EXOTIC (albeit a very shallow one in the latter).

Kepler-191d is part of a three planet system orbiting a 0.85M/sun star.  The planet has an orbital period of 5.9 days and has a radius of 2.28R/earth.  The system is 2219 light years from earth.  I still cannot quite get over the fact that this is possible with amateur equipment from the bottom of the garden...

AstroImageJ:

NASA EXOTIC:

Edited June 25, 2022 by AMcD
Corrected date.

[Xilman]

I have been recommend to use a R filter to reduce sky brightness and seeing. If you can't get a high enough SNR and cadence filtered, use unfiltered.

 

[Whirlwind]

On 26/06/2022 at 19:11, Xilman said:

I have been recommend to use a R filter to reduce sky brightness and seeing. If you can't get a high enough SNR and cadence filtered, use unfiltered.

 

For exoplanets you really want as much signal as you can get.  I think this might come from the principle that many short period planets are around cooler stars as even at short periods they might be habitable.  However around brighter hotter stars a red filter is just cutting out flux more than any benefit you will get from seeing or sky noise issues.   There is some benefit from using filters to identify binary stars (as depths will change dependent on the filter band).  But really you want as much signal as you can get.  If it is noisy just bin your data in time (not on the camera).

Also think you are doing something wrong in astroimagej as both your assessment are putting your data half a phase out of where the eclipse is.  So your T0 has been shifted for some reason.

Edited June 27, 2022 by Whirlwind
Missed something

[Xilman]

Just now, Whirlwind said:

For exoplanets you really want as much signal as you can get.  I think this might come from the principle that many short period planets are around cooler stars as even at short periods they might be habitable.  However around brighter hotter stars a red filter is just cutting out flux more than any benefit you will get from seeing or sky noise issues.   There is some benefit from using filters to identify binary stars (as depths will change dependent on the filter band).  But really you want as much signal as you can get.  If it is noisy just bin your data in time (not on the camera).

I was only passing on the advice given by the Exoclock collaboration.

As I understand it, which may be imperfectly, the use of a R filter can reduce the noise (from sky and from seeing) by more than the signal compared with unfiltered.

As for binning, I generally use 2x2 binning on the images downloaded from the camera. It doesn't reduce dynamic range but it does even out pixel-to-pixel sensitivity variations and it does reduce noise.  My advice: bin in time only if absolutely necessary to get the SNR. With a transit what is much more important, in pracfice, is precisionin  the orbital elements rather than in the size ratio of planet to the star. The former requires precise timing, the latter precise magnitudes.

But what do I know? I am not an exoplanetary expert, I just work with them.

[Whirlwind]

15 minutes ago, Xilman said:

As I understand it, which may be imperfectly, the use of a R filter can reduce the noise (from sky and from seeing) by more than the signal compared with unfiltered.

As for binning, I generally use 2x2 binning on the images downloaded from the camera. It doesn't reduce dynamic range but it does even out pixel-to-pixel sensitivity variations and it does reduce noise.  My advice: bin in time only if absolutely necessary to get the SNR. With a transit what is much more important, in pracfice, is precisionin  the orbital elements rather than in the size ratio of planet to the star. The former requires precise timing, the latter precise magnitudes.

I'm working on the principle and looking at the website that they are doing follow up detections.  Many of the space telescopes and even ground ones focus on cooler red stars.  Not only are the stars smaller, so transits have a larger impact they also occur more frequently.  On top of this their habitable zone is a lot closer to the star (so it's easier to identify potentially habitable planets).  Hence there is sense on what they are telling you as I expect many of the follow up stars are M and K stars.  Once you start to get hotter stars then a lot more flux is outside, what I assume is the R band filter.  Hence there is a balance that yes, red filters do reduce your noise but then you are also filtering a large fraction of light in bright, hotter stars.  However from a guidance perspective one simple message for the public is easier to explain.  It also ensures greater consistency of data (is the depth change because of noise or because it is a binary etc).

Yes, binning in time is for higher SNR, for most observatories (barring very large telescopes) you generally run multiple observations of the same object over and over to get the precision as you can phase fold the data.  But again the consortium are doing that with the various data sets I assume (again preference for consistency would be key in this approach).  On the other hand if you are doing it for 'fun' and just want to evidence you captured the object then time binning is likely to show the transit easier. 

[Xilman]

14 minutes ago, Whirlwind said:

I'm working on the principle and looking at the website that they are doing follow up detections.  Many of the space telescopes and even ground ones focus on cooler red stars.  Not only are the stars smaller, so transits have a larger impact they also occur more frequently.  On top of this their habitable zone is a lot closer to the star (so it's easier to identify potentially habitable planets).  Hence there is sense on what they are telling you as I expect many of the follow up stars are M and K stars.  Once you start to get hotter stars then a lot more flux is outside, what I assume is the R band filter.  Hence there is a balance that yes, red filters do reduce your noise but then you are also filtering a large fraction of light in bright, hotter stars.  However from a guidance perspective one simple message for the public is easier to explain.  It also ensures greater consistency of data (is the depth change because of noise or because it is a binary etc).

Yes, binning in time is for higher SNR, for most observatories (barring very large telescopes) you generally run multiple observations of the same object over and over to get the precision as you can phase fold the data.  But again the consortium are doing that with the various data sets I assume (again preference for consistency would be key in this approach).  On the other hand if you are doing it for 'fun' and just want to evidence you captured the object then time binning is likely to show the transit easier. 

Phase folding: the primary objective of the Exoclock project is to get accurate mid-eclipse timings. Mostly so that they can be predicted years in advance when the satellites fly. Time on them is limited and you don't want to miss a transit because the predictions are 20 minutes out based on ten year old observations! As I noted, the interest from amateur observations is accurate timings. Precise light curves, spectroscopy, etc can be done later by professionals with kit which does not yet exist.