Doubles stars whit Astroart7

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FrankAdam
Posts: 7
Joined: 12 Dec 2019, 14:42

Doubles stars whit Astroart7

Post by FrankAdam » 12 Dec 2019, 15:35

Hello, I think very seriously buy the latest version of the program Astroart. Since I am passionate about double stars, I would like to know if there is a presentation of the functions dedicated to the measurement and the position of the system of double stars in the last version. In case it would not have been wanted, do you plan to include some extensions related to this field of astrometry?

thank you so much

François

fabdev
Posts: 198
Joined: 03 Dec 2018, 21:43

Re: Doubles stars whit Astroart7

Post by fabdev » 12 Dec 2019, 20:19

Hello, once the image is platesolved (or astrometrically calibrated) the separation and position angle can be shown by the Stars Window. Select the two stars, then right click for the context menu:
other calculations could be done by a script, here is a simple example for calculating again the separation:

Code: Select all

ra1 = Image.Stars.RA(1)
de1 = Image.Stars.DEC(1)
ra2 = Image.Stars.RA(2)
de2 = Image.Stars.DEC(2)
deltaDE = de1 - de2
cosDE = Cos(DegToRad((de1+de2)/2))
deltaRA = (ra1-ra2) * cosDE
separation = Sqr(deltaDE^2 + deltaRA^2)
print ra1 ; de1 ; ra2 ; de2 ; separation * 3600
which calculations/features do you need exactly ?

FrankAdam
Posts: 7
Joined: 12 Dec 2019, 14:42

Re: Doubles stars whit Astroart7

Post by FrankAdam » 12 Dec 2019, 21:00

Thanks fabdev for this answer so fast, I appreciate it a lot. It's very exciting to see that it really seems very simple. How can I be sure that I am safe on the centroid of my star when I select it? I know there is the Profile function but I can not see the link being both.
Thank you very much for your advice!
François

fabdev
Posts: 198
Joined: 03 Dec 2018, 21:43

Re: Doubles stars whit Astroart7

Post by fabdev » 12 Dec 2019, 21:50

To be safe on the centroid you must choose an Aperture which contains pixels only of one star.
For this reason in that example I used an Aperture of 3 for the faint star and an Aperture of 5 for the bright one. The Aperture can be changed in the Preferences.

The centroids are calculated with weighted center of mass of the pixels inside the Aperture (with fractional weight for the border). For example, with an Aperture of 5 pixels, the Area (number of pixels used) is 2.5 x 2.5 x PI = 19.6349... pixels. The Aperture itself is placed on a fractional coordinates using an iterative algorithm, very close to the centroid.

If the two stars are so close that form a single "shape", then it's not possible to calculate with this method. In this case only a plugin which analyze the shape of the star could do the job.

FrankAdam
Posts: 7
Joined: 12 Dec 2019, 14:42

Re: Doubles stars whit Astroart7

Post by FrankAdam » 12 Dec 2019, 23:21

Thanks for these informations.
However, I would like to know how to display the information related to the angle position in relation to the north of the calibrated image? Aladin tells me a 57.8 degree angle separation while Astroart gives me 152.420 degrees.
thanks again
François

fabdev
Posts: 198
Joined: 03 Dec 2018, 21:43

Re: Doubles stars whit Astroart7

Post by fabdev » 12 Dec 2019, 23:57

The position angle is the trigonometric one, so measured from RA West (so it's not compatible for binary stars). To convert you need to subtract 90. Thanks for letting me know, in SP3 both angles will be shown. Meanwhile here's the script to calculate the correct P.A. for binary stars:

Code: Select all

ra1 = Image.Stars.RA(1)
de1 = Image.Stars.DEC(1)
ra2 = Image.Stars.RA(2)
de2 = Image.Stars.DEC(2)
deltaDE = de2 - de1
cosDE = Cos(DegToRad((de1+de2)/2))
deltaRA = (ra2 - ra1) * cosDE
separation = Sqr(deltaDE^2 + deltaRA^2)
posAngle = RadToDeg(atan2(deltaRa,deltaDe))
print separation*3600 ; posAngle


so, in your example the calculated P.A. will be 152.40 - 90 = 62.40 degrees. Maybe the difference is caused by the extreme saturation of the bright star (?)

FrankAdam
Posts: 7
Joined: 12 Dec 2019, 14:42

Re: Doubles stars whit Astroart7

Post by FrankAdam » 13 Dec 2019, 00:35

Since I'm really not very good at computer programming, am I supposed to copy this script to where in the program? One thing is certain your support is really great and you have convinced me to buy this program. Also, is there a version of the French help manual? Thank you a thousand times again!

fabdev
Posts: 198
Joined: 03 Dec 2018, 21:43

Re: Doubles stars whit Astroart7

Post by fabdev » 13 Dec 2019, 00:50

Thanks again for discovering the problem about binary stars position angles.

The Script Window can be opened from the menu: Plugin/Camera control 7.0/
There are several demo scripts to learn quickly the language. The french manual is not available though.

merlin66
Posts: 12
Joined: 08 Jan 2019, 05:38

Re: Doubles stars whit Astroart7

Post by merlin66 » 13 Dec 2019, 15:32

Frank,
For serious double star measurements I'd also consider REDUC, from florent_losse@yahoo.fr
It's a very versatile program.
http://astrosurf.com/hfosaf/
Drop Florent an email to obtain a copy.
Ken

FrankAdam
Posts: 7
Joined: 12 Dec 2019, 14:42

Re: Doubles stars whit Astroart7

Post by FrankAdam » 15 Dec 2019, 15:15

Thank's Ken i will ask for this program to.
Frank

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