Convention regarding inclination sign

[VChristiaens]

Hi @tomasstolker, first thanks for making this very nice and well-documented package public! I am sure it will be very useful to the community!
I was wondering what was the convention re: +/- sign in front of the inclination, in terms of where the near/far side of the disc is located in those respective cases.
Based on your LkCa15 example, am I right to assume that the part of the disc located counter-clockwise from the PA of semi-major axis is the far (resp. near) side when the sign is positive (resp. negative)?
Sorry if this information is provided somewhere and I missed it. Otherwise, I'd suggest to add it in the description of the inclination parameter. Thanks again!

[tomasstolker]

Hi @VChristiaens,

Good to hear that diskmap has been useful!

Based on your LkCa15 example, am I right to assume that the part of the disc located counter-clockwise from the PA of semi-major axis is the far (resp. near) side when the sign is positive (resp. negative)?

Yes that is correct. So for an inclination of 0-90 deg and a position angle of 0 deg, the near side will be on the right side of the image. By increasing the position angle, the mapping will rotate in counter-clockwise direction. To be sure, the easiest is to check the _radius.fits file with using a somewhat large inclination. In that case the distances on the near side will show up as more strongly compressed compared to the far side.

Thanks for pointing that out. I will make a note in the documentation!

[SwastikC]

Hi. @tomasstolker . I am little confused regarding the inclination angle. I am using radmc-3d to model my disk and there I have say -50 degrees as inclination angle and 60 as the posang. How would those convert to if I give them as input to diskmap ? Can you please help me out ? :)

[tomasstolker]

Hi @SwastikC,

This is best determined from the _radius.fits that is part of the output. Because of the vertical disk height, the projected disk surface will look compressed on the near side of the disk minor axis. See figure 1 and the contours in figure 2 of this article. Depending on the definition, it could be that instead of -50 deg, you would need to set -50+180 = 130 deg for the inclination.

In case it is not clear what the near side is in the RT model, then this can be tested by calculating a synthetic image at a wavelength (e.g. 1 micron) that shows mainly scattered light at large separations from the star. The near side is then usually brighter in total intensity compared to the far side.

I hope this helps but let me know otherwise!