# About HD 5388 b's mass and the true mass of exoplanets at high inclinations

## About HD 5388 b's mass and the true mass of exoplanets at high inclinations

True mass of an exoplanet can be obtained dividing minimum mass value by the sine of the inclination

To say:

Mass

Inclination = 1.5° and sin i = ca. 0.02356

Mass

This works well til the inclination is 90°, i.e. when planet is coplanar, right? When minimum and true mass coincide.

Things get strange when inclination value is greater than 90, and this is the case of HD 5388 b.

Its minimum mass was set at Mass

If I obtain sine of 178.3, I get 0.334 and doing the math the true mass I obtain is 5.87 Jupiter masses rather 69 ± 20 Jupiter masses displayed here.

Where's the error? Is there something I should add to calculation I am missing?

I need this answer for a planet building in a highly inclined binary system.

Thanks

To say:

Mass

_{min}= 6 Jupiter massesInclination = 1.5° and sin i = ca. 0.02356

Mass

_{true}= 6 : 0.02356 = ca. 254.7 Jupiter masses = ca. 0.25 Solar masses.This works well til the inclination is 90°, i.e. when planet is coplanar, right? When minimum and true mass coincide.

Things get strange when inclination value is greater than 90, and this is the case of HD 5388 b.

Its minimum mass was set at Mass

_{min}= 1.96 Jupiter masses and inclination value derived is i = 178.3°If I obtain sine of 178.3, I get 0.334 and doing the math the true mass I obtain is 5.87 Jupiter masses rather 69 ± 20 Jupiter masses displayed here.

Where's the error? Is there something I should add to calculation I am missing?

I need this answer for a planet building in a highly inclined binary system.

Thanks

**Edasich**- dM star
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## Re: About HD 5388 b's mass and the true mass of exoplanets at high inclinations

You're using grad instead of degrees in your use of the sine.

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**Sirius_Alpha**- Admin
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**Edasich**- dM star
- Number of posts : 1505

Location : Tau Ceti g - Mid Latitudes

Registration date : 2008-06-02

## Re: About HD 5388 b's mass and the true mass of exoplanets at high inclinations

The calculator that you are using to do the math, be sure you are in "degrees" mode, instead of "radians" or "grad."

You should get

sin(1.5°) = ~0.0262

sin(178.3°) = ~0.0297

You should get

sin(1.5°) = ~0.0262

sin(178.3°) = ~0.0297

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**Sirius_Alpha**- Admin
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## Re: About HD 5388 b's mass and the true mass of exoplanets at high inclinations

I got it. Had to calibrate my calculator. Now it works. Thanks Sirius

**Edasich**- dM star
- Number of posts : 1505

Location : Tau Ceti g - Mid Latitudes

Registration date : 2008-06-02

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