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galpy: A python Library for Galactic Dynamics

  • Authors: Jo Bovy

Bovy 2015 The Astrophysical Journal Supplement Series 216 29.

  • Provider: AAS Journals

Caption: Figure 24.

Oort functions A and B for a warm axisymmetric disk. The Oort functions A(R) and B(R) as well as the asymmetric drift (; v0 = vc(R0) = 1) are computed at R0 for warm diskdfs as a function of the radial-velocity-dispersion at R0. The difference between the Oort functions and the Oort constants, that is, the Oort functions for stars or gas on circular orbits, is displayed as a function of the asymmetric drift. The fiducial model is a dehnendf with an exponential surface-density profile with scale length hR = R0/3, an exponential radial-velocity-dispersion profile with scale length hσ = R0, and a flat rotation curve (β = 0). Different symbols indicate variations on this fiducial model. In particular, the triangle uses the family of shudf DFs, and the rotation-curve parameter β in vc(R) = vc(R0) (R/R0)β is varied over a wide range. The pair of "+" or "−" for each symbol indicates whether the difference whose absolute value is plotted is positive or negative for A and B, respectively; "?" for the Shu DF indicates that the sign of ΔB can be both positive and negative: all but the final three points are positive. All of the DF variations except for the one with the shorter hσ display the same close-to-linear trend with va for ΔA (this is difficult to see as many of the symbols overlap). The difference ΔB is also close to linear, but it depends more strongly on the form and parameters of the DF (all of the symbols including and below the lower sequence of diamonds are for |ΔB|). For a population on circular orbits A(va = 0) = (1 − β)/2 and B(va = 0) = −(1 + β)/2 in these natural units. Even though ΔB strongly depends on the properties of the DF, it only differs by ≲ 5% from the Oort constant B(va = 0), even for populations with large asymmetric drift.

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