tides.f

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      SUBROUTINE tides(QPERI,M1,M2,S1,S2,KSTAR,DE)
*
*
*       Tidal energy loss for interacting stars.
*       ----------------------------------------
*
      REAL*8  size(2),ratio(2),zeta(2),psi2(2),psi3(2),de(2),
     &        qperi,m1,m2,efac2,efac3,s1,s2,body(2)
      INTEGER kstar(2),ip(2)
*
*
*       Copy masses & radii to local arrays.
      body(1) = m1
      body(2) = m2
      SIZE(1) = s1
      SIZE(2) = s2
*
*       Assign the appropriate polytropic reference index (NP = 3/2 or 3).
      DO 5 k = 1,2
          kst = kstar(k)
          IF (kst.EQ.3.OR.kst.EQ.5.OR.kst.EQ.6) THEN
              ip(k) = 1
          ELSE
              ip(k) = 3
          END IF
    5 CONTINUE
*
*       Form dimensionless ratios & tidal efficiency factors for each star.
      DO 10 k = 1,2
          l = 3 - k
          ratio(k) = SIZE(k)/qperi
          IF (ratio(k).GT.0.1) THEN
              icase = ip(k)
              zeta(k) = sqrt((body(k)/(body(k) + body(l)))/ratio(k)**3)
              psi2(k) = efac2(zeta(k),icase)
              psi3(k) = efac3(zeta(k),icase)
          END IF
   10 CONTINUE
*
*       Obtain energy loss due to second & third order modes.
      DO 20 k = 1,2
          l = 3 - k
          IF (ratio(k).GT.0.1) THEN
              r2 = ratio(k)**2
              r6 = r2*r2*r2
              de(k) = r6*(psi2(k) + r2*psi3(k))*body(l)**2/SIZE(k)
          ELSE
              de(k) = 0.0
          END IF
   20 CONTINUE
*
      RETURN
*
      END