Simin Mahmoodifar

Viscous damping of r-modes: Large amplitude saturation

We analyze the viscous damping of r-mode oscillations of compact stars, taking into account non-linear viscous effects in the large-amplitude regime. The qualitatively different cases of hadronic stars, strange quark stars, and hybrid stars are studied. We calculate the viscous damping times of r-modes, obtaining numerical results and also general approximate analytic expressions that explicitly exhibit the dependence on the parameters that are relevant for a future spindown evolution calculation. The strongly enhanced damping of large amplitude oscillations leads to damping times that are considerably lower than those obtained when the amplitude dependence of the viscosity is neglected. Consequently, large-amplitude viscous damping competes with the gravitational instability at all physical frequencies and could stop the r-mode growth in case this is not done before by non-linear hydrodynamic mechanisms.

Where are the r-modes? Chandra Observations of Millisecond Pulsars

We present the results of {\it Chandra} observations of two non-accreting millisecond pulsars, PSRs J1640

Non‐linear viscous saturation of r‐modes

+

Suprathermal viscosity of dense matter

2224 (J1640) and J1709

Impact of r-modes on the cooling of neutron stars

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Viscous damping of r-modes: Small amplitude instability

2313 (J1709), with low inferred magnetic fields and spin-down rates in order to constrain their surface temperatures, obtain limits on the amplitude of unstable

Large amplitude behavior of the bulk viscosity of dense matter

r

Shear viscosity from kaon condensation in color-flavor-locked quark matter

-modes in them, and make comparisons with similar limits obtained for a sample of accreting low-mass X-ray binary (LMXB) neutron stars. We detect both pulsars in the X-ray band for the first time. They are faint, with inferred soft X-ray fluxes (

NICER detects a soft X-ray kilohertz QPO in 4U 0614+09

0.3-3

Fanning the Flames: X-ray Burst Probes of Nuclear Burning

keV) of