All Figures

Figure 1: Temperature profiles (temperature versus density) through an accreted heat-blanketing envelope of the canonical neutron star ( , R=10 km). The outer part of each model envelope (from the radiative surface to a cusp of a curve) is composed of 4He. The thickness of the helium layer is measured by parameter : , 10-12, and 10-8 (marked near the curves). The composition of the inner part of the envelope (after the cusp) is taken from Haensel & Zdunik (1990).

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In the text

	Figure 2: Effective temperature of the canonical neutron star as a function of the internal temperature for the HZ90 composition of the envelope (dashed lines) and for the HZ03 composition (solid lines).
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In the text

Figure 3: Theoretical quiescent thermal luminosity of neutron stars (with EOS N1 in the cores) versus mean mass accretion rate confronted with observations of five SXTs. The larger upper limit of the luminosity of SAX J1808.4-3658 assumes the blackbody (BB) surface emission; the smaller limit - lower horizontal bar - is obtained with the neutron-star atmosphere (NSA) model. The upper curves refer to the low-mass ( ) star (with strong proton superfluidity in the core), while the lower curves to the maximum-mass star. Four curves for the low-mass star are calculated assuming HZ90 or HZ03 accreted crusts, without or with a massive helium surface layer; singly hatched region shows ranges of variations of quiescent luminosity due to different mass of helium layer for the HZ03 crust; double hatched region is the same for the HZ90 crust. The heating curves for the high-mass star are the same but the solid curve (for the HZ03 crust without helium layer) is absent because of the partial ionization problem (see text); it is expected to be close to the dash-and-dot curve.

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In the text

	Figure 4: Theoretical quiescent thermal luminosity of neutron stars (with EOS N1 in the cores and the HZ90 or HZ03 crusts) in Aql X-1 and SAX J1808.4-3658 (as in Fig. 3) versus the mass of the surface He layer. The dotted lines refer to oversimplified (inaccurate) models which neglect partial ionization of heavy elements (Fe or Pd) in outermost layers.
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In the text

Figure 5: Quiescent thermal luminosity (left panel) or effective surface temperature (right panel) vs. for a star with a nucleon core (containing strongly superfluid protons) confronted with observations of Aql X-1. Set of four heating curves: with HZ90 or HZ03 crusts, with and without massive helium layer, is shown for the three EOSs in the stellar cores (EOSs N1, N2 and N3). Fixing the accreted crust model, we obtain almost the same luminosities (the curves for EOSs N1, N2, and N3 almost coincide; left panel) but different effective temperatures (right panel). Hatched regions in the left panel display ranges of possible variations of due to variable thickness of the He layer for the HZ90 and HZ03 crusts.

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In the text

Figure 6: Quiescent thermal luminosity vs. for maximum-mass neutron-star models confronted with observations of SAX J1808.4-3658. Based on 15 curves for five EOSs in the stellar core in the presence of massive helium surface layers (HZ90 and HZ03 crusts, hatched lines) and in the absence of these layers (HZ90 crust, solid lines). The EOS types are marked to the left of the lines. The curves for EOSs N2 and NH2 are almost indistinguishable. Taking the massive helium layer and a fixed EOS, we have two almost coincident curves for HZ90 and HZ03 crusts, plotted as a wide hatched line.

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In the text