masschg2_mod.f

MASSCHG2_MOD holds the quantities of the (experimental) thermal response of the convective envelope to accretion, shared by MASSLOSS, MDOT and COEFFT. It replaces COMMON/MASSCHG2/ (MHP via Claude, 10/14/26). All members are REAL*8.

What its variables hold, who sets them, who reads them.

• SCEN: the convective envelope's mass-averaged $(\mathcal R/\mu)(\tfrac32\ln T - \ln\rho)$ (an entropy per gram), computed by MASSLOSS and then set to 0 in both branches that follow; read by MDOT.
• SACC: the same quantity at the base of the envelope, set by MASSLOSS (massloss.f, line 201↗); read nowhere (only commented-out lines of MDOT and MASSLOSS read it).
• DLOGT, DLOGP: the changes of $\log T$ and $\log P$ that MDOT derives from SCEN and applies to the envelope; read also by COEFFT, which adds them in its entropy terms with accretion. Since SCEN = 0, they are zero in practice (MDOT's and MASSLOSS's notes ask whether this code is kept for later work).
• SMASS0: the total mass (solar units) after the step's mass change, set by MDOT (mdot.f, line 263↗); read nowhere (only a commented-out line of COEFFT reads it). Both are kept on purpose: they belong to the experimental mass-loss code, "not finished," not "dead" (settled from KNOWN_ISSUES.md, issue 12, Nov 9, 2026).

A blanket USE MASSCHG2_MOD. At rp_1, MASSLOSS declared DLOGT and DLOGP in the opposite order from MDOT and COEFFT, so under COMMON's storage association each name there held the other's value; MASSLOSS uses neither, so this had no effect, and the module removes the hazard.