Abstract
We present a comprehensive study of X-ray absorption by sulfur (S), argon (Ar), and calcium (Ca) in the interstellar medium (ISM) along the line of sight to the low-mass X-ray binary MAXI J1744–294 using high-resolution XRISM
Resolve
spectra. The analysis employed an updated
ISMabs
model, incorporating newly computed
R
-matrix photo-absorption cross sections for Ca
I
–Ca
III
and existing cross sections for higher ionization states. S and Ar are predominantly in low-ionization states, with S
II
and Ar
II
dominating the cold and warm ISM phases, while higher-ionization species are constrained by upper limits. Calcium is primarily detected in low-ionization states, consistent with strong depletion onto dust grains, with only marginal contributions from highly ionized ions. Using the measured ionic column densities, we inferred hydrogen column densities of
N
H
~ 1.1–1.3 × 10
23
cm
−2
from S and Ar, while the Ca-based value, tracing the neutral ISM, agrees with these estimates. This highlights the consistency across different tracers. Our results demonstrate the diagnostic power of combining multiple elements to probe the ISM ionization structure, elemental depletion, and dust composition, and they provide the first X-ray constraints on calcium absorption in the ISM.