Measuring the orbital inclination of Z Andromedae from Rayleigh scattering

TL;DR

This study measures the orbital inclination of Z Andromedae using Rayleigh scattering of UV spectra, narrowing down the inclination to approximately 59 degrees with implications for jet modeling.

Contribution

The paper introduces a novel method to determine the orbital inclination of Z Andromedae through UV spectral analysis and modeling of Rayleigh scattering effects.

Findings

Orbital inclination of Z And is approximately 59 degrees.

Systematic errors can increase the inclination estimate up to 74 degrees.

High inclination supports the interpretation of emission line features as collimated jets.

Abstract

The orbital inclination of the symbiotic prototype Z And has not been established yet. At present, two very different values are considered, i ~ 44 degrees and i >~ 73 degrees. The correct value of i is a key parameter in, for example, modeling the highly-collimated jets of Z And. The aim of this paper is to measure the orbital inclination of Z And. First, we derive the hydrogen column density (nH), which causes the Rayleigh scattering of the far-UV spectrum at the orbital phase phi = 0.961 plus/minus 0.018. Second, we calculate nH as a function of i and phi for the ionization structure during the quiescent phase. Third, we compare the nH(i,phi) models with the observed value. The most probable shaping of the HI/HII boundaries and the uncertainties in the orbital phase limit i of Z And to 59 -2/+3 degrees. Systematic errors given by using different wind velocity laws can increase i up to ~74 degrees. A high value of i is supported independently by the orbitally related variation in the far-UV continuum and the obscuration of the OI] 1641 A emission line around the inferior conjunction of the giant. The derived value of the inclination of the Z And orbital plane allows treating satellite components of H-alpha and H-beta emission lines as highly-collimated jets.