Exploring the Long-term Temporal Variability in Polarization through Multiepoch Optical Spectropolarimetry. II. A Sample of Symbiotic and Red Giant Stars

Abstract Measuring polarization and its temporal variability in the continuum and across emission features provides a powerful probe of the small-scale circumstellar environments of astrophysical sources, on spatial scales otherwise inaccessible to direct imaging techniques. However, the photon-hungry nature of spectropolarimetry has significantly limited the availability of such datasets in the literature. Here we present the results of a multiepoch spectropolarimetric survey of a sample of symbiotic and red giant stars. These observations were first conducted during the performance verification phase of a recently developed medium-resolution echelle spectropolarimeter, named ProtoPol, mounted on the Physical Research Laboratory (PRL) 2.5 m telescope, Mt. Abu, India. Considering the scarcity of such observing samples in the literature, the targets were reobserved over a period exceeding 26 months, from 2024 March to 2026 May, in order to explore the time variability of their polarimetric measurements. Our sample comprises 6 symbiotic stars and 18 red giant stars. Our observations found that, unlike the Raman-scattered λλ 6830, 7088 Å features, the H α emission in most of the symbiotics did not exhibit any notable polarization signature. However, the continuum polarization of most symbiotics and red giants in the sample showed significant variation between observation epochs. The observations presented here constitute one of the rare multiepoch spectropolarimetric datasets spanning more than 2 yr and should be of considerable interest to the broader astronomical community. This is Paper II of a two-part series of sample studies; corresponding results for Herbig Ae/Be and classical Be stars are presented in Paper I.