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Item Revised ephemeris and orbital period derivative of the supersoft X-ray source CAL 87 based on 34 yr of observations(Royal Astronomical Society) Stecchini, Paulo Eduardo Freire; Jablonski, Francisco José; Diaz, Marcos P.; D’Amico, Flávio; Oliveira, Alexandre Soares de; Palivanas, Natália; Saito, Roberto KalbuschIn this study, we present an analysis of over 34 yr of observational data from CAL 87, an eclipsing supersoft X-ray source. The primary aim of our study, which combines previously analysed measurements as well as unexplored publicly available data sets, is to examine the orbital period evolution of CAL 87. After meticulously and consistently determining the eclipse timings, we constructed an O − C (observed minus calculated) diagram using a total of 38 data points. Our results provide confirmation of a positive derivative in the system’s orbital period, with a determined value of s s−1. We observe a noticeable jitter in the eclipse timings and additionally identify a systematic delay in the X-ray eclipses compared to those observed in longer wavelengths. We discuss the interplay of the pertinent factors that could contribute to a positive period derivative and the inherent variability in the eclipses.Item Spectral energy distribution analysis of the supersoft X-ray source CAL 87: Multiwavelength constraints(Elsevier) Stecchini, Paulo Eduardo Freire; Jablonski, Francisco; Diaz, Marcos Perez; Oliveira, Alexandre Soares de; D’Amico, Flavio; Palivanas, NatáliaWe analyse the spectral energy distribution (SED) of the eclipsing supersoft X-ray source CAL 87 covering wavelengths from X-rays to the near-infrared. Our study incorporates 26 data points across ultraviolet to near-infrared, sourced from published literature, unpublished data, and new observations. In addition, archival XMM-Newton spectra were used to represent the X-ray emission. Care was taken to use out-of-eclipse flux measurements when the irradiated side of the companion faces the observer. The SED model includes contributions from a central source, a reprocessed accretion disk, and an irradiated companion star atmosphere, resulting in a good match to the observed fluxes. The revised and new parameters for the disk and the central source align with previous studies and match expectations for such systems. The temperature of the irradiated side of the companion star was estimated based on its B-V colour during the secondary eclipse. This work highlights the importance of broad wavelength coverage for understanding the properties of supersoft X-ray sources.