Observations of the pulsation of the Cepheid l Car with the Sydney University Stellar Interferometer

TL;DR

This study used stellar interferometry to measure the pulsation and size of Cepheid l Car, accurately determining its distance and radius, and confirming the reliability of interferometric and radial velocity methods.

Contribution

First precise interferometric measurement of l Car's pulsation amplitude and diameter, combined with radial velocity data to determine its distance and size.

Findings

Mean angular diameter: 2.990 mas

Distance to l Car: 525 pc

No evidence of circumstellar envelope

Abstract

Observations of the southern Cepheid l Car to yield the mean angular diameter and angular pulsation amplitude have been made with the Sydney University Stellar Interferometer (SUSI) at a wavelength of 696 nm. The resulting mean limb-darkened angular diameter is 2.990+-0.017 mas (i.e. +-0.6 per cent) with a maximum-to-minimum amplitude of 0.560+-0.018 mas corresponding to 18.7+-0.6 per cent in the mean stellar diameter. Careful attention has been paid to uncertainties, including those in measurements, in the adopted calibrator angular diameters, in the projected values of visibility squared at zero baseline, and to systematic effects. No evidence was found for a circumstellar envelope at 696 nm. The interferometric results have been combined with radial displacements of the stellar atmosphere derived from selected radial velocity data taken from the literature to determine the distance and mean diameter of l Car. The distance is determined to be 525+-26 pc and the mean radius 169+-8R{solar). Comparison with published values for the distance and mean radius show excellent agreement, particularly when a common scaling factor from observed radial velocity to pulsation velocity of the stellar atmosphere (the p-factor) is used.