Spectral variability of the peculiar A-type supergiant 3Pup

TL;DR

This study analyzes optical spectra of the peculiar supergiant 3Pup over a decade, revealing spectral peculiarities, velocity field variations, and providing insights into its classification and distance.

Contribution

It offers a detailed spectral analysis of 3Pup, identifying specific line profile features, velocity variations, and estimating its spectral type and distance for the first time.

Findings

Spectral lines show emission-raising wings and core depressions.

Velocity variations of up to 7 km/s in photospheric lines.

Estimated systemic velocity of 28.5 km/s and distance of 0.7 kpc.

Abstract

Optical spectra of the peculiar supergiant 3Pup taken in 1997-2008 are used to analyze the spectral peculiarities and velocity field in its atmosphere. The profiles of strong FeII lines and of the lines of other iron-group ions have a specific shape: the wings are raised by emissions, whereas the core is sharpened by a depression. The latter feature becomes more pronounced with the increasing line strength, and the increasing wavelength. Line profiles are variable: the magnitude and sign of the absorption asymmetry, and the blue-to-red emission intensity ratios vary from one spectrum to another. The temporal Vr variations are minimal for the forbidden emissions and sharp shell cores of the absorption features of FeII(42), and other strong lines of iron-group ions. The average velocity for the above lines can be adopted as the systemic velocity: Vsys=28.5+/-0.5km/s. The weakest photospheric absorptions and photospheric MgII, SiII absorptions exhibit well-defined day-to-day velocity variations of up to 7km/s. Quantitative spectral classification yields the spectral type of A2.7+/-0.3 Ib. The equivalent widths and profiles of Hdelta and Hgamma, and the equivalent width of the OI7774A triplet yield an absolute magnitude estimate of Mv=-5.5+/-0.3mag, implying the heliocentric distance of 0.7kpc.