Spectral Analyses of 4 Lacertae and ν Cephei

Abstract

Supergiants are the most luminous stars in galaxies that are currently forming many stars. Reliable abundance determinations, for the most part, reflect the values of the interstellar material out of which they formed. Thus, they can be used to trace the chemical history of their parent galaxies. This study derived the stellar atmospheric parameters and elemental abundances of the early spectral type supergiants 4 Lac (B9 Iab) (HR 8541, HD 212593) and n Cep (A2 Ia) (HR 8334, HD 207260) from Reticon and CCD exposures obtained with the long camera of the 1.22 m telescope of the Dominion Astrophysical Observatory in Victoria, British Columbia. They cover 3830–4950 A with signal-to-noise ratios of at least 200 and a 2 pixel resolution of 0.072 A. The spectra were measured with the graphics spectroscopic analysis program REDUCE (G. Hill & W. A. Fisher 1986, Publ. Dominion Astrophys. Obs., 16, 193). The tailored analyses were performed using the LTE plane-parallel model atmospheres code ATLAS9 (R. L. Kurucz 1993, Kurucz CD-ROM 13 [Cambridge: Smithsonian Astrophys. Obs.]). They are similar to those performed by K. A. Venn (1995, ApJS, 99, 659) and B. Albayrak (2000, A&A, 364, 237), who studied supergiants with similar and cooler effective temperatures. The study of 4 Lac extends this type of analysis to a slightly hotter effective temperature. For weak features, the lines were measured using profiles whose width was found from medium-strength unblended lines to aid the process of trying to deconvolve blended lines. For each spectrogram, I identified the cleanest spectral features and found the radial velocity using the laboratory wavelengths. The remaining lines were identified with A Multiplet Table of Astrophysical Interest (C. E. Moore 1945, Princeton: Princeton Univ. Obs.) and more recent references. The adopted values Teff p 10,250 K and log g p 1.85 for 4 Lac and Teff p 8400 K and log g p 1.10 for n Cep were determined using the wings of Hb, and Fe i/ii and Si ii/iii ionization equilibria for 4 Lac and the wings of Hb and Fe i/ii and Cr i/ii ionization equilibria for n Cep. A microturbulence of 2.8 km s for 4 Lac was found from Fe ii lines using WIDTH9 1