The optical and near infrared variability of eta Carinae: A binary luminous blue variable?

Details The optical and near infrared variability of eta Carinae: A binary luminous blue variable? The optical and near infrared variability of eta Carinae: A binary luminous blue variable?

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283...89v&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 89-110

Astronomy and Astrophysics

Astrophysics

40

Eclipsing Binary Stars, Infrared Photometry, Stellar Color, Stellar Envelopes, Stellar Luminosity, Variable Stars, Visual Photometry, Blue Stars, Light Curve, Stellar Spectrophotometry, Supergiant Stars

Scientific paper

We present an analysis of the long-term light variation in the interval 1935-1992 and of the light and color variation in VBLUW, uvby and JHKLM photometry in the interval 1971-1992 of eta Carinae. The very long-term or secular variation in visual light, showing a smothered gradual rise of approximately 1.5 mag in the interval 1935-1952 and approximately 1 mag in the interval 1952-1992, can be largely attributed to a decrease of the circumstellar extinction. Evolutionary causes are considered, but seem of negligible importance. An analysis of the light and color variations in the interval 1974-1992, revealed the occurrence of at least seven S Dor-type phenomena similar to luminous blue variables (LBVs) on a time scale of 1-3 yr and amplitudes of 0.1-0.2 mag. Thus the main object is almost certain an LBV. There are also minima of a short duration (a few days?), which show a progressively increasing depth to the ultraviolet. A period analysis revealed P approximately 52.4d, although 104.8d is also possible if secondary minima are present. A few facts cast doubt on the reliability of the presumed periodicity, e.g.: the relative large O-C values and the absence of a number of predicted minima. However, these inconsistencies can be explained in terms of an LBV binary, seen at such an inclination angle that the appearance of eclipses depends on the variable size of the psuedo-photosphere of the LBV primary and on the clumpiness of the gaseous material spread around. The variable depth differences between the various pass-bands (sometimes the dips are practically undetectable in visual light) suggest atmospheric type of eclipses. The spectral type of the hypothetical small companion, derived from the relative depths in the monochromatic light curves, is early type B V.

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