Near-infrared photometry of carbon stars

Author:

Whitelock Patricia A.123,Feast Michael W.2,Marang Freddy1,Groenewegen M. A. T.4

Affiliation:

1. South African Astronomical Observatory, PO Box 9, 7935 Observatory, South Africa

2. Astronomy Department, University of Cape Town, 7701 Rondebosch, South Africa

3. National Astrophysics and Space Science Programme, Department of Mathematics and Applied Mathematics, University of Cape Town, 7701 Rondebosch, South Africa

4. Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium

Abstract

Abstract Near-infrared, JHKL, photometry of 239 Galactic C-rich variable stars is presented and discussed. From these and published data, the stars were classified as Mira or non-Mira variables, and amplitudes and pulsation periods, ranging from 222 to 948 d for the Miras, were determined for most of them. A comparison of the colour and period relations with those of similar stars in the Large Magellanic Cloud indicates minor differences, which may be the consequence of sample selection effects. Apparent bolometric magnitudes were determined by combining the mean JHKL fluxes with mid-infrared photometry from IRAS and MSX. Then, using the Mira period luminosity relation to set the absolute magnitudes, distances were determined – to greater accuracy than has hitherto been possible for this type of star. Bolometric corrections to the K magnitude were calculated and prescriptions derived for calculating these from various colours. Mass-loss rates were also calculated and compared to values in the literature. Approximately one-third of the C-rich Miras and an unknown fraction of the non-Miras exhibit apparently random obscuration events that are reminiscent of the phenomena exhibited by the hydrogen-deficient R Coronae Borealis stars. The underlying cause of this is unclear, but it may be that mass loss, and consequently dust formation, is very easily triggered from these very extended atmospheres.

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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