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Ring-like features around young B stars

M. S. N. Kumar, T. Velusamy, C. J. Davis, W. P. Varricatt, L. K. Dewangan

Abstract
Aims. To investigate the nature of two targets namely IRAS20293+3952 and IRAS05358+3843, which display, well defined H2 emission rings around young intermediate mass stars.
Methods. Hi-Res deconvolution of finely sampled 3.6–8.0 µm Spitzer-IRAC images of IRAS20293+3952 and IRAS05358+3843 are carried out. Continuum-subtracted 2.122 µm H2 1-0 S(1) narrow-band images of both targets and HK band spectrum of two main stars in IRAS20293+3952 is presented. The Spectral energy distibutions (SED) of the stars enclosed in the H2 rings are constructed using photometry from the literature and combining with newly obtained Spitzer-MIPS 70 µm photometry. The SEDs are modelled using a popular grid of radiative transfer models to obtain estimates of the star, disk and envelope physical parameters.
Results. The Hi-Res processed Spitzer-IRAC images and the the continuum-subtracted narrow-band images reveal ring-like structures surrounding isolated young B-type stars. The modelling attributes a mass and age of ∼7M and ∼0.1 Myr respectively to the young stars, in agreement with other observational indicators. The HK band spectra of I20293 display the Brackett series of HI recombination lines, localised on the young star in this source. The ring around I20293 appears as a single well defined ellipse with the inner parts shining brightly in the Spitzer broad band images and the outer parts displaying strong H2 emission. In the source I05358, at least two ring’s are found, one circumscribing the other. The emission in the Spitzer bands and the H2 emission are mostly coincident for the inner ring. The outer ring is visible partly in the Spitzer bands and partly in H2 emission. The rings in both the sources, I20293 and I05358, have diameters of ∼25000-30000AU. The envelope sizes estimated by the SED modelling is consistent with the size of the rings estimated using the imaging data. The spectrum of H2 ring in I20293 is suggestive of flourescent excitation. In the source I05358, the inner ring display a combination of PAH and H2 line emission with excess PAH emission closer to the star.

Keywords
stars: formation - stars: emission-line, stars: rotation - HII region

Astronomy and Astrophysics
Volume 519, Number of pages A99_1
2010 September

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia