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On the X-ray and optical properties of the Be star HD 110432: a very hard-thermal X-ray emitter | | Raimundo Lopes de Oliveira
; Christian Motch
; Myron A. Smith
; Ignacio Negueruela
; Jose M. Torrejon
; | | Date: |
26 Jan 2007 | | Abstract: | (ABRIDGED) - HD 110432 is the first proposed, and best studied, member of a growing group of Be stars with X-ray properties similar to gamma Cas. These stars exhibit hard-thermal X-ray emissions that are variable on all measurable timescales. In this work we present XMM-Newton X-ray spectra and light curves in addition to new optical spectroscopic and photometric observations. The X-ray spectrum of HD 110432, complex and timing dependent, is well described in each observation by three thermal plasmas with temperatures ranging between 0.4-0.7, 3-6, and 21-37 keV. Thus, HD 110432 has the hottest thermal plasma of any known Be star. A sub-solar iron abundance (~ 0.3-0.5 x ZFe_sun) is derived for the hottest plasma. The star has a moderate 0.2-12 keV luminosity of ~ 5 x 10^32 erg/s. Recurrent flare-like events on time scales as short as ~ 10 seconds are superimposed over a slowly ~ 5-10 x 10^3 seconds varying basal flux, followed by similarly rapid hardness variabilities. There is no evidence for short pulsations from 0.005 to 2.5 Hz. Except for a ~ 14000 seconds oscillation recurrent in the hardness for two of the three XMM-Newton observations, no periodicity is detected in low frequencies. In the optical region the strong and quasi-symmetrical profile of the Halpha line (EW ~ -60 Angs.) as well as the detection of several metallic lines in emission strongly suggest a dense and/or large circumstellar disk. HD 110432 has several properties reminiscence of the cataclysmic variables such as a very hot X-ray temperature and its detailed spectral features. This suggests that it might be a Be star harbouring an accreting white dwarf. On the other hand, accumulating evidence of magnetic activities in the literature supports the surface-disk of the star as being the X-ray site. | | Source: | arXiv, astro-ph/0701767 | | Services: | Forum | Review | PDF | Favorites | |
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