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Multicolour high-speed photometry of pulsating subdwarf B stars with ULTRACAM

Publication Type : Journal Article

Publisher : MNRAS

Source : MNRAS

Url :

Campus : Amritapuri

School : School of Arts and Sciences

Year : 2004

Abstract : High-speed multicolour photometry is presented for two pulsating subdwarf B stars, KPD 2109+4401 and HS 0039+4302. The observations were obtained using the high-speed multichannel photometer ULTRACAM on the 4.2-m William Herschel Telescope with a sampling interval of 1 and 4 s, respectively, for the two targets. Both targets show multiperiodic oscillations, generally considered to be due to p-mode pulsations. The frequency spectra are similar to those observed previously, although the amplitudes of some modes have altered. The observations are compared with theoretical multicolour light curves for non-radially oscillating extreme horizontal branch stars using the amplitude ratio method. The radial and spherical degrees n and l of all unambiguously identified frequencies have been determined. In general, n≤ 3 and l≤ 2, but both stars show one l= 4 mode. The spectra of frequency versus spherical degree are compared with models for evolved extended horizontal branch stars. These confirm that KPD 2109+4401 has a post-zero-age horizontal branch age of approximately 47 Myr and an envelope mass ∼0.0002 M⊙. HS 0039+4302 lies on the upper edge of the horizontal branch and hence its envelope mass and age are less well determined spectroscopically. The pulsation properties suggest a more massive envelope and evolved structure. In both stars, the frequencies of the radial (l= 0) modes, if correctly identified, do not match the selected models well, suggesting that the density structure or opacity in the stellar envelopes may be incorrect.

Cite this Research Publication : C.S. Jeffery, V.S. Dhillon, T.R. Marsh & B. Ramachandran, “Multicolour high-speed photometry of pulsating subdwarf B stars with ULTRACAM”, MNRAS, 352, 699, 2004

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