[en] We made photometric and spectroscopic observations of the rapidly pulsating subdwarf B star EC 09582-1137 with the aim of determining the target's fundamental structural parameters from asteroseismology. This analysis forms part of a long-term programme geared towards distinguishing between different proposed formation scenarios for hot B subdwarfs on the basis of their internal characteristics. So far, secure asteroseismic solutions have been computed for 9 of these pulsators, and first comparisons with results from evolutionary calculations look promising. The new data comprise 30 h of fast time-series photometry obtained with SUSI2 at the NTT on La Silla, Chile, as well as 1 h of low-resolution spectroscopy gathered with EMMI, also mounted on the NTT. From the photometry we detected 5 independent harmonic oscillations in the 135-170 s period range with amplitudes up to 0.5% of the mean brightness of the star. In addition, we extracted two periodicities interpreted as components of a rotationally split multiplet that indicate a rotation period of the order of 2-5 days. We also recovered the first harmonic of the dominant pulsation, albeit at an amplitude below the imposed 4σ detection threshold. The spectroscopic observations led to the following estimates of the atmospheric parameters of EC 09582-1137: T_eff = 34 806±233 K, log{g} = 5.80±0.04, and log N(He)/N(H) = -1.68±0.06. Using the observed oscillations as input, we searched in model parameter space for unique solutions that present a good fit to the data. Under the assumption that the two dominant observed periodicities correspond to radial or dipole modes, we were able to isolate a well-constrained optimal model that agrees with the atmospheric parameters derived from spectroscopy. The observed oscillations are identified with low-order acoustic modes with degree indices ℓ = 0, 1, 2, and 4 and match the computed periods with a dispersion of 0.57%. Non-adiabatic calculations reveal all theoretical modes in the observed period range to be unstable, an important a posteriori consistency check for the validity of the optimal model. The inferred structural parameters of EC 09582-1137 are T_eff = 34 806 K (from spectroscopy), log{g} = 5.788±0.004, Mast = 0.485±0.011 Msun, log{(M_env/Mast)} = -4.39±0.10, R = 0.147±0.002 Rsun, and L = 28.6±1.7 Lsun. We additionally derive the absolute magnitude MV = 4.44±0.05 and the distance d = 1460±66 pc.
scite shows how a scientific paper has been cited by providing the context of the citation, a classification describing whether it supports, mentions, or contrasts the cited claim, and a label indicating in which section the citation was made.
Bibliography
Brassard, P., & Fontaine, G. 2008, in Hot Subdwarf Stars and Related Objects, ed. U. Heber, C. S. Jeffery, & R. Napiwotzki, ASP Conf. Ser., 392, 392
Charpinet, S., Fontaine, G., & Brassard, P. 2003, in White Dwarfs, ed. D. de Martino, R. Silvotti, J.-E. Solheim, & R. Kalytis, NATO ASIB Proc., 105, 105
Charpinet, S., Fontaine, G., Brassard, P., et al. 2005b, in 14th European Workshop on White Dwarfs, ed. D. Koester, & S. Moehler, ASP Conf. Ser., 334, 334
Charpinet, S., Fontaine, G., Brassard, P., Green, E. M., & Chayer, P. 2005c, A&A, 437, 437
Charpinet, S., Silvotti, R., Bonanno, A., et al. 2006, A&A, 459, 459
Charpinet, S., van Grootel, V., Reese, D., et al. 2008, A&A, 489, 377
D'Cruz, N. L., Dorman, B., Rood, R. T., & O'Connell, R. W. 1996, ApJ, 466, 466
Fontaine, G., & Brassard, P. 1994, in Stellar and Circumstellar Astrophysics, a 70th birthday celebration for K. H. Bohm and E. Bohm-Vitense, ed. G. Wallerstein, & A. Noriega-Crespo, ASP Conf. Ser., 57, 57
Fontaine, G., Brassard, P., Charpinet, S., et al. 2006b, in ESA SP, 624, 624
Fontaine, G., Brassard, P., Charpinet, S., et al. 2008, in Hot Subdwarf Stars and Related Objects, ed. U. Heber, C. S. Jeffery, & R. Napiwotzki, ASP Conf. Ser., 392, 392
This website uses cookies to improve user experience. Read more
Save & Close
Accept all
Decline all
Show detailsHide details
Cookie declaration
About cookies
Strictly necessary
Performance
Strictly necessary cookies allow core website functionality such as user login and account management. The website cannot be used properly without strictly necessary cookies.
This cookie is used by Cookie-Script.com service to remember visitor cookie consent preferences. It is necessary for Cookie-Script.com cookie banner to work properly.
Performance cookies are used to see how visitors use the website, eg. analytics cookies. Those cookies cannot be used to directly identify a certain visitor.
Used to store the attribution information, the referrer initially used to visit the website
Cookies are small text files that are placed on your computer by websites that you visit. Websites use cookies to help users navigate efficiently and perform certain functions. Cookies that are required for the website to operate properly are allowed to be set without your permission. All other cookies need to be approved before they can be set in the browser.
You can change your consent to cookie usage at any time on our Privacy Policy page.