000002200 001__ 2200
000002200 005__ 20160706143710.0
000002200 0247_ $$2DOI$$a10.1051/0004-6361/201219723
000002200 037__ $$aASTROimport-357
000002200 100__ $$aVos, J.
000002200 245__ $$aThe orbits of subdwarf B + main-sequence binaries. I. The sdB+G0 system PG 1104+243
000002200 260__ $$c2012
000002200 520__ $$aContext. The predicted orbital period histogram of a subdwarf B (sdB) population is bimodal with a peak at short (10 days) and long (>250 days) periods. Observationally, however, there are many short-period sdB systems known, but only very few long-period sdB binaries are identified. As these predictions are based on poorly understood binary interaction processes, it is of prime importance to confront the predictions to well constrained observational data. We therefore initiated a monitoring program to find and characterize long-period sdB stars.  Aims: In this contribution we aim to determine the absolute dimensions of the long-period binary system PG 1104+243 consisting of an sdB and a main-sequence (MS) component, and determine its evolution history.  Methods: High-resolution spectroscopy time-series were obtained with HERMES at the Mercator telescope at La Palma, and analyzed to determine the radial velocities of both the sdB and MS components. Photometry from the literature was used to construct the spectral energy distribution (SED) of the binary. Atmosphere models were used to fit this SED and determine the surface gravity and temperature of both components. The gravitational redshift provided an independent confirmation of the surface gravity of the sdB component.  Results: An orbital period of 753 ± 3 d and a mass ratio of q = 0.637 ± 0.015 were found for PG 1104+243 from the radial velocity curves. The sdB component has an effective temperature of Teff = 33 500 ± 1200 K and a surface gravity of log g = 5.84 ± 0.08 dex, while the cool companion is found to be a G-type star with Teff = 5930 ± 160 K and log g = 4.29 ± 0.05 dex. When a canonical mass of MsdB = 0.47 M? is assumed, the MS component has a mass of MMS = 0.74 ± 0.07 M?, and its temperature corresponds to what is expected for a terminal age main-sequence star with sub-solar metalicity.  Conclusions: PG 1104+243 is the first long-period sdB binary in which accurate and consistent physical parameters of both components could be determined, and the first sdB binary in which the gravitational redshift is measured. Furthermore, PG 1104+243 is the first sdB+MS system that shows consistent evidence for being formed through stable Roche-lobe overflow. An analysis of a larger sample of long-period sdB binaries will allow for the refinement of several essential parameters in the current formation channels.
000002200 700__ $$aØstensen, R. H.
000002200 700__ $$aDegroote, P.
000002200 700__ $$aDe Smedt, K.
000002200 700__ $$aGreen, E. M.
000002200 700__ $$aHeber, U.
000002200 700__ $$aVan Winckel, H.
000002200 700__ $$aAcke, B.
000002200 700__ $$aBloemen, S.
000002200 700__ $$aDe Cat, P.
000002200 700__ $$aExter, K.
000002200 700__ $$aLampens, P.
000002200 700__ $$aLombaert, R.
000002200 700__ $$aMasseron, T.
000002200 700__ $$aMenu, J.
000002200 700__ $$aNeyskens, P.
000002200 700__ $$aRaskin, G.
000002200 700__ $$aRingat, E.
000002200 700__ $$aRauch, T.
000002200 700__ $$aSmolders, K.
000002200 700__ $$aTkachenko, A.
000002200 773__ $$cA6$$pAstronomy and Astrophysics$$v548$$y2012
000002200 85642 $$ahttp://esoads.eso.org/abs/2012A%26A...548A...6V
000002200 905__ $$apublished in
000002200 980__ $$aREFERD