Single stars in the Hyades open cluster

Fiducial sequence for testing stellar and atmospheric models^⋆,⋆⋆

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: kopytova@mpia.de
² International Max-Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg, IMPRS-HD, Germany
³ University of Roma Tor Vergata, Department of Physics, via della Ricerca Scientifica 1, 00133 Roma, Italy
⁴ INFN, Section of Pisa, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
⁵ University of Pisa, Department of Physics ’E.Fermi’, Largo Bruno Pontecorvo 3, 56127 Pisa, Italy
⁶ Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611, USA
⁷ Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstr. 12-14, 69120 Heidelberg, Germany

Received: 23 July 2015
Accepted: 31 August 2015

Abstract

Context. Age and mass determinations for isolated stellar objects remain model-dependent. While stellar interior and atmospheric theoretical models are rapidly evolving, we need a powerful tool to test them. Open clusters are good candidates for this role.

Aims. We aim to create a fiducial sequence of stellar objects for testing stellar and atmospheric models.

Methods. We complement previous studies on the Hyades multiplicity by Lucky Imaging observations with the AstraLux Norte camera. This allows us to exclude possible binary and multiple systems with companions outside a 2–7 AU separation and to create a single-star sequence for the Hyades. The sequence encompasses 250 main-sequence stars ranging from A5V to M6V. Using the Tool for Astrophysical Data Analysis (TA-DA), we create various theoretical isochrones applying different combinations of interior and atmospheric models. We compare the isochrones with the observed Hyades single-star sequence on J vs. J−K_s, J vs. J−H, and K_s vs. H−K_s color–magnitude diagrams. As a reference we also compute absolute fluxes and magnitudes for all stars from X-ray to mid-infrared based on photometric measurements available in the literature(ROSAT X-ray, GALEX UV, APASS gri, 2MASS JHK_s, and WISE W1 to W4).

Results. We find that combinations of both PISA and DARTMOUTH stellar interior models with BT-Settl 2010 atmospheric models describe the observed sequence well. We use PISA in combination with BT-Settl 2010 models to derive theoretical predictions for physical parameters (T_eff, mass, log g) of 250 single stars in the Hyades. The full sequence covers the mass range of 0.13–2.30 M_⊙, and effective temperatures between 3060 K and 8200 K.

Conclusions. Within the measurement uncertainties, the current generation of models agree well with the single-star sequence. The primary limitations are the uncertainties in the measurement of the distances to individual Hyades members, and uncertainties in the photometry. Gaia parallaxes, photometry, and spectroscopy will greatly reduce the uncertainties in particular at the lowest mass range, and will enable us to test model predictions with greater confidence. Additionally, a small (~0.05 mag) systematic offset can be noted in J vs. J−K and K vs. H−K diagrams – the observed sequence is shifted to redder colors than the theoretical predictions.