Updating the orbital ephemeris of the dipping source XB 1254–690 and the distance to the source

作     者：Angelo F.Gambino Rosario Iaria Tiziana Di Salvo Marco Matranga Luciano Burderi Fabio Pintore Alessandro Riggio Andrea Sanna Angelo F. Gambino Rosario Iaria Tiziana Di Salvo Marco Matranga Luciano Burderi Fabio Pintore Alessandro Riggio[2 and Andrea Sanna2]

作者机构：Universita degli Studi di Palermo Dipartimento di Fisica e Chimica Universita degli Studi di Cagliari Dipartimento di Fisica INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica - Milano 

出 版 物：《Research in Astronomy and Astrophysics》 (天文和天体物理学研究（英文版）)

年 卷 期：2017年第17卷第10期

页      面：97-108页

核心收录：

学科分类：07[理学] 070402[理学-天体测量与天体力学] 0704[理学-天文学] 

基　　金：the Regione Autonoma della Sardegna through POR-FSE Sardegna 2007–2013, L.R. 7/2007 Progetti di Ricerca di Base e Orientata, Project N. CRP-60529 financial contribution from the agreement ASI-INAF I/037/12/0 the Sardinia Regional Government for financial support (P.O.R. Sardegna F.S.E. Operational Programme of the Autonomous Region of Sardinia, European Social Fund 2007–2013 - Axis IV Human Resources, Objective l.3, Line of Activity l.3.1.) 

主　　题：stars: neutron    stars: individual (XB 1254 690)    X rays: binaries    X rays: stars   Astrometry and celestial mechanics: ephemerides 

摘      要：XB 1254-690 is a dipping low mass X-ray binary system hosting a neutron star and showing type I X-ray bursts. We aim at obtaining a more accurate orbital ephemeris and at constraining the orbital period derivative of the system for the first time. In addition, we want to better constrain the distance to the source in order to locate the system in a well defined evolutive scenario. We apply, for the first time, an orbital timing technique to XB 1254-690, using the arrival times of the dips present in the light curves that have been collected during 26 yr of X-ray pointed observations acquired from different space missions. We estimate the dip arrival times using a statistical method that weights the count-rate inside the dip with respect to the level of persistent emission outside the dip. We fit the obtained delays as a function of the orbital cycles both with a linear and a quadratic function. We infer the orbital ephemeris of XB 1254-690, improving the accuracy of the orbital period with respect to previous estimates. We infer a mass of M2 = 0.42 ± 0.04 M for the donor star, in agreement with estimations already present in literature, assuming that the star is in thermal equilibrium while it transfers part of its mass via the inner Lagrangian point, and assuming a neutron star mass of 1.4 Mo. Using these assumptions, we also constrain the distance to the source, finding a value of 7.6±0.8 kpc. Finally, we discuss the evolution of the system, suggesting that it is compatible with a conservative mass transfer driven by magnetic braking.