Discovery of an OB runaway star inside SNR S147

MNRAS 448, 3196–3205 (2015) doi:10.1093/mnras/stv124 Discovery of an OB runaway star inside SNR S147 B. Dinçel,1‹ R. Neuhäuser,1 S. K. Yerli,2 A. Ankay,3 N. Tetzlaff,1 G. Torres4 and M. Mugrauer1 1 Astrophysikalisches Institut und Universitäts-Sternwarte Jena, D-07745 Jena, Germany of Physics, Orta Doğu Teknik Üniversitesi, 06531 Ankara, Turkey 3 Department of Physics, Boğaziçi University, 34342 İstanbul, Turkey 4 Harvard–Smithsonian Center for Astrophysics, 60 Garden St, Mail Stop 20, Cambridge, MA 02138, USA 2 Department ABSTRACT We present first results of a long-term study: Searching for OB-type runaway stars inside supernova remnants (SNRs). We identified spectral types and measured radial velocities by optical spectroscopic observations and we found an early type runaway star inside SNR S147. HD 37424 is a B0.5V-type star with a peculiar velocity of 74 ± 8 km s−1 . Tracing back the past trajectories via Monte Carlo simulations, we found that HD 37424 was located at the same position as the central compact object, PSR J0538+2817, 30 ± 4 kyr ago. This position is only ∼4 arcmin away from the geometrical centre of the SNR. So, we suggest that HD 37424 was the pre-supernova binary companion to the progenitor of the pulsar and the SNR. We found a distance of 1333+103 −112 pc to the SNR. The zero-age main sequence progenitor mass should be greater than 13 M . The age is 30 ± 4 kyr and the total visual absorption towards the centre is 1.28 ± 0.06 mag. For different progenitor masses, we calculated the pre-supernova binary parameters. The Roche lobe radii suggest that it was an interacting binary in the late stages of the progenitor. Key words: stars: early type – stars: individual: HD37424 – pulsars: individual: PSR J0538+2817 – ISM: individual objects: SNR G180.0−1.7 (S147) – ISM: supernova remnants. 1 I N T RO D U C T I O N High space velocities of OB runaway stars are explained by two independent mechanisms: dynamical ejection due to gravitational interactions of massive stars in cluster cores (Poveda, Ruiz & Allen 1967) and binary disruption as a result of a supernova (SN) explosion of the initially more massive component (Blaauw 1961). Both scenarios are viable, but whether one of the mechanisms is dominant is still uncertain. According to the virial theorem, through a symmetric SN explosion in a binary system, if more than half of the total mass of the system is released, then the new born neutron star (or black hole) and the non-degenerate component are no more gravitationally bound (Blaauw 1961). However, the energy stored in the orbit, in most cases, is not sufficient to produce the neutron star (NS) kick velocities that are typically in the range of 300–500 km s−1 (Lyne & Lorimer 1994; Allakhverdiev et al. 1997; Hansen & Phinney 1997; Hobbs et al. 2005). The asymmetry in SN explosions is responsible for such high velocities (Wongwathanarat, Janka & Müller 2013). Therefore, there are no pulsar companions to many of the OB runaway stars (Sayer, Nice & Kaspi 1996). In some cases, the compact object does not receive a significant kick and/or  E-mail: the majority of the total mass is stored on the secondary through conservative mass transfer, hence, the compact object remains bound to the companion star (van den Heuvel 1993). The runaway high-mass X-ray binaries like 4U1700-37 (Ankay et al. 2001) and Vela X–1 (Kaper et al. 1997) are such examples. Yet, the low rate of X-ray binaries and the high rate of isolated NSs by taking into consideration the selection effects, the binary disruption is likely to occur in most cases (Guseinov, Ankay & Tagieva 2005, hereafter G05). The kinematics of the binary disruption due to an asymmetric SN explosion is widely discussed in Tauris & Takens (1998). However, a sample of observationally confirmed OB runaway–NS couples is needed for a better understanding of the problem. The importance of searching for OB runaways inside supernova remnants (SNRs) was first mentioned in van den Bergh (1980). However, the kinematical study of known OB stars inside SNRs was concluded with a lack of OB runaways due to the poor sample of SNRs and OB stars. Still, there is no known O- or B-type runaway star that can be directly linked to an SNR given in the literature. In G05, the outcome of exploring runaway pairs from binary SN disruption is broadly discussed. First, identifying the explosion centres more precisely will be useful for determining the velocities of young NSs of which proper motion (pm) measurements have high uncertainties. Thus, the kick that is gained by the NS due to the asymmetry of the SN can be determined more precisely. Secondly,  C 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Accepted 2015 January 17. Received 2014 December 12; in original form 2014 May 25 Runaway in S147 The first criterion of the candidate selection is the restriction of the angular position. Most of the OB runaways have peculiar velocities lower than 80 km s−1 (Gies & Bolton 1986; Philp et al. 1996; Tetzlaff et al. 2011a). As the shock wave velocity of the SNRs are decelerated from roughly 10 000 km s−1 to several hundred km s−1 , it is expected that the runaway star cannot exceed one tenth of the angular diameter (θ) of the related SNR. This value is somewhat relaxed to θ /6 considering the uncertainties in the GCs of the SNRs. The stars in this region are expected to be consistent with the respective SNR in terms of distance and reddening. For this comparison, the adopted distances of SNRs given in Guseinov, Ankay & Tagieva (2003b, 2004b,c), and AV values from Neckel, Klare & Sarcander (1980) were used. 48 SNRs within 5 kpc from the Sun were selected for investigation. In this paper, the result of the runaway search in SNR G180.01.7 (S147) is given. The kinematic relation between the runaway star HD 37424 and the pulsar PSR J0538+2817 is shown, the possible host OB association is discussed, the SNR parameters are constrained and the pre-SN binary is constructed. 2 S 1 4 7 , P S R J 0 5 3 8 +2 8 1 7 A N D H D 3 7 4 2 4 S147 is a shell-type SNR located in the Galactic anticentre direction. It is 180 arcmin in diameter with a GC at α = 05h 39m 00s , δ = +27◦ 50 00 (Green 2009). It was first mentioned as an SNR candidate in Minkowski (1958). The compact object related to the SNR is radio pulsar PSR J0538+2817 (Anderson et al. 1996). In optical bands, the shell structure is well defined and dominated by filamentary emission in Hα. The emission is brighter in the north and south edges and mainly concentrated in the southern parts. Despite of its old age, it conserves the spherical symmetry except for the blowout regions in east and west (Fig. 1). The total absorption in the V band is AV = 0.7 ± 0.2 mag (Fesen, Blair & Kirshner 1985). Radio observations reveal that the spectral index is unusually varying. The shell structure observed at radio wavelengths coincides with that in (...truncated)