PSR J1641+3627F: A Low-mass He White Dwarf Orbiting a Possible High-mass Neutron Star in the Globular Cluster M13

Abstract

We report on the discovery of the companion star to the millisecond pulsar J1631+3627F in the globular cluster M13. By means of a combination of optical and near-UV high-resolution observations obtained with the Hubble Space Telescope, we identified the counterpart at the radio source position. Its location in the color–magnitude diagrams reveals that the companion star is a faint ( ) He-core white dwarf. We compared the observed companion magnitudes with those predicted by state-of-the-art binary evolution models and found out that it has a mass of , a radius of , and a surface temperature of K. Combining the companion mass with the pulsar mass function is not enough to determine the orbital inclination and the neutron star mass; however, the last two quantities become correlated: we found that either the system is observed at a low-inclination angle, or the neutron star is massive. In fact, assuming that binaries are randomly aligned with respect to the observer line of sight, there is a of probability that this system hosts a neutron star more massive than . In fact, the maximum and median mass of the neutron star, corresponding to orbital inclination angles of 90° and 60°, are and , respectively. On the other hand, also assuming an empirical neutron star mass probability distribution, we found that this system could host a neutron star with a mass of if orbiting with a low-inclination angle around 40°.

Slowly cooling white dwarfs in M13 from stable hydrogen burning

“…The photometric analysis was performed via the point-spread function (PSF) fitting method, by using DAOPHOT IV 27 and following the "UV-route" approach used in previous works [28][29][30][31][32][33][34] . Briefly, the photometric analysis was carried out on the "_flc" images (which are the UVIS calibrated exposures, including Charge Transfer Efficiency correction) and it consists in first searching for the stellar sources in the near-UV images, then force-fit the source detection at longer wavelengths at the same positions of the UV-selected stars.…”

Slowly Cooling White Dwarfs in NGC 6752

“…The photometric analysis was carried out on the _flc images (which are the UVIS calibrated frames, also corrected for charge transfer efficiency), after applying the Pixel Area Map (PAM) correction. We used DAOPHOT IV (Stetson 1987) to follow the so-called "UV-route," which consists of first searching for stellar sources in the near-UV images, then force-fitting the source detection at the same positions of the UV-selected stars in longer wavelength images (Ferraro et al 1997b(Ferraro et al , 2001(Ferraro et al , 2003Raso et al 2017;Dalessandro et al 2018bDalessandro et al , 2018aCadelano et al 2019Cadelano et al , 2020a. This procedure allows the optimal recovering of blue and faint objects, like WDs, because the crowding effect generated by giants and main-sequence turnoff (MS-TO) stars (which get brighter with increasing wavelengths) is strongly mitigated in near-UV images of old stellar populations (as Galactic GCs).…”

FAST Globular Cluster Pulsar Survey: Twenty-Four Pulsars Discovered in Fifteen Globular Clusters

“…This pulsar was discovered in a 500-700 MHz subband of the single beam ultra wide band receiver covering 270-1620 MHz with an 0.5-hr observation. With the same receiver, Wang et al (2020) reported the FAST discovery of M13F, which might be an extremely faint and scintillating pulsar, lately shown to be a high-mass neutron star (Cadelano et al 2020); they also confirmed that M13E is a back widow system. More GC pulsar discoveries were done with the 19-beam L-band receiver which replaced the single beam ultra wide band receiver on May of 2018.…”