A Puzzling Millisecond Pulsar Companion in NGC 6266

Abstract

We report on the optical identification of the companion to the eclipsing millisecond pulsar PSR J1701Ϫ3006B in the globular cluster NGC 6266. A relatively bright star with an anomalous red color and an optical variability (∼0.2 mag) that nicely correlates with the orbital period of the pulsar (∼0.144 days) has been found nearly coincident with the pulsar nominal position. This star is also found to lie within the error box position of an Xray source detected by Chandra observations, thus supporting the hypothesis that some interaction is occurring between the pulsar wind and the gas streaming off the companion. Although the shape of the optical light curve is suggestive of a tidally deformed star which has nearly completely filled its Roche lobe, the luminosity (∼1.9 L , ) and the surface temperature (∼6000 K) of the star, deduced from the observed magnitude and colors, would imply a stellar radius significantly larger than the Roche lobe radius. Possible explanations for this apparent inconsistency are discussed.

Radio Timing and Optical Photometry of the Black Widow System PSR J1518+0204c in the Globular Cluster M5

“…As can be seen, COM-M5C is located at faint magnitudes between the MS and the WD cooling sequence, thus suggesting that it is probably a nondegenerate or a semidegenerate, low-mass, swollen star. Indeed, similar objects have been previously identified in Galactic GCs (see Ferraro et al 2001b;Edmonds et al 2002;Cocozza et al 2008;Pallanca et al 2010Pallanca et al , 2013b. and right panel, respectively).…”

“…In GCs, it also represents a crucial tool for quantifying the occurrence of dynamical interactions, understanding the effects of crowded stellar environments on the evolution of binaries, determining the shape of the GC potential, and estimating the mass-to-light ratio in the GC cores (e.g., Phinney 1992;Bellazzini et al 1995;Possenti et al 2003;Ferraro et al 2003b). Despite their importance, only eight MSP companions in six GCs have been identified thus far (Edmonds et al 2001;Ferraro et al 2001a;Edmonds et al 2002;Sigurdsson et al 2003;Ferraro et al 2003a;Bassa et al 2003;Cocozza et al 2008;Pallanca et al 2010Pallanca et al , 2013b. Three of them are likely helium WDs, in agreement with the expectations of the MSP recycling scenario, while the other five are nondegenerate stars, which are thought to be either the result of a different evolutionary path or the product of an exchange interaction.…”

Uncloaking Globular Clusters in the Inner Galaxy

“…Beccari et al (2006) studied this cluster using a combination of BVI (ground) and U 255 U 336 V 555 (space) bands. Cocozza et al (2008) studied a pulsar in M 62 and used their HST data to show the B − R versus R CMD of the cluster. NGC 6266 is also included in the HST GGCs survey in B 439 V 555 published by Piotto et al (2002).…”

OPTICAL IDENTIFICATION OF He WHITE DWARFS ORBITING FOUR MILLISECOND PULSARS IN THE GLOBULAR CLUSTER 47 TUCANAE

“…The best-fit model is shown as a solid curve in Figure 7. Interestingly, the light curve structure is more similar to the ones observed for black widow than for redback companions, which usually, but not always shows a double minimummaximum structure due to tidal deformation (see, e.g., Ferraro et al 2003a;Cocozza et al 2008;Pallanca et al 2010;Li et al 2014). The CMD position of the companion during the maximum and at a mean phase (as derived by the adopted model) is shown in Figure 2.…”