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Disintegrating multiple systems have been previously discovered from kinematic studies of the Hipparcos catalogue. They are presumably the result of dynamical encounters taking place in the Galactic disc between single/multiple systems. In this paper, we aim to expand the search for such systems, to study their properties, as well as to characterize possible low-mass ejecta (i.e. brown dwarfs and planets). We have assembled a list of 15 candidate systems using astrometry from the Tycho-Gaia astrometric solution (later upgraded with Gaia DR3), and here we present the discovery and follow-up of five of them. We have obtained DECam imaging for all five systems and by combining near-infrared photometry and proper motion, we searched for ultracool ejected components. We find that the system consisting of TYC 7731-1951-1, TYC 7731-2128 AB, and TYC 7731-1995-1ABC?, contains one very promising ultracool dwarf candidate. Using additional data from the literature, we have found that three out of five disintegrating system candidates are likely to be true disintegrating systems.

 

We present photometric and spectroscopic observations of the extraordinary gamma-ray burst (GRB) 221009A in search of an associated supernova. Some past GRBs have shown bumps in the optical light curve that coincide with the emergence of supernova spectral features, but we do not detect any significant light-curve features in GRB 221009A, nor do we detect any clear sign of supernova spectral features. Using two well-studied GRB-associated supernovae (SN 2013dx,$M_{r,\max }=-19.54;$SN 2016jca,$M_{r,\max }=-19.04$) at a similar redshift as GRB 221009A (z= 0.151), we modeled how the emergence of a supernova would affect the light curve. If we assume the GRB afterglow to decay at the same rate as the X-ray data, the combination of afterglow and a supernova component is fainter than the observed GRB brightness. For the case where we assume the best-fit power law to the optical data as the GRB afterglow component, a supernova contribution should have created a clear bump in the light curve, assuming only extinction from the Milky Way. If we assume a higher extinction ofE(B−V) = 1.74 mag (as has been suggested elsewhere), the supernova contribution would have been hard to detect, with a limit on the associated supernova of$M_{r,\max }\approx -$19.54. We do not observe any clear supernova features in our spectra, which were taken around the time of expected maximum light. The lack of a bright supernova associated with GRB 221009A may indicate that the energy from the explosion is mostly concentrated in the jet, leaving a lower energy budget available for the supernova.

 

ABSTRACT Using RR Lyrae stars in the Gaia Data Release 2 and Pan-STARRS1 we study the properties of the Pisces overdensity, a diffuse substructure in the outer halo of the Milky Way. We show that along the line of sight, Pisces appears as a broad and long plume of stars stretching from 40 to 110 kpc with a steep distance gradient. On the sky Pisces’s elongated shape is aligned with the Magellanic Stream. Using follow-up VLT FORS2 spectroscopy, we have measured the velocity distribution of the Pisces candidate member stars and have shown it to be as broad as that of the Galactic halo but offset to negative velocities. Using a suite of numerical simulations, we demonstrate that the structure has many properties in common with the predicted behaviour of the Magellanic wake, i.e. the Galactic halo overdensity induced by the infall of the Magellanic Clouds.