We combined Chandra ACIS observations of the globular cluster 47 Tucanae (hereafter, 47 Tuc) from 2000, 2002, and 2014-15 to create a deeper X-ray source list, and study some of the faint radio millisecond pulsars (MSPs) present in this cluster. We have detected 370 X-ray sources within the half-mass radius (2 .79) of the cluster, 81 of which are newly identified, by including new data and using improved source detection techniques. The majority of the newly identified sources are in the crowded core region, indicating cluster membership. We associate five of the new X-ray sources with chromospherically active BY Dra or W UMa variables identified by Albrow et al. (2001). We present alternative positions derived from two methods, centroiding and image reconstruction, for faint, crowded sources. We are able to extract X-ray spectra of the recently discovered MSPs 47 Tuc aa, 47 Tuc ab, the newly timed MSP 47 Tuc Z, and the newly resolved MSPs 47 Tuc S and 47 Tuc F. Generally, they are well fit by black body or neutron star atmosphere models, with temperatures, luminosities and emitting radii similar to those of other known MSPs in 47 Tuc, though 47 Tuc aa and 47 Tuc ab reach lower X-ray luminosities. We limit X-ray emission from the full surface of the rapidly spinning (542 Hz) MSP 47 Tuc aa, and use this limit to put an upper bound for amplitude of r-mode oscillations in this pulsar as α < 2.5 × 10 −9 and constrain the shape of the r-mode instability window.

Context. The age–velocity dispersion relation is an important tool to understand the evolution of the disc of the Andromeda galaxy (M 31) in comparison with the Milky Way. Aims. We use planetary nebulae (PNe) to obtain the age–velocity dispersion relation in different radial bins of the M 31 disc. Methods. We separate the observed PNe sample based on their extinction values into two distinct age populations in the M 31 disc. The observed velocities of our high- and low-extinction PNe, which correspond to higher- and lower-mass progenitors, respectively, are fitted in de-projected elliptical bins to obtain their rotational velocities, Vϕ, and corresponding dispersions, σϕ. We assign ages to the two PN populations by comparing central-star properties of an archival sub-sample of PNe, that have models fitted to their observed spectral features, to stellar evolution tracks. Results. For the high- and low-extinction PNe, we find ages of ∼2.5 and ∼4.5 Gyr, respectively, with distinct kinematics beyond a deprojected radius RGC = 14 kpc. At RGC = 17–20 kpc, which is the equivalent distance in disc scale lengths of the Sun in the Milky Way disc, we obtain σϕ,  2.5 Gyr = 61 ± 14 km s−1 and σϕ,  4.5 Gyr = 101 ± 13 km s−1. The age–velocity dispersion relation for the M 31 disc is obtained in two radial bins, RGC = 14–17 and 17–20 kpc. Conclusions. The high- and low-extinction PNe are associated with the young thin and old thicker disc of M 31, respectively, whose velocity dispersion values increase with age. These values are almost twice and three times that of the Milky Way disc stellar population of corresponding ages, respectively. From comparison with simulations of merging galaxies, we find that the age–velocity dispersion relation in the M 31 disc measured using PNe is indicative of a single major merger that occurred 2.5–4.5 Gyr ago with an estimated merger mass ratio ≈1:5.

The existing open-cluster membership determination algorithms are either prior dependent on some known parameters of clusters or are not automatable to large samples of clusters. In this paper, we present ml-moc, a new machine-learning-based approach to identify likely members of open clusters using the Gaia DR2 data and no a priori information about cluster parameters. We use the k-nearest neighbour (kNN) algorithm and the Gaussian mixture model (GMM) on high-precision proper motions and parallax measurements from the Gaia DR2 data to determine the membership probabilities of individual sources down to G ∼ 20 mag. To validate the developed method, we apply it to 15 open clusters: M67, NGC 2099, NGC 2141, NGC 2243, NGC 2539, NGC 6253, NGC 6405, NGC 6791, NGC 7044, NGC 7142, NGC 752, Blanco 1, Berkeley 18, IC 4651, and Hyades. These clusters differ in terms of their ages, distances, metallicities, and extinctions and cover a wide parameter space in proper motions and parallaxes with respect to the field population. The extracted members produce clean colour–magnitude diagrams and our astrometric parameters of the clusters are in good agreement with the values derived in previous work. The estimated degree of contamination in the extracted members ranges between 2 ${{\ \rm per\ cent}}$ and 12 ${{\ \rm per\ cent}}$. The results show that ml-moc is a reliable approach to segregate open-cluster members from field stars.

Context. The Andromeda (M 31) galaxy subtends nearly 100 square degrees on the sky. Any study of its halo must therefore account for the severe contamination from the Milky Way halo stars whose surface density displays a steep gradient across the entire M 31 field of view. Aims. Our goal is to identify a population of stars firmly associated with the M 31 galaxy. Planetary nebulae (PNe) are one such population that are excellent tracers of light, chemistry, and motion in galaxies. We present a 16 square degree survey of the disc and inner halo of M 31 with the MegaCam wide-field imager at the CFHT to identify PNe, and characterise the luminosity-specific PN number and PN luminosity function (PNLF) in M 31. Methods. PNe were identified via automated detection techniques based on their bright [O iii] 5007 Å emission and absence of a continuum. Subsamples of the faint PNe were independently confirmed by matching with resolved Hubble Space Telescope sources from the Panchromatic Hubble Andromeda Treasury and spectroscopic follow-up observations with HectoSpec at the MMT. Results. The current survey reaches two magnitudes fainter than the previous most sensitive survey. We thus identify 4289 PNe, of which only 1099 were previously known. By comparing the PN number density with the surface brightness profile of M 31 out to ∼30 kpc along the minor axis, we find that the stellar population in the inner halo has a luminosity-specific PN number value that is seven times higher than that of the disc. We measure the luminosity function of the PN population and find a bright cut-off and a slope consistent with previous determinations. Interestingly, it shows a significant rise at the faint end, present in all radial bins covered by the survey. This rise in the M 31 PNLF is much steeper than that observed for the Magellanic clouds and Milky Way bulge. Conclusions. The significant radial variation of the PN specific frequency value indicates that the stellar population at deprojected minor-axis radii larger than ∼10 kpc is different from that in the disc of M 31. The rise at the faint end of the PNLF is a property of the late phases of the stellar population. M 31 shows two major episodes of star formation and the rise at the faint end of the PNLF is possibly associated with the older stellar population. It may also be a result of varying opacity of the PNe.