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Abstract:

We present preliminary results from a high-cadence photometric monitoring survey of the 130 Myr old open cluster M50. Using the semi-automated occultation detection process developed by Miller et al. [1], we uncovered eight low mass (< 1M⊙) eclipsing binary candidates in the cluster. Preliminary analysis of spectroscopic follow-up on five of these candidates confirms their binary nature. One candidate also exhibits a systemic velocity broadly consistent with the cluster radial velocity, indicating cluster membership. Confirmation of these eight candidates as true members of the M50 cluster will allow us to provide important constraints to the mass-radius relationship for objects below 1M⊙ at ages younger than lGyr, where current observations remain scarce. © 2009 American Institute of Physics.

Abstract:

We present a preliminary analysis of the H I properties of early-type galaxies in the ATLAS^3D sample. Using WSRT data for ~100 galaxies outside the Virgo cluster and data from the Alfalfa project for galaxies inside Virgo, we discuss the dependence of H I properties on environment. We detect H I in about half of the galaxies outside Virgo. For these systems, the H I morphology and kinematics change as a function of environment, going from regular, rotating systems around “isolated” galaxies to progressively more disturbed structures for galaxies with neighbours or in groups. In denser environment, inside Virgo, nearly none of the galaxies contains H I. We discuss future work in this field which will be enabled by next-generation, pre-SKA radio instruments. We present a simulated Apertif H I observation of an ATLAS^3D early-type galaxy, showing how its appearance and detection level vary as a function of redshift.

Abstract:

We present a statistical study of the low-mass X-ray binary (LMXB) populations of three nearby, old elliptical galaxies: NGC 3379, NGC 4278, and NGC 4697. With a cumulative 1 Ms Chandra ACIS observing time, we detect 90-170 LMXBs within the D25 ellipse of each galaxy. Cross-correlating Chandra X-ray sources and HST optical sources, we identify 75 globular cluster (GC) LMXBs and 112 field LMXBs with LX > 10³⁶ erg s^-1 (detections of these populations are 90% complete down to luminosities in the range of 6 × 10³⁶ to 1.5 × 10 ³⁷ergs^-1). At the higher luminosities explored in previous studies, the statistics of this sample are consistent with the properties of GC-LMXBs reported in the literature. In the low-luminosity range allowed by our deeper data (LX < 5 × 10³⁷ erg s^-1), we find a significant relative lack of GC-LMXBs, when compared with field sources. Using the co-added sample from the three galaxies, we find that the incompleteness-corrected X-ray luminosity functions (XLFs) of GC and field LMXBs differ at 4σ significance at LX < 5 × 10³⁷ erg s^-1. As previously reported, these XLFs are consistent at higher luminosities. The presently available theoretical models for LMXB formation and evolution in clusters are not sophisticated enough to provide a definite explanation for the shape of the observed GC-LMXB XLF. Our observations may indicate a potential predominance of GC-LMXBs with donors evolved beyond the main sequence, when compared to current models, but their efficient formation requires relatively high initial binary fractions in clusters. The field LMXB XLF can be fitted with either a single power-law model plus a localized excess at a luminosity of (5-6) × 10³⁷ erg s^-1, or a broken power law with a similar low-luminosity break. This XLF may be explained with NS-red-giant LMXBs, contributing to 15% of total LMXBs population at 5 × 10³⁷ erg s^-1. The difference in the GC and field XLFs is consistent with different origins and/or evolutionary paths between the two LMXB populations, although a fraction of the field sources are likely to have originated in GCs. © 2009 The American Astronomical Society. All rights reserved.