We present an extensive photometric and spectroscopic study of two high-redshift clusters of galaxies based on data obtained from the Keck 10m telescopes and the Hubble Space Telescope. The clusters Cl 0023+0423 (z=0.84) and Cl 1604+4304 (z=0.90) are part of a multiwavelength program of Oke, Postman & Lubin (1998AJ....116..549O, Paper I) to study nine candidate clusters at z>~0.6. Based on these observations, we study in detail both the field and cluster populations. From the confirmed cluster members, we find that Cl 0023+0423 actually consists of two components separated by ~2900km/s. A kinematic analysis indicates that the two components are a poor cluster with ~3x10^14^M_{sun}_ and a less massive group with ~10^13^M_{sun}_. Cl 1604+4304 is a centrally concentrated, rich cluster at z=0.8967 with a velocity dispersion of 1226km/s and a mass of ~3x10^15^M_{sun}_.
CCD photometric observations of the eclipsing contact binaries (EW type) V3 and V4 of the cluster NGC 2539 were made in the B and V bands using the 2m telescope at the IUCAA-Girawali Observatory in India. The light curves have been obtained and using the Wilson-Devinney code, the combined photometric solutions have been presented here. The photometric solutions have revealed that both V3 and V4 are W-type contact binary systems with mass ratios of 0.806 and 1.001 respectively. Revised orbital periods, absolute masses and radii of the components have been obtained.
We present spectroscopic and photometric observations of the eclipsing binary V32 located in the central field of the globular cluster NGC 6397. The variable is a single-line spectroscopic binary with an orbital period of 9.8783-days and a large eccentricity of e=0.32. Its systemic velocity (gamma=20.7km/s) and metallicity ([Fe/H]~-1.9) are both consistent with cluster membership.
3C295 is a bright, compact steep spectrum source with a well-studied integrated radio spectral energy distribution (SED) from 132MHz to 15GHz. However, spatially resolved spectral studies have been limited due to a lack of high resolution images at low radio frequencies. These frequencies are crucial for measuring absorption processes, and anchoring the overall spectral modelling of the radio SED. In this paper, we use International LOw-Frequency ARray (LOFAR) Telescope (ILT) observations of 3C295 to study its spatially resolved spectral properties with sub-arcsecond resolution at 132MHz. Combining our new 132MHz observation with archival data at 1.6GHz, 4.8GHz, and 15GHz, we are able to carryout a resolved radio spectral analysis. The spectral properties of the hotspots provides evidence for low frequency flattening. In contrast, the spectral shape across the lobes is consistent with a Jaffe-Perola spectral ageing model. Usingthe integrated spectral information for each component, we then fitted low-frequency absorption models to the hotspots,finding that both free-free absorption and synchrotron self-absorption models provide a better fit to the data than a standard power law. Although we can say there is low-frequency absorption present in the hot spots of 3C295, future observations with the Low Band Antenna of the ILT at 55MHz may allow us to distinguish the type of absorption.
We analyze new multicolor light curves and recently published radial velocity curves for close binaries QX And, RW Com, MR Del, and BD +07 3142 to determine the physical parameters of the components. The light curves are analyzed using a binary star model based on Roche geometry to fit the photometric observations. Spectroscopic parameters, such as the mass ratios and spectral types, were taken from recent spectroscopic studies of the systems in question.
The results of a UBVR photometry observations are presented for eclipsing variable EQ Ori. The binary was observed 1988 with the 1-m telescope at Maidanak Observatory (Uzbekistan).
We present a spectroscopic sample of 746 detached close binary systems from the Sloan Digital Sky Survey (SDSS) Fourth Data Release (2006ApJS..162...38A). The majority of these binaries consist of a white dwarf primary and a low-mass secondary (typically M dwarf) companion. We have determined the temperature and gravity for 496 of the white dwarf primaries and the spectral type and magnetic activity properties for 661 of the low-mass secondaries. We have estimated the distances for each of the white dwarf-main-sequence star binaries and use white dwarf evolutionary grids to establish the age of each binary system from the white dwarf cooling times.
Multiplicity is a fundamental property that is set early during stellar lifetimes, and it is a stringent probe of the physics of star formation. The distribution of close companions around young stars is still poorly constrained by observations. We present an analysis of stellar multiplicity derived from Apache Point Observatory Galactic Evolution Experiment-2 spectra obtained in targeted observations of nearby star-forming regions. This is the largest homogeneously observed sample of high-resolution spectra of young stars. We developed an autonomous method to identify double-lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass range of ~0.05-1.5 M_{sun}_, we find 399 binaries, including both radial velocity (RV) variables and SB2s. The mass ratio distribution of SB2s is consistent with being uniform for q<0.95 with an excess of twins for q>0.95. The period distribution is consistent with what has been observed in close binaries (<10 au) in the evolved populations. Three systems are found to have q~0.1, with a companion located within the brown dwarf desert. There are no strong trends in the multiplicity fraction as a function of cluster age from 1 to 100 Myr. There is a weak dependence on stellar density, with companions being most numerous at {Sigma}_*_~30 stars/pc^-2^ and decreasing in more diffuse regions. Finally, disk-bearing sources are deficient in SB2s (but not RV variables) by a factor of ~2; this deficit is recovered by the systems without disks. This may indicate a quick dispersal of disk material in short-period equal-mass systems that is less effective in binaries with lower q.
