34 research outputs found
A test method for analog circuits : using sensitivity analysis and the singular value decomposition
XVII+C.3hlm.;24c
Two new ultracool benchmark systems from WISE+2MASS
We have used the Two-Micron All-Sky Survey and the Wide-field Infrared Survey Explorer to look for ultracool dwarfs that are part of multiple systems containing main-sequence stars. We cross-matched L dwarf candidates from the surveys with Hipparcos and Gliese stars, finding two new systems. The first system, G255-34AB, is an L2 dwarf companion to a K8 star, at a distance of 36 pc. We estimate its bolometric luminosity as log L/L-circle dot = -3.78 +/- 0.045 and T-eff = 2080 +/- 260 K. The second system, GJ499ABC, is a triple, with an L5 dwarf as a companion to a binary with an M4 and K5 star. These two new systems bring the number of L dwarf plus main-sequence star multiple systems to 24, which we discuss. We consider the binary fraction for L dwarfs and main-sequence stars, and further assess possible unresolved multiplicity within the full companion sample. This analysis shows that some of the L dwarfs in this sample might actually be unresolved binaries themselves, since their M-J appears to be brighter than the expected for their spectral types.Peer reviewe
A Radial Velocity Study of CTCV J1300-3052
We present time-resolved spectroscopy of the eclipsing, short period
cataclysmic variable CTCV J1300-3052. Using absorption features from the
secondary star, we determine the radial velocity semi-amplitude of the
secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity
to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo
techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf
primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These
parameters are found to be in excellent agreement with previous mass
determinations found via photometric fitting techniques, supporting the
accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9
figures (black and white
76 T dwarfs from the UKIDSS LAS : benchmarks, kinematics and an updated space density
We report the discovery of 76 new T dwarfs from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS). Near-infrared broad- and narrow-band photometry and spectroscopy are presented for the new objects, along with Wide-field Infrared Survey Explorer (WISE) and warm-Spitzer photometry. Proper motions for 128 UKIDSS T dwarfs are presented from a new two epoch LAS proper motion catalogue. We use these motions to identify two new benchmark systems: LHS 6176AB, a T8p+M4 pair and HD 118865AB, a T5.5+F8 pair. Using age constraints from the primaries and evolutionary models to constrain the radii, we have estimated their physical properties from their bolometric luminosity. We compare the colours and properties of known benchmark T dwarfs to the latest model atmospheres and draw two principal conclusions. First, it appears that the H - [4.5] and J - W2 colours are more sensitive to metallicity than has previously been recognized, such that differences in metallicity may dominate over differences in T-eff when considering relative properties of cool objects using these colours. Secondly, the previously noted apparent dominance of young objects in the late-T dwarf sample is no longer apparent when using the new model grids and the expanded sample of late-T dwarfs and benchmarks. This is supported by the apparently similar distribution of late-T dwarfs and earlier type T dwarfs on reduced proper motion diagrams that we present. Finally, we present updated space densities for the late-T dwarfs, and compare our values to simulation predictions and those from WISE.Peer reviewe
HST and Optical Data Reveal White Dwarf Cooling, Spin and Periodicities in GW Librae 3-4 Years after Outburst
Since the large amplitude 2007 outburst which heated its accreting, pulsating
white dwarf, the dwarf nova system GW Librae has been cooling to its quiescent
temperature. Our Hubble Space Telescope ultraviolet spectra combined with
ground-based optical coverage during the 3rd and 4th year after outburst show
that the fluxes and temperatures are still higher than quiescence (T=19,700K
and 17,300K vs 16,000K pre-outburst for a log g=8.7 and d=100 pc). The K{wd} of
7.6+/-0.8 km/s determined from the CI1463 absorption line, as well as the
gravitational redshift implies a white dwarf mass of 0.79+/-0.08 Msun. The
widths of the UV lines imply a white dwarf rotation velocity vsin i of 40 km/s
and a spin period of 209 s (for an inclination of 11 deg and a white dwarf
radius of 7x10^{8} cm). Light curves produced from the UV spectra in both years
show a prominent multiplet near 290 s, with higher amplitude in the UV compared
to the optical, and increased amplitude in 2011 vs 2010. As the presence of
this set of periods is intermittent in the optical on weekly timescales, it is
unclear how this relates to the non-radial pulsations evident during
quiescence.Comment: 36 pages, 15 figures; Astrophysical Journal, 2012, 75
IGAPS: the merged IPHAS and UVEX optical surveys of the Northern Galactic Plane
The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Hα, g, and U_(RGO). The IGAPS footprint fills the Galactic coordinate range, |b| 5σ confidence)