A 2 epoch proper motion catalogue from the UKIDSS Large Area Survey

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedThe UKIDSS Large Area Survey (LAS) began in 2005, with the start of the UKIDSS program as a 7 year effort to survey roughly 4000 square degrees at high galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of 2-epoch J band observations, with epoch baselines ranging from 2 to 7 years. We present a proper motion catalogue for the 1500 square degrees of the 2 epoch LAS data, which includes some 800,000 sources with motions detected above the 5 sigma level. We developed a bespoke proper motion pipeline which applies a source-unique second order polynomial transformation to UKIDSS array coordinates of each source to counter potential local non-uniformity in the focal plane. Our catalogue agrees well with the proper motion data supplied in the current WFCAM Science Archive (WSA) DR9 catalogue where there is overlap, and in various optical catalogues, but it benefits from some improvements. One improvement is that we provide absolute proper motions, using LAS galaxies for the relative to absolute correction. Also, by using unique, local, 2nd order polynomial tranformations, as opposed to the linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by their pipeline

Measuring ultracool properties from the UKIDSS Large Area Survey

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedWe discuss the properties and of ultracool and brown dwarfs that can be measured from current large area surveys and how fundamental parameters, such as the mass function and formation history can be measured, describing our own first measurement of the formation history in the sub-stellar regime using data from the UKIDSS Large Area Survey

Primeval very low-mass stars and brown dwarfs -- II. The most metal-poor substellar object

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.SDSS J010448.46+153501.8 has previously been classified as an sdM9.5 subdwarf. However, it's very blue J-K colour (-0.15+/-0.17) suggests a much lower metallicity compared to normal sdM9.5 subdwarfs. Here we re-classify this object as a usdL1.5 subdwarf based on a new optical and near-infrared spectrum obtained with X-shooter on the Very Large Telescope. Spectral fitting with BT-Settl models leads to Teff = 2450+/-150 K, [Fe/H] = -2.4+/-0.2 and log g = 5.5+/-0.25. We estimate a mass for SDSS J010448.46+153501.8 of 0.0855+/-0.0015 M_{\sun} which is just below the hydrogen-burning minimum mass at [Fe/H] = -2.4 (\sim0.0875 M_{\sun}) according to evolutionary models. Our analysis thus shows SDSS J0104+15 to be the most metal-poor and highest mass substellar object known to date. We found that SDSS J010448.46+153501.8 is joined by another five known L subdwarfs (2MASS J05325346+8246465, 2MASS J06164006-6407194, SDSS J125637.16-022452.2, ULAS J151913.03-000030.0, and 2MASS J16262034+3925190) in a `halo brown dwarf transition zone' in the Teff-[Fe/H] plane, which represents a narrow mass range in which unsteady nuclear fusion occurs. This halo brown dwarf transition zone forms a `substellar subdwarf gap' for mid L to early T types.Peer reviewe

A blue depression in the optical spectra of M dwarfs

A blue depression is found in the spectra of M dwarfs from 4000 to 4500A. This depression shows an increase toward lower temperatures though is particularly sensitive to gravity and metallicity. It is the single most sensitive feature in the optical spectra of M dwarfs. The depression appears as centered on the neutral calcium resonance line at 4227A and leads to nearby features being weaker by about two orders of magnitude than predicted. We consider a variety of possible causes for the depression including temperature, gravity, metallicity, dust, damping constants, and atmospheric stratification. We also consider relevant molecular opacities which might be the cause identifying AlH, SiH, and NaH in the spectral region. However, none of these solutions are satisfactory. In the absence of a more accurate determination of the broadening of the calcium line perturbed by molecular hydrogen, we find a promising empirical fit using a modified Lorentzian line profile for the calcium resonance line. Such fits provide a simplistic line-broadening description for this calcium resonance line and potentially other un-modelled resonance lines in cool high-pressure atmospheres. Thus we claim the most plausible cause of the blue depression in the optical spectra of M dwarfs is a lack of appropriate treatment of line broadening for atomic calcium. The broad wings of the calcium resonance line develop at temperatures below about 4000K and are analogous to the neutral sodium and potassium features which dominate the red optical spectra of L dwarfs.Comment: Accepted in MNRA

The metal rich abundance pattern - spectroscopic properties and abundances for 107 main-sequence stars

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, ©: 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.We report results from the high resolution spectral analysis of the 107 metal rich (mostly [Fe/H]$\ge$7.67 dex) target stars from the Calan-Hertfordshire Extrasolar Planet Search program observed with HARPS. Using our procedure of finding the best fit to the absorption line profiles in the observed spectra, we measure the abundances of Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Ni, Cu, and Zn, and we then compare them with known results from different authors. Most of our abundances agree with these works at the level of $\pm$0.05 dex or better for the stars we have in common. However, we do find systematic differences that make direct inferences difficult. Our analysis suggests that the selection of line lists and atomic line data along with the adopted continuum level influence these differences the most. At the same time, we confirm the positive trends of abundances versus metallicity for Na, Mn, Ni, and to a lesser degree, Al. A slight negative trend is observed for Ca, whereas Si and Cr tend to follow iron. Our analysis allows us to determine the positively skewed normal distribution of projected rotational velocities with a maximum peaking at 3 km s$^{-1}$. Finally, we obtained a Gaussian distribution of microturbulent velocities that has a maximum at 1.2 km s$^{-1}$ and a full width at half maximum $\Delta v_{1/2}=$0.35 km s$^{-1}$, indicating that metal rich dwarfs and subgiants in our sample have a very restricted range in microturbulent velocity.Peer reviewedFinal Published versio

Identifying and characterizing ultracool dwarfs ejected from post-encounter disintegrating systems

Disintegrating multiple systems have been previously discovered from kinematic studies of the $\it Hipparcos$ catalogue. They are presumably the result of dynamical encounters taking place in the Galactic disk 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 $\it Gaia$ DR3), and here we present the discovery and follow-up of 5 of them. We have obtained DECam imaging for all 5 systems and by combining near-infrared photometry and proper motion, we searched for ultra-cool 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 ultra-cool dwarf candidate. Using additional data from the literature, we have found that 3 out of 5 disintegrating system candidates are likely to be true disintegrating systems.Comment: Accepted for publication in MNRAS. 17 pages, 8 figures, 4 table

The Transit Light Curve Project. VII. The Not-So-Bloated Exoplanet HAT-P-1b

We present photometry of the G0 star HAT-P-1 during six transits of its close-in giant planet, and we refine the estimates of the system parameters. Relative to Jupiter's properties, HAT-P-1b is 1.20 +/- 0.05 times larger and its surface gravity is 2.7 +/- 0.2 times weaker. Although it remains the case that HAT-P-1b is among the least dense of the known sample of transiting exoplanets, its properties are in accord with previously published models of strongly irradiated, coreless, solar-composition giant planets. The times of the transits have a typical accuracy of 1 min and do not depart significantly from a constant period.Comment: To appear in AJ [19pg, 3 figures]. New co-author added. Minor revisions to match published versio