Evolved solar systems in Praesepe

"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics." Original paper can be found at: http://scitation.aip.org/"We have obtained near-IR photometry for the 11 Praesepe white dwarfs, to search for an excess indicative of a dusty debris disk. All the white dwarfs are in the DAZ temperature regime, however we find no indications of a disk around any white dwarf. We have, however determined that the radial velocity variable white dwarf WD0837+185 could have an unresolved T8 dwarf companion that would not be seen as a near-IR excess.Final Accepted Versio

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Brown dwarf companions to white dwarfs

"Copyright 2011 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics."Brown dwarf companions to white dwarfs are rare, but recent infra-red surveys are slowly revealing examples. We present new observations of the post-common envelope binary WD0137-349, which reveals the effects of irradiation on the approximate to 0.05M(circle dot) secondary, and new observations of GD 1400 which show that it too is a close, post-common envelope system. We also present the latest results in a near-infrared photometric search for unresolved ultra-cool companions and to white dwarfs with UKIDSS. Twenty five DA white dwarfs were identified as having photometric excesses indicative of a low mass companion, with 8-10 of these having a predicted mass in the range associated with brown dwarfs. The results of this survey show that the unresolved (< 2 '') brown dwarf companion fraction to DA white dwarfs is 0.3 <= f(WD+BD) <= 1.3%.Final Accepted Versio

Component masses of young, wide, non-magnetic white dwarf binaries in the Sloan Digital Sky Survey Data Release 7

We present a spectroscopic component analysis of 18 candidate young, wide, non-magnetic, double-degenerate binaries identified from a search of the Sloan Digital Sky Survey Data Release 7 (DR7). All but two pairings are likely to be physical systems. We show SDSS J084952.47+471247.7 + SDSS J084952.87+471249.4 to be a wide DA + DB binary, only the second identified to date. Combining our measurements for the components of 16 new binaries with results for three similar, previously known systems within the DR7, we have constructed a mass distribution for the largest sample to date (38) of white dwarfs in young, wide, non-magnetic, double-degenerate pairings. This is broadly similar in form to that of the isolated field population with a substantial peak around M ∼ 0.6 M⊙. We identify an excess of ultramassive white dwarfs and attribute this to the primordial separation distribution of their progenitor systems peaking at relatively larger values and the greater expansion of their binary orbits during the final stages of stellar evolution. We exploit this mass distribution to probe the origins of unusual types of degenerates, confirming a mild preference for the progenitor systems of high-field-magnetic white dwarfs, at least within these binaries, to be associated with early-type stars. Additionally, we consider the 19 systems in the context of the stellar initial mass-final mass relation. None appear to be strongly discordant with current understanding of this relationship. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.link_to_subscribed_fulltex

High-field magnetic white dwarfs as the progeny of early-type stars?

We present an analysis of the newly resolved components of two hot, doubledegenerate systems, SDSS J074853.07+302543.5 + J074852.95+302543.4 and SDSS J150813.24+394504.9 + J150813.31+394505.6 (CBS 229). We confirm that each system has widely separated components (a > 100 au) consisting of a H-rich, non-magnetic white dwarf and a H-rich, high-field magnetic white dwarf (HFMWD). The masses of the nonmagnetic degenerates are found to be larger than typical of field white dwarfs. We use these components to estimate the total ages of the binaries and demonstrate that both magnetic white dwarfs are the progeny of stars with Minit > 2M⊙. We briefly discuss the traits of all known hot, wide, magnetic + non-magnetic double degenerates in the context of HFMWD formation theories. These are broadly consistent (chance probability, P≈0.065) with HFMWDs forming primarily from early-type stars and, in the most succinct interpretation, link their magnetism to the fields of their progenitors. Our results do not, however, rule out that HFMWDs can form through close binary interactions and studies of more young, wide double degenerates are required to reach firm conclusions on these formation pathways. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.link_to_subscribed_fulltex

Comprehensive phylogenomic time tree of bryophytes reveals deep relationships and uncovers gene incongruences in the last 500 million years of diversification

&lt;p class="MsoNormal"&gt;&lt;strong&gt;&lt;span&gt;Premise&lt;/span&gt;&lt;/strong&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;span&gt;Bryophytes, land plants defined by a free-living gametophyte and an unbranched sporophyte, form a major component of terrestrial plant biomass, structuring ecological communities in all biomes. &lt;/span&gt;&lt;span&gt;Our understanding of the evolutionary history of hornworts, liverworts and mosses has been significantly reshaped by inferences from molecular data, highlighting extensive homoplasy in various traits and repeated bursts of diversification. However, the timing of key events in the phylogeny, and the degree to which the observed homoplasy represents error or biological processes, remain poorly resolved.&lt;/span&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;strong&gt;&lt;span&gt;Methods&lt;/span&gt;&lt;/strong&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;span&gt;Using the GoFlag probe set, we sampled 405 exons representing 228 nuclear genes for 531 species from 51 of the 53 orders of bryophytes. We inferred the species phylogeny from gene tree analyses using concatenated and coalescence approaches, assessed gene conflict, and estimated the timing of divergences based on 29 fossil calibrations.&lt;/span&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;strong&gt;&lt;span&gt;Results&lt;/span&gt;&lt;/strong&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;span&gt;The phylogeny resolves many relationships across the bryophytes, enabling us to resurrect five liverwort orders and recognize three more, and propose ten new orders of mosses. Most orders originated in the Jurassic or earlier and diversified in the Cretaceous or later. The phylogenomic data also highlight topological conflict in parts of the tree, suggesting complex processes of diversification that cannot be adequately captured in a single gene tree topology. &lt;/span&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;strong&gt;&lt;span&gt;Conclusions&lt;/span&gt;&lt;/strong&gt;&lt;/p&gt; &lt;p class="MsoNormal"&gt;&lt;span&gt;We sampled hundreds of homologous loci across a broad phylogenetic spectrum spanning at least 450 Ma of evolution, and these data resolved many of the critical nodes of the diversification of bryophytes. The data also highlight the need to explore the mechanisms underlying the phylogenetic ambiguity at specific nodes. The phylogenomic data provide an expandable framework toward reconstructing a comprehensive phylogeny of bryophytes and for investigating the transformations of traits in this important group of plants.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;Funding provided by: National Science Foundation&lt;br&gt;Crossref Funder Registry ID: https://ror.org/021nxhr62&lt;br&gt;Award Number: 1541506&lt;/p&gt;&lt;p&gt;Funding provided by: National Science Foundation&lt;br&gt;Crossref Funder Registry ID: https://ror.org/021nxhr62&lt;br&gt;Award Number: 1541545&lt;/p&gt;&lt;p&gt;Funding provided by: National Science Foundation&lt;br&gt;Crossref Funder Registry ID: https://ror.org/021nxhr62&lt;br&gt;Award Number: 1753811&lt;/p&gt;&lt;p&gt;Funding provided by: Natural Sciences and Engineering Research Council&lt;br&gt;Crossref Funder Registry ID: https://ror.org/01h531d29&lt;br&gt;Award Number: 05967–2016&lt;/p&gt;&lt;p&gt;Funding provided by: Canadian Foundation for Innovation*&lt;br&gt;Crossref Funder Registry ID: &lt;br&gt;Award Number: 36781&lt;/p&gt;&lt;p&gt;Funding provided by: Canadian Foundation for Innovation*&lt;br&gt;Crossref Funder Registry ID: &lt;br&gt;Award Number: 39135&lt;/p&gt