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Manchester, United Kingdom

Chandler C.O.,San Francisco State University | McDonald I.,Jodrell Bank Center for Astrophysics | Kane S.R.,San Francisco State University
Astronomical Journal | Year: 2016

Locating planets in circumstellar habitable zones (HZs) is a priority for many exoplanet surveys. Space-based and ground-based surveys alike require robust toolsets to aid in target selection and mission planning. We present the Catalog of Earth-Like Exoplanet Survey Targets (CELESTA), a database of HZs around 37,000 nearby stars. We calculated stellar parameters, including effective temperatures, masses, and radii, and we quantified the orbital distances and periods corresponding to the circumstellar HZs. We gauged the accuracy of our predictions by contrasting CELESTA's computed parameters to observational data. We ascertain a potential return on investment by computing the number of HZs probed for a given survey duration. A versatile framework for extending the functionality of CELESTA into the future enables ongoing comparisons to new observations, and recalculations when updates to HZ models, stellar temperatures, or parallax data become available. We expect to upgrade and expand CELESTA using data from the Gaia mission as the data become available. © 2016. The American Astronomical Society. All rights reserved.. Source

Cordero M.J.,Indiana University Bloomington | Pilachowski C.A.,Indiana University Bloomington | Johnson C.I.,Harvard - Smithsonian Center for Astrophysics | McDonald I.,Jodrell Bank Center for Astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2014

47 Tuc is an ideal target to study chemical evolution and globular cluster (GC) formation in massive more metal-rich GCs, as it is the closest massive GC. We present chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu in 164 red giant branch stars in the massive GC 47 Tuc using spectra obtained with both the Hydra multifiber spectrograph at the Blanco 4 m telescope and the FLAMES multiobject spectrograph at the Very Large Telescope. We find an average [Fe/H] = -0.79 ± 0.09 dex, consistent with literature values, as well as overabundances of alpha-elements ([α/Fe] ∼ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r process-dominated ([Eu/La] = +0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anticorrelation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ∼ -0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A Kolmogorov-Smirnov test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na-Al correlation in 47 Tuc, which is consistent with current models of asymptotic giant branch nucleosynthesis yields. © 2014. The American Astronomical Society. All rights reserved. Source

McDonald I.,Jodrell Bank Center for Astrophysics | Sloan G.C.,Cornell University | Zijlstra A.A.,Jodrell Bank Center for Astrophysics | Matsunaga N.,University of Tokyo | And 4 more authors.
Astrophysical Journal Letters | Year: 2010

Iron, the universe's most abundant refractory element, is highly depleted in both circumstellar and interstellar environments, meaning it exists in solid form. The nature of this solid is unknown. In this Letter, we provide evidence that metallic iron grains are present around oxygen-rich asymptotic giant branch stars, where it is observationally manifest as a featureless mid-infrared excess. This identification is made using Spitzer Space Telescope observations of evolved globular cluster stars, where iron dust production appears ubiquitous and in some cases can be modeled as the only observed dust product. In this context, FeO is examined as the likely carrier for the 20 μm feature observed in some of these stars. Metallic iron appears to be an important part of the dust condensation sequence at low metallicity, and subsequently plays an influential role in the interstellar medium. We explore the stellar metallicities and luminosities at which iron formation is observed, and how the presence of iron affects the outflow and its chemistry. The conditions under which iron can provide sufficient opacity to drive a wind remain unclear. © 2010. The American Astronomical Society. All rights reserved.. Source

Hajduk M.,Nicolaus Copernicus Astronomical Center | van Hoof P.A.M.,Royal Observatory of Belgium | Zijlstra A.A.,Jodrell Bank Center for Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2013

We analyse the remnants of CK Vul (Nova Vul 1670) using optical imaging and spectroscopy. The imaging, obtained between 1991 and 2010, spans 5.6 per cent of the lifetime of the nebula. The flux of the nebula decreased during the last two decades. The central source still maintains the ionization of the innermost part of the nebula, but recombination proceeds in more distant parts of the nebula. Surprisingly, we discovered two stars located within 10 arcsec of the expansion centre of the radio emission that are characterized by pronounced long-term variations and one star with high proper motion. The high proper motion star is a foreground object, and the two variable stars are background objects. The photometric variations of two variables are induced by a dusty cloud ejected by CK Vul and passing through the line of sight to those stars. The cloud leaves strong lithium absorption in the spectra of the stars. We discuss the nature of the object in terms of recent observations. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Mcdonald I.,Jodrell Bank Center for Astrophysics | Johnson C.I.,University of California at Los Angeles | Zijlstra A.A.,Jodrell Bank Center for Astrophysics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2011

We herein determine the average integrated mass-loss from stars belonging to the dominant metal-poor population ([Fe/H] ~-1.7) of the Galactic globular cluster ω Centauri (NGC 5139) during their red giant and horizontal branch (HB) evolution. Masses are empirically calculated from spectroscopic measurements of surface gravity and photometric measurements of temperature and luminosity. Systematic uncertainties prevent an absolute measurement of masses at a phase of evolution. However, the relative masses of early asymptotic giant branch (AGB) stars and central red giant branch (RGB) stars can be measured, and used to derive the mass-loss between these two phases. This can then be used as a physical check of models of HB stars. For ω Centauri, the average difference is found to be 26 ± 4 per cent. Assuming initial and final masses of 0.83 and 0.53 M⊙, we determine that 0.21 ± 0.03 M⊙ is lost on the RGB and 0.09 ±~0.05 M⊙ is lost on the AGB. The implied HB stellar mass of 0.62 ± 0.04 M⊙ is commensurate with literature determinations of the masses of the cluster's HB stars. The accuracy of this measurement can be improved through better selection of stars and spectral coverage, and applied to other clusters where HB models do not currently agree. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS. Source

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