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C. G. Tinney

Publications and source records attributed to C. G. Tinney.

At least 127 records · Page 7Linked to original sources
arXiv2008

Fifteen new T dwarfs discovered in the UKIDSS Large Area Survey

We present the discovery of fifteen new T2.5-T7.5 dwarfs (with estimated distances between ~24-93pc, identified in the first three main data releases of the UKIRT Infrared Deep Sky Survey. This brings the total number of T dwarfs discovered in the Large Area Survey (to date) to 28. These discoveries are confirmed by near infrared spectroscopy, from which we derive spectral types on the unified scheme of Burgasser et al. (2006). Seven of the new T dwarfs have spectral types of T2.5-T4.5, five have spectral types of T5-T5.5, one is a T6.5p, and two are T7-7.5. We assess spectral morphology and colours to identify T dwarfs in our sample that may have non-typical physical properties (by comparison to solar neighbourhood populations). The colours of the full sample of LAS T dwarfs show a possible trend to bluer Y-J with decreasing effective temperature beyond T8. By accounting for the main sources of incompleteness (selection, follow-up and spatial) as well as the effects of unresolved binarity and Malmquist bias, we estimate that there are 17+-4 >=T4 dwarfs in the J<=19 volume of the LAS second data release. Comparing this to theoretical predictions is most consistent with a sub-stellar mass function exponent alpha between -1.0 and 0. This is consistent with the latest 2MASS/SDSS constraint (which is based on lower number statistics), and is significantly lower than the alpha~1.0 suggested by L dwarf field populations, possibly a result of the lower mass range probed by the T dwarf class.

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arXiv2008

The amplitude of solar oscillations using stellar techniques

The amplitudes of solar-like oscillations depend on the excitation and damping, both of which are controlled by convection. Comparing observations with theory should therefore improve our understanding of the underlying physics. However, theoretical models invariably compute oscillation amplitudes relative to the Sun, and it is therefore vital to have a good calibration of the solar amplitude using stellar techniques. We have used daytime spectra of the Sun, obtained with HARPS and UCLES, to measure the solar oscillations and made a detailed comparison with observations using the BiSON helioseismology instrument. We find that the mean solar amplitude measured using stellar techniques, averaged over one full solar cycle, is 18.7 +/- 0.7 cm/s for the strongest radial modes (l=0) and 25.2 +/- 0.9 cm/s for l=1. In addition, we use simulations to establish an equation that estimates the uncertainty of amplitude measurements that are made of other stars, given that the mode lifetime is known. Finally, we also give amplitudes of solar-like oscillations for three stars that we measured from a series of short observations with HARPS (gamma Ser, beta Aql and alpha For), together with revised amplitudes for five other stars for which we have previously published results (alpha Cen A, alpha Cen B, beta Hyi, nu Ind and delta Pav).

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arXiv2008

Beyond the Iron Peak: r- and s-process Elemental Abundances in Stars with Planets

We present elemental abundances of 118 stars (28 of which are known extrasolar planetary host stars) observed as part of the Anglo-Australian Planet Search. Abundances of O, Mg, Cr, Y, Zr, Ba, Nd and Eu (along with previously published abundances for C and Si) are presented. This study is one of the first to specifically examine planetary host stars for the heavy elements produced by neutron capture reactions. We find that the host stars are chemically different to both the standard solar abundance and non-host stars in all elements studied, with enrichments over non-host stars ranging from 0.06 dex (for O) to 0.11 dex (for Cr and Y). Such abundance trends are in agreement with other previous studies of field stars and lead us to conclude that the chemical anomalies observed in planetary host stars are the result of normal galactic chemical evolution processes. Based on this observation, we conclude that the observed chemical traits of planetary host stars are primordial in origin, coming from the original nebula and not from a ``pollution'' process occurring during or after formation and that planet formation occurs naturally with the evolution of stellar material.

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arXiv2008

The Impact of Stellar Oscillations on Doppler Velocity Planet Searches

We present a quantitative investigation of the effect of stellar oscillations on Doppler velocity planet searches. Using data from four asteroseismological observation campaigns, we find a power law relationship between the noise impact of these oscillations on Doppler velocities and both the luminosity-to-mass of the target stars, and observed integration times. Including the impact of oscillation jitter should improve the quality of Keplerian fits to Doppler velocity data. The scale of the effect these oscillations have on Doppler velocity measurements is smaller than that produced by stellar activity, but is most significant for giant and subgiant stars, and at short integration times (i.e. less than a few minutes). Such short observation times tend to be used only for very bright stars. However, since it is these very same stars that tend to be targeted for the highest precision observations, as planet searches probe to lower and lower planet masses, oscillation noise for these stars can be significant and needs to be accounted for in observing strategies.

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arXiv2007

Solar-like oscillations in the metal-poor subgiant nu Indi: II. Acoustic spectrum and mode lifetime

Convection in stars excites resonant acoustic waves which depend on the sound speed inside the star, which in turn depends on properties of the stellar interior. Therefore, asteroseismology is an unrivaled method to probe the internal structure of a star. We made a seismic study of the metal-poor subgiant star nu Indi with the goal of constraining its interior structure. Our study is based on a time series of 1201 radial velocity measurements spread over 14 nights obtained from two sites, Siding Spring Observatory in Australia and ESO La Silla Observatory in Chile. The power spectrum of the high precision velocity time series clearly presents several identifiable peaks between 200 and 500 uHz showing regularity with a large and small spacing of 25.14 +- 0.09 uHz and 2.96 +- 0.22 uHz at 330 uHz. Thirteen individual modes have been identified with amplitudes in the range 53 to 173 cm/s. The mode damping time is estimated to be about 16 days (1-sigma range between 9 and 50 days), substantially longer than in other stars like the Sun, the alpha Cen system or the giant xi Hya.

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arXiv2007

Solar-like oscillations in the G2 subgiant beta Hydri from dual-site observations

We have observed oscillations in the nearby G2 subgiant star beta Hyi using high-precision velocity observations obtained over more than a week with the HARPS and UCLES spectrographs. The oscillation frequencies show a regular comb structure, as expected for solar-like oscillations, but with several l=1 modes being strongly affected by avoided crossings. The data, combined with those we obtained five years earlier, allow us to identify 28 oscillation modes. By scaling the large frequency separation from the Sun, we measure the mean density of beta Hyi to an accuracy of 0.6%. The amplitudes of the oscillations are about 2.5 times solar and the mode lifetime is 2.3 d. A detailed comparison of the mixed l=1 modes with theoretical models should allow a precise estimate of the age of the star.

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arXiv2007

Two T dwarfs from the UKIDSS Early Data Release

We report on the first ultracool dwarf discoveries from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release (LAS EDR), in particular the discovery of T dwarfs which are fainter and more distant than those found using the 2MASS and SDSS surveys. We aim to show that our methodologies for searching the ~27 sq degs of the LAS EDR are successful for finding both L and T dwarfs $via$ cross-correlation with the Sloan Digital Sky Survey (SDSS) DR4 release. While the area searched so far is small, the numbers of objects found shows great promise for near-future releases of the LAS and great potential for finding large numbers of such dwarfs. Ultracool dwarfs are selected by combinations of their YJH(K) UKIDSS colours and SDSS DR4 z-J and i-z colours, or, lower limits on these red optical/infrared colours in the case of DR4 dropouts. After passing visual inspection tests, candidates have been followed up by methane imaging and spectroscopy at 4m and 8m-class facilities. Our main result is the discovery following CH4 imaging and spectroscopy of a T4.5 dwarf, ULASJ 1452+0655, lying ~80pc distant. A further T dwarf candidate, ULASJ 1301+0023, has very similar CH4 colours but has not yet been confirmed spectroscopically. We also report on the identification of a brighter L0 dwarf, and on the selection of a list of LAS objects designed to probe for T-like dwarfs to the survey J-band limit. Our findings indicate that the combination of the UKIDSS LAS and SDSS surveys provide an excellent tool for identifying L and T dwarfs down to much fainter limits than previously possible. Our discovery of one confirmed and one probable T dwarf in the EDR is consistent with expectations from the previously measured T dwarf density on the sky.

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arXiv2007

New Planets around Three G Dwarfs

Doppler velocity measurements from the Anglo-Australian Planet Search reveal planetary mass companions to HD23127, HD159868, and a possible second planetary companion to HD154857. These stars are all G dwarfs. The companions are all in eccentric orbits with periods ranging from 1.2 to >9.3yr, minimum (M sin i) masses ranging from 1.5 to >4.5 Mjup, and semimajor axes between 1 and >4.5 AU. The orbital parameters are updated for the inner planet to HD154857, while continued monitoring of the outer companion is required to confirm its planet status.

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arXiv2006

Four New Exoplanets and Hints of Additional Substellar Companions to Exoplanet Host Stars

We present four new exoplanets: HIP 14810 b & c, HD 154345 b, and HD 187123 c. The two planets orbiting HIP 14810, from the N2K project, have masses of 3.9 and 0.76 M_jup. We have searched the radial velocity time series of 90 known exoplanet systems and found new residual trends due to additional, long period companions. Two stars known to host one exoplanet have sufficient curvature in the residuals to a one planet fit to constrain the minimum mass of the outer companion to be substellar: HD 68988 c with 8 M_jup < M sini < 20 M_jup and HD 187123 c with 3 M_jup < msini < 7 M_jup$, both with P > 8 y. We have also searched the velocity residuals of known exoplanet systems for prospective low-amplitude exoplanets and present some candidates. We discuss techniques for constraining the mass and period of exoplanets in such cases, and for quantifying the significance of weak RV signals. We also present two substellar companions with incomplete orbits and periods longer than 8 y: HD 24040 b and HD 154345 b with M sini < 20 M_jup and M sini < 10 M_jup, respectively.

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arXiv2006

Catalog of Nearby Exoplanets

We present a catalog of nearby exoplanets, available at http://exoplanets.org and ApJ 646, 505 (published version available at the link above). It contains the 172 known low mass companions with orbits established through radial velocity and transit measurements around stars within 200 pc. We include 5 previously unpublished exoplanets orbiting the stars HD 11964, HD 66428, HD 99109, HD 107148, and HD 164922. We update orbits for 90 additional exoplanets including many whose orbits have not been revised since their announcement, and include radial velocity time series from the Lick, Keck, and Anglo-Australian Observatory planet searches. Both these new and previously published velocities are more precise here due to improvements in our data reduction pipeline, which we applied to archival spectra. We present a brief summary of the global properties of the known exoplanets, including their distributions of orbital semimajor axis, minimum mass, and orbital eccentricity.

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arXiv2006

An Activity Catalogue of Southern Stars

We have acquired high-resolution echelle spectra of 225 F6-M5 type stars in the southern hemisphere. The stars are targets or candidates to be targets for the Anglo-Australian Planet Search. CaII HK line cores were used to derive activity indices for all of these objects. The indices were converted to the Mt. Wilson system of measurements and logR'HK values determined. A number of these stars had no previously derived activity indices. In addition we have also included the stars from Tinney et al. (2002) using our Mt. Wilson calibration. The radial-velocity instability (also known as jitter) level was determined for all 21 planet-host stars in our dataset. We find the jitter to be at a level considerably below the radial-velocity signatures in all but one of these systems. 19 stars from our sample were found to be active (logR'HK > -4.5) and thus have high levels of jitter. Radial-velocity analysis for planetary companions to these stars should precede with caution.

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arXiv2006

High eccentricity planets from the Anglo-Australian Planet Search

We report Doppler measurements of the stars HD187085 and HD20782 which indicate two high eccentricity low-mass companions to the stars. We find HD187085 has a Jupiter-mass companion with a ~1000d orbit. Our formal `best fit' solution suggests an eccentricity of 0.47, however, it does not sample the periastron passage of the companion and we find that orbital solutions with eccentricities between 0.1 and 0.8 give only slightly poorer fits (based on RMS and chi^2) and are thus plausible. Observations made during periastron passage in 2007 June should allow for the reliable determination of the orbital eccentricity for the companion to HD187085. Our dataset for HD20782 does sample periastron and so the orbit for its companion can be more reliably determined. We find the companion to HD20782 has M sin i=1.77+/-0.22M_JUP, an orbital period of 595.86+/-0.03d and an orbit with an eccentricity of 0.92+/-0.03. The detection of such high-eccentricity (and relatively low velocity amplitude) exoplanets appears to be facilitated by the long-term precision of the Anglo-Australian Planet Search. Looking at exoplanet detections as a whole, we find that those with higher eccentricity seem to have relatively higher velocity amplitudes indicating higher mass planets and/or an observational bias against the detection of high eccentricity systems.

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arXiv2006

The 2:1 resonant exoplanetary system orbiting HD73526

We report the detection of a second exoplanet orbiting the G6V dwarf HD73526. This second planet has an orbital period of 377 d, putting it in a 2:1 resonance with the previously known exoplanet, the orbital period for which is updated to 188d. Dynamical modeling of the combined system allows solution for a self-consistent set of orbital elements for both components. HD73526 is the fourth exoplanetary system (of a total of 18 systems with 2 or more components currently known) to have components detected in 2:1 resonance. Finding such a large fraction of multiple planets (more than 20 per cent) in 2:1 resonance strongly suggests that orbital migration, halted by stabilisation in a trapping resonance, plays an important role in the evolution of exoplanets in multiple planet systems.

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arXiv2005

The 2MASS Wide-Field T Dwarf Search. IV Unting out T dwarfs with Methane Imaging

We present first results from a major program of methane filter photometry for low-mass stars and brown dwarfs. The definition of a new methane filter photometric system is described. A recipe is provided for the differential calibration of methane imaging data using existing 2MASS photometry. We show that these filters are effective in discriminating T dwarfs from other types of stars, and demonstrate this with Anglo-Australian Telescope observations using the IRIS2 imager. Methane imaging data and proper motions are presented for ten T dwarfs identified as part of the 2MASS "Wide Field T Dwarf Search" -- seven of them initially identified as T dwarfs using methane imaging. We also present near-infrared moderate resolution spectra for five T dwarfs, newly discovered by this technique. Spectral types obtained from these spectra are compared to those derived from both our methane filter observations, and spectral types derived by other observers. Finally, we suggest a range of future programs to which these filters are clearly well suited: the winnowing of T dwarf and Y dwarf candidate objects coming from the next generation of near-infrared sky surveys; the robust detection of candidate planetary-mass brown dwarfs in clusters; the detection of T dwarf companions to known L and T dwarfs via deep methane imaging; and the search for rotationally-modulated time-variable surface features on cool brown dwarfs.

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arXiv2005

The 2MASS Wide-Field T Dwarf Search. V. Discovery of a T Dwarf via Methane Imaging

We present the discovery of a T dwarf, 2M2151-4853, via differential imaging through methane filters. The filters are designed to highlight the strong absorption in the H band, due to methane found in the atmospheres of T dwarfs, and provide a very efficient means of searching for them. Subsequent J and H band spectroscopy confirms 2M2151-4853 as a T dwarf of type T4.5. It has an estimated spectrophotometric distance of 18 +/- 3 pc, and an estimated tangential velocity of v=50 +/- 10 km/s.

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arXiv2005

Observed Properties of Exoplanets: Masses, Orbits, and Metallicities

We review the observed properties of exoplanets found by the Doppler technique which has revealed 152 exoplanets to date. We focus on our ongoing 18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian Telescopes carried out with a uniform Doppler precision of 3 m/s. The 104 planets detected in our survey have masses as low as 15 M_Earth orbiting between 0.03 and 5.5 AU. The mass distribution rises toward the lowest detectable masses as dN/dM is proportional to M^-1.1. Nearly all giant planets orbiting within 2 AU of all FGK stars within 30 pc have now been discovered. The distribution of semi-major axes rises from 0.3 -- 3.0 AU (in bins of Delta log a), but remains unknown for larger orbits. Extrapolation suggests that 12% of the FGK stars harbor exoplanets within 20 AU. The median orbital eccentricity is =0.25 (excluding those tidally circularized), lower than previously measured . Planets orbiting beyond 3 AU continue to exhibit non-zero eccentricity, suggesting that the circular orbits of giant planets in our Solar System are unusual. The occurrence rate of ``hot Jupiters'' within 0.1 AU is 1.2$\pm$0.3 %. The probability of occurrence of planets varies as the square of the stellar metal abundance, $P \propto N^2_Fe, ranging from $<$3% for stars of subsolar metallicity to 25% for stars with [Fe/H] > +0.3. Nearly 14% of planet-bearing stars harbor multiple-planet systems, occasionally locked in resonances. Kepler and Corot should measure the occurrence of earth-sized planets. The Space Interferometry Mission (SIM) will detect planets with masses as low as 3 M_ Earth orbiting within 2 AU of nearby stars and will measure masses, orbits and multiplicity. These candidate rocky planets will motivate spectroscopic follow-up by the ``Terrestrial Planet Finder'' and Darwin.}

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arXiv2005

Science Programs for a 2 m-class Telescope at Dome C, Antarctica: PILOT, the Pathfinder for an International Large Optical Telescope

The cold, dry and stable air above the summits of the Antarctic plateau provides the best ground-based observing conditions from optical to sub-mm wavelengths to be found on the Earth. PILOT is a proposed 2 m telescope, to be built at Dome C in Antarctica, able to exploit these conditions for conducting astronomy at optical and infrared wavelengths. While PILOT is intended as a pathfinder towards the construction of future grand-design facilities, it will also be able to undertake a range of fundamental science investigations in its own right. This paper provides the performance specifications for PILOT, including its instrumentation. It then describes the kinds of science projects that it could best conduct. These range from planetary science to the search for other solar systems, from star formation within the Galaxy to the star formation history of the Universe, and from gravitational lensing caused by exo-planets to that produced by the cosmic web of dark matter. PILOT would be particularly powerful for wide-field imaging at infrared wavelengths, achieving near-diffraction limited performance with simple tip-tilt wavefront correction. PILOT would also be capable of near-diffraction limited performance in the optical wavebands, as well be able to open new wavebands for regular ground based observation; in the mid-IR from 17 to 40 microns and in the sub-mm at 200 microns.

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