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C. G. Tinney

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

At least 145 records · Page 8Linked to original sources
arXiv2004

Multiple Companions to HD 154857 and HD 160691

Precise Doppler measurements from the AAT/UCLES spectrometer reveal two companions to both HD 154857 and HD 160691. The inner companion to HD 154857 has a period of 398 d, an eccentricity of 0.51, and a minimum mass of 1.8 M_Jupiter An outer companion has a period much longer than 2 years and is currently detected only as a linear trend of 14 m/s per year. The inner companion to HD 160691, previously announced from AAT data, has a period of 645 d, an eccentricity of 0.20, and a minimum mass of 1.7 M_Jupiter. For the outer planet, whose orbit is less well constrained, a two Keplerian fit yields a period of 8.2 yr, an eccentricity of 0.57, and a minimum mass of 3.1 M_Jupiter. With these orbital parameters, its maximum separation from the star of 0.4 arcsec makes it a viable target for direct imaging.

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arXiv2003

A Planet in a Circular Orbit with a 6 Year Period

Precision Doppler velocity measurements from the 3.9--m Anglo-Australian Telescope reveal a planet with a 6 year period orbiting the G5 dwarf HD 70642. The a = 3.3 AU orbit has a low eccentricity (e = 0.1), and the minimum (\msini) mass of the planet is 2.0 \mjup. The host star is metal rich relative to the Sun, similar to most stars with known planets. The distant and approximately circular orbit of this planet makes it a member of a rare group to emerge from precision Doppler surveys.

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arXiv2003

Infrared Parallaxes for Methane T dwarfs

We report final results from our 2.5 year infrared parallax program carried out with the European Southern Observatory 3.5m New Technology Telescope and the SOFI infrared camera. Our program targeted precision astrometric observations of ten T type brown dwarfs in the J band. Full astrometric solutions (including trigonometric parallaxes) for nine T dwarfs are provided along with proper motion solutions for a further object. We find that HgCdTe-based infrared cameras are capable of delivering precision differential astrometry. For T dwarfs, infrared observations are to be greatly preferred over the optical, both because they are so much brighter in the infrared, and because their prominent methane absorptions lead to similar effective wavelengths through the J-filter for both target and reference stars, which in turn results in a dramatic reduction in differential colour refraction effects. We describe a technique for robust bias estimation and linearity correction with the SOFI camera, along with an upper limit to the astrometric distortion of the SOFI optical train. Colour-magnitude and spectral-type-magnitude diagrams for both L and T dwarfs are presented which show complex and significant structure, with major import for luminosity function and mass function work on T dwarfs. Based on the width of the early L dwarf and late T dwarf colour magnitude diagrams, we conclude the brightening of early T dwarfs in the J passband (the "early T hump") is not an age effect, but due to the complexity of brown dwarf cooling curves. Finally, empirical estimates of the "turn on" magnitudes for methane absorption in field T dwarfs and in young stars clusters are provided. These make the interpretation of the T6 dwarf sigma Ori J053810.1-023626 as a sigma Ori member problematic.

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arXiv2003

Time resolved spectroscopy of the variable brown dwarf Kelu-1

We report the results of observations designed to investigate the spectroscopic signatures of dust clouds on the L2 brown dwarf Kelu-1. Time resolved medium resolution spectra show no significant evidence of variability in the dust sensitive TiO, CrH and FeH bandheads on the timescale of 1--24 hours. We do however report periodic variability in the psuedo-equivelent width of H-alpha consistent with the 1.8 hour rotation period previously reported for this object Clarke, Tinney & Tolley (2002). Near-contemporaneous I-band photometry shows evidence for non-periodic variability at the level of 2%.

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arXiv2002

A Flaring L5 Dwarf: The Nature of HαEmission in Very Low Mass (Sub)Stellar Objects

Time series spectrophotometry of the L5 dwarf 2MASS 01443536-0716142 showed strong Hαemission which declined by nearly 75% in four consecutive exposures. The line was not detected in emission on a spectrum obtained eleven months later. This behavior constrasts with that of 2MASSI J1315309-264951, an L5 dwarf which has shown even stronger Hαemission on four separate occasions. The observational database suggests that L dwarfs can be found in such strong flares only occasionally, with a duty cycle of order 1%. In contrast, the few, continuously-strong Hαemitters, including PC 0025+0447 and 2MASSI J1237392+652615, must either be (1) objects no older than 10-100 Myrs with continuously-active accretion and/or chromospheres, but which apparently formed in isolation from known young stellar clusters and associations, or (2) objects empowered by a different and unknown mechanism for the Hαenergy.

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arXiv2002

Proper Motions of Dwarf Spheroidal Galaxies from Hubble Space Telescope Imaging. I: Method and a Preliminary Measurement for Fornax

This article presents and discusses a method for measuring the proper motions of the Galactic dwarf spheroidal galaxies using images taken with the Hubble Space Telescope. The method involves fitting an effective point spread function to the image of a star or quasi-stellar object to determine its centroid with an accuracy of about 0.005 pixel (0.25 milliarcseconds) -- an accuracy sufficient to measure the proper motion of a dwarf spheroidal galaxy using images separated by just a few years. The data consist of images, dithered to reduce the effects of undersampling, taken at multiple epochs with the Space Telescope Imaging Spectrograph or the Wide Field Planetary Camera. The science fields are in the directions of the Carina, Fornax, Sculptor, and Ursa Minor dwarf spheroidal galaxies and each has at least one quasi-stellar object whose identity has been established by other studies. The rate of change with time of the centroids of the stars of the dwarf spheroidal with respect to the centroid of the quasi-stellar object is the proper motion. Four independent preliminary measurements of the proper motion of Fornax for three fields agree within their uncertainties. The weighted average of these measurements is mu_alpha = 49 +- 13 milliarcseconds/century and mu_delta = -59 +- 13 milliarcseconds/century. The Galactocentric velocity derived from the proper motion implies that Fornax is near perigalacticon, may not be bound to the Milky Way, and is not a member of any of the proposed streams of galaxies and globular clusters in the Galactic halo. If Fornax is bound, the Milky Way must have a mass of at least (1.6 +- 0.8) x 10^{12} solar masses.

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arXiv2002

Oscillations in alpha Cen A observed with UCLES at the AAT

We report Doppler measurements of alpha Cen A from time-series spectroscopy made with UCLES at the 3.9-m AAT. Wavelength calibration using an iodine absorption cell produced high-precision velocity measurements, whose power spectrum shows the clear signature of solar-like oscillations, confirming the detection reported by Bouchy and Carrier (2001).

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arXiv2002

Four new planets orbiting somewhat metal-enriched stars

We report the detection of four new extra-solar planets from the Anglo-Australian Planet Search orbiting the somewhat metal-enriched stars HD73526, HD76700, HD30177 and HD2039. The planetary companion of HD 76700 has a circular orbit with a period of 3.98d. With M sin i=0.197+-0.017 Mjup, or 0.69 times the mass of Saturn, is one of the lowest minimum mass extra-solar planets yet detected. The remaining planets all have elliptical orbits with periods ranging from 190.5d to 4.4yr. All four planets have been found orbiting stars from a sub-sample of twenty metal-enriched and faint (V<9) stars, which was added to the Anglo-Australian Planet Search's magnitude-limited V$<$7.5 main sample in October 1998. These stars were selected to be metal-enriched on the basis of their Stromgren photometry, and their enrichment has been subsequently confirmed by detailed spectroscopic analysis.

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arXiv2002

On the Double Planet System Around HD 83443

The Geneva group has reported two Saturn-mass planets orbiting HD 83443 (K0V) with periods of 2.98 and 29.8 d. The two planets have raised interest in their dynamics because of the possible 10:1 orbital resonance and the strong gravitational interactions. We report precise Doppler measurements of HD 83443 obtained with the Keck/HIRES and the AAT/UCLES spectrometers. These measurements strongly confirm the inner planet with period of 2.985 d, with orbital parameters in very good agreement with those of the Geneva group. However these Doppler measurements show no evidence of the outer planet, at thresholds of 1/4 (3 m/s) of the reported velocity amplitude of 13.8 m/s. Thus, the existence of the outer planet is in question. Indeed, the current Doppler measurements reveal no evidence of any second planet with periods less than a year.

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arXiv2002

A mini-survey for variability in early L dwarfs

We report differential I-band photometry of four early L-dwarfs obtained to study variability. We detect variability on the timescale of hours in two objects, 2M0746425+200032 (at a level of 0.007 mag -- 6.5 sigma) and 2M1108307+683017 (0.012 mag -- 5 sigma). We also place upper limits of 0.02 mag (1 sigma) on the variability of two others.

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arXiv2002

Solar-Like Oscillations in beta Hydri: Evidence for Short-Lived High-Amplitude Oscillations

Velocity measurements of the G2 subgiant beta Hyi with both UCLES and CORALIE show a clear excess of power centred at 1.0 mHz. In the UCLES data we find evidence for a short-lived, high-amplitude oscillation event. If confirmed as a feature of subgiants, such `starquakes' would make it harder to measure accurate mode frequencies and perform asteroseismology.

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arXiv2002

Constraining the difference in convective blueshift between the components of alpha Cen with precise radial velocities

New radial velocities of alpha Cen A & B obtained in the framework the Anglo-Australian Planet Search programme as well as in the CORALIE programme are added to those by Endl et al. (2001) to improve the precision of the orbital parameters. The resulting masses are 1.105+/-0.0070 MSun and 0.934+/-0.0061 MSun for A and B respectively. The factors limiting how accurately these masses can be derived from a combined visual-spectroscopic solution are investigated. The total effect of the convective blueshift and the gravitational redshift is also investigated and estimated to differ by 215+/-8 m/s between the components. This suggests that the difference in convective blueshift between the components is much smaller than predicted from current hydrodynamical model atmosphere calculations.

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arXiv2002

Periodic photometric variability of the brown dwarf Kelu-1

We have detected a strong periodicity of 1.80+/-0.05 hours in photometric observations of the brown dwarf Kelu-1. The peak-to-peak amplitude of the variation is ~1.1% (11.9+/-0.8 mmag) in a 41nm wide filter centred on 857nm and including the dust/temperature sensitive TiO & CrH bands. We have identified two plausible causes of variability: surface features rotating into- and out-of-view and so modulating the light curve at the rotation period; or, elliposidal variability caused by an orbiting companion. In the first scenario, we combine the observed vsin(i) of Kelu-1 and standard model radius to determine that the axis of rotation is inclined at 65+/-12 degrees to the line of sight.

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arXiv2001

A probable planetary companion to HD 39091 from the Anglo-Australian Planet Search

We report the detection of a extrasolar planet candidate orbiting the G1 V star HD 39091. The orbital period is 2083 d and the eccentricity is 0.62. With a minimum (M sin $i$) mass of 10.3 M$_{\rm JUP}$ this object falls near the high mass end of the observed planet mass function, and may plausibly be a brown dwarf. Other characteristics of this system, including orbital eccentricity and metallicity, are typical of the well populated class of radial velocity planets in eccentric orbits around metal-rich stars.

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arXiv2001

Two extra-solar planets from the Anglo-Australian Planet Search

We report the detection of two new extra-solar planets from the Anglo-Australian Planet Search around the stars HD142 and HD23079. The planet orbiting HD142 has an orbital period of just under one year, while that orbiting HD23079 has a period of just under two years. HD142 falls into the class of "eccentric" gas giants. HD23079 lies in the recently uncovered class of "epsilon Ret-like" planets - extra-solar gas giant planets with near-circular orbits outside 0.1 a.u. The recent discovery of several more members of this class provides new impetus for the extension of existing planet searches to longer periods, in the search for Jupiter-like planets in Jupiter-like orbits.

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arXiv2000

First Results from the Anglo-Australian Planet Search - A Brown Dwarf Candidate and a 51 Peg-like Planet

We report results from the Anglo-Australian Planet Search -- a survey for planets around 200 solar-type stars in the southern hemisphere, which is being carried out on the 3.9m Anglo-Australian Telescope. Limiting Doppler precisions of 3m/s have been demonstrated from the first 2.5 years of operation, making this the highest precision planet search in the southern hemisphere. From these data we report results for two new sub-stellar detections. The first is a "51 Peg"-like planet around the star HD179949 with Msin i = 0.84 Mjup. Photometric study reveals this is not a transiting system. The second is a brown dwarf or very low-mass star companion to HD164427 in an eccentric orbit with Msin i = 46Mjup. Hipparcos data indicate this latter object is unlikely to have a mass greater than 0.18 Msol.

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arXiv2000

Spectral Evolution of the Peculiar Ic Supernova 1998bw

SN 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supenovae and probably the first supernova associated with a gamma-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the AAT, UKST and the SSO 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 days after V_band maximum in comparison to well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from the observations of classical Ic SNe, we find that the evolution from the photospheric to the nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10% - 50% higher than other SNe and on day 94 emission lines are 45% broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope.

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