Don Pollacco
University of Warwick, Physics, Faculty Member
WeBo 1 (PN G135.6+01.0), a previously unrecognized planetary nebula with a remarkable thin-ring morphology, was discovered serendipitously on Digitized Sky Survey images. The central star is found to be a late-type giant with... more
WeBo 1 (PN G135.6+01.0), a previously unrecognized planetary nebula with a remarkable thin-ring morphology, was discovered serendipitously on Digitized Sky Survey images. The central star is found to be a late-type giant with overabundances of carbon and s-process elements. The giant is chromospherically active and photometrically variable, with a probable period of 4.7 days; this suggests that the star is spotted, and that 4.7 days is its rotation period. We propose a scenario in which one component of a binary system became an AGB star with a dense stellar wind enriched in C and s-process elements; a portion of the wind was accreted by the companion, contaminating its atmosphere and spinning up its rotation. The AGB star has now become a hot subdwarf, leaving the optical companion as a freshly contaminated barium star inside an ionized planetary nebula.
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The WASP consortium operates two wide-field camera arrays in the northern (La Palma) and southern (Sutherland) hemispheres. Each installation comprises a robotic mount bearing 8 cameras, forming a mosaic with a field of view of 30 degrees... more
The WASP consortium operates two wide-field camera arrays in the northern (La Palma) and southern (Sutherland) hemispheres. Each installation comprises a robotic mount bearing 8 cameras, forming a mosaic with a field of view of 30 degrees in declination by 1 hour in right ascension. Here we describe the system performance, observing strategy, candidate selection procedures and follow-up campaigns, and the yield and physical characteristics of the 16 planets discovered in the course of the survey to date.
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Low-dispersion lUE spectra of V854 Cen show apparent shifts or splitting in the λ2325 C II], λ2800 Mg II, λ2851 Mg I and λ2965 C I lines which, if kinematic, indicate velocities in excess of 1000 km s-1. The variations are seen in all the... more
Low-dispersion lUE spectra of V854 Cen show apparent shifts or splitting in the λ2325 C II], λ2800 Mg II, λ2851 Mg I and λ2965 C I lines which, if kinematic, indicate velocities in excess of 1000 km s-1. The variations are seen in all the UV emission lines simultaneously. The line splitting seems to occur at times near phase 0.0 (maximum light) of the pulsation cycle of the star. Dust formation episodes in V854 Cen also occur at this phase. New high-dispersion spectra of V854 Cen of the Na I D lines show many high-velocity features, both red- and blueshifted, including one at almost -400 km s-1. The line profile variations may be a spectral signature of the gas from which the dust is condensing.
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We present the current status of the WASP project, a pair of wide angle photometric telescopes, individually called SuperWASP. SuperWASP-I is located in La Palma, and SuperWASP-II at Sutherland in South Africa. SW-I began operations in... more
We present the current status of the WASP project, a pair of wide angle photometric telescopes, individually called SuperWASP. SuperWASP-I is located in La Palma, and SuperWASP-II at Sutherland in South Africa. SW-I began operations in April 2004. SW-II is expected to be operational in early 2006. Each SuperWASP instrument consists of up to 8 individual cameras using ultra-wide field lenses backed by high-quality passively cooled CCDs. Each camera covers 7.8×7.8 sq degrees of sky, for nearly 500 sq degrees of total sky coverage. One of the current aims of the WASP project is the search for extra-solar planet transits with a focus on brighter stars in the magnitude range ˜8 to 13. Additionally, WASP will search for optical transients, track Near-Earth Objects, and study many types of variable stars and extragalactic objects. The collaboration has developed a custom-built reduction pipeline that achieves better than 1 percent photometric precision. We discuss future goals, which include: nightly on-mountain reductions that could be used to automatically drive alerts via a small robotic telescope network, and possible roles of the WASP telescopes as providers in such a network. Additional technical details of the telescopes, data reduction, and consortium members and institutions can be found on the web site at: http://www.superwasp.org/.
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We have examined the changes of line fluxes of RR Tel in the optical spectra taken in 2000 compared with the corresponding ones of the spectra taken in 1996. The fading of the lines leading to the apparent decrease of the radius of the... more
We have examined the changes of line fluxes of RR Tel in the optical spectra taken in 2000 compared with the corresponding ones of the spectra taken in 1996. The fading of the lines leading to the apparent decrease of the radius of the line emitting region can be understood as being spurious and explained by increased circumstellar dust absorption in the stellar wind of the mira. This dust obscuration event has given clues about stratification effects in the emitting region. In addition, infrared photometry performed from SAAO shows a change in the nature of colour behaviour. It is not yet clear if that is due to a change in dust properties.
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A programme is currently underway to study the kinematics and morphologies of PNe known to contain close-binary central stars. Three of the observed PNe have eclipsing binaries: Abell 63, Abell 46 and SuWt2.; these objects are important... more
A programme is currently underway to study the kinematics and morphologies of PNe known to contain close-binary central stars. Three of the observed PNe have eclipsing binaries: Abell 63, Abell 46 and SuWt2.; these objects are important because their physical parameters can be determined in a model independent way. The properties of these PNe can then be used as tests of stellar evolutionary theory. Long-slit spectra of northern sky targets were obtained in 2004 with the Manchester echelle spectrometer combined with the 2.1-m San Pedro Martir telescope. Southern sky targets were observed in 2005 using UCLES onboard the 3.9-m Anglo-Australian telescope, and the EMMI spectrograph combined with the 3.58-m ESO New Technology Telescope in La Silla. The test case of the programme is Abell 63 as it contains an almost totally eclipsing binary core. The nebula has two faint, elongated lobes and a tube-like appearance. Two end-caps are visible in [NII] at the tips of the lobes. Slits were positioned along the major and minor axes of the nebula. The longslit spectra from the major axis show clear Halpha line-splitting, which can be attributed to receding and approaching sides of an expanding hollow tube. The longslit spectra from the minor axis show a velocity ellipse, which is characteristic of viewing a hollow tube in cross-section. Soker (1998) predicted that bipolar nebulae with very elongated lobes must be produced by an intrinsically collimated fast wind (or jets) puncturing through a pre-existing spherical AGB wind. Soker proposed that the presence of a low-mass companion star is necessary for the production of jets via an accretion disk around the secondary. We tested this hypothesis for Abell 63 using a hydrodynamic simulation of a low-density 400 kms^-1 jet blowing into a uniform, static AGB wind. The resulting morphology closely resembled that of Abell 63.
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PLATO’s objective is to characterize exoplanets and their host stars in the solar neighbourhood. While it builds on the heritage from CoRoT and Kepler, the major breakthrough will come from its strong focus on bright targets (mV ≤ 11).... more
PLATO’s objective is to characterize exoplanets and their host stars in the solar neighbourhood. While it builds on the heritage from CoRoT and Kepler, the major breakthrough will come from its strong focus on bright targets (mV ≤ 11). The PLATO targets will also include a large number of very bright (mV ≤ 8) and nearby stars. The prime science goals of PLATO are: (i) the detection and characterization of exoplanetary systems of all kinds, including both the planets and their host stars, reaching down to small, terrestrial planets in the habitable zone; (ii) the identification of suitable targets for future, more detailed characterization, including a spectroscopic search for bio-markers in nearby habitable exoplanets. These ambitious goals will be reached by ultra-high precision, long (few years), uninterrupted photometric monitoring in the visible of very large samples of bright stars, which can only be done from space. The resulting high quality light curves will be used on the one hand to detect planetary transits, as well as to measure their characteristics, and on the other hand to provide a seismic analysis of the host stars of the detected planets, from which precise measurements of their radii, masses, and ages will be derived. The PLATO space-based data will be complemented by ground-based follow-up observations, in particular very precise radial velocity monitoring, which will be used to confirm the planetary nature of the detected events and to measure the planet masses. The full set of parameters of exoplanetary systems will thus be measured, including all characteristics of the host stars and the orbits, radii, masses, and ages of the planets, allowing us to derive planet mean densities, and estimate their temperature and radiation environment. Finally, the knowledge of the age of the exoplanetary systems will allow us to put them in an evolutionary perspective.
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The southern planetary nebula (PN) SuWt 2 consists of a bright, nearly edge-on ring, with faint bipolar lobes extending perpendicularly to the ring. A bright star located close to the geometric center of the PN has been found to be an... more
The southern planetary nebula (PN) SuWt 2 consists of a bright, nearly edge-on ring, with faint bipolar lobes extending perpendicularly to the ring. A bright star located close to the geometric center of the PN has been found to be an eclipsing binary composed of two nearly identical early A-type stars. There is no evidence in direct images and IUE UV spectra for a hot star in the system, although it is possible that a third star, now faded below detectability due to a high remnant mass, was responsible for ejection of the PN. Extensive photometry and spectroscopy of the 4.9-day binary shows that both stars are larger than main-sequence (MS) stars of their masses, implying that both are evolving off the MS, or conceivably that they are out of thermal equilibrium due to an interaction with the PN wind. Both stars appear to be rotating slower than synchronously with the orbital period. We discuss possible evolutionary scenarios for this bizarre system.
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We propose spectroscopic and photometric observations of the bizarre nucleus of the planetary nebula SuWt 2. Previous CTIO observations have shown the central star to be an eclipsing binary with a period of 4.9 days, surrounded by a... more
We propose spectroscopic and photometric observations of the bizarre nucleus of the planetary nebula SuWt 2. Previous CTIO observations have shown the central star to be an eclipsing binary with a period of 4.9 days, surrounded by a remarkable elliptical nebular ring. Very recent AAT spectra have revealed that the nucleus is a double- lined spectroscopic binary, consisting of two A-type stars. Given the absence of any ionizing star, we surmise that one of the A stars is the true central star, caught at the beginning of a ``born- again'' helium shell pulse. We will use the 1.5-m to obtain spectra and radial velocities which, combined with analysis of the light curve, will yield dynamical masses for both stars. We will also use the 0.9-m to obtain detailed coverage of the eclipses and to search for the predicted secular expansion of the born-again component. As time permits, we will also obtain spectra and photometry of other binary nuclei of planetary nebulae.
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We continue our investigation of the emitting region of the symbiotic nova RR Telescopii by analyzing the emission line fluxes from high quality AAT optical spectra obtained in 2000 and comparing these with previous observations. The... more
We continue our investigation of the emitting region of the symbiotic nova RR Telescopii by analyzing the emission line fluxes from high quality AAT optical spectra obtained in 2000 and comparing these with previous observations. The fading found in the recent spectra suggests increased circumstellar dust absorption in the stellar wind of the mira. Differing absorption of lines formed in
A study of the behaviour of the permitted Fe II and forbidden [Fe II] emission lines during a dust obscuration episode, suggests a larger flux decrease for the permitted than for the forbidden lines. No other correlation with line... more
A study of the behaviour of the permitted Fe II and forbidden [Fe II] emission lines during a dust obscuration episode, suggests a larger flux decrease for the permitted than for the forbidden lines. No other correlation with line properties have been found. Possible interpretations are discussed.
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... tinuum required E(B - V) = 0.1 ± 0.1 mag. Using SWP 9473 and LWR 8203 only, Feibelman (1982) derived a value of E(B - V) = 0.22 ± 0.02 mag. Kaler (1983) derived a logarithmic extinction c = 0.00 ± 0.23 from optical photometry,... more
... tinuum required E(B - V) = 0.1 ± 0.1 mag. Using SWP 9473 and LWR 8203 only, Feibelman (1982) derived a value of E(B - V) = 0.22 ± 0.02 mag. Kaler (1983) derived a logarithmic extinction c = 0.00 ± 0.23 from optical photometry, equivalent to E(B - V) = 0.00 ± 0.19 mag. ...
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... Girardi, L., Bressan, A., Bertelli, G., & Chiosi, C., 2000, A&AS, 141, 371 Hellier, C., et al., 2008, ApJ, submitted (arXiv:0805.2600) Henry, GW, Marcy, GW, Butler, RP, & Vogt, SS, 2000, ApJ, 529, L41 Joshi, YC, et al.,... more
... Girardi, L., Bressan, A., Bertelli, G., & Chiosi, C., 2000, A&AS, 141, 371 Hellier, C., et al., 2008, ApJ, submitted (arXiv:0805.2600) Henry, GW, Marcy, GW, Butler, RP, & Vogt, SS, 2000, ApJ, 529, L41 Joshi, YC, et al., 2008, MNRAS, submitted (arXiv:0806.1478) Kovács, G., Zucker ...
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A programme is currently underway to study the structures and kinematics of planetary nebulae known to contain close-binary central stars. Images and high-resolution spectroscopy are presented of the collimated nebula Abell 63 and the... more
A programme is currently underway to study the structures and kinematics of planetary nebulae known to contain close-binary central stars. Images and high-resolution spectroscopy are presented of the collimated nebula Abell 63 and the ring-like nebula Sp 1. A spatio-kinematical model shows that Abell 63 has a tube-like structure, which has the same inclination as the orbital plane of the
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ABSTRACT The wealth of information rendered by Kepler planets and planet candidates is indispensable for statistically significant studies of distinct planet populations, in both single and multiple systems. Empirical evidences suggest... more
ABSTRACT The wealth of information rendered by Kepler planets and planet candidates is indispensable for statistically significant studies of distinct planet populations, in both single and multiple systems. Empirical evidences suggest that Kepler's planet population shows different physical properties as compared to the bulk of known exoplanets. The SOAPS project, aims to shed light on Kepler's planets formation, their migration and architecture. By measuring v sini accurately for Kepler hosts with rotation periods measured from their high-precision light curves, we will assess the alignment of the planetary orbit with respect to the stellar spin axis. This degree of alignment traces the formation history and evolution of the planetary systems, and thus, allows to distinguish between different proposed migration theories. SOAPS will increase by a factor of 2 the number of spin-orbit alignment measurements pushing the parameters space down to the SuperEarth domain. Here we present our preliminary results.
ABSTRACT The Telescopio Nazionale Galileo (TNG)[9] hosts, starting in April 2012, the visible spectrograph HARPS-N. It is based on the design of its predecessor working at ESO's 3.6m telescope, achieving unprecedented results on... more
ABSTRACT The Telescopio Nazionale Galileo (TNG)[9] hosts, starting in April 2012, the visible spectrograph HARPS-N. It is based on the design of its predecessor working at ESO's 3.6m telescope, achieving unprecedented results on radial velocity measurements of extrasolar planetary systems. The spectrograph's ultra-stable environment, in a temperature-controlled vacuum chamber, will allow measurements under 1 m/s which will enable the characterization of rocky, Earth-like planets. Enhancements from the original HARPS include better scrambling using octagonal section fibers with a shorter length, as well as a native tip-tilt system to increase image sharpness, and an integrated pipeline providing a complete set of parameters. Observations in the Kepler field will be the main goal of HARPS-N, and a substantial fraction of TNG observing time will be devoted to this follow-up. The operation process of the observatory has been updated, from scheduling constraints to telescope control system. Here we describe the entire instrument, along with the results from the first technical commissioning.
... al. 1999; Keenan et al. 1999 and references therein). Previous high-resolution studies of RR Tel have failed to identify the [Cl II] emission lines (McKenna et al. 1997; Crawford et al. 1999; Selvelli & Bonifacio 2000). However ...