Dr Philip J Carter

orcid.org/0000-0001-5065-4625

Articles in review:

• Planetesimal Impact Vapor Plumes and Nebular Shocks form Chondritic Mixtures
  Stewart, Sarah T.; Carter, Philip J.; Lock, Simon J.; Davies, Erik J.; Petaev, Michail I.; Jacobsen, Stein B.,
  in prep.
  
  

Refereed articles:

1. Exploring the catastrophic regime: thermodynamics and disintegration in head-on planetary collisions
   Dou, Jingyao; Carter, Philip J.; Lock, Simon; Leinhardt, Zoë M.,
   2024, Monthly Notices of the Royal Astronomical Society, 534, 758.
   
   Head-on giant impacts (collisions between planet-sized bodies) are frequently used to study the planet formation process as they present an extreme configuration where the two colliding bodies are greatly disturbed. With limited computing resources, focusing on these extreme impacts eases the burden of exploring a large parameter space. Results from head-on impacts are often then extended to study oblique impacts with angle corrections or used as initial conditions for other calculations, for example, the evolution of ejected debris. In this study, we conduct a detailed investigation of the thermodynamic and energy budget evolution of high-energy head-on giant impacts, entering the catastrophic impacts regime, for target masses between 0.001 and 12 M⊕. We demonstrate the complex interplay of gravitational forces, shock dynamics, and thermodynamic processing in head-on impacts at high energy. Our study illustrates that frequent interactions of core material with the liquid side of the vapour curve could have cumulative effects on the post-collision remnants, leading to fragmentary disintegration occurring at lower impact energy. This results in the mass of the largest remnant diverging significantly from previously developed scaling laws. These findings suggest two key considerations: (1) head-on planetary collisions for different target masses do not behave similarly, so caution is needed when applying scaling laws across a broad parameter space; and (2) an accurate model of the liquid-vapour phase boundary is essential for modelling giant impacts. Our findings highlight the need for careful consideration of impact configurations in planetary formation studies, as head-on impacts involve a complex interplay between thermodynamic processing, shocks, gravitational forces, and other factors.
   arXiv:2410.00856 – ADS – doi:10.1093/mnras/stae2134 – PDF
   
   
2. Formation of super-Mercuries via giant impacts
   Dou, Jingyao; Carter, Philip J.; Leinhardt, Zoë M.,
   2024, Monthly Notices of the Royal Astronomical Society, 529, 2577.
   
   During the final stage of planetary formation, different formation pathways of planetary embryos could significantly influence the observed variations in planetary densities. Of the approximately 5000 exoplanets identified to date, a notable subset exhibits core fractions reminiscent of Mercury, potentially a consequence of high-velocity giant impacts. In order to better understand the influence of such collisions on planetary formation and compositional evolution, we conducted an extensive set of smoothed particle hydrodynamics giant impact simulations between two-layered rocky bodies. These simulations spanned a broad range of impact velocities from 1 to 11 times the mutual escape velocity. We derived novel scaling laws that estimate the mass and core mass fraction of the largest post-collision remnants. Our findings indicate that the extent of core vaporization markedly influences mantle stripping efficiency at low impact angles. We delineate the distinct roles played by two mechanisms - kinetic momentum transfer and vaporization-induced ejection - in mantle stripping. Our research suggests that collisional outcomes for multilayered planets are more complex than those for undifferentiated planetesimal impacts. Thus, a single universal law may not encompass all collision processes. We found a significant decrease in the mantle stripping efficiency as the impact angle increases. To form a 5 M⊕ super-Mercury at 45°, an impact velocity over 200 km s^-1 is required. This poses a challenge to the formation of super-Mercuries through a single giant impact, implying that their formation would favour either relatively low-angle single impacts or multiple collisions.
   arXiv:2403.03831 – ADS – doi:10.1093/mnras/stae644 – PDF
   
   
3. Post-giant impact planetesimals sustaining extreme debris discs
   Watt, Lewis; Leinhardt, Zoë M.; Carter, Philip J.,
   2024, Monthly Notices of the Royal Astronomical Society, 527, 7749.
   
   Extreme debris discs can show short-term behaviour through the evolution and clearing of small grains produced in giant impacts, and potentially a longer period of variability caused by a planetesimal population formed from giant impact ejecta. In this paper, we present results of numerical simulations to explain how a planetesimal populated disc can supply an observed extreme debris disc with small grains. We simulated a sample of giant impacts from which we form a planetesimal population. We then use the N-body code REBOUND to evolve the planetesimals spatially and collisionally. We adopt a simplistic collision criteria in which we define destructive collisions to be between planetesimals with a mutual impact velocity that exceeds two times the catastrophic disruption threshold, V*. We find that for some configurations, a planetesimal populated disc can produce a substantial amount of dust to sustain an observable disc. The semimajor axis at which the giant impact occurs changes the mass added to the observed disc substantially, while the orientation of the impact has less of an effect. We determine how the collision rate at the collision point changes over time and show that changes in semimajor axis and orientation only change the initial collision rate of the disc. Collision rates across all discs evolve at a similar rate.
   arXiv:2311.11376 – ADS – doi:10.1093/mnras/stad3606 – PDF
   
   
4. A super-massive Neptune-sized planet
   Naponiello, L.; Mancini, L.; Sozzetti, A.; Bonomo, A.; Morbidelli, A.; Dou, J.; Zeng, L.; Leinhardt, Z.; Biazzo, K.; Cubillos, P.; Pinamonti, M.; Locci, D.; Maggio, A.; Damasso, M.; Lanza, A.; Lissauer, J.; Collins, K.; Carter, P. J.; Jensen, E.; Bignamini, A.; Boschin, W.; Bouma, L.; Ciardi, D.; Cosentino, R.; Desidera, S.; Dumusque, X.; Fiorenzano, A.; Fukui, A.; Giacobbe, P.; Gnilka, C.; Ghedina, A.; Guilluy, G.; Harutyunyan, A.; Howell, S.; Jenkins, J,; Lund, M.; Kielkopf, J.; Lester, K.; Malavolta, L.; Mann, A.; Matson, R.; Matthews, E.; Nardiello, D.; Narita, N.; Pace, E.; Pagano, I.; Palle, E.; Pedani, M.; Seager, S.; Schlieder, J.; Schwarz, R.; Shporer, A.; Twicken, J.; Winn, J.; Ziegler, C.; Zingales, T.,
   2023, Nature, 622, 255.
   
   Neptune-sized planets exhibit a wide range of compositions and densities, depending on factors related to their formation and evolution history, such as the distance from their host stars and atmospheric escape processes. They can vary from relatively low-density planets with thick hydrogen–helium atmospheres to higher-density planets with a substantial amount of water or a rocky interior with a thinner atmosphere, such as HD 95338 b, TOI-849 b and TOI-2196 b. The discovery of exoplanets in the hot-Neptune desert, a region close to the host stars with a deficit of Neptune-sized planets, provides insights into the formation and evolution of planetary systems, including the existence of this region itself. Here we show observations of the transiting planet TOI-1853 b, which has a radius of 3.46 ± 0.08 Earth radii and orbits a dwarf star every 1.24 days. This planet has a mass of 73.2 ± 2.7 Earth masses, almost twice that of any other Neptune-sized planet known so far, and a density of 9.7 ± 0.8 grams per cubic centimetre. These values place TOI-1853 b in the middle of the Neptunian desert and imply that heavy elements dominate its mass. The properties of TOI-1853 b present a puzzle for conventional theories of planetary formation and evolution, and could be the result of several proto-planet collisions or the final state of an initially high-eccentricity planet that migrated closer to its parent star.
   arXiv:2309.01464 – ADS – doi:10.1038/s41586-023-06499-2
   
   
5. A compact multi-planet system transiting HIP 29442 (TOI-469) discovered by TESS and ESPRESSO
   Damasso, M.; Rodrigues, J.; Castro-González, A.; Lavie, B.; Davoult, J.; Zapatero Osorio, M. R.; Dou, J.; Sousa, S. G.; Owen, J. E.; Sossi, P.; Adibekyan, V.; Osborn, H.; Leinhardt, Z.; Alibert, Y.; Lovis, C.; Delgado Mena, E.; Sozzetti, A.; Barros, S. C. C.; Bossini, D.; Ziegler, C.; Ciardi, D. R.; Matthews, E. C.; Carter, P. J.; Lillo-Box, J.; Suárez Mascareño, A.; Cristiani, S.; Pepe, F.; Rebolo, R.; Santos, N. C.; Allende Prieto, C.; Benatti, S.; Bouchy, F.; Briceño, C.; Di Marcantonio, P.; D'Odorico, V.; Dumusque, X.; Egger, J. A.; Ehrenreich, D.; Faria, J.; Figueira, P.; Génova Santos, R.; Gonzales, E. J.; González Hernández, J. I.; Law, N.; Lo Curto, G.; Mann, A. W.; Martins, C. J. A. P.; Mehner, A.; Micela, G.; Molaro, P.; Nunes, N. J.; Palle, E.; Poretti, E.; Schlieder, J. E.; Udry, S.,
   2023, Astronomy & Astrophysics, 679, 33.
   
   We followed-up with ESPRESSO the K0V star HIP 29442 (TOI-469), already known to host a validated sub-Neptune companion TOI-469.01. We aim to verify the planetary nature of TOI-469.01. We modelled radial velocity and photometric time series to measure the dynamical mass, radius, and ephemeris, and to characterise the internal structure and composition of TOI-469.01. We confirmed the planetary nature of TOI-469.01. Thanks to ESPRESSO we discovered two additional close-in companions. We also detected their low signal-to-noise transit signals in the TESS light curve. HIP 29442 is a compact multi-planet system, and the three planets have orbital periods Porb,b=13.63083±0.00003, Porb,c=3.53796±0.00003, and Porb,d=6.42975+0.00009−0.00010 days, and we measured their masses with high precision: mp,b=9.6±0.8 M⊕, mp,c=4.5±0.3 M⊕, and mp,d=5.1±0.4 M⊕. We measured radii and bulk densities of all the planets (the 3σ confidence intervals are shown in parenthesis): Rp,b=3.48+0.07(+0.19)−0.08(−0.28) R⊕ and ρp,b=1.3±0.2(0.3)g cm−3; Rp,c=1.58+0.10(+0.30)−0.11(−0.34) R⊕ and ρp,c=6.3+1.7(+6.0)−1.3(−2.7)g cm−3; Rp,d=1.37±0.11(+0.32)(−0.43) R⊕ and ρp,d=11.0+3.4(+21.0)−2.4(−6.3)g cm−3. We used the more conservative 3σ confidence intervals for the radii as input to the interior structure modelling. We find that HIP 29442 b appears as a typical sub-Neptune, likely surrounded by a gas layer of pure H-He with a mass of 0.27+0.24−0.17M⊕ and a thickness of 1.4±0.5R⊕. For the innermost companions HIP 29442 c HIP 29442 d, the model supports an Earth-like composition.
   arXiv:2308.13310 – ADS – doi:10.1051/0004-6361/202347240
   
   
6. Did Earth Eat Its Leftovers? Impact Ejecta as a Component of the Late Veneer
   Carter, Philip J. & Stewart, Sarah T.,
   2022, The Planetary Science Journal, 3, 83.
   
   The presence of highly siderophile elements in Earth's mantle indicates that a small percentage of Earth's mass was delivered after the last giant impact in a stage of "late accretion." There is ongoing debate about the nature of late-accreted material and the sizes of late-accreted bodies. Earth appears isotopically most similar to enstatite chondrites and achondrites. It has been suggested that late accretion must have been dominated by enstatite-like bodies that originated in the inner disk, rather than ordinary or carbonaceous chondrites. Here we examine the provenances of "leftover" planetesimals present in the inner disk in the late stages of accretion simulations. Dynamically excited planet formation produces planets and embryos with similar provenances, suggesting that the Moon-forming impactor may have had a stable isotope composition very similar to the proto-Earth. Commonly, some planetesimal-sized bodies with similar provenances to the Earth-like planets are left at the end of the main stage of growth. The most chemically similar planetesimals are typically fragments of protoplanets ejected millions of years earlier. If these similar-provenance bodies are later accreted by the planet, they will represent late-accreted mass that naturally matches Earth's composition. The planetesimal-sized bodies that exist during the giant impact phase can have large core mass fractions, with core provenances similar to the proto-Earth. These bodies are an important potential source for highly siderophile elements. The range of core fractions in leftover planetesimals complicates simple inferences as to the mass and origin of late accretion based on the highly siderophile elements in the mantle.
   arXiv:2204.03979 – ADS – doi:10.3847/PSJ/ac6095 – PDF
   
   
7. Atmosphere loss in oblique Super-Earth collisions
   Denman, Thomas R.; Leinhardt, Zoë M.; Carter, Philip J.,
   2022, Monthly Notices of the Royal Astronomical Society, 513, 1680.
   
   Using smoothed particle hydrodynamics we model giant impacts of Super-Earth mass rocky planets between an atmosphere-less projectile and an atmosphere-rich target. In this work, we present results from head-on to grazing collisions. The results of the simulations fall into two broad categories: (1) one main post-collision remnant containing material from target and projectile; (2) two main post-collision remnants resulting from 'erosive hit-and-run' collisions. All collisions removed at least some of the target atmosphere, in contrast to the idealized hit-and-run definition in which the target mass is unchanged. We find that the boundary between 'hit-and-run' collisions and collisions that result in the projectile and target accreting/merging to be strongly correlated with the mutual escape velocity at the predicted point of closest approach. Our work shows that it is very unlikely for a single giant impact to remove all of the atmosphere. For all the atmosphere to be removed, head-on impacts require roughly the energy of catastrophic disruption (i.e. permanent ejection of half the total system mass) and result in significant erosion of the mantle. We show that higher impact angle collisions, which are more common, are less efficient at atmosphere removal than head-on collisions. Therefore, single collisions that remove all the atmosphere without substantially disrupting the planet are not expected during planet formation.
   arXiv:2203.17064 – ADS – doi:10.1093/mnras/stac923 – PDF
   
   
8. Colliding in the shadows of giants: Planetesimal collisions during the growth and migration of gas giants
   Carter, Philip J. & Stewart, Sarah T.,
   2020, The Planetary Science Journal, 1, 45.
   
   Giant planet migration is an important phenomenon in the evolution of planetary systems. Recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal-planetesimal collisions, during gas giant growth and migration. The numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. We find that giant planet growth alone has little effect on impact velocities, and most of the planetesimals scattered by growing giants do not undergo collisions with each other during the growth period. In contrast, we find that giant planet migration induces large numbers of high velocity collisions between planetesimals. These impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals, and to cause catastrophic disruption of the bodies. New bodies may form from impact debris. Collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt via giant planet growth and migration. A small fraction of the largest planetesimals implanted into the asteroid belt would have been processed via collisions. We identify important consequences of planetesimal collisions that have not been considered in planet accretion models. The prevalence of high velocity collisions during giant planet migration, and their potential links to the properties of meteorites, and the formation of chondrules, makes impact vaporization a critically important phenomenon. The consequences of vaporizing planetesimal constituents require further detailed study. New collision outcome models for impacts within the nebula, and models for new planetesimal formation are needed.
   arXiv:2008.05549 – ADS – doi:10.3847/PSJ/abaecc – PDF
   
   
9. Atmosphere loss in planet–planet collisions
   Denman, Thomas R.; Leinhardt, Zoë M.; Carter, Philip J.; Mordasini, Christoph,
   2020, Monthly Notices of the Royal Astronomical Society, 496, 1166.
   
   Many of the planets discovered by the Kepler satellite are close orbiting super-Earths or mini-Neptunes. Such objects exhibit a wide spread of densities for similar masses. One possible explanation for this density spread is giant collisions stripping planets of their atmospheres. In this paper, we present the results from a series of smoothed particle hydrodynamics (SPH) simulations of head-on collisions of planets with significant atmospheres and bare projectiles without atmospheres. Collisions between planets can have sufficient energy to remove substantial fractions of the mass from the target planet. We find the fraction of mass lost splits into two regimes - at low impact energies only the outer layers are ejected corresponding to atmosphere dominated loss, at higher energies material deeper in the potential is excavated resulting in significant core and mantle loss. Mass removal is less efficient in the atmosphere loss dominated regime compared to the core and mantle loss regime, due to the higher compressibility of atmosphere relative to core and mantle. We find roughly 20 per cent atmosphere remains at the transition between the two regimes. We find that the specific energy of this transition scales linearly with the ratio of projectile to target mass for all projectile-target mass ratios measured. The fraction of atmosphere lost is well approximated by a quadratic in terms of the ratio of specific energy and transition energy. We provide algorithms for the incorporation of our scaling law into future numerical studies.
   arXiv:2006.01881 – ADS – doi:10.1093/mnras/staa1623 – PDF
   
   
10. Spectroscopic and photometric periods of six ultracompact accreting binaries
    Green, M. J.; Marsh, T. R.; Carter, P. J.; Steeghs, D.; Breedt, E.; Dhillon, V. S.; Littlefair, S. P.; Parsons, S. G.; Kerry P.; Gentile Fusillo, N. P.; Ashley, R. P.; Bours, M. C. P.; Cunningham, T.; Dyer, M. J.; Gänsicke, B. T.; Izquierdo, P.; Pala, A. F.; Pattama, C.; Outmani, S. Sahman, D. I.; Sukaum, B.; Wild, J.,
    2020, Monthly Notices of the Royal Astronomical Society, 496, 1243.
    
    Ultracompact accreting binary systems each consist of a stellar remnant accreting helium-enriched material from a compact donor star. Such binaries include two related sub-classes, AM CVn-type binaries and helium cataclysmic variables, in both of which the central star is a white dwarf. We present a spectroscopic and photometric study of six accreting binaries with orbital periods in the range of 40-70 min, including phase-resolved VLT spectroscopy and high-speed ULTRACAM photometry. Four of these are AM CVn systems and two are helium cataclysmic variables. For four of these binaries we are able to identify orbital periods (of which three are spectroscopic). SDSS J1505+0659 has an orbital period of 67.8 min, significantly longer than previously believed, and longer than any other known AM CVn binary. We identify a Wide-field Infrared Survey Explorer (WISE) infrared excess in SDSS J1505+0659 that we believe to be the first direct detection of an AM CVn donor star in a non-direct impacting binary. The mass ratio of SDSS J1505+0659 is consistent with a white dwarf donor. CRTS J1028-0819 has an orbital period of 52.1 min, the shortest period of any helium cataclysmic variable. MOA 2010-BLG-087 is co-aligned with a K-class star that dominates its spectrum. ASASSN-14ei and ASASSN-14mv both show a remarkable number of echo outbursts following superoutbursts (13 and 10 echo outbursts respectively). ASASSN-14ei shows an increased outburst rate over the years following its superoutburst, perhaps resulting from an increased accretion rate.
    arXiv:2005.12616 – ADS – doi:10.1093/mnras/staa1509
    
    
11. IGAPS: the merged IPHAS and UVEX optical surveys of the Northern Galactic Plane
    Monguió, M.; Greimel, R.; Drew, J. E.; Barentsen, G.; Groot, P. J.; Irwin, M. J.; Casares, J.; Gänsicke, B. T.; Carter, P. J.; Corral-Santana, J. M.; Gentile-Fusillo, N. P.; Greiss, S.; van Haaften, L. M.; Hollands, M.; Jones, D.; Kupfer, T.; Manser, C. J.; Murphy, D. N. A.; McLeod, A. F.; Oosting, T.; Parker, Q. A.; Pyrzas, S.; Rodríguez-Gil, P.; van Roestel, J.; Scaringi, S.; Schellart, P.; Toloza, O.; Vaduvescu, O.; van Spaandonk, L.; Verbeek, K.; Wright, N. J.; Eislöffel, J.; Fabregat, J.; Harris, A.; Morris, R. A. H.; Phillipps, S.; Raddi, R.; Sabin, L.; Unruh, Y.; Vink, J. S; Wesson, R.; Cardwell, A.; Cochrane, R. K.; Doostmohammadi, S.; Mocnik, T.; Stoev, H.; Suárez-Andrés, L.; Tudor, V.; Wilson, T. G.; Zegmott, T. J.,
    2020, Astronomy & Astrophysics, 638, A18.
    
    The INT Galactic Plane Survey (IGAPS) is the merger of the optical photometric surveys, IPHAS and UVEX, based on data from the Isaac Newton Telescope (INT) obtained between 2003 and 2018. Here, we present the IGAPS point source catalogue. It contains 295.4 million rows providing photometry in the filters, i, r, narrow-band Halpha, g and U_RGO. The IGAPS footprint fills the Galactic coordinate range, |b| < 5deg and 30deg < l < 215deg. A uniform calibration, referred to the Pan-STARRS system, is applied to g, r and i, while the Halpha calibration is linked to r and then is reconciled via field overlaps. The astrometry in all 5 bands has been recalculated on the Gaia DR2 frame. Down to i ~ 20 mag (Vega system), most stars are also detected in g, r and Halpha. As exposures in the r band were obtained within the IPHAS and UVEX surveys a few years apart, typically, the catalogue includes two distinct r measures, r_I and r_U. The r 10sigma limiting magnitude is ~21, with median seeing 1.1 arcsec. Between ~13th and ~19th magnitudes in all bands, the photometry is internally reproducible to within 0.02 magnitudes. Stars brighter than r=19.5 have been tested for narrow-band Halpha excess signalling line emission, and for variation exceeding |r_I-r_U| = 0.2 mag. We find and flag 8292 candidate emission line stars and over 53000 variables (both at >5sigma confidence). The 174-column catalogue will be available via CDS Strasbourg.
    arXiv:2002.05157 – ADS – doi:10.1051/0004-6361/201937333
    
    
12. Silicate melting and vaporization during rocky planet formation
    Davies, E. J.; Carter, P. J.; Root, S.; Kraus, R. G.; Spaulding, D. K.; Stewart, S. T.; Jacobsen, S. B.,
    2020, Journal of Geophysical Research: Planets, 125, e2019JE006227.
    
    Collisions that induce melting and vaporization can have a substantial effect on the thermal and geochemical evolution of planets. However, the thermodynamics of major minerals are not well known at the extreme conditions attained during planet formation. We obtained new data at the Sandia Z Machine and use published thermodynamic data for the major mineral forsterite (Mg2SiO4) to calculate the specific entropy in the liquid region of the principal Hugoniot. We use our calculated specific entropy of shocked forsterite, and revised entropies for shocked silica, to determine the critical impact velocities for melting or vaporization upon decompression from the shocked state to 1 bar and the triple points, which are near the pressures of the solar nebula. We also demonstrate the importance of the initial temperature on the criteria for vaporization. Applying these results to N-body simulations of terrestrial planet formation, we find that up to 20% to 40% of the total system mass is processed through collisions with velocities that exceed the criteria for incipient vaporization at the triple point. Vaporizing collisions between small bodies are an important component of terrestrial planet formation.
    arXiv:2002.00998 – ADS – doi:10.1029/2019JE006227
    
    
13. Are exoplanetesimals differentiated?
    Bonsor, Amy; Carter, Philip J.; Hollands, Mark; Gänsicke, Boris T.; Leinhardt, Zoë M.; Harrison, John H. D.,
    2020, Monthly Notices of the Royal Astronomical Society, 492, 2683.
    
    Metals observed in the atmospheres of white dwarfs suggest that many have recently accreted planetary bodies. In some cases, the compositions observed suggest the accretion of material dominantly from the core (or the mantle) of a differentiated planetary body. Collisions between differentiated exoplanetesimals produce such fragments. In this work, we take advantage of the large numbers of white dwarfs where at least one siderophile (core-loving) and one lithophile (rock-loving) species have been detected to assess how commonly exoplanetesimals differentiate. We utilise N-body simulations that track the fate of core and mantle material during the collisional evolution of planetary systems to show that most remnants of differentiated planetesimals retain core fractions similar to their parents, whilst some are extremely core-rich or mantle-rich. Comparison with the white dwarf data for calcium and iron indicates that the data are consistent with a model in which 66^{+4}_{-6}% have accreted the remnants of differentiated planetesimals, whilst 31^{+5}_{-5}% have Ca/Fe abundances altered by the effects of heating (although the former can be as high as 100%, if heating is ignored). These conclusions assume pollution by a single body and that collisional evolution retains similar features across diverse planetary systems. These results imply that both collisions and differentiation are key processes in exoplanetary systems. We highlight the need for a larger sample of polluted white dwarfs with precisely determined metal abundances to better understand the process of differentiation in exoplanetary systems.
    arXiv:2001.04499 – ADS – doi:10.1093/mnras/stz3603 – PDF
    
    
14. The energy budgets of giant impacts
    Carter, Philip J.; Lock, Simon J.; Stewart, Sarah T.,
    2020, Journal of Geophysical Research: Planets, 125, e06042.
    
    Giant impacts dominate the final stages of terrestrial planet formation and set the configuration and compositions of the final system of planets. A giant impact is believed to be responsible for the formation of Earth's Moon, but the specific impact parameters are under debate. Because the canonical Moon-forming impact is the most intensely studied scenario, it is often considered the archetypal giant impact. However, a wide range of impacts with different outcomes are possible. Here we examine the total energy budgets of giant impacts that form Earth-mass bodies and find that they differ substantially across the wide range of possible Moon-forming events. We show that gravitational potential energy exchange is important, and we determine the regime in which potential energy has a significant effect on the collision outcome. Energy is deposited heterogeneously within the colliding planets, increasing their internal energies, and portions of each body attain sufficient entropy for vaporization. After gravitational re-equilibration, post-impact bodies are strongly thermally stratified, with varying amounts of vaporized and supercritical mantle. The canonical Moon-forming impact is a relatively low energy event and should not be considered the archetype of accretionary giant impacts that form Earth-mass planets. After a giant impact, bodies are significantly inflated in size compared to condensed planets of the same mass, and there are substantial differences in the magnitudes of their potential, kinetic and internal energy components. As a result, the conditions for metal-silicate equilibration and the subsequent evolution of the planet may vary widely between different impact scenarios.
    arXiv:1912.04936 – ADS – doi:10.1029/2019JE006042
    
    
15. Collisional stripping of planetary crusts
    Carter, Philip J.; Leinhardt, Zoë M.; Elliott, Tim; Stewart, Sarah T.; Walter, Michael J.,
    2018, Earth and Planetary Science Letters, 484, 276.
    
    Geochemical studies of planetary accretion and evolution have invoked various degrees of collisional erosion to explain differences in bulk composition between planets and chondrites. Here we undertake a full, dynamical evaluation of 'crustal stripping' during accretion and its key geochemical consequences. Crusts are expected to contain a significant fraction of planetary budgets of incompatible elements, which include the major heat producing nuclides. We present smoothed particle hydrodynamics simulations of collisions between differentiated rocky planetesimals and planetary embryos. We find that the crust is preferentially lost relative to the mantle during impacts, and we have developed a scaling law based on these simulations that approximates the mass of crust that remains in the largest remnant. Using this scaling law and a recent set of N-body simulations of terrestrial planet formation, we have estimated the maximum effect of crustal stripping on incompatible element abundances during the accretion of planetary embryos. We find that on average approximately one third of the initial crust is stripped from embryos as they accrete, which leads to a reduction of ∼20% in the budgets of the heat producing elements if the stripped crust does not reaccrete. Erosion of crusts can lead to non-chondritic ratios of incompatible elements, but the magnitude of this effect depends sensitively on the details of the crust-forming melting process on the planetesimals. The Lu/Hf system is fractionated for a wide range of crustal formation scenarios. Using eucrites (the products of planetesimal silicate melting, thought to represent the crust of Vesta) as a guide to the Lu/Hf of planetesimal crust partially lost during accretion, we predict the Earth could evolve to a superchondritic ¹⁷⁶Hf/¹⁷⁷Hf (3-5 parts per ten thousand) at present day. Such values are in keeping with compositional estimates of the bulk Earth. Stripping of planetary crusts during accretion can lead to detectable changes in bulk composition of lithophile elements, but the fractionation is relatively subtle, and sensitive to the efficiency of reaccretion.
    arXiv:1712.02790 – ADS – doi:10.1016/j.epsl.2017.12.012
    
    
16. Magnesium isotope evidence that accretional vapour loss shapes planetary compositions
    Hin, Remco C.; Coath, Christopher D.; Carter, Philip J.; Nimmo, Francis; Lai, Yi-Jen; Pogge von Strandmann, Philip A. E.; Willbold, Matthias; Leinhardt, Zoë M.; Walter, Michael J.; Elliott, Tim,
    2017, Nature, 549, 511.
    
    It has long been recognized that Earth and other differentiated planetary bodies are chemically fractionated compared to primitive, chondritic meteorites and, by inference, the primordial disk from which they formed. However, it is not known whether the notable volatile depletions of planetary bodies are a consequence of accretion or inherited from prior nebular fractionation. The isotopic compositions of the main constituents of planetary bodies can contribute to this debate. Here we develop an analytical approach that corrects a major cause of measurement inaccuracy inherent in conventional methods, and show that all differentiated bodies have isotopically heavier magnesium compositions than chondritic meteorites. We argue that possible magnesium isotope fractionation during condensation of the solar nebula, core formation and silicate differentiation cannot explain these observations. However, isotopic fractionation between liquid and vapour, followed by vapour escape during accretionary growth of planetesimals, generates appropriate residual compositions. Our modelling implies that the isotopic compositions of magnesium, silicon and iron, and the relative abundances of the major elements of Earth and other planetary bodies, are a natural consequence of substantial (about 40 per cent by mass) vapour loss from growing planetesimals by this mechanism.
    ADS – doi:10.1038/nature23899
    
    
17. Explaining the variability of WD 1145+017 with simulations of asteroid tidal disruption
    Veras, Dimitri; Carter, Philip J.; Leinhardt, Zoë M.; Gänsicke, Boris T.,
    2017, Monthly Notices of the Royal Astronomical Society, 465, 1008.
    
    Post-main-sequence planetary science has been galvanized by the striking variability, depth and shape of the photometric transit curves due to objects orbiting white dwarf WD 1145+017, a star which also hosts a dusty debris disc and circumstellar gas, and displays strong metal atmospheric pollution. However, the physical properties of the likely asteroid which is discharging disintegrating fragments remain largely unconstrained from the observations. This process has not yet been modelled numerically. Here, we use the N-body code PKDGRAV to compute dissipation properties for asteroids of different spins, densities, masses and eccentricities. We simulate both homogeneous and differentiated asteroids, for up to 2 yr, and find that the disruption time-scale is strongly dependent on density and eccentricity, but weakly dependent on mass and spin. We find that primarily rocky differentiated bodies with moderate (˜3-4 g cm-3) bulk densities on near-circular (e ≲ 0.1) orbits can remain intact while occasionally shedding mass from their mantles. These results suggest that the asteroid orbiting WD 1145+017 is differentiated, resides just outside of the Roche radius for bulk density but just inside the Roche radius for mantle density, and is more akin physically to an asteroid like Vesta instead of one like Itokawa.
    arXiv:1610.06926 – ADS – doi:10.1093/mnras/stw2748 – PDF
    
    
18. Modelling circumbinary protoplanetary disks. II. Gas disk feedback on planetesimal dynamical and collisional evolution in the circumbinary systems Kepler-16 and 34
    Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.,
    2016, Astronomy & Astrophysics, 590, A62.
    
    Aims: We investigate the feasibility of planetesimal growth in circumbinary protoplanetary disks around the observed systems Kepler-16 and Kepler-34 under the gravitational influence of a precessing eccentric gas disk. Methods: We embed the results of our previous hydrodynamical simulations of protoplanetary disks around binaries into an N-body code to perform 3D, high-resolution, inter-particle gravity-enabled simulations of planetesimal growth and dynamics that include the gravitational force imparted by the gas. Results: Including the full, precessing asymmetric gas disk generates high eccentricity orbits for planetesimals orbiting at the edge of the circumbinary cavity, where the gas surface density and eccentricity have their largest values. The gas disk is able to efficiently align planetesimal pericenters in some regions leading to phased, non-interacting orbits. Outside of these areas eccentric planetesimal orbits become misaligned and overlap leading to crossing orbits and high relative velocities during planetesimal collisions. This can lead to an increase in the number of erosive collisions that far outweighs the number of collisions that result in growth. Gravitational focusing from the static axisymmetric gas disk is weak and does not significantly alter collision outcomes from the gas free case. Conclusions: Due to asymmetries in the gas disk, planetesimals are strongly perturbed onto highly eccentric orbits. Where planetesimals orbits are not well aligned, orbit crossings lead to an increase in the number of erosive collisions. This makes it difficult for sustained planetesimal accretion to occur at the location of Kepler-16b and Kepler-34b and we therefore rule out in situ growth. This adds further support to our initial suggestions that most circumbinary planets should form further out in the disk and migrate inwards.
    arXiv:1604.01778 – ADS – doi:10.1051/0004-6361/201628349
    
    
19. The search for ZZ Ceti stars in the original Kepler mission
    Greiss, S.; Hermes, J. J.; Gänsicke, B. T.; Steeghs, D. T. H.; Bell, Keaton J.; Raddi, R.; Tremblay, P.-E.; Breedt, E.; Ramsay, G.; Koester, D.; Carter, P. J.; Vanderbosch, Z.; Winget, D. E.; Winget, K. I.,
    2016, Monthly Notices of the Royal Astronomical Society, 457, 2855.
    
    We report the discovery of 42 white dwarfs in the original Kepler mission field, including nine new confirmed pulsating hydrogen-atmosphere white dwarfs (ZZ Ceti stars). Guided by the Kepler-Isaac Newton Telescope Survey, we selected white dwarf candidates on the basis of their U - g, g - r, and r - Hα photometric colours. We followed up these candidates with high-signal-to-noise optical spectroscopy from the 4.2-m William Herschel Telescope. Using ground-based, time series photometry, we put our sample of new spectroscopically characterized white dwarfs in the context of the empirical ZZ Ceti instability strip. Prior to our search, only two pulsating white dwarfs had been observed by Kepler. Ultimately, four of our new ZZ Cetis were observed from space. These rich data sets are helping initiate a rapid advancement in the asteroseismic investigation of pulsating white dwarfs, which continues with the extended Kepler mission, K2.
    arXiv:1601.01316 – ADS – doi:10.1093/mnras/stw053
    
    
20. Hiding in the Shadows. II. Collisional Dust as Exoplanet Markers
    Dobinson, Jack; Leinhardt, Zoë M.; Lines, Stefan; Carter, Philip J.; Dodson-Robinson, Sarah E.; Teanby, Nick A.,
    2016, The Astrophysical Journal, 820, 29.
    
    Observations of the youngest planets (˜1-10 Myr for a transitional disk) will increase the accuracy of our planet formation models. Unfortunately, observations of such planets are challenging and time-consuming to undertake, even in ideal circumstances. Therefore, we propose the determination of a set of markers that can preselect promising exoplanet-hosting candidate disks. To this end, N-body simulations were conducted to investigate the effect of an embedded Jupiter-mass planet on the dynamics of the surrounding planetesimal disk and the resulting creation of second-generation collisional dust. We use a new collision model that allows fragmentation and erosion of planetesimals, and dust-sized fragments are simulated in a post-process step including non-gravitational forces due to stellar radiation and a gaseous protoplanetary disk. Synthetic images from our numerical simulations show a bright double ring at 850 μm for a low-eccentricity planet, whereas a high-eccentricity planet would produce a characteristic inner ring with asymmetries in the disk. In the presence of first-generation primordial dust these markers would be difficult to detect far from the orbit of the embedded planet, but would be detectable inside a gap of planetary origin in a transitional disk.
    arXiv:1601.03319 – ADS – doi:10.3847/0004-637X/820/1/29
    
    
21. Compositional Evolution during Rocky Protoplanet Accretion
    Carter, Philip. J.; Leinhardt, Zoë. M.; Elliott, Tim; Walter, Michael J.; Stewart, Sarah T.,
    2015, The Astrophysical Journal, 813, 72.
    
    The Earth appears non-chondritic in its abundances of refractory lithophile elements, posing a significant problem for our understanding of its formation and evolution. It has been suggested that this non-chondritic composition may be explained by collisional erosion of differentiated planetesimals of originally chondritic composition. In this work, we present N-body simulations of terrestrial planet formation that track the growth of planetary embryos from planetesimals. We simulate evolution through the runaway and oligarchic growth phases under the Grand Tack model and in the absence of giant planets. These simulations include a state-of-the-art collision model that allows multiple collision outcomes, such as accretion, erosion, and bouncing events, and enables tracking of the evolving core mass fraction of accreting planetesimals. We show that the embryos grown during this intermediate stage of planet formation exhibit a range of core mass fractions, and that with significant dynamical excitation, enough mantle can be stripped from growing embryos to account for the Earth’s non-chondritic Fe/Mg ratio. We also find that there is a large diversity in the composition of remnant planetesimals, with both iron-rich and silicate-rich fragments produced via collisions.
    arXiv:1509.07504 – ADS – doi:10.1088/0004-637X/813/1/72 – PDF
    
    
22. Modelling circumbinary protoplanetary disks. I. Fluid simulations of the Kepler-16 and 34 systems
    Lines, S.; Leinhardt, Z. M.; Baruteau, C.; Paardekooper, S.-J.; Carter, P. J.,
    2015, Astronomy & Astrophysics, 582, A5.
    
    Context. The Kepler mission's discovery of a number of circumbinary planets orbiting close (ap< 1.1 au) to the stellar binary raises questions as to how these planets could have formed given the intense gravitational perturbations the dual stars impart on the disk. The gas component of circumbinary protoplanetary disks is perturbed in a similar manner to the solid, planetesimal dominated counterpart, although the mechanism by which disk eccentricity originates differs. Aims: This is the first work of a series that aims to investigate the conditions for planet formation in circumbinary protoplanetary disks. Methods: We present a number of hydrodynamical simulations that explore the response of gas disks around two observed binary systems: Kepler-16 and Kepler-34. We probe the importance of disk viscosity, aspect-ratio, inner boundary condition, initial surface density gradient, and self-gravity on the dynamical evolution of the disk, as well as its quasi-steady-state profile. Results: We find there is a strong influence of binary type on the mean disk eccentricity, e̅d, leading to e̅d = 0.02 - 0.08 for Kepler-16 and e̅d = 0.10 - 0.15 in Kepler-34. The value of α-viscosity has little influence on the disk, but we find a strong increase in mean disk eccentricity with increasing aspect-ratio due to wave propagation effects. The choice of inner boundary condition only has a small effect on the surface density and eccentricity of the disk. Our primary finding is that including disk self-gravity has little impact on the evolution or final state of the disk for disks with masses less than 12.5 times that of the minimum-mass solar nebula. This finding contrasts with the results of self-gravity relevance in circumprimary disks, where its inclusion is found to be an important factor in describing the disk evolution.
    arXiv:1507.06998 – ADS – doi:10.1051/0004-6361/201526295
    
    
23. Numerically Predicted Indirect Signatures of Terrestrial Planet Formation
    Leinhardt, Zoë M.; Dobinson, Jack; Carter, Philip J.; Lines, Stefan,
    2015, The Astrophysical Journal, 806, 23.
    
    The intermediate phases of planet formation are not directly observable due to lack of emission from planetesimals. Planet formation is, however, a dynamically active process resulting in collisions between the evolving planetesimals and the production of dust. Thus, indirect observation of planet formation may indeed be possible in the near future. In this paper we present synthetic observations based on numerical N-body simulations of the intermediate phase of planet formation including a state-of-the-art collision model, EDACM, which allows multiple collision outcomes, such as accretion, erosion, and bouncing events. We show that the formation of planetary embryos may be indirectly observable by a fully functioning ALMA telescope if the surface area involved in planetesimal evolution is sufficiently large and/or the amount of dust produced in the collisions is sufficiently high in mass.
    arXiv:1506.05233 – ADS – doi:10.1088/0004-637X/806/1/23 – PDF
    
    
24. A collisional origin to Earth's non-chondritic composition?
    Bonsor, Amy; Leinhardt, Zoë M.; Carter, Philip J.; Elliott, Tim; Walter, Michael J.; Stewart, Sarah T.,
    2015, Icarus, 247, 291.
    
    Several lines of evidence indicate a non-chondritic composition for bulk Earth. If Earth formed from the accretion of chondritic material, its non-chondritic composition, in particular the super-chondritic 142Nd /144Nd and low Mg/Fe ratios, might be explained by the collisional erosion of differentiated planetesimals during its formation. In this work we use an N-body code, that includes a state-of-the-art collision model, to follow the formation of protoplanets, similar to proto-Earth, from differentiated planetesimals (>100 km) up to isolation mass (>0.16 M⊕). Collisions between differentiated bodies have the potential to change the core-mantle ratio of the accreted protoplanets. We show that sufficient mantle material can be stripped from the colliding bodies during runaway and oligarchic growth, such that the final protoplanets could have Mg/Fe and Si/Fe ratios similar to that of bulk Earth, but only if Earth is an extreme case and the core is assumed to contain 10% silicon by mass. This may indicate an important role for collisional differentiation during the giant impact phase if Earth formed from chondritic material.
    arXiv:1410.3421 – ADS – doi:10.1016/j.icarus.2014.10.019
    
    
25. The Hidden Population of AM CVn Binaries in the Sloan Digital Sky Survey
    Carter, P. J.; Marsh, T. R.; Steeghs, D.; Breedt, E.; Copperwheat, C. M.; Gansicke, B. T.; Groot, P. J.; Nelemans, G.,
    2015, Acta Polytechnica CTU proceedings, 2, 178.
    
    We present results from a spectroscopic survey designed to uncover AM Canum Venaticorum (AM CVn) binaries hidden in the photometric database of the Sloan Digital Sky Survey (SDSS). The discovery of only 7 new AM CVns in the observed part of our sample suggests a lower space density than previously predicted. Based on the complete g≤19 sample, we calculate an observed space density for AM CVns of (5 ± 3) × 10⁻⁷ pc⁻³. We also compare the cataclysmic variables (CVs) discovered via this survey to those found in the SDSS spectroscopy, and we discuss SBSS 1108+574, an unusually helium-rich CV that has a spectroscopically confirmed orbital period of 55 minutes, well below the CV period minimum (~80 min). SBSS 1108+574 may represent an AM CVn forming via the ‘evolved CV’ formation channel.
    ADS – doi:10.14311/APP.2015.02.0178
    
    
26. KIC 2856960: the impossible triple star
    Marsh, T. R.; Armstrong, D. J.; Carter, P. J.,
    2014, Monthly Notices of the Royal Astronomical Society, 445, 309.
    
    KIC 2856960 is a star in the Kepler field which was observed by Kepler for four years. It shows the primary and secondary eclipses of a close binary of period 0.258 d as well as complex dipping events that last for about 1.5 d at a time and recur on a 204 d period. The dips are thought to result when the close binary passes across the face of a third star. In this paper, we present an attempt to model the dips. Despite the apparent simplicity of the system and strenuous efforts to find a solution, we find that we cannot match the dips with a triple star while satisfying Kepler's laws. The problem is that to match the dips, the separation of the close binary has to be larger than possible relative to the outer orbit given the orbital periods. Quadruple star models can get round this problem but require the addition of a so-far undetected intermediate period of the order of 5-20 d that has been a near-perfect integer divisor of the outer 204 d period. Although we have no good explanation for KIC 2856960, using the full set of Kepler data we are able to update several of its parameters. We also present a spectrum showing that KIC 2856960 is dominated by light from a K3- or K4-type star.
    arXiv:1409.0722 – ADS – doi:10.1093/mnras/stu1733
    
    
27. The second data release of the INT Photometric Hα Survey of the Northern Galactic Plane (IPHAS DR2)
    Barentsen, Geert; Farnhill, H. J.; Drew, J. E.; González-Solares, E. A.; Greimel, R.; Irwin, M. J.; Miszalski, B.; Ruhland, C.; Groot, P.; Mampaso, A.; Sale, S. E.; Henden, A. A.; Aungwerojwit, A.; Barlow, M. J.; Carter, P. J.; Corradi, R. L. M.; Drake, J. J.; Eislöffel, J.; Fabregat, J.; Gänsicke, B. T.; Gentile Fusillo, N. P.; Greiss, S.; Hales, A. S.; Hodgkin, S.; Huckvale, L.; Irwin, J.; King, R.; Knigge, C.; Kupfer, T.; Lagadec, E.; Lennon, D. J.; Lewis, J. R.; Mohr-Smith, M.; Morris, R. A. H.; Naylor, T.; Parker, Q. A.; Phillipps, S.; Pyrzas, S.; Raddi, R.; Roelofs, G. H. A.; Rodríguez-Gil, P.; Sabin, L.; Scaringi, S.; Steeghs, D.; Suso, J.; Tata, R.; Unruh, Y. C.; van Roestel, J.; Viironen, K.; Vink, J. S.; Walton, N. A.; Wright, N. J.; Zijlstra, A. A.,
    2014, Monthly Notices of the Royal Astronomical Society, 444, 3230.
    
    The INT/WFC Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800 deg² imaging survey covering Galactic latitudes |b| < 5° and longitudes ℓ = 30°-215° in the r, i, and Hα filters using the Wide Field Camera (WFC) on the 2.5-m Isaac Newton Telescope (INT) in La Palma. We present the first quality-controlled and globally calibrated source catalogue derived from the survey, providing single-epoch photometry for 219 million unique sources across 92 per cent of the footprint. The observations were carried out between 2003 and 2012 at a median seeing of 1.1 arcsec (sampled at 0.33 arcsec pixel-1) and to a mean 5σ depth of 21.2 (r), 20.0 (i), and 20.3 (Hα) in the Vega magnitude system. We explain the data reduction and quality control procedures, describe and test the global re-calibration, and detail the construction of the new catalogue. We show that the new calibration is accurate to 0.03 mag (root mean square) and recommend a series of quality criteria to select accurate data from the catalogue. Finally, we demonstrate the ability of the catalogue's unique (r - Hα, r - i) diagram to (i) characterize stellar populations and extinction regimes towards different Galactic sightlines and (ii) select and quantify Hα emission-line objects. IPHAS is the first survey to offer comprehensive CCD photometry of point sources across the Galactic plane at visible wavelengths, providing the much-needed counterpart to recent infrared surveys.
    arXiv:1406.4862 – ADS – doi:10.1093/mnras/stu1651
    
    
28. Two new AM Canum Venaticorum binaries from the Sloan Digital Sky Survey III
    Carter, P. J.; Gänsicke, B. T.; Steeghs, D.; Marsh, T. R.; Breedt, E.; Kupfer, T.; Gentile Fusillo, N. P.; Groot, P. J.; Nelemans, G.,
    2014, Monthly Notices of the Royal Astronomical Society, 439, 2848.
    
    The AM Canum Venaticorum (AM CVn) binaries are a rare group of ultrashort period, mass-transferring white dwarf binaries, some of which may be Type Ia supernova progenitors. More than a third of the total known population of AM CVn binaries have been discovered via the Sloan Digital Sky Survey (SDSS). Here, we discuss our search for new AM CVns in the SDSS spectroscopic data base, and present two new AM CVns discovered in SDSS-III spectroscopy, SDSS J113732.32+405458.3 and SDSS J150551.58+065948.7. The AM CVn binaries exhibit a connection between their spectral appearance and their orbital period, the spectra of these two new AM CVns suggest that they may be long-period systems. Using the radial velocity variations of the emission lines, we measure a possible orbital period of 59.6 ± 2.7 min for SDSS J113732.32+405458.3. Since our search of SDSS spectroscopy has revealed only these two new systems, it is unlikely that a large population of AM CVn binaries have been missed, and their discovery should have little effect on previous calculations of the AM CVn space density.
    arXiv:1312.3335 – ADS – doi:10.1093/mnras/stu142
    
    
29. The AM Canum Venaticorum binary SDSS J173047.59+554518.5
    Carter, P. J.; Steeghs, D.; Marsh, T. R.; Kupfer, T.; Copperwheat, C. M.; Groot, P. J.; Nelemans, G.,
    2014, Monthly Notices of the Royal Astronomical Society, 437, 2894.
    
    The AM Canum Venaticorum (AM CVn) binaries are a rare group of hydrogen-deficient, ultrashort period, mass-transferring white dwarf binaries and are possible progenitors of Type Ia supernovae. We present time-resolved spectroscopy of the recently discovered AM CVn binary SDSS J173047.59+554518.5. The average spectrum shows strong double-peaked helium emission lines, as well as a variety of metal lines, including neon; this is the second detection of neon in an AM CVn binary, after the much brighter system GP Com. We detect no calcium in the accretion disc, a puzzling feature that has been noted in many of the longer period AM CVn binaries. We measure an orbital period, from the radial velocities of the emission lines, of 35.2 ± 0.2 min, confirming the ultracompact binary nature of the system. The emission lines seen in SDSS J1730 are very narrow, although double-peaked, implying a low-inclination, face-on accretion disc; using the measured velocities of the line peaks, we estimate i ≤ 11°. This low inclination makes SDSS J1730 an excellent system for the identification of emission lines.
    arXiv:1311.0008 – ADS – doi:10.1093/mnras/stt2103
    
    
30. The helium-rich cataclysmic variable SBSS 1108+574
    Carter, P. J.; Steeghs, D.; de Miguel, E.; Goff, W.; Koff, R. A.; Krajci, T.; Marsh, T. R.; Gänsicke, B. T.; Breedt, E.; Groot, P. J.; Nelemans, G.; Roelofs, G. H. A.; Rau, A.; Koester, D.; Kupfer, T.,
    2013, Monthly Notices of the Royal Astronomical Society, 431, 372.
    
    We present time-resolved spectroscopy and photometry of the dwarf nova SBSS 1108+574, obtained during the 2012 outburst. Its quiescent spectrum is unusually rich in helium, showing broad, double-peaked emission lines from the accretion disc. We measure a line flux ratio He I 5875/Hα = 0.81 ± 0.04, a much higher ratio than typically observed in cataclysmic variable stars (CVs). The outburst spectrum shows hydrogen and helium in absorption, with weak emission of Hα and He I 6678, as well as strong He II emission. From our photometry, we find the superhump period to be 56.34 ± 0.18 min, in agreement with the previously published result. The spectroscopic period, derived from the radial velocities of the emission lines, is found to be 55.3 ± 0.8 min, consistent with a previously identified photometric orbital period, and significantly below the normal CV period minimum. This indicates that the donor in SBSS 1108+574 is highly evolved. The superhump excess derived from our photometry implies a mass ratio of q = 0.086 ± 0.014. Our spectroscopy reveals a grazing eclipse of the large outbursting disc. As the disc is significantly larger during outburst, it is unlikely that an eclipse will be detectable in quiescence. The relatively high accretion rate implied by the detection of outbursts, together with the large mass ratio, suggests that SBSS 1108+574 is still evolving towards its period minimum.
    arXiv:1301.6761 – ADS – doi:10.1093/mnras/stt169
    
    
31. A search for the hidden population of AM CVn binaries in the Sloan Digital Sky Survey
    Carter, P. J.; Marsh, T. R.; Steeghs, D.; Groot, P. J.; Nelemans, G.; Levitan, D.; Rau, A.; Copperwheat, C. M.; Kupfer, T.; Roelofs, G. H. A.,
    2013, Monthly Notices of the Royal Astronomical Society, 429, 2143.
    
    We present the latest results from a spectroscopic survey designed to uncover the hidden population of AM Canum Venaticorum (AM CVn) binaries in the photometric data base of the Sloan Digital Sky Survey (SDSS). We selected ~2000 candidates based on their photometric colours, a relatively small sample which is expected to contain the majority of all AM CVn binaries in the SDSS (expected to be ~50). We present two new candidate AM CVn binaries discovered using this strategy: SDSS J104325.08+563258.1 and SDSS J173047.59+554518.5. We also present spectra of 29 new cataclysmic variables, 23 DQ white dwarfs and 21 DZ white dwarfs discovered in this survey. The survey is now approximately 70 per cent complete, and the discovery of seven new AM CVn binaries indicates a lower space density than previously predicted. From the essentially complete g ≤ 19 sample, we derive an observed space density of (5 ± 3) × 10^-7 pc^-3; this is lower than previous estimates by a factor of 3. The sample has been cross-matched with the GALEX All-Sky Imaging Survey data base, and with Data Release 9 of the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS). The addition of UV photometry allows new colour cuts to be applied, reducing the size of our sample to ~1100 objects. Optimizing our follow-up should allow us to uncover the remaining AM CVn binaries present in the SDSS, providing the larger homogeneous sample required to more reliably estimate their space density.
    arXiv:1211.6439 – ADS – doi:10.1093/mnras/sts485
    
    

Non-refereed publications:

1. The Formation of Chondritic Mixtures by Vaporizing Collisions Between Planetesimals
   Stewart, S. T.; Carter, P. J.; Lock, S. J.; Davies, E. J.; Petaev, M. I.; Jacobsen, S. B.,
   2024, 55th Lunar and Planetary Science Conference, held 11-15 March, 2024 at The Woodlands, Texas. LPI Contribution No. 3040, id.2449
   
   From impact's fiery kiss / Vapor blooms, chondrules take form / With stardust gathered.
   ADS – PDF
   
   
2. The Planetary Impacts Community Wiki Project
   Stewart, S. T.; Daly, R. T.; Cline, C. J.; Stickle, A. M.; Jaret, S. J.; Carter, P. J.; Kurosawa, K.; Citron, R. I.; Dou, J.; Harwell, M.; Amodeo, K. M.; Postema, A. N.; Collins, G. S.; Spaulding, D. K.,
   2023, 54th Lunar and Planetary Science Conference, held 13-17 March, 2023 at The Woodlands, Texas. LPI Contribution No. 2806, id.1844
   
   Impacts Wiki for / The crater community / Share, chat, and discuss.
   ADS – PDF
   
   
3. Collision Fragments as a Chemically Similar Source for Late Accretion
   Carter, P. J.; Stewart, S. T.,
   2021, 52nd Lunar and Planetary Science Conference, held virtually, March 2021. LPI Contribution No. 2548, id.2288
   
   Young Earth's leftovers / Look chemically alike / So late impacts match.
   ADS – PDF
   
   
4. Is there an isotopic signature from vaporizing collisions during planet formation?
   Stewart, S. T. ; Carter, P. J. ; Davies, E.,
   2020, American Geophysical Union, Fall Meeting 2020, abstract #DI021-04
   
   During terrestrial planet formation, collision velocities surpass the thresholds that lead to partial vaporization of all the major chemical components: ices, iron alloys, and silicates. Vaporization is commonly associated with mass-dependent fractionation of isotopes; however, only small isotopic variations are observed in moderately volatile elements such as potassium even though the concentrations observed in planetary bodies and meteorites vary by orders of magnitude. Here, we examine the question of whether or not impact-induced vaporization should be accompanied by large isotopic fractionation of vaporized components. The preservation of an isotopic fractionation during vaporization requires separation of the vapor from the condensed components. We find that the evolution of the impact-produced vapor is different for collisions between planetesimals versus collisions between protoplanets. In the case of accretionary collisions between protoplanets, the generated vapor is bound by the gravitational well of the growing planet. Thus, the isotopes are not fractionated because the vapor is not separated. In the case of vaporizing collisions between planetesimals, the impact velocities generally exceed the catastrophic disruption threshold and the partially vaporized material is dispersed in an impact vapor plume. We examined the thermodynamic path and opacity of plumes expanding into vacuum. We find that most of the vapor is produced at high pressures and temperatures, which limits the magnitude of the initial isotopic fractionation, and most of the silicate mass cools to the triple point within the expanding liquid-vapor mixture. Hence, much of the vapor in impact ejecta recondenses before physical separation from the liquid component and mass-dependent isotopic fractionation will be limited. In general, large mass-dependent isotopic fractionation is not expected from vaporizing collisions during planet formation.
   ADS
   
   
5. Volatile loss, Differentiation and Collisions: Key to the Composition of Rocky Exoplanets
   Bonsor, A. ; Harrison, J. ; Shorttle, O. ; Carter, P. ; Kama, M. ; Hollands, M. ; Gaensicke, B. ; Leinhardt, Z.,
   2017, 14th Europlanet Science Congress 2020, held virtually, 2020, id. EPSC2020-387
   
   Many of the key characteristics and geology of our planet Earth today were determined during the planet's formation. What about rocky exoplanets? How does rocky planet formation determine the properties, composition, geology and ultimately, presence of life on rocky exoplanets? In this talk I will discuss projects that investigate the link between rocky planet formation and the composition of rocky exoplanets. This work utilises unique observations that provide us with the bulk composition of rocky exoplanetary material. These observations come from the old, faint remnants of stars like our Sun, known as white dwarfs. White dwarfs should have clean hydrogen or helium atmospheres. This means that planetary bodies as small as asteroids can show up in the white dwarf's atmosphere. Metallic species such as Fe, Mg or Ca provide the bulk composition of the accreted body. Several thousand polluted white dwarfs are now known.Models indicate that outer planetary systems, like our Solar System beyond Mars, should survive the star"s evolution to the white dwarf phase. Scattering is a common process, and any bodies that are scattered inwards, a bit like sun-grazing comets in our Solar System, would show up in the white dwarf atmosphere.What determines the composition of the rocky exoplanetary bodies accreted by white dwarfs? Models presented in Harrison et al, 2018, 2020 (submitted) find that the abundances observed in the atmospheres of white dwarfs can be explained by three key processes, notably galactic chemical evolution, loss of volatiles (thermal processing) and large scale melting which leads to the segregation of material between the core, mantle and crust. Galactic chemical evolution determines the initial composition of the planet forming material. Thermal processing determines the loss of volatiles, be that CO and other gases, water, or moderate volatile species such as Na. Collisions between planetary bodies that have differentiated to form a core can lead to fragments dominated by core-rich or mantle-rich material. Core-Mantle differentiation is a common process in exoplanetary systemsHigh abundances of siderophile (iron-loving) compared to lithophile (silicate loving) speeches in some polluted white dwarfs indicate that accretion of a planetary body composed primarily of material from a planetary core (or alternatively mantle). Harrison et al, 2020, based on data from Hollands et al, 2017, 2018, present several examples of systems with extreme abundances, core-rich, mantle-rich or crust-rich. Bonsor et al, 2020 concludes that most polluted white dwarfs (>60%) have accreted the fragment of a differentiated exoplanetesimal. Post-Nebula volatilisation in exoplanetary bodiesMn and Na trace the loss of volatiles in planetary bodies. The difference in behaviour of Mn and Na under oxidising/reducing conditions makes them a strong indicator of the conditions prevalent when volatile loss occurred. Mn/Na for the Moon/Mars indicate post-Nebula volatile loss (Siebert et al, 2018). Harrison et al, 2020, in prep, provides the first evidence of post-nebula volatilisation in exoplanetary bodies utilising the Mn/Na abundances of polluted white dwarfs.
   ADS
   
   
6. Colliding in the shadows of giants
   Carter, P. J.; Stewart, S. T.,
   2020, AAS Division of Planetary Science meeting #52, id. 205.02. Bulletin of the American Astronomical Society, Vol. 52, No. 6 e-id 2020n6i205p02
   
   Several recent works have shown that giant planet growth and migration can play an important role in shaping the asteroid belt, but these works have not considered the effects of interactions between planetesimals. We have calculated the evolution of planetesimal disks, including planetesimal-planetesimal impacts, during the periods of gas giant growth and migration. The numbers and impact velocities of these collisions, and when and where they occur, depend on the specific growth and migration path. Giant planet migration induces large numbers of high velocity collisions between planetesimals. These impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals, and to cause catastrophic disruption of the bodies. Collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt via giant planet growth and migration. The prevalence of high velocity collisions during giant planet migration, and their potential links to the observed properties of meteorites, and the formation of chondrules, makes impact vaporization in planetesimals a critically important phenomenon.
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7. The Composition of Late-Accreted Planetesimals
   Carter, P. J.; Stewart, S. T.,
   2020, Goldschmidt 2020, 21–26 June 2020
   
   doi:10.46427/gold2020.330 – PDF
   
   
8. The Composition of Late-Impacting Planetesimals
   Carter, P. J.; Stewart, S. T.,
   2020, 51st Lunar and Planetary Science Conference (cancelled). LPI Contribution No. 2326, id.2966
   
   Impacts make bodies / Look chemically alike / So late impacts match.
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9. Thermodynamics of Impact Generated Vapor Plumes After Dispersal of the Solar Nebula
   Davies, E. J.; Carter, P. J.; Duncan, M. S.; Stewart, S. T.; Jacobsen, S. B.,
   2020, 51st Lunar and Planetary Science Conference (cancelled). LPI Contribution No. 2326, id.2927
   
   Impacts vaporize / Vast vapor plume expansion / Drives fractionation.
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10. Size Distribution of Chondrules Set by Droplet Breakup and Coupling During Vaporizing Collisions in the Nebula
    Lock, S. J.; Stewart, S. T.; Carter, P. J.; Davies, E. J.; Petaev, M. I.; Jacobsen, S. B.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1783
    
    Droplets are broken / Down to millimeter size / Large chunks left behind.
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11. Impact Vaporization Criteria During Planet Formation
    Davies, E. J.; Root, S.; Carter, P. J.; Duncan, M. S.; Spaulding, D. K.; Kraus, R. G.; Stewart, S. T.; Jacobsen, S. B.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1257
    
    When planets collide / When do ice, rock and iron / Vaporize? Look here.
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12. Impact Generated Vapor Plumes After Dispersal of the Solar Nebula
    Davies, E. J.; Carter, P. J.; Duncan, M. S.; Root, S.; Spaulding, D. K.; Kraus, R. G.; Stewart, S. T.; Jacobsen, S. B.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1256
    
    Impacts generate / Vapor plumes: liquids, vapor / Expand together.
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13. Collapsing Impact Vapor Plume Model for Chondrule and Chondrite Formation
    Stewart, S. T.; Carter, P. J.; Davies, E. J.; Lock, S. J.; Kraus, R. G.; Root, S.; Petaev, M. I.; Jacobsen, S. B.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1251
    
    Impact disturbance / In nebula makes warm cloud / Of chondrules and dust.
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14. Impact Vapor Plume Expansion and Hydrodynamic Collapse in the Solar Nebula
    Stewart, S. T.; Carter, P. J.; Davies, E. J.; Lock, S. J.; Kraus, R. G.; Root, S.; Petaev, M. I.; Jacobsen, S. B.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1250
    
    Nebula displaced / By bow shock; plume unstable / Collapse makes a cloud.
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15. Collapsing Impact Vapor Plumes: A New Planetesimal Formation Environment
    Carter, P. J.; Davies, E. J.; Lock, S. J.; Stewart, S. T.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1247
    
    Vapor plumes collapse / Inward flow collects debris / New bodies accrete.
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16. High Collision Velocities Between Planetesimals During Planet Growth and Migration
    Carter, P. J.; Davies, E. J.; Lock, S. J.; Stewart, S. T.,
    2019, 50th Lunar and Planetary Science Conference, held 18-22 March, 2019 at The Woodlands, Texas. LPI Contribution No. 2132, id.1246
    
    Big planets excite / Planetesimals hit fast / Vapor plumes ensue.
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17. Magnesium isotope evidence that accretional vapour loss shapes planetary compositions
    Hin, R.; Coath, C.; Carter, P. J.; Nimmo, F.; Lai, Y.-J.; Pogge von Strandmann, P.; Willbold, M.; Leinhardt, Z. M.; Walter, M. J.; Elliott, T.,
    2018, American Geophysical Union, Fall Meeting 2018, abstract #V11G-0087
    
    Chondrites are thought to chemically represent the building blocks of the Earth. However, refractory element (e.g. Al) contents in the silicate Earth relative to many other elements are not the same as in any chondrite [1]. Although broadly explained by core formation and nebular volatile depletion, in detail such processes cannot explain all deviations relative to chondrites. Several studies have investigated mass-dependent fractionation of Mg isotopes in Earth and chondrites to better constrain Earth’s accretion history. Results have varied, most likely due to analytical issues. We have developed a critical mixture double spiking procedure to generate more accurate and precise isotope ratios in systems with three isotopes, such as Mg [2]. Our Mg isotope analyses show that Earth has 25Mg/24Mg significantly heavier by ~0.02‰ than chondrites, as are samples from Mars and the eucrite and angrite parent bodies [3]. We propose that vapour-liquid fractionation during vapour loss from planetesimals is the most plausible explanation for the heavy 25Mg/24Mg of differentiated planetary bodies. We have simulated the chemical consequences of such vapour loss for Mg, Si and Fe isotope ratios and for concentrations of nine major and minor elements. Constrained by the observed Mg isotope difference between Earth and chondrites, the model implies that ~40% vapour loss occurred. Such vapour loss transforms the initially chondritic element and isotope ratios of the residual silicate into approximately the bulk silicate Earth composition. Physical models suggest that impacts between planetesimals can cause substantial melting and that vapour associated with this melt escapes. Our models also imply that total vapour losses may accumulate to tens of percent, supporting the hypothesis that accretionary loss of ~40% vapour from planetesimals early in Earth’s accretion history may have shaped our planet’s composition. A consequence of such large vapour loss is that the planetesimals from which the early Earth grew were void of volatiles and that these were delivered by volatile-rich material late in Earth’s accretion.
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18. The Energy Budgets of Giant Impacts
    Carter, P. J.; Lock, S. J.; Stewart, S. T.,
    2018, 49th Lunar and Planetary Science Conference 19-23 March, 2018, held at The Woodlands, Texas LPI Contribution No. 2083, id.2731
    
    Large amounts of energy are exchanged during giant impacts. How different are the energy budgets amongst proposed models for the Moon-forming impact?
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19. A Mechanism for Planetesimal Mass-loss and Volatile Depletion
    Nimmo, F.; Hin, R.; Carter, P. J.; Bierson, C. J.,
    2017, American Geophysical Union, Fall Meeting 2017, abstract #P53F-02
    
    Differentiated planetary bodies, both large and small, show signs of volatile depletion relative to chondrites, as indicated by K/U ratios [1]. Isotopic ratios of elements such as Zn [2], Si [3] and Mg [4] also show evidence for possible mass loss. How such mass loss could occur is an open question [5].Here I investigate one pathway for mass loss, via impact-generated melting. The vapour pressure above a localized melt pool depends on the melt temperature, and so does the vapour sound speed. For small bodies, this sound speed may be comparable to (or exceed) the escape velocity, in which case rapid vapour escape can occur [6]. This mechanism is potentially more efficient than direct vaporization via impact, because the threshold velocity required is lower.Vapour escape is limited by the cooling of the melt pool, which will occur via direct radiative cooling and also by evaporative cooling due to mass loss. Vapour loss is most effective in small bodies; Earth-mass bodies do not suffer vapour loss owing to the high escape velocity. Elements (such as K) with higher vapour pressures will be preferentially lost first. The escape itself will not generate significant isotopic fractionation [7], but the conversion of melt to vapour will. Numerical simulations [8] show that in a calm accretionary disk vapour loss is very limited, in agreement with [9]. But in a dynamically-excited disk, impact velocities are higher, resulting in wide-spread melting. As a result, significant mass loss can occur in 1000 km-scale bodies. The volatile-depleted nature of the terrestrial planets can thus potentially be explained by melt-driven mass loss on smaller precursor bodies [4]. [1] McCubbin et al. GRL 2012[2] Day & Moynier PTRSL 2014[3] Pringle et al. PNAS 2014[4] Hin et al. Nature in press[5] Albarede Nature 2009[6] Lehmer et al. Ap. J. 2017[7] Hunten et al. Icarus 1987[8] Carter et al. Ap. J. 2015[9] Dauphas et al. EPSL 2015
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20. Constraining properties of disintegrating exoplanets
    Veras, D.; Carter, P. J.; Leinhardt, Z. M.; Gänsicke, B. T.,
    2017, European Planetary Science Congress 2017, held 17-22 September, 2017 in Riga Latvia, id. EPSC2017-47
    
    Evaporating and disintegrating planets provide unique insights into chemical makeup and physical constraints. The striking variability, depth (~10 - 60%) and shape of the photometric transit curves due to the disintegrating minor planet orbiting white dwarf WD 1145+017 has galvanised the post-main- sequence exoplanetary science community. We have performed the first tidal disruption simulations of this planetary object, and have succeeded in constraining its mass, density, eccentricity and physical nature. We illustrate how our simulations can bound these properties, and be used in the future for other exoplanetary systems.
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21. Simulating the tidal disruption of the asteroid orbiting white dwarf WD 1145+017
    Veras, Dimitri; Carter, Philip; Leinhardt, Zoe; Gänsicke, Boris,
    2017, American Astronomical Society, DDA meeting #48, id.101.04
    
    Post-main-sequence planetary science has been galvanised by the striking variability, depth and shape of the photometric transit curves due to objects orbiting white dwarf WD 1145+017, a star which also hosts a dusty debris disc and circumstellar gas, and displays strong metal atmospheric pollution. However, the physical properties of the likely asteroid which is discharging disintegrating fragments remain largely unconstrained from the observations. This process has not yet been modelled numerically. Here, we use the N-body code PKDGRAV to compute dissipation properties for asteroids of different spins, densities, masses, and eccentricities. We simulate both homogeneous and differentiated asteroids, for up to two years, and find that the disruption timescale is strongly dependent on density and eccentricity, but weakly dependent on mass and spin. We find that primarily rocky differentiated bodies with moderate (~3-4 g/cm^3) bulk densities on near-circular (e <~ 0.1) orbits can remain intact while occasionally shedding mass from their mantles. These results suggest that the asteroid orbiting WD 1145+017 is differentiated, resides just outside of the Roche radius for bulk density but just inside the Roche radius for mantle density, and is more akin physically to an asteroid like Vesta instead of one like Itokawa.
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22. Lunar Accretion After a High-Energy, High-Angular Momentum Giant Impact
    Hollyday, G. O.; Stewart, S. T.; Leinhardt, Z. M.; Carter, P. J.; Lock, S. J.,
    2017, 48th Lunar and Planetary Science Conference, held 20-24 March 2017, at The Woodlands, Texas. LPI Contribution No. 1964, id.2606
    
    Making the Moon from bulk silicate Earth vapor.
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23. The Effects of Collisions and Dynamical Excitation on the Composition of Growing Terrestrial Planet Embryos
    Carter, P. J.; Leinhardt, Z. M.; Elliott, T.; Walter, M. J.; Stewart, S. T.,
    2016, 47th Lunar and Planetary Science Conference, held March 21-25, 2016 at The Woodlands, Texas. LPI Contribution No. 1903, p.2300
    
    Exploring the effects of imperfect collisions and excitation from Jupiter's Grand Tack on the compositions of embryos during terrestrial planet formation.
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24. GRB 110205A: NOT redshift confirmation.
    Vreeswijk, P.; Groot, P.; Carter, P.; Xu, D.; De Cia, A.; Jakobsson, P.; Fynbo, J.,
    2011, GRB Coordinates Network, Circular Service, No. 11640, #1 (2011)
    
    We have observed the field of GRB 110205A (Beardmore et al., GCN 11629) with the 2.5m NOT telescope at Roque de los Muchachos Observatory (La Palma, Spain) equipped with ALFOSC starting at 3:25 UT (1.4h after the burst). Despite thick clouds, the optical afterglow is clearly detected at R ~ 16.7 (as compared to nearby USNO-B1.0 stars). Preliminary reduction of the subsequent spectroscopic observations shows a clear DLA and several metal absorption lines (OI/OI*, CII/CII*, CIV, AlII, FeII) at a common redshift z=2.22, confirming the redshift measurement by Cenko et al. (GCN 11638).
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