Most stars become white dwarfs after they have exhausted their nuclear fuel (the Sun will be one such). Between one-quarter and one-half of white dwarfs have elements heavier than helium in their ...atmospheres, even though these elements ought to sink rapidly into the stellar interiors (unless they are occasionally replenished). The abundance ratios of heavy elements in the atmospheres of white dwarfs are similar to the ratios in rocky bodies in the Solar System. This fact, together with the existence of warm, dusty debris disks surrounding about four per cent of white dwarfs, suggests that rocky debris from the planetary systems of white-dwarf progenitors occasionally pollutes the atmospheres of the stars. The total accreted mass of this debris is sometimes comparable to the mass of large asteroids in the Solar System. However, rocky, disintegrating bodies around a white dwarf have not yet been observed. Here we report observations of a white dwarf--WD 1145+017--being transited by at least one, and probably several, disintegrating planetesimals, with periods ranging from 4.5 hours to 4.9 hours. The strongest transit signals occur every 4.5 hours and exhibit varying depths (blocking up to 40 per cent of the star's brightness) and asymmetric profiles, indicative of a small object with a cometary tail of dusty effluent material. The star has a dusty debris disk, and the star's spectrum shows prominent lines from heavy elements such as magnesium, aluminium, silicon, calcium, iron, and nickel. This system provides further evidence that the pollution of white dwarfs by heavy elements might originate from disrupted rocky bodies such as asteroids and minor planets.
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IJS, KISLJ, NUK, SBMB, UL, UM, UPUK
Astronomers have discovered thousands of planets outside the Solar System
, most of which orbit stars that will eventually evolve into red giants and then into white dwarfs. During the red giant ...phase, any close-orbiting planets will be engulfed by the star
, but more distant planets can survive this phase and remain in orbit around the white dwarf
. Some white dwarfs show evidence for rocky material floating in their atmospheres
, in warm debris disks
or orbiting very closely
, which has been interpreted as the debris of rocky planets that were scattered inwards and tidally disrupted
. Recently, the discovery of a gaseous debris disk with a composition similar to that of ice giant planets
demonstrated that massive planets might also find their way into tight orbits around white dwarfs, but it is unclear whether these planets can survive the journey. So far, no intact planets have been detected in close orbits around white dwarfs. Here we report the observation of a giant planet candidate transiting the white dwarf WD 1856+534 (TIC 267574918) every 1.4 days. We observed and modelled the periodic dimming of the white dwarf caused by the planet candidate passing in front of the star in its orbit. The planet candidate is roughly the same size as Jupiter and is no more than 14 times as massive (with 95 per cent confidence). Other cases of white dwarfs with close brown dwarf or stellar companions are explained as the consequence of common-envelope evolution, wherein the original orbit is enveloped during the red giant phase and shrinks owing to friction. In this case, however, the long orbital period (compared with other white dwarfs with close brown dwarf or stellar companions) and low mass of the planet candidate make common-envelope evolution less likely. Instead, our findings for the WD 1856+534 system indicate that giant planets can be scattered into tight orbits without being tidally disrupted, motivating the search for smaller transiting planets around white dwarfs.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Between 30% and 50% of white dwarfs (WDs) show heavy elements in their atmospheres. This pollution is thought to arise from the accretion of planetesimals perturbed by outer planet(s) to ...within the WD’s tidal disruption radius. A small fraction of these WDs show either emission or absorption from circumstellar (C-S) gas. The abundances of metals in the photospheres of WDs with C-S gas are mostly similar to the bulk composition of the Earth. The C-S component arises from gas produced through collisions and/or the sublimation of disintegrating planetesimals. High-resolution spectroscopic observations of WD 1124−293 reveal photospheric and C-S absorption of Ca in multiple transitions. Here, we present high signal-to-noise ratio spectra, an updated WD atmosphere analysis, and a self-consistent model of its C-S gas. We constrain the abundances of Ca, Mg, and Fe in the photosphere of WD 1124−293, and find agreement with the abundances of these three species in the C-S gas. We find the location of the C-S gas is ∼100 white dwarf radii, the C-S and photospheric compositions are thus far consistent, the gas is not isothermal, and the amount of C-S Ca has not changed in two decades. We also demonstrate how to use Cloudy to model C-S gas viewed in absorption around polluted WDs. Modeling the abundances of gas around polluted WDs with Cloudy provides a new method to measure the composition of exoplanetesimals and will allow a direct comparison to the composition of rocky bodies in the solar system.
The photospheres of some white dwarfs (WDs) are "polluted" by accretion of material from their surrounding planetary debris. WDs with dust disks are often heavily polluted and high-resolution ...spectroscopic observations of these systems can be used to infer the chemical compositions of extrasolar planetary material. Here, we report spectroscopic observation and analysis of 19 WDs with dust disks or candidate disks. The overall abundance pattern very much resembles that of bulk Earth and we are starting to build a large enough sample to probe a wide range of planetary compositions. We found evidence for accretion of Fe-rich material onto two WDs as well as O-rich but H-poor planetary debris onto one WD. In addition, there is a spread in Mg/Ca and Si/Ca ratios and it cannot be explained by differential settling or igneous differentiation. The ratios appear to follow an evaporation sequence. In this scenario, we can constrain the mass and number of evaporating bodies surrounding polluted WDs.
The most heavily polluted white dwarfs often show excess infrared radiation from circumstellar dust disks, which are modeled as a result of tidal disruption of extrasolar minor planets. Interaction ...of dust, gas, and disintegrating objects can all contribute to the dynamical evolution of these dust disks. Here, we report two infrared variable dusty white dwarfs, SDSS J1228+1040 and G29-38. For SDSS J1228+1040, compared to the first measurements in 2007, the IRAC 3.6 and 4.5 fluxes decreased by 20% before 2014 to a level also seen in the recent 2018 observations. For G29-38, the infrared flux of the 10 m silicate emission feature became 10% stronger between 2004 and 2007, We explore several scenarios that could account for these changes, including tidal disruption events, perturbation from a companion, and runaway accretion. No satisfactory causes are found for the flux drop in SDSS J1228+1040 due to the limited time coverage. Continuous tidal disruption of small planetesimals could increase the mass of small grains and concurrently change the strength of the 10 m feature of G29-38. Dust disks around white dwarfs are actively evolving and we speculate that there could be different mechanisms responsible for the temporal changes of these disks.
Abstract
We present observations and analyses of eight white dwarf stars (WDs) that have accreted rocky material from their surrounding planetary systems. The spectra of these helium-atmosphere WDs ...contain detectable optical lines of all four major rock-forming elements (O, Mg, Si, and Fe). This work increases the sample of oxygen-bearing WDs with parent body composition analyses by roughly 33%. To first order, the parent bodies that have been accreted by the eight WDs are similar to those of chondritic meteorites in relative elemental abundances and oxidation states. Seventy-five percent of the WDs in this study have observed oxygen excesses implying volatiles in the parent bodies with abundances similar to those of chondritic meteorites. Three WDs have oxidation states that imply more reduced material than found in CI chondrites, indicating the possible detection of Mercury-like parent bodies, but are less constrained. These results contribute to the recurring conclusion that extrasolar rocky bodies closely resemble those in our solar system, and do not, as a whole, yield unusual or unique compositions.
Abstract
Excess infrared flux from white dwarf stars is likely to arise from a dusty debris disk or a cool companion. In this work, we present near-infrared spectroscopic observations with ...Keck/MOSFIRE, Gemini/GNIRS, and Gemini/Flamingos-2 of seven white dwarfs with infrared excesses identified in previous studies. We confirmed the presence of dust disks around four white dwarfs (Gaia J0611–6931, Gaia J0006+2858, Gaia J2100+2122, and WD 0145+234) as well as two new white dwarf–brown dwarf pairs (Gaia J0052+4505 and Gaia J0603+4518). In three of the dust disk systems, we detected for the first time near-infrared metal emissions (Mg
i
, Si I, and possibly Fe I) from a gaseous component of the disk. We developed a new Markov Chain Monte Carlo framework to constrain the geometric properties of each dust disk. In three systems, the dust disk and the gas disk appear to coincide spatially. For the two brown dwarf–white dwarf pairs, we identified broad molecular absorption features typically seen in L dwarfs. The origin of the infrared excess around Gaia J0723+6301 remains a mystery. Our study underlines how near-infrared spectroscopy can be used to determine sources of infrared excess around white dwarfs, which has now been detected photometrically in hundreds of systems.
WD 1145+017 is a unique white dwarf system that has a heavily polluted atmosphere, an infrared excess from a dust disk, numerous broad absorption lines from circumstellar gas, and changing transit ...features, likely from fragments of an actively disintegrating asteroid. Here, we present results from a large photometric and spectroscopic campaign with Hubble Space Telescope, Keck, Very Large Telescope (VLT), Spitzer, and many other smaller telescopes from 2015 to 2018. Somewhat surprisingly the ultraviolet (UV) transit depths are always shallower than those in the optical. We develop a model that can quantitatively explain the observed "bluing" and confirm the previous finding that: (1) the transiting objects, circumstellar gas, and white dwarf are all aligned along our line of sight; (2) the transiting object is blocking a larger fraction of the circumstellar gas than of the white dwarf itself. Because most circumstellar lines are concentrated in the UV, the UV flux appears to be less blocked compared to the optical during a transit, leading to a shallower UV transit. This scenario is further supported by the strong anticorrelation between optical transit depth and circumstellar line strength. We have yet to detect any wavelength-dependent transits caused by the transiting material around WD 1145+017.
Abstract Context Patients with gastrointestinal cancer are at high risk for deterioration of nutrition. Home parenteral nutrition (HPN) could improve nutritional status and quality of life (QoL). ...Objectives The purpose of this study was 1) to evaluate the impact of HPN on QoL, 2) to assess changes in nutritional status, and 3) to assess proxy perception of patient well-being. Methods We conducted a prospective, observational, and a multicenter study. Inclusion criteria were adult patients with gastrointestinal cancer, for whom HPN was indicated and prescribed for at least 14 days. The physician, the patient, and a family member completed questionnaires at inclusion and 28 days later. The QoL was assessed by the patients using the Functional Assessment of Cancer Therapy-General questionnaire, at inclusion and 28 days later. Results The study included 370 patients with gastrointestinal cancer. The HPN was indicated for cancer-related undernutrition in 89% of the patients and was used as a complement to oral intake in 84%. After 28 days of parenteral intake, global QoL was significantly increased (48.9 at inclusion vs. 50.3, P = 0.007). The patients' weight improved significantly by 2.7% ( P < 0.001). The nutrition risk screening also decreased significantly (3.2 ± 1.1 vs. 2.8 ± 1.3, P = 0.003). Conclusion HPN could provide benefit for malnourished patients with gastrointestinal cancer. However, randomized controlled studies are required to confirm this benefit and the safety profile.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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