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Register a new userRelentless and Complex Transits from a Planetesimal Debris Disk
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This article reports quasi-continuous transiting events towards WD 1054-226 at d=36.2 pc and V=16.0 mag, based on simultaneous, high-cadence, multi-wavelength imaging photometry using ULTRACAM over 18 nights from 2019 to 2020 March. The predominant period is 25.02 h, and corresponds to a circular orbit with blackbody Teq = 323 K, where a planetary surface can nominally support liquid water. The light curves reveal remarkable night-to-night similarity, with changes on longer timescales, and lack any transit-free segments of unocculted starlight. The most pronounced dimming components occur every 23.1 min -- exactly the 65th harmonic of the fundamental period -- with depths of up to several per cent, and no evident color dependence. Myriad additional harmonics are present, as well as at least two transiting features with independent periods, one longer and one shorter than, yet both similar to, the underlying period. High-resolution optical spectra are consistent with stable, photospheric absorption by multiple, refractory metal species, with no indication of circumstellar gas. Spitzer observations demonstrate a lack of detectable dust emission, suggesting that the otherwise hidden circumstellar disk orbiting WD 1054-226 may be typical of polluted white dwarfs, and only detected via favorable geometry. Future observations are required to constrain the orbital eccentricity, but even if periastron is near the Roche limit, sublimation cannot drive mass loss in refractory parent bodies, and collisional disintegration is necessary for dust production.
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Finding and characterizing extrasolar Earth analogs will rely on interpretation of the planetary systems environmental context. The total budget and fractionation between C-H-O species sensitively affect the climatic and geodynamic state of terrestrial worlds, but their main delivery channels are poorly constrained. We connect numerical models of volatile chemistry and pebble coagulation in the circumstellar disk with the internal compositional evolution of planetesimals during the primary accretion phase. Our simulations demonstrate that disk chemistry and degassing from planetesimals operate on comparable timescales and can fractionate the relative abundances of major water and carbon carriers by orders of magnitude. As a result, individual planetary systems with significant planetesimal processing display increased correlation in the volatile budget of planetary building blocks relative to no internal heating. Planetesimal processing in a subset of systems increases the variance of volatile contents across planetary systems. Our simulations thus suggest that exoplanetary atmospheric compositions may provide constraints on $when$ a specific planet formed.
Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4min periodic variation in the strength and shape of the CaII emission line profiles originating from the debris disc around the white dwarf SDSSJ122859.93+104032.9. We interpret this short-period signal as the signature of a solid body held together by its internal strength.
We present far- and near-ultraviolet absorption spectroscopy of the $sim$23 Myr edge-on debris disk surrounding the A0V star $eta$ Telescopii, obtained with the Hubble Space Telescope Space Telescope Imaging Spectrograph. We detect absorption lines from C I, C II, O I, Mg II, Al II, Si II, S II, Mn II, Fe II, and marginally N I. The lines show two clear absorption components at $-22.7pm0.5$ km s$^{-1}$ and $-17.8pm0.7$ km s$^{-1}$, which we attribute to circumstellar (CS) and interstellar (IS) gas, respectively. CO absorption is not detected, and we find no evidence for star-grazing exocomets. The CS absorption components are blueshifted by $-16.9pm2.6$ km s$^{-1}$ in the stars reference frame, indicating that they are outflowing in a radiatively driven disk wind. We find that the C/Fe ratio in the $eta$ Tel CS gas is significantly higher than the solar ratio, as is the case in the $beta$ Pic and 49 Cet debris disks. Unlike those disks, however, the measured C/O ratio in the $eta$ Tel CS gas is consistent with the solar value. Our analysis shows that because $eta$ Tel is an earlier type star than $beta$ Pic and 49 Cet, with more substantial radiation pressure at the dominant C II transitions, this species cannot bind the CS gas disk to the star as it does for $beta$ Pic and 49 Cet, resulting in the disk wind.
We present follow-up photometry and spectroscopy of ZTF J0328$-$1219 strengthening its status as a white dwarf exhibiting transiting planetary debris. Using TESS and Zwicky Transient Facility photometry, along with follow-up high speed photometry from various observatories, we find evidence for two significant periods of variability at 9.937 and 11.2 hr. We interpret these as most likely the orbital periods of different debris clumps. Changes in the detailed dip structures within the light curves are observed on nightly, weekly, and monthly timescales, reminiscent of the dynamic behavior observed in the first white dwarf discovered to harbor a disintegrating asteroid, WD 1145+017. We fit previously published spectroscopy along with broadband photometry to obtain new atmospheric parameters for the white dwarf, with $M_{star} = 0.731 pm 0.023,M_{odot}$, $T_{mathrm{eff}} = 7630 pm 140,$K, and $mathrm{[Ca/He]}=-9.55pm0.12$. With new high-resolution spectroscopy, we detect prominent and narrow Na D absorption features likely of circumstellar origin, with velocities $21.4pm1.0$ km s$^{-1}$ blue-shifted relative to atmospheric lines. We attribute the periodically modulated photometric signal to dusty effluents from small orbiting bodies such as asteroids or comets, but are unable to identify the most likely material that is being sublimated, or otherwise ejected, as the environmental temperatures range from roughly 400K to 600K.
We present ALMA mosaic observations at 1.3 mm (223 GHz) of the Fomalhaut system with a sensitivity of 14 $mu$Jy/beam. These observations provide the first millimeter map of the continuum dust emission from the complete outer debris disk with uniform sensitivity, enabling the first conclusive detection of apocenter glow. We adopt a MCMC modeling approach that accounts for the eccentric orbital parameters of a collection of particles within the disk. The outer belt is radially confined with an inner edge of $136.3pm0.9$ AU and width of $13.5pm1.8$ AU. We determine a best-fit eccentricity of $0.12pm0.01$. Assuming a size distribution power law index of $q=3.46pm 0.09$, we constrain the dust absorptivity power law index $beta$ to be $0.9<beta<1.5$. The geometry of the disk is robustly constrained with inclination $65.!!^circ6pm0.!!^circ3$, position angle $337.!!^circ9pm0.!!^circ3$, and argument of periastron $22.!!^circ5pm4.!!^circ3$. Our observations do not confirm any of the azimuthal features found in previous imaging studies of the disk with HST, SCUBA, and ALMA. However, we cannot rule out structures $leq10$ AU in size or which only affect smaller grains. The central star is clearly detected with a flux density of $0.75pm0.02$ mJy, significantly lower than predicted by current photospheric models. We discuss the implications of these observations for the directly imaged Fomalhaut b and the inner dust belt detected at infrared wavelengths.
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