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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

A White Dwarf with Transiting Circumstellar Material Far outside the Roche Limit

We report the discovery of a white dwarf exhibiting deep, irregularly shaped transits, indicative of circumstellar planetary debris. Using Zwicky Transient Facility DR2 photometry of ZTF J013906.17+524536.89 and follow-up observations from the Las Cumbres Observatory, we identify multiple transit events that recur every ≈107.2 days, much longer than the 4.5–4.9 hr orbital periods observed in WD 1145+017, the only other white dwarf known with transiting planetary debris. The transits vary in both depth and duration, lasting 15–25 days and reaching 20%–45% dips in flux. Optical spectra reveal strong Balmer lines, identifying the white dwarf as a DA with ${T}_{\mathrm{eff}}=10,530\pm 140\,{\rm{K}}$ and $\mathrm{log}(g)=7.86\pm 0.06$. A Ca ii K absorption feature is present in all spectra both in and out of transit. Spectra obtained during one night at roughly 15% transit depth show increased Ca ii K absorption with a model atmospheric fit suggesting [Ca/H] = –4.6 ± 0.3, whereas spectra taken on three nights out of transit have [Ca/H] of –5.5, –5.3, and –4.9 with similar uncertainties. While the Ca ii K line strength varies by only 2σ, we consider a predominantly interstellar origin for Ca absorption unlikely. Here, we suggest a larger column density of circumstellar metallic gas along the line of site or increased accretion of material onto the white dwarf's surface are responsible for the Ca absorption, but further spectroscopic studies are required. In addition, high-speed time series photometry out of transit reveals variability with periods of 900 and 1030 s, consistent with ZZ Ceti pulsations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

A Census of the 32 Ori Association with Gaia*

I have used high-precision photometry and astrometry from the third data release of Gaia (DR3) to identify candidate members of the 32 Ori association. Spectral types and radial velocities have been measured for subsets of the candidates using new and archival spectra. For the candidates that have radial velocity measurements, I have used UVW velocities to further constrain their membership, arriving at a final catalog of 169 candidates. I estimate that the completeness of the survey is ~90% for spectral types of ≲M7 (≳0.06 M ⊙ ). The histogram of spectral types for the 32 Ori candidates exhibits a maximum at M5 (~0.15 M ⊙ ), resembling the distributions measured for other young clusters and associations in the solar neighborhood. The available UVW velocities indicate that the association is expanding, but they do not produce a well-defined kinematic age. Based on their sequences of low-mass stars in color–magnitude diagrams, the 32 Ori association and Upper Centaurus-Lupus/Lower Centaurus-Crux (UCL/LCC) are coeval to within ±1.2 Myr, and they are younger than the β Pic moving group by ~3 Myr, which agrees with results from previous analysis based on the second data release of Gaia. Finally, I have used mid-IR photometry from the Wide-field Infrared Survey Explorer to check for excess emission from circumstellar disks among the 32 Ori candidates. Disks are detected for 18 candidates, half of which are reported for the first time in this work. The fraction of candidates at ≤M6 that have full, transitional, or evolved disks is 10/149 = 0.07$^{+0.03}_{-0.02'}$ which is consistent with the value for UCL/LCC.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Periodic Eruptive Variability of the Isolated Pre-main-sequence Star V347 Aurigae

V347 Aurigae is associated with the small dark cloud L1438 and appears to be an isolated pre-main-sequence star located at distance d ≈ 200 pc. Multi-epoch, archival photometry reveals periodic brightness variations with amplitude V ≈ 2.0 mag occurring on timescales of ~160 days that have persisted for decades. Regular-cadence, optical imaging of the source with the Zwicky Transient Facility shows that a small reflection nebula illuminated by V347 Aur also fluctuates in brightness, at times fading completely. Multi-epoch, Keck/HIRES data suggests the presence of two distinct spectral components: a prominent emission-line-dominated spectrum with a heavily veiled continuum correlated with the bright photometric state, and an M-type absorption line spectrum associated with quiescence. All spectra exhibit strong Balmer and He i line emission, consistent with accretion, as well as high velocity emission arising from the forbidden transitions of [O i], [N ii], and [S ii] that are generally associated with collimated jets and disk winds. There is no evidence in existing high-dispersion spectroscopy or high-resolution imaging for binarity of V347 Aur. The repeating outburst events are possibly linked to accretion instabilities induced by an undetected companion or a structure within the circumstellar disk that periodically increases the mass accretion rate. V347 Aur is perhaps analogous to an EXor-type variable, though more regularly recurring.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Outward Migration of Super-Jupiters

We report recent simulations show that giant planets of about 1 M J migrate inward at a rate that differs from the type II prediction. Here we show that at higher masses, planets migrate outward. Our result differs from previous ones because of our longer simulation times, lower viscosity, and boundary conditions that allow the disk to reach a viscous steady state. We show that, for planets on circular orbits, the transition from inward to outward migration coincides with the known transition from circular to eccentric disks that occurs for planets more massive than a few Jupiters. In an eccentric disk, the torque on the outer disk weakens due to two effects: the planet launches weaker waves, and those waves travel further before damping. As a result, the torque on the inner disk dominates, and the planet pushes itself outward. Our results suggest that the many super-Jupiters observed by direct imaging at large distances from the star may have gotten there by outward migration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

The Anatomy of an Unusual Edge-on Protoplanetary Disk. II. Gas Temperature and a Warm Outer Region

We present high-resolution {sup 12}CO and {sup 13}CO 2–1 ALMA observations, as well as optical and near-infrared spectroscopy, of the highly inclined protoplanetary disk around SSTC2D J163131.2–242627. The spectral type we derive for the source is consistent with a 1.2 M {sub ⊙} star inferred from the ALMA observations. Despite its massive circumstellar disk, we find little to no evidence for ongoing accretion on the star. The CO maps reveal a disk that is unusually compact along the vertical direction, consistent with its appearance in scattered light images. The gas disk extends about twice as far away as both the submillimeter continuum and the optical scattered light. CO is detected from two surface layers separated by a midplane region in which CO emission is suppressed, as expected from freeze-out in the cold midplane. We apply a modified version of the tomographically reconstructed distribution method presented by Dutrey et al. to derive the temperature structure of the disk. We find a temperature in the CO-emitting layers and the midplane of ∼33 K and ∼20 K at R < 200 au, respectively. Outside of R > 200 au, the disk’s midplane temperature increases to ∼30 K, with a nearly vertically isothermal profile. The transition in CO temperature coincides with a dramatic reduction in the submicron and submillimeter emission from the disk. We interpret this as interstellar UV radiation providing an additional source of heating to the outer part of the disk.

47 OTHER INSTRUMENTATION↗