scholarly journals The dust never settles: collisional production of gas and dust in evolved planetary systems

2020 ◽  
Vol 496 (4) ◽  
pp. 5233-5242 ◽  
Author(s):  
Andrew Swan ◽  
Jay Farihi ◽  
Thomas G Wilson ◽  
Steven G Parsons
Keyword(s):  
Time Scales ◽  
White Dwarf ◽  
Dust Emission ◽  
Canonical Model ◽  
Minor Planets ◽  
Infrared Photometry ◽  
Dust Production ◽  
Thick Disc ◽  
Observed Behaviour ◽  
Host Stars

ABSTRACT Multi-epoch infrared photometry from Spitzer is used to monitor circumstellar discs at white dwarfs, which are consistent with disrupted minor planets whose debris is accreted and chemically reflected by their host stars. Widespread infrared variability is found across the population of 37 stars with two or more epochs. Larger flux changes occur on longer time-scales, reaching several tens of per cent over baselines of a few years. The canonical model of a geometrically thin, optically thick disc is thus insufficient, as it cannot give rise to the observed behaviour. Optically thin dust best accounts for the variability, where collisions drive dust production and destruction. Notably, the highest infrared variations are seen in systems that show Ca ii emission, supporting planetesimal collisions for all known debris discs, with the most energetic occurring in those with detected gaseous debris. The sample includes the only polluted white dwarf with a circumbinary disc, where the signal of the day–night cycle of its irradiated substellar companion appears diluted by dust emission.

scholarly journals Near-infrared variability in dusty white dwarfs: tracing the accretion of planetary material

2020 ◽  
Vol 494 (2) ◽  
pp. 2861-2874 ◽  
Author(s):  
Laura K Rogers ◽  
Siyi Xu (许偲艺) ◽  
Amy Bonsor ◽  
Simon Hodgkin ◽  
Kate Y L Su ◽  
...  
Keyword(s):  
Time Scales ◽  
White Dwarf ◽  
White Dwarfs ◽  
Near Infrared ◽  
Dust Emission ◽  
Infrared Emission ◽  
Wide Field ◽  
Infrared Telescope ◽  
Infrared Monitoring ◽  
K Band

ABSTRACT The inwards scattering of planetesimals towards white dwarfs is expected to be a stochastic process with variability on human time-scales. The planetesimals tidally disrupt at the Roche radius, producing dusty debris detectable as excess infrared emission. When sufficiently close to the white dwarf, this debris sublimates and accretes on to the white dwarf and pollutes its atmosphere. Studying this infrared emission around polluted white dwarfs can reveal how this planetary material arrives in their atmospheres. We report a near-infrared monitoring campaign of 34 white dwarfs with infrared excesses with the aim to search for variability in the dust emission. Time series photometry of these white dwarfs from the United Kingdom Infrared Telescope (Wide Field Camera) in the J-, H-, and K-bands was obtained over baselines of up to 3 yr. We find no statistically significant variation in the dust emission in all three near-infrared bands. Specifically, we can rule out variability at ∼1.3 per cent for the 13 white dwarfs brighter than 16th mag in K-band, and at ∼10 per cent for the 32 white dwarfs brighter than 18th mag over time-scales of 3 yr. Although to date two white dwarfs, SDSS J095904.69−020047.6 and WD 1226+110, have shown K-band variability, in our sample we see no evidence of new K-band variability at these levels. One interpretation is that the tidal disruption events that lead to large variabilities are rare occur on short time-scales, and after a few years the white dwarfs return to being stable in the near-infrared.

scholarly journals Variable dust formation by the double-line spectroscopic binary WR 70 (HD 137603, WC9vd+B0I)

2003 ◽  
Vol 212 ◽  
pp. 261-262
Author(s):  
Peredur M. Williams ◽  
Karel A. van der Hucht ◽  
Fred Marang
Keyword(s):  
Time Scales ◽  
Dust Emission ◽  
Dust Formation ◽  
Infrared Photometry ◽  
Double Line ◽  
Underlying Process ◽  
Spectroscopic Binary ◽  
Show Evidence

Infrared photometry of the WC9vd+B0I spectroscopic binary WR 70 over two decades shows variable dust emission. The variations are relatively slow and show evidence for an underlying process with a period P = 1045 ± 60 d, together with modulation on shorter and longer time-scales.

scholarly journals Constraining planet formation around 6–8 M⊙ stars

2020 ◽  
Vol 493 (1) ◽  
pp. 765-775 ◽  
Author(s):  
Dimitri Veras ◽  
Pier-Emmanuel Tremblay ◽  
J J Hermes ◽  
Catriona H McDonald ◽  
Grant M Kennedy ◽  
...  
Keyword(s):  
White Dwarf ◽  
White Dwarfs ◽  
Main Sequence ◽  
Planet Formation ◽  
Mass Range ◽  
Minor Planets ◽  
Spectroscopic Analyses ◽  
M Stars ◽  
Host Stars ◽  
Rubble Pile

ABSTRACT Identifying planets around O-type and B-type stars is inherently difficult; the most massive known planet host has a mass of only about $3\, \mathrm{M}_{\odot }$. However, planetary systems which survive the transformation of their host stars into white dwarfs can be detected via photospheric trace metals, circumstellar dusty and gaseous discs, and transits of planetary debris crossing our line of sight. These signatures offer the potential to explore the efficiency of planet formation for host stars with masses up to the core-collapse boundary at $\approx 8\, \mathrm{M}_{\odot }$, a mass regime rarely investigated in planet formation theory. Here, we establish limits on where both major and minor planets must reside around $\approx 6\rm {-}8\, \mathrm{M}_{\odot }$ stars in order to survive into the white dwarf phase. For this mass range, we find that intact terrestrial or giant planets need to leave the main sequence beyond approximate minimum star–planet separations of, respectively, about 3 and 6 au. In these systems, rubble pile minor planets of radii 10, 1.0, and 0.1 km would have been shorn apart by giant branch radiative YORP spin-up if they formed and remained within, respectively, tens, hundreds, and thousands of au. These boundary values would help distinguish the nature of the progenitor of metal pollution in white dwarf atmospheres. We find that planet formation around the highest mass white dwarf progenitors may be feasible, and hence encourage both dedicated planet formation investigations for these systems and spectroscopic analyses of the highest mass white dwarfs.

scholarly journals Host-star and exoplanet compositions: a pilot study using a wide binary with a polluted white dwarf

2021 ◽  
Vol 503 (2) ◽  
pp. 1877-1883
Author(s):  
Amy Bonsor ◽  
Paula Jofré ◽  
Oliver Shorttle ◽  
Laura K Rogers ◽  
Siyi Xu(许偲艺) ◽  
...  
Keyword(s):  
White Dwarf ◽  
Planetary System ◽  
Kuiper Belt ◽  
Wide Binary ◽  
Elemental Abundances ◽  
Exoplanetary Systems ◽  
Planetary Bodies ◽  
Refractory Composition ◽  
Observational Errors ◽  
Host Stars

ABSTRACT Planets and stars ultimately form out of the collapse of the same cloud of gas. Whilst planets, and planetary bodies, readily loose volatiles, a common hypothesis is that they retain the same refractory composition as their host star. This is true within the Solar system. The refractory composition of chondritic meteorites, Earth, and other rocky planetary bodies are consistent with solar, within the observational errors. This work aims to investigate whether this hypothesis holds for exoplanetary systems. If true, the internal structure of observed rocky exoplanets can be better constrained using their host star abundances. In this paper, we analyse the abundances of the K-dwarf, G200-40, and compare them to its polluted white dwarf companion, WD 1425+540. The white dwarf has accreted planetary material, most probably a Kuiper belt-like object, from an outer planetary system surviving the star’s evolution to the white dwarf phase. Given that binary pairs are chemically homogeneous, we use the binary companion, G200-40, as a proxy for the composition of the progenitor to WD 1425+540. We show that the elemental abundances of the companion star and the planetary material accreted by WD 1425+540 are consistent with the hypothesis that planet and host-stars have the same true abundances, taking into account the observational errors.

Observation of a Variable, ZZ Ceti White Dwarf: GD154

1993 ◽  
Vol 134 ◽  
pp. 201-204
Author(s):  
B. Pfeiffer ◽  
G. Vauclair ◽  
N. Dolez ◽  
M. Chevreton ◽  
J. R. Fremy ◽  
...  
Keyword(s):  
Time Scales ◽  
Effective Temperature ◽  
White Dwarf ◽  
White Dwarfs ◽  
Nonlinear Phenomena ◽  
Instability Strip ◽  
Temperature Range

The ZZ Ceti stars form a class of variable white dwarfs: the hydrogen dominated atmosphere ones, which do pulsate in an instability strip in the effective temperature range 13000K-11500K. We know 22 such ZZ Ceti white dwarfs. Their variations are caused by nonradial g-mode pulsations with periods are in the range 100-1000 seconds.A subsample of the ZZ Ceti stars shows amplitude variations on time scales of the order of one month. These variations could be driven by nonlinear phenomena.

scholarly journals The lifetimes of planetary debris discs around white dwarfs

2020 ◽  
Vol 496 (2) ◽  
pp. 2292-2308 ◽  
Author(s):  
Dimitri Veras ◽  
Kevin Heng
Keyword(s):  
Steady State ◽  
White Dwarf ◽  
White Dwarfs ◽  
Input Parameter ◽  
Evolutionary Constraints ◽  
Minor Planets ◽  
Evolutionary Models ◽  
Tidal Disruption ◽  
Different Types ◽  
Break Up

ABSTRACT The lifetime of a planetary disc that orbits a white dwarf represents a crucial input parameter into evolutionary models of that system. Here we apply a purely analytical formalism to estimate lifetimes of the debris phase of these discs, before they are ground down into dust or are subject to sublimation from the white dwarf. We compute maximum lifetimes for three different types of white dwarf discs, formed from (i) radiative YORP break-up of exo-asteroids along the giant branch phases at 2–100 au, (ii) radiation-less spin-up disruption of these minor planets at ${\sim} 1.5\!-\!4.5\, \mathrm{R}_{\odot }$, and (iii) tidal disruption of minor or major planets within about $1.3\, \mathrm{R}_{\odot }$. We display these maximum lifetimes as a function of disc mass and extent, constituent planetesimal properties, and representative orbital excitations of eccentricity and inclination. We find that YORP discs with masses of up to 1024 kg live long enough to provide a reservoir of surviving cm-sized pebbles and m- to km-sized boulders that can be perturbed intact to white dwarfs with cooling ages of up to 10 Gyr. Debris discs formed from the spin or tidal disruption of these minor planets or major planets can survive in a steady state for up to, respectively, 1 or 0.01 Myr, although most tidal discs would leave a steady state within about 1 yr. Our results illustrate that dust-less planetesimal transit detections are plausible, and would provide particularly robust evolutionary constraints. Our formalism can easily be adapted to individual systems and future discoveries.

Near-Infrared Photometry of Southern Galactic Wolf-Rayet Stars

1982 ◽  
Vol 99 ◽  
pp. 67-72
Author(s):  
C. Sterken ◽  
C. de Loore
Keyword(s):  
Infrared Radiation ◽  
Interstellar Dust ◽  
Near Infrared ◽  
Thermal Emission ◽  
Dust Emission ◽  
Circumstellar Dust ◽  
Infrared Photometry ◽  
Energy Distributions ◽  
Circumstellar Shell

Allen et al. (1972) observed 40 WR stars in the |1.6µ| and |2.2µ| bands, and found evidence of interstellar dust emission in the WC9 stars Ve 2–45, AS320 and HD 313643. Hackwell et al. (1974) reported 2.3 to 23 µ photometry of 19 WR stars and concluded that the excess infrared radiation from the Wolf-Rayet stars (except for the WC9 stars) could be explained by free-free emission from a hot circumstellar shell. Gehrz and Hackwell (1974) found from 2.3 to 23 µ photometry that three out of four WC stars appear to be embedded in thick circumstellar dust (graphite) shells, and concluded that WC9 stars may form a distinct Wolf-Rayet class. Cohen et al. (1975) derived energy distributions of 23 Wolf-Rayet stars from 3µ-11µ scanner spectrophotometry and infrared photometry, and concluded that WN stars show only free-free emission whereas only WC stars show dust. The excesses in WC9 stars are interpreted as thermal emission by graphite grains.

scholarly journals Link between Mass-loss and Variability Type for AGB Stars?

1999 ◽  
Vol 191 ◽  
pp. 395-400 ◽  
Author(s):  
Željko Ivezić ◽  
Gillian R. Knapp
Keyword(s):  
Mass Loss ◽  
Time Scales ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Dust Emission ◽  
Agb Stars ◽  
Similar Time ◽  
Color Distribution ◽  
K 12

We find that AGB stars separate in the 25–12 vs. 12-K color-color diagram according to their chemistry (O, S vs. C) and variability type (Miras vs. SRb/Lb). While discrimination according to the chemical composition is not surprising, the separation of Miras from SRb/Lb variables is unexpected.We show that “standard” steady-state radiatively driven models provide excellent fits to the color distribution of Miras of all chemical types. However, these models are incapable of explaining the dust emission from O-rich SRb/Lb stars. The models can be altered to fit the data by postulating different optical properties for silicate grains, or by assuming that the dust temperature at the inner envelope radius is significantly lower (300–400 K) than typical condensation temperatures (800–1000 K), a possibility which is also supported by the detailed characteristics of LRS data. While such lower temperatures are required only for O- and S-rich SRb/Lb stars, they are also consistent with the colors of C-rich SRb/Lb stars.The absence of hot dust for SRb/Lb stars can be interpreted as a recent (order of 100 yr) decrease in the mass-loss rate. The distribution of O-rich SRb/Lb stars in the 25–12 vs. K-12 color-color diagram shows that the mass-loss rate probably resumes again, on similar time scales. It cannot be ruled out that the mass-loss rate is changing periodically on such time scales, implying that the stars might oscillate between the Mira and SRb/Lb phases during their AGB evolution as proposed by Kerschbaum et al. (1996). Such a possibility appears to be supported by recent HST images of the Egg Nebula obtained by Sahai et al. (1997), the discovery of multiple CO winds reported by Knapp et al. (1998), and long-term visual light-curve changes detected for some stars by Mattei (1998).

scholarly journals Know thy star, know thy planet: chemo-kinematically characterizing TESS targets

2019 ◽  
Vol 491 (3) ◽  
pp. 4365-4381 ◽  
Author(s):  
Andreia Carrillo ◽  
Keith Hawkins ◽  
Brendan P Bowler ◽  
William Cochran ◽  
Andrew Vanderburg
Keyword(s):  
Distribution Functions ◽  
Target List ◽  
Thick Disc ◽  
Thin Disc ◽  
Candidate Target ◽  
Stellar Properties ◽  
The Individual ◽  
Host Stars ◽  
Gaia Dr2 ◽  
Kinematic Properties

ABSTRACT The Transiting Exoplanet Survey Satellite (TESS) has already begun to discover what will ultimately be thousands of exoplanets around nearby cool bright stars. These potential host stars must be well understood to accurately characterize exoplanets at the individual and population levels. We present a catalogue of the chemo-kinematic properties of 2218 434 stars in the TESS Candidate Target List using survey data from Gaia DR2, APOGEE, GALAH, RAVE, LAMOST, and photometrically derived stellar properties from SkyMapper. We compute kinematic thin disc, thick disc, and halo membership probabilities for these stars and find that though the majority of TESS targets are in the thin disc, 4 per cent of them reside in the thick disc and <1 per cent of them are in the halo. The TESS Objects of Interest in our sample also display similar contributions from the thin disc, thick disc, and halo with a majority of them being in the thin disc. We also explore metallicity and [α/Fe] distributions for each Galactic component and show that each cross-matched survey exhibits metallicity and [α/Fe] distribution functions that peak from higher to lower metallicity and lower to higher [α/Fe] from the thin disc to the halo. This catalogue will be useful to explore planet occurrence rates, among other things, with respect to kinematics, component membership, metallicity, or [α/Fe].

scholarly journals Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population

2019 ◽  
Vol 485 (4) ◽  
pp. 5573-5589 ◽  
Author(s):  
S Torres ◽  
C Cantero ◽  
A Rebassa-Mansergas ◽  
G Skorobogatov ◽  
F M Jiménez-Esteban ◽  
...  
Keyword(s):  
Random Forest ◽  
White Dwarf ◽  
Thick Disc ◽  
Thin Disc ◽  
Gaia Dr2
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