Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/~debes/data/ESS_Debes2.pdf Дата изменения: Mon Sep 19 18:41:36 2011 Дата индексирования: Tue Oct 2 07:41:41 2012 Кодировка: Поисковые слова: jupiter

Directly Linking Planetary Systems to Dusty and Polluted White Dwarfs
1

Space Telescope Science Ins/tute, 2NASA/Goddard Space Flight Center, 3 Department of Terrestrial Magne/sm, Carnegie Ins/tu/on of Washington, 3 South West Research Ins/tute


John H. Debes

1,2,

C. S

3, tark

K. Walsh

4

It has long been suspected that metal polluted white dwarfs (types DAZ, DBZ, and DZ) and white dwarfs (WDs) with dusty disks possess planetary systems, but a specific physical mechanism for perturbing a planetesimal within the Kdal disrupKon radius of a WD and that material's subsequent accreKon has not yet been fully posited. In this poster we demonstrate that mass loss from a central star during post main sequence evoluKon can sweep planetesimals into mean moKon interior resonances with a single giant planet. These planetesimals are slowly removed through chaoKc excursions of eccentricity that in Kme create highly eccentric orbits capable of Kdally disrupKng the planetesimal. These resonances require giant planets not much more massive than Jupiter, or else relic planetesimals do not survive in sufficient numbers. Numerical simulaKons of the solar system show that a sufficient number of planetesimals are perturbed to explain observed WDs with both dust and metal polluKon. Finally, we show that once a planetesimal is perturbed into a Kdal crossing orbit, it will become disrupted, someKme within the first pass of the white dwarf, where a highly eccentric stream of debris forms the main reservoir for dust producing collisions. These simulaKons, in concert with observaKons of WDs, place interesKng limits on the frequency of planetary systems around main sequence stars, the frequency of planetesimal belts, and the probability that dust may obscure future terrestrial planet finding missions.

Abstract

Polluted"

Our Model"

Dusty WD Age vs. Polluted WD Age


qThe pr e se nc e of disk s and polluKon appears bi modal vs. cooling age qWhen compared to the total age of the system (tcool+tMS), = 1.8 Gyr, =2.9 Gyr

qConvert observed accreKon rates to asteroid belt mass A Solar System WD Laboratory qAlthough model dependent, qTake the Solar System's asteroid results suggest that asteroid belt belt--can it produce dusty/polluted masses for other stars have WDs? median of ~10 MSS. qYES! N body sim s s h o w 2 : 1 qThis work has implicaKons for resonance with Jupiter can perturb calculaKons of average zodi levels asteroids on disrupHng orbits for terrestrial planet missions.
Fig. 2: Eccentricity vs. Period raKo of Jupiter to asteroids near the 2:1 mean moKon resonance (MMR). Blue dots are Solar System asteroids selected to be >10 km in orbits > 3 AU. Red squares are asteroids that suffered Kdal disrupKon during our simulaKons. The solid black line is the libraKon width of the 2:1 MMR, while the dashed line is the same curve ader mass loss. Many asteroids are caught in the 2:1 MMR during post main sequence evoluKon, experience random walks in eccentricity when in the MMR, and are either ejected, collide with Jupiter, or are disrupted by the white dwarf.

Fig. 1: (Top) Histogram of Polluted WDs (solid line) and Dusty WDs (dash/dojed line) as a funcKon of cooling age. (Bojom) Same as the top, but as a funcKon of total age.



q Wi th as tero i d mas s es qTidal disrupKons peak at ~30 (assuming tdisk lifeKme=1 Myr), Myr ader central star > WD can predict dMmetal/dt for WDs qAverage disrupKon is of a ~60 qBased on our models, a Solar km asteroid, but incomplete System asteroid belt accounts <40 km for observed polluted WDs PredicHng the DistribuHon of Asteroid Belt Masses for Stars

Fig. 4: (Top) Normalized number of Kdal distrupKons as a funcKon of Kme for our simulaKons. IniKally, there are few disrupKons unKl about 30 Myr ader the central star loses mass. (Bojom) Normalized DistribuKon of disrupted asteroid radii. Our sample is incomplete below 40 km.

Fig. 5: By taking Fig. 4, averaging over asteroid mass, and assuming a disrupted disk lifeKme of 1 Myr, we can calculate ex[ected accreKon rates. Black diamonds are observed polluted WDs, red squares are dusty WDs, and asterisks are the results of our simulaKons. The dashed line represents an extrapolaKon of our simulaKons.

Fig. 6: Histogram of inferred asteroid belt mass for dusty and polluted WDs in units of the mass of the Solar System's asteroid belt. Most belts appear to fall within a factor of 100 of the Solar System, implying that extremely massive asteroid belts are rare.



Modeling DisrupHons



Interior Resonances with giant planets cause Dusty/Polluted WDs

qInterior mean moKon resonances perturb asteroids that survive stellar evoluKon q~1% of al l l arge aste roi ds are perturbed out to several hundred Myr
Fig. 3:Histogram of asteroids in one of our simulaKons before mass loss (solid black line) and ader mass loss of the central star (orange solid curve). Asteroids are primarily removed in regions near MMRs Fig. 7: CumulaKve distribuKons of debris fragments from rubble pile simulaKons of small asteroids being Kdally disrupted by a white dwarf. Each q value represents the pericenter of the asteroid's orbit in WD radii. For example, q80=80 RWD

qUsing rubble pile simulaKons, we have demonstrated that asteroids disrupt ader the first pass of the WD qSize distribuKon of debris retains a largely eccentric orbit ader disrupKon