33 research outputs found
Sublimation of ices during the early evolution of Kuiper belt objects
Kuiper belt objects, such as Arrokoth, the probable progenitors of
short-period comets, formed and evolved at large heliocentric distances, where
the ambient temperatures appear to be sufficiently low for preserving volatile
ices. By detailed numerical simulations, we follow the long-term evolution of
small bodies, composed of amorphous water ice, dust, and ices of other volatile
species that are commonly observed in comets. The heat sources are solar
radiation and the decay of short-lived radionuclides. The bodies are highly
porous and gases released in the interior flow through the porous medium. The
most volatile ices, CO and CH , are found to be depleted down to the center
over a time scale on the order of 100 Myr. Sublimation fronts advance from the
surface inward, and when the temperature in the inner part rises sufficiently,
bulk sublimation throughout the interior reduces gradually the volatile ices
content until they are completely lost. All the other ices survive, which is
compatible with data collected by New Horizons on Arrokoth, showing the
presence of methanol, and possibly, HO, CO, NH and CH, but
no hypervolatiles. The effect of short-lived radionuclides is to increase the
sublimation equilibrium temperatures and reduce volatile depletion times. We
consider the effect of the bulk density, abundance ratios and heliocentric
distance. At 100~au, CO is depleted, but CH survives to present time,
except for a thin outer layer. Since CO is abundantly detected in comets, we
conclude that the source of highly volatile species in active comets must be
gas trapped in amorphous ice.Comment: 8 pages, 7 figure
Non-Equipartition of Energy, Masses of Nova Ejecta, and Type Ia Supernovae
The total masses ejected during classical nova eruptions are needed to answer
two questions with broad astrophysical implications: Can accreting white dwarfs
be pushed towards the Chandrasekhar mass limit to yield type Ia supernovae? Are
Ultra-luminous red variables a new kind of astrophysical phenomenon, or merely
extreme classical novae? We review the methods used to determine nova ejecta
masses. Except for the unique case of BT Mon (nova 1939), all nova ejecta mass
determinations depend on untested assumptions and multi-parameter modeling. The
remarkably simple assumption of equipartition between kinetic and radiated
energy (E_kin and E_rad, respectively) in nova ejecta has been invoked as a way
around this conundrum for the ultra-luminous red variable in M31. The deduced
mass is far larger than that produced by any classical nova model. Our nova
eruption simulations show that radiation and kinetic energy in nova ejecta are
very far from being in energy equipartition, with variations of four orders of
magnitude in the ratio E_kin/E_rad being commonplace. The assumption of
equipartition must not be used to deduce nova ejecta masses; any such
"determinations" can be overestimates by a factor of up to 10,000. We
data-mined our extensive series of nova simulations to search for correlations
that could yield nova ejecta masses. Remarkably, the mass ejected during a nova
eruption is dependent only on (and is directly proportional to) E_rad. If we
measure the distance to an erupting nova and its bolometric light curve then
E_rad and hence the mass ejected can be directly measured.Comment: 9 pages, 4 figures, awaiting publication in ApJ
A fully 3-dimensional thermal model of a comet nucleus
A 3-D numerical model of comet nuclei is presented. An implicit numerical
scheme was developed for the thermal evolution of a spherical nucleus composed
of a mixture of ice and dust. The model was tested against analytical
solutions, simplified numerical solutions, and 1-D thermal evolution codes. The
3-D code was applied to comet 67P/Churyumov-Gerasimenko; surface temperature
maps and the internal thermal structure was obtained as function of depth,
longitude and hour angle. The effect of the spin axis tilt on the surface
temperature distribution was studied in detail. It was found that for small
tilt angles, relatively low temperatures may prevail on near-pole areas,
despite lateral heat conduction. A high-resolution run for a comet model of
67P/Churyumov-Gerasimenko with low tilt angle, allowing for crystallization of
amorphous ice, showed that the amorphous/crystalline ice boundary varies
significantly with depth as a function of cometary latitude.Comment: 19 pages, 10 figure
The Red Nova-like Variable in M31 - A Blue Candidate in Quiescence
M31-RV was an extraordinarily luminous (~10^6 Lsun) eruptive variable,
displaying very cool temperatures (roughly 1000 Kelvins) as it faded. The
photometric behavior of M31-RV (and several other very red novae, i.e. luminous
eruptive red variables) has led to several models of this apparently new class
of astrophysical object. One of the most detailed models is that of
"mergebursts": hypothetical mergers of close binary stars. These are predicted
to rival or exceed the brightest classical novae in luminosity, but to be much
cooler and redder than classical novae, and to become slowly hotter and bluer
as they age. This prediction suggests two stringent and definitive tests of the
mergeburst hypothesis. First, there should always be a cool red remnant, and
NOT a hot blue remnant at the site of such an outburst. Second, the inflated
envelope of a mergeburst event should be slowly contracting, hence it must
display a slowly rising effective temperature. We have located a luminous,
UV-bright object within 0.4 arcsec (1.5 sigma of the astrometric position) of
M31-RV in archival WFPC2 images taken 10 years after the outburst: it resembles
an old nova. Twenty years after the outburst, the object remains much too hot
to be a mergeburst. Its behavior remains consistent with that of theoretical
nova models which erupt on a low mass white dwarf. Future Hubble UV and visible
images could determine if the M31-RV analogs (in M85 and in M99) are also
behaving like old novae.Comment: Accepted for publication in ApJ, comments welcom