Kristen Menou

University of Toronto

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Adiv Paradise

University of Toronto

Sara Seager

Massachusetts Institute of Technology

Ryan Cloutier

McMaster University

Zoltán Haiman

Columbia University

Emily Rauscher

University of Michigan–Ann Arbor

Drake Deming

University of Maryland, College Park

René Doyon

Université du Québec à Montréal

F. Bouchy

University of Geneva

Bradley M. S. Hansen

University of California, Los Angeles

N. Astudillo-Defru

Universidad Católica de la Santísima Concepción

Cooperative Institutions

Princeton University

Centre National de la Recherche Scientifique

Fermi National Accelerator Laboratory

Center for Astrophysics Harvard & Smithsonian

University of Toronto

Max Planck Society

California Institute of Technology

University of Chicago

Massachusetts Institute of Technology

University of California, Berkeley

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Disc instability models for X-ray transients: evidence for evaporation and low -viscosity?

Monthly Notices of the Royal Astronomical Society (2000)

Kristen Menou J. M. Hameury J. P. Lasota Ramesh Narayan

We construct time-dependent models of accretion discs around black holes and neutron stars. We investigate the effect that evaporation of the inner disc regions during quiescence has upon the predictions of the disc instability model (DIM) for these systems. We do not include irradiation of the disc in the models.

Rayleigh–Taylor instability

10.1046/j.1365-8711.2000.03357.x

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Citations (55)

The Snowball Bifurcation on Tidally Locked Planets

AGU Fall Meeting Abstracts (2019)

J. Checlair Dorian S. Abbot Malte F. Jansen Kristen Menou Stephanie L. Olson

Snowball Earth

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WITNESSING THE BIRTH OF A QUASAR

The Astronomical Journal (2010)

Takamitsu Tanaka Zoltán Haiman Kristen Menou

The coalescence of a supermassive black hole binary (SMBHB) is thought to be accompanied by an electromagnetic (EM) afterglow, produced by the viscous infall of the surrounding circumbinary gas disk after the merger. It has been proposed that once the merger has been detected in gravitational waves (GWs) by LISA, follow-up EM searches for this afterglow can help identify the EM counterpart of the LISA source. Here we study whether the afterglows may be sufficiently bright and numerous to be detectable in EM surveys alone. The viscous afterglow, which lasts for years to decades for SMBHBs in LISA's sensitivity window, is characterized by rapid increases in both the bolometric luminosity and in the spectral hardness of the source. If quasar activity is triggered by the same major galaxy mergers that produce SMBHBs, then the afterglow could be interpreted as a signature of the birth of a quasar. Using an idealized model for the post-merger viscous spreading of the circumbinary disk and the resulting light curve, and using the observed luminosity function of quasars as a proxy for the SMBHB merger rate, we delineate the survey requirements for identifying such birthing quasars. If circumbinary disks have a high disk surface density and viscosity, an all-sky soft X-ray survey with a sensitivity of ~<3x10^-14 erg s^-1 cm^-2 and a time resolution of ~months could identify dozens of birthing quasars with sustained brightening rates of >10%/yr. If >1% of the X-ray emission is reprocessed into optical frequencies, birthing quasars could also be identified in optical transient surveys such as the LSST. Distinguishing a birthing quasar from other variable sources may be facilitated by the monotonic hardening of its spectrum, but will likely remain challenging. This reinforces the notion that joint EM-plus-GW observations offer the best prospects for identifying the EM signatures of SMBHB mergers.

10.1088/0004-6256/140/2/642

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Citations (19)

Predicting the Long-Term Stability of Compact Multi-Planet Systems

Zenodo (CERN European Organization for Nuclear Research) (2020)

Daniel Tamayo Miles Cranmer Sam Hadden Hanno Rein Peter Battaglia

REBOUND N-body simulation archives used to train and test the machine learning models in Tamayo et al. (2020), 'Predicting the Long-Term Stability of Compact Multi-Planet Systems'. See https://github.com/dtamayo/spock for scripts to process the data, train and test the SPOCK XGBoost model.

10.5281/zenodo.3723291

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Citations (1)

ExoPlaSim: Extending the Planet Simulator for exoplanets

Monthly Notices of the Royal Astronomical Society (2022)

Adiv Paradise Evelyn Macdonald Kristen Menou Christopher Lee Bo Lin Fan

The discovery of a large number of terrestrial exoplanets in the habitable zones of their stars, many of which are qualitatively different from Earth, has led to a growing need for fast and flexible 3D climate models, which could model such planets and explore multiple possible climate states and surface conditions. We respond to that need by creating ExoPlaSim, a modified version of the Planet Simulator (PlaSim) that is designed to be applicable to synchronously rotating terrestrial planets, planets orbiting stars with non-solar spectra, and planets with non-Earth-like surface pressures. In this paper we describe our modifications, present validation tests of ExoPlaSim's performance against other GCMs, and demonstrate its utility by performing two simple experiments involving hundreds of models. We find that ExoPlaSim agrees qualitatively with more-sophisticated GCMs such as ExoCAM, LMDG, and ROCKE-3D, falling within the ensemble distribution on multiple measures. The model is fast enough that it enables large parameter surveys with hundreds to thousands of models, potentially enabling the efficient use of a 3D climate model in retrievals of future exoplanet observations. We describe our efforts to make ExoPlaSim accessible to non-modellers, including observers, non-computational theorists, students, and educators through a new Python API and streamlined installation through pip, along with online documentation.

10.1093/mnras/stac172

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Citations (17)

Disc instability models, evaporation and radius variations

J. M. Hameury G. Dubus J. P. Lasota Kristen Menou

We show that the outcome of disc instability models is strongly influenced by boundary conditions such as the position of the inner and outer disc edges. We discuss other sources of uncertainties, such as the tidal torque, and we conclude that disc illumination, disk size variations and a proper prescription for the tidal torque must be included in models if one wishes to extract meaningful physical information on e.g. viscosity from the comparison of predicted and observed lightcurves.

Position (finance)

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Climate uncertainties caused by unknown land distribution on habitable M-Earths

Monthly Notices of the Royal Astronomical Society (2022)

Evelyn Macdonald Adiv Paradise Kristen Menou Christopher Lee

ABSTRACT A planet’s surface conditions can significantly impact its climate and habitability. In this study, we use the 3D general circulation model exoplasim to systematically vary dayside land cover on a synchronously rotating, temperate rocky planet under two extreme and opposite continent configurations, in which either all of the land or all of the ocean is centred at the substellar point. We identify water vapour and sea ice as competing drivers of climate, and we isolate land-dependent regimes under which one or the other dominates. We find that the amount and configuration of land can change the planet’s globally averaged surface temperature by up to ∼20 K, and its atmospheric water vapour content by several orders of magnitude. The most discrepant models have partial dayside land cover with opposite continent configurations. Since transit spectroscopy may permit observations of M-dwarf planets’ atmospheres, but their surfaces will be difficult to observe, these land-related climate differences likely represent a limiting uncertainty in a given planet’s climate, even if its atmospheric composition is known. Our results are robust to variations in atmospheric CO2 concentration, stellar temperature, and instellation.

Habitability

Planetary habitability

Tidal locking

Limiting

10.1093/mnras/stac1040

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Citations (11)

The Giant X-Ray Flare of NGC 5905: Tidal Disruption of a Star, a Brown Dwarf, or a Planet?

American Astronomical Society Meeting Abstracts (2002)

L. X. Li Ramesh Narayan Kristen Menou

We model the 1990 giant X-ray flare of the quiescent galaxy NGC 5905 as the tidal disruption of a star by a supermassive black hole. From the observed rapid decline of the luminosity, over a timescale of a few years, we argue that the flare was powered by the fallback of debris rather than subsequent accretion via a thin disk. The fallback model allows constraints to be set on the black hole mass and the mass of debris. The latter must be very much less than a solar mass to explain the very low luminosity of the flare. The observations can be explained either as the partial stripping of the outer layers of a low-mass main-sequence star or as the disruption of a brown dwarf or a giant planet. We find that the X-ray emission in the flare must have originated within a small patch rather than over the entire torus of circularized material surrounding the black hole. We suggest that the patch corresponds to the where the stream of returning debris impacts the torus. Interestingly, although the peak luminosity of the flare was highly sub-Eddington, the peak flux from the bright spot was close to the Eddington limit. We speculate on the implications of this result for observations of other flare events.

Flare

Black hole (networking)

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Predicting the long-term stability of compact multiplanet systems

Proceedings of the National Academy of Sciences (2020)

Daniel Tamayo Miles Cranmer Sam Hadden Hanno Rein Peter Battaglia

Significance Observations of planets beyond our solar system (exoplanets) yield uncertain orbital parameters. Particularly in compact multiplanet systems, a significant fraction of observationally inferred orbital configurations can lead to planetary collisions on timescales that are short compared with the age of the system. Rejection of these unphysical solutions can thus sharpen our view of exoplanetary orbital architectures. Long-term stability determination is currently performed through direct orbital integrations. However, this approach is computationally prohibitive for application to the full exoplanet sample. By speeding up this process by up to five orders of magnitude, we enable precise exoplanet characterization of compact multiplanet systems and our ability to examine the stability properties of the multiplanet exoplanet sample as a whole.

Orbital elements

Orbital mechanics

10.1073/pnas.2001258117

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Citations (71)

Activity From Tidal Disruptions in Galactic Nuclei

The Astrophysical Journal (2001)

Kristen Menou Eliot Quataert

The tidal disruption of a star by a supermassive black hole is expected to lead to a short bright flare followed by an extended period of low-level emission. Existing models of the late-time accretion of the stellar debris via a thin disk imply that the Galactic center source Sgr A* should be brighter than currently observed by several orders of magnitude. A similar problem exists for M31 and M32. This problem could be avoided if thin disk accretion transitions to low radiative efficiency accretion (e.g., advection-dominated or convection-dominated accretion flows) at low accretion rates (via "evaporation" of the thin disk). Alternatively, we show that the outer portions of a thin disk may become neutral and unable to sustain MHD turbulence on a timescale of less than the time between tidal disruption events; this may dramatically shorten the duration of the late accretion phase.

Thin disk

Flare

Accretion disc

Intermediate polar

10.1086/338195

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Citations (12)