The Origins Seminar series aim to bring together ISM, star and planet formation people, exoplanets experts, planetary scientists and astrobiologists including topics from molecular clouds through star and planet formation to exoplanets detection and characterization and astrobiology. A number of slots are reserved per semester for the presentation of original research by the EOS/NExSS exoplanet collaboration. The seminar series is organized by Elena Manjavacas, Serena Kim and Gijs Mulders. For more information, contact the organizers.
All talks are from noon – 1:00pm. The room location varies.
UPCOMING ORIGINS SEMINARS
December 4, 2017; LPL 309
Erin May, graduate student, University of Michigan
Understanding the smallest gas exoplanets – theoretical and observational studies of their atmospheric properties
In our solar system, there exists a significant size gap between the largest terrestrial planet, Earth, and the smallest Jovian planet, Neptune. Meanwhile, these intermediate size planets make up around half of the confirmed exoplanets to date. Without a direct comparison in our solar system, and with most of these planets lacking either a mass or radius measurement, we must turn to a variety of observational and theoretical methods to better understand these planets as a whole. In this talk, I will present work from our optical transmission spectra survey with the Magellan Baade telescope, which is seeing its first results for Neptune-like planets. In addition, I will discuss our work to modify a general circulation model in order to study the atmospheres of exoplanets across the entire transition from terrestrial to gaseous with a unified, consistent approach. Through both of these projects, we hope to contribute to a complete picture of the possible diversity among small gaseous exoplanets.
January 22, 2018; SO N305
Mihkel Kama, Marie Curie Fellow at Cambridge University
January 29, 2018; SO LPL 309
Lynne Hillenbrand, professor at Caltech.
February 5, 2018; SO N305
February 12, 2018; LPL 309
Cheng Li, postdoc at Caltech/JPL
February 19, 2018; SO N305
February 26, 2018; LPL 309
March 5, 2018; SO N305
March 12, 2018; LPL 309
March 19, 2018; SO N305
Cassandra Hall, Postgraduate Student at The University of Edinburgh
March 26, 2018; LPL 309
April 2, 2018; SO N305
April 9, 2018; LPL 309
April 16, 2018; SO N305
April 23, 2018; LPL 309
April 30, 2018; SO N305
May 7, 2018; LPL 309
May 14, 2018; SO N305
PAST ORIGINS SEMINARS
November 27, 2017; SO N305
Emilie Dunham, grad student, ASU
Deciphering clues in meteorites to learn about the violent environment of Solar System formation
Calcium-aluminum rich inclusions (CAI) found in meteorites were the first-formed solids in the Solar System. They contain specific radionuclides (short-lived and stable) which indicate that our Solar System had close encounters with particular exotic nucleosynthetic sources such as supernovae and AGB stars. In this presentation, I will discuss the meteoritic evidence for these sources as well as other processes such as irradiation, using recent analytical data. A few motivating questions include: did a supernova trigger the collapse our parent molecular cloud? Can all the radionuclides observed in a CAIs be explained by a single astrophysical process? Is our Solar System exceptional, or was its formation typical of star-forming regions in our galaxy?
November 20, 2017; LPL 309
Prajkta Mane, postdoc, LPL
“Calcium-Aluminum-rich Inclusions: A window to the early Solar System”
In this presentation, I will talk about investigations involving isotopic and microtextural analyses of Calcium-Aluminum-rich Inclusions (CAIs), hosted in primitive meteorites. CAIs are the first-formed solids in the Solar System and record some of the earliest processes that occurred in the solar nebula. These earliest-formed solids are surrounded by concentric multi-mineralic rim sequences, known as the Wark-Lovering (WL) rims. As such, the WL rims record a universal event that marks the end of the growth period of CAIs. I will talk about the recent results from isotopic dating and microstructural investigations of these inclusions and their rim sequences.
November 13, 2017; SO N305
Jing Luan, postdoc, Berkeley
“Enceladus: three-stage limit cycle and current state”
Enceladus is one of the most popular worlds that might accommodate life outside our own earth. We study its evolutionary path, especially focus on the physical processes that drive Enceladus to its current state. I will also discuss possible applications of these physical processes to other bodies in our solar system. Below is a brief summary of the evolution path for Enceladus.
Eccentricity (e) growth as Enceladus migrates deeper into mean motion resonance with Dione results in increased tidal heating. As the bottom of the ice shell melts, the rate of tidal heating jumps and runaway melting ensues. At the end of run-away melting, the shell’s thickness has fallen below the value at which the frequency of free libration equals the orbital mean motion and e has damped to well below its current value. Subsequently, both the shell thickness and e partake in a limit cycle. As e damps toward its minimum value, the shell’s thickness asymptotically approaches its resonant value from below. After minimum e, the shell thickens quickly and e grows even faster. This cycle is likely to have been repeated multiple times in the past.
Currently, e is much smaller than its equilibrium value corresponding to the shell thickness. Physical libration resonance resolves this mystery, it ensures that the low-e and medium-thickness state is present for most of the time between consecutive limit cycles. It is a robust scenario that avoids fine tuning or extreme parameter choice, and naturally produces episodic stages of high heating, consistent with softening of topographical features on Enceladus.
November 6, 2017; LPL 309
Ji Wang, postdoc, Caltech
“New Frontier of Exoplanetary Science: High Dispersion Coronagraphy”
Thousands of exoplanets have been discovered, but only a handful of them are amendable for atmospheric spectroscopic study. Spectroscopy leads to understanding of physical and chemical processes taking place in an exoplanet. Spectroscopy of exoplanets can also detect biomarkers in potential habitable planets around other stars. The high dispersion coronagraphy (HDC) provides a pathway to search for biomarkers in planets around M dwarfs with next-generation ground-based extremely large telescopes (ELTs, e.g., TMT and GMT). The HDC combines high resolution spectroscopy (HRS) with a coronagraph operating behind an extreme adaptive optics (AO) system. The coronagraph spatially filters out starlight while the HRS spectrally discriminates starlight from planet light, reaching a starlight suppression level that enables biomarker detection. I will discuss a roadmap to achieve this ambitious goal. The roadmap consists of rigorous science cases at different stages of hardware developments, from existing facilities to future instruments on ELTs, and to future space missions such as HabEx/LUVOIR.
October 30, 2017; SO N305
Everett Schlawin, postdoc at Steward Observatory
“Dust Particle Constraints in Brown Dwarf Atmospheres with Ground-Based Spectrophotometry”
L dwarfs exhibit low-level, rotationally-modulated photometric variability generally associated with heterogeneous, cloud-covered atmospheres. The spectral character of these variations yields insight into the particle sizes and vertical structure of the clouds. I will present the results of a ground-based near-infrared spectral monitoring study of brown dwarfs. Our technique, originally employed in exoplanet transmission spectroscopy, is to use a simultaneous nearby reference star to correct for time-variable systematics, enabling <0.15% per-band sensitivity in relative brightness changes across the 0.9–2.4um bandwidth. We find that one of the brown dwarfs in this program, 2MASS J18212815+1414010, varies by up to +/-1.5% at 0.9 um, with the variability amplitude declining toward longer wavelengths. This result extends the variability trend observed in prior HST/WFC3 spectral monitoring of 2MASS J1821+1414 (Yang et al. 2015). We show that the full 0.9-2.4 um variability amplitude spectrum can be reproduced by Mie extinction from dust particles with a log-normal particle size distribution with a median radius of 0.24 um. I will discuss 2MASS 1821 in comparison to a similar L-dwarf and how these cloud measurements can be examined through a broader survey.
October 23, 2017; LPL 309
Gijs Mulders, postdoc, LPL
“Constraining protoplanetary disk evolution with ALMA and X-Shooter”
Angular momentum transport is one of the fundamental drivers of protoplanetary disk evolution. It determines how mass is distributed in the disk over time, drives accretion onto the star, and contributes to the dispersal of the disk. While significant progress has been made in understanding and simulating different mechanisms of angular momentum transport, such as (magneto)hydrodynamic instabilities and disk winds, there are few observational constraints on these mechanisms.
In this talk, I will show how observations of disk mass and mass accretion rate can be used to constrain evolutionary models of protoplanetary disks. We leverage the power of large homogenous datasets from ALMA and VLT/X-shooter to test often used alpha-disk models. We find that some substantial modifications to the standard picture of disk evolution are needed to explain the data for the combined datasets for the Lupus and Chamaeleon I star forming regions.
October 16, 2017; SO N305
October 9, 2017; LPL 309
Pierre Haenecour, postdoc, LPL
“Circumstellar and interstellar grains in Antarctic Micrometeorites”
Antarctic micrometeorites are small extraterrestrial particles, with sizes ranging from about 50 µm to 1 mm, collected typically from melting Antarctic snow or blue ice. They are of particular interest, as previous studies suggested that they may have contributed a significant amount of water and organics to the early Earth. However, their origin(s) and possible relationships to other extraterrestrial materials (primitive meteorites and interplanetary dust particles) are still debated, and both asteroidal (related to carbonaceous chondrites) and cometary origins have been proposed. Similarly to primitive meteorite and cometary material, isotopic anomalies in several elements (e.g., H, C, N, O, Si) have been reported in micrometeorites that are associated with circumstellar (presolar) grains and organic matter. Presolar grains (also called stardust) are tiny condensates that formed in the circumstellar envelopes of stars or in the ejecta of stellar explosions (e.g., core-collapse supernovae or novae) before the formation of our Solar System, and, thus, constitute the only remnants of the original building blocks of the Solar System. I will discuss presolar grains and organic matter in fine-grained Antarctic micrometeorites, and what they tell us about their origin(s).
October 2, 2017; SO N305
Kyle Kaplan, postdoc, Steward Observatory
“Probing the Conditions at Ionized/Molecular Gas Interfaces With High Resolution Near-Infrared Spectroscopy”
“Photo-dissociation” or “Photon-dominated” Regions (PDRs) exist in the ISM at the interfaces between photo-ionized and molecular gas, where UV radiation sets the ionization state, chemistry, and excitation at the edge of the molecular zone. In these regions, excited rotational-vibrational (“rovibrational”) states of the ground electronic state of H2 are fluorescently populated when the absorption of far-UV photons conveys the molecules into excited electronic states from which they rapidly decay. Downward transitions from the excited rovibrational states produce a rich spectrum of near-infrared emission lines. Since these quadrupole lines are generally optically thin, their fluxes scale with the populations of the upper levels of the respective transitions, providing excellent probes of the excitation and physical conditions in the emitting regions. We present and compare high resolution (R~45,000) near-infrared (1.45-2.45 μm) spectra, obtained on the 2.7 m Harlan J. Smith Telescope at McDonald Observatory with the Immersion Grating INfrared Spectrometer (IGRINS) (Park et al. 2014, SPIE, 9147, 1), for a variety of Galactic PDRs including regions of high mass star formation, reflection nebulae, and planetary nebulae. Typically a large number of transitions, up to about 100 individual lines, are seen in each source. We fit grids of Cloudy models (Ferland et al. 2013, RMxAA, 49, 137) to the observed H2 emission to constrain physical parameters such as the temperature, density, and UV field of each PDR and explore the similarities and differences between the various environments where PDRs arise.
This work used the Immersion Grating INfrared Spectrometer (IGRINS), developed under a collaboration between the University of Texas at Austin and the Korea Astronomy and Space Science Institute (KASI) with the financial support of the US National Science Foundation (NSF grant AST-1229522) to the University of Texas at Austin, and the Korean GMT Project of KASI. We also acknowledge support from the NSF grant AST-0708245 and JPL RSA 1427884.
September 25, 2017; LPL 309
Diego Munoz, postdoc, Steward Observatory
“The Inferred Obliquity of Kepler Systems”
The stellar obliquity or spin-orbit angle of exoplanet hosts provides important clues on the formation and evolution of planetary systems. Data on these obliquities are difficult to obtain. Here, we present a compiled list of 553 Kepler planetary-system host targets for which we derive line-of-sight stellar inclination angles I_*, and use these values to study the distribution of stellar obliquities. With a dataset that is 8 times larger than in similar studies, we explore the dependence of the obliquity distribution on stellar and planetary properties. We report on four main findings. (1) We find that the fraction of systems with low obliquities is larger than previously reported, suggesting that the distribution of obliquities is likely to come from a mixture of well-aligned (95%) and very-misaligned (5%) populations. (2) Hot Jupiters are more oblique than the general sample, confirming trends obtained with Rossiter-Maclaughlin measurements. (3) The obliquity dependence on planet multiplicity is weaker than previously reported, finding much higher correlations with planetary radius and stellar rotational period. (4) In hot Jupiters, we detect hints of a dependence of obliquity on stellar effective temperature with small statistical significance, which is in consistency with previous studies.
September 18, 2017; Steward N305
Marta Bryan, grad student, Caltech
“Lurking in the Shadows: Long Period Gas Giant Planets as Tracers of Planet Formation”
Over the past decade surveys using a variety of techniques have uncovered a diverse array of exoplanet systems. Many of these new systems are difficult to explain within the framework of standard planet formation theories, and have forced theorists and observers alike to re-evaluate their narratives for planet formation and migration. For example, direct imaging surveys have discovered a growing population of extremely young, planetary-mass companions at separations of > 100 AU, which pose significant challenges to in-situ formation models. The rotation rates of these young giant planets provide a unique window into the late stages of accretion, and can provide clues to past formation histories as well as present-day properties such as planetary atmospheric composition or the presence of moons and rings. In this talk I will discuss my work using radial velocity, direct imaging, and high-resolution spectroscopy techniques to study long period gas giant planets as tracers of formation and migration histories of planetary systems.
September 11, 2017; LPL 309
Taran Esplin, postdoc (Strittmatter Fellow), Steward Observatory
“Searching for the Bottom of the Initial Mass Function”
Because brown dwarfs are the product of the process of star formation, detecting the minimum mass at which they form is a fundamental test of star formation theories. We have performed a search for planetary-mass brown dwarfs in the Chamaeleon I and Taurus star-forming regions using proper motions measured with IRAC and other wide-field surveys and using optical and near-infrared photometry. Through near-infrared spectroscopy, we have confirmed 6 and 18 candidates as new late-type members of Chamaeleon I and Taurus, respectively. These objects include the faintest known members in both regions, which should have masses of 3–6 M_Jup according to evolutionary models.TBA
August 28, 2017; Steward N305
Yancy Shirley, Associate Professor, Steward Observatory
“Complex Organic Molecules Observed Towards Prestellar Cores”
In the last 5 years, complex organic molecules (COMs) have been detected in the gas phase toward prestellar cores. These observations have challenged the theory that COMs predominately form from energetic
processing of ice mantles and are released into the gas phase once the
protostar begins to form. Alternative theories have developed that adjust
gas phase formation rates and also rely of formation of precursor radicals in
the ice which then chemically desorb to assist formation of COMs in the
gas phase. I shall review the current state of observations and theory
and present new observations of COMs detected toward a very young
prestellar core that constrain the formation timescale of COMs. These
observations show that prebiotic molecules are present in the gas phase
within 10^5 years of dense core formation and up to a million
year prior to protostar formation.
Monday, June 12; 2017; Steward N305
“Characterizing Debris Disks and the Late Stages of Planet Formation” by Jacob White, grad student, University of British Columbia
The planet formation process shapes the morphology and grain size distribution of circumstellar disks, encoding the formation history of a given system. Remnants of planet formation, such as comets and asteroids, collisionally evolve and can replenish the dust and small solids that would otherwise be cleared on short timescales. These grains are observed through reprocessed starlight at submm to cm wavelengths.
The spectrum of the mm/cm emission reveals details of the grain population. However, one confounding parameter in studying these grains around stars is the stars themselves. The emission from stars in the mm/cm is nontrivial and generally not well-constrained. I’ll present examples of debris systems (HD 141569 and Fomalhaut) studied by ALMA and the VLA, in which unconstrained stellar emission is biasing the flux of the disk and thus inhibiting an accurate characterization of the disk. When comparing the behavior of these disk’s host stars to the Sun, it appears as though these A/B stars exhibit similar atmospheric processes, which are commonly assumed not to occur in massive stars.
Sirius A is a bright, nearby star with no known debris. Ongoing radio observations (SMA, JCMT, VLA) of Sirius A are being used to set an observationally determined standard for stellar atmosphere modeling and debris disk studies around A stars, as well as to take the first step toward characterizing potential intrinsic uncertainty in stellar emission at these wavelengths. This talk will highlight the effort to characterize stellar atmospheres through a project known as MESAS (Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths) which is imperative to the success of current and future debris disk studies.
Monday, May 22; 2017; Steward N305
“The Evolution of the Dust Disk-Stellar Mass Scaling Relation” by Ilaria Pascucci, Associate Professor, Lunar and Planetary Laboratory
The disk mass is among the most important input parameter of planet formation models as it determines the number and masses of the planets that can form. I will present gas and dust disk masses from our ALMA millimeter survey of the nearby Chamaeleon I star-forming region. I will discuss the evidence for a steep dust disk-stellar mass scaling relation at ~2 Myr and for its temporal evolution. I will show that theoretical models of grain growth, drift, and fragmentation can reproduce the observed evolution if drift is faster around lower mass stars. I will conclude by linking these results to the planetary systems that can form around lower mass stars.
Wednesday (!), May 17; 2017; Steward N305
“Linear polarimetry as a tool to characterize ultra-cool atmospheres” by Paulo Miles Paez, postdoc, Western University
The low temperatures present in the neutral atmospheres of very low mass stars and brown dwarfs (“ultra-cool dwarfs”, Teff < 2700 K) favor the appearance of condensates: solid and liquid particles that likely draw together to form “dusty clouds”. Most of the observational work to characterize these ultra-cool atmospheres has, so far, been performed mainly on the basis of the intensity of their light. However, the state of polarization of the electromagnetic radiation is an important and frequently overlooked aspect. In particular, linear polarimetry is a powerful technique to probe the presence of photospheric dust grains, and to derive some physical properties such as the grain size and the distribution of the “cloudy” structures.
In this talk, and as part of our goal to provide tools for the characterization of ultra-cool atmospheres, I will present an on-going effort to obtain the linear polarimetry indices at optical and near infrared wavelengths for a sample of field ultra-cool dwarfs at different ages. In addition, I will also present the first results of my postdoctoral stay at the University of Western Ontario: a search for H-alpha emission in ultra-cool dwarfs to seek a correlation between magnetic activity and photometric variability.
Monday, May 15; 2017; Lunar and Planetary Laboratory 309
EOS talk: “ACCESSing exoplanet atmospheres and constraining stellar photospheres” by Ben Rackham, grad student, Steward Observatory
Transmission spectroscopy offers the exciting possibility of studying terrestrial exoplanet atmospheres in the near-term future. The TESS mission, scheduled for launch next year, is expected to discover thousands of transiting exoplanets around bright host stars, including an estimated twenty habitable zone super-Earths. Atmospheric follow-up for the majority of these exciting exoplanets will come from ground-based observations, due to time pressure on space-based facilities. At the same time, unprecedented precisions from both ground- and space-based instruments will enable searches for atmospheric signatures from smaller and cooler exoplanets. However, these observations will be increasingly subject to noise introduced by heterogeneities in the host star photospheres such as star spots and faculae. In this talk, I will discuss ACCESS, the largest ground-based transmission spectroscopy survey to date, and how we are laying the groundwork for atmospheric follow-up of TESS targets. I will also summarize our work on understanding the effects of heterogeneous stellar photospheres on current and future transit observations. The combination of these foundational steps will allow us to successfully identify and correctly interpret exoplanet transmission spectra from exciting TESS targets.
Monday, May 8; 2017; Steward N305
“Feeling hot, hot, hot! magma ocean evolution on rocky exoplanets” by Laura Schaefer, postdoc, School of Earth and Space Exploration, ASU
All rocky planets in the Solar System likely went through a magma ocean stage during their formation and accretion. Many of the rocky exoplanets that have been discovered to date are interior to their star’s habitable zones, and so probably experienced more extended magma ocean stages. Some may even still have magma oceans today, whether because they are so close to their stars that silicate vaporizes at the equilibrium temperatures or through massive greenhouse warming of their surfaces. I will discuss the range of magma ocean planets that may be in our current exoplanet sample and some of the implications for atmospheric composition and long-term evolution of these planets. Atmospheric erosion of these planets may leave them significantly different in bulk composition than the planets of our Solar System.
Friday(!), May 5, 2017; Steward N505
FLASH-Origins talk: “From gas-giants to rocky exo-Earths: atmospheric characterization of transiting exoplanets” by Nikolay Nikolov, postdoc, University of Exeter
Over the past decade, transit observations reveal a prevalence of condensate clouds and hazes, a huge diversity and a continuum from clear to cloudy atmospheres. Currently no obvious pattern with planet properties has emerged to show why some planets have clear atmospheres, revealing broad absorption features, and some are dominated by clouds and hazes. Large spectroscopic surveys, combined together with previous results could allow us to establish correlations and help elucidate the main processes shaping the formation and evolution of exoplanet atmospheres. I will discuss how new ongoing observational efforts allow us to address some of those challenges. With HST-Spitzer transit and eclipse observations we constrain the compositions and atmospheric thermal structure of twenty of the brightest exoplanets. With the unprecedented access of VLT FORS2 to the abundance of fainter systems that HST cannot observe we measure the optical transmission spectra of twenty exoplanets from gas giants down to Earth-mass, cooler worlds. Combining both and previous surveys we ultimately aim to increase the number of characterized exoplanet atmospheres by a factor of five, enabling a statistical investigation into the relationship between clouds/hazes and fundamental properties such as mass, radius, temperature, and metallicity.
Monday, May 1; 2017; Lunar and Planetary Laboratory 309
“Imaging Giant Planet Formation in Multi-Star Systems: From Conception to Ejection“ by Kevin Wagner, grad student, Steward Observatory
Two decades of exoplanet science have revealed that planets are as numerous as stars in the galaxy. Many stars have multiple planets, and some planets even orbit multiple stars. The observed planet population carries an important message of how planets form and what types of planetary systems exist for future scientific exploration. In particular, multi-star systems provide a dynamical laboratory that can be used to test and refine various planet formation models. I will present an overview of our current direct imaging search for planets in the nearby binary-rich Scorpius-Centaurus association, as well as our discovery of one of the first directly imaged planets, Scorpion-1b, in a hierarchical triple system. Unlike the majority of exoplanets discovered through indirect means, the planets that we find through imaging may be followed up with spectroscopy of their gaseous atmospheric content and astrometric monitoring of their orbital properties–both of which provide important clues to how and where they formed in their natal circumstellar/circumbinary disks. I will provide an update on our current understanding of the formation and evolution of Scorpion-1b, including the latest results from our MagAO follow-up campaign.
Monday, April 24; 2017; Steward N305
“A Pursuit of Accuracy — RECTE: A Physical Model-Based Correction for HST/WFC3 Light Curve Systematics” by Yifan Zhou, grad student, Steward Observatory
Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) near-infrared channel is currently one of the most important instruments in spectroscopic characterizations of transiting exoplanets because of its excellent performance in time-resolved observations. However, the accuracy of all WFC3 IR light curves is significantly affected by the infamous “ramp effect” systematics. The widely adopted empirical methods of ramp effect corrections require additional HST orbits to “pre-condition” the detector, which cost more than 100 HST orbits in total for such observations. To improve the ramp effect correction, we developed RECTE, a powerful new, solid state physics-motivated detector model that accurately corrects for the ramp effect and reaches essentially photon-noise limited performance for even the most affected orbits. Importantly, RECTE corrections will help increase WFC3’s efficiency for infrared transit spectroscopy by about 20-25% (no more need to discard first orbits). RECTE starts to be adopted as part of WFC3 transmission spectroscopic data reduction pipeline and is expected to enhance the reliability, efficiency, and reproducibility of WFC3 IR time-resolved observations.
Monday, April 17; 2017; Lunar and Planetary Laboratory 309
“Stop Planet Migration, Prevent Runaway Accretion, and Drive Disk Transport, All with One Tweak” by Jeffrey Fung, Sagan fellow, UC Berkeley
Super-Earths represent the largest population of known planets mostly found at sub-AU distances from their host stars. The theory of their
formation requires answers to two main questions: 1) how to stop fast planet migration, and 2) how to prevent runaway accretion. We can go a long way toward solving both problems if the disk gas surrounding planets has no intrinsic diffusivity (“viscosity”). In inviscid disks, a planet readily repels gas away from its orbit, and zero viscosity gas accumulates inside a planet’s orbit to slow migration by orders of magnitude. After planet migration stops, it gradually carves open a gap in the disk, and lowers its gas accretion rate to prevent runaway
accretion. Using numerical simulations that run up to 100,000 orbits, we directly show that the migration of super-Earths, even systems of super-Earths, can be stalled, and they can open gaps that have surface densities 30 times lower than the background disk density. At the same time, the spiral shocks launched by the planets provide a mechanism for
angular momentum transport, allowing the zero viscosity disk to accrete. The disk transport rates range up to 1e-7 solar mass per year and scales with planet mass to the power of 3/2. We find that planets are porous barriers to the accretion flow, and a chain of planets can drive accretion over a large radial range. Super-Earths may therefore be
capable of driving large-scale gas depletion such as those characterizing transition disks.
Monday, April 10; 2017; Steward N305
“On the coevolution of life and planet habitability” by Regis Ferriere, Associate Professor, Ecology and Evolutionary Biology, UofA and Ecole Normale Superieure & Antonin Affholder, grad student, School of Biology, Ecole Normale Supérieure, Paris
Planet Earth today hosts many intricate interactions among life forms and the planet’s geochemistry across multiple scales, from microscopic to global. But what role did these interactions play in the very emergence of life, in its Darwinian evolution and complexification? What have been the consequences for the early and subsequent habitability of our planet? Chopra and Lineweaver (2016 Astrobiology) claimed that “rocky planets need to be inhabited to remain habitable”. They argue that the maintenance of planetary habitability is a property “more associated with an unusually rapid evolution of biological regulation of surface volatiles than with the physical conditions that define the habitable zone”. Thus, the emergence of life’s abilities to modify its environment and regulate initially abiotic feedback mechanisms between the planet’s geochemistry and its habitability could be the most significant factor responsible for life’s persistence. Research in our lab aims at recasting these verbal ideas in a quantitative ecological and evolutionary framework. We will present our first steps in the construction of an ecosystem model designed to be coupled with geo-climate models of early Earth and Mars. The model will be used to answer two main questions: How does the ecosystem emergence and Darwinian evolution alter the planet’s geo-climate? How does this planetay environmental change feed back on the ecosystem’s further evolution and function?
Monday, March 27; 2017; Steward N305
“A global and ALMA view of quiescent protoclusters in the Milky Way” by Brian Svoboda, grad student, Steward Observatory
Progress in understanding high-mass star formation has been hindered by the large distances, deeply-embedded environments, and historical lack of blind surveys to identify the earliest phases (“starless clumps”). To this end, we identify a subsample of 2223 (47.5% total) starless clump candidates (SCCs) from the λ=1.1mm Bolocam Galactic Plane Survey. In a global view we analyze the physical properties, boundedness, and timescales of SCCs compared to protostellar clumps with statistically robust samples. At high-resolution with ALMA, targeted observations of the 12 most massive SCCs within 5 kpc show significant fragmentation, chemical diversity, and hitherto unobserved low-luminosity protostellar activity. Analysis of the fragmentation mass and length scale distributions are used to place this unique sample in the context of HMSF theories and simulations.
Monday, March 20; 2017; Lunar and Planetary Laboratory 309
“Robust spectral indices for exoplanets observed with JWST” by Taisiya Kopytova, postdoc, ASU
The James Webb Space Telescope will enable us to obtain exoplanet transit spectra with unprecedented precision over the wide spectral range (0.6 – 28.3 microns). We aim to determine spectral indices that are most sensitive to certain exoplanet parameters, such as effective temperature, surface gravity, and chemical abundances. The spectral indices will serve the community with a faster way of characterizing exoplanets, as oppose to comparison of observations to the entire grid of theoretical models.
To determine spectral indices, we use a machine algorithm that allows to train a model representing flux at each wavelength as a function of exoplanet parameters. The approach uses the PETIT atmospheric model grid to calculate spectral indices.
I will also discuss how precisely exoplanet parameters can be predicted using the spectral indices and how our approach can be combined with recent studies for optimization of JWST observations using the information theory.
Monday, March 13; 2016; Steward N305
“Pre-Main-Sequence ages – Environmental Impact on Disc Lifetime“ by Jon Rees, postdoc, Steward Observatory
Understanding circumstellar discs and their evolution is important for both young stars and planet formation. It has been argued that these discs will last longer in low stellar density environments because stellar encounters and UV radiation all erode disks. Discs are the nurseries for planets and thus longer disc lifetimes in low-density regions will allow for longer periods of planet formation. There have also been suggestions that stellar mass may be determined by the length of the accretion phase, and thus dependent on the longevity of the disc.
I will present our work on deriving robust ages from fitting the pre-main-sequence for young clusters, including the Taurus-Auriga and Chamaeleon regions. We show that both Taurus-Auriga and Chamaeleon show an excess in disc fraction compared to the decline in disc fraction in denser clusters of similar age, suggesting that discs survive longer in their low-density, low-mass environments.
Monday, March 6; 2017; Steward 550
EOS talk: “The Initial Masses of Protoplanetary Disks” by Josh Eisner, Associate Professor, Steward Observatory
The masses of protoplanetary disks provide a key constraint to any theory of planet formation. Measuring the distribution of disk masses requires observations with high sensitivity and angular resolution, which are now becoming available with ALMA. I will describe some early ALMA observations that constrain the disk mass distribution in the ~1 Myr old Orion Nebula cluster. I will also discuss a larger program that is now underway, and the challenges to obtaining accurate disk mass measurements.
Monday, February 27, 2017; Steward N305
“Space telescope Exo-P coronagraph contrast limited by polarization” by Jim Breckinridge, Adjunct Professor of Optical Sciences UofA, Visiting associate California Institute of Technology
Direct imaging spectroscopy to characterize the surface and atmosphere features of exoplanets is a high priority. Our ability to directly image exoplanets is determined by image quality and therefore depends on the design and implementation of the telescope, instrument, detector and calibration methodologies. In space, there is no atmosphere and one might assume that for a telescope perfectly corrected for geometric aberrations, scattered light is limited only by diffraction. This is wrong!
Classic telescope/instrument systems are designed and optimized using geometric aberration to minimize optical path length (trigonometry) errors. Exo-P coronagraphs, with contrast requirements exceeding 10+7 are not classic optical systems. Neither geometric aberration analysis (ray-trace) nor scalar-wave analysis (scalar diffraction) describe the image quality needed by space coronagraphers.
In this Origins Seminar, we examine the role of vector-waves in image formation and show that contrast depends on the phase and amplitude properties (polarization aberrations) of individual surfaces, and masks within the optics train. Exoplanet coronagraphs that are not compensated for polarization aberrations appear to be limited to contrasts between 10+6 and 10+7. We also discovered a source of astrometric errors that might limit gravitational microlensing accuracy and fundamental astrometry.
Under certain conditions, polarization aberrations become important for ground-based telescopes, particularly for the GMT, TMT and the E-ELT.
Monday, February 20, 2017; Steward Observatory 550
EOS talk: “A revision of Star formation history in Taurus” by Min Fang, postdoc, Steward Observatory
The Taurus star forming region is one of nearest active low-mass star-forming region in solar neighbourhood, and provides a unique laboratory to study various hot topics related to star and planet formation. Star formation in Taurus is believed to start at about 1-2 Myr ago. Recently, we have discovered a new old pre-main sequence moving group at the east of Taurus. This moving group show kinematics and distance similar to Taurus, and thus could be part of Taurus. This find complicates the star formation history in Taurus. In this talk, I will present some results from this study.
Monday, February 13; 2017; Steward N305
“Comparative Exoplanetology from observations to cloud models” by Hannah Wakeford, NPP fellow Goddard Space Flight Center
To understand our own solar system formation and composition in a galactic context, comparative climatology is needed with more detailed understanding of planets on an individual and grouped basis. The Hubble Space Telescope (HST) has played a pivotal role in the characterization of exoplanet atmospheres. From the first planets available for such observations we have learned that their atmospheres are incredibly diverse. I present the most recent observation with HST and discuss the impact that clouds can have on observational results and the implications on planetary characterization.
Monday, February 6, 2017; Lunar and Planetary Laboratory 309
“Design of NEID and HPF, two large Echelle spectrographs to search for habitable planets“ by Chris Schwab, Senior Lecturer Department of Physics and Astronomy, Macquarie University
Extreme precision radial velocities is a key technique in the quest to discover earth like planets. Our team was recently awarded a NASA contract to build a new visible range Doppler spectrograph for the WIYN telescope. This facility, called NEID, will provide better than 25 cm/s Doppler precision, leading the efforts of the US exoplanet community to obtain RV signatures of habitable worlds around solar type stars. In this talk, I will present the instrument architecture, and focus on optical and optomechanical design choices that allow for this Doppler precision to become attainable. I will also present the optical design of the Habitable Zone Planet Finder spectrograph HPF for the Hobby Eberly Telescope, which operates in the near-IR. HPF and NEID share the vacuum tank and environmental control design, an and while similar in size and resolution, use a different optical design to achieve the desired image quality.
Monday, January 23, 2017; Lunar and Planetary Laboratory 309
“HPF and NEID: A new generation of US precision radial velocity machines for exoplanet discovery” by Chad Bender, Associate Astronomer, Steward Observatory
The field of exoplanet characterization via ground-based radial
velocity measurements is entering a golden era as new purpose-built
spectrometers come online over the coming few years. These
instruments will provide unprecedented RV precision and push into new
wavelength regimes. I will provide a general update on the
development status of two of these spectrometers where I am serving as
Instrument Scientist, the near-IR HPF and the visible light NEID, and
will discuss the science programs that they enable.
HPF is an NSF supported instrument that will provide R~50,000 spectra
covering ~0.8 – 1.3 microns, with RV precision of ~1 m/s. It will be
deployed to the 10-m Hobby-Eberly Telescope later this year to
carryout a survey for Earth-mass planets orbiting in the HZ of
M-dwarfs. NEID is a NASA supported instrument that will provide
R~100,000 spectra covering 0.38 – 0.92 microns, with RV precision of
~30 cm/s. It will be deployed to the 3.5-m WIYN telescope in 2019,
where it will provide support for TESS and carryout a GTO search
program to discover Earth-twins.
Monday, December 12, 2016; Steward Observatory N305
EOS talk:“Orion: a test bed for studying evolution of protoplanetary disks” by Min Fang, postdoc, Steward Observatory
The Orion complex is the most active star-forming region in solar neighborhood, and provides a unique laboratory to study disk evolution because (1) there are a large sample of young stars in wide ranges of stellar masses and ages, and (2) the star formation environments vary from the massive clusters, the medium-size clusters, to the distributed population, which provide us a great opportunity to study disk evolution in different environments at a similar distance. An investigation of protoplanetary disk evolution in Orion, especially in its clusters: NGC 1980, NGC 1977, and Orion Nebula cluster, is part of the large NASA exoplanet program: Earths in Other Solar Systems. In this talk, I will present some results from this project.
Monday, December 5, 2016; Lunar and Planetary Laboratory 309
“Confronting models of gas and dust evolution in protoplanetary disks with observations” by Paola Pinilla, postdoc/ Hubble Fellow, Steward Observatory
Powerful telescopes such as ALMA and VLT/SPHERE, with their unprecedented sensitivity and spatial resolution, are revealing fascinating structures in protoplanetary disks at different wavelengths. In this seminar, I will summarize the current theoretical efforts to explain these observations. My current models combine hydrodynamical simulations of gas evolution and dust growth, which include the coagulation and fragmentation of particles. I will present how new detailed observations are providing significant insights about how different physical conditions rule the evolution of protoplanetary disks, such as snow lines, potential embedded planets, and spatial changes of disk viscosity. This bridge between models and observations is extending our knowledge of how planets form, and it allows us to have a better understanding of the large diversity of extrasolar systems.
Monday, November 21, 2016; Lunar and Planetary Laboratory 309
“Studying the habitable zone architecture of exoplanetary systems through observations of exozodiacal dust” by Steve Ertel, postdoc,Steward Observatory/LBTI
Exozodiacal dust is the extrasolar analog of our own zodiacal dust, i.e., dust inside and around the habitable zone of other planetary systems. Thus, it is an important tracer of the architecture of the inner regions of such systems. Moreover, the dust poses a significant challenge for future space missions attempting to directly image and characterize habitable exoplanets. The dust can be the most luminous component of a system after the host star, but emits predominantly in the near- to mid-infrared where it is outshone by the host star. Thus – and due to the small angular separation from even nearby host stars – it is mostly detected using infrared interferometry which can spatially disentangle the dust emission from the stellar one.
Since the first detection in 2006, we have come a long way of investigating the nature and origin of this dust, including two large surveys and about 35 detections. The detected dust is more massive and often hotter than our own zodiacal dust which is a significant challenge to explain its presence. I will summarize the state of the art of exozodiacal dust research from observations to modeling and theoretical investigation. I will present recent results and also give an update of the HOSTS survey at the LBTI, currently the most advanced survey searching for habitabe zone dust around nearby main sequence stars.
Monday, November 14, 2016; Steward Observatory N305
“Exoplanet in the Era of JWST” by Jonathan Fraine, postdoc, Steward Observatory
I plan to discuss the four science instruments (NIRISS, NIRSPec, NIRCam, MIRI); I will detail each instruments time series observation modes, the limitations and functionality thereof. I’ll then discuss the most optimal science that each instrument expects to achieve for exoplanet atmospheres and brown dwarfs; both directly imaged and transiting exoplanets.
Monday, November 7, 2016; Lunar and Planetary Laboratory 309
“First 3D radiation non-ideal magnetohydrodynamical simulations” by Mario Flock, postdoc,Interstellar and Heliospheric Physics group, JPL
Many planets orbit within an AU of their stars, raising questions about their origins. Particularly puzzling are the planets found near the silicate sublimation front. We investigate conditions near the front in the protostellar disk around a young intermediate-mass star, using the first global 3-D radiation non-ideal MHD simulations in this context.
The results show magnetorotational turbulence around the sublimation front at 0.5 AU. Beyond 0.8 AU is the dead zone, cooler than 1000 K and with turbulence orders of magnitude weaker. A local pressure maximum just inside the dead zone concentrates solid particles, allowing for efficient growth. Over many orbits, a vortex develops at the dead zone’s inner edge, increasing the disk’s thickness locally by around 10%.
We synthetically observe the results using Monte Carlo transfer calculations, finding the sublimation front is bright in the near-infrared. The models with vertical magnetic flux develop extended, magnetically-supported atmospheres that reprocess extra starlight, raising the near-infrared flux 20%. The vortex throws a non-axisymmetric shadow on the outer disk.
Radiation-MHD models of the kind we demonstrate open a new window for investigating protoplanetary disks’ central regions. They are ideally suited for exploring young planets’ formation environment, interactions with the disk, and orbital migration, in order to understand the origins of the close-in exoplanets.
Monday, October 31, 2016; Steward Observatory N305
“Partitioning of water between surface and mantle: what makes a waterworld?” by Tad Komacek, grad student, LPL
Terrestrial exoplanets in the canonical habitable zone may have a variety of initial water fractions due to random volatile delivery by planetesimals. If the total planetary water complement is high, the entire surface may be covered in water, forming a “waterworld.” On a planet with active tectonics, competing mechanisms act to regulate the abundance of water on the surface by determining the partitioning of water between interior and surface. We have explored how the incorporation of different mechanisms for the degassing and regassing of water changes the volatile evolution of a planet. For all of the models considered, volatile cycling reaches an approximate steady-state after ~2 Gyr. Using these steady-states, we find that if volatile cycling is either solely dependent on temperature or seafloor pressure, exoplanets require a high abundance (more than 0.3% of the total mass) of water to have fully inundated surfaces. However, if degassing is more dependent on seafloor pressure and regassing mainly dependent on mantle temperature, the degassing rate is relatively large at late times and a steady-state between degassing and regassing is reached with a substantial surface water fraction. If this hybrid model is physical, super-Earths with a total water fraction similar to that of the Earth can become waterworlds. As a result, further understanding of the processes that drive volatile cycling on terrestrial planets is needed to determine the water fraction at which they are likely to become waterworlds.
Monday, October 24, 2016; Lunar and Planetary Laboratory 309
“OSIRIS-REx: NASA’s Mission to Sample an Ancient Asteroid” by Alessondra Springmann, grad student, LPL
NASA’s OSIRIS-REx asteroid sample return mission launched on September 8 to visit asteroid Bennu, a carbon-rich, near-Earth asteroid. The spacecraft will rendezvous with the asteroid in 2018 and ultimately bring samples of Bennu back to Earth in 2023. Returning up to 2 kg of extraterrestrial material, samples from asteroid Bennu may hold clues to the origin of the solar system and the organic molecules that could have seeded life on Earth. After an exciting launch of OSIRIS-REx last month to its asteroid target, I will talk about what scientists have learned about asteroid Bennu already from terrestrial telescopes, scientific results we expect from the mission upon arrival at the asteroid, and the importance of bringing samples of an asteroid to Earth for further study.
Monday, October 17, 2016; Steward Observatory N305
“Probing External Feedback on Young Stars: Proplyds in NGC 1977 and YSOs in W3-AFGL333” by Jinyoung Serena Kim, Associate Astronomer, Steward Observatory
The star formation environment is likely to affect the evolution of circumstellar disks around young stars. UV radiation driven winds from massive stars can shorten the lifetime of protoplanetary disks in their immediate surroundings. I will present seven new proplyds around a B1 star we identified in NGC 1977 (30’north of the Orion Nebula Cluster), a direct sign of feedback from a massive star. I will also mention our findings of a very low mass proplyds in Orion Nebula Cluster. I will then discuss studies of the young stellar objects in AFGL333 in W3, located in a high density layer between an expanding H II region and a giant molecular cloud.
The proplyds in the vicinity of the B1 star (c Ori) in NGC 1977 are the first proplyds found near a B star. Previously known proplyds are all found in immediate vicinity of O stars, e.g., theta^1 Ori C. I will show the proplyds identified in archival HST and Spitzer images. The sizes of the proplyds are consistent with our calculation for FUV radiation from a B1 star, about 10-30 times less than that around the O star in the Orion Nebula Cluster.
In the second half of the talk I will present our recent studies of the young stellar population in W3-AFGL333, located in a high density layer between the expanding W4 HII region and the W3 giant molecular cloud. We find that the young stellar population in AFGL333 lacks massive stars, compared to other known clusters in main W3 complex including IC 1795 and W3-Main. Star formation activity in AFGL333 is comparable to that of nearby low-mass star forming regions despite being near OB stars.
Monday, October 10, 2016; Lunar and Planetary Laboratory 309
“Technology Needs to Discover Earth 2.0“ by Nick Siegler, Technology Development Manager for the NASA Exoplanet program, JPL
The first evidence of life on an exoplanet is likely to be based on various lines of evidence, most importantly being “bio-hints” in the atmospheres of these distant worlds. While spectroscopy of extremely faint sources is not trivial the primary technology challenge, the “tall tent pole”, is starlight suppression – blocking the bright light from the target star so as to capture the faint reflected light of the exoplanet. Today I will present the status of technology development directed towards internal occulters (aka coronagraphs) and external occulters (aka starshades), along with a look forward.
Monday, October 3, 2016; Steward Observatory N305
“Polarization of Young Brown Dwarfs” by Elena Manjavacas, postdoc, Steward Observatory
Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases with the degree of oblateness, which is inversely proportional to the surface gravity. We therefore expect a higher degree of linear polarization for young brown dwarfs. We aimed to measure optical linear polarization for a sample of six young brown dwarfs, with spectral types between M6 and L2, and cataloged previously as objects with low gravity using spectroscopy. We collected linear polarimetric data in the I and R-band using CAFOS at the 2.2 m telescope in Calar Alto Observatory. We employed the flux ratio method to determine the linear polarization degrees for our targets. With a confidence of 3-sigma, our data indicate that all targets in our sample have a linear polarimetry degree in average below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were observed. We only detected positive linear polarization for object 2M0422 with a degree of p* = 0:81 0:17% in the R-band.
Monday, September 26, 2016; Lunar and Planetary Laboratory 309
“Juno at Jupiter: initial science orbit” by Bill Hubbard, professor, LPL
The solar-powered geophysical orbiter Juno was successfully injected into a low-periapse Jupiter orbit on 4 July. The first bound orbit completed one month ago, with the first perijove (PJ1) on 27 August. Virtually all science instruments acquired data during an hour or two while the spacecraft approached to within ~5000 km of the cloudtops. The radio-science/gravity experiment of primary interest to interior studies was deliberately not operating at highest precision during this initial pass. There will now be a hiatus until after PJ2 (19 October) due to a further main-engine burn to reduce Juno’s orbital period to 14 days for the main part of the mission. I expect to see the first high-precision gravity results after PJ3 on 2 November, although initial results are quite good and eliminate some models already. My talk will touch on some of the theoretical work on Jupiter’s interior that we are testing with Juno, and I’ll describe the most relevant experiments. During 2017 we’ll harvest new data every two weeks, steadily driving down the noise floor and filling in a gravity and compositional mosaic.
Tuesday, September 6, 2016; Steward Observatory N305
“Demystifying brown dwarf protoplanetary disk chemistry through thermochemical modelling” by Aaron Greenwood, grad student, Kapteyn Astronomical Institute, University of Groningen
The physical properties of brown dwarf disks, in terms of their shapes and sizes, are still largely unexplored by observations. Only with ALMA can we observe these disks in detail. To what extent brown dwarf disks and T Tauri disks are similar is currently unknown, and this work is a motivation towards establishing a relationship through observations.
We use the code ProDiMo to produce 2D thermochemical models of the protoplanetary disks around brown dwarfs, with the aim of accurately modelling the disk chemistry. We use previous observations of the brown dwarf disk ISO-Oph 102 to inform a fiducial model around which we build a small grid of brown dwarf disk models, in order to explore the structure of CO isotopologue, HCN, and HCO+ lines. Although these two lines have not yet been observed in a brown dwarf disk in the sub-mm, they are useful tracers of warm surface-layer gas and disk ionization.
We present the idea that the physical and chemical processes in brown dwarf disks are similar to those that occur in T Tauri disks, because our models suggest that these smaller disks are driven by the same chemical processes. Being able to characterize the chemical and dust properties of brown dwarf disks will have wide-reaching implications towards the eventual goal of assessing the prospects for planet formation in these disks.
Wednesday, August 17, 2016; Steward Observatory N550
“First Results From the Near-InfraRed Disk Survey (NIRDS)” by Carey M. Lisse, Principal Staff Scientist SRE, SES, Johns Hopkins
Understanding the origin & evolution of our own Solar System is a major NASA strategic goal, and recent planetary science missions (e.g., Dawn, MESSENGER, New Horizons, Rosetta) have produced a wealth of new insights. However, much of the local evolutionary evidence has been erased over the last 4.5 Gyr. Circumstellar exo-disks are not just the signposts of exosystems with planets, but the signposts of systems that are rapidly evolving. Finding analogs in nearby systems for solar system events – like the collisionally active Kuiper Belt + Late Heavy Bombardment in η Corvi; the dense zodiacal cloud formed by asteroid belt collisions in HD69830; or the silica rich torus found around HD172555 , a relic of a planetary scale massive hypervelocity impact like the ones that created the Earth’s Moon, stripped Mercury of its surface crust, & knocked Uranus on its side – allows us to learn more about the physics causing these processes to occur, what they create, and how systems evolve.
In 2010 we began a near-infrared (NIR) spectral survey of bright debris disks with reported IRAS excesses and optically resolved disks. Our novel R~1000, 1% precision Near IR Disk Survey (NIRDS) was performed using the SpeX instrument at the NASA/IRTF from 0.8-5.0 um at a precision and resolution never before undertaken. For disks, the NIR is a poorly studied spectral regime, as the star is typically assumed to dominate the system’s emergent flux. Even for “famous” & well-studied systems there is a dearth of good NIR spectra in the literature, and primary star classifications are often in error. But with 1% precision and 10% accuracy, we have been able to detect excess emission above the photosphere due to circumstellar dust and gas down to as low as 1.5 µm, while finding many important new results for supposedly well-studied and picked-over systems. There is also a strong need amongst observer teams performing state of the art coronographic & interferometric H/K-band imaging (e.g., CHARA, FLUOR, GPi, LBT, SPHERE), to understand the spectral behavior of the system over the entire 0.8 – 5.3 µm wavelength grasp.
To date we have observed 45 NIRDS systems. In this talk we report the first aggregate findings of our survey of 40+ disk systems to help answer the following questions: (1) Are gas- and hot dust-rich rich YSOs and transition disks common amongst the known circumstellar disk population? (2) How many of the known circumstellar disk systems have incorrectly typed primary stars that could affect our understanding of star-disk-planet interactions and disk/planet hosting frequencies? (3) Do dense warm dust systems preferentially occur for disk systems in the 10 – 300 Myr terrestrial planet formation era? (4) Does the “typical” circumstellar disk states of primary star + Kuiper Belt Star show evidence for material from each of the different kinds of small outer solar system bodies (Comets, Centaurs, KBOs) like the active comet debris in HR4796A and the icy KBO debris in Fomalhaut and HD 32297? Are large radius, narrowly confined rings the signposts of outer planet formation? (5) What causes the diffuse > 1000 K hot dust in older systems? Magnetic trapping of charged sungrazing body debris or evaporation of zody cloud dust infalling due to P-R Production of close-in dust from close-in evaporating planets? (6) Is there more evidence for mature solar system processes, like (η Corvi’s Late Geavy Bombardment and HD 69830’s asteroid family formation, in the disk record?
Monday, April 25, 2016; Steward Observatory N305
“Raising the questions of exo-ecosystem emergence, function, and feedbacks on exoplanet environment” by Regis Ferriere, Associate Professor, Ecology and Evolutionary Biology, UofA and Ecole Normale Superieure
Monday, April 18, 2016; Lunar and Planetary Laboratory 309
EOS talk: “Tracing solids and vapor during dust growth in planet-forming regions” by Sebastiaan Krijt, postdoc, Department of the Geophysical Sciences, University of Chicago
The distribution of volatiles (e.g., water, CO) in planet-forming environments is intimately tied to the dynamical and collisional evolution of the solid dust population. I will present new numerical models that treat dust coagulation/fragmentation, dust dynamics, simple gas-grain chemistry, and vapor diffusion simultaneously, and explore the connection between the water vapor in the disk atmosphere and the size-distribution and ice-to-rock ratios of the dust grains growing in the midplane.
Monday, April 11, 2016; Steward Observatory N305
“The Late-time Formation of Close-in Exoplanets” by Eve Lee, grad student, UC Berkeley
Close-in exoplanets come in various sizes and masses. I will discuss the origin of three types of such planets: super-Earths, the most common; and the rarer super-puffs and hot Jupiters. The riddle posed by super-Earths (1–4 Earth radii, 2–20 Earth masses) is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. I will show that this puzzle is solved if super-Earths formed late, in the inner cavities of transitional disks. Super-puffs present the inverse problem of being too voluminous for their small masses (4–10 Earth radii, 2–6 Earth masses). I will show that super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside ~1 AU then migrate in just after super-Earths appear. Finally, I will review theoretical and observational reasons why I believe hot Jupiters migrated to their current locations. Through N-body calculations, I will show that if hot Jupiters migrated by Lidov-Kozai oscillations driven by external planetary perturbers, close-in super-Earth companions would have been perturbed onto their host stars. This naturally explains why most hot Jupiters have no close-in transiting neighbour.
Monday, April 4, 2016; Steward Observatory 550
“Maximizing Transiting Exoplanet Science with JWST” by Everett Schlawin, postdoc, Steward Observatory
JWST offers unprecedented sensitivity, stability and wavelength coverage for transiting exoplanet science, enabling studies of planet composition, metallicity and cloud coverage. The wavelengths added beyond Hubble Space Telescope’s WFC3 grism (1.7um) enable compositional constraints of key atmospheric gases like CH4, CO2, CO and NH3 in addition to the H2O abundances already measured. There are many different instruments and modes available to observe planets during primary transit, secondary eclipse and phase curves, so I will discuss the strategies for observing with JWST and the relative benefits of different configurations. I will discuss the forecasted results and planetary parameters that can be retrieved with different instruments, considering cloudy versus clear compositions. The NIRCam instrument will be a vital tool for the 1-5 um wavelength range and I will discuss its existing and not-yet-approved operational modes. I will also present recent laboratory tests of the flight NIRCam instrument to prepare and calibrate it for the extremely high precision measurements needed for transiting planet science.
Monday, March 28, 2016; Steward Observatory N305
“Orbital Stability of High Mass Planets & Implications for Debris Disk Systems” by Sarah Morrison, grad student, LPL
I will discuss the relationships between planet separation, mass, and stability timescale for high mass multi-planet systems containing planet masses and multiplicities relevant for planetary systems detectable via direct imaging. I apply these results to compare to giant planet occurrence and detection rates derived from direct imaging within young debris disk systems of the ScoCen association. These efforts begin to probe the ease of giant planet formation at wider separations than typically sampled by other exoplanet detection methods and perhaps on scales more similar to our Solar System.
Monday, March 7, 2016; Lunar and Planetary Laboratory 309
EOS talk: “Delivery of water and organics to early Earth: insights from quantum chemistry” by Krishna Muralidharan, Assistant Professor, Materials Science and Engineering, UofA
Using first-principles methods, we show that molecular water and a wide-variety of organics found in the solar nebula could have been directly incorporated on to planetary grains, implying a possible endogenous source of life on Earth.
Monday, February 29, 2016 ; Steward Observatory N305
“The Formation and Evolution of Protoclusters in the Milky Way” by Brian Svoboda, grad student, Steward Observatory
High-mass stars strongly influence the evolution of galaxies and the ISM, yet their formation remains and open problem in contemporary astrophysics. A major bottleneck in the study of high-mass star formation is the difficulty in identifying and systematically analyzing the properties of massive starless clumps, the incipient phase of protocluster evolution. To this end, we classify a sample of 4683 molecular cloud clumps identified from the Bolocam Galactic Plane Survey by combining observational diagnostics of star formation activity from a variety of Galactic plane surveys. We identify a sub-sample of 2222 (47.4%) starless clump candidates, representing the largest and most robust sample of pre-protocluster candidates to date. We find that starless clumps are colder, less turbulent, smaller, less massive, and less centrally concentrated than protostellar clumps. I will also discuss clump growth and lifetimes, as well as recent W-band GBT and K-band VLA observations for a sub-sample of the most massive and nearby starless clump candidates.
Monday, February 22, 2016; Lunar and Planetary Laboratory 309
“Imaging Protoplanets: Observing Transition Disks With Non-Redundant Masking” by Steph Sallum, grad student, Steward Observatory
Transition disks, protoplanetary disks with inner clearings, provide an opportunity to study planet formation in action. I will present new spatially resolved observations of the T Cha and LkCa 15 transition disks, both of which host posited substellar companions. Multi-epoch VLT and MagAO observations of T Cha are incompatible with the presence of a companion. Conversely, new LBT and MagAO datasets confirm the previous detection in LkCa 15. These new observations along with re-analyzed archival Keck data suggest the presence of multiple forming planets in the LkCa 15 disc gap. I will describe how scattered light from the outer disk can match the T Cha datasets, why such a model is unsuitable for LkCa 15, and the characteristics of the LkCa 15 protoplanetary system.
Monday, February 15, 2016; Steward Observatory N305
“Composition and distribution of clouds in hot Jupiters : an L/T-like transition ?” by Vivien Parmentier, postdoc, LPL
Over a large range of equilibrium temperatures clouds seem to dominate the transmission spectrum of hot Jupiters atmospheres but no trend allowing the classification of these objects have yet emerged. Recently observations of the light reflected by these planets provided insight on the cloud distribution on the dayside of these planets : for a handful of planets clouds seem more abundant on the western than on the eastern side of the dayside hemisphere and, more importantly, this asymmetry depends on the equilibrium temperature of the planet.
Using state-of-the-art three dimensional models of hot Jupiters atmospheres I will show that longitudinal and latitudinal assymetry in the cloud coverage is expected for these hot planets. Such an asymetry can strongly bias the retieved abundances from transmission and secondary eclipse spectra. The longitudinal cloud asymetry being a strong function of the condensation temperature of the cloud species, it is a telltale of the cloud composition. An L/T transition is expected for hot Jupiters and possibly seen in the data : silicate clouds should disappear from the cooler planets and be replaced by to sulfide clouds.
Monday, February 8, 2016; Lunar and Planetary Laboratory 309
“Imaging planetary systems with the LBTI” by Denis Defrere, postdoc, Steward Observatory/LBTI
The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for high-sensitivity, high-contrast, and high-resolution infrared (1.5-13 microns) imaging of nearby planetary systems. To carry out a wide range of high-spatial resolution observations, it features various single-pupil imaging modes (e.g., AO imaging, coronagraphy, integral field spectroscopy, non redundant aperture masking) and can combine the two AO-corrected 8.4-m apertures for Fizeau or nulling interferometry. It also has broadband, narrowband and spectrally dispersed capabilities. In this talk, I present its two key surveys and review its latest scientific highlights. I also describe recent instrumental milestones such as first-light images with the integral field spectrograph and record-setting interferometric nulling observations.
Monday, November 23, 2015; Steward Observatory N305
EOS talk: “Quantifying the Transition from Non-Living to Living Matter” by Sara Imari Walker, Assistant Professor, School of Earth and Space Exploration, Arizona State University
An important goal in astrobiology is to identify what features of biological organization may be universal to life and potentially distinguish living systems from other classes of physical system. The concept of “information”, for example, is increasingly cited as an important property of biological systems, but it is unclear in what sense information can uniquely characterize life. To address this problem, I present two models, which demonstrate how concepts from information theory can be used to uniquely identify the living state. The first model presents a phase transition from “non-life” to “life”, characterized as non-replicating and replicating respectively, which displays several features suggestive of interesting physics underlying the origin of life. The second set of models compare the informational properties of biological networks to two classes of null models, using the fission yeast (Schizosaccharomyces Pombe) and the budding yeast (Saccharomyces cerevisiae) cell cycle regulatory networks as a case study. Our results show that informational structure can distinguish biological networks from random, even in cases when topology alone is insufficient. I discuss implications for our understanding any distinctive physics operative in life that might apply to life here on Earth and potentially elsewhere.
Monday, November 23, 2015; Lunar and Planetary Laboratory 309
EOS talk: “Extreme-AO Imaging of Disks around Intermediate-Mass Stars: Discovery of a Two-Armed Spiral Disk and a Warped Edge-on Debris Disk” by Kevin Wagner, grad student, Steward Observatory
In their first years of operation, extreme adaptive optics and coronagraphic imaging facilities (e.g. SPHERE, GPI, LBT/AO, MagAO, SCExAO) are pushing forward the boundaries of discovery in protoplanetary disks. These recent observations are revealing structures previously unresolved/undetected and discovering disks that have never before been imaged. This talk will focus on our new discoveries with VLT/SPHERE of a beautiful two-armed spiral disk with a large gap (the third known of its kind) and an edge-on warped debris disk – similar to the warp induced by the planet in Beta Pic. Following the details of the discoveries, these disks will be placed in the context of the few other presently identified examples of similar disks, which provide important constrains on models of planet-disk interactions and protoplanetary disk evolution.
Monday, November 23, 2015; Lunar and Planetary Laboratory 309
EOS talk: “Planets Around Low-mass Stars: Population Statistics and Formation History” by Gijs Mulders, postdoc, LPL
Exoplanet studies around stars of very different masses can pin down specific physical processes shaping the final architecture of planetary systems. Our recent work based on data from the Kepler Space Telescope shows that the population of planets at short orbital periods is stellar-mass dependent. Lower mass stars contain fewer giants, but more planets overall. The heavy-element mass of planetary systems anti-correlates with stellar mass, in stark contrast with observed protoplanetary disk masses which show a positive correlation. The increased efficiency at which low-mass stars form planetary systems close to their host stars shows that inward migration of planetary building blocks plays a crucial role in the planet formation process.