Estimating the Magnetic Field Strength of the Hot Jupiter HD 189733b
Tuesdaqy, May 5, 2015
12:40 pm – CAS 413 (please note change)
Magnetic fields play a vital role in the evolution of planets by protecting their atmospheres from stellar winds and cosmic rays. Our current knowledge of planetary magnetic fields is almost entirely limited to those we have observed in our own solar system. Recent observations of material orbiting ahead of hot Jupiter (HJ) exoplanets may provide insight into the field strengths of these planets, providing the first opportunity to measure magnetic fields of planets outside of the solar system. I will present our recent work with high resolution optical spectra of the HJ HD 189733b. We detect a strong pre-transit absorption signal that is well described by a bow shock orbiting ahead of the planet. If the bow shock is mediated by a magnetosphere, the planetary magnetic field strength can be estimated by assuming pressure balance between the interplanetary medium and the planetary magnetosphere. The estimated field strength has implications for models of mass loss from HJs and star-planet interactions. Observations such as those presented here provide the best current method for expanding our knowledge of exoplanetary magnetic fields which is a crucial step in the complete characterization of exoplanets and their evolutionary histories.
Structure and Dynamics of Mercury’s Magnetosphere Inferred from MESSENGER Observations and
Highlights from the MESSENGER mission
￼￼Johns Hopkins University Applied Physics Laboratory
3:00 pm – Refreshments, CAS 502
3:30 pm – Seminar, CAS 502
Ranging (MESSENGER) spacecraft into orbit around Mercury on 18 March 2011, the probe has returned the most comprehensive dataset of the innermost planet of our solar system to date. This presentation will show results from the orbital phase of the MESSENGER mission in two parts. The first part will focus on observations of the structure and dynamics of Mercury’s magnetosphere inferred from observations by the Magnetometer and Fast Imaging Plasma Spectrometer. Because Mercury’s dynamo magnetic field is weak – the dipole moment is 190 nT RM3, where RM=2440 km is Mercury’s radius – the magnetopause stands, on average, only 1.45 RM off the subsolar surface. Consequently, Mercury’s magnetosphere is much smaller than that of the Earth, and evidence for rapid reconnection through frequent load- ing and unloading of the magnetic tail on ~2 min. time scales, commensurate with this magnetosphere’s Dungey cycle, is plentiful. Similar to the terrestrial magnetosphere, plasmas entering the nightside magnetosphere via reconnection and diffusion processes are transported toward the equatorial plane forming the plasma sheet and thence to the dayside by convection. However, owing to weak corotation and gradient-curvature drifts and highly variable convection electric fields and external magnetic fields, which exhibit magnitudes comparable to the dipole field even close to the planet, particle motion is much more chaotic and precipitation to the surface exhibits a strong north–south asymmetry resulting from the substantial, ~480 km, northward offset of the planetary field. The second part of the presentation will feature highlights across various disciplines of the MESSENGER mission, including geological mapping of the planet, determination of surface and exosphere composition, and detection of water ice and ancient crustal magnetic fields. Reflecting on the remarkable accomplishment of this NASA Discovery mission, we wait together as MESSENGER rides into the sunset and is scheduled to impact Mercury on 30 April 2015 after all onboard fuel reserves are exhausted.
MINERVA: The MINiature Exoplanet Radial Velocity Array
￼￼Harvard-Smithsonian Center for Astrophysics
3:30 pm – Refreshments, CAS 502
4:00 pm – Seminar, CAS 502
MINERVA will be a robotic observatory with four 0.7 meter telescopes at Mt. Hopkins, Arizona. All four telescopes feed the same precision spectrograph capable of sub m/s radial velocities of bright, nearby stars, to discover and characterize small exoplanets. We can robotically switch between the fiber fed spectrograph and wide field imagers capable of precise photometry. I will discuss the scientific motivation behind MINERVA, the design and implementation, its current status, future plans, and present the first photometric results which demonstrate sub-millimag precision on 3-5 minute timescales over several hours. These results show that MINERVA is well-equipped to address its secondary science goal of searching for transits of known and newly discovered super-Earth exoplanets detected by radial velocity, including future detections from the MINERVA spectrograph.
The AGN population as seen through the Chandra and NuSTAR surveys of the COSMOS field
Francesca Civano (Yale)
CAS 500, 12:40pm, April 28, 2015
The equatorial 2 deg2 COSMOS area is the only large field for which a complete, deep, pan-chromatic data set exists, from an outstanding survey effort, and that all large telescopes can observe. During 2013, this pioneering and ambitious COSMOS survey had a major extension, pushing its frontiers via the newly approved Chandra COSMOS Legacy Survey, the second largest Chandra extragalactic survey ever approved, plus new deep Spitzer, JVLA and NuSTAR surveys all aimed to study the formation of the structures in the high redshift Universe and the role of active super massive black holes.
The Chandra COSMOS-Legacy survey uniformly covers the 1.7 deg2 COSMOS/HST field with 2.8 Ms of Chandra ACIS-I imaging at ~150 ksec depth. At Chandra energies, we are able to detect unobscured and obscured sources, up to columns of NH=10^23. Therefore, to have a complete selection with no obscuration bias, we employed 3 Megaseconds of NuSTAR time to cover the same Chandra area and have the best unbiased view of the X-ray sky.
In this talk, I will present the first results from both surveys focusing on rare sources (the high-z sample and the Compton Thick sources).
Wednesday April 22 seminar; James Lowenthal, Smith College; Proto‐planetary Disks and High‐z Galaxies
Chasing Proto‐planetary Disks and High‐z Galaxies with the LMT
Wednesday, April 22, 2015
3:15 pm – Refreshments, CAS 502
3:30 pm – Seminar, CAS 502
The 50-meter Large Millimeter Telescope (LMT) — a joint project of UMass Amherst and INAOE, Mexico — is nearing completion on 5000m Sierra La Negra, and is now operating with a 32-m surface in “Early Science” mode. Some of the most luminous galaxies in the Universe are dusty starbursts at redshifts z>4 that are invisible in the optical but easily detected at 1-3 mm with LMT. I will review the status of this new facility and some of its recent results, including redshifts measured using CO emission lines, resolution of previously blended Herschel sources, gravitationally lensed submillimeter galaxies out to z~5, and dust maps of proto-planetary disks in nearby Galactic star-forming regions.
Gyrochronology and asteroseismology with Kepler and K2
Tuesday April 21, 2015
12:40 pm – CAS 500
Gyrochronology, the method of inferring stellar ages from rotation period and mass measurements, is the only dating method available for thousands of Kepler stars. However, we find that a simple gyrochronology model cannot reproduce the predicted ages for the Kepler asteroseismic stars. The tension between gyrochronology and asteroseismology may not be resolvable with the currently available data, however, the repurposed Kepler (K2) mission will provide new gyrochonological and asteroseismic ages. It will also target stars in clusters with precisely determined ages. We have developed a new method for the extraction of periodic information from K2 light curves which is applicable to both rotation period measurement and asteroseismic oscillation mode detection. By conducting Principle Component Analysis (PCA) on all light curves observed by K2, we construct an empirical noise model of the data. K2 light curves are then modelled as a linear combination of the top PCA components, plus an additional sinusoidal signal. I will demonstrate the quality of the systematics-insensitive periodograms produced using this method and discuss the applications to gyrochronology and asteroseismology.
Geospace Structure and Dynamics in the Coupled Plasmasphere-Magnetosphere-Ionosphere System:
New Observational Insights
Massachusetts Institute of Technology Haystack Observatory
Thursday, April 16, 2015
3:00 pm – Refreshments, CAS 500
3:30 pm – Seminar, CAS 502
There has been a recent increase in the number of in-situ observational assets in near-Earth space that can be brought to bear on topics of magnetosphere-ionosphere coupling in the sub auroral region. These recent platforms include NASA’s Van Allen Probes twin spacecraft with a large suite of advanced plasma sensors capable of analyzing inner magnetosphere ion and electron composition and dynamics from near thermal levels to highly energetic, ultra-relativistic particle populations. When added to existing spacecraft missions including the THEMIS spacecraft (three in highly elliptical orbits, and two in lunar orbit) and when further combined with powerful ground based remote sensors such as GPS based total electron content (TEC) and wide field incoherent scatter radar observations, potentials are greatly enhanced for new and exciting insights into mass flows and feedback mechanisms in the coupled geospace system. We will describe two recent results from ongoing multi-instrument collaborative studies of coupled plasmasphere and inner magnetosphere dynamics that demonstrate the power of this diagnostic perspective.
After a review of phenomenology related to sub auroral polarization stream (SAPS) and storm enhanced density (SED) structures found at storm times in the boundary layer between the plasmasphere and magnetosphere, we will first describe results that employ Van Allen Probes in-situ magnetospheric electric field data combined with ground based Millstone Hill ionospheric radar flow measurements, synoptic GPS based TEC maps, and topside ionosphere DMSP spacecraft observations. The combination of these views with proper analysis provides multipoint quantitative diagnostics of stormtime mass flux moving plasmasphere material from the inner plasmasphere outward to several earth radii. Along the way, we will provide some tutorial details on how the observation technique works for GPS TEC and ionospheric large aperture high power radar.
We will subsequently focus on the impact of this cold, dense plasmaspheric plume material on the efficiency of energy transfer into the Earth system from incident solar wind and magnetospheric configurations. Using ground-based TEC maps and measurements from THEMIS platforms, we more fully complete the picture of how plasmaspheric plume material, streaming from the MLT dusk sector, can extend from regions near the Earth all the way out to the magnetopause and magnetospheric reconnection point. The presence of this plasma has direct effects on reconnection rates based on recent theories by Cassak and Shay, and we will review these predictions and combine them with observations to demonstrate that a negative geospace feedback mechanism exists between storm time energy input and system response.
From filaments, to cores, to…filaments?!
The role of magnetic fields in multi-scale, filamentary star formation
Center for Astrophysics
Tuesday, April 14, 2015
12:40 pm – CAS 500
In just the past few years, it has become clear that filamentary structure is present in the star-formation process across many orders of magnitude in spatial scale, from the galactic scales probed by Planck and Herschel all the way down to the AU-scale structures that ALMA has revealed within protoplanetary disks. A similar story can be told of magnetic fields, which play a role in star formation across the same vast range of size scales. Here I will first review my work on 1000 AU-scale dust polarization and magnetic fields in Class 0 protostellar envelopes, which were observed as part of the TADPOL survey using the 1.3 millimeter dual-polarization receiver system at CARMA. I will then highlight two 1000 AU-scale filamentary structures seen with CARMA before I reveal new, high resolution (150 AU!) ALMA 1.3 mm continuum observations of three protostars in Serpens. Even at such high resolution, these sources have a number of filamentary blobs/condensations/companions, several of which coincide in a tantalizing way with the magnetic fields we mapped with CARMA. I will muse on what this all means, and on what questions may soon be answered by ALMA polarization observations of the same three sources…
Revisiting Laron’s 1981 Scaling Relationships
in Galactic Molecular Clouds
University of Massachusetts
Department of Astronomy
Monday, April 13, 2015
3:15pm – Refreshments, CAS 500
3:30pm – Seminar, CAS 502
For over thirty years, the Larson (1981) scaling relationships have provided the primary observational constraint to the dynamics of molecular clouds in the Milky Way. The relationships include a sub-linear scaling between velocity dispersion and size, an inverse scaling between mean density and size, and a constant ratio of virial mass to luminous cloud mass. In my presentation, I examine these relationships in detail using molecular line data gathered over the last 15 years. Owing to the sensitivity and sampling of these new data, a fundamental plane for molecular clouds is identified that extends the Larson relationships.
I discuss the various size-line width relationships defined by observers and the connection to the velocity spectrum of interstellar turbulence. The fundamental plane emerges from the near universality of the turbulence in molecular clouds and the equipartition between gravitational and turbulent kinetic energy densities.
Finally, I show preliminary efforts to calibrate the fundamental plane of molecular clouds to estimate distances in the Milky Way.
The Earth’s Dynamical Radiation Belts:
New insights from the Van Allen Probes mission
NASA Goddard Space Flight Center
Thursday, April 9, 2015
3:00 pm – Refreshments, CAS 500
3:30 pm – Seminar, CAS 502
The Earth’s radiation belts first discovered by James Van Allen and named after him, comprise charged particles trapped in the geomagnetic field. There are two belts separated by the so-called slot region. The outer belt containing chiefly electrons, is very dynamic and a number of physical processes operate there which affect their fluxes via energization and loss mechanisms. The study of these processes is interesting not only scientifically but also has practical consequences.
The Van Allen Probes, a major NASA mission was launched late August 2012 to study the radiation belts in a detailed way. The mission comprises two identically instrumented spacecraft carrying a comprehensive suite of instruments that characterize charged particles, electric and magnetic fields, and plasma waves in the Earth’s radiation belts. In particular, the ECT suite of instruments comprising of HOPE, MagEIS and REPT instruments measure electrons, protons and ions and their angular distributions over energies ranging from a few eV to several tens of MeV. Measurements from Van Allen Probes have made significant and paradigm-shifting contributions towards the understanding of the physics of charged particles in the Earth’s radiation belts.
I will describe the Van Allen Probes mission emphasizing the ECT instrument suite and present some of the science results pertaining to the dynamics of electron energization and loss in the outer radiation belt.
I am also leading the CeREs CubeSat mission, which is currently being built at Goddard and slated to be launched mid-2016. The primary goal of this tiny mission is to study electron microbursts, a particular loss mechanism of energetic electrons from the outer belt. CeREs carries a single com- pact instrument, called MERiT to measure electrons and protons. Measurements made by CeREs can potentially enhance science returns from Van Allen probes. In my talk, I will also describe the CeREs CubeSat and the MERiT instrument.