How Stellar Activity can be Good for Life

Dr. Paul Rimmer

University of Cambridge, UK

Tuesday, Aug 7, 2018

Abstract

It is likely that the building blocks of life were formed photochemically from hydrogen cyanide on the surface of the Early Earth. This requires both sufficient UV light and a source of hydrogen cyanide (HCN). Flares and coronal mass ejections (CMEs) on stars are not always detrimental to habitability. CMEs ionize and dissociate molecular nitrogen, providing a source of atmospheric HCN that is orders of magnitude more efficient than photochemistry near a planet’s surface, where the HCN is needed. Additionally, when considering the rates to form sugars in the presence of the UV light and HCN, and the rates at which inert adducts form in the dark, and comparing with UV spectra of cool stars, we find that sufficiently active M dwarfs, with flares of energy greater than 5e34 erg with frequency greater than than once every 50 days, may provide enough energy to drive the formation of sugars. We are most interested in planets on which life started long ago, since it is unlikely we will be able to detect life that has just begun on an exoplanetary surface. Therefore it is important to have a good understanding of how flare rates change with stellar age.

Do we really need to worry about binary stars?

JJ Eldridge

Tuesday, Aug 21, 2018

Abstract

This answer to this question depends on who you ask but in nearly all parts of astrophysics the answer should be yes. Yet most stellar evolution models that are widely used today assume that stars are single. This is at odds with our growing understanding that most stars are in binary systems close enough the two stars can interact and experience very different evolution to that of single stars. I will discuss how the Binary Population and Spectral Synthesis (BPASS) code provides a tool to be able to include these different evolutionary pathways when studying stellar systems. I will show the importance of accounting for binary interactions by discussing a few examples. These will include stellar populations in HII regions, open clusters and globular clusters, galaxies near and far and the variety of both electromagnetic and gravitational transients.

Constraining Cosmic Reionization with Hubble, James Webb, and WFIRST

Brant Robertson

Tuesday, Aug 28, 2018

Abstract

Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. Through a series of intense observational campaigns with Wide Field Camera 3 aboard Hubble Space Telescope we have now systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. High-redshift observations with HST including UDF12, CANDELS, and the Frontier Fields provide the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize results from these HST campaigns and the most recent constraints from Planck CMB observations to infer redshift-dependent ultraviolet luminosity densities, reionization histories, and the electron scattering optical depth evolution consistent with the available data. We will then preview how James Webb Space Telescope and eventually WFIRST will provide a new window into the reionization epoch and teach us about the physics of galaxy formation in the early universe.

The Search for Sources of IceCube Astrophysical Neutrinos

Erik Blaufuss

UMD

Tuesday, Sep 11, 2018

Abstract

The IceCube Neutrino Observatory instruments a cubic-kilometer of glacial ice under the Amundsen-Scott South Pole Station, Antarctica to detect neutrinos above ~100 GeV and perform astro-particle observations of the Universe. Astrophysical neutrinos are expected to be created in the birthplaces of high-energy cosmic rays, and point the way back to these elusive sources. Since IceCube's detection of a diffuse flux of high-energy astrophysical neutrinos in 2013, identifying their sources has been the primary science goal. This talk with will present the latest measurements of the astrophysical neutrino flux and highlight results from realtime alerts generated by astrophysical neutrino detections that trigger rapid follow-up observations by the community. In particular, a neutrino alert in September, 2017 triggered world-wide astronomical observations, and provide evidence that the Fermi-LAT identified blazar TXS 0506+056 is the first multi-messenger source producing neutrinos, as well as an accelerator of cosmic rays. Potential upgrades to IceCube will also be discussed, including the physics potential of a future IceCube-Gen2 facility at the South Pole.

A new dawn: gravitational-wave observations of binary systems on the ground and in space

Emanuele Berti

Tuesday, Sep 18, 2018

Abstract

The observation of compact binary mergers by the LIGO/Virgo collaboration marked the dawn of a new era in astronomy. LISA will fulfill this vision by opening a new observational window at low frequencies. The gravitational radiation emitted by compact binary systems in these two frequency windows encodes important information on their astrophysical formation mechanism. Furthermore, compact objects - whether in isolation or in binaries - are excellent astrophysical laboratories to probe our understanding of high-energy physics and strong-field gravity. I will highlight the potential of Earth- and space-based detectors to further our understanding of the formation and evolution of compact binaries. I will also discuss potential smoking guns of new physics in gravitational-wave detectors, and the theoretical and observational challenges associated with their search.

What's next for LIGO: from O3 to the next generation of gravitational wave detectors

Lisa Barsotti

MIT

Tuesday, Sep 25, 2018

Abstract

The LIGO gravitational wave detectors are undertaking a series of improvements with the goal of coming back on-line even more sensitive in their next Observing Run O3, scheduled for early 2019. In parallel, the world-wide gravitational wave community is ramping up the effort to prepare for the next generation of ground-based gravitational wave instruments. In my talk, I will give an update on the current status of the LIGO detectors, how the global network of detectors will evolve in the upcoming years, and prospects for improving their sensitivity by more than a factor of 10 in new facilities.

The Origins Space Telescope

M. Meixner (STScI), D. Leisawitz (605), and M. DiPirro (552)

Tuesday, Oct 02, 2018

Abstract

The Origins Space Telescope (OST) is the subject of one of the four community-led large mission studies sponsored by the HQ Astrophysics Division in preparation for the upcoming Decadal Survey, and one of the two mission studies in which Goddard is playing a major role. OST will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did the universe evolve in response to its changing ingredients? How common are life-bearing planets? To accomplish its scientific objectives, OST will operate at mid- and far-infrared wavelengths (3 – 600 microns) and offer superlative sensitivity and new spectroscopic capabilities. Dr. Meixner will give an overview of the science drivers that frame the OST mission concept, and describe the vast discovery space that OST Guest Observers will be able to exploit to further their objectives. Dr. Leisawitz will describe the OST team’s study approach, summarize two mission concepts, and give the rationale for key design decisions. Dr. DiPirro will give an overview of the OST technology roadmap and describe how the OST telescope and instruments will be cooled to ~4 K, which is essential to achieving astronomical background photon noise-limited performance and reaching the required far-IR sensitivity.

Fast Radio Bursts are Happening

Sarah Spolaor

West Virginia University

Tuesday, Oct 09, 2018

Abstract

Fast radio bursts (FRBs) are intense flashes of light almost as bright as an active galactic nucleus, but lasting only a few milliseconds. They appear to be coming from distant galaxies, and happen once every few seconds somewhere in the sky. Their first discovery happened exactly one decade ago, but in just the past few years our understanding of them has begun to unfold. In only the past year, the total number of detected FRB sources has doubled (now ~60). If we are able to localize FRBs to distant host galaxies and measure their distance, we might be able to use FRBs to map the ionization history of the Universe and study diffuse magnetic fields, among other applications. Importantly, localizing FRBs will also be critical for performing deep multi-wavelength follow-up, and identifying the FRB progenitor. The race is on to detect more FRBs, localize them, and discover what creates these mysterious flashes. The Realfast detector on the Karl G. Jansky Very Large Array is so far the only system with a demonstrated capability to localize a FRB to a host galaxy. This talk will provide an overview for the current context and future of this field, and review the promise of Realfast and other upcoming detectors to allow multi-wavelength follow-up and begin to allow the use of FRBs as probes of the Universe.

Probing the High-Energy Radiation Environment of Exoplanets around Low-Mass Stars with SPARCS, the Star Planet Activity Research CubeSat

Evgenya Shkolnik

Arizona State University

Tuesday, Oct 16, 2018

Abstract

Roughly seventy-five billion M dwarfs in our galaxy host at least one small planet in the habitable zone (HZ). The stellar ultraviolet (UV) radiation from M dwarfs is strong and highly variable, and impacts planetary atmospheric loss, composition and habitability. These effects are amplified by the extreme proximity of their HZs (0.1–0.4 AU). Knowing the UV environments of M dwarf planets will be crucial to understanding their atmospheric composition and a key parameter in discriminating between biological and abiotic sources for observed biosignatures. The NASA-funded Star-Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M stars in the far-UV and near-UV, measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. For each target, SPARCS will observe continuously over at least one complete stellar rotation (5 - 45 days). SPARCS will also advance UV detector technology by flying high quantum efficiency, UV-optimized detectors developed at JPL. These “2-D” (collectively referring to delta-doped and superlattice-doped) detectors have demonstrated greater than five times the quantum efficiency of the detectors used by GALEX. SPARCS will pave the way for their application in missions like LUVOIR or HabEx, including interim UV-capable missions. SPARCS may also be capable of ‘target-of-opportunity’ UV observations for the rocky planets in M dwarf HZs soon to be discovered by NASA’s TESS mission, providing the needed UV context for the first habitable planets that JWST will characterize.

Dancing to ChaNGa: The Formation of Close Pairs of Supermassive Black Holes in Cosmological Simulations

Michael Tremmel

Tuesday, Oct 23, 2018

Abstract

I present the first self-consistent prediction for close Supermassive Black Hole (SMBH) pair formation timescales following galaxy mergers. Using Romulus25, the first large-scale cosmological simulation to accurately track the orbital evolution of SMBHs within their host galaxies down to sub-kpc scales, we predict that it is relatively rare for galaxy mergers to result in the formation of close SMBH pairs with sub-kpc separation and those that do form are often the result of Gyrs of orbital evolution following the galaxy merger. The likelihood and timescale to form a close SMBH pair depends on the mass and morphology of the merging galaxies. When galaxies are disrupted during a merger, their SMBHs are deposited on long lived, kpc-scale orbits that result in a population of ‘wandering’ SMBHs. I discuss the implications of these results for predictions of SMBH merger rates and examine the population of wandering SMBHs that our simulations predict should reside in massive halos.

SN 2010da/NGC 300 ULX-1: From Supernova Impostor to Ultraluminous (?) X-ray Source

Breanna Binder

Tuesday, Oct 30, 2018

Abstract

The optical/IR transient SN 2010da was first observed in NGC 300 in May of 2010, and quickly recognized to be a “supernova impostor.” Follow-up multi-wavelength observations subsequently revealed that the system is a young (<5 Myr), variable high mass X-ray binary (with X-ray luminosities on the order of ~10^36-10^37 erg/s) powered by a neutron star primary and a supergiant donor. During the summer of 2016, the X-ray flux of SN 2010da dramatically increased by ~2-3 orders of magnitude, implying an X-ray luminosity of ~10^39 erg/s and signaling a transition to an ultraluminous X-ray source (ULX)-like state. In this talk I will present and overview of the SN 2010da evolution since its discovery in 2010 and near-simultaneous Swift/XRT imaging and Gemini GMOS spectroscopy obtained during the summer of 2017. The observed X-ray emission is consistent with an inhomogeneous wind that partially obscures a central, bright inner accretion disk. Optical spectra from Gemini exhibit numerous emission lines (e.g., Hα, Hβ, He II λ4686) which suggest that the neutron star primary is photoionizing material in the immediate vicinity of the binary. By comparing the He~II λ4686 line luminosity (~7-9 x10^35 erg/s) to the contemporaneous soft X-ray emission, we find the X-ray emission is broadly consistent with the observed He II line luminosity. The combination of our X-ray observations and optical spectroscopy suggest that geometric beaming effects in the ULX-1 system are minimal. I will additionally discuss the observed spin-period evolution and energy-dependent pulse fraction seen in deep Swift, XMM-Newton, and NuSTAR observations of SN 2010da, and place SN 2010da into context with other ULX systems.

Journey to the Center of the Super-Earth

Leslie Rogers

University of Chicago

Tuesday, Nov 06, 2018

Abstract

Sub-Neptune, super-Earth size exoplanets are a new planet class. Though absent from the Solar System, they are found by microlensing, radial velocity, and transit surveys to be common around distant stars. In this talk, I'll review both recent developments and outstanding puzzles in our understanding of the nature and origin of these enigmatic planets.

Measuring the Radiative Properties of Astrophysical Matter Using the Z X-ray Source

James Bailey, ZAPP Team

Sandia National Laboratories, Albuquerque, New Mexico

Tuesday, Nov 13, 2018

Abstract

The radiative properties of hot dense matter – opacity, the response of atoms to plasma environments, and radiation transport - are often an essential ingredient for building physical descriptions of cosmic objects. Alternatively, understanding radiative properties is essential for correctly interpreting astronomical spectra. In the past, these properties were difficult or impossible to measure in terrestrial laboratories because the required temperature, density, and spectral irradiance were unobtainable or uncontrollable. Today, megaJoule-class pulsed x-ray sources are beginning to make benchmark experiments for astrophysical conditions possible for the first time. The Z Astrophysical Plasma Properties (ZAPP) collaboration is using Z, the most energetic x-ray source on earth, to stage experiments that simultaneously investigate multiple topics in radiative properties of hot dense matter. The astrophysics questions presently guiding this research are: 1) Why can’t we predict the location of the convection zone base in the Sun? 2) How does radiation transport affect spectrum formation in accretion-powered objects? 3) How accurately can we determine White Dwarf stellar masses using spectroscopy? and 4) How well do we understand the physics of heating and ionization in photoionized plasmas? Recent progress will be described, emphasizing the first two topics. Opacity models are an essential ingredient of stellar models and are highly sophisticated, but laboratory opacity tests have only now become possible at the conditions existing inside stars. Our opacity research emphasizes measuring iron at conditions relevant to the base of the solar convection zone, where the electron temperature and density are believed to be 2.2million Kelvin and 9x1022 e/cc, respectively. The results exhibit large disagreements between iron opacity measurements and models and ongoing research is aimed at testing hypotheses for this discrepancy. The second project is motivated by the fact that emission lines from L-shell ions are not observed from iron in black hole accretion disks, but are observed from silicon in x-ray binaries. These disparate observations may be explained by differences in the radiation transport within the plasmas, but models for the spectral line formation and transport in photoionized plasmas have never been tested. We investigate photoionized silicon plasmas using absorption spectroscopy to infer the plasma conditions and emission spectroscopy to determine the dependence of spectral emission on plasma column density.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

Intensity mapping to probe the interstellar medium

Anthony Pullen

Tuesday, Nov 27, 2018

Abstract

Line intensity mapping (LIM), in which line emission from unresolved galaxies is mapped onto a 3D field, has emerged as a unique probe of the gas content and star formation history of the Universe as well as large-scale structure across cosmic time. In this talk I will present the science potential of LIM as well as the surveys which will provide the data for these analyses. After a brief introduction to LIM, I will introduce the various candidate emission lines being considered and explain what mapping these lines can teach us about star formation and the interstellar medium. I will then discuss the various LIM surveys that are currently observing as well as some that will come online in the near future in terms of their expected science output. Finally, I will describe the recently NASA-funded LIM survey EXCLAIM, whose survey team is based at GSFC and whose mission is to map microwave line emission over cosmic time to probe star formation and the ISM.

Investigating the Symmetry and Progenitors of Supernova Remnants using X-ray Observations

Laura Lopez

Ohio State

Tuesday, Dec 4, 2018

Abstract

Supernovae (SNe) play an essential role in the Universe. They are routinely detected through dedicated robotic surveys, but most of these SNe are often too distant (~1-100 Mpc) to resolve the SN ejecta and immediate surroundings of the exploded stars. Fortunately, supernova remnants (SNRs) offer the means to study explosions and dynamics at sub-pc scales. In this talk, I will review recent advances in the understanding of SNe based on studies of SNRs, particularly using Chandra and NuSTAR X-ray observations. I will highlight investigations of SN asymmetry, based on morphologies and heavy metal (like iron and titanium) kinematics and abundances, and I will compare the results to predictions of recent, high-fidelity SN models. Furthermore, I will discuss recent work to constrain SNR progenitors using X-ray observations as well as star-formation histories in the proximity of SNRs.

Astromineralogy and dust grain growth with X-ray imaging and spectroscopy

Lia Corrales

University of Michigan

Tuesday, Dec 11, 2018

Abstract

The journey that interstellar metals take – from their nuclear reactive origins to their incorporation in planets, plants, and animals – is a highly uncertain one. The X-ray energy band is sensitive to absorption by all abundant metals in the interstellar medium (ISM), both in gas and dust form, enabling us to answer key questions in dust grain growth and processing. X-ray photoelectric absorption edges observed in high resolution spectra of Galactic X-ray binaries directly reveal the mineral composition of interstellar dust. X-ray imaging of dust scattering halos is an important tool for measuring dust grain sizes and their 3D spatial distribution. I will review open problems in the field of astromineralogy, including problems in reconciling X-ray absorption spectroscopy with ISM observations at other wavelengths. I will describe how X-ray missions in process for the near future - XRISM, ARCUS, and Athena - will contribute.

Measurements of Astrophysical Polarization from Spider

Bill Jones

Princeton

Tuesday, Dec 18, 2018

Abstract

Spider is a balloon borne instrument designed to provide high fidelity measurements of the intensity and linear polarization of the Cosmic Microwave Background and diffuse Galactic foregrounds. During a flight from Antarctica in 2015 Spider was the most sensitive microwave telescope ever built. We will describe the current state of analysis of these data, including our measurements of CMB polarization and the contributions from Galactic foregrounds - primarily thermal dust emission - over 10% of the full sky. In addition, we will describe the new 285 GHz receivers to be flown on a flight next year, and implications for the search for the signature of primordial gravitational waves in the cosmic microwave background.