The Eventful Universe
March 17-20, 2010
Two reasons motivate us to build a complete inventory of transients in the local universe (d < 200 Mpc). First, there exists a glaring six-magnitude luminosity gap between the brightest novae and faintest supernovae, especially on short timescales. Theorists predict a variety of mechanisms to produce transients in the gap and observers have the bes chance of finding them in the local universe. Second, the budding fields of gravitational waves, neutrinos, ultra high energy cosmic rays and TeV astronomy are also limited to ~100 Mpc horizon either due to instrumental sensitivity or physical effects. The Palomar Transient Factory (PTF) is now fully operational and has proven to be an extremely efficient transient discovery and classification machine. We systematically target local galaxy-light concentrations over a large area (~18000 galaxies) and are unique in our depth (m<21), cadence (1-day) and follow-up. Here, I present first results from PTF’s search for transients in the local universe.
The current generation of wide-field surveys like PanSTARRS probe the time-domain universe in unprecedented cadence, depth, and sky coverage. When stacked, these new data sets contain a wealth of information on the static Universe, whereas the differences in successive observations provide an unprecedented view of the variable Universe. PanSTARRS has recently started its science operation, and we are just now starting to tap into this vast pool of transients. I will give an overview of the current status and first results.
Killer Asteroids and Exploding Galaxies—The Catalina Sky Survey and the Catalina Real Time Transient Survey
The Catalina Sky Survey (CSS) is part of a NASA-supported program to inventory the largest Near-Earth Objects (NEOs) in the solar system. With two telescopes in Arizona and one at Siding Spring, Australia, CSS has been operating in its present configuration since late 2004, and is the current discovery leader, finding about 70 percent of all new NEOs in each of the past three years. The CSS search program and image data set will be described, and the current status of the search summarized.
In October of 2008, Catalina’s Mt. Lemmon facility discovered 2008 TC3, the first asteroid on a collision course with Earth detected before impact. Catalina’s detection methodologies allowed news of its discovery to be circulated immediately, and TC3 was observed for nearly 20 hours before it entered the atmosphere over North Africa. Later, valuable fragments of TC3 were recovered in Northern Sudan. This discovery will be discussed in more detail, along with implications for future surveys.
Details of the Catalina Real Time Transient Survey (CRTS), an effort to mine the Catalina dataset for objects of astrophysical interest, will be briefly mentioned. CRTS will be discussed in detail by George Djorgovski in a talk immediately following this one.
Catalina Real-Time Transient Survey (CRTS) is a synoptic sky survey done in collaboration between Caltech and UAz/LPL. The survey uses data streams from 3 telescopes to cover up to 2000 deg2 per day, with a total area coverage of about 30,000 deg2, and time baselines ranging from tens of minutes to years. Transient events are identified in real time and made public immediately, without any proprietary period; this is the only fully open synoptic sky survey currently in operation, intended to serve the entire community. As of the late 2009, over 1100 unique, high-amplitude transients have been discovered, including nearly 300 SNe (including some peculiar and ultra-luminous ones), over 300 CVs (about 75% of them previously unknown), many blazars, flaring stars, etc. The survey feeds multiple scientific studies, and serves as a testbed for many cyber-infrastructure technologies needed for the exploration of the time domain. In particular, we have a strong program to develop automated classification of transients, and decision making for their follow-up. We have started a “citizen science” project using CRTS transients, both as an educational/outreach venue, and as a way of harvesting the human pattern recognition skills to help develop a next generation of automated classifiers.
Timothy M. Brown
Las Cumbres Observatory Global Telescope (LCOGT) is in the process of building and deploying a world-wide network of small telescopes dedicated to time-domain astronomy. The network as we now visualize it will consist of at least 5 sites, with 2 x 2m, at least 12 x 1m, and at least 20 x 0.4m robotic telescopes. 2010 is the year in which we will begin to deploy our network of 1m and 0.4m telescopes, starting with a cluster of telescopes at CTIO. I will give a brief description of the status of this project and our plans for the future, with particular emphasis on our ideas concerning interaction with large survey projects (such as PTF, PanSTARRS, and LSST), and on the prospects for using LCOGT facilities for event-driven astronomy.
Scratching Decadal Itches with Gamma-Ray Bursts
Joshua S. Bloom
The past several years of gamma-ray burst (GRB) observations have revealed an increasing diversity in both the phenomenology and the underlying origins of the events. At the same time that we try to come to grips with the richness of the events themselves, we are also making using use of GRBs as probes in a vast spectrum of astrophysical inquiry. Many of the most promising arenas — in particular, studying reionization and connecting electromagnetic activity to the gravity-wave universe — lie at the heart of the grand pursuits of this next decade. I will discuss both observational and theoretical progress which place GRBs at the nexus of such pursuits.
The Calan/Tololo Supernova Survey was a supernova survey that ran from 1989-1995 at the University of Chile and the Cerro Tololo Inter-American Observatory to measure a Hubble diagram for Type Ia supernovae out to reshifts of 0.1. The Survey used the CTIO Curtis Schmidt telescope with IIa-O photographic plates, each plate covering a field of 25 sq-deg on the sky. The plates were developed and sent to Santiago, Chile the next morning, and searched for supernovae at the Department of Astronomy at the University of Chile. Any supernova candidates were then observed the next night using the 0.9m telescope at CTIO with a CCD camera. This was one of the first studies done in astronomy where the telescope time was scheduled to observe objects not yet discovered. The calibration of Type Ia supernovae as standard candles led to the precise measurements of the Hubble Constant and the deceleration parameter, the latter indicating the presence of a dark energy or cosmological constant dominating the mass/energy of the Universe.
I will provide a discussion of the various types of nonsupernova transients from massive stars and what they tell us about stellar evolution. The distinction between bright massive star outbursts and faint supernovae, especially those with circumstellar interaction, is not always obvious, and the links between transient sources that may soon explode as core-collapse SNe will provide new and vital clues to the latest phases of massive star evolution.
I will present two case studies of optical transients with outburst luminosities intermediate between those of classical novae and supernovae. V838 Mon, a 2002 transient in the Milky Way, illuminates a spectacular light echo, extensively imaged with HST. Polarimetric imaging with HST yields a geometric distance, using a novel new technique. We have discovered that V838 Mon belongs to a sparse young cluster in the Outer Arm of the Milky Way, whose distance confirms the polarimetric technique. As dusty ejecta from the outburst slowly expand, V838 Mon has become a maser source, and it has recently ingested its B3 V companion star, making it disappear from the spectrum. A proposed outburst scenario is that it resulted from a merger or collision of two stars. In apparent support of this scenario, in which the merged object would be a rotating active supergiant, we have recently detected V838 Mon as a variable X-ray source. The 2008 optical transient in the nearby galaxy NGC 300 also lies in the gap between novae and SNe. We have used archival HST and Spitzer data to show that the progenitor was optically extremely faint, but luminous in the IR; thus the outburst occurred on a deeply dust-enshrouded red supergiant. This event could be related to LBV eruptions, or perhaps was an electron-capture SN. These new types of intermediate-luminosity events appear to be much more frequent than SNe, and upcoming synoptic surveys ought to find them in large numbers.
Radioactively Powered Optical Counterparts of Neutron Star Mergers
The most promising astrophysical sources of gravitational waves (GWs) with ground-based interferometers such as LIGO are the inspiral and merger of binary neutron star (NS) and black hole systems. Maximizing the scientific benefits of a GW detection will require identifying a coincident electromagnetic counterpart. One of the most likely sources of isotropic emission from NS mergers is a supernova-like transient powered by the radioactive decay of heavy elements synthesized in the merger ejecta. I will present the first calculations of the optical transients from NS mergers that selfconsistently determine the radioactive heating using a nuclear reaction network and which determine the resulting light curve with a Monte Carlo radiation transfer calculation. Due to the rapid evolution and low luminosity of NS merger transients, optical counterpart searches triggered by a GW detection will require close collaboration between the GW and astronomical communities. NS merger transients may also be detectable following a short duration Gamma-Ray Burst or “blindly” with present or upcoming optical transient surveys. Because the emission produced by the merger ejecta is powered by the formation of rare r-process elements, I will show how current transient surveys can directly constrain the unknown origin of the heaviest elements in the Universe.
I will review what we know about variability of galactic nuclei (both active and inactive), focusing on flares of large amplitude and brief duration. These are of interest because they may represented a poorly studied mode of variability of active nuclei, or the tidal disruption of stars or other unusual events in inactive nuclei. Such events are also of interest as electromagnetic counterparts of sources of gravitational radiation. In addition to a review of the observations I will present an overview of theoretical models, leading up to predictions of what upcoming surveys may discover.
Knowledge of stellar variability has a long history but continues to grow with new surveys and instruments. The various general categories of variability (geometrical, eruptive and pulsating) will be reviewed in terms of our present knowledge and how the observations were obtained to determine that knowledge. As we move toward wider and deeper sky coverage and longer baseline time coverage, we can expect to answer unresolved questions in these types of known variables, as well as uncover new forms of variability. However, this will require the proper color, cadence and followup observations to fully realize the potential of future discoveries.
Steven B. Howell
The NASA Kepler mission was launched in March 2009 and has been in science operations for approximately 10 months. While designed to detect Earth-like planets via the transit technique, Kepler is collecting unprecedented time series light curves with photometric precisions never before observed. I will present a general overview of the mission aimed not at its planet detection abilities, but rather with a look at the nature of the variable, and non-variable, stars Kepler has observed. Presentation of a variety of light curves will enhance the talk. I will then place the Kepler observations into context with some ground-based photometric variability surveys and discuss what Kepler is telling us about the time domain universe.
The sun is an eventful place on time scales of 10-6 to 1017 seconds. I will review some of the most significant solar events that have taken place over the lifetime of Kitt Peak. These range from solar cycle changes, through flows at and below the solar surface, to flares and magnetic reconnection. I will also discuss how these events affect modern society.
Much of the variability or ‘transient’ nature of objects in our Solar System comes from the fact that they move—quickly, visibly, on timescales of minutes to days. This motion is the aspect that plays havoc with searches for other (stationary) transient or variable objects, but it provides the key to studying the small bodies of our Solar System. Deriving orbits for moving objects tells us what the objects are, what their likely history has been, and where they are going to be in the future for more in-depth studies. The orbital distribution of these remnants of planetary formation gives us clues to the orbital evolution of the giant planets. Their physical composition, revealed approximately through broad-band colors or more precisely through spectroscopy, tell us about the primordial solar nebula. Characteristics of binaries and families in different populations constrain the collisional history of these populations. Combining these parameters, along with more data such as the size distribution, provides insights into the formation and evolution of the Solar System.
But how do you know when you’ve found a Solar System object and how can its orbit be determined? Like most other transient and variable objects which require ‘followup’, Solar System objects —whether Near Earth Object (NEO) or Trans-Neptunian (TNO)—require more than one observation, even for simple identification. ‘Followup’ in the Solar System, however, has additional challenges: how do you know where an object will be if you don’t know how it is moving? Even just for the first step of discovery, to distinguish moving objects from other transients or variables, multiple images within a fairly limited time-frame are necessary. The detections have to be linked between frames by some variation on a basic premise of “look for the thing that moves between images”, where that motion is typically assumed to be linear and within some likely range of velocities for the type of Solar System object being hunted. Techniques have ranged from blinking frames by eye to sophisticated software searches using either images or catalogs, where the catalogs themselves can be generated through a variety of methods, including catalogs of difference images. Usually these searches are tuned to detect a particular kind of Solar System object; surveys for NEOs rarely have the right observational cadence for detecting TNOs, for example, and the software can also be tuned to look for moving objects at a limited range of distances from Earth. Detecting moving objects at all distances and in all populations requires a more extensive software pipeline, as well as a more intensive observational cadence. Pan-Starrs and LSST are meeting this need through their “Moving Object Pipeline”. Even after linking detections within the short time-frame where the motion remains linear, identifying further detections of the same object can be tricky—degeneracies in potential orbits and increases in uncertainty with time dictate the needs for further followup observations. With enough observations over the right time-frame, however, an orbit can be secured.
From Near Earth Objects, through the Main Belt asteroids, all the way out to the Trans-Neptunian region, these small bodies provide a fascinating view into the origin and evolution of our planetary system, a view which is ever-changing and quickly moving — our hurtling, whirling Solar System.
An overview of transient phenomena of small solar system bodies will be given and implications for observations in the future will be discussed. A discussion about variability in comets, asteroids, centaurs, and trans-Neptunian objects will be presented and what has been and can be learned from such variability. A look at future observational surveys in this context will also be included.
A Global Network for Planet Detection and Asteroseismology Study using Extremely high Precision Extrasolar Planet Tracker Instruments
A global network is being established to hunt for low mass exoplanets and measure stellar oscillations using Extremely High Precision Extrasolar Planet Tracker Instruments (EXPERT) on 2 meter class telescopes. EXPERT is a combination of a thermally compensated monolithic interferometer and a high throughput cross-dispersed echelle spectrograph to have a low cost and compact design while offering high precision radial velocity measurement capability. EXPERT has a spectral resolution of R=18,000 and a wavelength coverage of 0.39-0.7 A^μm in a single exposure. EXPERT is designed to achieve 1 m/s for a V=8 solar type star in 30 min using a 2 meter telescope. The first EXPERT was commissioned at the Kitt Peak 2.1m in September 2009 and the second one is to be commissioned at the LiJiang 2.4m telescope in China in late March 2010. More EXPERT instruments will be gradually added to the network to have continuous phase coverage of precision radial velocity measurements of a selected target over a long time. The Kitt Peak commissioning data have demonstrated a Doppler precision of about 1 m/s for a solar type star with S/N~100 per pixel. By bypassing the interferometer, EXPERT can also offer traditional stellar spectroscopy with R=27,000 and a simultaneous wavelength coverage of 0.39-1.0 A^μm. This network will be primarily used for time sensitive extremely high precision Doppler measurements such as hunting for Earth like rocky planets and monitoring stellar oscillations. The network will also be used for following up planet candidates from the ongoing SDSS-III Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) and space missions.
The Wide-field Infrared Survey Explorer (WISE) was launched on Dec. 14, 2009 and has begun surveying the entire sky in four mid-infrared bands, 3.4, 4.6, 12, and 22 microns. During WISE's expected 9 month cryogenic mission, each point on the sky will be imaged between ~8 and ~2000 independent times on the ecliptic equator and poles, respectively. We present methods currently being used to detect flux transients using repeated WISE observations and discuss the unique challenges posed by the varying depth-of-coverage and sampling cadence that varies from ~1.5 hours to 9 months. Transient and variable source classification is also attempted and we discuss these methods, including Fourier decomposition and neural network architecture.
The Wide-Field Infrared Survey Explorer (WISE) launched on December 14, 2009 and is imaging the entire sky at four midinfrared wavelengths. WISE will enable the search for the closest brown dwarfs to the Sun and the most luminous distant galaxies, as well as detecting thousands of main belt asteroids and hundreds of near-Earth object. The WISE 3.4, 4.6, 12 and 22 um bandpasses sample the flux from most inner-solar system bodies near the peak of their thermal emission, making WISE particularly sensitive to the the darkest members of those populations. WISE orbits the earth in a Sun-synchronous, 525 km orbit every 95 minutes, and repeatedly observes the same sky region a minimum of eight times over approximately two days. We have adapted for the WISE cadence elements of the Moving Object Pipeline System, originally developed for the PanSTARRS and LSST moving object search programs, and have implemented semi-automated verification tools to identify moving object candidates from the stream of WISE source detections. To date, tens of NEO candidates and hundreds of Main Belt objects have been detected and published to the Minor Planet Center, including tens of comets. WISE is credited for the discovery of two confirmed NEOs and one new comet. We will give a brief overview of the WISE moving object pipeline detection system and its performance with the first two months of survey data.
The rush of events from current telescopes and surveys will become even more intense as future surveys turn on the spigot, including the LSST. The characterization and classification of these events will present greater challenges, thus requiring novel approaches. Among these are operational approaches, such as citizen science engagement, and others are algorithmic approaches, such as automated pipelines. The new Zooniverse project aims to blend these approaches, using massive training sets (viewed by many) in combination with machine learning algorithms (trained by many). We will introduce Zooniverse, its research plans, and preliminary results. In particular, we report on early efforts to mine the Sloan database for associations between the pipeline measured scientific parameters and the Galaxy Zoo participant contributed visual classifications. These results will ultimately inform the design of improved classifiers for non-standard morphologies, such as tidally disturbed and merging galaxies, but applicable to any non-standard behavior. This is possible because human cognition is more powerful than computer algorithms at identifying and characterizing unusual behaviors and outliers. This is particularly true in the time domain, since change detection and event characterization are often more easily deduced by humans. Computer algorithms can then be trained on moderate-sized data streams today, by modeling these identifications and characterizations with data mining algorithms (feature detection, pattern recognition, machine vision), in order to produce more accurate pipeline-produced classifications on the massive data streams of the future. Additional examples and research opportunities (such as Zooniverse machine learning challenges) will be mentioned, including early design concepts from the LSST project for a Light Curve Zoo for variable stars.
Airborne astronomy has historically been a powerful astronomy tool for following transient events in ways that required rapid response and or special geographic location. In the case of the former, the bolometric and spectral behavior of SN1987a was charted in great detail in the mid and far infrared, and in the case of the latter, the discovery of the rings of Uranus, and insights into the atmospheric structure of Pluto were key accomplishments. These were done with the 0.9m Kuiper Airborne Observatory (KAO), now retired. The Stratospheric Observatory for Infrared Astronomy (SOFIA) will be a 2.5m telescope following the KAO legacy that will regularly observe from the stratosphere, where it will do infrared observations that, for reasons of atmospheric opacity, would otherwise only be possible from space. With a hands-on instrument complement, SOFIA will be responsive to special instrumentation requirements (e.g. filter sets) that would otherwise be unavailable for the observational needs. SOFIA will be also be responsive to new events for observations that may require a particular timing and geographic location. SOFIA has recently achieved the first open-door flights in the stratosphere. With aircraft operations based in Palmdale, California managed by Dryden Federal Research Center, and a science operations center at NASA Ames Research Center in the San Francisco Bay area, SOFIA will provide opportunities for a host of scientists, over a large range of observational capabilities. We will report on the progress of SOFIA, the rampup of science observations, the scientific accommodation of guest observers, the data archiving that will optimize the scientific output, and the many and regular opportunities for new cutting edge instrumentation.
Cool molecular hydrogen H2 may be the ultimate possible constituent to the Milky-Way baryonic hidden matter. I will describe a new way to search for such transparent matter in the Galactic discs and halo, through its diffractive and refractive effects on the light of background stars. I will show that the relative configuration of the sources and the hypothetic hydrogen clouds is such that the expected scintillation contrast and characteristic time (a few minutes) make possible a detection at the optical wavelengths with LSST. Results from simulations and preliminary results from a test performed with the ESO-NTT telescope will be presented and discussed.
We present high time-resolution astronomical observations recorded with the Berkeley Visible Image Tube (BVIT) photon counting detector mounted on the 10m South African Large Telescope (SALT). Relative B and V-band photometric fluxes were obtained as a function of time for targets that included Polar-type cataclysmic variables (UZ For, OY Car, V1033 Cen), low-mass X-ray binaries (GX 339-4, UY Vol), pulsars (PSR 0540-69), dMe flare stars (CN Leo) and active galactic nucleii (Mkn 618). These observations, which were recorded during several nights of engineering time at SALT in early 2009, indicate that there are many types of astrophysical processes operating over very short time-scales in a wide variety of astronomical objects. The high-time resolution capability of the BVIT detector allowed emission features occurring on time-scales as short as tens of milli-seconds to be revealed. In particular, we have measured the optical period of the PSR 0540-69 pulsar to be 0.05065018808s and we have also detected several quasi-periodic oscillations operating on time-scales of < 0.5 s in the emitted flux from the X-ray transient source, GX 339-4. These preliminary data indicate that the new field of high time-resolution astronomy is providing important new insights into the transient nature of the Universe.
The time domain of the radio wavelength sky has been only sparsely explored. Nevertheless, recent discoveries from limited surveys and serendipitous discoveries indicate that there is much to be found on timescales from nanoseconds to years and at wavelengths from meters to millimeters. These observations have revealed unexpected phenonmena such as rotating radio transients and coherent pulses from brown dwarfs. Additionally, archival studies have revealed an unknown class of radio transients without radio, optical, or high-energy hosts. The new generation of centimeter-wave radio telescopes such as the Allen Telescope Array will exploit wide fields of view and flexible digital signal processing to systematically explore radio transient parameter space, as well as lay the scientific and technical foundation for the Square Kilometer Array. Known unknowns that will be the target of future transient surveys include orphan gamma-ray burst afterglows, radio supernovae, tidally-disrupted stars, flare stars, and magnetars. While proving the variable sky, these surveys will also provide unprecedented information on the static radio sky. I will present results from three ATA surveys: the Fly’s Eye survey, the ATA Twenty CM Survey (ATATS), and the Pi GHz Survey (PiGSS).
Aerodynamical properties of meteoroid fragments in the terrestrial atmosphere
There is significant evidence that some fraction of meteoric bodies is destroyed in the atmosphere. The evolution of the fragment cloud depends on a large number of factors, among them: the meteoroidâ€™s altitude and velocity at the moment of breakup, fragments sizes and properties of a body material. The interaction of shock waves forming in front of the fragments may lead to both an increase and decrease of the midsection area of the fragment cloud. In this work, we consider the inter action of the fragments in a supersonic flow. The configuration properties of two spherical bodies of different radii are considered. Via numerical simulations, we calculate the pressure distribution in the flow around the two bodies for different relative positions. We construct the functions of the coefficients of transverse and drag forces from the angle between the central line of the two bodies and the flow direction for different distances between the two fragments. We find the conditions for the collimation effect, i.e., fragment involving into the wake of the leading (usually, the largest) fragment. We systematize the simulation results for drag and forces and infer the basic aerodynamic properties of the meteoroid fragments. Moreover, in the work dynamics of two spherical fragments in a supersonic stream is defined on the basis of numerical calculations. The aerodynamic properties are accurately expressed in a dynamic picture. Besides, it is obtained, that fragments connect and move as a unit due to aerodynamic interaction.
Quark novae as engines for super-luminous supernovae
Super-luminous supernovae (more than a 100 times brighter than a typical supernova; e.g. SN2006gy, SN2005gj, SN2005ap, SN2008fz, SN2003ma) have been a challenge to explain by standard models. For example, pair instability supernovae which are luminous enough seem to have too slow a rise time, and core collapse supernova do not seem to be luminous enough. We present an alternative scenario involving a quark-nova (QN), an explosive transition of the newly born neutron star to a quark star in which a second explosion (delayed) occurs inside the already expanding ejecta of a normal SN. The reheated SN ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic expansion losses, unlike the standard SN case. Our model is successfully applied to SN2006gy, SN2005gj, SN2005ap, SN2008fz, SN2003ma with encouraging fits to the light curves.
The NOAO Mosaic Imager Moving Object Pipeline
The NOAO Science Data Management division (SDM) developed and operates a pipeline to produce and archive calibrated data products from its two Mosaic Imagers; one at KPNO and one at CTIO. This occurs automatically for all programs, as well as part of a planned project to process and archive legacy observations. The pipeline is run as part of a data center after the observing program (aka run) is completed. Currently only unbinned 4-meter observations are processed. Recently a moving object pipeline has been added. This detects moving objects when the observing program includes multiple overlapping exposures in a night or block of nights. The algorithm is to stack the exposures, difference each exposure relative to the stack, detect sources in the difference, and finally search for the signature of a moving object from the catalogs of difference sources. There are a number of steps in the search though in its simplest terms the search is for multiple detections along a nearly linear path on the sky. This contribution describes the method in more detail, the challenges of excluding the much larger class of transient instrumental sources (cosmic rays, crosstalk, scattered light, etc), and provides some example detections. Because this is a serendipitous search using whatever observations are taken by heterogenous programs it is difficult to characterize the depth and completeness of the detections. Also it is rare that multiple night detections are produced. One driver for the development of the NOAO Mosaic pipeline was to someday provide a quick reduce and transient alert pipeline for observers at the telescope. I gratefully acknowledge the sabbatical time granted by NOAO during which the moving object pipeline developed.