Stockdale, Weiler, et al.: A Bright Radio Future for Core Collapse Supernovae
1. Prior to explosion, a supernova progenitor slowly loses significant amounts of its hydrogen envelope in a stellar wind. After the explosion, the blastwave interacts with this wind producing synchrotron emission. A year of radio observations allows us to probe the progenitor evolution for a thousand years. The EVLA represents an order of magnitude improvement in our ability to explore the pre-explosion lives of a significantly large population of supernova progenitor stars. It will allow us to move beyond the crude optical classifications and develop a deeper physical understanding of how massive stars live and die.
Matthews et al.: VLA/EVLA Imaging of HI in CSEs3. The asymptotic giant branch (AGB) stage of late stellar evolution is characterized by copious mass-loss in the form of cool, low-velocity winds. The material ejected from AGB stars forms extensive circumstellar envelopes (CSEs), up to a parsec or more in diameter. During the past few years, our group has been using the VLA/EVLA to study the mass-loss histories of evolved stars through a previously little-used observational tracer: the HI 21-cm line. Because HI is not destroyed by the interstellar radiation field, it can probe CSEs at significantly larger distances from the star than molecular lines, thereby probing stellar mass-loss over very extended timescales. The distribution and kinematics of HI also supplies unique information on the interaction between CSEs and their interstellar environments. I will describe some recent results from our ongoing work, including the discovery of extended HI "tail" from Mira as well as disk- and shell-like features associated with other nearby AGB stars. I will also highlight prospects for future EVLA studies.
Miodiszewski, Rupen, & Dhawan: Stepping over the edge: detecting the afterlife of stars with the EVLA5. The EVLA continuum sensitivity will be an improvement of a factor of ten over the VLA. The remnants of stellar death, white dwarfs, neutron stars and black holes, tend to be on the edge of detectability in the radio, so that even if they are detected it is difficult to study them well, except for the handful of objects that are pathologically bright. The increased sensitivity will allow both the study of known, but poorly sampled objects, like neutron star X-ray binaries and novae, as well as objects that are too faint to detect currently such as faint X-ray transients and single black holes. In other words, the EVLA will enable both the discovery and analysis of full samples of different types of degenerate objects but also a more detailed examination of individual objects.
Kasliwal: The Palomar Transient Factory (Invited)6. The Palomar Transient Factory (PTF), a new wide-field dedicated survey for optical transients, is on-track to be fully commissioned by June 2009. We have already discovered over three dozen transients in searching less than six nights of data. PTF's key strength is in its built-in unbiased discovery-followup approach. We expect to find thousand(s) of supernovae annually by charting the sky at 5-day cadence. We will also systematically probe the local universe (at 1-day cadence) for transients in the gap between novae and supernovae. The opportunity for EVLA follow-up of the most intriguing PTF transients is exciting.
Brown & Harper: EVLA Continuum Studies of Red Giant and Supergiant Winds7. EVLA studies of red giants and supergiants will provide new physical insights into their wind physics, enabled by its order of magnitude increase in sensitivity and improved long wavelength coverage. Combining UV wind velocity diagnostics with EVLA thermal radio flux constraints will allow simultaneous mapping out of the advection dominated wind ionization and gas temperature profiles as a function of radius. These can then be used to study potential wind driving mechanisms. These studies require either integrated flux density measurements over the full frequency range available to the EVLA, and/or spatially-resolved imaging of the largest stars.
Kothes: Probing Interstellar Magnetic Fields with Supernova Remnants8. Expanding supernovae compress their ambient magnetic field; consequently we can use SNRs as magnifyiers for interstellar magnetic fields. I will describe simple simulations to determine observable characteristics of mature SNRs and how we can exploit these to gain information about large-scale magnetic fields in our Galaxy and electron acceleration at supernova shocks. Two examples will be discussed. The high latitude SNR DA530 probes the magnetic field in the interface region between Galactic halo and Galactic plane. The anti-centre SNR G182.4+4.3 may help to decide whether the large-scale magnetic field of our Galaxy is azimuthal or following a spiral arm pattern.
Dhawan: X-Ray Binaries with the EVLA: Lines in disks, winds & outflows ?10. Microquasars, and their parents the X-ray binaries, present a range of opportunities for studies of accretion and outflow. WIDAR will serve up a spectrum in every bite so we might expect a feast of lines, from molecules in the outer circumbinary disks to recombination lines from photoionized regions, to masers in the inner Keplerian disks. However, the inner accretion regions of XRB are an order of magnitude hotter than the molecular tori around AGN where megamasers are found. The question for the assembled experts is what to look for and where, and how to interpret what we may see.
Soderberg: Revealing Radio Faint Supernovae with EVLA (Invited)11. Radio observations of young supernovae provide unique diagnostics on the fastest ejecta and local explosion environment (within 1 pc, enriched by the progenitor mass loss history). The current sensitivity of the VLA restricts the detectability of SNe to include only those expanding into dense environments (e.g. Type II). With the improved sensitivity of the EVLA, we will be able to probe the radio emission from even those SNe expanding into low density environs including Type Ibc and, even more excitingly, Type Ia supernovae. These measurements will provide crucial clues as to the nature of the progenitor systems.
Berger: Properties of Magnetic Fields in Low Mass Stars and Brown Dwarfs13. Over the past few years we have used the VLA to demonstrate the existence of magnetic fields at the bottom of the main sequence and beyond, and to measure the field properties. In this talk I will review the current state of radio magnetic field observations, and discuss the crucial impact that EVLA will have for this study.
Hofner: Radio Continuum Studies of Massive Protostars14. Candidates for massive protostars are selected by high FIR luminosity in the absence of radio continuum emission. However, when observed at sub-mJy sensitivity radio continuum emission is readily detected toward these objects. In this talk I will summarize recent efforts of detection of radio continuum toward massive protostars, discuss models which attempt to explain the emission, and what can be learned from these observations. With both the EVLA and e-MERLIN nearing completion much progress in this research area is expected in the near future.
Loinard: Proper Motions of Thermal Radio Sources (Invited)15. Compact radio sources are often present in young stellar objets. They can be associated with HII regions, accretion disks, jets, or the active magnetospheres of the stars themselves. Multi-epoch (E)VLA observations can be used to track the motion of these radio sources, and therefore provide valuable information on the structure and evolution of young systems. In this talk, I will illustrate the potential of multi-epoch radio observation with three specific examples: the BN/KL region, the famous young star T Tauri, and the very young Solar-type protostar IRAS 16293-2422. These cases will exemplify the range of situations that can be encountered and studied with multi-epoch data: identification of high-velocity run-away stars, mass determination through orbital motion tracking, and spectacular bipolar jet ejections. I will end my talk by mentioning what might become possible with the highly increased continuum sensitivity of the EVLA.
Cordes, Deneva, Lazio: A Program for Finding and Using Pulsars to Probe Sgr A*16. Pulsars in the star cluster surrounding Sgr A* can provide unique opportunities for probing the environs and spacetime of the nearest massive black hole and for studying stellar evolution and plasmas in the region. This talk will present the motivating astrophysics and fundamental physics for a survey program with follow-up timing. Radio-wave scattering presents severe obstacles for both the survey and timing parts of the program. We will discuss recent successes in finding pulsars in the 2 to 5 GHz range using the Green Bank and Parkes telescopes that demonstrate the existence of a GC population of neutron stars. We will discuss the prospects for using the EVLA for finding pulsars in close orbits around Sgr A* in blind surveys and targeted searches. The ability to move to higher frequencies with high sensitivity allows the scattering obstacles to be largely mitigated, so the EVLA can be used to great success in this area.
Linsky & Yang: Magnetic Fields on Brown and M Dwarfs (Poster)17. Brown dwarfs differ from M dwarfs in mass, effective temperature, internal structure, and photospheric ionization. Do these differences produce different magnetic field structures and the resultant magnetically-powered phenomena including UV and X-ray emission, flares, and nonthermal radio emission? Only a few VLA and X-ray observations of brown dwarfs are available, but the EVLA can greatly increase our understanding of nonthermal radio emission, both slowly variable gyrosynchrotron emission and rapidly variable coherent emission. We will also describe our upcoming survey of ultraviolet emission from brown dwarfs with the new COS instrument on HST.
Ransom: Pulsar Science with the EVLA (Invited)18. While the VLA has not been particularly well known for its pulsar science, the EVLA just might change that. The dramatic improvements in bandwidth, dynamic range, and correlator capabilities will make the EVLA one of the world's best telescopes for high precision pulsar timing and astrometry. In addition, while unique targeted pulsar searches will be possible early on, with expected improvements in correlator throughput and data handling capabilities, as well as the potential E-array configuration, the EVLA could undertake a very sensitive survey of a large fraction of the sky, using antenna-array techniques that will be essential for the planned pulsar surveys of the next 20 years.
Richards et al.: The Role of e-MERLIN+EVLA in Resolving Evolved Stars and Their Mass-Loss Mechanisms19. The only distant star ever imaged in detail is Betelgeuse (VLA and MERLIN). The EVLA plus e-MERLIN will resolve many more AGB and RSG, following the pioneering work of Reid & Menten. Multi-frequency monitoring can track photospheric disturbances and relationships between convection cells and clumpy mass loss. MERLIN has shown that water maser cloud size scales with stellar mass; the EVLA, VLBA, e-MERLIN, EVN, VLTI and ALMA will establish where these clouds form and trace their evolution in the wind, through maser species and dust. e-MERLIN will also complement the EVLA in resolving phenomena such as binary mass transfer/wind collimation.
Melis et al.: Grain Growth and Sedimentation in Protoplanetary Disks (Poster)21. Current theories require the interstellar grains that initially populate protostellar disks to be gradually assembled into larger particles, then planetesimals, and eventually planets. VLA observations are only capable of probing a handful of protoplanetary disks at 7mm and beyond, a regime that is critical for testing these theories through investigating grain growth and spatially-dependent dust properties. We present VLA results, past and present, exhibiting current capabilities at detecting and resolving protoplanetary disks. We then discuss advances in this exciting area of research that will be possible with the new capabilities of the EVLA.
Mason: VLA, GMRT, and Optical Observations of the Magnetic Cataclysmic Variable AR UMa22. I will introduce the general classes of cataclysmic variables, including polars, intermediate polars and non-magnetic CVs and I will present results from a multiple wavelength campaign to observe the polar AR UMa. This magnetic cataclysmic variable star contains the highest magnetic field of any known accreting white dwarf. Radio emission from AR UMa occurs even when there is little or no accretion onto the white dwarf. I will present models for the emission and discuss the constraints that observations currently place on models. Lastly, I discuss the potential impact that the EVLA will have on cataclysmic variable stars studies.
Irwin & Henriksen: Star Formation Activity and Disk-Halo Outflows in Nearby Galaxies24. While galaxy halos and outflows have been indirectly related to star forming activity in underlying disks, the resolution and sensitivity of existing instruments have not been sufficient to directly link the two. This paper will investigate possible new opportunities for exploring the connection between star formation activity, the propagation of CRs, magnetic fields and disk-halo outfows, using the EVLA.
Araya, Hofner, Goss, Kurtz: Periodic Maser Flares (Poster)28. We report the discovery of (quasi)periodic formaldehyde maser flares from a young massive stellar object. The periodicity of the flares is ~235 days. We also discovered simultaneous variability of the H2CO maser and one CH3OH 6.7GHz maser component. High angular resolution observations show that the masers are in different locations, which indicates that the masers have the same excitation mechanism. The data presented here together with the detection of other periodic CH3OH masers, show that the masers are probing detailed and predictable physical phenomena associated with massive star formation, perhaps due to pulsations of massive protostars.
Menten: Circumstellar Envelopes (Invited)32. The EVLA will allow studies of circumstellar material on all scales with resolutions matching the sizes of stellar photospheres (for nearby objects) to the those of expanding outflows. The greatly enhanced spectral line capability afforded by the WIDAR correlator will not only allow observations of tens of km/s wide spectra with adequate (sub-km/s) velocity resolution, but also imaging of many lines simultaneously. Imaging of vibrationally excited lines from many species will yield unique chemical information on the hottest gas before it depletes into dust grains and partakes in the outflow. The EVLA's flexibility and speed will allow surveys of tens of thousands of stars for maser emission, greatly increasing kinematic information for various stellar populations.
Forbrich: Multi-wavelength observations and Variability of YSOs (Invited)33. Young Stellar Objects can now routinely be observed in a wide wavelength range, including in X-rays and the mid-infrared range. Like pieces in a jigsaw puzzle, information from these very different regimes can be combined to yield a more complete picture of the underlying physics in these objects. The capabilities of particularly X-ray and infrared observatories have evolved considerably in recent times, resulting in a better understanding of YSOs at these wavelengths than at radio wavelengths. In the context of multi-wavelength observations, I will discuss radio properties of YSOs and how the EVLA will catch up and again become an important part of multi-wavelength research on (very) Young Stellar Objects.
Miller-Jones, Maccarone, Migliari: Fast Variablity from Faint Radio Jets in X-Ray Binaries (Invited)34. Certain classes of X-ray binary systems exhibit fast variability at radio wavelengths. The unparalleled sensitivity of the EVLA will provide high time-resolution radio lightcurves of such sources, whose intrinsic faintness has hitherto precluded such studies. I will discuss how the frequency-dependence of short-timescale variability can be used to probe the jets in quiescent black hole systems on spatial scales smaller than can be resolved by VLBI, and outline how correlations between rapid radio and X-ray variability can provide insights into the accretion/ejection connection and the cause of spectral state transitions in the rapidly variable Z-source neutron star X-ray binaries.
Umana: The LBV Phenomenon: Towards a Better Understanding of Massive Stars Evolution. (Invited)35. Luminous Blue Variables (LBVs) are luminous, evolved massive stars, which undergo episodes of mass-loss, leading to the formation of extended circumstellar nebulae (LBVN). They represent a relatively short phase of massive stars evolution, between core-hydrogen burning O-type stars and helium burning Wolf-Rayet stars and are quite rare in our Galaxy. The study of the geometry and of the physical properties of stellar ejecta around LBVs is very important as LBV winds constitute a major contributor of processed material (gas+dust) and mechanical energy to the ISM. Moreover, since LBVs are SN progenitors, the structure of their ejecta may also influence the geometry of SN remnants. Finally, the analysis of the nebula associated to a LBV can be used to recover the mass-loss history of the central object, allowing to estimate the total amount of mass lost during the LBV phase. A better understanding of the LBV phenomenon requires high-resolution, multi wavelength maps, tracing the different emitting components coexisting in the stellar ejecta: the ionized/neutral/molecular gas and the dust. The study of such components provides two kind of information: current mass-loss, via direct observations of stellar winds (ionized gas component), and mass loss history of the central star, by analysis of the neutral/molecular gas and dust component/s. We will illustrate how the EVLA capabilities would strongly contribute to this field and how a synergistic use of different instrumentation would provide a detailed knowledge of the gas and dust distribution. This would allow to evaluate the total (gas+dust) mass of the nebula, to point out the presence of different shells, related to different mass-loss episodes, to provide observational evidences of mutual interaction between gas and dust components for a better understanding of the cause of the observed morphology of the nebulae.
Zapata: Tracing the Evolutionary Phases of Early O-type Protostars in the W51-IRS2 Cluster36. I will present the results of recent radio observations using the Submillimeter Array and the Very Large Array toward the young massive cluster W51 IRS2. These observations revealed a marked evolution sequence within some O-type protostars in the cluster. Whereas some massive protostars present evidence of dusty circumstellar disks, powerful molecular outflows, and strong molecular emission from rings, other present, hyper- and ultra- compact HII regions and bright infrared sources with not or faint signs of outflow activity. This result suggests that this type of stars could be formed in a similar way as low-mass stars and that mechanisms, such as mergers of low- and intermediate- mass stars, might be not necessary for forming very massive stars.
Cerrigone, Umana, Trigilio: The EVLA and the transition from post-AGB stars to Planetary Nebulae37. Planetary Nebulae (PNe) are the product of evolution of intermediate-mass stars. The shaping of PN envelopes appears to be quite challenging, because of the various morphologies observed. It is likely that most of the shaping occurs very early after the AGB, therefore post-AGB stars are fundamental to understand this evolutionary phase. Although the hot central star develops a hard radiation field (i.e., onset of the PN phase), the ionized and neutral components in PNe are usually observed to be well mixed. With its enhanced sensitivity, the EVLA will find newly ionized envelopes in post-AGB stars, thus allowing to trace the evolution after the ionization starts. Also, its angular resolution will tell us to what extent the different components match in spatial distribution. Complementary observations from other facilities such as ALMA (cold dust) and JWST (hot dust) will improve our knowledge of these intriguing astrophysical targets.
Osten: The EVLA at the Bottom of the Main Sequence (Invited)38. The VLA revolutionized our understanding of radio emission on cool stars, and has given us a glimpse of interesting behavior in substellar objects. I will review the current status of radio emission from brown dwarfs, how that fits in with studies at other wavelengths, and what prospects the EVLA holds for extending our knowledge to cooler and younger objects.
Lim: Observational Tests of Binary/Multiple Protostellar Formation Models39. Most Sun-like stars form as binary or multiple systems. Theoretical models suggest that such systems most likely form through fragmentation of dense molecular cores. In these models, the protostars are predicted to orbit in the same direction as the rotation of their surrounding circumsystem material (pseudodisk), and have circumstellar disks aligned with their surrounding pseudodisk. We demonstrate from VLA+PT observations that the two main protostellar components in L1551 IRS5 exhibit just these properties, thus providing the first direct observational support for fragmentation. The EVLA+PT will make possible study of many more such systems, and test the prediction that the individual protostellar components accrete through matter streams that penetrate a central gap driven into their surrounding material.
Maccarone: Compact Binary Stars (Invited)40. I will review the current status of radio observations of binaries containing compact object accretors. I will then discuss the prospects for the EVLA to improve our understanding of these objects by allowing us to observe black hole X-ray binaries at the lowest fractions of the Eddington luminosity; to obtain high signal-to-noise observations of the radio emission from neutron star and white dwarf binaries; and to open up studies of extragalactic X-ray binaries in the radio.
Rodriguez: EVLA Studies of Young Stellar Objects (Invited)42. The growth of a forming star takes place by accretion from the surrounding dense medium, facilitated by a circumstellar disk. But at the same time the forming system produces collimated outflows of gas that remove excess angular momentum and magnetic flux. In this talk, I will review recent observations with the VLA and discuss some areas in which the EVLA should greatly improve our understanding of this phenomenon.
Chomiuk & Wilcots: A Universal Luminosity Function for Radio Supernova Remnants43. We explore the supernova remnant (SNR) luminosity function (LF) at 20 cm in 19 nearby galaxies ranging from the SMC to Arp 220. The radio LF constrains SNR evolution, diffusive shock acceleration (DSA) and magnetic field amplification (MFA) in more evolved remnants (at or after the Sedov time). We find that the LF is well fit by a power law that has constant index and scaling that depends linearly on star formation rate. It appears that radio supernova remnant populations are strikingly invariant across a wide range of galaxies, and can be well fit with current models of DSA+MFA.
Bastian: Observations of the Sun and Heliosphere with the EVLA (Invited)45. The Sun is an ordinary star rendered extraordinary by its proximity. It confronts us with many of the fascinating problems found in more extreme forms on other stars: a magnetic dynamo, magnetic energy release in flares and coronal mass ejections, non-radiative heating, particle acceleration, and mass loss. The EVLA offers several capabilities that will allow new insights to be gained into the physics of the Sun and heliosphere. These capabilities include a greatly enhanced instantaneous RF bandwidth, access to a large and contiguous bandwidth, and an enormous increase in continuum sensitivity. These will be discussed briefly in the context of three specific scientific objectives: 1) the nature of magnetic energy release; 2) coronal magnetography; 3) the solar wind and space weather.
Guedel: Radio Emission from Cool Main-Sequence Stars (Invited)48. Continuous radio emission from cool main-sequence and subgiant stars was identified 3 decades ago, but the detection of radiation analogous to steady solar radio emission awaits the advent of higher sensitivity. Radio emission from stellar flares has been modeled successfully based on the solar analogy, but here narrow-band observations have usually limited its physical interpretation. Radio emission from planetary companions to cool stars has been out of reach of the VLA. I will review our knowledge of radio emission from cool stars and speculate what the EVLA may add to our understanding of magnetic fields, high-energy processes, and hot plasma on and around them.
DeLaney: Exciting Supernova Remnant Science with the EVLA (Invited)49. The increased sensitivity and larger bandwidth of the EVLA provides exciting possibilities for supernova remnant science. In this talk, I will concentrate on two science topics. 1. Low-frequency free-free absorption will be used to discover and study cold, unshocked ejecta in SNRs. The unshocked ejecta may be the dominant mass component in SNRs and will tell us about the dynamics of the explosion. 2. Rotation measure synthesis will be used to study magnetic fields by looking at a range of Faraday depths along the line of sight. We can "remove" depolarization and study turbulence in the supernova ejecta.
This page last updated on 2009 May 08 by Mark Claussen.