Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2019 ( 645 )

2018 ( 893 )

2017 ( 823 )

2016 ( 1171 )

Custom range...

Search Results: 1 - 10 of 480844 matches for " Paul A. Scowen "
All listed articles are free for downloading (OA Articles)
Page 1 /480844
Display every page Item
Mapping the Recent Star Formation History of the Disk of M51
Catherine C. Kaleida,Paul A. Scowen
Physics , 2010, DOI: 10.1088/0004-6256/140/2/379
Abstract: Using data acquired as part of a unique Hubble Heritage imaging program of broadband colors of the interacting spiral system M51/NGC 5195, we have conducted a photometric study of the stellar associations across the entire disk of the galaxy in order to assess trends in size, luminosity, and local environment associated with recent star formation activity in the system. Starting with a sample of over 900 potential associations, we have produced color-magnitude and color-color diagrams for the 120 associations that were deemed to be single-aged. It has been found that main sequence turnoffs are not evident for the vast majority of the stellar associations in our set, potentially due to the overlap of isochronal tracks at the high mass end of the main sequence, and the limited depth of our images at the distance of M51. In order to obtain ages for more of our sample, we produced model spectral energy distributions (SEDs) to fit to the data from the GALEXEV simple stellar population (SSP) models of Bruzual and Charlot (2003). These SEDs can be used to determine age, size, mass, metallicity, and dust content of each association via a simple chi-squared minimization to each association's B, V, and I-band fluxes. The derived association properties are mapped as a function of location, and recent trends in star formation history of the galaxy are explored in light of these results. This work is the first phase in a program that will compare these stellar systems with their environments using ultraviolet data from GALEX and infrared data from Spitzer, and ultimately we plan to apply the same stellar population mapping methodology to other nearby face-on spiral galaxies.
HST Observations of the Wolf-Rayet Nebula NGC 6888
Brian D. Moore,J. Jeff Hester,Paul A. Scowen
Physics , 2000, DOI: 10.1086/301389
Abstract: We present Hubble Space Telescope WFPC2 images of a portion of the bright northeast rim of NGC 6888, the nebular shell physically associated with the Wolf-Rayet star HD 192163. The exposures are taken in the light of Halpha 6563, [O III] 5007, and [S II] 6717,6731. The images are used to constrain models of the ionization structure of nebular features. From these models we infer physical conditions within features, and estimate elemental abundances within the nebula. The results of our analysis, together with the degree of small scale inhomogeneity apparent in the images, call into question the assumptions underlying traditional methodologies for interpretation of nebular spectroscopy. The thermal pressure of photoionized clumps is higher than the inferred internal pressure of the shocked stellar wind, implying that the current physical conditions have changed significantly over less than a few thousand years. These results are discussed within the context of published three-wind evolutionary scenarios for the formation of the nebula. We also discuss the nature of a back-illuminated radiative shock driven into the cavity surrounding NGC 6888.
Tod R. Lauer,S. M. Faber,Edward A. Ajhar,Carl J. Grillmair,Paul A. Scowen
Physics , 1998, DOI: 10.1086/300617
Abstract: WFPC-2 images are used to study the central structure of M31, M32, and M33. The dimmer peak, P2, of the M31 double nucleus is centered on the bulge to 0.1", implying that it is the dynamical center of M31. P2 contains a compact source discovered by King et al. (1995) at 1700 A. This source is resolved, with r_{1/2} approx0.2 pc. It dominates the nucleus at 3000 A, and is consistent with late B-early A stars. This probable cluster may consist of young stars and be an older version of the cluster of hot stars at the center of the Milky Way, or it may consist of heavier stars built up from collisions in a possible cold disk of stars orbiting P2. In M32, the central cusp rises into the HST limit with gamma approx0.5, and the central density rho_0>10^7M_sol pc^-3. The V-I and U-V color profiles are flat, and there is no sign of an inner disk, dust, or any other structure. This total lack of features seems at variance with a nominal stellar collision time of 2 X 10^10 yr, which implies that a significant fraction of the light in the central pixel should come from blue stragglers. InM33, the nucleus has an extremely steep gamma=1.49 power-law profile for 0.05" 2 10^6M_sol pc^-3, and the implied relaxation time is only ~3 X 10^6 yr, indicating that the nucleus is highly relaxed. The accompanying short collision time of 7 X 10^9 yr predicts a central blue straggler component quantitatively consistent with the strong V-I and B-R color gradients seen with HST and from the ground.
Scientific Objectives for UV/Visible Astrophysics Investigations: A Summary of Responses by the Community (2012)
Paul A. Scowen,Mario R. Perez,Susan G. Neff,Dominic J. Benford
Physics , 2013, DOI: 10.1007/s10686-013-9363-0
Abstract: Following several recommendations presented by the Astrophysics Decadal Survey 2010 centered around the need to define "a future ultraviolet-optical space capability," on 2012 May 25, NASA issued a Request for Information (RFI) seeking persuasive ultraviolet (UV) and visible wavelength astrophysics science investigations. The goal was to develop a cohesive and compelling set of science objectives that motivate and support the development of the next generation of ultraviolet/visible space astrophysics missions. Responses were due on 10 August 2012 when 34 submissions were received addressing a number of potential science drivers. A UV/visible Mission RFI Workshop was held on 2012 September 20 where each of these submissions was summarized and discussed in the context of each other. We present a scientific analysis of these submissions and presentations and the pursuant measurement capability needs, which could influence ultraviolet/visible technology development plans for the rest of this decade. We also describe the process and requirements leading to the inception of this community RFI, subsequent workshop and the expected evolution of these ideas and concepts for the remainder of this decade.
Galaxy Assembly and SMBH/AGN-growth from Cosmic Dawn to the End of Reionization
Rolf A. Jansen,Rogier Windhorst,James Rhoads,Sangeeta Malhotra,Daniel Stern,Robert O'Connell,Paul Scowen,Matthew Beasley
Physics , 2009,
Abstract: [abridged] We propose a tiered, UV--near-IR, cosmological broad- and medium-band imaging and grism survey that covers ~10 deg^2 in two epochs to m_AB=28, ~3 deg^2 in seven epochs to m_AB=28, and ~1 deg^2 in 20 epochs to m_AB=30 mag. Such a survey is an essential complement to JWST surveys (<~0.1 deg^2 to m_AB<~31 mag at lambda>1100nm and z>~8). We aim to: (1) understand in how galaxies formed from perturbations in the primordial density field by studying faint Ly\alpha-emitting and Lyman-break galaxies at 5.5<~z<~8 and trace the metal-enrichment of the IGM; (2) measure the evolution of the faint end of the galaxy luminosity function (LF) from z~8 to z~0 by mapping the ramp-up of PopII star formation, (dwarf) galaxy formation and assembly, and hence, the objects that likely completed the H-reionization at z~6; (3) directly study the lambda<91.2nm escape fractions of galaxies and weak AGN from z~4.0--2.5, when the He reionization finished; (4) measure the mass- and environment-dependent galaxy assembly process from z~5 to z~0, combining accurate (sigma_z/(1+z) <~ 0.02) photo-z's with spatially resolved stellar populations and kpc-scale structure for >~5x10^6 galaxies; (5) trace the strongly epoch-dependent galaxy merger rate and constrain how Dark Energy affected galaxy assembly and the growth of SMBHs; (6) study >~10^5 weak AGN/feeding SMBHs in the faint-end of the QSO LF, over 10 deg^2 and measure how the growth of SMBHs kept pace with galaxy assembly and spheroid growth, and how this process was shaped by various feedback processes over cosmic times since z~8. The proposed study is not feasible with current instrumentation but argues for a wide-field (>~250 arcmin^2), high-resolution (<~0.02--0.11 [300--1700 nm]), UV--near-IR imaging facility on a 4m-class space observatory.
A Systematic Study of the Stellar Populations and ISM in Galaxies out to the Virgo Cluster
Rolf A. Jansen,Paul Scowen,Matthew Beasley,John Gallagher,Robert O'Connell,Daniela Calzetti,Sally Oey,Rogier Windhorst,Robert Woodruff
Physics , 2009,
Abstract: We present a compelling case for a systematic and comprehensive study of the resolved and unresolved stellar populations, ISM, and immediate environments of galaxies throughout the local volume, defined here as D < 20 Mpc. This volume is our cosmic backyard and the smallest volume that encompasses environments as different as the Virgo, Ursa Major, Fornax and (perhaps) Eridanus clusters of galaxies, a large number and variety of galaxy groups, and several cosmic void regions. In each galaxy, through a pan-chromatic (160--1100nm) set of broad-band and diagnostic narrow-band filters, ISM structures and individual luminous stars to >~1 mag below the TRGB should be resolved on scales of <5 pc (at D <~ 20 Mpc, lambda ~ 800nm, for mu_I >~ 24 mag/arcsec^2 and m_{I,TRGB} <~ 27.5 mag). Resolved and unresolved stellar populations would be analyzed through color-magnitude and color-color diagram fitting and population synthesis modeling of multi-band colors and would yield physical properties such as spatially resolved star formation histories. The ISM within and around each galaxy would be analyzed using key narrow-band filters that distinguish photospheric from shock heating and provide information on the metallicity of the gas. Such a study would finally allow unraveling the global and spatially resolved star formation histories of galaxies, their assembly, satellite systems, and the dependences thereof on local and global environment within a truly representative cosmic volume. The proposed study is not feasible with current instrumentation but argues for a wide-field (>~250 arcmin^2), high-resolution (<~0.020"--0.065" [300--1000nm]), ultraviolet--near-infrared imaging facility on a 4m-class space-based observatory.
From Protostars to Planetary Systems : FUV Spectroscopy of YSOs, Protoplanetary Disks, and Extrasolar Giant Planets
Paul A. Scowen,Rolf Jansen,Matthew Beasley,Steve Desch,Alex Fullerton,Mark McCaughrean,Sally Oey,Debbie Padgett,Aki Roberge,Nathan Smith
Physics , 2009,
Abstract: The last two decades have seen remarkable progress in our long-standing goal of determining the abundance and diversity of worlds in the Galaxy. Understanding of this subject involves tracing the path of interstellar material from dense cloud cores, to young stellar objects, protoplanetary disks, and finally extrasolar planets. Here we discuss the critical information provided on these objects by point-source far-ultraviolet spectroscopy with a large aperture, high resolution spectrograph of a large sample of unique protostellar and protoplanetary objects that will leverage our existing knowledge to lay out a path to new and powerful insight into the formation process. We lay out a systematic case of coordinated observations that will yield new knowledge about the process of assembly for both protostellar and protoplanetary systems - that addresses specific uncertainties in our current knowledge and takes advantage of potential new technologies to acquire the data needed.
Understanding Global Galactic Star Formation
Paul A. Scowen,Rolf Jansen,Matthew Beasley,Daniela Calzetti,Steven Desch,John Gallagher,Mark McCaughrean,Robert O'Connell,Sally Oey,Deborah Padgett,Aki Roberge,Nathan Smith
Physics , 2009,
Abstract: We propose to the community a comprehensive UV/optical/NIR imaging survey of Galactic star formation regions to probe all aspects of the star formation process. The primary goal of such a study is to understand the evolution of circumstellar protoplanetary disks and other detailed aspects of star formation in a wide variety of different environments. This requires a comprehensive emission-line survey of nearby star-forming regions in the Milky Way, where a high spatial resolution telescope+camera will be capable of resolving circumstellar material and shock structures. In addition to resolving circumstellar disks themselves, such observations will study shocks in the jets and outflows from young stars, which are probes of accretion in the youngest protoplanetary disks still embedded in their surrounding molecular clouds. These data will allow the measurement of proper motions for a large sample of stars and jets/shocks in massive star-forming regions for the first time, opening a new window to study the dynamics of these environments. It will require better than 30 mas resolution and a stable PSF to conduct precision astrometry and photometry of stars and nebulae. Such data will allow production of precise color-color and color magnitude diagrams for millions of young stars to study their evolutionary states. One can also determine stellar rotation, multiplicity, and clustering statistics as functions of environment and location in the Galaxy. For the first time we can systematically map the detailed excitation structure of HII regions, stellar winds, supernova remnants, and supershells/superbubbles. This survey will provide the basic data required to understand star formation as a fundamental astrophysical process that controls the evolution of the baryonic contents of the Universe.
Large Focal Plane Arrays for Future Missions
Paul A. Scowen,Shouleh Nikzad,Michael Hoenk,Ivair Gontijo,Andrew Shapiro,Frank Greer,Todd Jones,Suresh Seshadri,Blake Jacquot,Steve Monacos,Doug Lisman,Matthew Dickie,Jordana Blacksberg
Physics , 2009,
Abstract: We outline the challenges associated with the development and construction of large focal plane arrays for use both on the ground and in space. Using lessons learned from existing JPL-led and ASU/JPL partnership efforts to develop technology for, and design such arrays and imagers for large focal planes, we enumerate here the remaining problems that need to be solved to make such a venture viable. Technologies we consider vital for further development include: (1) architectures, processes, circuits, and readout solutions for production and integration of four-side buttable, low-cost, high-fidelity, high-performance, and high-reliability CCD and CMOS imagers; (2) modular, four-side buttable packaging of CCD/CMOS imagers; (3) techniques and hardware to test and characterize the large number of chips required to produce the hundreds of flight-grade detectors needed for large focal-plane missions being conceived at this time; (4) ground based testbed needs, such as a large format camera mounted on a ground-based telescope, to field test the detectors and the focal plane technology solutions; and (5) validation of critical sub-components of the design on a balloon mission to ensure their flight-readiness. This paper outlines the steps required to provide a mature solution to the astronomical community with a minimal investment, building on years of planning and investments already completed at JPL.
The Magellanic Clouds Survey: a Bridge to Nearby Galaxies
Paul A. Scowen,Rolf Jansen,Matthew Beasley,Daniela Calzetti,Alex Fullerton,John Gallagher,Mark McCaughrean,Robert O'Connell,Sally Oey,Nathan Smith
Physics , 2009,
Abstract: We outline to the community the value of a Magellanic Clouds Survey that consists of three components: I) a complete-area, high resolution, multi-band UV-near-IR broadband survey; II) a narrowband survey in 7 key nebular filters to cover a statistically significant sample of representative HII regions and a large-area, contiguous survey of the diffuse, warm ISM; and III) a comprehensive FUV spectroscopic survey of 1300 early-type stars. The science areas enabled by such a dataset are as follows: A) assessment of massive star feedback in both HII regions and the diffuse, warm ISM; B) completion of a comprehensive study of the 30 Doradus giant extragalactic HII region (GEHR); C) development and quantitative parameterization of stellar clustering properties; D) extensive FUV studies of early-type stellar atmospheres and their energy distributions; and E) similarly extensive FUV absorption-line studies of molecular cloud structure and ISM extinction properties. These data will also allow a number of additional studies relating to the underlying stellar populations.
Page 1 /480844
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.