[show abstract][hide abstract] ABSTRACT: BigBOSS is a Stage IV ground-based dark energy experiment to study baryon
acoustic oscillations (BAO) and the growth of structure with a wide-area galaxy
and quasar redshift survey over 14,000 square degrees. It has been
conditionally accepted by NOAO in response to a call for major new
instrumentation and a high-impact science program for the 4-m Mayall telescope
at Kitt Peak. The BigBOSS instrument is a robotically-actuated, fiber-fed
spectrograph capable of taking 5000 simultaneous spectra over a wavelength
range from 340 nm to 1060 nm, with a resolution R = 3000-4800.
Using data from imaging surveys that are already underway, spectroscopic
targets are selected that trace the underlying dark matter distribution. In
particular, targets include luminous red galaxies (LRGs) up to z = 1.0,
extending the BOSS LRG survey in both redshift and survey area. To probe the
universe out to even higher redshift, BigBOSS will target bright [OII] emission
line galaxies (ELGs) up to z = 1.7. In total, 20 million galaxy redshifts are
obtained to measure the BAO feature, trace the matter power spectrum at smaller
scales, and detect redshift space distortions. BigBOSS will provide additional
constraints on early dark energy and on the curvature of the universe by
measuring the Ly-alpha forest in the spectra of over 600,000 2.2 < z < 3.5
BigBOSS galaxy BAO measurements combined with an analysis of the broadband
power, including the Ly-alpha forest in BigBOSS quasar spectra, achieves a FOM
of 395 with Planck plus Stage III priors. This FOM is based on conservative
assumptions for the analysis of broad band power (kmax = 0.15), and could grow
to over 600 if current work allows us to push the analysis to higher wave
numbers (kmax = 0.3). BigBOSS will also place constraints on theories of
modified gravity and inflation, and will measure the sum of neutrino masses to
0.024 eV accuracy.
[show abstract][hide abstract] ABSTRACT: The Wide-Field Infrared Survey Telescope mission (WFIRST) is the Decadal Survey's highest recommended space mission. Its three mandates are (1) to study dark energy via measurement of the expansion history of the universe and the growth of large-scale structure, thereby providing tight constraints on the equation of state of dark energy and test the validity of general relativity; (2) to conduct intensive imaging of selected regions for exoplanet microlensing; and (3) to provide a general purpose surveying capability for the near infrared waveband. During the coming year, a Science Definition Team will be empaneled to prioritize the mission payload features and operations plans. To begin the misson definition process, we present four alternative WFIRST concepts and compare their quantitative science yields based on survey rates. We contrast these with alternative missions that have been proposed previously. Our WFIRST calculations are based on a newly developed unobscured focal TMA optical concept offering distinct simultaneous focal lengths for imaging and spectroscopy, reported in a companion poster by Sholl et al, and on a large modular focal plane concept reported on on a companion poster by Jelinsky et al. With these advances, we show that WFIRST can deliver a science yield superior to previously discussed dark energy and exoplanet missions.
[show abstract][hide abstract] ABSTRACT: We present a list of 534 objects detected jointly in the Extreme Ultraviolet Explorer (EUVE) 100 Å all-sky survey and in the ROSAT X-Ray Telescope 0.25 keV band. The joint selection criterion permits use of a low count rate threshold in each survey. This low threshold is roughly 60% of the threshold used in the previous EUVE all-sky surveys, and 166 of the objects listed here are new EUV sources, appearing in neither the Second EUVE Source Catalog nor the ROSAT Wide Field Camera Second Catalog. The spatial distribution of this all-sky catalog shows three features: an enhanced concentration of objects in Ursa Major, where the Galactic integrated H I column reaches its global minimum; an enhanced concentration in the third quadrant of the Galaxy (lII from 180° to 270°) including the Canis Major tunnel, where particularly low H I columns are found to distances beyond 200 pc; and a particularly low number of faint objects in the direction of the fourth quadrant of the Galaxy, where nearby intervening H I columns are appreciable. Of particular interest is the composition of the 166 detections not previously reported in any EUV catalog. We offer preliminary identifications for 105 of these sources. By far the most numerous (81) of the identifications are late-type stars (F, G, K, M), while 18 are other stellar types, only five are white dwarfs (WDs), and none are extragalactic. The paucity of WDs and extragalactic objects may be explained by a strong horizon effect wherein interstellar absorption strongly limits the effective new-source search volume and, thereby, selectively favors low-luminosity nearby sources over more luminous but distant objects.
The Astrophysical Journal Supplement Series 01/2009; 108(2):545. · 16.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: A compact far ultraviolet (FUV) spectrograph has been developed and applied to space observation on a micro-satellite. The dual channel imaging spectrograph utilized two micro-channel plate (MCP) detectors with a single crossed delay line (XDL) anode to record photon arrival events. The unconventional anode design allows for the use of a single set of position encoding electronics for both detector fields, thereby reducing the size, weight, and power of the associated electronics. The ground and on-orbit performance tests verified the successful application of the system for astrophysical observations. In this note, we report the design, the development, and the test results of the system, focusing on the XDL anode system.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 06/2007; 575(3):527-531. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The EURD instrument has been designed to measure diffuse emission in the extreme ultraviolet (350–1100 Å). This new design
provides an unprecedented 4–5 Å spectral resolution and 200 photons/sec/cm2/sr sensitivity after only 100 hours of observations. One of the goals of this project is to search for spectral lines of
highly ionized species from the high temperature component (105 – 106 K) of the interstellar medium that fills the Local Bubble. It is expected that EURD will detect lines due to a thermalized
hot component of the interstellar medium, and it will also provide critical diagnostics of the physical properties of this
gas. With EURD data we could also detect a spectral line due to the decay of massive neutrinos as well as study oxygen lines
from the upper atmosphere airglow. EURD is on board the Spanish MINISAT-01 satellite.
[show abstract][hide abstract] ABSTRACT: We compare and contrast the Korsch (1972) full-field three-mirror anastigmat telescope (TMA) to the Korsch (1977) annular-field TMA. Both TMAs offer flat fields with comparably good aberration correction and comparably good telephoto advantage. Both offer good accessibility of the focal plane. The advantages of the FFTMA are its extremely uniform focal length over its field, its nearly telecentric final focus, and the fact that there is no hole in the center of its field. The advantages of the AFTMA are its complete accessible cold stop (essential if a warm telescope is to be used to image the sky at near-IR wavelengths) and its low sensitivity to mirror location error. Either alternative can deliver diffraction-limited visible-wavelength images over a one degree diameter field with a two meter aperture.
[show abstract][hide abstract] ABSTRACT: Global imaging of the heliosphere with ultra-high spectral resolution at 30.4 nm would open a new window on important physical processes in the heliosphere and at its galactic frontier. The radiation reaching an observer includes glow of the interstellar plasma beyond the heliopause, glow of pickup ions in the solar wind, characteristic emissions produced by charge exchange of solar wind alpha-particles on interplanetary atomic hydrogen, and emissions of hot plasmas in the Local Bubble. Global maps will reveal asymmetry of the heliopause and allow monitoring of the three-dimensional flow pattern of the solar wind, including in the regions over the sun's poles. Recent feasibility studies have shown a promising way of meeting challenges of developing the enabling instrumentation. Lunar space would provide an ideal platform for global imaging of the heliosphere, minimizing the interference of the magnetosphere and geocorona and simplifying operations and thermal and attitude control of spacecraft. The Earth-Moon libration points have been considered, but lunar surface observatory offers unique advantages for performing 30.4-nm imaging. The Return to the Moon Program will enable remote exploration of the solar system galactic frontier in EUV and visualize the evolution of the solar wind global flow pattern during the solar cycle.
[show abstract][hide abstract] ABSTRACT: Precision near infrared (NIR) measurements are essential for the next
generation of ground and space based instruments. The SuperNova
Acceleration Probe (SNAP) will measure thousands of type Ia supernovae
up to a redshift of 1.7. The highest redshift supernovae provide the
most leverage for determining cosmological parameters, in particular the
dark energy equation of state and its possible time evolution. Accurate
NIR observations are needed to utilize the full potential of the highest
redshift supernovae. Technological improvements in NIR detector
fabrication have lead to high quantum efficiency, low noise detectors
using a HgCdTe diode with a band-gap that is tuned to cutoff at 1.7
μm. The effects of detector quantum efficiency, read noise, and dark
current on lightcurve signal to noise, lightcurve parameter errors, and
distance modulus fits are simulated in the SNAPsim framework. Results
show that improving quantum efficiency leads to the largest gains in
photometric accuracy for type Ia supernovae. High quantum efficiency in
the NIR reduces statistical errors and helps control systematic
uncertainties at the levels necessary to achieve the primary SNAP
[show abstract][hide abstract] ABSTRACT: To probe theoretical models of dark energy and predictions of the
expansion of the universe, observational techniques are needed that
offer reduced random and systematic errors. The SuperNova Acceleration
Probe (SNAP) is a spaceborne observatory to study dark energy using type
Ia supernovae and gravitational weak lensing. We have baselined a
two-meter-class all-reflecting telescope of the annular-field three
mirror anastigmat type (Korsch 1977). The benefits of this configuration
are its large flat diffraction-limited field of view (1.6 degrees =
620mm diameter) and its compact overall dimensions. A recent
thermomechanical study showed that point spread function variability
will not be a significant limitation to weak lensing shear
determination. Two industry studies are under way to develop plans for
telescope fabrication and test to help guide the planning for the SNAP
We gratefully acknowledge the support by the Office of Science, U.S
Department of Energy, contract DE-AC03-76SF00098.
[show abstract][hide abstract] ABSTRACT: The He+ ion provides a valuable tracer of solar wind dynamics and the heliospheric boundary. Mapping the heliosphere in the 30.4 nm resonance line of the He+ ion with high spectral resolution will open access to the heliopause and reveal the three-dimensional flow of the solar wind. The emission fluxes are however faint, just a few mR, which poses a serious limitation on the mapping rate at high signal-to-noise ratio. We have developed a spectrometer configuration for narrowband EUV emission that offers important advantages over previous designs: high throughput (~1cps/mR), high resolution (several thousand), no moving parts, and modest instrument size and mass. The concept combines a conventional normal-incidence Rowland mount grating and an efficient multilayer coating, with a microchannel plate detector performing two dimensional photon counting. One key innovation is the use of a large-area multi-slit at the spectrometer entrance. This multislit is a one dimensional sequence of open and opaque zones, against which pattern the accumulated spectral image can be correlated to recover the incident spectrum. The other innovation is arranging that each member of the multislit group is curved in such a way that the off-plane grating aberrations (which extend and rotate the image of each object point) do not introduce significant wavelength broadening. The curved slit arrangement yields a large well-corrected image field, and a high throughput for diffuse emission is achieved. The curved-multislit Rowland spectrometer may have a variety of other applications sensing diffuse fluxes with high spectral resolution.
[show abstract][hide abstract] ABSTRACT: The glow of interstellar plasma and solar wind pickup ions and solar wind emissions at 30.4 nm provide a way of ex-ploring important physical processes in the heliosphere. Imaging the heliosphere at this wavelength with high spectral resolution will map the heliopause, probe pickup ions in the solar wind, and reveal the three-dimensional flow pattern of the solar wind, including in the regions over the sun's poles. The required high-throughput, high-resolution spectrome-ter for diffuse radiation should be able to measure 1 milli-Rayleigh irradiance in 10000 seconds with a 0.005-nm spec-tral resolution across pixels subtending a few degrees of celestial arc. The desired performance characteristics can be achieved by combining multiple entrance slits with an optimized spectrometer design. We present a concept of a space experiment to image the heliosphere at 30.4 nm and discuss the scientific rationale and required instrumentation.
[show abstract][hide abstract] ABSTRACT: The He+ ion provides a valuable tracer of solar wind dynamics and the
heliospheric boundary. Mapping the heliosphere from 1 AU in 30.4nm with
high spectral resolution will open access to the heliopause and reveal
the three-dimensional flow of the solar wind. The scattered and
emission fluxes are however faint, just a few milli-Rayleighs (mR),
which poses a serious limitation on the mapping rate at high
signal-to-noise ratio. We explore a spectrometer concept for narrowband
EUV emission that offers important advantages over previous designs:
high throughput (~1cps/mR), high spectral resolution (several thousand),
no moving parts, and modest instrument size and mass. The concept
combines a conventional normal-incidence Rowland mount grating and an
efficient multilayer coating, with a microchannel plate detector
performing two dimensional photon counting. One key innovation is the
use of a large-area multi-slit at the spectrometer entrance. This
multislit is a one dimensional sequence of open and opaque zones,
against which pattern the accumulated spectral image can be correlated
to recover the incident spectrum. The other innovation is arranging
that each member of the multislit group is curved in such a way that
the off-plane grating aberrations (which extend and rotate the image of
each object point) do not introduce significant wavelength broadening.
The curved slit arrangement yields a large well-corrected image field,
and a high throughput for diffuse emission is achieved. This
presentation concentrates on the design of the wide-field mount that
maximizes the working area populated by the slits. The curved-multislit
Rowland spectrometer will have a variety of other applications in
astrophysics, aeronomy, and space physics sensing diffuse fluxes with
high spectral resolution and sensitivity.
[show abstract][hide abstract] ABSTRACT: The Supernova / Acceleration Probe (SNAP) is a proposed space-based experiment designed to study the dark energy and alternative explanations of the acceleration of the Universe's expansion by performing a series of complementary systematics-controlled measurements. We describe a self-consistent reference mission design for building a Type Ia supernova Hubble diagram and for performing a wide-area weak gravitational lensing study. A 2-m wide-field telescope feeds a focal plane consisting of a 0.7 square-degree imager tiled with equal areas of optical CCDs and near infrared sensors, and a high-efficiency low-resolution integral field spectrograph. The SNAP mission will obtain high-signal-to-noise calibrated light-curves and spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A wide-field survey covering one thousand square degrees resolves ~100 galaxies per square arcminute. If we assume we live in a cosmological-constant-dominated Universe, the matter density, dark energy density, and flatness of space can all be measured with SNAP supernova and weak-lensing measurements to a systematics-limited accuracy of 1%. For a flat universe, the density-to-pressure ratio of dark energy can be similarly measured to 5% for the present value w0 and ~0.1 for the time variation w'. The large survey area, depth, spatial resolution, time-sampling, and nine-band optical to NIR photometry will support additional independent and/or complementary dark-energy measurement approaches as well as a broad range of auxiliary science programs. (Abridged) Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.gov
[show abstract][hide abstract] ABSTRACT: Observations with the Extreme Ultraviolet Explorer (EUVE) have shown the Coma Cluster to be a source of EUV emission in excess of that produced by X-ray gas in the cluster. We have reexamined the EUVE data on this cluster in an attempt to obtain clues as to the origin of this emission. We find two important new results. First, the ratio between the azimuthally averaged EUV excess emission and the ROSAT hard X-ray flux is constant as a function of distance from the cluster center outward. Second, a correlation analysis between the EUV excess emission and the X-ray emission shows that on a detailed level the EUV excess is spatially closely related to the X-ray emission. These findings contradict previous suggestions as to the underlying source of the diffuse EUV emission in Coma and provide important information in regard to the true source of this emission. We propose a new explanation for the source of this emission: inverse Compton scattering of microwave background photons by secondary electrons and positrons. We explore this possibility in some detail and show that it is consistent with all of the available observational evidence. The parent cosmic-ray protons may have been produced by any of a number of sources, including supernovae, active galaxies, galactic winds, and cluster formation shocks, but we believe that the most likely source is cluster formation shocks. If the EUV emission in the Coma Cluster is, in fact, the result of secondary electrons, this may be the only direct evidence for secondary electrons in the intracluster medium of a cluster of galaxies, since recent work suggests that secondary electrons may not be the cause of radio halos.
The Astrophysical Journal 04/2004; 605:168-178. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Supernova/Acceleration Probe (SNAP; http://snap.lbl.gov), a space mission planned for launch in 2009, will observe over 2000 Type Ia supernovae out to a redshift of z=1.7 in order to measure the equation of state of the Universe and its time derivative. In order to accomplish this goal, the supernova light curves must be accurately measured at a variety of wavelengths spanning the optical and near infrared. Furthermore, the fluxes measured in the optical and in the near infrared must be well calibrated relative to each other. The flux calibration of the SNAP instruments will be based upon a combination of spectrophotometric standards, including hot white dwarfs and solar analogs. Most current HST spectrophotometric standards have apparent magnitudes brighter than about V = 13. SNAP, however, will routinely measure objects fainter than V = 25 and, under normal operations, the SNAP imaging detectors will saturate for such bright standards. Clearly fainter standards are needed. To this end, we in the SNAP Calibration Group are currently pursuing a project to calibrate a set spectrophotometric standards in the SNAP North field down to V=19 using data from the Sloan Digital Sky Survey, the ARC 3.5m telescope, and the HST STIS and NICMOS instruments. Here, we describe this project and our initial results.
[show abstract][hide abstract] ABSTRACT: The Supernova/Acceleration Probe (SNAP; http://snap.lbl.gov) will
observe over 2000 Type Ia supernova. The photometric observations will
cover the wavelength range 0.35 - 1.7 microns, essentially the Johnson B
to Glass H filter range. These filters will allow coverage of the
supernovae out to a redshift of z=1.7. The filter set will be composed
of nine wideband filters, redshifted from the restframe. Due to the
"non-standard" design, calibration of the observations will require a
new system of standard stars.
We present our plans to develop the standard star network to support the
SNAP science mission. The science requirements for the program require
an accuarcy in color determination of 2% in the optical and 3% in the
near infrared. In turn, these requirements drive the precision of the
standard stars to be approximately one-half these uncertainties. While
that precision is not difficult for most standard star systems, our
flight detectors saturate at about V=19, requiring the SNAP standard
star network to be fainter than any other system currently in use.