Ryan McLean

THE ON-ORBIT PERFORMANCE OF THE GALAXY EVOLUTION EXPLORER

We report the first years on-orbit performance results for the Galaxy Evolution Explorer (GALEX), a NASA Small Explorer that is performing a survey of the sky in two ultraviolet bands. The instrument comprises a 50 cm diameter modified Ritchey-Chretien telescope with a 125 field of view, selectable imaging and objective-grism spectroscopic modes, and an innovative optical system with a thin-film multilayer dichroic beam splitter that enables simultaneous imaging by a pair of photon-counting, microchannel-plate, delay-line readout detectors. Initial measurements demonstrate that GALEX is performing well, meeting its requirements for resolution, efficiency, astrometry, bandpass definition, and survey sensitivity.

The galaxy evolution explorer

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer Mission planned for launch in Fall 2002, will perform the first Space Ultraviolet sky survey. Five imaging surveys in each of two bands (1350-1750Å and 1750-2800Å) will range from an all-sky survey (limit mAB~20-21) to an ultra-deep survey of 4 square degrees (limit mAB~26). Three spectroscopic grism surveys (R=100-300) will be performed with various depths (mAB~20-25) and sky coverage (100 to 2 square degrees) over the 1350-2800Å band. The instrument includes a 50 cm modified Ritchey-Chrétien telescope, a dichroic beam splitter and astigmatism corrector, two large sealed tube microchannel plate detectors to simultaneously cover the two bands and the 1.2 degree field of view. A rotating wheel provides either imaging or grism spectroscopy with transmitting optics. We will use the measured UV properties of local galaxies, along with corollary observations, to calibrate the UV-global star formation rate relationship in galaxies. We will apply this calibration to distant galaxies discovered in the deep imaging and spectroscopic surveys to map the history of star formation in the universe over the red shift range zero to two. The GALEX mission will include an Associate Investigator program for additional observations and supporting data analysis. This will support a wide variety of investigations made possible by the first UV sky survey.

The area of complete scotopic spatial summation enlarges with age

The maximal area of complete scotopic spatial summation (Riccos area) was determined for 50 subjects ranging in age from 19 to 87 yr. Increment thresholds were measured for 10-ms, 520-nm circular test lights of varying diameters that were superimposed and concentric with a 10 degrees, 640-nm circular background. The test lights were imaged in Maxwellian view along the horizontal meridian, 6 degrees nasal from a foveal fixation point. The results demonstrate a statistically significant enlargement of Riccos area with age. The average angular subtenses of Riccos areas for the ten youngest (mean = 26 yr) and ten oldest (mean = 75 yr) observers were approximately 48 and 69 arc min, respectively. Model simulations based on a series of optical transfer functions of the eye and varying degrees of intraocular light scatter for younger and older observers show that preneural factors cannot account for these results. Therefore changes in neural mechanisms must be invoked to explain the enlargement in the size of Riccos area under scotopic conditions.

Networked sensing systems for detecting people carrying radioactive material

The goal of the research described in this paper is to help prevent scenarios such as the following: a terrorist detonates a device that distributes radioactive material such as Cesium-137 or Cobalt-60 in an open space used for public sports events or demonstrations. This paper studies the efficacy of networks of static sensors on street lamps or similar infrastructures. This paper describes individual sensors, evaluates the benefits of networks of stationary sensors, and briefly discusses the potential value of integrated networks of wireless-equipped mobile security personnel with stationary radiation sensors and cameras. The paper presents mathematical analysis coupled with simulation results.

Long-Term Multiwavelength Observations of GRS 1758–258 and the Advection-dominated Accretion Flow Model

We present a long-term multiwavelength light curve of Galactic black hole candidate GRS 1758-258 by combining previously published and archival data from Granat, ROSAT, the Compton Gamma Ray Observatory, the Rossi X-Ray Timing Explorer, BeppoSAX, ASCA, EXOSAT, and the Very Large Array. In addition, we include the first spectral results from the balloon-borne Gamma-Ray Arcminute Telescope Imaging System (GRATIS). In light of divergent analyses of the 1991-1993 ROSAT observations, we have reanalyzed these data; we find that the soft X-rays track the hard X-rays and that the fits require no blackbody component—indicating that GRS 1758-258 did not go to the high state in 1993. We offer an interpretation of these long-baseline data based on the advection-dominated accretion flow (ADAF) model for a system with crit. We find that the 1990-1993 coeval hard and soft X-ray observations support the ADAF predictions. We discuss a new way to constrain black hole mass with spectral data and the ADAF theory and apply this technique to GRS 1758-258 to find M1 8-9 M☉ at an assumed distance of 8.5 kpc. Further investigations of the ADAF model allow us to evaluate the model critically against the 1996 data and flux-flux diagram of Barret, McClintock, & Grindlay and to understand the limits of the latters X-ray burster box.We present a long-term multi-wavelength light curve of Galactic black hole candidate GRS 1758–258 by combining previously published and archival data from GRANAT, ROSAT, CGRO, RXTE, BeppoSAX, ASCA, EXOSAT, and the VLA. In addition we include first spectral results from the balloon-borne Gamma-ray Arcminute Telescope Imaging System (GRATIS). In light of divergent analyses of the 1991–1993 ROSAT observations, we have re-analyzed these data; we find the soft X-rays track the hard X-rays, and that the fits require no black-body component— indicating that GRS 1758–258 did not go to the high state in 1993. We offer an interpretation based on the ADAF model for a system with ṁ < ∼ ṁcrit. We find the 1990–1993 coeval hard and soft X-ray observations support the ADAF predictions. We discuss a new way to constrain black-hole mass with spectral data and the ADAF theory, and apply this technique to GRS 1758–258 to find M1 >∼ 8–9 M⊙ at an assumed distance of 8.5 kpc. Further investigations of the ADAF model allow us to evaluate the model critically against the data and flux-flux diagram of Barret, McClintock, & Grindlay (1996) and to understand the limits of the latter’s “X-ray burster box.” Subject headings: stars: individual (GRS 1758–258)— gamma-rays: observations— radio continuum: stars— X-rays: stars— accretion, accretion disks— black hole physics Columbia Astrophysics Laboratory, 538 W. 120th St., New York, NY 10027 Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore CA, 94550 Space Radiation Laboratory, California Institute of Technology, M.S. 220-47, Pasadena, CA 91125 Department of Physics, University of California, Santa Barbara

FIREBALL: the Faint Intergalactic medium Redshifted Emission Balloon: overview and first science flight results

FIREBALL (the Faint Intergalactic Redshifted Emission Balloon) is a balloon-borne 1m telescope coupled to an ultraviolet fiber-fed spectrograph. FIREBALL is designed to study the faint and diffuse emission of the intergalactic medium, until now detected primarily in absorption. FIREBALL is a path finding mission to test new technology and make new constraints on the temperature and density of this gas. We report on the first successful science flight of FIREBALL, in June 2009, which proved every aspect of the complex instrument performance, and provided the strongest measurements and constraints on IGM emission available from any instrument.

The FIREBall fiber-fed UV spectrograph

FIREBall (Faint Intergalactic Redshifted Emission Balloon) had a successful first engineering flight in July of 2007 from Palestine, Texas. Here we detail the design and construction of the spectrograph. FIREBall consists of a 1m telescope coupled to a fiber-fed ultraviolet spectrograph flown on a short duration balloon. The spectrograph is designed to map hydrogen and metal line emission from the intergalactic medium at several redshifts below z=1, exploiting a small window in atmospheric oxygen absorption at balloon altitudes. The instrument is a wide-field IFU fed by almost 400 fibers. The Offner mount spectrograph is designed to be sensitive in the 195-215nm window accessible at our altitudes of 35-40km. We are able to observe Lyα, as well as OVI and CIV doublets, from 0.3 < z < 0.9. Observations of UV bright B stars and background measurements allow characterization of throughput for the entire system and will inform future flights.

Calibration and alignment of metrology system for the Nuclear Spectroscopic Telescope Array mission

A metrology system to measure the on-orbit movement of a ten meter mast has been built for the Nuclear Spectroscopic Telescope Array (NuSTAR) x-ray observatory. In this paper, the metrology system is described, and the performance is measured. The laser beam stability is discussed in detail. Pre-launch alignment and calibration are also described. The invisible infrared laser beams must be aligned to their corresponding detectors without deploying the telescope in Earth’s gravity. Finally, a possible method for in-flight calibration of the metrology system is described.

The hot carbon, oxygen, and nitrogen echelle spectrograph

The hot carbon, oxygen, and nitrogen echelle spectrograph (HotCONes) sounding rocket payload allows a unique probe of the local interstellar medium through R=λ/δλ≳200 000 spectroscopy of C+3, N+4, and O+5. It is a practical proof of the low-order echelle spectrograph design, which may prove extremely useful in conjunction with emerging technology. We present the scientific motivation, instrument design, and measured performance.

FIREBALL: instrument pointing and aspect reconstruction

The Faint Intergalactic Redshifted Emission Balloon (FIREBALL) had its first scientific flight in June 2009. The instrument is a 1 meter class balloon-borne telescope equipped with a vacuum-ultraviolet integral field spectrograph intended to detect emission from the inter-galactic medium at redshifts 0.3 < z < 1.0. The scientific goals and the challenging environment place strict constraints on the pointing and tracking systems of the gondola. In this manuscript we briefly review our pointing requirements, discuss the methods and solutions used to meet those requirements, and present the aspect reconstruction results from the first successful scientific flight.