Search Publications
Bulk Comptonization spectra in blazars
Ghisellini, G.; Fabian, A. C.; Celotti, A.
We study the time-dependent spectra produced via the bulk Compton process by a cold, relativistic shell of plasma moving (and accelerating) along the jet of a blazar, scattering on external photons emitted by the accretion disc and reprocessed in the broad-line region (BLR). The bulk Comptonization of disc photons is shown to yield a spectral comp…
Hubble and Spitzer Observations of an Edge-on Circumstellar Disk around a Brown Dwarf
Luhman, K. L.; McLeod, Kim K.; Hartmann, Lee +7 more
We present observations of a circumstellar disk that is inclined close to edge-on around a young brown dwarf in the Taurus star-forming region. Using data obtained with SpeX at the NASA Infrared Telescope Facility, we find that the slope of the 0.8-2.5 µm spectrum of the brown dwarf 2MASS J04381486+2611399 cannot be reproduced with a photosp…
The light curve of the companion to PSR B1957+20
Fruchter, A. S.; Torres, M. A. P.; Gibbons, R. A. +3 more
We present a new analysis of the light curve for the secondary star in the eclipsing binary millisecond pulsar system PSR B1957+20. Combining previous data and new data points at minimum from the Hubble Space Telescope, we have 100 per cent coverage in the R-band. We also have a number of new Ks-band data points, which we use to constra…
Constraints on the Cosmic Near-Infrared Background Excess from NICMOS Deep Field Observations
Fan, Xiaohui; Kennicutt, Robert C.; Rieke, Marcia +2 more
NICMOS observations of the resolved object fluxes in the Hubble Deep Field-North and the Hubble Ultra Deep Field are significantly below the fluxes attributed to a 1.4-1.8 µm near-infrared background excess (NIRBE) from previous low spatial resolution NIRS measurements. Tests placing sources in the NICMOS image with fluxes sufficient to acco…
The Distance to the Isolated Neutron Star RX J0720.4-3125
van Kerkwijk, M. H.; Anderson, J.; Kaplan, D. L.
We have used a set of dedicated astrometric data from the Hubble Space Telescope to measure the parallax and proper motion of the nearby neutron star RX J0720.4-3125. At each of eight epochs over 2 years, we used the High Resolution Camera of the Advanced Camera for Surveys to measure the position of the B=26.6 target to a precision of ~2 mas (~0.…
Environmental dependence of active galactic nuclei activity in the supercluster A901/2
Gray, M. E.; Wolf, C.; Meisenheimer, K. +5 more
We present XMM data for the supercluster A901/2, at z ~ 0.17, which is combined with deep imaging and 17-band photometric redshifts (from the COMBO-17 survey), two degree field (2dF) spectra and Spitzer 24µm data, to identify active galactic nuclei (AGN) in the supercluster. The 90 ksec XMM image contains 139 point sources, of which 11 are i…
Recent glaciation at high elevations on Arsia Mons, Mars: Implications for the formation and evolution of large tropical mountain glaciers
Head, James W.; Fastook, James L.; Marchant, David R. +1 more
The ~166,000 km2 fan-shaped deposit at Arsia Mons contains three characteristic facies (ridged, knobby, and smooth), which are interpreted as the depositional remains of a cold-based glacier that was present on the west-northwestern flanks in the Late Amazonian period of Mars history. Here, we consider several high-elevation graben on t…
Evidence for strong evolution of the cosmic star formation density at high redshifts
Maiolino, R.; Marconi, A.; Mannucci, F. +2 more
Deep HST/ACS and VLT/ISAAC data of the GOODS-South field were used to look for high-redshift galaxies in the rest-frame UV wavelength range and to study the evolution of the cosmic star-formation density at z∼ 7. The GOODS-South area was surveyed down to a limiting magnitude of about (J+Ks)AB = 25.5, looking for drop-out objects in the …
Fine Structures of Solar X-Ray Jets Observed with the X-Ray Telescope aboard Hinode
Shimojo, Masumi; Narukage, Noriyuki; Kano, Ryohei +7 more
The X-Ray Telescope (XRT) aboard Hinode has revealed the fine structure of solar X-ray jets. One of the fine structures observed by XRT is an expanding loop. The loop appeared near the footpoint of the jet when footpoint brightening was observed. Additionally, we have found that the X-ray jets began just after the expanding loop ``breaks''. Other …
Solar Magnetic Activity and Total Irradiance Since the Maunder Minimum
Charbonneau, P.; Tapping, K. F.; Crouch, A. +3 more
We develop a model for estimating solar total irradiance since 1600 AD using the sunspot number record as input, since this is the only intrinsic record of solar activity extending back far enough in time. Sunspot number is strongly correlated, albeit nonlinearly with the 10.7-cm radio flux (F10.7), which forms a continuous record back …