Search Publications
Deriving the Electron Density of the Solar Corona from the Inversion of Total Brightness Measurements
Howard, R. A.; Vourlidas, A.; Hayes, A. P.
Usually, the electron density structure of the white-light solar corona is estimated from the inversion of polarized brightness measurements. The inversion technique was developed in the 1950s and has remained largely unchanged since. Here, for the first time, we expand this technique to total brightness observations to take advantage of the exten…
Supermassive Black Holes in Bulges
Filippenko, Alexei V.; Ho, Luis C.; Shields, Joseph C. +5 more
We present spatially extended gas kinematics at parsec-scale resolution for the nuclear regions of four nearby disk galaxies and model them as rotation of a gas disk in the joint potential of the stellar bulge and a putative central black hole. The targets were selected from a larger set of long-slit spectra obtained with the Hubble Space Telescop…
Star Formation in the Field and Clusters of NGC 5253
Heckman, Timothy M.; Calzetti, Daniela; Leitherer, Claus +1 more
We investigate the star formation history of both the bright star clusters and the diffuse ``field star'' population in the dwarf starburst galaxy NGC 5253 using long-slit ultraviolet spectroscopy obtained with the Space Telescope Imaging Spectrograph. The slit covers a physical area of 370 pc×1.6 pc and includes eight apparent clusters and severa…
Structure of the X-Ray Emission from the Jet of 3C 273
Murray, S. S.; Mathur, S.; Drake, J. J. +12 more
We present images from five observations of the quasar 3C 273 with the Chandra X-Ray Observatory. The jet has at least four distinct features that are not resolved in previous observations. The first knot in the jet (A1) is very bright in X-rays. Its X-ray spectrum is well fitted with a power law with α=0.60+/-0.05 (where Sν~ν-α
The Distance to the Vela Pulsar Gauged with Hubble Space Telescope Parallax Observations
Caraveo, P. A.; Bignami, G. F.; De Luca, A. +1 more
The distance to the Vela pulsar (PSR B0833-45) has been traditionally assumed to be 500 pc. Although affected by a significant uncertainty, this value stuck to both the pulsar and the supernova remnant. In an effort to obtain a model-free distance measurement, we have applied high-resolution astrometry to the pulsar V~23.6 optical counterpart. Usi…
The Bright Optical Companion to the Eclipsing Millisecond Pulsar in NGC 6397
Ferraro, Francesco R.; Sabbi, Elena; Possenti, Andrea +1 more
We report the optical identification of the companion to the eclipsing millisecond pulsar PSR J1740-5340 in the globular cluster NGC 6397. A bright variable star with an anomalous red color and optical variability (~0.2 mag) that nicely correlates to the orbital period of the pulsar (~1.35 days) has been found close to the pulsar position. The pec…
Models for Old, Metal-poor Stars with Enhanced α-Element Abundances. III. Isochrones and Isochrone Population Functions
VandenBerg, Don A.; Bergbusch, Peter A.
An isochrone population function (IPF) gives the relative distribution of stars along an isochrone. IPFs contain the information needed to calculate both luminosity functions and color functions, and they provide a straightforward way of generating synthetic stellar populations. An improved algorithm for interpolating isochrones and IPFs, based on…
Far-Infrared Investigation of Class 0 Sources: Line Cooling
Giannini, Teresa; Nisini, Brunella; Lorenzetti, Dario
We have investigated with the Long Wavelength Spectrometer (LWS) of the Infrared Space Observatory (ISO) the far-infrared spectra (43-197 µm) of a sample of 17 class 0 sources and their associated outflows. In addition to [O I] 63 µm, the pure rotational lines of abundant molecules such as CO, H2O, and OH are frequently obse…
An Evaluation of Coronal Heating Models for Active Regions Based on Yohkoh, SOHO, and TRACE Observations
Aschwanden, Markus J.
Recent soft X-ray and EUV data from space observations with Yohkoh, the Solar and Heliospheric Observatory (SOHO), and the Transition Region and Coronal Explorer (TRACE) established three important observational constraints for coronal heating models: (1) coronal loops in active regions have an overdensity that can be supplied only by upflows of h…
The Optical-Near-Infrared Spectrum of the M87 Jet fromHubble Space Telescope Observations
Perlman, Eric S.; Sparks, William B.; Macchetto, F. Duccio +2 more
We present 1998 Hubble Space Telescope observations of M87 that yield the first single-epoch optical and radio-optical spectral index image of the jet at 0.15" resolution. We find <αro>~0.67, comparable to previous measurements, and <αo>~0.9 (Fν~ν-α), slightly flatter than previous workers. R…