Patricia Lee Bornmann

A Catalog of Nearby Poor Clusters of Galaxies

A catalog of 732 optically selected, nearby poor clusters of galaxies covering the entire sky north of -3° declination is presented. The poor clusters, called WBL clusters, were identified as concentrations of three or more galaxies with photographic magnitudes brighter than 15.7, possessing a galaxy surface overdensity of 104/3. These criteria are consistent with those used in the identification of the original Yerkes poor clusters, and this new catalog substantially increases the sample size of such objects. These poor clusters cover the entire range of galaxy associations up to and including Abell clusters, systematically including poor and rich galaxy systems spanning over 3 orders of magnitude in the cluster mass function. As a result, this new catalog contains a greater diversity of richness and structures than other group catalogs, such as the Hickson and Yerkes catalogs. The information on individual galaxies includes redshifts and cross-references to other galaxy catalogs. The entries for the clusters include redshift (where available) and cross-references to other group and cluster catalogs.

GOES solar x-ray imager: overview and operational goals

The first solar x-ray imager (SXI) will provide a major advance in real-time, continuous monitoring of solar- terrestrial conditions. This instrument, which will fly on a Geostationary Operational Environmental Satellite (GOES), will provide full-disk images of the Sun once a minute in the 0.6-6 nm range with 5 arcsec pixels. SXIs images will complement x-ray fluxes from the disk-integrating GOES x-ray sensor and optical images from ground-based observatories. THe automated sequence of SXI images will make it easy for forecasters, researchers, and image processing algorithms to interpret the images. SXI is being built to meet five operational goals for real-time prediction of solar- terrestrial disturbances: 1) SXI will provide clear evidence of x-ray coronal holes that are associate with recurrent geomagnetic storms. 2) SXI will provide flare locations that are used to estimate the magnitude and timing of energetic particle events, including flares from regions behind the solar limb that are not visible at other wavelengths. 3) SXI could provide a significant improvement in forecasting geomagnetic disturbances if CME-associated brightenings can be readily observed. 4) SXI images will show the complexity of the active regions, which will be used to estimate each regions flare potential.

High-Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission for the next (2000) solar maximum

The primary scientific objective of the High Energy Solar Spectroscopic Imager (HESSI) Small Explorer mission selected by NASA is to investigate the physics of particle acceleration and energy release in solar flares. Observations will be made of x-rays and (gamma) rays from approximately 3 keV to approximately 20 MeV with an unprecedented combination of high resolution imaging and spectroscopy. The HESSI instrument utilizes Fourier- transform imaging with 9 bi-grid rotating modulation collimators and cooled germanium detectors. The instrument is mounted on a Sun-pointed spin-stabilized spacecraft and placed into a 600 km-altitude, 38 degrees inclination orbit.It will provide the first imaging spectroscopy in hard x-rays, with approximately 2 arcsecond angular resolution, time resolution down to tens of ms, and approximately 1 keV energy resolution; the first solar (gamma) ray line spectroscopy with approximately 1-5 keV energy resolution; and the first solar (gamma) -ray line and continuum imaging,with approximately 36-arcsecond angular resolution. HESSI is planned for launch in July 2000, in time to detect the thousands of flares expected during the next solar maximum.

GOES x-ray sensor and its use in predicting solar-terrestrial disturbances

The X-ray sensor (XRS) on the GOES provides a standard reference for essentially continuous monitoring solar activity and characterizing solar flares. Disk-integrated x- ray fluxes observed by XRS are used by forecasters and researchers around the world as a measure of the strength and duration of solar flares. The peak 0.1-0.8 nm x-ray flux during flares is used to distinguish between C, M, and X flares; flares that differ by an order of magnitude in the peak flux. Forecasters use this peak flux to predict the magnitude of proton events, and the x-ray duration is used to estimate whether coronal mass ejection may have occurred that could cause a geomagnetic disturbance if it hits the Earth. Recipients of the data use the peak flux and the duration of the flare to estimate the disturbances expected on radio communication systems. The magnitudes of XRS- observed flares are also used to determine when to issue alerts of changed communication systems. The magnitudes of XRS-observed flares are also used to determine when to issue alerts of changed ionospheric conditions that can disrupt communications and GPS signals. XRS fluxes are also used to augment solar radio observations to alert users of radio frequencies of times when the solar signal may interfere with their operations. The non-flaring x-ray flux, otherwise known as the x-ray background flux, is used as a proxy for he solar EUV emissions that are used to predict the atmospheric density as satellite orbits; variations in the daily averaged solar x-ray flux are used to estimate changes in the atmospheric drag on spacecraft orbits.

Space environment monitoring mission beyond GOES-M

Conditions in the near-Earth space environment are of every increasing importance to our human activities on Earth and in space. The provision of the space environment services required in future depends on improving our understanding of solar activity and the coupling of this activity to our local region of space, as well as improving our remote sensing and in-situ monitoring of conditions and events in the solar system. Our present service is largely analogous to the state of terrestrial weather forecasting rom a local weather office before the advent of numerical modeling and remote atmospheric sensing technology. Numerical models of the local space environment and of interplanetary space are being developed. However, these models are limited in performance by our understanding of the underlying physical processes, and their practical applications is restricted by the paucity of observational data. Instruments on the GOES provide a critical resource to NOAAs space environment services. GOES is our most effective operational platform for real-time remote sensing of the Sun, the near-Earth environment, and processes in interplanetary space. It also makes important in-situ measurements in a critical region of space that is now of huge commercial importance. This paper will discuss the planned and potential extensions of the GOES space environment monitor in the overall context of the data required to meet the future needs for space environment services.

Improving the performance of the GOES solar x-ray imager with a back-illuminated x-ray sensitive CCD

NOAA has commissioned a solar x-ray imager to be built for use on the GOES spacecraft. The mission of the SXI is to provide soft x-ray imagery of the Sun. The current instrument design employs a microchannel plate detector stack to convert the incident x-rays to an electrically detectable signal. In this paper, we discuss the SXI performance improvements possible by replacing the detector with a back-illuminated, x-ray sensitive CCD fabricated using technology developed at MIT/LL. In addition to a description of the x-ray sensitive CCD, we discuss possible improvements in data quality, reduction in instrument mass and power requirements, and simplified instrument handling.