L. W. Brown

The On-Orbit Performance of the Space Telescope Imaging Spectrograph

The Space Telescope Imaging Spectrograph (STIS) was successfully installed into the Hubble Space Telescope (HST) in 1997 February, during the second HST servicing mission, STS-82. STIS is a versatile spectrograph, covering the 115-1000 nm wavelength range in a variety of spectroscopic and imaging modes that take advantage of the angular resolution, unobstructed wavelength coverage, and dark sky offered by the HST. In the months since launch, a number of performance tests and calibrations have been carried out and are continuing. These tests demonstrate that the instrument is performing very well. We present here a synopsis of the results to date.

The galactic radio spectrum between 130 and 2600 kHz.

The IMP-6 radio astronomy experiment has provided new measurements of the galactic background spectrum at 22 frequencies between 130 and 2600 kHz. A highly accurate spectrum is presented which corresponds to the minimum galactic radiation observed with a short dipole antenna. The estimated maximum spectrum is presented also. The data demonstrate the need to include the effect of the ambient plasma on synchrotron emission in low-frequency galactic models.

Three-Dimensional Fabry-Perot Imaging Spectroscopy of the Crab Nebula, Cassiopeia A, and Nova GK Persei

A three-dimensional model of the [0 III] A5007 line-emitting gas in the Crab Nebula has been developed from imaging spectroscopy taken with the Goddard Fabry-Perot Imager mounted on the McGrawHill 1.3m telescope of Michigan-Dartmouth-MIT Observatory. Several interesting morphological features revealed in three-dimensional isophotal displays are discussed.

Discovery of a Ly-alpha galaxy near a damped Ly-alpha absorber at z = 2.3

The detection of a galaxy associated with the damped Ly-alpha absorbing cloud seen at z = 2.309 toward the QSO PHL 957 is reported. In addition to a strong but narrow Ly-alpha emission line and weaker C IV and He II lines, the object shows continuum at V about 24, with a slope rising slightly toward the red. This is similar to what is seen in high-redshift radio galaxies, but this galaxy does not correspond to any known radio source. The detected emission lines and continuum are most easily interpreted as light from hot, recently formed stars, implying a sizable star formation rate and a scarcity of dust. The spatial correlation of the absorbing cloud and the companion galaxy supports the interpretation of damped Ly-alpha clouds as objects fundamentally different from the lower column density Ly-alpha forest clouds, which show weak or no clustering.

Fabry-Perot images of NGC 1275 and its puzzling high-velocity system

We report the first images obtained with the Goddard Fabry-Perot imager, a very sensitive and tunable imaging system designed to achieve the high levels of performance required in the optical studies of faint emission-line extragalactic objects. A velocity sequence of calibrated narrow-band CCD images (FWHM ∼7 A) has been obtained to cover the 3000 km s −1 velocity space between the redshifted Hα emission lines of NGC 1275 (the central dominant galaxy of the Perseus cluster), its extended associated system of low-velocity (LV) filaments and the high velocity (HV) system of knots, projected on the same line of sight in the sky

Emission-Line Properties of the Large Magellanic Cloud Bubble N70

We present a spectrophotometric imaging study of the emission bubble N70 (DEM 301) in the Large Magellanic Cloud. N70 is approximately 100 pc in size with a nearly circular shell-like morphology. The nebular emission is powered by an uncertain combination of EUV photons, intense winds, and supernova shock waves from the central population of high-mass stars (the OB association LH 114). We have obtained narrowband images (FWHM ~ 6 A) of N70 in the light of Hα λ6563, [N ii] λ6584, [S ii] λλ6717, 6731, and [O iii] λ5007, along with the corresponding red and green continua. The resulting line fluxes and flux ratios are used to derive ionization rates, nebular densities, volume filling fractions, and excitation indices. The photoionizing luminosity inferred from the embedded stellar population is more than adequate to account for the observed hydrogen ionization rate.We compare the emission-line photometry with that derived from similar imaging of the Orion Nebula and with data collected from the literature on other emission-line regions in the LMC. Compared with the Orion Nebula, N70 shows much higher [S ii]/Hα intensity ratios that increase smoothly with radius—from less than 0.3 near the center to greater than 1.0 toward the outer filamentary shell. The measured intensity ratios in N70 more closely match the range of excitation spanned by giant and supergiant H ii shells and by some of the supernova remnants observed in the LMC. The contending ionization and excitation processes in the interior and outer shell of N70 are evaluated in terms of the available data. EUV photons probably contribute most of the inner nebulas ionization, whereas a combination of photoionization plus collisional ionization and excitation of sulfur atoms by low-velocity shocks seems to best fit the emission-line luminosities and intensity ratios observed in the outer shell. Considerations of the radiative and mechanical energetics that are involved may indicate the need for one or two supernova explosions having occurred during the last ~Myr.

H-alpha imaging of galaxies in the Bootes void

We report H-alpha and continuum imaging of 12 galaxies in the Bootes void. The H-alpha emission in ten galaxies is due to star formation; one galaxy is probably a narrow emission line Active Galactic Nuclei (AGN), and one a Seyfert 1. Star formation rates range from 3-55 solar mass/yr, with the most active galaxies producing stars at almost three times the rate found in normal field disk systems. Eleven galaxies have strong H-alpha emission in the nucleus. The morphology of several of the galaxies is disturbed. There are at least five spirals, three of which are probably one-armed spirals, and three edge-on disk systems. Three galaxies not identifiable as spirals have H-alpha emission from regions outside the nuclear point source. 1510+4727, which has the highest rate of star formation in our sample, does not have the strong far-infrared emission expected from a galaxy experiencing significant star formation. The galaxies are quite luminous M(sub B) = -21 to -23 mag), and are not the type predicted to be found in voids.

EXTRAORDINARY LINE-EMITTING KNOTS IN THE CRAB NEBULA

Extraordinary, semistellar, line-emitting knots are apparent in images of the Crab Nebula which were obtained with the Goddard Fabry-Perot imager at the Michigan-Dartmouth-MIT Observatory. The knots are most prominent for (O III) lambda 5007 emission through a 5.3 A (Full Width at Half Maximum (FWHM)) bandpass centered at 5015.3 A, with representative fluxes of roughly 10(exp -14) ergs/sq cm. They are aligned in arcs, seven to the north and four to the south, from the pulsar. The northern group appears to be in a bounded corridor through the filamentary structure. Measurements over a 2 year baseline yield proper motions of order 0.1 sec/yr, corresponding to transverse velocities of order 900 km/s for a distance of 1830 pc. The knots are characterized by remarkably strong (Ar III) emission, possibly indicating high argon abundances, high gas temperatures, or anomalous physical processes.

Jupiter emission observed near 1 MHz

Emission from Jupiter has been observed by the IMP-6 spacecraft at 19 frequencies between 600 and 9900 kHz covering the period from April 1971 to October 1972. The Jovian bursts were identified in the IMP-6 data through the phase of the observed modulated signal detected from the spinning dipole antenna. Initial data reduction has isolated 177 events over a span of 500 days. These events persisted over a period between 1 and 60 min. Of these events at least 48 occurred during times in which Jupiter emission was being observed at either 16.7 or 22.2 MHz by ground-based instruments of the Goddard Space Flight Center Jupiter monitoring system. Large bursts were detectable from 9900 kHz down to 600 kHz, while smaller bursts ranged down to 1030 kHz.-

Differential imaging of forbidden Fe X in IC 443

This paper presents images of two areas of the supernova remnant IC 443 showing emission from the forbidden 6374 A red coronal line taken with an emission-line differential imaging camera. The areas are in the vicinity of strong soft X-ray emission as observed with the Einstein Observatory. The forbidden Fe X emission is patchy on the scale of seconds of arc. For the brightest emission regions, an electron density of approximately 60/cu cm and gas pressures of 0.l7 x 10 to the 8th/cu cm K are found. These estimates are speculative because of the large correction for interstellar dust, and the assumption of sheetlike structure. Although this region has the highest average surface brightness, no direct correlation is found between the X-ray and forbidden Fe X knots. The implied physical conditions in the region suggest that the forbidden Fe X knots are being evaporated.