%...Journal: PASP %...MainTag: '30) objects at high redshift (z>4), where the prism recovers 80% of redshifts, while the filters recover barely 35% to similar accuracy. The primary discovery space of {\em NGST} will be at the faintest magnitudes and the highest redshifts. Many important objects will be too faint for follow-up at higher spectral resolution, so prism observations are the optimal technique to study them. Prism observations also reduce the contamination of high-redshift samples by lower redshift interlopers. %K Galaxies: Distances and Redshifts %K infrared: galaxies %K Instrumentation: Spectrographs %K Techniques: Spectroscopic %I (1) Laboratory for Astronomy and Solar Physics, Code 681, NASA Goddard Space Flight Center, Greenbelt, MD 20771. %I (2) NOAO Research Associate. %I (3) Raytheon ITSS Corporation, Lanham, MD 20706. %I (4) Laboratory for Astronomy and Solar Physics, Code 685, NASA Goddard Space Flight Center, Greenbelt, MD 20771. %I (5) Sternberg Astronomical Institute, MV Lomonosov, Moscow State University, Moscow, Russian Federation. %I (6) Laboratory for Extraterrestrial Physics, Code 693, NASA Goddard Space Flight Center, Greenbelt, MD 20771. %I (7) Systems, Technology, And Advanced Concepts (STAAC), Code 730, NASA Goddard Space Flight Center, Greenbelt, MD 20771. %I (8) Instrument Technology Center, Code 551, NASA Goddard Space Flight Center, Greenbelt, MD 20771. %R 2000PASP..112.1200H %F ori/PASPv112n775 %J-1211 %T Resolving the Controversy over the Core Radius of 47 Tucanae (NGC 104)(1,2). %A Howell, Justin H. %A Guhathakurta, Puragra (3) %I UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064; (jhhowell@ucolick.org), (raja@ucolick.org) and %A Gilliland, Ronald L. %I Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; (gillil@stsci.edu) %B This paper investigates the discrepancy between recent measurements of the density profile of the globular cluster 47 Tuc that have used {\em Hubble Space Telescope} data sets. A large core radius would support the long-held view that 47 Tuc is a relaxed cluster, while a small core radius may indicate that it is in a post-core-collapse phase or possibly even on the verge of core collapse, as suggested by a variety of unusual objects--millisecond pulsars, X-ray sources, high-velocity stars--observed in the core of the cluster. Guhathakurta et al. used pre-refurbishment Wide Field Planetary Camera 1 (WFPC1) {\em V}-band images to derive r_core_=23''+/-2''. Calzetti et al. suggested that the density profile is instead a superposition of two King profiles, one with a small, 8'' core radius and the other with a 25'' core radius, based on {\em U}-band Faint Object Camera (FOC) images. More recently, De Marchi et al. have used deep WFPC1 {\em U}-band images to derive r_core_=12''+/-2''. The cluster centers used in these studies are in agreement with one another; differences in the adopted centers are not the cause of the discrepancy. Our independent analysis of the data used by De Marchi et al. reaches the following conclusions:\begin{itemize} \item(1. )\par De Marchi et al.'s r_core_~12'' value is spuriously low, a result of radially varying bias in the star counts in a magnitude-limited sample; photometric errors and a steeply rising stellar luminosity function cause more stars to scatter across the limiting magnitude into the sample than out of it, especially near the cluster center, where crowding effects are most severe. \item(2. )\par Changing the limiting magnitude to the main-sequence turnoff, away from the steep part of the luminosity function, partially alleviates the problem and results in r_core_=18''. \item(3. )\par Combining such a limiting magnitude with accurate photometry derived from point-spread function fitting, instead of the less accurate aperture photometry employed by De Marchi et al., results in a reliable measurement of the density profile that is well fitted by r_core_=22''+/-2''.\end{itemize} \par The Calzetti et al. FOC-based density profile measurement is also likely to have been biased by a poor choice of limiting magnitude and large radially varying photometric errors associated with aperture photometry. Archival Wide Field Planetary Camera 2 (WFPC2) data are used to derive a star list with a higher degree of completeness, greater photometric accuracy, and wider area coverage than the WFPC1 and FOC data sets; the WFPC2-based density profile supports the above conclusions, yielding r_core_=24".0+/-1".9. %K globular clusters: individual (47 Tucanae, NGC 104) %K Galaxy: Globular Clusters: General %K Methods: Data Analysis %K Techniques: Photometric %I (1) Based on observations with the NASA/ESA {\em Hubble Space Telescope}, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. %I (2) Lick Observatory Bulletin 1395. %I (3) Alfred P. Sloan Research Fellow. %R 2000PASP..112.1212D %F ori/PASPv112n775 %J-1214 %T Imaging of the Possible Nebula around the Cataclysmic Variable V1101 Aquilae. %A Downes, Ronald A. (1) %I Space Telescope Science Institute, Baltimore, MD 21218 %B I have obtained H{alpha} and [O III] {lambda}5007 imaging observations of the cataclysmic variable V1101 Aql to study the nearby nebulosity recently reported by N. Masetti and M. Della Valle. My images reveal only the southern half of the nebulosity and find that it is not an emission-line source, but it is likely a mid-G star. The northern part of the suspected nebulosity, if real, is likely a variable source unrelated to the southern object. %K Stars: Novae, Cataclysmic Variables %K stars: individual (V1101 Aquilae) %I (1) Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. %R 2000PASP..112.1215H %F ori/PASPv112n775 %J-1235 %T A Primer on Far-Infrared Polarimetry. %A Hildebrand, R.H. (1)(2) %A Davidson, J.A. (3) %A Dotson, J.L. (4) %A Dowell, C.D. (5) %A Novak, G. (6) %A Vaillancourt, J.E. (1) %B We present an introduction to observing procedures and principles of analysis used in far-infrared polarimetry. The observing procedures are those for single-dish observations of thermal emission from aligned dust grains. We discuss techniques for removing backgrounds and for reducing and evaluating errors. The principles of analysis are those required for interpreting polarization maps and polarization spectra in terms of opacity, field structure, and variations in temperature and polarizing efficiency. %K infrared: ISM: continuum %K ISM: Clouds %K ISM: Magnetic Fields %K Polarization %K Techniques: Polarimetric %I (1) University of Chicago, Enrico Fermi Institute and Department of Astronomy and Astrophysics, 5640 Ellis Avenue, Chicago, IL 60637; (roger@oddjob.uchicago.edu), (johnv@oddjob.uchicago.edu). %I (2) Department of Physics, University of Chicago. %I (3) Universities Space Research Association, NASA Ames Research Center, MS T3B, Moffett Field, CA 94035; (jdavidson@mail.arc.nasa.gov). %I (4) SETI, NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035; (dotson@cygnus.arc.nasa.gov). %I (5) California Institute of Technology, Mail Code 320-47, 1200 East California Boulevard, Pasadena, CA 91125; (cdd@ submm.caltech.edu). %I (6) Department of Physics and Astronomy, Dearborn Observatory, Northwestern University, Evanston, IL 60208-2900; (g{lowbar}novak@nwu.edu). %R 2000PASP..112.1236B %F ori/PASPv112n775 %J-1242 %T A New Technique for Measuring Impact-broadened Radio Recombination Lines in HII Regions: Confrontation with Theory at High Principal Quantum Numbers. %A Bell, M.B. (1) %A Avery, L.W. (2) %A Seaquist, E.R. (3) %A Vall\'ee, J.P. (2) %B New, low-noise receivers have allowed detection, in several giant H II regions, of Rydberg-Rydberg transitions of hydrogen that cover a large range of {Delta}n-values in a single observing window. This, in turn, allows lines covering a large range in principal quantum number {\em n} to be detected simultaneously with the same antenna beam. We have employed a new frequency-switching technique which allows a very precise determination of the line widths. We have used this technique with the NRAO 140 foot telescope to observe lines in W51 and Orion A near 6 GHz, with {Delta}n-values that vary by a factor of ~21 ({Delta}n=1-~21) and corresponding {\em n}-values that vary by a factor of 2.7 (n=102-274). By generating Voigt line profiles using Griem's theory of impact broadening by electrons, inserting them into a telescope data file, and processing them in a manner identical to that of the telescope data, we have been able to examine how the observing and reduction techniques affect both the line widths and line areas as {\em n} increases. For n{<=}180, {Delta}n{<=}6, our restored line widths and areas give densities of N_e_=2500 and 4000 cm^-3^ in W51 and Orion A, respectively. These densities are higher than reported previously with a 5' beamwidth. For higher {\em n}-values we are unable to fit our data using Griem's theory. For n>180, {Delta}n>6, our telescope-measured line widths fall rapidly below predicted values, while the line areas simultaneously increase above predicted values. This behavior of the line area as the line widths decrease is inconsistent with Griem's theory or an instrumental effect. Observations of Orion A at 17.6 GHz, with a 1'.7 beamwidth, require a density in excess of N_e_=20,000 cm^-3^ to fit. Although the detected lines cover a range in {\em n} and {Delta}n from 71 to 177 and 1 to 17, respectively, there is no evidence for a line width decrease at the high {Delta}n-values. We conclude from this that the line narrowing seen at 6 GHz is related to the principal quantum number. %K ISM: H II Regions %K ISM: Abundances %K radio lines: ISM %I (1) Herzberg Institute of Astrophysics, National Research Council of Canada, 100 Sussex Drive, Ottawa, ON K1A 0R6, Canada; (morley.bell@nrc.ca). %I (2) Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V8X 4M6, Canada. %I (3) Department of Astronomy, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada. %R 2000PASP..112.1243W %F ori/PASPv112n775 %J-1261 %T The Ultraviolet and Optical Spectra of Metal-deficient O Stars in the Small Magellanic Cloud(1). %A Walborn, Nolan R. %I Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218; (walborn@stsci.edu) %A Lennon, Daniel J. (2) %I Isaac Newton Group, Apartado 321, 38700 Santa Cruz de La Palma, Canary Islands, Spain; (djl@ing.iac.es) %A Heap, Sara R. %A Lindler, Don J. (3) %I Laboratory for Astronomy and Solar Physics, Code 681, NASA Goddard Space Flight Center, Greenbelt, MD 20771; (heap@srh.gsfc.nasa.gov), (lindler@rockit.gsfc.nasa.gov) %A Smith, Linda J. (4) %A Evans, Christopher J. %I Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, England, UK; (ljs@star.ucl.ac.uk), (cje@star.ucl.ac.uk) %A Parker, Joel Wm. %I Southwest Research Institute, 1050 Walnut Street, Suite 426, Boulder, CO 80302; (joel@boulder.swri.edu) %B An ultraviolet and optical spectral atlas of 15 O stars in the Small Magellanic Cloud (SMC) is presented and described. The echelle data have resolving powers of order 10^4^; they were obtained with the {\em Hubble Space Telescope} Space Telescope Imaging Spectrograph in the UV, and at the Anglo-Australian Telescope or the European Southern Observatory 3.6 m in the optical. The ultimate objective is to develop metal-deficient templates for the interpretation of distant starbursts, but here we discuss interesting new properties of the SMC stars themselves, revealed by the high quality of these data. The SMC metal deficiency produces anomalously weak stellar-wind profiles along the entire O main sequence, as well as at intermediate luminosities; the first intermediate Si IV {lambda}1400 wind profile in the SMC is shown. The second known Of star in the SMC displays wind peculiarities that are identical to those of its spectral classmate, again likely due to the low systemic metallicity. Several objects display marked CNO anomalies, including the first cases of C III {lambda}4650 emission without N III {lambda}4640 in O-type spectra. The N/C ratio appears to increase with mass, extent of evolution away from the zero-age main sequence, and/or rotational velocity in the young cluster NGC 346. In addition, the first examples of Onfp (Oef) and Of?p spectra in the SMC have been found (the latter being only the fourth member of its peculiar shell category known anywhere). The UV wind characteristics of these objects correlate with their optical peculiarities. All these spectroscopic phenomena provide diagnostics of the evolutionary status of metal-deficient massive stars. %K Galaxies: Magellanic Clouds %K open clusters and associations: individual (NGC 346) %K Stars: Early-Type %K Stars: Fundamental Parameters %K Stars: Winds, Outflows %K Ultraviolet: Stars %I (1) Based in part on observations with the NASA/ESA {\em Hubble Space Telescope} obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Also based on observations obtained at the Anglo-Australian Observatory, Siding Spring, and at the European Southern Observatory, La Silla. %I (2) Visiting Observer, European Southern Observatory. %I (3) Advanced Computer Concepts. %I (4) Visiting Observer, Anglo-Australian Telescope. %R 2000PASP..112.1262S %F ori/PASPv112n775 %J-1268 %T The RR Lyrae Star V442 Herculis: An Extreme Case of Light-Curve Modulation. %A Schmidt, E.G. %A Lee, K.M. %I Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588-0111; (eschmidt1@unl.edu), (klee6@unl.edu) %B We have obtained photometric observations of the peculiar RR Lyrae star V442 Her during six observing seasons spanning an elapsed time of nearly 9 years. The period has undergone two large, abrupt changes in the past 5 years. Although light-curve modulation is fairly common among RR Lyrae stars, the modulation of the light curve of V442 Her is highly unusual for its large amplitude, long period, extreme alterations in light-curve shape, and large period changes. %K stars: individual (V442 Herculis) %K Stars: Variables: Other %R 2000PASP..112.1269T %F ori/PASPv112n775 %J-1276 %T Spectroscopy and Component Masses of the Eclipsing Dwarf Nova HS 0907+1902. %A Thorstensen, John R. %I Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755; (john.thorstensen@dartmouth.edu) %B HS 0907+1902 was recently discovered to be one of a handful of deeply eclipsing dwarf novae with periods longward of the 2-3 hr ``gap.'' This paper presents orbit-resolved spectra and time-series photometry of an eclipse. The apparent velocity amplitude of the M-dwarf secondary is K_2_=297+/-15 km.s^-1^. The phase of the radial velocities of the H{alpha} emission-line wings agrees accurately (for once) with the phase of the white dwarf motion deduced from the eclipse, and an estimate of the emission-line velocity amplitude yields K_1_=115+/-7 km.s^-1^. The eclipse width is {Delta}{phi}=0.060+/-0.005. At face value, these measurements yield mass estimates of M_1_=0.99+/-0.12 M_{sun}_ for the white dwarf and M_2_=0.38+/-0.06 M_{sun}_ for the secondary. The eclipse width and nominal mass ratio constrain the binary inclination {\em i} to be 77{deg}.3+/-0{deg}.9. The influence of systematic uncertainties on these values is discussed; the conclusion that the white dwarf is somewhat more massive than typical field white dwarfs appears to be robust.\par The H{alpha} emission-line profile out of eclipse is only slightly double-peaked, but the line shows a strong rotational disturbance in eclipse. Models of the line profile through eclipse using a flat, Keplerian disk do not give a good quantitative match to the observations. %K Stars: Binaries: Eclipsing %K Stars: Binaries: Spectroscopic %K Stars: Novae, Cataclysmic Variables %K Stars: Fundamental Parameters %K stars: individual (HS 0907+1902) %K Stars: White Dwarfs %R 2000PASP..112.1277R %F ori/PASPv112n775 %J-1277 %T Infrared Spectroscopic Investigations of Stellar Winds from Red Giants. (Dissertation Summary). %A Ryde, Nils %I Present address: Uppsala Astronomical Observatory, Box 515, SE-751 20 Uppsala, Sweden; (Nils.Ryde@astro.uu.se)Thesis work conducted at Uppsala Astronomical Observatory, Uppsala University, SwedenPh.D. thesis directed by Bengt Gustafsson and Kjell Eriksson; Ph.D. degree awarded 2000 March %K Dissertation Summaries %K Stars: AGB and Post-AGB %K Stars: Circumstellar Matter %K Stars: Evolution %K Stars: Late-Type %K Stars: Winds, Outflows %K Infrared: Stars %R 2000PASP..112.1278D %F ori/PASPv112n775 %J-1279 %T Astronomy with Radioactivities(1). (Conference Highlights). %A Diehl, Roland %A Hartmann, Dieter %I Max-Planck-Institut f\"ur extraterrestrische Physik, D-80740 Garching, Germany; and Department of Physics and Astronomy, Clemson University, Clemson, SC 29634; (rod@mpe.mpg.de) %K Conference Highlights %I (1) Conference held at Ringberg Castle, Germany, in 1999 September/October. Proceedings have been published in R. Diehl & D. Hartmann, eds., MPE Report 274, Astronomy with Radioactivities (Garching: MPE); see also .