Showing papers in "Astrophysical Journal Supplement Series in 2002"

Using Strong Lines to Estimate Abundances in Extragalactic H II Regions and Starburst Galaxies

Abstract: We have used a combination of stellar population synthesis and photoionization models to develop a set of ionization parameter and abundance diagnostics based only on the use of the strong optical emission lines. These models are applicable to both extragalactic H II regions and star-forming galaxies. We show that, because our techniques solve explicitly for both the ionization parameter and the chemical abundance, the diagnostics presented here are an improvement on earlier techniques based on strong emission-line ratios. Our techniques are applicable at all metallicities. In particular, for metallicities above half solar, the ratio [N II]/[O II] provides a very reliable diagnostic since it is ionization parameter independent and does not have a local maximum. This ratio has not previously been used historically because of worries about reliable calibration over such a long baseline, and reddening correction concerns. However, we show that the use of classical reddening curves and standard calibration are quite sufficient to allow this [N II]/[O II] diagnostic to be used with confidence as a reliable abundance indicator. As we had shown, the commonly used abundance diagnostic R23 depends strongly on the ionization parameter, while the commonly used ionization parameter diagnostic [O III]/[O II] depends strongly on abundance. The iterative method of solution presented here allows both of these parameters to be obtained without recourse to the use of temperature-sensitive line ratios involving faint emission lines. We compare three commonly used abundance diagnostic techniques and show that individually, they contain systematic and random errors. This is a problem affecting many abundance diagnostics, and the errors generally have not been properly studied or understood due to the lack of a reliable comparison abundance, except for very low metallicities, where the [O III] λ4363 auroral line is used. Here we show that the average of these techniques provides a fairly reliable comparison abundance indicator against which to test new diagnostic methods. The cause of the systematic effects are discussed, and we present a new optimal abundance diagnostic method based on the use of line ratios involving [N II], [O II], [O III], [S II], and the Balmer lines. This combined diagnostic appears to suffer no apparent systematic errors, can be used over the entire abundance range and significantly reduces the random error inherent in previous techniques. Finally, we give a recommended procedure for the derivation of abundances in the case that only spectra of limited wavelength coverage are available so that the optimal method can no longer be used.

Chandra Deep Field South: The 1 Ms Catalog

Abstract: In this paper we present the source catalog obtained from a 942 ks exposure of the Chandra Deep Field South (CDFS), using the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. Eleven individual pointings made between 1999 October and 2000 December were combined to generate the final image used for object detection. Catalog generation proceeded simultaneously using two different methods; a method of our own design using a modified version of the SExtractor algorithm, and a wavelet transform technique developed specifically for Chandra observations. The detection threshold has been set in order to have less than 10 spurious sources, as assessed by extensive simulations. We subdivided the catalog into four sections. The primary list consists of objects common to the two detection methods. Two secondary lists contain sources which were detected by (1) the SExtractor algorithm alone and (2) the wavelet technique alone. The fourth list consists of possible diffuse or extended sources. The flux limits at the aimpoint for the soft (0.5-2 keV) and hard (2-10 keV) bands are 5.5 × 10-17 erg s-1 cm-2 and 4.5 × 10-16 erg s-1 cm-2, respectively. The total number of sources is 346; out of them, 307 were detected in the 0.5-2 keV band, and 251 in the 2-10 keV band. We also present optical identifications for the cataloged sources. Our primary optical data are R band imaging from VLT/FORS1 to a depth of R ~ 26.5 (Vega). In regions of the field not covered by the VLT/FORS1 deep imaging, we use R-band data obtained with the Wide Field Imager (WFI) on the ESO-MPI 2.2 m telescope, as part of the ESO Imaging Survey (EIS), which cover the entire X-ray survey. We found that the FORS1/Chandra offsets are small, ~1''. Coordinate cross-correlation finds 85% of the Chandra sources covered by FORS1 R to have counterparts within the 3 σ error box (15 depending on off-axis angle and X-ray signal-to-noise). The unidentified fraction of sources, approximately ~10%-15%, is close to the limit expected from the observed X-ray flux to R-band ratio distribution for the identified sample.

A Wavelet-Based Algorithm for the Spatial Analysis of Poisson Data

Abstract: Wavelets are scalable, oscillatory functions that deviate from zero only within a limited spatial regime and have average value zero, and thus may be used to simultaneously characterize the shape, location, and strength of astronomical sources. But in addition to their use as source characterizers, wavelet functions are rapidly gaining currency within the source detection field. Wavelet-based source detection involves the correlation of scaled wavelet functions with binned, two-dimensional image data. If the chosen wavelet function exhibits the property of vanishing moments, significantly nonzero correlation coefficients will be observed only where there are high-order variations in the data; e.g., they will be observed in the vicinity of sources. Source pixels are identified by comparing each correlation coefficient with its probability sampling distribution, which is a function of the (estimated or a priori known) background amplitude. In this paper, we describe the mission-independent, wavelet-based source detection algorithm "WAVDETECT," part of the freely available Chandra Interactive Analysis of Observations (CIAO) software package. Our algorithm uses the Marr, or "Mexican Hat" wavelet function, but may be adapted for use with other wavelet functions. Aspects of our algorithm include: (1) the computation of local, exposure-corrected normalized (i.e., flat-fielded) background maps; (2) the correction for exposure variations within the field of view (due to, e.g., telescope support ribs or the edge of the field); (3) its applicability within the low-counts regime, as it does not require a minimum number of background counts per pixel for the accurate computation of source detection thresholds; (4) the generation of a source list in a manner that does not depend upon a detailed knowledge of the point spread function (PSF) shape; and (5) error analysis. These features make our algorithm considerably more general than previous methods developed for the analysis of X-ray image data, especially in the low count regime. We demonstrate the robustness of WAVDETECT by applying it to an image from an idealized detector with a spatially invariant Gaussian PSF and an exposure map similar to that of the Einstein IPC; to Pleiades Cluster data collected by the ROSAT PSPC; and to simulated Chandra ACIS-I image of the Lockman Hole region.

Radial Velocities for 889 Late-Type Stars*

Abstract: We report radial velocities for 844 FGKM-type main-sequence and subgiant stars and 45 K giants, most of which had either low-precision velocity measurements or none at all. These velocities differ from the stand- ard stars of Udry et al. by 0.035 km s � 1 (rms) for the 26 FGK standard stars in common. The zero point of our velocities differs from that of Udry et al.: hVPresentVUdry i¼þ 0:053 km s � 1 . Thus, these new velocities agree with the best known standard stars both in precision and zero point, to well within 0.1 km s � 1 . Nonetheless, both these velocities and the standards suffer from three sources of systematic error, namely, convective blueshift, gravitational redshift, and spectral type mismatch of the reference spectrum. These sys- tematic errors are here forced to be zero for G2 V stars by using the Sun as reference, with Vesta and day sky as proxies. But for spectral types departing from solar, the systematic errors reach 0.3 km s � 1 in the F and K stars and 0.4 km s � 1 in M dwarfs. Multiple spectra were obtained for all 889 stars during 4 years, and 782 of them exhibit velocity scatter less than 0.1 km s � 1 . These stars may serve as radial velocity standards if they remain constant in velocity. We found 11 new spectroscopic binaries and report orbital parameters for them. Subject headings: binaries: spectroscopic — catalogs — stars: fundamental parameters — stars: kinematics — stars: late-type — techniques: radial velocities — techniques: spectroscopic On-line material: machine-readable tables

The DEEP Groth Strip Survey. II. Hubble Space Telescope Structural Parameters of Galaxies in the Groth Strip

Abstract: The quantitative morphological classification of distant galaxies is essential to the understanding of the evolution of galaxies over the history of the universe This paper presents Hubble Space Telescope WFPC2 F606W and F814W photometric structural parameters for 7450 galaxies in the Groth Strip These parameters are based on a two-dimensional bulge + disk surface brightness model and were obtained using an automated reduction and analysis pipeline described in detail here A first set of fits was performed separately in each bandpass, and a second set of fits was performed simultaneously on both bandpasses The information produced by these two types of fits can be used to explore different science goals Systematic and random fitting errors in all structural parameters as well as bulge and disk colors are carefully characterized through extensive sets of simulations The results of these simulations are given in catalogs similar to the real science catalogs so that both real and simulated measurements can be sampled according to the same selection criteria to show biases and errors in the science data subset of interest The effects of asymmetric structures on the recovered bulge+disk fitting parameters are also explored through simulations The full multidimensional photometric survey selection function of the Groth Strip is also computed This selection function, coupled to bias maps from simulations, provides a complete and objective reproduction of the observational limits, and these limits can be applied to theoretical predictions from galaxy evolution models for direct comparisons with the data

Optical and Near-Infrared Imaging of the IRAS 1 Jy Sample of Ultraluminous Infrared Galaxies. II. The Analysis

Abstract: An imaging survey of the IRAS 1 Jy sample of 118 ultraluminous infrared galaxies was conducted at optical (R) and near-infrared (K') wavelengths using the University of Hawaii 2.2 m telescope. The methods of observation and data reduction are described. An R and K' atlas of the entire sample is presented along with some of the basic astrometric and photometric parameters derived from these images. A more detailed analysis of these data is presented in a companion paper.

Unusual broad absorption line quasars from the Sloan Digital Sky Survey

Abstract: The Sloan Digital Sky Survey has confirmed the existence of populations of broad absorption line (BAL) quasars with various unusual properties. We present and discuss twenty-three such objects and consider the implications of their wide range of properties for models of BAL outflows and quasars in general. We have discovered one BAL quasar with a record number of absorption lines. Two other similarly complex objects with many narrow troughs show broad Mgii absorption extending longward of their systemic host galaxy redshifts. This can be explained as absorption of an extended continuum source by the rotation-dominated base of a disk wind. Five other objects have absorption which removes an unprecedented ∼90% of all flux shortward of Mgii. The absorption in one of them has varied across the ultraviolet with an amplitude and rate of change as great as ever seen. This same object may also show broad Hβ absorption. Numerous reddened BAL quasars have been found, including at least one reddened mini-BAL quasar with very strong Feii emission. The five reddest objects have continuum reddenings of E(B − V ) ≃ 0.5, and in two of them we find strong evidence that the reddening curve is even steeper than that of the SMC. We have found at least one object with absorption from Feiii but not Feii. This may be due to a high column density of moderately high-ionization gas, but the Feiii level populations must also be affected by some sort of resonance. Finally, we have found two luminous, probably reddened high-redshift objects which may be BAL quasars whose troughs partially cover different regions of the continuum source as a function of velocity.

A UBVR CCD Survey of the Magellanic Clouds

Abstract: We present photometry and a preliminary interpretation of a UBVR survey of the Large and Small Magellanic Clouds, which covers 14.5 deg2 and 7.2 deg2, respectively. This study is aimed at obtaining well-calibrated data on the brighter, massive stars, complementing recent, deeper CCD surveys. Our catalog contains 179,655 LMC and 84,995 SMC stars brighter than V ~ 18.0, and is photometrically complete to U ~ B ~ V ~ 15.7 and R ~ 15.2, although stars in crowded regions are selectively missed. We compare our photometry to that of others, and describe the need for gravity-dependent corrections to our CCD U-band photometry. We provide a preliminary cross-reference between our catalog stars and the stars with existing spectroscopy. We discuss the population of stars seen toward the two Clouds, identifying the features in the color-magnitude diagram, and using existing spectroscopy to help construct H-R diagrams. We derive improved values for the blue-to-red star ratios in the two Clouds, emphasizing the uncertainties involved in this before additional spectroscopy. We compare the relative number of red supergiants and Wolf-Rayet stars in the LMC and SMC with that of other galaxies in the Local Group, demonstrating a very strong, tight trend with metallicity, with the ratio changing by a factor of 160 from the SMC to M31. We also reinvestigate the initial mass function of the massive stars found outside of the OB associations. With the newer data, we find that the initial mass function (IMF) slope of this field population is very steep, with Γ ~ -4 ± 0.5, in agreement with our earlier work. This is in sharp contrast to the IMF slope found for the massive stars with OB associations (Γ ~ -1.3). Although much more spectroscopy is needed to make this result firm, incompleteness can no longer be invoked as an explanation.

The Y2 Isochrones for α-Element Enhanced Mixtures

Abstract: We present a new set of isochrones in which the effect of the α-element enhancement is fully incorporated. These isochrones are an extension of the already published set of Y2 Isochrones (our Paper I), constructed for the scaled-solar mixture. As in Paper I, helium diffusion and convective core overshoot have been taken into account. The range of chemical compositions covered is 0.00001 ≤ Z ≤ 0.08. The models were evolved from the pre-main-sequence stellar birthline to the onset of helium burning in the core. The age range of the full isochrone set is 0.1-20 Gyr, while younger isochrones of age 1-80 Myr are also presented up to the main-sequence turn-off. Combining this set with that of Paper I for scaled-solar mixture isochrones, we provide a consistent set of isochrones that can be used to investigate populations of any value of α-enhancement. We confirm the earlier results of Paper I that inclusion of α-enhancement effects further reduces the age estimates of globular clusters by approximately 8% if [α/Fe]= +0.3. It is important to note the metallicity dependence of the change in age estimates (larger age reductions in lower metallicities). This reduces the age gap between the oldest metal-rich and metal-poor Galactic stellar populations and between the halo and the disk populations. We also investigate whether the effects of α-enhancement can be mimicked by increasing the total metal abundance in the manner proposed by Salaris and collaborators. We find such simple scaling formulae are valid at low metallicities but not at all at high metallicities near and above solar. Thus, it is essential to use the isochrones rigorously computed for α-enhancement when modeling metal-rich populations, such as bright galaxies. The isochrone tables, together with interpolation routines have been made available via internet.

The Organic Refractory Material in the Diffuse Interstellar Medium: Mid-Infrared Spectroscopic Constraints

Abstract: This is an analysis of the 4000¨1000 cm~1 (2.5¨10 km) region of the spectrum of diUuse interstellar medium (DISM) dust compared with the spectra of 13 materials produced in the laboratory which serve as analogs to the interstellar material. The organic signatures of extragalactic dust, carbonaceous chondritic material, and E. coli bacteria are also presented because these have been discussed in the literature as relevant to the diUuse interstellar medium. Spectral analysis of the DISM allows us to place signi—cant constraints on the applicability of proposed candidate materials. The spectra of candidate materials are evaluated using four spectral characteristics based on the interstellar data: (i) comparisons of the pro—le and subpeak positions of the 2940 cm~1 (3.4 km) aliphatic CH stretching-mode band, (ii) the ratio of the optical depth (O.D.) of the aliphatic CH stretch to the O.D. of the OH stretch near 3200 cm~1 (3.1 km), (iii) the ratio of the O.D. of the aliphatic CH stretch to the O.D. of the carbonyl band near 1700 cm~1 (5.9 km), and (iv) the ratio of the O.D. of the aliphatic CH stretch feature to the O.D. of the CH deformation modes near 1470 cm~1 (6.8 km) and 1370 cm~1 (7.25 km). We conclude that the organic refractory material in the diUuse interstellar medium is predominantly hydrocarbon in nature, possessing little nitrogen or oxygen, with the carbon distributed between the aromatic and aliphatic forms. Long alkane chains with n much greater than 4 or 5 are not major constituents H 3 Cw(CH 2 ) n w of this material. Comparisons to laboratory analogs indicate the DISM organic material resembles plasma processed pure hydrocarbon residues much more so than energetically processed ice residues. This result is consistent with a birth site for the carrier of the 3.4 km band in the out—ow region of evolved carbon stars. The organic material extracted from the Murchison carbonaceous meteorite and the spectrum of E. coli bacteria reveal spectral features in the 5¨10 km region that are absent in the DISM. Although the presence of unaltered circumstellar components in the Murchison meteorite has been established through several lines of evidence, it is unclear whether or not the aliphatic component which gives rise to the 3.4 km band is in that category. Considering the complete 2¨10 km wavelength region, there is no spectral evidence for a biological origin of the 3.4 km interstellar absorption band. The similarity of the aliphatic CH stretch region of dust from our own Galaxy compared with that of distant galaxies suggests that the organic component of the ISM is widespread and may be an important universal reservoir of prebiotic organic carbon. )

The VLBA Calibrator Survey—VCS1

Abstract: A catalog containing milliarcsecond-accurate positions of 1332 extragalactic radio sources distributed over the northern sky is presented—the Very Long Baseline Array Calibrator Survey (VCS1). The positions have been derived from astrometric analysis of dual-frequency 2.3 and 8.4 GHz VLBA snapshot observations; in a majority of cases, images of the sources are also available. These radio sources are suitable for use in geodetic and astrometric experiments, and as phase-reference calibrators in high-sensitivity astronomical imaging. The VCS1 is the largest high-resolution radio survey ever undertaken and triples the number of sources available to the radio astronomy community for VLBI applications. In addition to the astrometric role, this survey can be used in active galactic nuclei, Galactic, gravitational lens, and cosmological studies. Subject headings: astrometry — radio continuum: general — reference systems — surveys — techniques: interferometric On-line material: machine-readable tables

The Physical Conditions for Massive Star Formation: Dust Continuum Maps and Modeling

Abstract: Fifty-one dense cores associated with water masers were mapped at 350 μm. These cores are very luminous, 103 < Lbol/L☉ < 106, indicative of the formation of massive stars. Dust continuum contour maps, radial intensity profiles, and photometry are presented for these sources. The submillimeter dust emission peak is, on average, nearly coincident with the water maser position. The spectral energy distributions and normalized radial profiles of dust continuum emission were modeled for 31 sources using a one-dimensional dust radiative transfer code, assuming a power-law density distribution in the envelope, n = nf(r/rf)-p. The best-fit density power-law exponent, p, ranged from 0.75 to 2.5 with p = 1.8 ± 0.4, similar to the mean value found recently by Beuther and coworkers in a large sample of massive star-forming regions. The mean value of p is also comparable to that found in regions forming only low-mass stars, but nf is over 2 orders of magnitude greater for the massive cores. The mean p is incompatible with a logatropic sphere (p = 1), but other star formation models cannot be ruled out. Different mass estimates are compared and mean masses of gas and dust are reported within a half-power radius determined from the dust emission, log M(< rdec) = 2.0 ± 0.6, and within a radius where the total density exceeds 104 cm-3, log M(< rn) = 2.5 ± 0.6. Evolutionary indicators commonly used for low-mass star formation, such as Tbol and Lbol/Lsmm, may have some utility for regions forming massive stars. Additionally, for comparison with extragalactic star formation studies, the luminosity-to-dust mass ratio is calculated for these sources, Lbol/MD = 1.4 × 104 L☉/M☉, with a method most parallel to that used in studies of distant galaxies. This ratio is similar to that seen in high-redshift starburst galaxies.

Abundances of 30 elements in 23 metal-poor stars

Abstract: We report the abundances of 30 elements in 23 metal-poor ([Fe/H] < -1.7) giants. These are based on 7774 equivalent widths and spectral synthesis of 229 additional lines. Hyperfine splitting is taken into account when appropriate. Our choice of model atmospheres has the most influence on the accuracy of our abundances. We consider the effect of different model atmospheres on our results. In addition to the random errors in Teff, log g, and microturbulent velocity, there are several sources of systematic error. These include using Teff determined from Fe I lines rather than colors, ignoring non-LTE effects on the Fe I/Fe II ionization balance, using models with solar [α/Fe] ratios, and using Kurucz models with overshooting. Of these, only the use of models with solar [α/Fe] ratios had a negligible effect. However, while the absolute abundances can change by greater than 0.10 dex, the relative abundances, especially between closely allied atoms such as the rare earth group, often show only small (less than 0.03 dex) changes. We found that some strong lines of Fe I, Mn I, and Cr I consistently gave lower abundances by ~0.2 dex, a number larger than the quoted errors in the gf-values. After considering a model with depth-dependent microturbulent velocity and a model with hotter temperatures in the upper layers, we conclude that the latter did a better job of resolving the problem and agreeing with observational evidence for the structure of stars. The error analysis includes the effects of correlation of Teff, log g, and ξ errors, which is crucial for certain element ratios, such as [Mg/Fe]. The abundances presented here are being analyzed and discussed in a separate series of papers.

The Mass Function

Abstract: We present the mass functions for different mass estimators for a range of cosmological models. We pay particular attention to how universal the mass function is, and how it depends on the cosmology, halo identification, and mass estimator chosen. We investigate quantitatively how well we can relate observed masses to theoretical mass functions.

On Validating an Astrophysical Simulation Code

Abstract: We present a case study of validating an astrophysical simulation code Our study focuses on validating FLASH, a parallel, adaptive-mesh hydrodynamics code for studying the compressible, reactive flows found in many astrophysical environments We describe the astrophysics problems of interest and the challenges associated with simulating these problems We describe methodology and discuss solutions to difficulties encountered in verification and validation We describe verification tests regularly administered to the code, present the results of new verification tests, and outline a method for testing general equations of state We present the results of two validation tests in which we compared simulations to experimental data The first is of a laser-driven shock propagating through a multilayer target, a configuration subject to both Rayleigh-Taylor and Richtmyer-Meshkov instabilities The second test is a classic Rayleigh-Taylor instability, where a heavy fluid is supported against the force of gravity by a light fluid Our simulations of the multilayer target experiments showed good agreement with the experimental results, but our simulations of the Rayleigh-Taylor instability did not agree well with the experimental results We discuss our findings and present results of additional simulations undertaken to further investigate the Rayleigh-Taylor instability

X-Ray Properties of LINERs and Low-Luminosity Seyfert Galaxies Observed with ASCA. I. Observations and Results

Abstract: This paper presents a comprehensive study of the X-ray properties of low-ionization nuclear emission-line regions (LINERs) and low-luminosity Seyfert galaxies based on observations obtained with the ASCA satellite. We analyzed data of 53 observations of 21 LINERs and 17 low-luminosity Seyferts. X-ray emission has been detected in all but one object. The X-ray luminosities in the 2-10 keV band range from 4 × 1039 to 5 × 1041 ergs s-1, which are 1-3 orders of magnitude smaller than in classical Seyfert galaxies. The X-ray spectra of most objects are well described by a canonical model which consists of (1) a soft component from a thermal plasma with kT < 1 keV and (2) a hard component represented by a power law with a photon index of Γ ≈ 1.8 or thermal bremsstrahlung emission with kT ≈ 10 keV. Several objects do not require the soft thermal component, and their continua are well fitted by a single power-law model. Some objects show heavy absorption with column densities in excess of 1023 cm-2. We detect in several objects Fe K line emission with equivalent widths ranging from 50 eV to 2 keV. Variability on timescales less than a day is uncommon in our sample. By comparing multiple observations made with ASCA or with published 2-10 keV observations from other satellites, we show that at least eight objects are variable on timescales of a week to several years. We find that the morphologies of many objects, both in the soft and hard bands, are consistent with being pointlike relative to the telescope point-spread function; a few are clearly extended in either or both energy bands. The second paper of this series will discuss the physical interpretation of the X-ray emission and its implications for low-luminosity active galactic nuclei.

A Catalog of Candidate Intermediate-Luminosity X-Ray Objects

Abstract: ROSAT, and now Chandra, X-ray images allow studies of extranuclear X-ray point sources in galaxies other than our own. X-ray observations of normal galaxies with ROSAT and Chandra have revealed that off-nuclear, compact, intermediate-luminosity (LX[2-10 keV] ≥1039.0 ergs s-1) X-ray objects (IXOs, a.k.a. ULXs [ultraluminous X-ray sources]) are quite common. Here we present a catalog and finding charts for 87 IXOs in 54 galaxies, derived from all of the ROSAT HRI imaging data for galaxies with cz ≤ 5000 km s-1 from the Third Reference Catalog of Bright Galaxies. We have defined the cutoff LX for IXOs so that it is well above the Eddington luminosity of a 1.4 M☉ black hole (1038.3 ergs s-1), so as not to confuse IXOs with "normal" black hole X-ray binaries. This catalog is intended to provide a baseline for follow-up work with Chandra and XMM-Newton, and with space- and ground-based survey work at wavelengths other than X-ray. We demonstrate that elliptical galaxies with IXOs have a larger number of IXOs per galaxy than nonelliptical galaxies with IXOs and note that they are not likely to be merely high-mass X-ray binaries with beamed X-ray emission, as may be the case for IXOs in starburst galaxies. Approximately half of the IXOs with multiple observations show X-ray variability, and many (19) of the IXOs have faint optical counterparts in DSS optical B-band images. Follow-up observations of these objects should be helpful in identifying their nature.

Near-Infrared and Optical Morphology of Spiral Galaxies

Abstract: We announce the initial release of data from the Ohio State University (OSU) Bright Spiral Galaxy Survey, a BVRJHK imaging survey of a well-defined sample of 205 bright, nearby spiral galaxies. We present H-band morphological classification on the Hubble sequence for the OSU Survey sample. We compare the H-band classification to B-band classification from our own images and from standard galaxy catalogs. Our B-band classifications match well with those of the standard catalogs. On average, galaxies with optical classifications from Sa through Scd appear about one T type earlier in the H band than in the B band, but with large scatter. This result does not support recent claims made in the literature that the optical and near-IR morphologies of spiral galaxies are uncorrelated. We present detailed descriptions of the H-band morphologies of our entire sample, as well as B- and H-band images for a set of 17 galaxies chosen as type examples and BRH color-composite images of six galaxies chosen to demonstrate the range in morphological variation as a function of wavelength.

The effects of thermonuclear reaction rate variations on nova nucleosynthesis: a sensitivity study

Abstract: We investigate the effects of thermonuclear reaction-rate uncertainties on nova nucleosynthesis. One-zone nucleosynthesis calculations have been performed by adopting temperature-density-time profiles of the hottest hydrogen-burning zone (i.e., the region in which most of the nucleosynthesis takes place). We obtain our profiles from seven different, recently published, hydrodynamic nova simulations covering peak temperatures in the range from Tpeak = 0.145 to 0.418 GK. For each of these profiles, we individually varied the rates of 175 reactions within their associated errors and analyzed the resulting abundance changes of 142 isotopes in the mass range below A = 40. In total, we performed ≈7350 nuclear reaction network calculations. We use the most recent thermonuclear reaction-rate evaluations for the mass ranges A = 1-20 and 20-40. For the theoretical astrophysicist, our results indicate the extent to which nova nucleosynthesis calculations depend on currently uncertain nuclear physics input, while for the experimental nuclear physicist, our results represent at least a qualitative guide for future measurements at stable and radioactive ion beam facilities. We find that present reaction-rate estimates are reliable for predictions of Li, Be, C, and N abundances in nova nucleosynthesis. However, rate uncertainties of several reactions have to be reduced significantly in order to predict more reliable O, F, Ne, Na, Mg, Al, Si, S, Cl, and Ar abundances. Results are presented in tabular form for each adopted nova simulation.

Atomic hydrogen gas in dark-matter minihalos and the compact high velocity clouds

Abstract: We calculate the coupled hydrostatic and ionization structures of spherically symmetric, pressure-supported gas clouds that are confined by gravitationally dominant dark matter (DM) minihalos and by an external bounding pressure provided by a hot medium. We focus on clouds that are photoionized and heated by the present-day background metagalactic field and determine the conditions for the formation of warm (WNM) and multiphased (CNM/WNM) neutral atomic hydrogen (H I) cores in the DM-dominated clouds. We consider ΛCDM halos with cuspy (NFW) and constant density (Burkert) cores. We compute models for a wide range of halo masses, total cloud gas masses, and external bounding pressures. We present models for the pressure-supported H I structures observed in the Local Group dwarf irregular galaxies Leo A and Sag DIG. We find that the hydrogen gas becomes neutral for projected H I column densities exceeding 1019 cm-2. We identify the H I cloud boundaries observed in Leo A and Sag DIG with the ionization fronts, and we derive an upper limit of PHIM/k 100 cm-3 K for the ambient pressure of the intergalactic medium in the Local Group. The observed H I gas scale heights in Leo A and Sag DIG imply characteristic DM densities of 1.2 amu cm-3 (or 0.03 M⊙ pc-3), consistent with the DM densities previously inferred via H I rotation curve studies of dwarf and low surface brightness galaxies. Leo A and Sag DIG obey the scaling correlations that are expected for typical (median) DM halos in a ΛCDM cosmology, provided that the halos contain constant density cores, as suggested by Burkert. We construct explicit minihalo models for the multiphased (and low-metallicity) compact high-velocity H I clouds (CHVCs). If the CHVC halos are drawn from the same family of halos that successfully reproduce the dwarf galaxy observations, then the CHVCs must be circumgalactic objects, with characteristic distances of 150 kpc. For such systems we find that multiphased behavior occurs for peak WNM H I column densities between 2 × 1019 and 1 × 1020 cm-2, consistent with observations. In contrast, if the CHVCs are extragalactic objects with distances 750 kpc, then their associated halos must be very underconcentrated, with characteristic DM densities 0.08 cm-3, much smaller than expected for their mass and significantly smaller than observed in the dwarf galaxies. Furthermore, multiphased cores then require higher shielding columns. We favor the circumgalactic hypothesis. If the large population of CHVCs represent missing low-mass DM satellites of the Galaxy, then these H I clouds must be pressure confined to keep the gas neutral. For an implied CHVC minihalo scale velocity of vs = 12 km s-1, the confining pressure must exceed ~50 cm-3 K. A hot (~2 × 106 K) Galactic corona could provide the required pressure at 150 kpc. Our static minihalo models are able to account for many properties of the CHVCs, including their observed peak H I columns, core sizes, and multiphased behavior. However, important difficulties remain, including the presence in some objects of extended low column density H I wings and Hα emission line fluxes in several CHVCs that are significantly larger than expected.

ASCA X-Ray Source Catalog in the Galactic Center Region

Abstract: The ASCA satellite made 107 pointing observations on a 5 × 5 deg2 region around the center of our Galaxy from 1993 to 1999. In the X-ray images of the 0.7-3 keV or 3-10 keV bands, we found 52 point sources and a dozen diffuse sources. All the point sources are uniformly fitted with an absorbed power-law model. For selected bright sources, Sgr A*, AX J1745.6-2901, A1742-294, SLX 1744-300, GRO J1744-28, SLX 1737-282, GRS 1734-292, AX J1749.2-2725, KS 1741-293, GRS 1741.9-2853, and an unusual flare source XTE J1739-302, we present further detailed spectral and timing analyses and discuss their nature. The dozen extended X-ray sources comprise radio supernova remnants, giant molecular clouds, and some new discoveries. Most show emission lines from either highly ionized atoms or low-ionized irons. The X-ray spectra were fitted with either a thin thermal or power-law model. This paper summarizes the results and provides the ASCA X-ray source catalog in the Galactic center region.

Weak Gravitational Lensing by a Sample of X-Ray Luminous Clusters of Galaxies. I. The Data Set*

Abstract: We present weak gravitational lensing mass measurements of a sample of 38 highly X-ray luminous clusters of galaxies with well-defined selection criteria The clusters were observed with either monolithic 20482 CCDs, the UH8K mosaic CCD camera, or both The weak shear caused by gravitational lensing was measured using recently developed techniques to correct for the effects of realistic point-spread functions and to optimally weight the contribution of each galaxy to the final shear estimate The results are presented in the form of maps of the reconstructed dimensionless surface density κ and plots of the radial cluster mass profiles The κ maps are compared to mass-traces-light predictions for κ based on two-color, V- and I-band galaxy photometry in the observed fields About 30% of the clusters in our sample show evidence of significant dynamical activity related to mergers of subclumps More than half of the clusters show signs of strong lensing Our data set more than doubles the total number of galaxy clusters with a detected weak lensing signal The data for all the clusters have been reduced and analyzed in a consistent way, and this makes our data set uniquely suitable for statistical studies of cluster properties, which will be the subject of future papers in this series

Abundances of Deuterium, Nitrogen, and Oxygen in the Local Interstellar Medium: Overview of First Results from the FUSE Mission

Abstract: Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D I, O I, and N I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 pc to 179 pc. Five of the sight lines are within the Local Bubble and two penetrate the surrounding H I wall. Reliable values of N(H I) were determined for five of the sight lines from HST data, IUE data, and published EUVE measurements. The weighted mean of DI/H I for these five sight lines is (1.52 +/- 0.08) x l0(exp -5)(1 sigma uncertainty in the mean). It is likely that the D I/H I ratio in the Local Bubble has a single value. The D I/O I ratio for the five sight lines within the Local Bubble is (3.76 +/- 0.20) x 10(esp -2). It is likely that O I column densities can serve as a proxy for H I in the Local Bubble. The weighted mean for O I/ H I for the seven FUSE sight lines is (3.03 +/- 0.21) x 10(esp -4), comparable to the weighted mean (3.43 +/- 0.15) x 10(exp -4) reported for 13 sight lines probing larger distances and higher column densities. The FUSE weighted mean of N I/ H I for five sight lines is half that reported by Meyer et al. for seven sight lines with larger distances and higher column densities. This result combined with the variability of O I/ N I (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O I, N I cannot be used as a proxy for H I or as a metallicity indicator in the LISM.

CHIANTI—An Atomic Database for Emission Lines. V. Comparison with an Isothermal Spectrum Observed with SUMER

Abstract: CHIANTI is a database consisting of critically evaluated atomic data and transition probabilities necessary to analyze spectral observations of optically thin plasmas. Previous papers described the content of the database and compared it to a solar active region spectrum between 170 and 450 A. The aim of the present paper is to compare CHIANTI predictions to off-disk spectral observations of the solar corona between 500 and 1500 A. The observed spectra were recorded by the SUMER instrument on board the Solar and Heliospheric Observatory using the full spectral range allowed by the instrument. Earlier works have demonstrated that the particular emitting plasma is isothermal at a temperature of 1.35 × 106 K, making it ideal for the assessment of the accuracy of the CHIANTI database. This assessment of the CHIANTI database allowed us (1) to select lines and ions for which the agreement between theory and observation is good, (2) to identify several lines which are blended, and (3) to stress inconsistencies between a few lines and theory, thus showing where improvements to atomic data and transition probabilities are necessary.

Global Far-Ultraviolet (912-1800 Å) Properties of Star-forming Galaxies*

Abstract: We present the results of an archival study of the Hopkins Ultraviolet Telescope (HUT) Astro-2 database. Nineteen spectra of star-forming regions and starburst galaxies were retrieved, reprocessed, and analyzed. The spectra cover the wavelength region 912-1800 A, providing access to the domain of peak luminosity from a young stellar population. We created an atlas of galaxy spectra documenting the continuum and line properties with an emphasis on the relatively unexplored spectral region below 1200 A. The dust obscuration law was derived from a comparison of the HUT spectra with synthetic population models. The law is similar to the commonly adopted starburst reddening curve at longer wavelengths and approaches the Milky Way law near the Lyman break. A simple power-law parameterization is given, which allows users to express the reddening law in terms of the stellar or nebular color excess at ultraviolet or optical wavelengths. The star formation histories were derived from the reddening-corrected continua and the ultraviolet line profiles. We find typical ages of tens of Myr and star formation densities ranging from less than 0.1 to more than 10 M⊙ yr-1 kpc-2. The absorbed ultraviolet luminosity correlates very well with the far-infrared luminosity, as expected if the dominant dust absorption occurs in a foreground screen. This correlation holds even for the most luminous galaxies in our sample, whose IRAS luminosity is in excess of 1011 L⊙.

Nuclear Deexcitation Gamma-Ray Lines from Accelerated Particle Interactions

Abstract: Total cross sections for the production of gamma-ray lines from nuclear deexcitation as a function of the projectile energy are evaluated and presented. Included are proton and α reactions with He, C, N, O, Ne, Mg, Al, Si, S, Ca, and Fe. Such functions are essential for interpretation of gamma-ray line observations of astrophysical sites which contain large fluxes of energetic particles such as solar flares, the Earth's atmosphere, planetary atmospheres and surfaces, the interstellar medium, and galactic nebulae.

Star Formation Rates in Interacting Starburst Galaxies

Abstract: By narrowband imaging in Hα and in the adjacent red stellar continuum we have studied the rate and distribution of star formation in 43 systems of luminous and ultraluminous IR galaxies currently undergoing interaction and merging. These galaxies are amongst the most luminous at 60 μm and range in distance from ~50 up to 100 Mpc. Here we present the Hα and the adjacent red-continuum narrowband images, and we compare the star formation rates derived from Hα with those estimated from the IR luminosity. We find clear evidence for substantial extinction and obscuration of star-forming regions in the optical. Without correction for reddening in the host galaxy or correction for [N II] contamination, the star formation rates derived for Hα are typically 0.5-1.0 dex lower than those estimated from the IR flux, and the scatter in the correlation is very large. However, an unexpected result is that when spectroscopic data are used to eliminate objects dominated by an active nucleus, to determine the galaxian extinction, and to correct the Hα flux for both reddening and for the contamination by the [N II] emission, a remarkably good correlation emerges between the star formation rates estimated from the Hα flux and those derived from the FIR continuum. In addition, a strong correlation is found between the extinction in the line-emitting region, AHα, and the rate of star formation. Our results invalidate the use of Hα imaging as a reliable indicator of star formation in starburst galaxies unless spectroscopic data are also available. This has important implications for the determination of star formation rates in high-redshift galaxies. Finally, we find no correlation between the measured star formation rates, and the interaction class, suggesting that the enhanced star formation rates triggered by the interaction continue throughout the whole of the merging sequence.

Mapping Initial Hydrostatic Models in Godunov Codes

Abstract: We look in detail at the process of mapping an astrophysical initial model from a stellar evolution code onto the computational grid of an explicit, Godunov-type code while maintaining hydrostatic equilibrium. This mapping process is common in astrophysical simulations, when it is necessary to follow short-timescale dynamics after a period of long-timescale buildup. We look at the effects of spatial resolution, boundary conditions, the treatment of the gravitational source terms in the hydrodynamics solver, and the initialization process itself. We conclude with a summary detailing the mapping process that yields the lowest ambient velocities in the mapped model.

The Structure of the Local Interstellar Medium. I. High-Resolution Observations of Fe II, Mg II, and Ca II toward Stars within 100 Parsecs

Abstract: High-resolution absorption measurements (λ/Δλ 100,000) of the resonance lines of Fe II, Mg II, and Ca II are presented for all available observed targets within 100 pc. The Fe II and Mg II spectra were obtained with the Goddard High Resolution Spectrograph (GHRS) and the Space Telescope Imaging Spectrograph (STIS) instruments aboard the Hubble Space Telescope (HST). Of the 63 observations of targets within 100 pc, we present new measurements for 24 lines of sight. We also compiled all published absorption measurements based on Ca II spectra obtained by various ground-based instruments. For each observation we provide measurements of the central velocity, Doppler parameter, and column density for each absorption component. These three ions provide the best opportunity to measure the component velocity structure. Because these are the heaviest ions observed in absorption through the warm local interstellar medium (LISM), the narrow line widths minimize significant blending of components and allow for accurate measurements of the central velocity. We present a statistical analysis of the LISM absorption measurements, which provides an overview of some physical characteristics of warm clouds in the LISM, such as, temperature, turbulent velocity, ionization degree, and depletion. The complete collection and reduction of all LISM absorption measurements provides an important database for studying the structure of nearby warm clouds. Subsequent papers will present models for the morphology and physical properties of individual structures (clouds) in the LISM.