Table of contents

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman. We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 10⁶—10⁹ yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at a Web site, which allows users to run specific models with nonstandard parameters as well. We also make the source code available to the community.

To increase the redshift range and look-back time over which the radio luminosity function can be measured directly, we identified 1157 galaxies in the Las Campanas Redshift Survey (LCRS) having isophotal (red) magnitudes m_iso ≤ 18.0 with radio sources brighter than 2.5 mJy beam^-1 in the 1.4 GHz NRAO VLA Sky Survey (NVSS). Since the NVSS has 45'' FWHM angular resolution, these radio and optical limits include nearly all LCRS galaxies with 1.4 GHz luminosities L ≥ 10^22.4 W Hz^-1 at z ≈ 0.05 to L ≥ 10^23.6 W Hz^-1 at z ≈ 0.2. The mean redshift ⟨z⟩ ≈ 0.14 of the radio-detected galaxies is higher than the mean redshift ⟨z⟩ ≈ 0.10 of the optical sample. This indicates that, statistically, the radio emission was detected from galaxies with the highest optical luminosities. Of the 1157 galaxies, 261 were also identified with far-infrared (FIR) sources in the IRAS Point Source Catalog and Faint Source Catalog. The principal radio energy sources in all identified galaxies were classified as either "starburst" or "AGN" on the basis of their FIR-radio flux ratios, FIR spectral indices, and radio-optical flux ratios. We show that the radio-optical flux ratio can be effectively used to classify the dominant energy source for the radio emission even if FIR fluxes and radio morphological data are not available.

The third catalog of high-energy gamma-ray sources detected by the EGRET telescope on the Compton Gamma Ray Observatory includes data from 1991 April 22 to 1995 October 3 (cycles 1, 2, 3, and 4 of the mission). In addition to including more data than the second EGRET catalog and its supplement, this catalog uses completely reprocessed data (to correct a number of mostly minimal errors and problems). The 271 sources (E > 100 MeV) in the catalog include the single 1991 solar flare bright enough to be detected as a source, the Large Magellanic Cloud, five pulsars, one probable radio galaxy detection (Cen A), and 66 high-confidence identifications of blazars (BL Lac objects, flat-spectrum radio quasars, or unidentified flat-spectrum radio sources). In addition, 27 lower confidence potential blazar identifications are noted. Finally, the catalog contains 170 sources not yet identified firmly with known objects, although potential identifications have been suggested for a number of those. A figure is presented that gives approximate upper limits for gamma-ray sources at any point in the sky, as well as information about sources listed in the second catalog and its supplement, that do not appear in this catalog.

The Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory has been operating for over 7 yr since its launch in 1991 April. This span of time far exceeds the design lifetime of 2 yr. As the instrument has aged, several changes have occurred owing to spark chamber gas exchanges as well as some hardware degradation and failures, all of which have an influence on the instrument sensitivity. This paper describes postlaunch measurements and analysis that are done to calibrate the instrument response functions. The updated instrument characteristics are incorporated into the analysis software.

In order to construct a sample of planetary nebulae (PNe) unbiased by dust extinction, we first selected the 1358 sources in the IRAS Point Source Catalog north of J2000 declination δ = -40° having measured S(25 μm) ≥ 1 Jy and colors characteristic of PNe: detections or upper limits consistent with both S(12 μm) ≤ 0.35S(25 μm) and S(25 μm) ≥ 0.35S(60 μm). The majority are radio-quiet contaminating sources such as asymptotic giant branch stars. Free-free emission from genuine PNe should make them radio sources. The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog were used to reject radio-quiet mid-infrared sources. We identified 454 IRAS sources with radio sources brighter than S ≈ 2.5 mJy beam^-1 (equivalent to T ≈ 0.8 K in the 45'' FHWM NVSS beam) by positional coincidence. They comprise 332 known PNe in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae and 122 candidate PNe, most of which lie at very low Galactic latitudes. Exploratory optical spectroscopic observations suggest that most of these candidates are indeed PNe optically dimmed by dust extinction, although some contamination remains from H II regions, Seyfert galaxies, etc. Furthermore, the NVSS failed to detect only 4% of the known PNe in our infrared sample. Thus it appears that radio selection can greatly improve the reliability of PN candidate samples without sacrificingcompleteness.

We present a new catalog of 406 dense cores optically selected by using the STScI Digitized Sky Survey (DSS). In this catalog 306 cores have neither an embedded young stellar object (EYSO) nor a pre-main-sequence (PMS) star, 94 cores have EYSOs (one core has both an EYSO and a PMS star), and six cores have PMS stars only. Our sample of dense cores in the catalog is fairly complete within a category of northern Lynds class 5 and 6 clouds and southern Hartley et al. class A clouds, providing a database useful for the systematic study of dense cores. Most of the cores listed in the catalog have diameters between 0.05 and 0.36 pc with a mean of ~0.24 pc. The sizes (~0.33 pc in the mean) of cores with EYSOs are found to be usually larger than the sizes (~0.22 pc in the mean) of starless cores. The typical mean gas density of the cores is ~7 × 10³ cm^-3. Most of the cores are more likely elongated than spherical (mean aspect ratio: ~2.4). The ratio of the number of cores with EYSOs to the number of starless cores for our sample is about 0.3, suggesting that the typical lifetime of starless cores is 0.3-1.6 Myr, about 3 times longer than the duration of the class 0 and class I phases. This lifetime is shorter than expected from models of ambipolar diffusion, by factors of 2-44.

Maximum entropy image reconstruction (Doppler imaging) is applied to HII 686 (K4 V, v sin i = 64 km s^-1) and HII 3163 (K0 V, v sin i = 70 km s^-1), two zero-age main-sequence stars of the Pleiades cluster. Their surface temperature distributions are determined in order to study the nature of magnetic activity in ultrafast rotators of known evolutionary status. Specific intensity line profiles used in the Doppler imaging (DI) algorithm are synthesized. The sensitivity of the reconstructions to the choice of input stellar and atomic data is investigated. The quality of the fit to the average disk-integrated line profile is found to be more important to DI analysis than the exact parameters used to generate the fit when the shape of the disk-integrated line profile is dominated by rotational broadening. Fifteen absorption lines are used to generate 15 individual reconstructions of each Pleiades target. Averaging reduces noise in the reconstructions. However, simulations reveal that spurious features tend to cluster systematically at subobserver longitudes and can therefore persist in the images even after averaging several reconstruction together. Such "phase-ghosting" becomes more severe as the signal-to-noise ratio decreases and does not appear to depend on the spot morphology. HII 686 shows one predominant feature at 77° latitude, which is 860 K cooler than the surrounding photosphere. HII 3163 shows a predominant feature centered at approximately 70° latitude, which has two temperature minima (780 K cooler than the photosphere) separated by approximately 130° in longitude. However, photometric observations suggest that this double-lobed morphology is a consequence of poor phase sampling. One temperature minimum located midway in longitude better reproduces the observed light curve. We are unable to make any reliable detections of low-latitude features on the surface of either star. The results are discussed in light of recent theoretical observations and existing image reconstructions of similar objects. No correlations are found among reconstructions that could be attributed to line characteristics: equivalent width, excitation potential, or depth of formation. This is also true for the Li I and K I resonance lines. Despite their temperature sensitivity, they yield results that are consistent with those determined from lines that are not temperature sensitive. For each object, the chromospheric residual emission (Hα, Ca II 8498 Å) is measured as a function of rotational phase. Maximum emission does not consistently occur at the phase of spot transit.

We present a library of Penn State Fiber Optic Echelle (FOE) observations of a sample of field stars with spectral types F to M and luminosity classes V to I. The spectral coverage is from 3800 to 10000 Å with a nominal resolving power of 12,000. These spectra include many of the spectral lines most widely used as optical and near-infrared indicators of chromospheric activity such as the Balmer lines (Hα to H), Ca II H & K, the Mg I b triplet, Na I D₁, D₂, He I D₃, and Ca II IRT lines. There are also a large number of photospheric lines, which can also be affected by chromospheric activity, and temperature-sensitive photospheric features such as TiO bands. The spectra have been compiled with the goal of providing a set of standards observed at medium resolution. We have extensively used such data for the study of active chromosphere stars by applying a spectral subtraction technique. However, the data set presented here can also be utilized in a wide variety of ways ranging from radial velocity templates to study of variable stars and stellar population synthesis. This library can also be used for spectral classification purposes and determination of atmospheric parameters (T_eff, log g, [Fe/H]). A digital version of all the fully reduced spectra is available via ftp and the World Wide Web (WWW) in FITS format.

Collision strengths for electron impact excitation of fine-structure levels in sulfur-like Fe XI are calculated in a semirelativistic R-matrix approach. The 38 fine-structure levels arising from the 20 LS states 3s²3p⁴³P,¹D,¹S; 3s3p⁵³P^o,¹P^o; 3s²3p³(⁴S^o)3d³D^o, 3s²3p³(²P^o)3d^1,3P^o,^1,3D^o,^1,3F^o, 3s²3p³(²D^o)3d^1,3S^o,^1,3P^o,^1,3D^o,^1,3F^o are included in our calculation. The target levels are represented by configuration interaction wave functions. The relativistic effects are considered in the Breit-Pauli approximation by including one-body mass correction, Darwin term, and spin-orbit terms in the scattering equations. Collision strengths for transitions from the 3s²3p⁴³P_2,1,0 levels to the fine-structure levels of the 3s²3p³3d configuration are compared with the distorted-wave results of Bhatia & Doschek at 8.0, 16.0, 24.0 ryd. There are some significant discrepancies between the two calculations, mostly caused by the difference in target wave functions. The collision strengths are integrated over a Maxwellian distribution of electron energies to obtain effective collision strengths over the temperature range from 5 × 10⁵ to 5 × 10⁶ K.

Collision strengths for fine-structure transitions among the levels of the (1s²) 2s²2p², 2s2p³, 2p⁴, 2s²2p3s, 2s²2p3p, and 2s²2p3d configurations of O III have been computed over a wide range of energies below 13.0 ryd using the R-matrix program. All partial waves with L ≤ 40 have been included to ensure the convergence of results. Excitation rate coefficients, in the form of dimensionless effective collision strengths, have also been computed at temperatures below 200,000 K. The results are compared with available calculations, and accuracy of the data is assessed.