Dan F. Lester

CHARA Array K'-Band Measurements of the Angular Dimensions of Be Star Disks

We present the firstK 0 -band,long-baseline interferometric observations of the northern Be starsCas,� Per,� Tau, andDra. The measurements were made with multiple telescope pairs of the CHARA Array interferometer and in every case the observations indicate that the circumstellar disks of the targets are resolved. We fit the interferometric visibilities with predictions from a simple disk model that assumes an isothermal gas in Keplerian rotation. We derive fitsof thefourmodelparameters(diskbasedensity,radialdensityexponent,disknormalinclination,andpositionangle) for each of the targets. The resulting densities are in broad agreement with prior studies of the IR excess flux, and the resultingorientationsgenerallyagreewiththosefrominterferometricHandcontinuumpolarimetricobservations.We find that the angular size of the K 0 diskemissionis smaller thanthatdeterminedfor the Hemission, and weargue that thedifferenceisthe resultof a larger Hopacityandtherelativelylarger neutral hydrogenfractionwithincreasingdisk radius. All the targets are known binaries with faint companions, and we find that companions appear to influence the interferometric visibilities in the cases ofPer andDra. We also present contemporaneous observations of the H� , H� ,andBremissionlines.Syntheticmodelprofilesoftheselinesthatarebasedonthesamediskinclinationandradial densityexponentasderivedfromtheCHARA Arrayobservationsmatchtheobservedemissionlinestrengthif thedisk base density is reduced by � 1.7 dex.

A near-infrared spectroscopic study of the starburst core of M82

Near-IR spectroscopy of the M82 starburst core is presented, including complete J, H, and K band spectra with a resolution of 0.0035-micron for the inner 60 pc of the galaxy. Also, spatial profiles along the starburst ridge are presented for Br-gamma, molecular hydrogen, and forbidden Fe II line fluxes. Emission from shocked molecular hydrogen is detected from the core of M82. The distribution of features across the starburst disk are mapped to study the relationships between spectral diagnostics. The observations are used to test the appropriateness of single-beam, aggregate models for studying the physical conditions in starbursts. 68 refs.

Early observations of SN 1993J in M81 at McDonald observatory

The visual light and color curves of SN 1993J show behavior unlike that of other Type II supernovae. The initial flash peaked at V=10.7 on JD=2,449,076.8, 3 days following the shock outbreak which is estimated to have occurred at JD 2,449,074.5=March 28.0 UT. High-dispersion spectra show 10 velocity components in each of the Na D lines. Early optical and IR spectra show a nearly blackbody continuum cooling from 14,900±1000 K to 11,800±700 K from March 31.2 to April 1.2 UT. Superposed on this continuum are broad, weak Balmer, Paschen, and He I lines. From blackbody fits to early spectra the color excess is estimated to be about E(B−V)=0.15±0.02

High angular resolution far-infrared observations of Sagittarius B2

High-angular-resolution FIR observations of the continuum emission from the Sagittarius B2 molecular cloud core are reported. Evidence is found for a significantly spatially extended component of the FIR emission at 50- and 100-micron wavelength, which has an angular extent of 1 x 2 arcmin. Its approximate spatial coincidence with a low-level extended component of the radio free-free emission and with the portion of the SGR B2 core having densities not less than 10 exp 5 cu cm derived from molecular observations suggests that the ionizing radiation from the massive stars in the compact sources is diffusing through a region with a beam-averaged visual extinction not less than a few hundred mag. It is inferred that the gas and the dust in the central portion of the cloud surrounding the compact radio free-free/FIR sources are highly clumped.

Far-infrared line observations of planetary nebulae. I - The forbidden O III spectrum

Observations of the far-infrared fine structure lines of O III have been obtained for six planetary nebulae. The infrared measurements are combined with optical O III line fluxes to probe physical conditions in the gas. From the observed line intensity ratios, a simultaneous solution was obtained for electron temperature and density, as well as means of evaluating the importance of inhomogeneities. Densities determined from the far-infrared O III lines agree well density diagnostics from other ions, indicating a fairly homogeneous density in the emitting gas. Temperatures are determined separately from the O III 4363/5007 A and 5007 A/52 micron intensity ratios and compared. Systematically higher values are derived from the former ratio, which is expected from a nebula which is not isothermal. Allowance for the presence of temperature variations within these nebulae raises their derived oxygen abundances, determinations to be reconciled with the solar value.

Far-infrared measurements of N/O in H II regions - Evidence for enhanced CN process nucleosynthesis in the inner Galaxy

Measurements of the far-infrared lines of forbidden O III 51.8 microns, 88.4 microns, and forbidden N III 57.3 microns are presented for 13 H II regions covering a wide range in Galactocentric distance. These lines are used to measure the variation of N(2+)/O(2+) with Galactic radius from the center out to 12 kpc. It is argued that this ratio is indicative of the elemental ratio N/O. It is shown that the line flux ratio 57.3 microns forbidden N III/51.7 microns forbidden O III is nearly equal to the N(2+)/O(2+) abundance ratio and is only weakly dependent on nebular conditions. The derived N(2+)/O(2+) values show an inverse correlation with distance from the Galactic center. N(2+)/O(2+) tends to increase as the H II region electron temperature decreases, a behavior consistent with a model of Galactic enrichment in which N-14 is secondary to primary O-16, a scenario that is the natural result of CN processing. 72 references.

Properties of the gas and stellar content of the superluminous galaxy NGC 6240

H and K band spectra of the luminous far-infared galaxy NGC 6240 at resolving powers between 160 and 625 are presented. Line fluxes for six H2 lines are measured. The Br-gamma hydrogen recombination line is detected. The galaxy is found to be a strong source of forbidden Fe II emission. The v = 1 levels of the H2 are populated thermally at a temperature of 1300 K. The H2 emission appears to be coextensive with the broad-line component of shock-ionized gas that is seen optically near the nuclei. The strength of the B-gamma line indicates that the extinction toward the source is about A(v) = 3. NGC 6240 does not appear to be simply a scaled-up version of a bona fide starburst as in M82. Evidence that the molecular line-emitting region is rouglly twice the size of the continuum source indicates that the shocked H2 does not originate in young stars. 30 references.

Far-infrared image restoration analysis of the protostellar cluster in S140

Image restoration techniques are applied to one-dimensional scans at 50 and 100 microns of the protostellar cluster in S140. These measurements resolve the surrounding nebula clearly, and Fourier methods are used to match the effective beam profiles at these wavelengths. This allows the radial distribution of temperature and dust column density to be derived at a diffraction limited spatial resolution of 23 arcsec (0.1 pc). Evidence for heating of the S140 molecular cloud by a nearby ionization front is established, and the dissociation of molecules inside the ionization front is spatially well correlated with the heating of the dust. The far-infrared spectral distribution of the three near-infrared sources within 10 arcsesc of the cluster center is presented. 22 references.

A Spectrophotometric Survey of K-Band Emission Lines in Planetary Nebulae

We present observations of 16 planetary nebulae (PNs) in the 2 μm (K band) spectral region, obtained with a long-slit near-infrared spectrometer at McDonald Observatory. In general, the strongest features in our spectra are recombination lines of H I, He I, and (in some cases) He II. Half the sample shows emission from vibrationally excited H2. Some of the observed PNs (e.g., M 1-13) display H2 line ratios characteristic of shocked, thermalized gas, while others (e.g., BD +30 3639) have ratios intermediate between pure radiative (UV) and shock excitation, consistent with either a combination of the mechanisms or UV illumination of dense material. Our spectra of J900 and M 1-13 confirm that published narrowband images trace the H2 emission, and we find that the H2 emission in SwSt 1 has a larger spatial extent than previously reported. In IC 5117, SwSt 1, and NGC 40 we detect the [Kr III] 2.199 μm line identified by Dinerstein in 2001, with strengths indicating that krypton is enriched relative to the solar abundance, most markedly so in NGC 40. We also detect several lines from the 3G term of [Fe III] in Vy 2-2, SwSt 1, and marginally in Cn 3-1. The [Kr III] and [Fe III] lines fall near in wavelength to H2 transitions, which are often used as diagnostics for UV excitation because they arise from higher vibrationally excited levels (v = 2, 3). For moderate spectral resolving power, R ≤ 600, these lines may be blended with, or even mistaken for, the corresponding H2 lines, leading to misinterpretation of the H2 emission. The strength of both the Kr and Fe nebular emission lines can be enhanced by special circumstances, Kr because of nucleosynthetic self-enrichment in the progenitor star and Fe due to inefficient initial dust condensation or partial destruction of the dust after formation, causing a larger fraction of the elemental iron to reside in the gas phase.

Far-infrared emission from the AG Carinae ring

A maximum entropy deconvolution technique has been used to resolve far-infrared emission from cool dust associated with the galactic S Doradus variable AG Car. The 50 and 100 micron fluxes are shown to peak at about 9 arsec from Ag Car in the densest part of the ionized ring structure seen around the star. Similarities noted between AG Car and R71 suggest that circumstellar dust ring structures like that of AG Car may often be associated with evolved massive emission-line stars. The results indicate that the ring structure may be due to material that was lost by AG Car during a prior evolutionary state and has subsequently been swept up by the present hot supergiant wind. 42 references.