Search

The 1-0 S(1) line of molecular hydrogen has been observed at high spectral resolution in several sources where the emission was suspected of being fluorescent. In NGC 2023, the Orion Bar, and Parsamyan 18, the S(1) line is unresolved, and the line center close to the rest velocity of the ambient molecular cloud. Such behavior is expected for UV-excited line emission. The H2 line widths in molecular clouds thus can serve as diagnostic for shocked and UV-excitation mechanisms. If the lines are broader than several km/s or velocity shifts are observed across a source it is likely that shocks are responsible for the excitation of the gas.

An important means of studying the unusual activity within the central ~0.15 parsec of the galaxy is to obtain detailed information on the high velocity ionized gas there. This gas was first reported by Hall, Kleinmann, and Scoville (1982), who observed the He I line at 2.06 μm. Subsequent observations of this line and the Br ∝ and Br γ lines of H I (4.05 μm and 2.17 μm, respectively) by Geballe et al. (1984, 1987) have defined the coarse spatial and spectral properties more accurately. Briefly, the broad (i.e., |v| > 400 km/s) line emission, as observed at velocity resolutions as high as 400 km/s and angular resolutions as high as 2.5″ (1) extends approximately to +/– 700 km/s (e.g., see Fig. 1), (2) is spatially resolved, with a characteristic dimension of 3″, (3) is centered approximately on IRS 16C, and (4) appears to be due neither to rotational motion nor to a simple radial flow from or onto a single compact object. These properties are difficult to understand in terms of simple models, and point out the necessity for further measurements at higher spectral and spatial resolutions.

The rate of evolution of CO from Comet Kohoutex is presented. The observations were made approximately two months after perihelion. The rate of evolution of CO at that time was apparently less than that of CH3CN observed before perihelion.

Spectra of 4.7 microns fundamental band absorption lines of carbon monoxide in GL 2591 and OMC-1:IRc2 are presented. In GL 2591 the observed lines have total velocity widths of about 100 km/s, far larger than that in the 2.6 mm CO line seen toward this object. The spectra indicate ejection of material at 100 km/s at a distance of approximately 10 to the 15th cm from the central object, followed by deceleration. The single CO line profile observed in IRc2 appears similar to those seen previously in BN except for the possible presence of a faint blue wing. The lack of strong absorption at highly blueshifted velocities in IRc2 implies that if IRc2 is the source of the high-velocity molecular outflow in OMC-1, then that outflow must be oriented so that little or no high-velocity gas is along the line of sight to IRc2. 22 references.

An infrared spectrometer for the 1 μm < λ < 5 μm wavelength band is described. The instrument consists of a grating spectrometer cooled to solid nitrogen temperature, which can be used with a piezoelectrically scanned Fabry-Perot interferometer. Resolving powers between 102 and 105 can be achieved with this instrument. This particular combination of spectrometer components leads to high sensitivities longward of the 2 μm band, where Fourier transform spectrometers are more severely limited by noise from the thermal background.

Three lines of the fundamental vibration-rotation band of CO have been detected in emission toward H2 Peak 1 in OMC-1. Both the velocities of maximum line intensity and the linewidths appear to be similar to those of the H2 S(1) line, implying that the bulk of the line emission occurs in a shock within the molecular cloud. The relative line intensities, which are coupled to the populations of rotational levels in the ground vibrational state, yield average gas temperatures of about 1000 K. The luminosity of the CO fundamental band is nearly one-half of that from shocked H2, a considerably larger fraction than has been predicted previously. A search for Br-alpha line emission at Peak 1 produced an upper limit for that line flux which, including extinction, is less than one percent of the H2 S(1) flux. 22 references.

Recent observations of the 12.8-micron Ne II emission from the galactic center have revealed a region of primarily blueshifted emission in addition to the previously detected redshifted emission. It appears most likely that the blueshifted and redshifted emission come from separate clouds and that the dynamics of the ionized gas is dominated by the gravitational potential of the massive core at the galactic center. On the basis of the velocities and velocity dispersions, the total mass within a radius of 1 pc about the galactic center is estimated to be of the order of 4 million solar masses.

High-spectral-resolution observations of the 3.3 and 3.4 microns features in the three planetary nebulae NGC 7027, IC 418, and BD +30 deg 3639, in the H II region S106, and in the 'red rectangle' HD 44179 are presented. The profile of the unidentified 3.3 microns emission feature is similar in all five sources. The unidentified feature previously referred to as the 3.4 microns feature actually consists of two components, a low-level emission from 3.35 to 3.60 microns and a narrow emission peak at 3.40 microns. The strength of the latter feature relative to that of the 3.3 microns feature varies by a a factor of three from source to source. The origin and properties of these features may be explained by further development of the small-grain models of Sellgren (1984) and Leger and Puget (1984).

Spectra of the B-gamma recombination line of hydrogen in the Galactic center show that the line has central velocities and shapes similar to those reported previously for the Ne II line. Observations are made at 10 positions within the infrared cluster of the Galactic center with a circular diaphragm of diameter 5 arcsec and with a spectral resolution of approximately 85 km/sec. The spectra confirm that the ionized gas in the Galactic center is distributed in discrete clouds.

New infrared observations of Ne II, Ar III, and S IV are used in optical observations of other ionization states of the considered elements to evaluate the abundances of neon, argon, and sulfur in 18 planetary nebulae. Attention is also given to one or more of the infrared lines in 18 other nebulae. It is pointed out that S IV was detected in approximately 90% of the observed objects, while Ar III was found in about 80%, and Ne II in roughly one-third. It is noted that optical observations typically include only a limited region of the nebula, while the infrared measurements frequently involve integration over the entire nebular image.

IRAS 17516-2525 is a cool object at infrared wavelengths between 1 and 60μm. Spectroscopy in the wavelength ranges 2 - 2.5μm and 3 - 3.5μm shows the presence of Brα, Brγ, Pfγ emission lines and of a weak C2H2 absorption band, all clearly associated with the IRAS source. At the infrared position a faint star with a visual magnitude of about 20 is found.

High-spectral-resolution Fabry-Perot observations of the H{sub 2} 2.12-micron line emissions of several Herbig-Haro (HH) objects are discussed. It is shown that H{sub 2} emission by the shock heating of external molecular gas in the wings of the bow shock associated with the working surface of a high-velocity jet may occur for HH objects associated with the jet's end. The shock heating of external molecular gas entrained in the flow by internal shocks occurring in the jet itself and/or in its boundary layer may be the H{sub 2} emission mechanism for HH objects observed along the flow axis. 59 refs.

We present high spatial resolution infrared images of the planetary nebulae NGC 7027, M2-9, BD +30 3639, NGC 7099 and NGC 7662. These were taken through a selection of broad and narrow-band line and continuum filters (including a Fabry-Pérot interferometer) using the 2D infrared array “IRCAM” on the United Kingdom Infrared Telescope, UKIRT, in July 1987. Comparison is made with recently published high-resolution VLA radio maps (Basart and Daub 1987, Ap. J., 317, 412) and mid-IR Wyoming Infrared Telescope raster-scanning maps (Bentley et al.1984, Ap. J., 278, 665).

The 12.8-micron fine-structure line of Ne II has been mapped in the central 25 arcsec of NGC 253 with a 6-arcsec beam and 0.1-0.15-kayser spectral resolution. As in visible studies, both circular and noncircular motions were observed. However, there are major differences between the Ne II velocities and those measured in the optical and radio regions.

Portions of the 5- m fundamental vibration-rotation band of CO have been observed and analyzed for a number of late-type giant and supergiant stars. In at least one of these, 0 Cet, lines of H2 0 also appear to be present in the spectrum near 5 m. Analysis using synthetic spectra computed from model atmospheres yields values for 12C/13C of approximately 30 in a Her, 15 in a Sco, and 10 in a Ori. 160/170 is 500 in a Her; similar values are indicated for a Ori and a Sco. No evidence for values of 160/180 significantly different from the terrestrial value is found for these three stars. The elemental abundance ratio [C/H] is found to be lower than the cosmic value for all three stars; however, the ratios are dependent on the assumed continuum temperatures at 5 Lm, which are somewhat uncertain. The present results imply the mixing of CN-cycle products of main-sequence burning into the envelopes of these stars. Post-main-sequence processing of the envelopes of a Sco and a Ori is implied by their low '2C/'3() values. If the envelope of a Her has not undergone post-main-sequence CN processing (as is suggested by its '2C/13C ratio), then mixing down to the region of main-sequence NO processing is suggested by its low value of 160/170. Key words: stellar spectra-infrared-late-type stars

The molecular ion H3(+) is thought to play a fundamental role in the chemistry of the interstellar medium. Here, a search for infrared vibration-rotation lines of H3(+) at 4 microns toward five obscured infrared objects is reported. Upper limits corresponding to H3+ column densities of (4-10) x 10 to the 14th/sq cm are found. 45 refs.

Spectra of the H2 nu = 1-0 S(1) emission line in Orion, observed at various positions with a resolution of 20 km/s, are presented. The intrinsic full width at half-maximum of the line ranges from 18 to 58 km/s over the observed positions. Analysis of the line profiles shows that the emitting gas is probably expanding from a region near the BN and KL infrared sources at velocities typically of 40 km/s but as high as 100 km/s, and that it is associated with the source of the broad lines seen in the spectra of many other molecules. Strong constraints are placed on models of the physical processes responsible for the broad emission lines.

Observations of the H/sub 2/ Nu 1 yields O S(1) and Q(3) lines in the planetary nebula NGC 7027 yield an intrinsic Q(3)/S(1) line intensity ratio of 0.74 + or - 0.08. This value is consistent with the theoretical ratio of the Einstein A coefficients of these transitions. The HI 20-5 line intensity in NGC 7027 is also reported and discussed.

A 1-micron CCD picture and maps of the Ne II and Ar III fine-structure lines have been obtained in a region roughly one arcmin in size centered on the core of the compact H II region G333.6 - 0.2. The two emission-line maps show nearly identical intensity distributions, although much different fluxes. The maps are similar to the 1-micron picture smoothed to their angular resolutions. The infrared line of S IV also was detected and appears to have a spatial intensity distribution similar to that of the other fine-structure lines. The 1-micron picture reveals a small number of objects of nearly stellar appearance in the core, suggesting that G333.6 - 0.2 is powered by a compact cluster of sources. Stellar continuum radiation probably is responsible in part for the low equivalent width of the B-gamma line in the core.

Observations of the v=1-0 S(1) and S(0), and v=2-1 S(1) emission lines of H2 in the Orion molecular cloud are presented, showing that the emission region has an approximately circular symmetry, which may be divided into a central and a peripheral region. The emission lines in the central region have a large range of velocities, and predominantly occur at the negative velocities of 0 to -100 km/sec, while those at the periphery are symmetric. The brightness of the peak emission is generally higher at positions in the periphery than in the central region. These results lead to a model of H2 line emission in which there is gas undergoing radial expansion at velocities of up to about 100 km/sec within a region of some 2.5 x 10 to the 17th cm in diameter around the cluster of IR sources. A substantial part of the H2 line emission comes from the outside boundary of this expansion region, where the flow collides with the gas in the molecular cloud.

The high-velocity wings of the Br-alpha (405 micron) line at the Galactic center have been mapped with a 2.5 arcsec beam and at a velocity resolution of 400 km/s. The peak intensity of the high-velocity line emission is coincident with the position of the source IRS 16 Center. It is suggested that the broad-line emission either is from more than one compact wind source or is the result of an interaction between an ultrahigh velocity wind and slower moving ionized gas in the bar whose trajectory brings it close to the wind source. 31 references.

Profiles of the Br-alpha line of H I at a velocity resolution of 45 km/s are presented for the compact imbedded infrared objects BN, S106/IRS 3, GLS 490, GL 961, GL 989, Mon. R2/IRS 2, and for the visible objects LkH-alpha 101, T Tau, and R Mon. A proportionality obtained between Br-alpha luminosity and bolometric luminosity is shown to extend over three orders of magnitude, supporting the idea that the physical conditions and gas motions in the circumstellar envelopes of stellar objects are closely related over a wide range of luminosities. The Br-alpha line strengths are compared to radio continuum flux densities in the context of stellar wind models. Momentum deposition rates deduced from Br-alpha or radio continuum fluxes are consistent with those available in the radiation fields, which appear capable of driving the ionized gas outflows in the vicinity of the core sources. The results of a comparison of the H-alpha and Br-alpha profiles for T Tau are discussed.

We report on 2 micrometers spectroscopy of three Seyfert and two star burst galactic nuclei. We have detected line emission from vibrationally excited H2 in the Seyfert galactic nuclei NGC 1275, NGC 3227, and NGC 4151. For NGC 1275 and NGC 4151, these detections are the first reported detections of molecular line emission. We have also measured the Br(gamma) line flux in NGC 4151 and obtained an upper limit on the Br(gamma) line flux in NGC 1275. There is large range in the observed S(1) to Br(gamma) line ratio for both Seyfert and starburst galaxies (measured in this work and by others). We rule out UV fluorescence based on the S(1) to Br(gamma) line ration and the H2 line ratios in the Seyfert galaxy NGC 1275. Shocks probably excite the H2 emission in this galaxy. UV fluorescence may be the excitation mechanism in the Seyfert 1 galaxies NGC 4151 and NGC 3227. The H2 lines are not formed in the broad-line regions these Seyfert 1 galaxies based on our measured upper limits on the S(1) line widths. Simple starburst models cannot account for the highest of the measured ratios of S(1) to Br(gamma) line flux, most notably in the starburst galaxy NGC 6240 and in the peculiar Seyfert NGC 1275. Since the galaxies with the largest values of this ratio also have strong morphological evidence of galaxy-galaxy interactions, global shocks rather than shocks within young stellar outflows and remnants may be responsible for the excitation of the molecular hydrogen in these galaxies.

A sample was selected from the IRAS Point Source Catalogue based on the following selection criteria: very red (“cold”) IRAS-colours: roughly F25/F12 > 2.5 and F60/F25 < 1.2; and low IR-variability: VAR < 30. These non-variable IR-sources may be stars that have evolved beyond the AGB (Asymptotic Giant Branch); a large fraction (40%) is associated with known planetary nebulae (Van der Veen and Habing, 1987, Astron. Astrophys., in press). To determine the nature of the other 60% additional observations were made mainly in the infrared: 1–13 μm, during 4 observing runs: ESO (La Silla, Chile) in July 1986 and June 1987; UKIRT (Hawaii) in August 1986 and June 1987. A total number of 58 sources was observed. A summary of the observations: -IR broad band photometry at 1.2, 1.6, 2.2, 3.8 and 4,6 μm for all 58 sources. -IR broad band photometry at 8.4, 9.7 and 12.8 μm for 19 sources. -IR small band photometry for 4 sources in the ranges 2–2.5 μm and 3–3.5 μm. -IR spectroscopy for 10 sources in the ranges 2–2.5 μm and 3–3.5 μm, -V, R, I observations (0.55, 0.7 and 0.9 μm) for 5 sources associated with a star of visual magnitude 8–9. These observations were carried out by D. de Winter (Amsterdam) with the 0.5-m ESO telescope at La Silla (Chile). -Walraven photometry (0.32, 0.36, 0.38, 0.43 and 0.54 μm) for 21 stars brighter than V = 15 and within 10“ from the IRAS position. These observations were carried out by M. van Haarlem (Leiden) with the 0.9-m Dutch telescope at La Silla (Chile).

Column densities of molecular hydrogen have been calculated from 19 infrared vibration-rotation and pure rotational line intensities measured at peak 1 of the Orion molecular outflow. The run of column density with energy level is similar to a simple coolng zone model of the line-emitting region, but is not well fitted by predictions of C-shock models current in the literature.

The J = 2 to 1 transition of the first excited vibrational state (v = 1) Si(28)O(16) has recently been shown to produce maser amplification near 86,245 MHz in Orion A and in several stars. Two possible pumping mechanisms are proposed for such masers. One involves the near coincidence between the frequencies of the 1-0 (RO) and 3-2 (R18) transitions in Si(28)O(16). The other requires emission by SiO and reabsorption without the necessity for an accidental frequency coincidence. Each of these types of mechanisms may occur for other transitions of molecules in a medium illuminated by intense infrared radiation, or with strong temperature gradients.

Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.

Observations of infrared fine-structure line emission from compact clouds of ionized gas within Sgr A West are presented. These clouds have diameters of 0.1-0.5 pc, internal velocity dispersions of 100 km/s (FWHM), and line center velocities up to + or - 260 km/s. Their masses are not accurately determined but are probably between 0.1 and 10 solar masses. They are ionized by radiation like that of stars of effective temperature not greater than 35,000 K. The clouds are shown to have lifetimes of 10,000 yr and so must be generated and dissipated at a rate of a few per 1000 yr. From analysis of the distribution of the velocities of the clouds, a most probable mass distribution is derived which includes a central pointlike mass of several x 10 to the 6th solar masses in addition to several x 10 to the 6th solar masses of stars within 1 pc of the center.

Planetary nebulae NGC 6572, NGC 7009, NGC 7027 IR line emission, examining fine structure for Ne II, Cl IV, S IV and Ar III

The fine-structure line of Ar iii at 1112 cm-1 has been observed in the planetary nebulae NGC 7027 and NGC 6572. The measured line intensities are compared with theorctical estimates for these nebulae.

Planetary nebula NGC 7027 IR line spectra emission, examining S IV and AR III line intensities