Near-Infrared Spectroscopy of Photodissociation Regions: The Orion Bar and Orion S

To test the PDR model spectra under the physical conditions present in Orion, we have obtained moderate-resolution (R=3000) J-, H-, and K-band long-slit spectra of the Orion bar and Orion S regions These observations provide conclusive evidence for the PDR origin (rather than shocks) of the H_2 emission in each of these regions and demonstrate significant departures in the observed chemical structure from that predicted by models of homogeneous PDRs.Comment: Accepted to Astrophysical Journa

Oscillator Strengths and Damping Constants for Atomic Lines in the J and H Bands

We have built a line list in the near-infrared J and H bands (1.00-1.34, 1.49-1.80 um) by gathering a series of laboratory and computed line lists. Oscillator strengths and damping constants were computed or obtained by fitting the solar spectrum. The line list presented in this paper is, to our knowledge, the most complete one now available, and supersedes previous lists.Comment: Accepted, Astrophysical Journal Supplement, tentatively scheduled for the Sep. 1999 Vol. 124 #1 issue. Text and tables also available at http://www.iagusp.usp.br/~jorge

The coronal line regions of planetary nebulae NGC6302 and NGC6537: 3-13um grating and echelle spectroscopy

We report on advances in the study of the cores of NGC6302 and NGC6537 using infrared grating and echelle spectroscopy. In NGC6302, emission lines from species spanning a large range of ionization potential, and in particular [SiIX]3.934um, are interpreted using photoionization models (including CLOUDY), which allow us to reestimate the central star's temperature to be about 250000K. All of the detected lines are consistent with this value, except for [AlV] and [AlVI]. Aluminium is found to be depleted to one hundredth of the solar abundance, which provides further evidence for some dust being mixed with the highly ionized gas (with photons harder than 154eV). A similar depletion pattern is observed in NGC6537. Echelle spectroscopy of IR coronal ions in NGC6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (< 22km/s FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [NeV]3426A. We note the absence of a hot bubble, or a wind blown bipolar cavity filled with a hot plasma, at least on 1'' and 10km/s scales. We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle.Comment: Accepted for publication in MNRA

Tissue-specific changes in remobilisation of fructan in the xerophytic tussock species Festuca novae-zelandiae in response to a water deficit

Cellular responses of the native New Zealand grass species Festuca novae-zelandiae ( Hack.) Cockayne to a water deficit and re-hydration treatment were investigated. Leaf extension ceased after 28 d of withholding water, while mitotic activity within the intercalary meristem still continued. By 35 d, no evidence of mitotic activity could be detected. At the apical meristem, cell division commenced 24 h post re-watering after 49 d of dry-down and was accompanied by synthesis of storage oligosaccharides of the fructan type. Changes in water-soluble carbohydrates over the course of the water deficit were examined in consecutive leaf segments comprising the leaf base ( meristem region), elongation zone, the enclosed and the exposed lamina, as well as basal sheath segments from the two next oldest leaves. In fully hydrated leaf tissue, the fructan pool was mainly composed of the low molecular weight fructans of the inulin and neokestose series with higher concentrations towards the leaf base. Fructan concentrations decreased over the course of the water deficit with the leaf base retaining significantly higher concentrations than any other tissue, until tissue water content fell below 45%. Sucrose content increased in each tissue during the course of the dry-down, and was highest at the leaf base, where a concentration of 200 mumol g DW-1 was measured after 49 d of dry-down. In 1.5 h after re-watering, levels of 1-kestotriose increased relative to the level of sucrose at the leaf base, indicating re-synthesis of fructans from accumulated sucrose. By 24 h post re-watering, the ratio of sucrose to 1-kestotriose declined from six in non-watered plants to two and higher molecular weight fructans became detectable. The negative correlation between fructan and sucrose content, which indicates an inter-conversion depending on tissue water content, suggests that, in this species, fructans serve as a carbohydrate pool, while sucrose stabilises the meristem during extreme water deficit