Astronomical instrumentation

Abstract:

We report on advances in the study of the cores of NGC 6302 and 6537 using infrared grating and echelle spectroscopy. In NGC 6302, emission lines from species spanning a large range of ionization potential, and in particular [Si IX] 3.934 μm, are interpreted using photoionization models (including CLOUDY), which allow us to re-estimate the temperature of the central star to be about 250 000 K. All of the detected lines are consistent with this value, except for [Al V] and [Al VI]. 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 154 eV). A similar depletion pattern is observed in NGC 6537. Echelle spectroscopy of IR coronal ions in NGC 6302 reveals a stratified structure in ionization potential, which confirms photoionization to be the dominant ionization mechanism. The lines are narrow (<22km s-1 FWHM), with no evidence of the broad wings found in optical lines from species with similar ionization potentials, such as [Ne V] 3426 Å. We note the absence of a hot bubble, or a wind-blown bipolar cavity filled with a hot plasma, at least on 1 arcsec and 10 km s-1 scales. The systemic heliocentric velocities for NGC 6302 and 6537, measured from the echelle spectra of IR recombination lines, are found to be -34.8±1 km s-1 and -17.8±3 km s-1. We also provide accurate new wavelengths for several of the infrared coronal lines observed with the echelle.

Abstract:

We present CCD (charge-coupled device) photometry for galaxies around 204 bright (mZ < 15.5) Zwicky galaxies in the equatorial extension of the APM Galaxy Survey, sampling an area over 400 deg2, which extends 6 h in right ascension. We fit a best linear relation between the Zwicky magnitude system, mZ, and the CCD photometry, BCCD, by doing a likelihood analysis that corrects for Malmquist bias. This fit yields a mean scale error in Zwicky of 0.38 mag mag-1: i.e. ΔmZ ≃ (0.62 ± 0.05)ΔBCCD and a mean zero-point of 〈BCCD - mZ〉 = -0.35 ± 0.15 mag. The scatter around this fit is about 0.4 mag. Correcting the Zwicky magnitude system with the best-fitting model results in a 60 per cent lower normalization and 0.35-mag brighter M* in the luminosity function. This brings the CfA2 luminosity function closer to the other low-redshift estimations (e.g. Stromlo-APM or LCRS). We find a significant positive angular correlation of magnitudes and position in the sky at scales smaller than about 5 arcmin, which corresponds to a mean separation of 120h-1 kpc. We also present colours, sizes and ellipticities for galaxies in our fields, which provides a good local reference for the studies of galaxy evolution.

Abstract:

We present 8-13 μm spectropolarimetry of 55 sources and 16-22 μm spectropolarimetry of six of these. This represents a substantial fraction of star formation regions that can be observed in this way with current technology on 4-m class telescopes (i.e. brighter than about 20 Jy at 10 μm in a 4-arcsec beam). Most of the sources are embedded young stellar objects (YSOs), H II regions containing sites of star formation or bipolar protoplanetary nebulae (PPN), although a few other sources (e.g. NGC 1068, MWC 349) are also included. The majority have oxygen-rich chemistry but there are three carbon-rich sources. Many of the oxygen-rich sources show deep silicate absorption overlying featureless or optically thin silicate emission. Absorptive polarization with polarization per optical depth (pa/τ) ≃ 1-3 per cent is common, and many also show evidence for an emissive polarization component as well, although pure polarization in emission is rare. The observed ranges of pa/τ and pe are very similar, rather surprising in view of their origin from very different environments. Typically the absorptive polarization profiles are similar to the archetypal silicate polarization found in OMC1 BN, but an exception is AFGL 2591, which displays an additional narrow polarization feature at 11.2 μm, which has been attributed to annealed silicates. Many of the intensity absorption spectra also show an inflection near 11.2 μm, which might also be attributable to annealed silicates. The carbon-rich sources have nearly featureless polarizations in the 0.5-1 per cent range, which we ascribe to dichroism in carbon-based grains; this is the first evidence that such grains can be aligned. In two of these sources the polarization appears to be caused by absorption by SiC. A few of the polarization spectra have no straightforward interpretation.

Abstract:

Integral-field-spectroscopy and multi-object-spectroscopy provide the high multiplex gain required for efficient use of the upcoming generation of extremely large telescopes. We present instrument developments and designs for both concepts, and how these designs can be applied to cryogenic near-infrared instrumentation. Specifically, the fiber-based concept stands out the possibility to expand it to any number of image points, and its modularity predestines it to become the new concept for multi-field-spectroscopy. Which of the three concepts --- integral-field-, multi-object-, or multi-field-spectroscopy --- is best suited for the largest telescopes is discussed considering the size of the objects and their density on the sky.

Abstract:

Integral-field-spectroscopy and multi-object-spectroscopy provide the high multiplex gain required for efficient use of the upcoming generation of extremely large telescopes. We present instrument developments and designs for both concepts, and how these designs can be applied to cryogenic near-infrared instrumentation. Specifically, the fiber-based concept stands out the possibility to expand it to any number of image points, and its modularity predestines it to become the new concept for multi-field-spectroscopy. Which of the three concepts --- integral-field-, multi-object-, or multi-field-spectroscopy --- is best suited for the largest telescopes is discussed considering the size of the objects and their density on the sky.