Infrared spectroscopy and analysis of brown dwarf and planetary mass objects in the Orion nebula cluster
Monthly Notices of the Royal Astronomical Society 392:2 (2009) 817-846
Abstract:
We present near-infrared long-slit and multislit spectra of low-mass brown dwarf candidates in the Orion nebula cluster. The long-slit data were observed in the H and K bands using NIRI on the Gemini-North Telescope. The multi-object spectroscopic observations were made using IRIS2 on the Anglo-Australian Telescope at H band. We develop a spectral typing scheme based on optically calibrated, near-infrared spectra of young sources in the Taurus and IC 348 star-forming regions with spectral types M3.0 to M9.5. We apply our spectral typing scheme to 52 sources, including previously published UKIRT and GNIRS spectra. 40 objects show strong water absorption with spectral types of M3 to >M9.5. The latest type objects are provisionally classified as early L types. We plot our sources on Hertzsprung-Russell diagrams overlaid with theoretical pre-main-sequence isochrones. The majority of our objects lie close to or above the 1-Myr isochrone, leading to an average cluster age that is <1 Myr. We find 38 sources lie at or below the hydrogen-burning limit (0.075 M ⊙). 10 sources potentially have masses below the deuterium-burning limit (0.012 M⊙). We use a Monte Carlo approach to model the observed luminosity function with a variety of cluster age and mass distributions. The lowest χ2 values are produced by an age distribution centred at 1 Myr, with a mass function that declines at substellar masses according to an Mα power law in the range α = 0.3-0.6. We find that truncating the mass function at 0.012 M ⊙ produces luminosity functions that are starved of the faintest magnitudes, even when using bimodal age populations that contain 10-Myr-old sources. The results of these Monte Carlo simulations therefore support the existence of a planetary mass population in the ONC. © 2008 RAS.The spatial variation of the 3-μm dust features in Circinus
Monthly Notices of the Royal Astronomical Society 394:4 (2009) 2043-2049
Abstract:
We report spatially resolved variations in the 3.4-μm hydrocarbon absorption feature and the 3.3-μm polycyclic aromatic hydrocarbon (PAH) emission band in the Circinus galaxy over the central few arcsec. The absorption is measured towards warm emitting dust associated with Coronal line regions to the east and west of the nucleus. There is an absorption optical depth τ 3.4μm~0.1 in the core which decreases to the west and increases to the east. This is consistent with increased extinction out to ~40pc east of the core, supported by the Coronal emission line intensities which are significantly lower to the east than the west. PAH emission is measured to be symmetrically distributed out to ±4 arcsec, outside the differential extinction region. The asymmetry in the 3.4-μm absorption band reflects that seen in the 9.7-μm silicate absorption band reported by Roche et al., and the ratio of the two absorption depths remains approximately constant across the central regions, with τ 3.4μm/τ 9.7μm~0.06 ± 0.01. This indicates wellmixed hydrocarbon and silicate dust populations, with no evidence for significant changes near the nucleus. © 2009 The Authors. Journal compilation © 2009 RAS.Design of a Mid-IR polarimeter for SOFIA
Proceedings of SPIE - The International Society for Optical Engineering 7014 (2008)
Abstract:
Mid-infrared polarimetry remains an underexploited technique; where available it is limited in spectral coverage from the ground, and conspicuously absent from the Spitzer, JWST and Herschel instrument suites. The unique characteristics of SOFIA afford unprecedented spectral coverage and sensitivity in the mid-infrared waveband. We discuss the preliminary optical design for a 5-40 m spectro-polarimeter for use on SOFIA, the SOFIA Mid-InfraRed Polarimeter (SMIRPh). The design furthers the existing 5-40μm imaging and spectroscopic capabilities of SOFIA, and draws on experience gained through the University of Florida's mid-IR imagers, spectrometer and polarimeter designs of T-ReCS and CanariCam. We pay special attention to the challenges of obtaining polarimetric materials suitable at both these wavelengths and cryogenic temperatures. Finally, we (briefly) present an overview of science highlights that could be performed from a 5-40μm imaging- and spectro-polarimeter on SOFIA. Combined with the synergy between the possible future far-IR polarimeter, Hale, this instrument would provide the SOFIA community with unique and exciting science capabilities, leaving a unique scientific legacy.Gemini mid-ir polarimetry of NGC 1068
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias 32 (2008) 137
Abstract:
The dusty molecular torus, cornerstone of the unified model of AGN, has been the subject of much observational and theoretical scrutiny in recent years, and much progress has been made with observations and models aiming to reveal, explain and predict its properties. ©2008: Instituto de Astronomía.Science of Active Galactic Nuclei with the GTC and CanariCam
Proceedings of SPIE - The International Society for Optical Engineering 7014 (2008)