Showing papers by "Joseph L. Hora published in 2000"
TL;DR: In this article, the distribution of hot neutral (molecular hydrogen) and ionized circumstellar material in the young planetary nebulae NGC 7027 was studied using the HST/NICMOS data.
Abstract: We report results from a Hubble Space Telescope (HST) and Near-Infrared Camera and Multiobject Spectrometer (NICMOS) program to study the distribution of hot neutral (molecular hydrogen) and ionized circumstellar material in the young planetary nebulae NGC 7027. HST/NICMOS provided very high spatial resolution imaging in line and continuum emission, and the stability and large dynamic range needed for investigating detailed structures in the circumstellar material. We present dramatic new images of NGC 7027 that have led to a new understanding of the structure in this important planetary nebula. The central star is clearly revealed, providing near-infrared fluxes that are used to directly determine the stellar temperature very accurately (T = 198,000 K). It is found that the photodissociation layer as revealed by near-infrared molecular hydrogen emission is very thin (ΔR ~ 6 × 1015 cm) and is biconical in shape. The interface region is structured and filamentary, suggesting the existence of hydrodynamic instabilities. We discuss evidence for the presence of one or more highly collimated, off-axis jets that might be present in NGC 7027. The NICMOS data are combined with earlier Hubble Space Telescope data to provide a complete picture of NGC 7027 using the highest spatial resolution data to date. The evolutionary future of NGC 7027 is discussed.
105 citations
TL;DR: In this article, the distribution of hot neutral (molecular hydrogen) and ionized circumstellar material in the young planetary nebulae NGC 7027 was studied using the HST/NICMOS data.
Abstract: We report results from a Hubble Space Telescope (HST) and Near-Infrared Camera and Multiobject Spectrometer (NICMOS) program to study the distribution of hot neutral (molecular hydrogen) and ionized circumstellar material in the young planetary nebulae NGC 7027. HST/NICMOS provided very high spatial resolution imaging in line and continuum emission, and the stability and large dynamic range needed for investigating detailed structures in the circumstellar material. We present dramatic new images of NGC 7027 that have led to a new understanding of the structure in this important planetary nebula. The central star is clearly revealed, providing near-infrared fluxes that are used to directly determine the stellar temperature very accurately (T = 198,000 K). It is found that the photodissociation layer as revealed by near-infrared molecular hydrogen emission is very thin, and is biconical in shape. The interface region is structured and filamentary, suggesting the existence of hydrodynamic instabilities. We discuss evidence for the presence of one or more highly collimated, off-axis jets that might be present in NGC 7027. The evolutionary future of NGC 7027 is discussed.
102 citations
TL;DR: In this paper, the first images of Mercury were obtained in thermal emission using the MIRAC (mid-infrared array camera) and analyzed to obtain new information regarding the thermal and chemical makeup of Mercury's surface.
40 citations
TL;DR: In this paper, the authors presented mid-infrared images of the ultracompact H II region complex G34.3+0.2 taken on the IRTF through a 1.8% circular variable filter wheel at 8.0, 9.7, 11.8, 12.2, and 13.6 μm.
Abstract: We present mid-infrared images of the ultracompact H II region complex G34.3+0.2 taken on the IRTF through a 1.8% circular variable filter wheel at 8.0, 9.7, 11.2, 12.8, and 13.2 μm and through a 6.8% filter at 20.6 μm. Infrared emission was detected at the radio components A, C (the "cometary" component), and D. In addition, two new sources of emission were found south of C at 20.6 μm; we assign them names of E and F. Infrared emission was not detected at B, and C does not have the famous cometary shape that is observed in radio continuum emission. Photometric flux densities and source sizes are determined for A, C, and E. Radiative transfer models are then presented to match the observed dust emission for these sources. Based on the observations and models, an overview of the complex is suggested in which C is an approximately spherical centrally heated source that was not formed from material in the adjacent ultracompact molecular core. C is not a blister source, and it is not colliding with the molecular core.
25 citations
TL;DR: The NIRI for the Gemini North telescope is now undergoing acceptance testing as discussed by the authors, and is equipped with a pupil imaging system to evaluate the telescope emissivity and to optimize the alignment of the instrument with the telescope.
Abstract: The NIRI for the Gemini North telescope is now undergoing acceptance testing. NIRI is the main near-IR facility camera on the Gemini North telescope and is designed to fully exploit the excellent characteristics of the site and the expected high performance o the telescope. NIRI offers 3 different pixel scales for wide-field, tip-tilt corrected and diffraction-limited imaging. It is equipped with a pupil imaging system to evaluate the telescope emissivity and to optimize the alignment of the instrument with the telescope. NIRI has an IR wavefront sensor so that tip-tilt and focus corrections can be obtained even in dark cloud regions or during daytime observing.
24 citations
16 Nov 2000
TL;DR: The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF) as mentioned in this paper, which is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8 and 8 microns.
Abstract: The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
14 citations
TL;DR: In this paper, the infrared morphologies of radio-continuity sources were analyzed and it was shown that the radiometric energy distributions of these sources closely resemble the radio continuum emission, consistent with thermal emission from dust grains heated to a few hundred K.
Abstract: Several compact radio continuum sources in W49A show detectable 8-20 μm emission in MIRAC2 images obtained at the IRTF. In general, the infrared morphologies of these sources closely resemble the radio continuum emission. Spectral energy distributions indicate an infrared continuum excess above the level expected from free-free emission, consistent with thermal emission from dust grains heated to a few hundred K. The bright radio continuum sources concentrated at the western end of the ring of ultracompact H II regions are not detected in the mid-infrared, while those at other positions in the ring are detected. This could be due to a localized region of high extinction along the line of sight. In addition, there are a few new infrared sources with no radio continuum counterparts. Finally, several infrared sources show strong 12.8 μm [Ne II] emission, yielding neon abundances that are typically a few percent of the cosmic abundance of neon but are high considering the expected Ne++/Ne+ ratios for the range of spectral types of the ionizing sources. We conclude that the [Ne II] emission must come from shells around the ultracompact H II regions, where the neon is able to survive as Ne+ rather than Ne++ because the radiation field has been softened by absorption of hard UV photons within the H II regions.
14 citations
TL;DR: In this paper, the authors presented subarcsecond-resolution images of one massive young stellar object, AFGL 2591, and its immediate surroundings, at 11.7, 12.5, and 18.0 μm, revealing a knot of emission ≈6'' southwest of the star, which may be evidence for a recent ejection event or an embedded companion star.
Abstract: Most, if not all, stars are now believed to produce energetic outflows during their formation. Yet, almost 20 years after the discovery of bipolar outflows from young stars, the origins of this violent phenomenon are not well understood. One of the difficulties of probing the outflow process, particularly in the case of massive embedded stars, is a deficit of high spatial resolution observations. Here we present subarcsecond-resolution mid-infrared images of one massive young stellar object, AFGL 2591, and its immediate surroundings. Our images, at 11.7, 12.5, and 18.0 μm, reveal a knot of emission ≈6'' southwest of the star, which may be evidence for a recent ejection event or an embedded companion star. This knot is roughly coincident with a previously seen near-infrared reflection nebula and a radio source, and it lies within the known large-scale CO outflow. We also find a new faint northwest source that may be another embedded lower luminosity star. The IRAS mid-infrared spectrum of AFGL 2591 shows a large silicate absorption feature at 10 μm, implying that the primary source is surrounded by an optically thick dusty envelope. We discuss the interrelationship of these phenomena and suggest that mid-infrared imaging and spectroscopy provide powerful tools for probing massive star birth.
12 citations
16 Nov 2000
TL;DR: The Infrared Array Camera (IRAC) is one of three science instruments that will fly aboard the Space Infrared Telescope Facility mission scheduled for launch in December, 2001.
Abstract: The Infrared Array Camera (IRAC) is one of three science instruments that will fly aboard the Space Infrared Telescope Facility mission scheduled for launch in December, 2001. This paper summarizes the `as built' design of IRAC along with important integration and testing results.
4 citations
Posted Content•
TL;DR: In particular, the [Fe II] lobes are clearly resolved and shown to be distinct from the molecular hydrogen emission structures as discussed by the authors, which suggests that several mass ejection events are responsible for producing this structure.
Abstract: Images of Hubble 12 were obtained with the HST/NICMOS instrument in the F110W, F164N, and F166N filters of NIC1, and the F160W, F187N, F190N, F212N, F215N filters of NIC2. The images show the structure of the inner ``torus'' and lobes much clearer than previous ground-based images. In particular, the [Fe II] lobes are clearly resolved and shown to be distinct from the molecular hydrogen emission structures. Apparent changes in the inner ionized and neutral bipolar shell implies periodic mass loss or changes in stellar wind shape or direction. The molecular hydrogen in the ``eye'' is radiatively excited and shows a complex morphology that suggests that several mass ejection events are responsible for producing this structure. The position angle of the molecular hydrogen and [Fe II] lobes differ, indicating a possible precession of the ejection axis.
01 Jan 2000
TL;DR: The Near-Infrared Imager (NIRI) for the Gemini North telescope is now undergoing acceptance testing and is equipped with a pupil imaging system to evaluate the telescope emissivity and to optimize the alignment of the instrument with the telescope as mentioned in this paper.
Abstract: The Near-Infrared Imager (NIRI) for the Gemini North telescope is now undergoing acceptance testing. NIRI is the main near-infrared facility camera on the Gemini North telescope and is designed to fully exploit the excellent characteristics of the site and the expected high performance of the telescope. NIRI offers 3 different pixel scales for wide-field, tip-tilt corrected and diffraction-limited imaging. It is equipped with a pupil imaging system to evaluate the telescope emissivity and to optimize the alignment of the instrument with the telescope. NIRI has an infrared wavefront sensor so that tip-tilt and focus corrections can be obtained even in dark cloud regions or during daytime observing.
01 Jan 2000
TL;DR: In particular, the (Fe II) lobes are clearly resolved and shown to be distinct from the H2 emission structures as mentioned in this paper, indicating a possible precession of the ejection axis.
Abstract: Images of Hubble 12 were obtained with the HST/NICMOS instrument in the F110W, F164N, and F166N filters of NIC1, and the F160W, F187N, F190N, F212N, F215N filters of NIC2. The images show the structure of the inner "torus" and lobes much clearer than previous ground-based images. In particular, the (Fe II) lobes are clearly resolved and shown to be distinct from the H2 emission structures. Apparent changes in the inner ionized and neutral bipolar shell implies periodic mass loss or changes in stellar wind shape or direction. The H2 in the "eye" is radiatively excited and shows a complex morphology that sug- gests that several mass ejection events are responsible for producing this structure. The position angle of the H2 and (Fe II) lobes differ, indicating a possible precession of the ejection axis.
Posted Content•
TL;DR: In this article, the authors describe multi-wavelength (8-20 micron) diffraction-limited, mid-infrared images of the OMC-1 cloud core in Orion, covering an approximately two arcminute area around the Trapezium and BN/KL regions.
Abstract: We describe multi-wavelength (8--20 micron), diffraction-limited, mid-infrared images of the OMC-1 cloud core in Orion, covering an approximately two arcminute area around the Trapezium and BN/KL regions We have detected mid-infrared emission at the locations of a subset of the previously identified proplyds in the Orion Nebula along with two new infrared sources The Ney-Allen nebula surrounding the OB star theta 1 Ori d exhibits a ring or toroidal structure at the longest wavelengths The BN/KL complex appears as an extended, butterfly-shaped structure with significant bipolar symmetry which is bifurcated by a dust lane at the longer wavelengths The infrared sources IRc3, 4, and 5 give the appearance of a ring-like structure with a possible jet-like protrusion from its center along a line from IRc2 Derived color temperature and dust opacity maps suggest that IRc3, 4, and 5 may not be self-luminous objects
TL;DR: In this paper, the authors presented sub-arcsecond-resolution images of one massive young stellar object, AFGL 2591, and its immediate surroundings, revealing a knot of emission 6'' SW of the star, which may be evidence for a recent ejection event or an embedded companion star.
Abstract: Most, if not all, stars are now believed to produce energetic outflows during their formation. Yet, almost 20 years after the discovery of bipolar outflows from young stars, the origins of this violent phenomenon are not well understood. One of the difficulties of probing the outflow process, particularly in the case of massive embedded stars, is a deficit of high spatial resolution observations. Here, we present sub-arcsecond-resolution mid-infrared images of one massive young stellar object, AFGL 2591, and its immediate surroundings. Our images, at 11.7, 12.5 and 18.0 microns, reveal a knot of emission ~6'' SW of the star, which may be evidence for a recent ejection event or an embedded companion star. This knot is roughly coincident with a previously seen near-infrared reflection nebula and a radio source, and lies within the known large-scale CO outflow. We also find a new faint NW source which may be another embedded lower-luminosity star. The IRAS mid-infrared spectrum of AFGL 2591 shows a large silicate absorption feature at 10 microns, implying that the primary source is surrounded by an optically thick dusty envelope. We discuss the interrelationship of these phenomena and suggest that mid-infrared imaging and spectroscopy provide powerful tools for probing massive star birth.