Showing papers by "Joseph L. Hora published in 1997"

Adaptive optics infrared imaging polarimetry and optical hst imaging of hubble's variable nebula (R monocerotis/NGC 2261): A close look at a very young active herbig Ae/Be star

Abstract: We present high-resolution (FWHM = 02) near-IR (J, H, and K') adaptive optics images of the Herbig Ae/Be star R Monocerotis Optical Hubble Space Telescope (HST) WFPC2 PC camera archival images are also presented For the first time, adaptive optics was utilized to make high-resolution (FWHM = 02) IR-imaging polarimetry maps of R Mon In addition, the first mid-IR array images (at 117 and 208 ?m) of R Mon have been obtained We also present new 316, 393, and 467 ?m images We have found that R Mon is a 069 binary star with a companion that dereddens onto the classical T Tauri locus Based on the near-infrared photometry of this companion we believe it is a 15 M?, very young ( + 800?280 pc distant based on previous proper-motion and radial velocity measurements of R Mon's jet Our high-resolution (FWHM ~ 02) adaptive optics infrared polarimetry maps agree with the current interpretation that NGC 2261 is a reflection nebula illuminated by R Mon Interior to the parabolic shell there is a complex of twisted filaments along the eastern edge These filaments resemble a double-helical structure which is well described by a power law from ~103 to 105 AU from R Mon This double helix may trace a twisted magnetic field above R Mon Based on H I emission-line ratios, we find the direct extinction toward R Mon to be AV = 131 mag in the infrared (? > 128 ?m), falling to a lower value of AV = 36 mag in the optical (? < 128 ?m), where scattered light increasingly lowers the effective extinction in the line ratios The large AV = 131 extinction is likely due to the dusty atmosphere of an inclined R ~ 100 AU optically thick accretion disk surrounding R Mon A simple model of such an accretion disk + star system (with Macc ~ 8 ? 10-5 M? yr-1, M* = 104 M?, R* = 2 R?, and T* ~ 35 ? 104 K) reproduces the observed dereddened R Mon spectral energy distribution (SED) from the optical (04 ?m) to the millimeter region Consideration of the lower extinction (AV = 36) on the path followed by the scattered visible light eliminated any need for an inner gap in the accretion disk model to reproduce the SED In general, young stellar objects (YSOs) that are obscured in the optical but directly visible in the infrared will have different effective optical and infrared extinctions Infrared extinctions derived from optical observations dominated by scattered light will be underestimates of the true IR extinction along the direct path The use of an independent estimator of both the optical and infrared extinctions such as common upper-level H I recombination lines is highly desirable The utilization of the correct optical and infrared extinctions may relieve the need for optically thin inner-disk gaps to explain YSO near-IR SEDs

Infrared observations of dust emission from comet hale-bopp

Abstract: We present infrared imaging and photometry of the bright, giant comet C/1995 O1 (Hale-Bopp) The comet was observed in an extended infrared and optical observing campaign in 1996–1997 The infrared morphology of the comet was observed to change from the 6 to 8 jet “porcupine” structure in 1996 to the “pinwheel” structure seen in 1997; this has implications for the position of the rotational angular momentum vector Long term light curves taken at 113 μm indicate a dust production rate that varies with heliocentric distance as ∶ r−14 Short term light curves taken at perihelion indicate a rotational periodicity of 113 hours and a projected dust outflow speed of ∶ 04 km s−1 The spectral energy distribution of the dust on October 31, 1996 is well modeled by a mixture of 70% silicaceous and 30% carbonaceous non-porous grains, with a small particle dominated size distribution like that seen for comet P/Halley (McDonnell et al, 1991), an overall dust production rate of 2 × 105 kg s−1, a dust-to-gas ratio of ∶5, and an albedo of 39%

Near-Infrared Spectroscopy of Molecular Filaments in the Reflection Nebula NGC 7023

Abstract: We present near-infrared spectroscopy of Nuorescent molecular hydrogen emission from molecu- (H 2 ) lar -laments in the reNection nebula NGC 7023. We derive the relative column densities of H 2 rotational-vibrational states from the measured line emission and compare these results with several model photodissociation regions covering a range of densities, incident UV -elds, and excitation mecha- nisms. Our best--t models for one -lament suggest, but do not require, either a combination of di†erent densities, suggesting clumps of 106 cm~3 in a1 0 4 E105 cm~3 -lament, or a combination of Nuorescent excitation and thermally excited gas, perhaps due to a shock from a bipolar outNow. We derive densities and UV -elds for these molecular -laments that are in agreement with previous determinations. Subject headings: infrared: ISM: lines and bands E ISM: individual (NGC 7023) E ISM: molecules E ISM: structure E reNection nebulae

The infrared bright nuclei in the mid-infrared

Abstract: We present arcsecond angular-resolution mid-IR images of three IR-bright galaxies, NGC 6240, IRAS 0518-25, and the NGC 3690-IC 694 (Arp 299) system, and we compare the sizes of their emission regions in the mid-IR and near-IR. In all these galaxies, most ({approximately}75{percent}) of the mid-IR flux, as measured in the IRAS 12 {mu}m observations, is found in our images to be concentrated within the central few hundred parsecs. In the two galaxies which show a single IR source in the nucleus, IRAS 0518-25 and IC 694, the mid-IR emission is more compact than the near-IR. This suggests that the mid-IR source, warm dust heated by an active galactic nucleus or an unresolved starburst, is more compact than the population of cooler, older stars. In the two galaxies which show double sources in the nucleus, the reverse is the case. That is, the mid-IR is more extended than the near-IR. Similar results are obtained for a handful of other galaxies for which we have high-resolution mid-IR data. Thus in our small sample, the double source nuclei contain starbursts which are more extended than the older stars and the single source nuclei do not. Some of the double sources seen in themore » IR bright galaxies, for example NGC 3690, are probably starbursts in conjunction with a galactic nucleus rather than twin galactic nuclei. {copyright} {ital 1997} {ital The American Astronomical Society}« less

Investigating the Near-IR Properties of PN: Deep Imaging of Molecular Hydrogen Emission

Abstract: We present the first results of a deep near-infrared narrowband imaging study of several planetary nebulae. The data were acquired using the University of Hawaii 2.2m telescope on Mauna Kea and the “QUIRC” 1024 × 1024 array camera. With these sensitive high spatial resolution imaging data, we are able to explore in detail where H2 is found relative to the ionized region in planetary nebulae at various stages of evolution (See Figure 1, for an example). The objects were selected from previous studies to have evidence for extended emission from H2, and they are at several differing phases of central star evolution. The presence of molecules in the UV-flooded environment of a planetary nebula cannot be explained without highly non-spherical geometries and high densities, or clumping. Although there can be an ambiguity in the excitation mechanism (UV photons or shocks), the location of H2 emission identifies regions of the nebula with sufficient dust shielding and density for the survival of molecular species. The emission morphology also provides information that helps identify which excitation mechanism is most likely. When combined with data provided by other molecular studies, we can examine how the photodissociation region evolves through the circumstellar envelope as the planetary nebula tracks across the top of the HR diagram. We can also consider how morphological evolution of the nebula, through interacting winds and shocks, might provide the conditions necessary for molecular survival.

Infrared instrumentation for the SUBARU Telescope

Abstract: The infrared instrumentation plan for the Subaru Telescope is described. Four approved infrared instruments and one testobservation system are now in the construction phase. They are Coronagraph Imager using Adaptive Optics (CIAO), CooledMid-Infrared Camera and Spectrograph (COMICS), Infrared Camera and Spectrograph (IRCS), OH-Airglow Suppresser Spectrograph (OHS) and Mid-Infrared Test Observation System (MIRTOS). Their performance goals and constructionschedules are summarized. The plan for procurement and evaluation of infrared arrays required by these instruments is briefly described.Keywords: infrared instrumentation, Subaru Telescope, infrared camera, infrared spectrograph 1. INTRODUCTION In the history of infrared astronomy, the first phase, approximately the first 20 years, was when basic technology such asdetector, telescope and instrumentation were developed and when the number of researchers increased gradually through theobservations and discoveries utilizing these early technologies. Since 1980's, infrared astronomy entered the second phase,the era of infrared array technology. The dramatic results that the array technology introduced were vividly presented, forexample, in the series of the proceedings from the workshops held in the United States since late 1980's. The third phaseseems to be just starting now, when the matured array technology couples with the advent of the new generation of largeground based telescopes equipped with well-planned contingency of versatile and powerful infrared instrumentation. Japan

Mid-Infrared Imaging of Dust Shells around Young Planetary and Proto-Planetary Nebulae

Abstract: The results presented here are from an ongoing mid-infrared imaging study of PPNe and PNe, using MIRAC2 the UA/SAO mid-IR camera. Our 8–21 μm observations have a spatial resolution of about 0.7″ to 1.5″, and a pixel scale of 0.25″/pixel (at UKIRT) or 0.34″/pixel (at IRTF). The high S/N and good spatial sampling in our images of IRAS 22272+5435 and IRAS 07134+1005 allow us to construct temperature and optical depth maps. Using our 11.7μm and 20.6μm images we also construct maps which isolate the 11.3μm (UIR) and 21μm emission features (Justannont et al. 1995). As a second part of this project, we are modelling the dust emission from PPNe and young PNe, using a axisymmetrical radiative transfer code.

Near-Infrared Spectroscopy of Molecular Filaments in the Reflection Nebula NGC 7023

Abstract: We present near-infrared spectroscopy of fluorescent molecular hydrogen (H_2) emission from molecular filaments in the reflection nebula NGC 7023. We derive the relative column densities of H_2 rotational-vibrational states from the measured line emission and compare these results with several model photodissociation regions covering a range of densities, incident UV-fields, and excitation mechanisms. Our best-fit models for one filament suggest, but do not require, either a combination of different densities, suggesting clumps of 10^6 cm^{-3} in a 10^4 - 10^5 cm^{-3} filament, or a combination of fluorescent excitation and thermally-excited gas, perhaps due to a shock from a bipolar outflow. We derive densities and UV fields for these molecular filaments that are in agreement with previous determinations.