A5056099322- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- History and Developments in Astronomy
- Molecular Spectroscopy and Structure
- Calibration and Measurement Techniques
- Adaptive optics and wavefront sensing
- Scientific Research and Discoveries
- Superconducting Materials and Applications
- Space Exploration and Technology
- Spectroscopy and Laser Applications
- Astrophysical Phenomena and Observations
- Advanced Chemical Physics Studies
- Laser Design and Applications
- Atomic and Molecular Physics
- Atmospheric Ozone and Climate
- Advanced Semiconductor Detectors and Materials
- Pulsars and Gravitational Waves Research
- Spectroscopy Techniques in Biomedical and Chemical Research
- Inorganic Fluorides and Related Compounds
- Magnetic confinement fusion research
- Astronomical and nuclear sciences
Southeastern Universities Research Association
2019-2023
Valparaiso University
2014-2023
Cyberport
2019
University of Hong Kong
2019
University of Cambridge
2019
Herzberg Institute of Astrophysics
1997-2013
Dominion Astrophysical Observatory
1981-2008
Association of Universities For Research In Astronomy
1999-2003
U.S. National Science Foundation
1999-2003
Kitt Peak National Observatory
1999-2003
view Abstract Citations (241) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A 21 Micron Emission Feature in Four Proto--Planetary Nebulae Kwok, Sun ; Volk, Kevin M. Hrivnak, Bruce J. The discovery of an unidentified emission feature at microns the LRS spectra four IRAS sources is reported. These objects all show large FIR excesses due to a circumstellar dust envelope surrounding carbon-rich central star and are likely be evolutionary phase...
view Abstract Citations (227) References (73) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of Several F and G Supergiant-like Stars with Infrared Excesses as Candidates for Proto--Planetary Nebulae Hrivnak, Bruce J. ; Kwok, Sun Volk, Kevin M. Ground-based observations have been obtained eight supergiant-like stars showing large IR excesses. The combination ground-based IRAS data shows that these objects dual-peak energy distributions, comparable...
This paper reports variations of polycyclic aromatic hydrocarbons (PAHs) features that were found in Spitzer Space Telescope spectra carbon-rich post-asymptotic giant branch (post-AGB) stars the Large Magellanic Cloud (LMC). The consists two parts. first part describes our spectral observing programme 24 including post-AGB candidates. latter half this presents analysis PAH 20 LMC, assembled from archive as well own programme. We five showed a broad feature with peak at 7.7 micron, had not...
We present the data from a mid-infrared (MIR) imaging survey of 66 proto-planetary nebula candidates using two MIR cameras (MIRAC2 and Berkcam) at NASA Infrared Telescope Facility United Kingdom Telescope. The goal this is to determine size, flux, morphology emission regions, which sample inner regions circumstellar dust shells nebulae. imaged these nebulae with narrowband filters(Δλ/λ~10%) wavelengths notable features. With our typical angular resolution 1'', we resolve 17 sources, find 48...
Infrared Space Observatory (ISO) 2-45 μm observations of seven proto-planetary nebulae (PPNs) and two other carbon-rich objects are presented. The unidentified emission features at 21 30 detected in six sources, including four new detections the feature. This previously unresolved feature is now resolved found to consist a broad peaking 27.2 (the "30 μm" feature) narrower 25.5 "26 feature). 26 eight sources particularly strong IRAS Z02229+6208 16594-4656. infrared (UIR) 3.3, 6.2, 7.7, 11.3...
view Abstract Citations (112) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Unusual 3 Micron Emission Features in Three Proto--Planetary Nebulae Geballe, T. R. ; Tielens, A. G. M. Kwok, S. Hrivnak, B. J. Medium-resolution 3-4 micron spectra have been obtained of three objects, IRAS 04296 + 3429, 22272 5435, and CRL 2688, which are transition between the asymptotic red giant branch planetary nebula phase. All show unusual 3-micron emission...
We report Hubble Space Telescope Wide Field Planetary Camera 2 imaging of the bipolar proto-planetary nebula IRAS 17150-3224. find a series concentric arcs superposed on two reflection nebular lobes, similar to those observed in AFGL 2688. This suggests that periodic mass-loss enhancement is common phenomenon asymptotic giant branch (AGB) phase. The near circular shape mass loss spherically symmetric during AGB phase and morphology develops only after end possible evolution from nebulae...
Spitzer Space Telescope mid-infrared spectroscopy has been obtained for 15 carbon-rich protoplanetary nebulae (PPNe) in the Large Magellanic Cloud (LMC) and two other such stars Small (SMC). Of these 17 PPNe, unidentified 21 μm feature is strong 7 spectra, weak 2 very or questionable 4 spectra. Two of four spectra without have a near 11 μm, similar to observed some planetary (PNe) LMC. We attribute this unusual SiC dust, although feature-to-continuum ratio much larger than features Galactic...
Post-AGB stars are exquisite probes of AGB nucleosynthesis. However, the previous lack accurate distances jeopardised comparison with theoretical models. The $Gaia$ Early Data Release 3 ($Gaia$ EDR3) has now allowed for a breakthrough in this research landscape. In study, we focus on sample single Galactic post-AGBs which chemical abundance studies were completed. We combined photometry geometric to carry out spectral energy distribution (SED) analysis and derive luminosities. subsequently...
We present Infrared Space Observatory SWS06 mode observations of the 21 μm feature in eight sources, including a first detection IRAS Z02229+6208. The observed peak-to-continuum ratios range from 0.13 Z02229+6208 to 1.30 07134+1005. normalized spectra, obtained by removal underlying continua and scaling features same peak flux value, show that all have intrinsic profile wavelength. There is no evidence for any discrete substructure due molecular bands suggesting either solid substance or...
view Abstract Citations (92) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Spectroscopy of Carbon-rich Proto--Planetary Nebulae Hrivnak, Bruce J. In this paper, we present a medium-resolution (3 A) spectroscopic study six proto-planetary nebulae (PPN), post-asymptotic giant branch (AGB) objects with large infrared excesses. All are found to display the spectra G supergiants. However, they also show molecular carbon features, C2 and...
We present an atlas of Spitzer Space Telescope Infrared Spectrograph (IRS) spectra highly luminous, compact, mid-IR sources in the Large Magellanic Cloud. Sources were selected on basis IR colors and 8 μm (Midcourse Experiment) fluxes indicative evolved, intermediate-to-high-mass stars with current or recent mass loss at large rates. determine chemistry circumstellar envelope from continuum spectral features classify types stars. In sample 60 sources, we find 21 red supergiants (RSGs), 16...
We have carried out long-term (14 years) V and R photometric monitoring of 12 carbon-rich proto-planetary nebulae. The light color curves display variability in all them. are complex suggest multiple periods, changing and/or amplitudes, which attributed to pulsation. A dominant period has been determined for each found be the range ~150 d coolest (G8) 35-40 warmest (F3). clear, linear inverse relationship sample between pulsation effective temperature also an amplitude variation temperature....
We have carried out mid-infrared spectroscopy of seven Galactic protoplanetary nebulae (PPNs) using the Spitzer Space Telescope. They were observed from 10 to 36 μm at relatively high spectral resolution, R ≈ 600. The sample was chosen because they all gave some evidence in visible a carbon-rich chemistry. All sources show broad, unidentified 21 emission feature; three them are new detections (IRAS 06530 − 0213, 07430+1115, and 19477+2401) others higher signal-to-noise ratio than previous...
The shaping of the nebula is currently one outstanding unsolved problems in planetary (PN) research. Several mechanisms have been proposed, most which require a binary companion. However, direct evidence for companion lacking PNs. We addressed this problem by obtaining precise radial velocities seven bright proto-planetary nebulae (PPNs), objects transition from asymptotic giant branch to PN phases stellar evolution. These F-G spectral types and advantage over PNs having more sharper lines,...
In this paper, we present an LTE abundance analysis of two new proto-planetary nebulae, IRAS Z02229+6208 and 07430+1115, based on high-resolution (R ≈ 55,000) optical echelle spectra. Results show that both stars are metal-poor ([Fe/H] = -0.5) overabundant in C, N, s-process elements. The average elemental abundances [C/Fe] +0.8, [N/Fe] +1.2, and[s-process/Fe] +1.4 for Z02229+6208, +0.6, +0.4, [s-process/Fe] +1.6 07430+1115. These suggest the have experienced nucleosynthesis asymptotic giant...
The bipolar proto-planetary nebula IRAS 17441-2411 (the "Silkworm Nebula") was observed with the Hubble Space Telescope. By fitting spectral energy distribution and V-band image by a two-dimensional radiation transfer model, we derive properties of circumstellar wind proposed "disk." We suggest that structures are probably more common than actually observed, because objects similar intrinsic may simply appear stellar their orientation in sky.
view Abstract Citations (67) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Spectroscopy of Proto--Planetary Nebulae Hrivnak, Bruce J. ; Kwok, Sun Geballe, T. R. Sixteen proto-planetary nebulae were observed with low-resolution infrared spectroscopy in the H and K bands, four L band. In band, most objects show hydrogen Brackett lines (from n = 10 goes to 4 20 4) absorption. absorption bands (delta (nu) 2) CO as high nu 6 4,...
Medium-resolution spectra have been obtained of seven carbon-rich proto-planetary nebulae (PPNs) and one young planetary nebula from 3.2 to 3.8 μm, an interval containing the prominent hydrocarbon C–H stretches at 3.3 3.4 μm due aromatic aliphatic structures, respectively. The feature is newly identified in IRAS 23304+6147, 22223+4327, 06530-0213 confirmed Z02229+6208. Three PPNs emit feature, two these being new identifications, 20000+3239 01005+7910, with others showing possible...
Circumstellar arcs have been discovered using the Hubble Space Telescope in two proto–planetary nebulae (PPNs), IRAS 16594-4656, and 20028+3910. This raises to five number of PPNs which such detected suggests that they are not rare may even be common features. All these display a bipolar morphology, but this correlation result selection effect deeper images taken central star is obscured. Two pairs oppositely directed "searchlight beams" seen 20028+3910, similar those AFGL 2688 17150-3224....
view Abstract Citations (57) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Four Newly Identified Sources with 21 Micron Emission Kwok, Sun ; Hrivnak, Bruce J. Geballe, T. R. Mid-infrared spectroscopy and near- mid-infrared photometry have been obtained for four carbon-rich cool IRAS sources whose low-resolution spectra are similar to those of proto-planetary nebulae (PPNs) possessing the unusual microns emission feature. The feature is...
Deep Hubble Space Telescope (HST) F814W images were obtained of six proto–planetary nebulae (PPNs), each which shows a bipolar morphology but with difference in orientation. Two these (IRAS 17245-3951 and IRAS 22574+6609) show dark lane separating lobes appear to be seen approximately edge-on. The other four 16594-4656, 17106-3046, 19477+2401, 20028+3910) at intermediate orientations, all one case, the central star is seen. In addition, bright PPN 20136+1309) was observed that slightly...
The intrinsic emission profile of the unidentified broad 30 μm feature is derived from Infrared Space Observatory (ISO) spectra proto-planetary nebulae (PPNs). resolved into two components: a narrower at 26 and broader 33 μm. profiles these features their varying strengths in PPNs are determined. chemical origin processes responsible for changing asymptotic giant branch (AGB) stars to planetary discussed.
THE LARGE MAGELLANIC CLOUD'S TOP 250: CLASSIFICATION OF MOST LUMINOUS COMPACT 8 μm SOURCES IN CLOUD, Joel H. Kastner, Stephen L. Thorndike, Paul A. Romanczyk, Catherine Buchanan, Bruce J. Hrivnak, Raghvendra Sahai, Michael Egan
Recent infrared spectroscopic observations have shown that proto-planetary nebulae (PPNs) are sites of active synthesis organic compounds in the late stages stellar evolution. This paper presents a study Spitzer/Infrared Spectrograph spectra for sample carbon-rich PPNs, all except one which show unidentified 21 μm emission feature. The strengths aromatic band, μm, and 30 features obtained by decomposition spectra. observed variations peak wavelengths support model newly synthesized gradually...