Search Publications
The extragalactic background light and the gamma-ray opacity of the universe
Dwek, Eli; Krennrich, Frank
The extragalactic background light (EBL) is one of the fundamental observational quantities in cosmology. All energy releases from resolved and unresolved extragalactic sources, and the light from any truly diffuse background, excluding the cosmic microwave background (CMB), contribute to its intensity and spectral energy distribution. It therefor…
Interstellar Water Chemistry: From Laboratory to Observations
van Dishoeck, Ewine F.; Neufeld, David A.; Herbst, Eric
Water is observed throughout the universe, from diffuse interstellar clouds to protoplanetary disks around young stars, and from comets in our own solar system and exoplanetary atmospheres to galaxies at high redshifts. This review summarizes the spectroscopy and excitation of water in interstellar space as well as the basic chemical processes tha…
A Young Protoplanet Candidate Embedded in the Circumstellar Disk of HD 100546
Amara, Adam; Meyer, Michael R.; Girard, Julien H. +3 more
We present high-contrast observations of the circumstellar environment of the Herbig Ae/Be star HD 100546. The final 3.8 µm image reveals an emission source at a projected separation of 0.''48 ± 0.''04 (corresponding to ~47 ± 4 AU) at a position angle of 8.°9 ± 0.°9. The emission appears slightly extended with a point source component with a…
Water in star-forming regions with Herschel (WISH). III. Far-infrared cooling lines in low-mass young stellar objects
Liseau, R.; Fedele, D.; van Dishoeck, E. F. +22 more
Context. Understanding the physical phenomena involved in the earlierst stages of protostellar evolution requires knowledge of the heating and cooling processes that occur in the surroundings of a young stellar object. Spatially resolved information from its constituent gas and dust provides the necessary constraints to distinguish between differe…
Embedded Protostars in the Dust, Ice, and Gas In Time (DIGIT) Herschel Key Program: Continuum SEDs, and an Inventory of Characteristic Far-infrared Lines from PACS Spectroscopy
Herczeg, Gregory J.; Lee, Jeong-Eun; Dunham, Michael M. +18 more
We present 50-210 µm spectral scans of 30 Class 0/I protostellar sources, obtained with Herschel-PACS, and 0.5-1000 µm spectral energy distributions, as part of the Dust, Ice, and Gas in Time Key Program. Some sources exhibit up to 75 H2O lines ranging in excitation energy from 100 to 2000 K, 12 transitions of OH, and CO rot…
The Structure, Origin, and Evolution of Interstellar Hydrocarbon Grains
Tielens, A. G. G. M.; Chiar, J. E.; Ricca, A. +1 more
Many materials have been considered for the carrier of the hydrocarbon absorption bands observed in the diffuse interstellar medium (ISM). In order to refine the model for ISM hydrocarbon grains, we analyze the observed aromatic (3.28, 6.2 µm) and aliphatic (3.4 µm) hydrocarbon absorption features in the diffuse ISM along the line of s…
Unidentified Infrared Emission Bands: PAHs or MAONs?
Zhang, Yong; Kwok, Sun
We suggest that the carrier of the unidentified infrared emission (UIE) bands is an amorphous carbonaceous solid with mixed aromatic/aliphatic structures, rather than free-flying polycyclic aromatic hydrocarbon molecules. Through spectral fittings of the astronomical spectra of the UIE bands, we show that a significant amount of the energy is emit…
Fossil Imprint of a Powerful Flare at the Galactic Center along the Magellanic Stream
Sutherland, Ralph S.; Bland-Hawthorn, J.; Maloney, Philip R. +1 more
The Fermi satellite discovery of the gamma-ray emitting bubbles extending 50° (10 kpc) from the Galactic center has revitalized earlier claims that our Galaxy has undergone an explosive episode in the recent past. We now explore a new constraint on such activity. The Magellanic Stream is a clumpy gaseous structure free of stars trailing behind the…
Optical constants of refractory oxides at high temperatures. Mid-infrared properties of corundum, spinel, and α-quartz, potential carriers of the 13 µm feature
Mutschke, H.; Zeidler, S.; Posch, Th.
Context. Many cosmic dust species, among them refractory oxides, form at temperatures higher than 300 K. Nevertheless, most astrophysical studies are based on the room-temperature optical constants of solids, such as corundum and spinel. A more realistic approach is needed for these materials, especially in the context of modeling late-type stars.…
The Excitation of HCN and HCO+ in the Galactic Center Circumnuclear Disk
Morris, M. R.; Mills, E. A. C.; Güsten, R. +1 more
We present new observations of HCN and HCO+ in the circumnuclear disk (CND) of the Galaxy, which we obtained with the Atacama Pathfinder Experiment telescope. We mapped emission in rotational lines of HCN J = 3-2, 4-3, and 8-7, as well as of HCO+ J = 3-2, 4-3, and 9-8. We also present spectra of H13CN J = 3-2 and 4…