Browsing by Subject "embedded protostars"

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An Analysis Of The Environments Of Fu Orionis Objects With Herschel
(2013-08) Green, Joel D.; Evans, Neal J.; Kospal, Agnes; Herczeg, Gregory; Quanz, Sascha P.; Henning, Thomas; van Kempen, Tim A.; Lee, Jeong-Eun; Dunham, Michael M.; Meeus, Gwendolyn; Bouwman, Jeroen; Chen, Jo-Hsin; Gudel, Manuel; Skinner, Stephen L.; Liebhart, Armin; Merello, Manuel; Green, Joel D.; Evans, Neal J.; Merello, Manuel
We present Herschel-HIFI, SPIRE, and PACS 50-670 mu m imaging and spectroscopy of six FU Orionis-type objects and candidates (FU Orionis, V1735 Cyg, V1515 Cyg, V1057 Cyg, V1331 Cyg, and HBC 722), ranging in outburst date from 1936 to 2010, from the "FOOSH" (FU Orionis Objects Surveyed with Herschel) program, as well as ancillary results from Spitzer Infrared Spectrograph and the Caltech Submillimeter Observatory. In their system properties (L-bol, T-bol, and line emission), we find that FUors are in a variety of evolutionary states. Additionally, some FUors have features of both Class I and II sources: warm continuum consistent with Class II sources, but rotational line emission typical of Class I, far higher than Class II sources of similar mass/luminosity. Combining several classification techniques, we find an evolutionary sequence consistent with previous mid-IR indicators. We detect [O I] in every source at luminosities consistent with Class 0/I protostars, much greater than in Class II disks. We detect transitions of 13CO (J(up) of 5-8) around two sources (V1735 Cyg and HBC 722) but attribute them to nearby protostars. Of the remaining sources, three (FU Ori, V1515 Cyg, and V1331 Cyg) exhibit only low-lying CO, but one (V1057 Cyg) shows CO up to J = 23 -> 22 and evidence for H2O and OH emission, at strengths typical of protostars rather than T Tauri stars. Rotational temperatures for "cool" CO components range from 20 to 81 K, for similar to 10(50) total CO molecules. We detect [C I] and [N II] primarily as diffuse emission.
The c2d Spitzer Spectroscopic Survey Of Ices Around Low-Mass Young Stellar Objects. I. H2O And The 5-8 Mu M Bands
(2008-05) Boogert, Adwin C. A.; Pontoppidan, Klaus M.; Knez, Claudia; Lahuis, Fred; Kessler-Silacci, J.; van Dishoeck, Ewine F.; Blake, Geoffrey A.; Augereau, Jean-Charles; Bisschop, S. E.; Bottinelli, Sandrine; Brooke, Tyler Y.; Brown, Justin; Crapsi, Antonio; Evans, Neal J.; Fraser, Helen J.; Geers, V.; Huard, Tracy L.; Jorgensen, Jes K.; Oberg, Karin I.; Allen, Lori E.; Harvey, Paul M.; Koerner, David W.; Mundy, Lee G.; Padgett, Deborah L.; Sargent, Anneila I.; Stapelfeldt, Karl R.; Evans, Neal J.; Harvey, Paul M.; Kessler-Silacci, J.
To study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low-luminosity YSOs (L similar to 0.1-10 L-circle dot) using 3-38 mu m Spitzer and ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well-studied massive YSOs (L similar to 10(5) L-circle dot). The long-known 6.0 and 6.85 mu m bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. The 6.0 mu m band is often deeper than expected from the bending mode of pure solid H2O. The additional 5-7 mu m absorption consists of five independent components, which, by comparison to laboratory studies, must be from at least eight different carriers. Much of this absorption is due to simple species likely formed by grain surface chemistry, at abundances of 1%-30% for CH3OH, 3%-8% for NH3, 1%-5% for HCOOH, similar to 6% for H2CO, and similar to 0.3% for HCOO- relative to solid H2O. The 6.85 mu m band has one or two carriers, of which one may be less volatile than H2O. Its carrier(s) formed early in the molecular cloud evolution and do not survive in the diffuse ISM. If an NH4+- containing salt is the carrier, its abundance relative to solid H2O is similar to 7%, demonstrating the efficiency of low-temperature acid-base chemistry or cosmic-ray-induced reactions. Possible origins are discussed for enigmatic, very broad absorption between 5 and 8 mu m. Finally, the same ices are observed toward massive and low-mass YSOs, indicating that processing by internal UV radiation fields is a minor factor in their early chemical evolution.
Herschel Key Program, "Dust, Ice, and Gas in Time" (DIGIT): the Origin of Molecular and Atomic Emission in Low-Mass Protostars in Taurus
(2014-10) Lee, Jeong-Eun; Lee, Jinhee; Lee, Seokho; Evans, Neal J., II; Green, Joel D.; Lee, Jeong-Eun; Evans, Neal J., II; Green, Joel D.
Six low-mass embedded sources (L1489, L1551-IRS5, TMR1, TMC1-A, L1527, and TMC1) in Taurus have been observed with Herschel-PACS to cover the full spectrum from 50 to 210 mu m as part of the Herschel key program, "Dust, Ice, and Gas In Time." The relatively low intensity of the interstellar radiation field surrounding Taurus minimizes contamination of the [C II] emission associated with the sources by diffuse emission from the cloud surface, allowing study of the [C II] emission from the source. In several sources, the [C II] emission is distributed along the outflow, as is the [O I] emission. The atomic line luminosities correlate well with each other, as do the molecular lines, but the atomic and molecular lines correlate poorly. The relative contribution of CO to the total gas cooling is constant at similar to 30%, while the cooling fraction by H2O varies from source to source, suggesting different shock properties resulting in different photodissociation levels of H2O. The gas with a power-law temperature distribution with a moderately high density can reproduce the observed CO fluxes, indicative of CO close to LTE. However, H2O is mostly subthermally excited. L1551-IRS5 is the most luminous source (L-bol = 24.5 L-circle dot) and the [O I] 63.1 mu m line accounts for more than 70% of its FIR line luminosity, suggesting complete photodissociation of H2O by a J shock. In L1551-IRS5, the central velocity shifts of the [O I] line, which exceed the wavelength calibration uncertainty (similar to 70 km s(-1)) of PACS, are consistent with the known redshifted and blueshifted outflow direction.