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Stutz A.M.,Max Planck Institute for Astronomy | Tobin J.J.,U.S. National Radio Astronomy Observatory | Stanke T.,ESO | Megeath S.T.,University of Toledo | And 14 more authors.
Astrophysical Journal | Year: 2013

We perform a census of the reddest, and potentially youngest, protostars in the Orion molecular clouds using data obtained with the PACS instrument on board the Herschel Space Observatory and the LABOCA and SABOCA instruments on APEX as part of the Herschel Orion Protostar Survey (HOPS). A total of 55 new protostar candidates are detected at 70 μm and 160 μm that are either too faint (m24 > 7 mag) to be reliably classified as protostars or undetected in the Spitzer/MIPS 24 μm band. We find that the 11 reddest protostar candidates with log λFλ70/λF λ24 > 1.65 are free of contamination and can thus be reliably explained as protostars. The remaining 44 sources have less extreme 70/24 colors, fainter 70 μm fluxes, and higher levels of contamination. Taking the previously known sample of Spitzer protostars and the new sample together, we find 18 sources that have log λFλ70/ λFλ24 > 1.65; we name these sources "PACS Bright Red sources," or PBRs. Our analysis reveals that the PBR sample is composed of Class 0 like sources characterized by very red spectral energy distributions (SEDs; Tbol < 45 K) and large values of sub-millimeter fluxes (Lsmm/Lbol > 0.6%). Modified blackbody fits to the SEDs provide lower limits to the envelope masses of 0.2-2 M⊙ and luminosities of 0.7-10 L⊙. Based on these properties, and a comparison of the SEDs with radiative transfer models of protostars, we conclude that the PBRs are most likely extreme Class 0 objects distinguished by higher than typical envelope densities and hence, high mass infall rates. © 2013. The American Astronomical Society. All rights reserved.

Fischer W.J.,University of Toledo | Megeath S.T.,University of Toledo | Ali B.,NHSC IPAC Caltech | Tobin J.J.,University of Michigan | And 23 more authors.
Astronomy and Astrophysics | Year: 2010

We present 70 and 160 μm Herschel science demonstration images of a field in the Orion A molecular cloud that contains the prototypical Herbig-Haro objects HH 1 and 2, obtained with the Photodetector Array Camera and Spectrometer (PACS). These observations demonstrate Herschel's unprecedented ability to study the rich population of protostars in the Orion molecular clouds at the wavelengths where they emit most of their luminosity. The four protostars previously identified by Spitzer 3.6-40 μm imaging and spectroscopy are detected in the 70 μm band, and three are clearly detected at 160 μm. We measure photometry of the protostars in the PACS bands and assemble their spectral energy distributions (SEDs) from 1 to 870 μm with these data, Spitzer spectra and photometry, 2MASS data, and APEX sub-mm data. The SEDs are fit to models generated with radiative transfer codes. From these fits we can constrain the fundamental properties of the protostars. We find luminosities in the range 12-84 L⊙ and envelope densities spanning over two orders of magnitude. This implies that the four protostars have a wide range of envelope infall rates and evolutionary states: two have dense, infalling envelopes, while the other two have only residual envelopes. We also show the highly irregular and filamentary structure of the cold dust and gas surrounding the protostars as traced at 160 μm. © 2010 ESO.

Fischer W.J.,University of Toledo | Megeath S.T.,University of Toledo | Tobin J.J.,U.S. National Radio Astronomy Observatory | Hartmann L.,University of Michigan | And 9 more authors.
Astrophysical Journal | Year: 2014

Edge-on protostars are valuable for understanding the disk and envelope properties of embedded young stellar objects, since the disk, envelope, and envelope cavities are all distinctly visible in resolved images and well constrained in modeling. Comparing Two Micron All Sky Survey, Wide-field Infrared Survey Explorer, Spitzer, Herschel, and APEX photometry and an IRAM limit from 1.2 to 1200 μm, Spitzer spectroscopy from 5 to 40 μm, and high-resolution Hubble imaging at 1.60 and 2.05 μm to radiative transfer modeling, we determine envelope and disk properties for the Class I protostar HOPS 136, an edge-on source in Orion's Lynds 1641 region. The source has a bolometric luminosity of 0.8 L , a bolometric temperature of 170 K, and a ratio of submillimeter to bolometric luminosity of 0.8%. Via modeling, we find a total luminosity of 4.7 L(larger than the observed luminosity due to extinction by the disk), an envelope mass of 0.06 M , and a disk radius and mass of 450 AU and 0.002 M . The stellar mass is highly uncertain but is estimated to fall between 0.4 and 0.5 M . To reproduce the flux and wavelength of the near-infrared scattered-light peak in the spectral energy distribution, we require 5.4 × 10-5 Mof gas and dust in each cavity. The disk has a large radius and a mass typical of more evolved T Tauri disks in spite of the significant remaining envelope. HOPS 136 appears to be a key link between the protostellar and optically revealed stages of star formation. © 2014. The American Astronomical Society. All rights reserved.

Adams J.D.,Cornell University | Herter T.L.,Cornell University | Osorio M.,Institute Astrofisica Of Andalucia | MacIas E.,Institute Astrofisica Of Andalucia | And 17 more authors.
Astrophysical Journal Letters | Year: 2012

We examine eight young stellar objects in the OMC-2 star-forming region based on observations from the SOFIA/FORCAST early science phase, the Spitzer Space Telescope, the Herschel Space Observatory, Two Micron All Sky Survey, Atacama Pathfinder Experiment, and other results in the literature. We show the spectral energy distributions (SED) of these objects from near-infrared to millimeter wavelengths, and compare the SEDs with those of sheet collapse models of protostars and circumstellar disks. Four of the objects can be modeled as protostars with infalling envelopes, two as young stars surrounded by disks, and the remaining two objects have double-peaked SEDs. We model the double-peaked sources as binaries containing a young star with a disk and a protostar. The six most luminous sources are found in a dense group within a 0.15 × 0.25 pc region; these sources have luminosities ranging from 300 L⊙ to 20 L⊙. The most embedded source (OMC-2 FIR 4) can be fit by a class 0 protostar model having a luminosity of 50 L⊙ and mass infall rate of 10-4 M⊙ yr-1. © 2012 The American Astronomical Society. All rights reserved.

Fischer W.J.,University of Toledo | Megeath S.T.,University of Toledo | Tobin J.J.,U.S. National Radio Astronomy Observatory | Stutz A.M.,Max Planck Institute for Astronomy | And 9 more authors.
Astrophysical Journal | Year: 2012

Individual outbursting young stars are important laboratories for studying the physics of episodic accretion and the extent to which this phenomenon can explain the luminosity distribution of protostars. We present new and archival data for V2775Ori (HOPS 223), a protostar in the L1641 region of the Orion molecular clouds that was discovered by Caratti o Garatti etal. to have recently undergone an order-of-magnitude increase in luminosity. Our near-infrared spectra of the source have strong blueshifted He I λ10830 absorption, strong H2O and CO absorption, and no H I emission, all typical of FU Orionis sources. With data from the Infrared Telescope Facility, the Two Micron All Sky Survey, the Hubble Space Telescope, Spitzer, the Wide-field Infrared Survey Explorer, Herschel, and the Atacama Pathfinder Experiment that span from 1 to 70 μm pre-outburst and from 1 to 870 μm post-outburst, we estimate that the outburst began between 2005 April and 2007 March. We also model the pre- and post-outburst spectral energy distributions of the source, finding it to be in the late stages of accreting its envelope with a disk-to-star accretion rate that increased from ∼ 2 × 10-6 M ⊙ yr-1 to ∼10-5 M ⊙ yr-1 during the outburst. The post-outburst luminosity at the epoch of the FU Orionis-like near-IR spectra is 28 L ⊙, making V2775Ori the least luminous documented FU Orionis outburster with a protostellar envelope. The existence of low-luminosity outbursts supports the notion that a range of episiodic accretion phenomena can partially explain the observed spread in protostellar luminosities. © © 2012. The American Astronomical Society. All rights reserved.

Manoj P.,University of Rochester | Watson D.M.,University of Rochester | Neufeld D.A.,Johns Hopkins University | Megeath S.T.,University of Toledo | And 14 more authors.
Astrophysical Journal | Year: 2013

We present far-infrared (57-196 μm) spectra of 21 protostars in the Orion molecular clouds. These were obtained with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space observatory as part of the Herschel Orion Protostar Survey program. We analyzed the emission lines from rotational transitions of CO, involving rotational quantum numbers in the range Jup = 14-46, using PACS spectra extracted within a projected distance of ≲2000 AU centered on the protostar. The total luminosity of the CO lines observed with PACS (LCO) is found to increase with increasing protostellar luminosity (Lbol). However, no significant correlation is found between LCO and evolutionary indicators or envelope properties of the protostars such as bolometric temperature, Tbol, or envelope density. The CO rotational (excitation) temperature implied by the line ratios increases with increasing rotational quantum number J, and at least 3-4 rotational temperature components are required to fit the observed rotational diagram in the PACS wavelength range. The rotational temperature components are remarkably invariant between protostars and show no dependence on Lbol, Tbol, or envelope density, implying that if the emitting gas is in local thermodynamic equilibrium, the CO emission must arise in multiple temperature components that remain independent of Lbol over two orders of magnitudes. The observed CO emission can also be modeled as arising from a single-temperature gas component or from a medium with a power-law temperature distribution; both of these require sub-thermally excited molecular gas at low densities (n(H2) ≲ 106 cm -3) and high temperatures (T ≳ 2000 K). Our results suggest that the contribution from photodissociation regions, produced along the envelope cavity walls from UV-heating, is unlikely to be the dominant component of the CO emission observed with PACS. Instead, the "universality" of the rotational temperatures and the observed correlation between LCO and Lbol can most easily be explained if the observed CO emission originates in shock-heated, hot (T ≳ 2000 K), sub-thermally excited (n(H2) ≲ 106 cm-3) molecular gas. Post-shock gas at these densities is more likely to be found within the outflow cavities along the molecular outflow or along the cavity walls at radii ≳ several 100-1000 AU. © 2013. The American Astronomical Society. All rights reserved.

Fischer W.J.,University of Toledo | Megeath S.T.,University of Toledo | Stutz A.M.,Max Planck Institute for Astronomy | Stutz A.M.,University of Arizona | And 6 more authors.
Astronomische Nachrichten | Year: 2013

Surveys with the Spitzer and Herschel space observatories are now enabling the discovery and characterization of large samples of protostars in nearby molecular clouds, providing the observational basis for a detailed understanding of star formation in diverse environments. We are pursuing this goal with the Herschel Orion Protostar Survey (HOPS), which targets 328 Spitzer -identified protostars in the Orion molecular clouds, the largest star-forming region in the nearest 500 pc. The sample encompasses all phases of protostellar evolution and a wide range of formation environments, from dense clusters to relative isolation. With a grid of radiative transfer models, we fit the 1-870 μm spectral energy distributions (SEDs) of the protostars to estimate their envelope densities, cavity opening angles, inclinations, and total luminosities. After correcting the bolometric luminosities and temperatures of the sources for foreground extinction and inclination, we find a spread of several orders of magnitude in luminosity at all evolutionary states, a constant median luminosity over the more evolved stages, and a possible deficit of high-inclination, rapidly infalling envelopes among the Spitzer -identified sample. We have detected over 100 new sources in the Herschel images; some of them may fill this deficit. We also report results from modeling the pre- and post-outburst 1-870 μm SEDs of V2775 Ori (HOPS 223), a known FU Orionis outburster in the sample. It is the least luminous FU Ori star with a protostellar envelope. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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