Engineering topics

Green, Joel D.

Publications and source records attributed to Green, Joel D..

12 records

DOE OSTI2017

The class 0 protostar BHR71: Herschel observations and dust continuum models

We use Herschel spectrophotometry of BHR71, an embedded Class 0 protostar, to provide new constraints on its physical properties. We detect 645 (non-unique) spectral lines among all spatial pixels. At least 61 different spectral lines originate from the central region. A CO rotational diagram analysis shows four excitation temperature components, 43, 197, 397, and 1057 K. Low-J CO lines trace the outflow while the high-J CO lines are centered on the infrared source. The low-excitation emission lines of H{sub 2}O trace the large-scale outflow, while the high-excitation emission lines trace a small-scale distribution around the equatorial plane. We model the envelope structure using the dust radiative transfer code, hyperion, incorporating rotational collapse, an outer static envelope, outflow cavity, and disk. The evolution of a rotating collapsing envelope can be constrained by the far-infrared/millimeter spectral energy distribution along with the azimuthally averaged radial intensity profile, and the structure of the outflow cavity plays a critical role at shorter wavelengths. Emission at 20–40 μm requires a cavity with a constant-density inner region and a power-law density outer region. The best-fit model has an envelope mass of 19 M{sub ⊙} inside a radius of 0.315 pc and a central luminosity of 18.8 L{sub ⊙}. The time since collapse began is 24,630–44,000 years, most likely around 36,000 years. The corresponding mass infall rate in the envelope (1.2 × 10{sup −5} M{sub ⊙} yr{sup −1}) is comparable to the stellar mass accretion rate, while the mass-loss rate estimated from the CO outflow is 20% of the stellar mass accretion rate. We find no evidence for episodic accretion.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

THE MID-INFRARED EVOLUTION OF THE FU ORIONIS DISK

We present new SOFIA-FORCAST observations obtained in 2016 February of the archetypal outbursting low-mass young stellar object FU Orionis, and we compare the continuum, solid-state, and gas properties with mid-infrared data obtained at the same wavelengths in 2004 with Spitzer -IRS. In this study, we conduct the first mid-infrared spectroscopic comparison of an FUor over a long time period. Over a 12-year period, UBVR monitoring indicates that FU Orionis has continued its steady decrease in overall brightness by ∼14%. We find that this decrease in luminosity occurs only at wavelengths ≲20 μ m. In particular, the continuum shortward of the silicate emission complex at 10 μ m exhibits a ∼12% (∼3 σ ) drop in flux density but no apparent change in slope; both the Spitzer and SOFIA spectra are consistent with a 7200 K blackbody. Additionally, the detection of water absorption is consistent with the Spitzer spectrum. The silicate emission feature at 10 μ m continues to be consistent with unprocessed grains, unchanged over 12 years. We conclude that either the accretion rate in FU Orionis has decreased by ∼12–14% over this time baseline or the inner disk has cooled, but the accretion disk remains in a superheated state outside the innermost region.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

Testing the binary trigger hypothesis in FUors

We present observations of three FU Orionis objects (hereafter, FUors) with nonredundant aperture-mask interferometry at 1.59 μm and 2.12 μm that probe for binary companions on the scale of the protoplanetary disk that feeds their accretion outbursts. We do not identify any companions to V1515 Cyg or HBC 722, but we do resolve a close binary companion to V1057 Cyg that is at the diffraction limit (ρ=58.3±1.4 mas or 30 ± 5 au) and currently much fainter than the outbursting star (ΔK{sup ′}=3.34±0.10 mag). Given the flux excess of the outbursting star, we estimate that the mass of the companion (M∼0.25M{sub ⊙}) is similar to or slightly below that of the FUor itself, and therefore it resembles a typical T Tauri binary system. Our observations only achieve contrast limits of ΔK{sup ′}∼4 mag, and hence we are only sensitive to companions that were near or above the pre-outburst luminosity of the FUors. It remains plausible that FUor outbursts could be tied to the presence of a close binary companion. However, we argue from the system geometry and mass reservoir considerations that these outbursts are not directly tied to the orbital period (i.e., occurring at periastron passage), but instead must only occur infrequently.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

THE CDF ARCHIVE: HERSCHEL PACS AND SPIRE SPECTROSCOPIC DATA PIPELINE AND PRODUCTS FOR PROTOSTARS AND YOUNG STELLAR OBJECTS

We present the COPS-DIGIT-FOOSH (CDF) Herschel spectroscopy data product archive, and related ancillary data products, along with data fidelity assessments, and a user-created archive in collaboration with the Herschel-PACS and SPIRE ICC groups. Our products include datacubes, contour maps, automated line fitting results, and best 1D spectra products for all protostellar and disk sources observed with PACS in RangeScan mode for two observing programs: the DIGIT Open Time Key Program (KPOT-nevans-1 and SDP-nevans-1; PI: N. Evans), and the FOOSH Open Time Program (OT1-jgreen02-2; PI: J. Green). In addition, we provide our best SPIRE-FTS spectroscopic products for the COPS Open Time Program (OT2-jgreen02-6; PI: J. Green) and FOOSH sources. We include details of data processing, descriptions of output products, and tests of their reliability for user applications. We identify the parts of the data set to be used with caution. The resulting absolute flux calibration has improved in almost all cases. Compared to previous reductions, the resulting rotational temperatures and numbers of CO molecules have changed substantially in some sources. On average, however, the rotational temperatures have not changed substantially (<2%), but the number of warm (T{sub rot} ∼ 300 K) CO molecules has increased by about 18%.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

HIGH RESOLUTION OPTICAL AND NIR SPECTRA OF HBC 722

We present the results of high resolution (R ≥ 30,000) optical and near-IR spectroscopic monitoring observations of HBC 722, a recent FU Orionis object that underwent an accretion burst in 2010. We observed HBC 722 in the optical/near-IR with the Bohyunsan Optical Echelle Spectrograph, Hobby–Eberly Telescope-HRS, and Immersion Grating Infrared Spectrograph, at various points in the outburst. We found atomic lines with strongly blueshifted absorption features or P Cygni profiles, both evidence of a wind driven by the accretion. Some lines show a broad double-peaked absorption feature, evidence of disk rotation. However, the wind-driven and disk-driven spectroscopic features are anti-correlated in time; the disk features became strong as the wind features disappeared. This anti-correlation might indicate that the rebuilding of the inner disk was interrupted by the wind pressure during the first 2 years. The half-width at half-depth of the double-peaked profiles decreases with wavelength, indicative of the Keplerian rotation; the optical spectra with the disk feature are fitted by a G5 template stellar spectrum convolved with a rotation velocity of 70 km s{sup −1} while the near-IR disk features are fitted by a K5 template stellar spectrum convolved with a rotation velocity of 50 km s{sup −1}. Therefore, the optical and near-IR spectra seem to trace the disk at 39 and 76 R{sub ⊙}, respectively. We fit a power-law temperature distribution in the disk, finding an index of 0.8, comparable to optically thick accretion disk models.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

EVIDENCE FOR DECAY OF TURBULENCE BY MHD SHOCKS IN THE ISM VIA CO EMISSION

We utilize observations of sub-millimeter rotational transitions of CO from a Herschel Cycle 2 open time program (“COPS”, PI: J. Green) to identify previously predicted turbulent dissipation by magnetohydrodynamic (MHD) shocks in molecular clouds. We find evidence of the shocks expected for dissipation of MHD turbulence in material not associated with any protostar. Two models fit about equally well: model 1 has a density of 10{sup 3} cm{sup −3}, a shock velocity of 3 km s{sup −1}, and a magnetic field strength of 4 μG; model 2 has a density of 10{sup 3.5} cm{sup −3}, a shock velocity of 2 km s{sup −1}, and a magnetic field strength of 8 μG. Timescales for decay of turbulence in this region are comparable to crossing times. Transitions of CO up to J of 8, observed close to active sites of star formation, but not within outflows, can trace turbulent dissipation of shocks stirred by formation processes. Although the transitions are difficult to detect at individual positions, our Herschel-SPIRE survey of protostars provides a grid of spatially distributed spectra within molecular clouds. We averaged all spatial positions away from known outflows near seven protostars. We find significant agreement with predictions of models of turbulent dissipation in slightly denser (10{sup 3.5} cm{sup −3}) material with a stronger magnetic field (24 μG) than in the general molecular cloud.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

“Dust, ice, and gas in time” (DIGIT) herschel observations of GSS30-IRS1 in Ophiuchus

As a part of the “Dust, Ice, and Gas In Time” (DIGIT) key program on Herschel, we observed GSS30-IRS1, a Class I protostar located in Ophiuchus (d = 120 pc), with Herschel/Photodetector Array Camera and Spectrometer. More than 70 lines were detected within a wavelength range from 50 to 200 μm, including CO, H{sub 2}O, OH, and two atomic [O i] lines at 63 and 145 μm. The [C ii] line, known as a tracer of externally heated gas by the interstellar radiation field (ISRF), is also detected at 158 μm. All lines, except [O i] and [C ii], are detected only at the central spaxel of 9.″4 × 9.″4. The [O i] emissions are extended along a NE–SW orientation, and the [C ii] line is detected over all spaxels, indicative of an external photodissociation region. The total [C ii] intensity around GSS30 reveals that the far-ultraviolet radiation field is in the range of 3 to 20 G{sub 0}, where G{sub 0} is in units of the Habing Field, 1.6 × 10{sup −3} erg cm{sup −2} s{sup −1}. This enhanced external radiation field heats the envelope of GSS30-IRS1, causing the continuum emission to be extended, unlike the molecular emission. The best-fit continuum model of GSS30-IRS1 with the physical structure including flared disk, envelope, and outflow shows that the internal luminosity is 10 L{sub ⊙}, and the region is externally heated by a radiation field enhanced by a factor of 130 compared to the standard local ISRF.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2015

Color variability of HBC 722 in the post-outburst phases

We carried out photometric observations for HBC 722 in the Sloan Digital Sky Survey r, i, and z bands from 2011 April to 2013 May with the Camera for QUasars in EArly uNiverse attached to the 2.1 m Otto Struve telescope at McDonald Observatory. The post-outburst phenomena were classified into five phases according to not only brightness but also color variations, which might be caused by physical changes in the emitting regions of optical and near-infrared bands. A series of spectral energy distributions (SEDs) is presented to support color variations and track the time evolution of the SED in optical/near-infrared bands after the outburst. Given two years of data, possible periodicities of r, i, and z bands were checked. We found three families of signals around ∼6, ∼10, and ∼1 days in three bands, which is broadly consistent with Green et al. We also examined short-term variability (intra-day and day scales) to search for evidences of flickering by using the micro-variability method. We found clear signs of day scale variability and weak indications of intra-day scale fluctuations, which implies that the flickering event occurs in HBC 722 after outburst.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

L1448-MM OBSERVATIONS BY THE HERSCHEL KEY PROGRAM, ''DUST, ICE, AND GAS IN TIME'' (DIGIT)

We present Herschel/Photodetector Array Camera and Spectrometer (PACS) observations of L1448-MM, a Class 0 protostar with a prominent outflow. Numerous emission lines are detected at 55 <λ < 210 μm including CO, OH, H{sub 2}O, and [O I]. We investigate the spatial distribution of each transition to find that lines from low energy levels tend to distribute along the outflow direction while lines from high energy levels peak at the central spatial pixel. Spatial maps reveal that OH emission lines are formed in a relatively small area, while [O I] emission is extended. According to the rotational diagram analysis, the CO emission can be fitted by two (warm and hot) temperature components. For H{sub 2}O, the ortho-to-para ratio is close to 3. The non-LTE large velocity gradient (LVG) calculations suggest that CO and H{sub 2}O lines could instead be formed in a high kinetic temperature (T > 1000 K) environment, indicative of a shock origin. For OH, IR-pumping processes play an important role in the level population. The molecular emission in L1448-MM is better explained with a C-shock model, but the atomic emission of PACS [O I] and Spitzer/Infrared Spectrograph [Si II] emission is not consistent with C-shocks, suggesting multiple shocks in this region. Water is the major line coolant of L1448-MM in the PACS wavelength range, and the best-fit LVG models predict that H{sub 2}O and CO emit (50%-80%) of their line luminosity in the PACS wavelength range.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

AN ANALYSIS OF THE ENVIRONMENTS OF FU ORIONIS OBJECTS WITH HERSCHEL

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{sub bol}, T{sub 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 {sup 13}CO (J{sub 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 {yields} 22 and evidence for H{sub 2}O 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 {approx} 10{sup 50} total CO molecules. We detect [C I] and [N II] primarily as diffuse emission.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2013

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

We present 50-210 {mu}m spectral scans of 30 Class 0/I protostellar sources, obtained with Herschel-PACS, and 0.5-1000 {mu}m spectral energy distributions, as part of the Dust, Ice, and Gas in Time Key Program. Some sources exhibit up to 75 H{sub 2}O lines ranging in excitation energy from 100 to 2000 K, 12 transitions of OH, and CO rotational lines ranging from J = 14 {yields} 13 up to J = 40 {yields} 39. [O I] is detected in all but one source in the entire sample; among the sources with detectable [O I] are two very low luminosity objects. The mean 63/145 {mu}m [O I] flux ratio is 17.2 {+-} 9.2. The [O I] 63 {mu}m line correlates with L{sub bol}, but not with the time-averaged outflow rate derived from low-J CO maps. [C II] emission is in general not local to the source. The sample L{sub bol} increased by 1.25 (1.06) and T{sub bol} decreased to 0.96 (0.96) of mean (median) values with the inclusion of the Herschel data. Most CO rotational diagrams are characterized by two optically thin components ( = (0.70 {+-} 1.12) x 10{sup 49} total particles). N{sub CO} correlates strongly with L{sub bol}, but neither T{sub rot} nor N{sub CO}(warm)/N{sub CO}(hot) correlates with L{sub bol}, suggesting that the total excited gas is related to the current source luminosity, but that the excitation is primarily determined by the physics of the interaction (e.g., UV-heating/shocks). Rotational temperatures for H{sub 2}O ( = 194 +/- 85 K) and OH ( = 183 +/- 117 K) are generally lower than for CO, and much of the scatter in the observations about the best fit is attributed to differences in excitation conditions and optical depths among the detected lines.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2009

Molecular Cooling as a Probe of Star Formation: Spitzer Looking Forward to Herschel

We explore here the question of how cloud physics can be more directly probed when one observes the majority of cooling emissions from molecular gas. For this purpose we use results from a recent Spitzer Space Telescope study of the young cluster of embedded objects in NGC1333. For this study we mapped the emission from eight pure H2 rotational lines, from S(0) to S(7). The H2 emission appears to be associated with the warm gas shocked by the multiple outflows present in the region. The H2 lines are found to contribute to 25 - 50% of the total outflow luminosity, and can be used to more directly ascertain the importance of star formation feedback on the natal cloud. From these lines, we determine the outflow mass loss rate and, indirectly, the stellar infall rate, the outflow momentum and the kinetic energy injected into the cloud over the embedded phase. The latter is found to exceed the binding energy of individual cores, suggesting that outflows could be the main mechanism for cores disruption. Given the recent launch of Herschel and the upcoming operational lifetime of SOFIA we discuss how studies of molecular cooling can take a step beyond understanding thermal balance to exploring the origin, receipt, and transfer of energy in atomic and molecular gas in a wide range of physical situations.

Bergin, Edwin A.↗