[en] 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"3 cm"−"3, a shock velocity of 3 km s"−"1, and a magnetic field strength of 4 μG; model 2 has a density of 10"3"."5 cm"−"3, a shock velocity of 2 km s"−"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"3"."5 cm"−"3) material with a stronger magnetic field (24 μG) than in the general molecular cloud

[en] We present dual-epoch Hubble Space Telescope imaging of the great disk shadow in the Serpens star-forming region. The near-infrared images show strong variability of the disk shadow, revealing dynamics of the inner disk on timescales of months. The Great Shadow is projected onto the Serpens reflection nebula by an unresolved protoplanetary disk surrounding the young intermediate-mass star SVS2/CK3/EC82. Since the shadow extends out to a distance of at least 17,000 au, corresponding to a light-travel time of 0.24 yr, the images may reveal detailed changes in the disk scale height and position angle on timescales as short as a day, corresponding to the angular resolution of the images, and up to the 1.11 yr span between two observing epochs. We present a basic retrieval of temporal changes in the disk density structure, based on the images. We find that the inner disk changes position angle on timescales of months, and that the change is not axisymmetric, suggesting the presence of a non-axisymmetric dynamical forcing on ∼1 au size scales. We consider two different scenarios, one in which a quadrupolar disk warp orbits the central star, and one in which an unequal-mass binary orbiting out of the disk plane displaces the photocenter relative to the shadowing disk. Continued space-based monitoring of the great disk shadow is required to distinguish between these scenarios, and could provide unique and detailed insight into the dynamics of inner protoplanetary disks not available through other means.

[en] 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 $\mathrm{\mu <!--\; ??\; -->}\mathrm{m}$, including CO, H₂O, OH, and two atomic [O i] lines at 63 and 145 $\mathrm{\mu <!--\; ??\; -->}\mathrm{m}$. The [C ii] line, known as a tracer of externally heated gas by the interstellar radiation field (ISRF), is also detected at 158 $\mathrm{\mu <!--\; ??\; -->}\mathrm{m}$. 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 $G_0$, where $G_0$ is in units of the Habing Field, 1.6 × 10⁻³ erg cm⁻² s⁻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 $L_{\odot <!--\; ???\; -->}$, and the region is externally heated by a radiation field enhanced by a factor of 130 compared to the standard local ISRF.

[en] 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 ($\mathrm{\rho <!--\; ??\; -->}=58.3\pm <!--\; ??\; -->1.4$ mas or 30 ± 5 au) and currently much fainter than the outbursting star ($\mathrm{\Delta <!--\; ??\; -->}{K}^{\mathrm{\prime <!--\; ???\; -->}}=3.34\pm <!--\; ??\; -->0.10$ mag). Given the flux excess of the outbursting star, we estimate that the mass of the companion ($M\sim <!--\; ???\; -->0.25M_{\odot <!--\; ???\; -->}$) 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 $\mathrm{\Delta <!--\; ??\; -->}{K}^{\mathrm{\prime <!--\; ???\; -->}}\sim <!--\; ???\; -->4$ 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.

[en] 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 μm 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 ∼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 (Ł_bol = 24.5 L _☉) and the [O I] 63.1 μm 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 (∼70 km s^–1) of PACS, are consistent with the known redshifted and blueshifted outflow direction

[en] 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 ${\mathrm{H}}_2\mathrm{O}$ 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 $M_{\odot <!--\; ???\; -->}$ inside a radius of 0.315 pc and a central luminosity of 18.8 $L_{\odot <!--\; ???\; -->}$. 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 × 10⁻⁵ $M_{\odot <!--\; ???\; -->}{\mathrm{y}\mathrm{r}}^{-<!--\; ???\; -->1}$) 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.

[en] 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.

[en] We present the detection of day-timescale periodic variability in the r-band lightcurve of newly outbursting FU Orionis-type object HBC 722, taken from >42 nights of observation with the CQUEAN instrument on the McDonald Observatory 2.1 m telescope. The optical/near-IR lightcurve of HBC 722 shows a complex array of periodic variability, clustering around 5.8-day (0.044 mag amplitude) and 1.28-day (0.016 mag amplitude) periods, after removal of overall baseline variation. We attribute the unusual number of comparable strength signals to a phenomenon related to the temporary increase in accretion rate associated with FUors. We consider semi-random 'flickering', magnetic braking/field compression and rotational asymmetries in the disk instability region as potential sources of variability. Assuming that the 5.8-day period is due to stellar rotation and the 1.28-day period is indicative of Keplerian rotation at the inner radius of the accretion disk (at 2 R _*), we derive a B-field strength of 2.2-2.7 kG, slightly larger than typical T Tauri stars. If instead the 5.8-day signal is from a disk asymmetry, the instability region has an outer radius of 5.4 R _*, consistent with models of FUor disks. Further exploration of the time domain in this complicated source and related objects will be key to understanding accretion processes.

[en] Observations from the Herschel Space Observatory have more than doubled the number of wide debris disks orbiting Sunlike stars to include over 30 systems with R  > 100 AU. Here, we present new Herschel PACS and reanalyzed Spitzer MIPS photometry of five Sunlike stars with wide debris disks, from Kuiper Belt size to R  > 150 AU. The disk surrounding HD 105211 is well resolved, with an angular extent of >14″ along the major axis, and the disks of HD 33636, HD 50554, and HD 52265 are extended beyond the PACS point-spread function size (50% of energy enclosed within radius 4.″23). HD 105211 also has a 24 μ m infrared excess, which was previously overlooked, because of a poorly constrained photospheric model. Archival Spitzer IRS observations indicate that the disks have small grains of minimum radius a _min ∼ 3 μ m, although a _min is larger than the radiation-pressure blowout size in all systems. If modeled as single-temperature blackbodies, the disk temperatures would all be <60 K. Our radiative transfer models predict actual disk radii approximately twice the radius of a model blackbody disk. We find that the Herschel photometry traces dust near the source population of planetesimals. The disk luminosities are in the range 2 × 10⁻⁵ ⩽  L / L _⊙ ⩽ 2 × 10⁻⁴, consistent with collisions in icy planetesimal belts stirred by Pluto-size dwarf planets.

[en] 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.