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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Radio properties of young stellar objects in the core of the Serpens South Infrared Dark Cloud

We present deep radio continuum observations of the star-forming core of the Serpens South Infrared Dark Cloud with the Karl G. Jansky Very Large Array. Observations were conducted in two bands centered at 7.25 GHz (4.14 cm) and 4.75 GHz (6.31 cm) with a σ{sub rms} of 8.5 and 11.1 μJy/beam, respectively. We also use 2MASS, Spitzer and Herschel data to put our radio observations in the context of young stellar populations characterized by near and far-infrared observations. Within a 5′ × 5′ region of interest around the central cluster, we detect roughly eighteen radio sources, seven of which we determine are protostellar in nature due to their radio spectral indices and their association with infrared sources. We find evidence for a previously undetected embedded Class 0 protostar and reaffirm Class 0 protostellar classifications determined by previous millimeter wavelength continuum studies. We use our infrared data to derive mid-infrared luminosities for three of our protostellar sources and find relative agreement between the known young stellar object (YSO) radio luminosity versus bolometric luminosity correlation. Lastly, we marginally detect an additional six radio sources at the 2–3σ level that lie within two arcseconds of infrared YSO candidates, providing motivation for higher sensitivity studies to clarify the nature of these sources and further probe embedded and/or low luminosity YSOs in Serpens South.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

STRUCTURAL STUDIES OF EIGHT BRIGHT RIMMED CLOUDS IN THE SOUTHERN HEMISPHERE

We carried out deep- and wide-field near- and mid-infrared observations for a sample of eight bright-rimmed clouds (BRCs). Supplemented with the Spitzer archival data, we have identified and classified 44 to 433 young stellar objects (YSOs) associated with these BRCs. The Class I sources are generally located toward the places with higher extinction and are relatively closer to each other than the Class II sources, confirming that the young protostars are usually found in regions with denser molecular material. On the other hand the comparatively older population, Class II objects, are more randomly found throughout the regions, which can be due to their dynamical evolution. Using the minimal sampling tree analyses, we have extracted 13 stellar cores of eight or more members, which contain 60% of the total YSOs. The typical core is ∼0.6 pc in radii and somewhat elongated (aspect ratio of 1.45), of relatively low stellar density (surface density 60 pc{sup −2}), consisting of a small (35) number of YSOs of relatively young sources (66% Class I), and partially embedded (median A{sub K} = 1.1 mag). But the cores show a wide range in their mass distribution (∼20 to 2400 M {sub ⊙}), with a median value of around 130 M {sub ⊙}. We found the star-formation efficiencies in the cores to be between 3% and 30% with an average of ∼14%, which agrees with the efficiencies needed to link the core mass function to the initial mass function. We also found a linear relation between the density of the clouds and the number of YSOs. The peaked nearest neighbor spacing distributions of the YSOs and the ratio of Jeans lengths to the YSO separations indicates a significant degree of non-thermally driven fragmentation in these BRCs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Vertical structure of magnetized accretion disks around young stars

We model the vertical structure of the magnetized accretion disks that are subject to viscous and resistive heating and irradiation by the central star. We apply our formalism to the radial structure of the magnetized accretion disks that are threaded by the poloidal magnetic field dragged during the process of star formation, which was developed by Shu and coworkers. We consider disks around low-mass protostars, T Tauri, and FU Orionis stars, as well as two levels of disk magnetization: λ{sub sys}=4 (strongly magnetized disks) and λ{sub sys}=12 (weakly magnetized disks). The rotation rates of strongly magnetized disks have large deviations from Keplerian rotation. In these models, resistive heating dominates the thermal structure for the FU Ori disk, and the T Tauri disk is very thin and cold because it is strongly compressed by magnetic pressure; it may be too thin compared with observations. Instead, in the weakly magnetized disks, rotation velocities are close to Keplerian, and resistive heating is always less than 7% of the viscous heating. In these models, the T Tauri disk has a larger aspect ratio, which is consistent with that inferred from observations. All the disks have spatially extended hot atmospheres where the irradiation flux is absorbed, although most of the mass (∼90%–95%) is in the disk midplane. With the advent of ALMA one expects direct measurements of magnetic fields and their morphology at disk scales. It will then be possible to determine the mass-to-flux ratio of magnetized accretion disks around young stars, an essential parameter for their structure and evolution. Our models contribute to the understanding of the vertical structure and emission of these disks.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

ALMA observation of the 658 GHz vibrationally excited H{sub 2}O maser in Orion KL source I

We present an observational study of the vibrationally excited H{sub 2}O line at 658 GHz (ν{sub 2} = 1, 1{sub 1,0}-1{sub 0,1}) toward Orion KL using the Atacama Large Millimeter/Submillimeter Array (ALMA). This line is clearly detected at the position of the massive protostar candidate, Source I. The spatial structure is compact, with a size of about 100 AU, and is elongated along the northeast–southwest low-velocity (18 km {sup −1}) bipolar outflow traced by 22 GHz H{sub 2}O masers, SiO masers, and thermal SiO lines. A velocity gradient can be seen perpendicular to the bipolar outflow. The overall spatial and velocity structure seems to be analogous to that of the 321 GHz H{sub 2}O maser line previously detected with ALMA and vibrationally excited SiO maser emission. The brightness temperature of the 658 GHz H{sub 2}O line is estimated to be higher than 2 × 10{sup 4} K, implying that it is emitted via maser action. Our results suggest that the 658 GHz H{sub 2}O maser line is emitted from the base of the outflow from a rotating and expanding accretion disk as observed for the SiO masers and the 321 GHz H{sub 2}O maser. We also search for two other H{sub 2}O lines at 646 GHz (9{sub 7,3}-8{sub 8,0} and 9{sub 7,2}-8{sub 8,1}), but they are not detected in Orion KL.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

CS EMISSION NEAR MIR-BUBBLES

We survey 44 young stellar objects located near the edges of mid-IR-identified bubbles in CS (1–0) using the Green Bank Telescope. We detect emission in 18 sources, indicating young protostars that are good candidates for being triggered by the expansion of the bubble. We calculate CS column densities and abundances. Three sources show evidence of infall through non-Gaussian line-shapes. Two of these sources are associated with dark clouds and are promising candidates for further exploration of potential triggered star formation. We obtained on-the-fly maps in CS (1–0) of three sources, showing evidence of significant interactions between the sources and the surrounding environment.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

GAS KINEMATICS AND STAR FORMATION IN THE FILAMENTARY IRDC G34.43+0.24

We performed a multiwavelength study toward the infrared dark cloud (IRDC) G34.43+0.24. New maps of {sup 13}CO J = 1–0 and C{sup 18}O J = 1–0 were obtained from the Purple Mountain Observatory (PMO) 13.7 m radio telescope. At 8 μm (Spitzer-IRAC), IRDC G34.43+0.24 appears to be a dark filament extended by 18′ along the north–south direction. Based on the association with the 870 μm and C{sup 18}O J = 1–0 emission, we suggest that IRDC G34.43+0.24 should not be 18′ in length, but extend to 34′. IRDC G34.43+0.24 contains some massive protostars, UC H ii regions, and infrared bubbles. The spatial extend of IRDC G34.43+0.24 is about 37 pc, assuming a distance of 3.7 kpc. IRDC G34.43+0.24 has a linear mass density of ∼1.6 × 10{sup 3} M{sub ⊙} pc{sup −1}, which is roughly consistent with its critical mass to length ratio. The turbulent motion may help stabilize the filament against the radial collapse. Both infrared bubbles N61 and N62 show a ringlike structure at 8 μm. In particular, N61 has a double-shell structure that has expanded into IRDC G34.43+0.24. The outer shell is traced by 8 μm and {sup 13}CO J = 1–0 emission, while the inner shell is traced by 24 μm and 20 cm emission. We suggest that the outer shell (9.9 × 10{sup 5} years) is created by the expansion of H ii region G34.172+0.175, while the inner shell (4.1 ∼ 6.3 × 10{sup 5} years) may be produced by the energetic stellar wind of its central massive star. From the GLIMPSE I catalog, we selected some Class I sources with an age of ∼10{sup 5} years. These Class I sources are clustered along the filamentary molecular cloud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

HELICAL MAGNETIC FIELDS IN THE NGC 1333 IRAS 4A PROTOSTELLAR OUTFLOWS

We present Submillimeter Array polarization observations of the CO J = 3–2 line toward NGC 1333 IRAS 4A. The CO Stokes I maps at an angular resolution of ∼1″ reveal two bipolar outflows from the binary sources of NGC 1333 IRAS 4A. The kinematic features of the CO emission can be modeled by wind-driven outflows at ∼20° inclined from the plane of the sky. Close to the protostars the CO polarization, at an angular resolution of ∼2.″3, has a position angle approximately parallel to the magnetic field direction inferred from the dust polarizations. The CO polarization direction appears to vary smoothly from an hourglass field around the core to an arc-like morphology wrapping around the outflow, suggesting a helical structure of magnetic fields that inherits the poloidal fields at the launching point and consists of toroidal fields at a farther distance of outflow. The helical magnetic field is consistent with the theoretical expectations for launching and collimating outflows from a magnetized rotating disk. Considering that the CO polarized emission is mainly contributed from the low-velocity and low-resolution data, the helical magnetic field is likely a product of the wind–envelope interaction in the wind-driven outflows. The CO data reveal a PA of ∼30° deflection in the outflows. The variation in the CO polarization angle seems to correlate with the deflections. We speculate that the helical magnetic field contributes to ∼10° deflection of the outflows by means of Lorentz force.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

COEVAL INTERMEDIATE-MASS STAR FORMATION IN N4W

Protostars are mostly found in star-forming regions, where the natal molecular gas still remains. At about 5{sup ′} west of the molecular bubble N4, N4W is identified as a star-forming clump hosting three Class II (IRS 1–3), and one Class I (IRS 4) young stellar objects (YSOs), as well as a submillimeter source SMM1. The near-IR polarization imaging data of N4W reveal two infrared reflection nebulae close to each other, which are in favor of the outflows of IRS 1 and IRS 2. The bipolar mid-IR emission centered on IRS 4 and the arc-like molecular gas shell are lying on the same axis, indicating a bipolar molecular outflow from IRS 4. There are two dust temperature distributions in N4W. The warmer one is widely distributed and has a temperature of T{sub d}≳28 K, with the colder one being from the embedded compact submillimeter source SMM1. N4W’s mass is estimated to be ∼2.5×10{sup 3} M{sub ⊙}, and the mass of SMM1 is ∼5.5×10{sup 2} M{sub ⊙} at T{sub d}=15 K, calculated from the CO 1 − 0 emission and 870 μm dust continuum emission, respectively. Based on the estimates of the bolometric luminosity of IRS 1–4, these four sources are intermediate-mass YSOs at least. SMM1 is gravitationally bound, and is capable of forming intermediate-mass stars or even possibly massive stars. The co-existence of the IR bright YSOs and the submillimeter source represents potential sequential star formation processes separated by ∼0.5 Myr in N4W. This small age spread implies that the intermediate-mass star formation processes happening in N4W are almost coeval.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE BOLOCAM GALACTIC PLANE SURVEY. XIV. PHYSICAL PROPERTIES OF MASSIVE STARLESS AND STAR-FORMING CLUMPS

We sort 4683 molecular clouds between 10° < ℓ < 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 μm sources, mid-IR color-selected YSOs, H{sub 2}O and CH{sub 3}OH masers, and UCH ii regions. We also present a combined NH{sub 3}-derived gas kinetic temperature and H{sub 2}O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (α ∼ 0.7) with >75% of clumps with known distance being gravitationally bound (α < 2). These samples show a statistically significant increase in the median clump mass of ΔM ∼ 170–370 M {sub ⊙} from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at M-dot ∼200--440 M {sub ⊙} Myr{sup −1} for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼M {sup −0.4}. By comparing to the observed number of CH{sub 3}OH maser containing clumps, we estimate the phase lifetime of massive (M > 10{sup 3} M {sub ⊙}) starless clumps to be 0.37 ± 0.08 Myr (M/10{sup 3} M {sub ⊙}){sup −1}; the majority (M < 450 M {sub ⊙}) have phase lifetimes longer than their average freefall time.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE ROLE OF SiO AS A TRACER OF PAST STAR FORMATION EVENTS: THE CASE OF THE HIGH-MASS PROTOCLUSTER NGC 2264-C

NGC 2264-C is a high-mass protocluster where several star formation events are known to have occurred. To investigate whether past protostellar activity has left a chemical imprint in this region, we mapped it in SiO(J=2−1), which is a shock tracer, and several other molecular lines with the Nobeyama 45 m telescope. Our observations show the presence of a complex network of protostellar outflows. The strongest SiO emission lies beyond a radius of ∼0.1 pc with respect to the center of the clump and is characterized by broad (>10 km s{sup −1}) lines and abundances of ∼1.4×10{sup −8} with respect to H{sub 2}. Interestingly, SiO appears to be relatively depleted (χ{sub SiO}∼4×10{sup −9}) within this radius, despite it being affected by molecular outflow activity. We attribute this to the fast condensation of SiO back onto dust grains and/or rapid gas-phase destruction of SiO, which is favored by the high density present in this area (>10{sup 6} cm{sup −3}). Finally, we identify a peripheral, narrow-line (∼2 km s{sup −1}) component where SiO has an abundance of a few times 10{sup −11}. After considering different options, we conclude that this weak emission may be tracing protostellar shocks from the star formation episode that preceded the current one, which have decelerated over time and eventually resulted in SiO being largely depleted/destroyed. Alternatively, a population of unresolved, low-mass protostars may be responsible for the narrow SiO emission. High-angular resolution observations are necessary to distinguish between these two possibilities, and thus to understand the role of SiO as a chemical tracer of past star formation episodes in massive protoclusters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

PHOTO-REVERBERATION MAPPING OF A PROTOPLANETARY ACCRETION DISK AROUND A T TAURI STAR

Theoretical models and spectroscopic observations of newborn stars suggest that protoplantary disks have an inner “wall” at a distance set by the disk interaction with the star. Around T Tauri stars, the size of this disk hole is expected to be on a 0.1 au scale that is unresolved by current adaptive optics imaging, though some model-dependent constraints have been obtained by near-infrared interferometry. Here we report the first measurement of the inner disk wall around a solar-mass young stellar object, YLW 16B in the ρ Ophiuchi star-forming region, by detecting the light-travel time of the variable radiation from the stellar surface to the disk. Consistent time lags were detected on two nights, when the time series in H (1.6 μ m) and K (2.2 μ m) bands were synchronized while the 4.5 μ m emission lagged by 74.5 ± 3.2 s. Considering the nearly edge-on geometry of the disk, the inner rim should be 0.084 au from the protostar on average, with an error of order 0.01 au. This size is likely larger than the range of magnetospheric truncations and consistent with an optically and geometrically thick disk front at the dust sublimation radius at ∼1500 K. The widths of the cross-correlation functions between the data in different wavebands place possible new constraints on the geometry of the disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Massive quiescent cores in orion. VI. The internal structures and a candidate of transiting core in NGC 2024 filament

We present a multiwavelength observational study of the NGC 2024 filament using infrared to submillimeter continuum and the NH{sub 3} (1,1) and (2,2) inversion transitions centered on FIR-3, the most massive core therein. FIR-3 is found to have no significant infrared point sources in the Spitzer/IRAC bands. But the NH{sub 3} kinetic temperature map shows a peak value at the core center with T{sub k}=25 K, which is significantly higher than the surrounding level (T{sub k} = 15–19 K). Such internal heating signature without an infrared source suggests an ongoing core collapse possibly at a transition stage from first hydrostatic core (FHSC) to protostar. The eight dense cores in the filament have dust temperatures between 17.5 and 22 K. They are much cooler than the hot ridge (T{sub d}∼55 K) around the central heating star IRS-2b. Comparison with a dust heating model suggests that the filament should have a distance of 3–5 pc from IRS-2b. This value is much larger than the spatial extent of the hot ridge, suggesting that the filament is spatially separated from the hot region along the line of sight.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

DENSE MOLECULAR CORES BEING EXTERNALLY HEATED

We present results of our study of eight dense cores, previously classified as starless, using infrared (3–160 μ m) imaging observations with the AKARI telescope and molecular line (HCN and N{sub 2}H{sup +}) mapping observations with the KVN telescope. Combining our results with the archival IR to millimeter continuum data, we examined the starless nature of these eight cores. Two of the eight cores are found to harbor faint protostars having luminosities of ∼0.3–4.4 L {sub ⊙}. The other six cores are found to remain starless and probably are in a dynamically transitional state. The temperature maps produced using multi-wavelength images show an enhancement of about 3–6 K toward the outer boundary of these cores, suggesting that they are most likely being heated externally by nearby stars and/or interstellar radiation fields. Large virial parameters and an overdominance of red asymmetric line profiles over the cores may indicate that the cores are set into either an expansion or an oscillatory motion, probably due to the external heating. Most of the starless cores show a coreshine effect due to the scattering of light by the micron-sized dust grains. This may imply that the age of the cores is of the order of ∼10{sup 5} years, which is consistent with the timescale required for the cores to evolve into an oscillatory stage due to external perturbation. Our observational results support the idea that the external feedback from nearby stars and/or interstellar radiation fields may play an important role in the dynamical evolution of the cores.

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DOE OSTI2016

Rapid circumstellar disk evolution and an accelerating star formation rate in the infrared dark cloud M17 SWex

We present a catalog of 840 X-ray sources and first results from a 100 ks Chandra X-ray Observatory imaging study of the filamentary infrared (IR) dark cloud G014.225–00.506, which forms the central regions of a larger cloud complex known as the M17 southwest extension (M17 SWex). In addition to the rich population of protostars and young stellar objects with dusty circumstellar disks revealed by archival data from the Spitzer Space Telescope, we discover a population of X-ray-emitting, intermediate-mass pre-main-sequence stars that lack IR excess emission from circumstellar disks. We model the IR spectral energy distributions of this source population to measure its mass function and place new constraints on the destruction timescales for the inner dust disk for 2–8 M {sub ☉} stars. We also place a lower limit on the star formation rate (SFR) and find that it is quite high ( M-dot ⩾0.007 M {sub ☉} yr{sup −1}), equivalent to several Orion Nebula Clusters in G14.225–0.506 alone, and likely accelerating. The cloud complex has not produced a population of massive, O-type stars commensurate with its SFR. This absence of very massive (≳20 M {sub ☉}) stars suggests that either (1) M17 SWex is an example of a distributed mode of star formation that will produce a large OB association dominated by intermediate-mass stars but relatively few massive clusters, or (2) the massive cores are still in the process of accreting sufficient mass to form massive clusters hosting O stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Tracking the distribution of {sup 26}Al and {sup 60}Fe during the early phases of star and disk evolution

The short-lived {sup 26}Al and {sup 60}Fe radionuclides are synthesized and expelled into the interstellar medium by core-collapse supernova events. The solar system’s first solids, calcium–aluminum refractory inclusions (CAIs), contain evidence for the former presence of the {sup 26} Al nuclide defining the canonical {sup 26}Al/{sup 27} Al ratio of ∼5×10{sup −5}. A different class of objects temporally related to canonical CAIs are CAIs with fractionation and unidentified nuclear effects (FUN CAIs), which record a low initial {sup 26}Al/{sup 27}Al of 10{sup −6}. The contrasting level of {sup 26}Al between these objects is often interpreted as reflecting the admixing of the {sup 26}Al nuclides during the early formative phase of the Sun. We use giant molecular cloud scale adaptive mesh-refinement numerical simulations to trace the abundance of {sup 26}Al and {sup 60}Fe in star-forming gas during the early stages of accretion of individual low-mass protostars. We find that the {sup 26}Al/{sup 27}Al and {sup 60}Fe/{sup 56}Fe ratios of accreting gas within a vicinity of 1000 au of the stars follow the predicted decay curves of the initial abundances at the time of star formation without evidence of spatial or temporal heterogeneities for the first 100 kyr of star formation. Therefore, the observed differences in {sup 26}Al/{sup 27}Al ratios between FUN and canonical CAIs are likely not caused by admixing of supernova material during the early evolution of the proto-Sun. Selective thermal processing of dust grains is a more viable scenario to account for the heterogeneity in {sup 26}Al/{sup 27}Al ratios at the time of solar system formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

IRAS 16253–2429: THE FIRST PROTO-BROWN DWARF BINARY CANDIDATE IDENTIFIED THROUGH THE DYNAMICS OF JETS

The formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD in the embedded phase. IRAS 16253–2429 is classified as a very low-luminosity object (VeLLO) with an internal luminosity of <0.1 L {sub ⊙}. VeLLOs are believed to be very low-mass protostars or even proto-BDs. We observed the jet/outflow driven by IRAS 16253–2429 in CO (2–1), (6–5), and (7–6) using the IRAM 30 m and Atacama Pathfinder Experiment telescopes and the Submillimeter Array (SMA) in order to study its dynamical features and physical properties. Our SMA map reveals two protostellar jets, indicating the existence of a proto-binary system as implied by the precessing jet detected in H{sub 2} emission. We detect a wiggling pattern in the position–velocity diagrams along the jet axes, which is likely due to the binary orbital motion. Based on this information, we derive the current mass of the binary as ∼0.032 M{sub ⊙}. Given the low envelope mass, IRAS 16253–2429 will form a binary that probably consist of one or two BDs. Furthermore, we found that the outflow force as well as the mass accretion rate are very low based on the multi-transition CO observations, which suggests that the final masses of the binary components are at the stellar/substellar boundary. Since IRAS 16253 is located in an isolated environment, we suggest that BDs can form through fragmentation and collapse, similar to low-mass stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A cautionary note about composite galactic star formation relations

We explore the pitfalls that affect the comparison of the star formation relation for nearby molecular clouds with that for distant compact molecular clumps. We show that both relations behave differently in the (Σ{sub gas}, Σ{sub SFR}) space, where Σ{sub gas} and Σ{sub SFR} are, respectively, the gas and star formation rate surface densities, even when the physics of star formation is the same. This is because the star formation relation of nearby clouds relates the gas and star surface densities measured locally, that is, within a given interval of gas surface density, or at a given protostar location. We refer to such measurements as local measurements, and the corresponding star formation relation as the local relation. In contrast, the stellar content of a distant molecular clump remains unresolved. Only the mean star formation rate can be obtained, e.g., from the clump infrared luminosity. One clump therefore provides one single point to the (Σ{sub gas}, Σ{sub SFR}) space, that is, its mean gas surface density and star formation rate surface density. We refer to this star formation relation as a global relation since it builds on the global properties of molecular clumps. Its definition therefore requires an ensemble of cluster-forming clumps. We show that although the local and global relations have different slopes, this cannot per se be taken as evidence for a change in the physics of star formation with gas surface density. It therefore appears that great caution should be taken when physically interpreting a composite star formation relation, that is, a relation combining local and global relations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE JCMT GOULD BELT SURVEY: EVIDENCE FOR DUST GRAIN EVOLUTION IN PERSEUS STAR-FORMING CLUMPS

The dust emissivity spectral index, β , is a critical parameter for deriving the mass and temperature of star-forming structures and, consequently, their gravitational stability. The β value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present β , dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting spectral energy distributions to combined Herschel and JCMT observations in the 160, 250, 350, 500, and 850 μ m bands. Most of the derived β and dust temperature values fall within the ranges of 1.0–2.7 and 8–20 K, respectively. In Perseus, we find the β distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant localized β variations within individual clumps and find low- β regions correlate with local temperature peaks, hinting at the possible origins of low- β grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.

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