ABSTRACT The dust extinction curve is a critical component of many observational programs and an important diagnostic of the physics of the interstellar medium. Here we present new measurements of ...the dust extinction curve and its variation toward tens of thousands of stars, a hundred-fold larger sample than in existing detailed studies. We use data from the APOGEE spectroscopic survey in combination with ten-band photometry from Pan-STARRS1, the Two Micron All-Sky Survey, and Wide-field Infrared Survey Explorer. We find that the extinction curve in the optical through infrared is well characterized by a one-parameter family of curves described by R(V). The extinction curve is more uniform than suggested in past works, with ( R ( V ) ) = 0.18 , and with less than one percent of sight lines having R ( V ) > 4 . Our data and analysis have revealed two new aspects of Galactic extinction: first, we find significant, wide-area variations in R(V) throughout the Galactic plane. These variations are on scales much larger than individual molecular clouds, indicating that R(V) variations must trace much more than just grain growth in dense molecular environments. Indeed, we find no correlation between R(V) and dust column density up to E ( B − V ) 2 . Second, we discover a strong relationship between R(V) and the far-infrared dust emissivity.
We compare the structure of star-forming molecular clouds in different regions of Orion A to determine how the column density probability distribution function (N-PDF) varies with environmental ...conditions such as the fraction of young protostars. A correlation between the N-PDF slope and Class 0 protostar fraction has been previously observed in a low-mass star-formation region (Perseus); here we test whether a similar correlation is observed in a high-mass star-forming region. We used Herschel PACS and SPIRE cold dust emission observations to derive a column density map of Orion A. We used the Herschel Orion Protostar Survey catalog to accurately identify and classify the Orion A young stellar object content, including the cold and relatively short-lived Class 0 protostars (with a lifetime of ~0.14 Myr). We divided Orion A into eight independent regions of 0.25 square degrees (13.5 pc2); in each region we fit the N-PDF distribution with a power law, and we measured the fraction of Class 0 protostars. We used a maximum-likelihood method to measure the N-PDF power-law index without binning the column density data. We find that the Class 0 fraction is higher in regions with flatter column density distributions. We tested the effects of incompleteness, extinction-driven misclassification of Class 0 sources, resolution, and adopted pixel-scales. We show that these effects cannot account for the observed trend. Our observations demonstrate an association between the slope of the power-law N-PDF and the Class 0 fractions within Orion A. Various interpretations are discussed, including timescales based on the Class 0 protostar fraction assuming a constant star-formation rate. The observed relation suggests that the N-PDF can be related to an evolutionary state of the gas. If universal, such a relation permits evaluating the evolutionary state from the N-PDF power-law index at much greater distances than those accessible with protostar counts.
ABSTRACT We present key results from the Herschel Orion Protostar Survey: spectral energy distributions (SEDs) and model fits of 330 young stellar objects, predominantly protostars, in the Orion ...molecular clouds. This is the largest sample of protostars studied in a single, nearby star formation complex. With near-infrared photometry from 2MASS, mid- and far-infrared data from Spitzer and Herschel, and submillimeter photometry from APEX, our SEDs cover 1.2-870 m and sample the peak of the protostellar envelope emission at ∼100 m. Using mid-IR spectral indices and bolometric temperatures, we classify our sample into 92 Class 0 protostars, 125 Class I protostars, 102 flat-spectrum sources, and 11 Class II pre-main-sequence stars. We implement a simple protostellar model (including a disk in an infalling envelope with outflow cavities) to generate a grid of 30,400 model SEDs and use it to determine the best-fit model parameters for each protostar. We argue that far-IR data are essential for accurate constraints on protostellar envelope properties. We find that most protostars, and in particular the flat-spectrum sources, are well fit. The median envelope density and median inclination angle decrease from Class 0 to Class I to flat-spectrum protostars, despite the broad range in best-fit parameters in each of the three categories. We also discuss degeneracies in our model parameters. Our results confirm that the different protostellar classes generally correspond to an evolutionary sequence with a decreasing envelope infall rate, but the inclination angle also plays a role in the appearance, and thus interpretation, of the SEDs.
Abstract
Models aiming to explain the formation of massive black hole seeds, and in particular the direct collapse scenario, face substantial difficulties. These are rooted in rather ad hoc and ...fine-tuned initial conditions, such as the simultaneous requirements of extremely low metallicities and strong radiation backgrounds. Here, we explore a modification of such scenarios where a massive primordial star cluster is initially produced. Subsequent stellar collisions give rise to the formation of massive (104−105 M⊙) objects. Our calculations demonstrate that the interplay among stellar dynamics, gas accretion, and protostellar evolution is particularly relevant. Gas accretion on to the protostars enhances their radii, resulting in an enhanced collisional cross-section. We show that the fraction of collisions can increase from 0.1 to 1 per cent of the initial population to about 10 per cent when compared to gas-free models or models of protostellar clusters in the local Universe. We conclude that very massive objects can form in spite of initial fragmentation, making the first massive protostellar clusters viable candidate birth places for observed supermassive black holes.
We study the fragmentation of the nearest high line-mass filament, the integral shaped filament (ISF, line-mass ~400 M⊙ pc-1) in the Orion A molecular cloud. We have observed a 1.6 pc long section of ...the ISF with the Atacama Large Millimetre/submillimeter Array (ALMA) at 3 mm continuum emission, at a resolution of ~3″ (1200 AU). We identify from the region 43 dense cores with masses about a solar mass. 60% of the ALMA cores are protostellar and 40% are starless. The nearest neighbour separations of the cores do not show a preferred fragmentation scale; the frequency of short separations increases down to 1200 AU. We apply a two-point correlation analysis on the dense core separations and show that the ALMA cores are significantly grouped at separations below ~17 000 AU and strongly grouped below ~6000 AU. The protostellar and starless cores are grouped differently: only the starless cores group strongly below ~6000 AU. In addition, the spatial distribution of the cores indicates periodic grouping of the cores into groups of ~30 000 AU in size, separated by ~50 000 AU. The groups coincide with dust column density peaks detected by Herschel. These results show hierarchical, two-mode fragmentation in which the maternal filament periodically fragments into groups of dense cores. Critically, our results indicate that the fragmentation models for lower line-mass filaments (~16 M⊙ pc-1) fail to capture the observed properties of the ISF. We also find that the protostars identified with Spitzer and Herschel in the ISF are grouped at separations below ~17 000 AU. In contrast, young stars with disks do not show significant grouping. This suggests that the grouping of dense cores is partially retained over the protostar lifetime, but not over the lifetime of stars with disks. This is in agreement with a scenario where protostars are ejected from the maternal filament by the slingshot mechanism, a model recently proposed for the ISF. The separation distributions of the dense cores and protostars may also provide an evolutionary tracer of filament fragmentation.
Abstract
We present a catalog of 315 protostellar outflow candidates detected in SiO
J
= 5 − 4 in the ALMA-IMF Large Program, observed with ∼2000 au spatial resolution, 0.339 km s
−1
velocity ...resolution, and 2–12 mJy beam
−1
(0.18–0.8 K) sensitivity. We find median outflow masses, momenta, and kinetic energies of ∼0.3
M
⊙
, 4
M
⊙
km s
−1
, and 10
45
erg, respectively. Median outflow lifetimes are 6000 yr, yielding median mass, momentum, and energy rates of
M
̇
= 10
−4.4
M
⊙
yr
−1
,
P
̇
= 10
−3.2
M
⊙
km s
−1
yr
−1
, and
E
̇
= 1
L
⊙
. We analyze these outflow properties in the aggregate in each field. We find correlations between field-aggregated SiO outflow properties and total mass in cores (∼3
σ
–5
σ
), and no correlations above 3
σ
with clump mass, clump luminosity, or clump luminosity-to-mass ratio. We perform a linear regression analysis and find that the correlation between field-aggregated outflow mass and total clump mass—which has been previously described in the literature—may actually be mediated by the relationship between outflow mass and total mass in cores. We also find that the most massive SiO outflow in each field is typically responsible for only 15%–30% of the total outflow mass (60% upper limit). Our data agree well with the established mechanical force−bolometric luminosity relationship in the literature, and our data extend this relationship up to
L
≥ 10
6
L
⊙
and
P
̇
≥ 1
M
⊙
km s
−1
yr
−1
. Our lack of correlation with clump
L
/
M
is inconsistent with models of protocluster formation in which all protostars start forming at the same time.
Abstract
We analyze the gas mass distribution, the gas kinematics, and the young stellar objects of the California Molecular Cloud L1482 filament. The mean Gaia DR2 YSO distance is
pc. In terms of ...the gas, the line-mass (M/L) profiles are symmetric scale-free power laws consistent with cylindrical geometry. We calculate the gravitational potential and field profiles based on these. Our IRAM 30 m multi-tracer position–velocity diagrams highlight twisting and turning structures. We measure the C
18
O velocity profile perpendicular to the southern filament ridgeline. The profile is regular, confined (projected
r
≲ 0.4 pc), antisymmetric, and, to first order, linear, with a break at
r
∼ 0.25 pc. We use a simple solid-body rotation toy model to interpret it. We show that the centripetal force, compared to gravity, increases toward the break; when the ratio of forces approaches unity, the profile turns over, just before the implied filament breakup. The timescales of the inner (outer) gradients are ∼0.7 (6.0) Myr. The timescales and relative roles of gravity to rotation indicate that the structure is stable, long lived (∼a few times 6 Myr), and undergoing outside-in evolution. This filament has practically no star formation, a perpendicular Planck plane-of-the-sky magnetic field morphology, and 2D “zig-zag” morphology, which together with the rotation profile lead to the suggestion that the 3D shape is a “corkscrew” filament. These results, together with results in other regions, suggest evolution toward higher densities as rotating filaments shed angular momentum. Thus, magnetic fields may be an essential feature of high-mass (
M
∼ 10
5
M
⊙
) cloud filament evolution toward cluster formation.
ACL-reconstruction aims to restore joint stability and prevent osteoarthritis; however, malfunction and osteoarthritis are often the sequelae. Our study asks whether ACL-reconstruction or ...conservative treatment lead to better long-term results. In this retrospective cohort study, 136 patients with isolated ACL-rupture who had been treated by bone-ligament-bone transplant or conservatively were identified. Twenty-seven of these were excluded because of a revision operation in the 11.1 years follow-up period, leaving 109 patients (60 reconstructions and 49 conservatively treated) for evaluation based on clinical, radiological and internationally accepted knee-scores (Tegner, IKDC, Kellgren and Lawrence). An individual cohort study is classified as EBM level 2b according to the Oxford Centre of EBM. We observed significantly better knee-stability (
P =
0.008) but more osteoarthritis (Grade II or higher) after ACL-reconstruction (42% vs. 25%). Physical activity levels were similar in both groups during the follow-up period (
P =
0.16). Eleven years after ACL-rupture the physical activity levels are similar for both groups. After ACL-reconstruction, stability is higher as is osteoarthritis, whereby the result is not necessarily perceived as better subjectively. Specifically, this retrospective study yielded a 24% incidence of oseoarthrits 11 years after conservative management of ACL-rupture in patients not needing secondary surgery. The risk of secondary meniscal tears is reduced after ACL reconstruction, which reduces the negative effects of OA after surgery. The ultimate objective would be to achieve a good subjective outcome by conservative treatment followed by a rehabilitation program designed to keep secondary meniscus tears at a low level.
We describe and benchmark a new quantum charge-coupled device (QCCD) trapped-ion quantum computer based on a linear trap with periodic boundary conditions, which resembles a race track. The new ...system successfully incorporates several technologies crucial to future scalability—including electrode broadcasting, multilayer rf routing, and magneto-optical trap (MOT) loading—while maintaining, and in some cases exceeding, the gate fidelities of previous QCCD systems. The system is initially operated with 32 qubits, but future upgrades will allow for more. We benchmark the performance of primitive operations, including an average state preparation and measurement error of 1.6(1)×10^{-3}, an average single-qubit gate infidelity of 2.5(3)×10^{-5}, and an average two-qubit gate infidelity of 1.84(5)×10^{-3}. The system-level performance of the quantum processor is assessed with mirror benchmarking, linear cross-entropy benchmarking, a quantum volume measurement of QV=2^{16}, and the creation of 32-qubit entanglement in a GHZ state. We also tested application benchmarks, including Hamiltonian simulation, QAOA, error correction on a repetition code, and dynamics simulations using qubit reuse. We also discuss future upgrades to the new system aimed at adding more qubits and capabilities.
Abstract
Observations of the Orion A integral shaped filament (ISF) have shown indications of an oscillatory motion of the gas filament. This evidence is based on both the wave-like morphology of the ...filament and the kinematics of the gas and stars, where the characteristic velocities of the stars require a dynamical heating mechanism. As proposed by Stutz & Gould, such a heating mechanism (the ‘Slingshot’) may be the result of an oscillating gas filament in a gas-dominated (as opposed to stellar-mass dominated) system. Here we test this hypothesis with the first stellar-dynamical simulations in which the stars are subjected to the influence of an oscillating cylindrical potential. The accelerating, cylindrical background potential is populated with a narrow distribution of stars. By coupling the potential to N-body dynamics, we are able to measure the influence of the potential on the stellar distribution. The simulations provide evidence that the slingshot mechanism can successfully reproduce several stringent observational constraints. These include the stellar spread (both in projected position and in velocity) around the filament, the symmetry in these distributions, and a bulk motion of the stars with respect to the filament. Using simple considerations, we show that star–star interactions are incapable of reproducing these spreads on their own when properly accounting for the gas potential. Thus, properly accounting for the gas potential is essential for understanding the dynamical evolution of star-forming filamentary systems in the era of Gaia (Gaia Collaboration 2016).
PDF
