Abstract
pyspeckit
is a toolkit and library for spectroscopic analysis in Python. We describe the
pyspeckit
package and highlight some of its capabilities, such as interactively fitting a model to ...data, akin to the historically widely-used
splot
function in
IRAF
.
pyspeckit
employs the Levenberg–Marquardt optimization method via the
mpfit
and
lmfit
implementations, and important assumptions regarding error estimation are described here. Wrappers to use
pymc
and
emcee
as optimizers are provided. A parallelized wrapper to fit lines in spectral cubes is included. As part of the
astropy
affiliated package ecosystem,
pyspeckit
is open source and open development, and welcomes input and collaboration from the community.
We present long-baseline Atacama Large Millimeter/submillimeter Array observations of the 870 m dust continuum emission and CO (3-2) from the protoplanetary disk around the Herbig Ae/Be star HD ...100546, which is one of the few systems claimed to have two young embedded planets. These observations achieve a resolution of 4 au (3.8 mas), an rms noise of 66 Jy beam−1, and reveal an asymmetric ring between ∼20 and 40 au with largely optically thin dust continuum emission. This ring is well fit by two concentric and overlapping Gaussian rings of different widths and a Vortex. In addition, an unresolved component is detected at a position consistent with the central star, which may trace the central inner disk (<2 au in radius). We report a lack of compact continuum emission at the positions of both claimed protoplanets. We use this result to constrain the circumplanetary disk (CPD) mass and size of 1.44 M⊕ and 0.44 au in the optically thin and thick regimes, respectively, for the case of the previously directly imaged protoplanet candidate at ∼55 au (HD 100546 b). We compare these empirical CPD constraints to previous numerical simulations. This suggests that HD 100546 b is inconsistent with several planet accretion models, while gas-starved models are also still compatible. We estimate the planetary mass as 1.65 MJ using the relation between planet, circumstellar, and circumplanetary masses derived from numerical simulations. Finally, the CO-integrated intensity map shows a possible spiral arm feature that could match the spiral features identified in near-infrared scattered light polarized emission, which suggests a real spiral feature in the disk surface that needs to be confirmed with further observations.
We present 3 mm ALMA continuum and line observations at resolutions of 6.5 au and 13 au, respectively, toward the Class 0 system IRAS 16293-2422 A. The continuum observations reveal two compact ...sources toward IRAS 16293-2422 A, coinciding with compact ionized gas emission previously observed at radio wavelengths (A1 and A2), confirming the long-known radio sources as protostellar. The emission toward A2 is resolved and traces a dust disk with an FWHM size of ∼12 au, while the emission toward A1 sets a limit to the FWHM size of the dust disk of ∼4 au. We also detect spatially resolved molecular kinematic tracers near the protostellar disks. Several lines of the J = 5−4 rotational transition of HNCO, NH2CHO, and t-HCOOH are detected, with which we derived individual line-of-sight velocities. Using these together with the CS (J = 2−1), we fit Keplerian profiles toward the individual compact sources and derive masses of the central protostars. The kinematic analysis indicates that A1 and A2 are a bound binary system. Using this new context for the previous 30 yr of Very Large Array observations, we fit orbital parameters to the relative motion between A1 and A2 and find that the combined protostellar mass derived from the orbit is consistent with the masses derived from the gas kinematics. Both estimations indicate masses consistently higher (0.5 M1 M2 2 ) than previous estimations using lower-resolution observations of the gas kinematics. The ALMA high-resolution data provides a unique insight into the gas kinematics and masses of a young deeply embedded bound binary system.
The CARMA-NRO Orion Survey Kong, Shuo; Arce, Héctor G.; Feddersen, Jesse R. ...
The Astrophysical journal. Supplement series,
06/2018, Letnik:
236, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present the first results from a new, high-resolution 12CO(1-0), 13CO(1-0), and C18O(1-0) molecular-line survey of the Orion A cloud, hereafter referred to as the CARMA-NRO Orion Survey. CARMA ...observations have been combined with single-dish data from the Nobeyama 45 m telescope to provide extended images at about 0.01 pc resolution, with a dynamic range of approximately 1200 in spatial scale. Here we describe the practical details of the data combination in uv space, including flux scale matching, the conversion of single-dish data to visibilities, and joint deconvolution of single-dish and interferometric data. A Δ-variance analysis indicates that no artifacts are caused by combining data from the two instruments. Initial analysis of the data cubes, including moment maps, average spectra, channel maps, position-velocity diagrams, excitation temperature, column density, and line ratio maps, provides evidence of complex and interesting structures such as filaments, bipolar outflows, shells, bubbles, and photo-eroded pillars. The implications for star formation processes are profound, and follow-up scientific studies by the CARMA-NRO Orion team are now underway. We plan to make all the data products described here generally accessible; some are already available at https://dataverse.harvard.edu/dataverse/CARMA-NRO-Orion.
Annular structures (rings and gaps) in disks around pre-main-sequence stars have been detected in abundance towards class II protostellar objects that are approximately 1,000,000 years old
. These ...structures are often interpreted as evidence of planet formation
, with planetary-mass bodies carving rings and gaps in the disk
. This implies that planet formation may already be underway in even younger disks in the class I phase, when the protostar is still embedded in a larger-scale dense envelope of gas and dust
. Only within the past decade have detailed properties of disks in the earliest star-forming phases been observed
. Here we report 1.3-millimetre dust emission observations with a resolution of five astronomical units that show four annular substructures in the disk of the young (less than 500,000 years old)
protostar IRS 63. IRS 63 is a single class I source located in the nearby Ophiuchus molecular cloud at a distance of 144 parsecs
, and is one of the brightest class I protostars at millimetre wavelengths. IRS 63 also has a relatively large disk compared to other young disks (greater than 50 astronomical units)
. Multiple annular substructures observed towards disks at young ages can act as an early foothold for dust-grain growth, which is a prerequisite of planet formation. Whether or not planets already exist in the disk of IRS 63, it is clear that the planet-formation process begins in the initial protostellar phases, earlier than predicted by current planet-formation theories
.
We report ALMA observations with resolution 0 5 at 3 mm of the extended Sgr B2 cloud in the Central Molecular Zone (CMZ). We detect 271 compact sources, most of which are smaller than 5000 au. By ...ruling out alternative possibilities, we conclude that these sources consist of a mix of hypercompact H ii regions and young stellar objects (YSOs). Most of the newly detected sources are YSOs with gas envelopes that, based on their luminosities, must contain objects with stellar masses M * 8 M . Their spatial distribution spread over a ∼12 × 3 pc region demonstrates that Sgr B2 is experiencing an extended star formation event, not just an isolated "starburst" within the protocluster regions. Using this new sample, we examine star formation thresholds and surface density relations in Sgr B2. While all of the YSOs reside in regions of high column density ( N ( H 2 ) 2 × 10 23 cm − 2 ), not all regions of high column density contain YSOs. The observed column density threshold for star formation is substantially higher than that in solar vicinity clouds, implying either that high-mass star formation requires a higher column density or that any star formation threshold in the CMZ must be higher than in nearby clouds. The relation between the surface density of gas and stars is incompatible with extrapolations from local clouds, and instead stellar densities in Sgr B2 follow a linear * - gas relation, shallower than that observed in local clouds. Together, these points suggest that a higher volume density threshold is required to explain star formation in CMZ clouds.
The determination of the specific angular momentum radial profile, j(r), in the early stages of star formation is crucial to constrain star and circumstellar disk formation theories. The specific ...angular momentum is directly related to the largest Keplerian disk possible, and it could constrain the angular momentum removal mechanism. We determine j(r) toward two Class 0 objects and a first hydrostatic core candidate in the Perseus cloud, which is consistent across all three sources and well fit with a single power-law relation between 800 and 10,000 au: . This power-law relation is in between solid body rotation (∝r2) and pure turbulence (∝r1.5). This strongly suggests that even at 1000 au, the influence of the dense core's initial level of turbulence or the connection between core and the molecular cloud is still present. The specific angular momentum at 10,000 au is 3× higher than previously estimated, while at 1000 au, it is lower by 2×. We do not find a region of conserved specific angular momentum, although it could still be present at a smaller radius. We estimate an upper limit to the largest Keplerian disk radius of 60 au, which is small but consistent with published upper limits. Finally, these results suggest that more realistic initial conditions for numerical simulations of disk formation are needed. Some possible solutions include: (a) using a larger simulation box to include some level of driven turbulence or connection to the parental cloud or (b) incorporating the observed j(r) to set up the dense core kinematics initial conditions.
Abstract
Prestellar cores, the birthplace of Sun-like stars, form from the fragmentation of the filamentary structure that composes molecular clouds, from which they must inherit at least partially ...the kinematics. Furthermore, when they are on the verge of gravitational collapse, they show signs of subsonic infall motions. How extended these motions are, which depends on how the collapse occurs, remains largely unknown. We want to investigate the kinematics of the envelope that surrounds the prototypical prestellar core L1544, studying the cloud-core connection. To our aims, we observed the HCO
+
(1–0) transition in a large map. HCO
+
is expected to be abundant in the envelope, making it an ideal probe of the large-scale kinematics in the source. We modeled the spectrum at the dust peak by means of a nonlocal thermodynamical equilibrium radiative transfer. In order to reproduce the spectrum at the dust peak, a large (∼1 pc) envelope is needed, with low density (tens of cm
−3
at most) and contraction motions, with an inward velocity of ≈ 0.05 km s
−1
. We fitted the data cube using the Hill5 model, which implements a simple model for the optical depth and excitation temperature profiles along the line of sight, in order to obtain a map of the infall velocity. This shows that the infall motions are extended, with typical values in the range 0.1–0.2 km s
−1
. Our results suggest that the contraction motions extend in the diffuse envelope surrounding the core, which is consistent with recent magnetic field measurements in the source, which showed that the envelope is magnetically supercritical.
Recent observations of global velocity gradients across and along molecular filaments have been interpreted as signs of gas accreting onto and along these filaments, potentially feeding star-forming ...cores and protoclusters. The behavior of velocity gradients in filaments, however, has not been studied in detail, particularly on small scales (<0.1 pc). In this paper, we present MUFASA, an efficient, robust, and automatic method to fit ammonia lines with multiple velocity components, generalizable to other molecular species. We also present CRISPy, a Python package to identify filament spines in 3D images (e.g., position-position-velocity cubes), along with a complementary technique to sort fitted velocity components into velocity-coherent filaments. In NGC 1333, we find a wealth of velocity gradient structures on a beam-resolved scale of ∼0.05 pc. Interestingly, these local velocity gradients are not randomly oriented with respect to filament spines and their perpendicular, i.e., radial, component decreases in magnitude toward the spine for many filaments. Together with remarkably constant velocity gradients on larger scales along many filaments, these results suggest a scenario in which gas falling onto filaments is progressively damped and redirected to flow along these filaments.
We use data gathered by the COMPLETE survey of star-forming regions to find new calibrations of the 'X-factor' and super(13)CO abundance within the Perseus molecular cloud. We divide Perseus into six ...subregions, using groupings in a dust temperature vs. LSR velocity plot. The standard X- factor, image, is derived both for the whole Perseus complex and for each of the six subregions with values consistent with previous estimates. However, the X-factor is heavily affected by the saturation of the emission above image mag, and variations are also found between regions. Linear fits to relate image and image using only points below 4 mag of extinction yield a better estimate of the image than the X-factor. Linear relations of image, and image with image are derived. The extinction thresholds above which super(13)CO(1-0) and C super(18)O(1-0) are detected are about 1 mag larger than previous estimates, so that a more efficient shielding is needed for the formation of CO than previously thought. The super(12)CO and super(13)CO lines saturate above 4 and 5 mag, respectively, whereas C super(18)O(1-0) never saturates in the whole image range probed by our study (up to 10 mag). Approximately 60% of the positions with super(12)CO(1-0) emission have subthermally excited lines, and almost all positions have excitation temperatures below the dust temperature. PDR models, using the Meudon code, can explain the super(12)CO(1-0) and super(13)CO(1- 0) emission with densities ranging between 10 super(3) and 10 super(4) cm super(-3). In general, local variations in the volume density and nonthermal motions (linked to different star formation activity) can explain the observations. Higher densities are needed to reproduce CO data toward active star-forming sites, such as NGC 1333, where the larger internal motions driven by the young protostars allow more photons from the embedded high-density cores to escape the cloud. In the most quiescent region, B5, the super(12)CO and super(13)CO emission appears to arise from an almost uniform thin layer of molecular material at densities around 10 super(4) cm super(-3), and in this region the integrated intensities of the two CO isotopologues are the lowest in the whole complex.
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