Perseus Molecular Cloud Research Articles

A search for fast photometric variability in very low mass stars and brown dwarfs

We present here I-band time-series photometric studies of a few very low-mass stars (VLMs) and brown dwarfs (BDs) in the young (age of 2-3 Myr) IC348 star-forming region in the Perseus Molecular Cloud. Our main aim is to explore the fast rotating (of time scale of a few hours) BDs and VLMs in the I-band. From our preliminary results, we find significant variability in the young M5 dwarf 2MASS J03443896+3203196 with a rotation period of 16.037 hours.

Mapping Distances across the Perseus Molecular Cloud Using CO Observations, Stellar Photometry, and Gaia DR2 Parallax Measurements

Abstract We present a new technique to determine distances to major star-forming regions across the Perseus Molecular Cloud, using a combination of stellar photometry, astrometric data, and 12CO spectral-line maps. Incorporating the Gaia DR2 parallax measurements when available, we start by inferring the distance and reddening to stars from their Pan-STARRS1 and Two Micron All Sky Survey photometry, based on a technique presented by Green et al. and implemented in their 3D “Bayestar” dust map of three-quarters of the sky. We then refine their technique by using the velocity slices of a CO spectral cube as dust templates and modeling the cumulative distribution of dust along the line of sight toward these stars as a linear combination of the emission in the slices. Using a nested sampling algorithm, we fit these per-star distance–reddening measurements to find the distances to the CO velocity slices toward each star-forming region. This results in distance estimates explicitly tied to the velocity structure of the molecular gas. We determine distances to the B5, IC 348, B1, NGC 1333, L1448, and L1451 star-forming regions and find that individual clouds are located between ≈275 and 300 pc, with typical combined uncertainties of ≈5%. We find that the velocity gradient across Perseus corresponds to a distance gradient of about 25 pc, with the eastern portion of the cloud farther away than the western portion. We determine an average distance to the complex of 294 ± 17 pc, about 60 pc further than the distance derived to the western portion of the cloud using parallax measurements of water masers associated with young stellar objects. The method we present is not limited to the Perseus Complex, but may be applied anywhere on the sky with adequate CO data in the pursuit of more accurate 3D maps of molecular clouds in the solar neighborhood and beyond.

Deuterium Fractionation Survey Toward Protostellar Sources in the Perseus Molecular Cloud: HNC Case

Abstract A survey observation of the DNC (J = 1−0 and J = 3−2) and HN13C (J = 1−0 and J = 3−2) emission toward 34 Class 0 and I protostellar sources in the Perseus molecular cloud has been conducted with the NRO 45 m and IRAM 30 m telescopes to explore how the deuterium ratio of the neutral species changes after the birth of a protostar. We have detected the J = 1−0 and J = 3−2 lines of DNC toward 32 sources and the J = 1−0 and J = 3−2 lines of HN13C toward 31 and 26 sources, respectively. A mean deuterium ratio of HNC, which is defined as R D(HNC) = N(DNC)/N(HNC), is found to be 0.049–0.056. We compare R D(HNC) with physical parameters of the sources, and find a negative correlation between R D(HNC) and the bolometric temperature. This result suggests that R D(HNC) decreases as a protostar evolves. Compared with the deuterium ratio of the molecular ion , R D(HNC) seems to decrease slowly with the protostellar evolution.

The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems

Abstract We present Atacama Large Millimeter/submillimeter Array observations of multiple protostar systems in the Perseus molecular cloud, previously detected by the Karl G. Jansky Very Large Array. We observe 17 close (<600 au separation) multiple systems at 1.3 mm in continuum and five molecular lines (i.e., 12CO, C18O, 13CO, H2CO, SO) to characterize the circum-multiple environments in which these systems are forming. We detect at least one component in the continuum for the 17 multiple systems. In three systems one companion is not detected, and for two systems the companions are unresolved at our observed resolution. We also detect circum-multiple dust emission toward eight out of nine Class 0 multiples. Circum-multiple dust emission is not detected toward any of the eight Class I multiples. Twelve systems are detected in the dense gas tracers toward their disks/inner envelopes. For these 12 systems, we use the dense gas observations to characterize their formation mechanism. The velocity gradients in the circum-multiple gas are clearly orthogonal to the outflow directions in eight out of the 12 systems, consistent with disk fragmentation. Moreover, only two systems with separations <200 au are inconsistent with disk fragmentation, in addition to the two widest systems (>500 au). Our results suggest that disk fragmentation via gravitational instability is an important formation mechanism for close multiple systems, but further statistics are needed to better determine the relative fraction formed via this method.

The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). V. 18 Candidate Disks around Class 0 and I Protostars in the Perseus Molecular Cloud

Abstract We present the full disk-fit results VANDAM survey of all Class 0 and I protostars in the Perseus molecular cloud. We have 18 new protostellar disk candidates around Class 0 and I sources, which are well described by a simple, parametrized disk model fit to the 8 mm VLA dust continuum observations. 33% of Class 0 protostars and just 11% of Class I protostars have candidate disks, while 78% of Class 0 and I protostars do not have signs of disks within our 12 au disk diameter resolution limit, indicating that at 8 mm most disks in the Class 0 and I phases are <10 au in radius. These small radii may be a result of surface brightness sensitivity limits. Modeled 8 mm radii are similar to the radii of known Class 0 disks with detected Keplerian rotation. Since our 8 mm data trace a population of larger dust grains that radially drift toward the protostar and are lower limits on true disk sizes, large disks at early times do not seem to be particularly rare. We find statistical evidence that Class 0 and I disks are likely drawn from the same distribution, meaning disk properties may be defined early in the Class 0 phase and do not undergo large changes through the Class I phase. By combining our candidate disk properties with previous polarization observations, we find a qualitative indication that misalignment between inferred envelope-scale magnetic fields and outflows may indicate disks on smaller scales in Class 0 sources.

The Gould’s Belt Distances Survey (GOBELINS). V. Distances and Kinematics of the Perseus Molecular Cloud

Abstract We derive the distance and structure of the Perseus molecular cloud by combining trigonometric parallaxes from Very Long Baseline Array (VLBA) observations, taken as part of the GOBELINS survey and Gaia Data Release 2. Based on our VLBA astrometry, we obtain a distance of 321 ± 10 pc for IC 348. This is fully consistent with the mean distance of 320 ± 26 measured by Gaia. The VLBA observations toward NGC 1333 are insufficient to claim a successful distance measurement to this cluster. Gaia parallaxes, on the other hand, yield a mean distance of 293 ± 22 pc. Hence, the distance along the line of sight between the eastern and western edges of the cloud is ∼30 pc, which is significantly smaller than previously inferred. We use Gaia proper motions and published radial velocities to derive the spatial velocities of a selected sample of stars. The average velocity vectors with respect to the LSR are = (−6.1 ± 1.6, 6.8 ± 1.1, −0.9 ± 1.2) and (−6.4 ± 1.0, 2.1 ± 1.4, −2.4 ± 1.0) km s−1 for IC 348 and NGC 1333, respectively. Finally, our analysis of the kinematics of the stars has shown that there is no clear evidence of expansion, contraction, or rotational motions within the clusters.

Rotation in the NGC 1333 IRAS 4C Outflow

Abstract We report molecular line observations of the NGC 1333 IRAS 4C outflow in the Perseus Molecular Cloud with the Atacama Large Millimeter/Submillimeter Array. The CCH and CS emission reveal an outflow cavity structure with clear signatures of rotation with respect to the outflow axis. The rotation is detected from about 120 au up to about 1400 au above the envelope/disk midplane. As the distance to the central source increases, the rotation velocity of the outflow decreases while the outflow radius increases, which gives a flat specific angular momentum distribution along the outflow. The mean specific angular momentum of the outflow is about 100 . On the basis of reasonable assumptions on the outward velocity of the outflow and the protostar mass, we estimate the range of outflow-launching radii to be 5–15 au. Such a launching radius rules out that this outflow is launched as an X-wind, but rather, it is more consistent to be a slow disk wind launched from relatively large radii on the disk. The radius of the centrifugal barrier is roughly estimated, and the role of the centrifugal barrier in the outflow launching is discussed.

MASSES: An SMA Large Project Surveying Protostars to Reveal How Stars Gain their Mass

AbstractLow-mass stars form from the gravitational collapse of dense molecular cloud cores. While a general consensus picture of this collapse process has emerged, many details on how mass is transferred from cores to stars remain poorly understood. MASSES (Mass Assembly of Stellar Systems and their Evolution with the SMA), an SMA large project, has just finished surveying all 74 Class 0 and Class I protostars in the nearby Perseus molecular cloud to reveal the interplay between fragmentation, angular momentum, and outflows in regulating accretion and setting the final masses of stars. Scientific highlights are presented in this proceedings, covering the topics of episodic accretion, hierarchical thermal Jeans fragmentation, angular momentum transfer, envelope grain sizes, and disk evolution.

Mass Assembly of Stellar Systems and Their Evolution with the SMA (MASSES)—1.3 mm Subcompact Data Release

We present the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey, which uses the Submillimeter Array (SMA) interferometer to map the continuum and molecular lines for all 74 known Class 0/I protostellar systems in the Perseus molecular cloud. The primary goal of the survey is to observe an unbiased sample of young protostars in a single molecular cloud so that we can characterize the evolution of protostars. This paper releases the MASSES 1.3 mm data from the subcompact configuration ($\sim$4$^{\prime\prime}$ or $\sim$1000 au resolution), which is the SMA's most compact array configuration. We release both $uv$ visibility data and imaged data for the spectral lines CO(2-1),$^{13}$CO(2-1), C$^{18}$O(2-1), and N$_2$D$^+$(3-2), as well as for the 1.3 mm continuum. We identify the tracers that are detected toward each source. We also show example images of continuum and CO(2-1) outflows, analyze C$^{18}$O(2-1) spectra, and present data from the SVS 13 star-forming region. The calculated envelope masses from the continuum show a decreasing trend with bolometric temperature (a proxy for age). Typical C$^{18}$O(2-1) linewidths are 1.45 km s$^{-1}$, which is higher than the C$^{18}$O linewidths detected toward Perseus filaments and cores. We find that N$_2$D$^+$(3-2) is significantly more likely to be detected toward younger protostars. We show that the protostars in SVS 13 are contained within filamentary structures as traced by C$^{18}$O(2-1) and N$_2$D$^+$(3-2). We also present the locations of SVS 13A's high velocity (absolute line-of-sight velocities $>$150 km s$^{-1}$) red and blue outflow components. Data can be downloaded from https://dataverse.harvard.edu/dataverse/MASSES .

Chemical Survey toward Young Stellar Objects in the Perseus Molecular Cloud Complex

Chemical diversity of the gas in low-mass protostellar cores is widely recognized. In order to explore its origin, a survey of chemical composition toward 36 Class 0/I protostars in the Perseus molecular cloud complex, which are selected in an unbiased way under certain physical conditions, has been conducted with IRAM 30 m and NRO 45 m telescope. Multiple lines of C2H, c-C3H2 and CH3OH have been observed to characterize the chemical composition averaged over a 1000 au scale around the protostar. The derived beam-averaged column densities show significant chemical diversity among the sources, where the column density ratios of C2H/CH3OH are spread out by 2 orders of magnitude. From previous studies, the hot corino sources have abundant CH3OH but deficient C2H, their C2H/CH3OH column density ratios being relatively low. In contrast, the warm-carbon-chain chemistry (WCCC) sources are found to reveal the high C2H/CH3OH column density ratios. We find that the majority of the sources have intermediate characters between these two distinct chemistry types. A possible trend is seen between the C2H/CH3OH ratio and the distance of the source from the edge of a molecular cloud. The sources located near cloud edges or in isolated clouds tend to have a high C2H/CH3OH ratio. On the other hand, the sources having a low C2H/CH3OH ratio tend to be located in inner regions of the molecular cloud complex. This result gives an important clue to an understanding of the origin of the chemical diversity of protostellar cores in terms of environmental effects.

Multi-phase Turbulence Density Power Spectra in the Perseus Molecular Cloud

Abstract We derive two-dimensional spatial power spectra of four distinct interstellar medium tracers, H i, 12CO(J = 1–0), 13CO(J = 1–0), and dust, in the Perseus molecular cloud, covering linear scales ranging from ∼0.1 pc to ∼90 pc. Among the four tracers, we find the steepest slopes of −3.23 ± 0.05 and −3.22 ± 0.05 for the uncorrected and opacity-corrected H i column density images. This result suggests that the H i in and around Perseus traces a non-gravitating, transonic medium on average, with a negligible effect from opacity. On the other hand, we measure the shallowest slope of −2.72 ± 0.12 for the 2MASS dust extinction data and interpret this as the signature of a self-gravitating, supersonic medium. Possible variations in the dust-to-gas ratio likely do not alter our conclusion. Finally, we derive slopes of −3.08 ± 0.08 and −2.88 ± 0.07 for the 12CO(1–0) and 13CO(1–0) integrated intensity images. Based on theoretical predictions for an optically thick medium, we interpret these slopes of roughly −3 as implying that both CO lines are susceptible to the opacity effect. While simple tests for the impact of CO formation and depletion indicate that the measured slopes of 12CO(1–0) and 13CO(1–0) are not likely affected by these chemical effects, our results generally suggest that chemically more complex and/or fully optically thick media may not be a reliable observational tracer for characterizing turbulence.

ALMA’s Polarized View of 10 Protostars in the Perseus Molecular Cloud

Abstract We present 870 μm ALMA dust polarization observations of 10 young Class 0/I protostars in the Perseus Molecular Cloud. At ∼0.″35 (80 au) resolution, all of our sources show some degree of polarization, with most (9/10) showing significantly extended emission in the polarized continuum. Each source has incredibly intricate polarization signatures. In particular, all three disk-candidates have polarization vectors roughly along the minor axis, which is indicative of polarization produced by dust scattering. On ∼100 au scales, the polarization is at a relatively low level (≲1%) and is quite ordered. In sources with significant envelope emission, the envelope is typically polarized at a much higher (≳5%) level and has a far more disordered morphology. We compute the cumulative probability distributions for both the small (disk-scale) and large (envelope-scale) polarization percentage. We find that the two are intrinsically different, even after accounting for the different detection thresholds in the high/low surface brightness regions. We perform Kolmogorov–Smirnov and Anderson–Darling tests on the distributions of angle offsets of the polarization from the outflow axis. We find disk-candidate sources are different from the non-disk-candidate sources. We conclude that the polarization on the 100 au scale is consistent with the signature of dust scattering for disk-candidates and that the polarization on the envelope-scale in all sources may come from another mechanism, most likely magnetically aligned grains.

Morphology and Kinematics of Filaments in the Serpens and Perseus Molecular Clouds

Abstract We present H13CO+ (J = 1–0) and HNC (J = 1–0) maps of regions in Serpens South, Serpens Main, and NGC 1333 containing filaments. We also observe the Serpens regions using H13CN (J = 1–0). These dense gas tracer molecular line observations carried out with CARMA have an angular resolution of ∼7″, a spectral resolution of ∼0.16 km s−1, and a sensitivity of 50–100 mJy beam−1. Although the large-scale structure compares well with the Herschel dust continuum maps, we resolve finer structure within the filaments identified by Herschel. The H13CO+ emission distribution agrees with the existing CARMA N2H+ (J = 1–0) maps, so they trace the same morphology and kinematics of the filaments. The H13CO+ maps additionally reveal that many regions have multiple structures partially overlapping in the line of sight. In two regions, the velocity differences are as high as 1.4 km s−1. We identify eight filamentary structures having typical widths of 0.03–0.08 pc in these tracers. At least 50% of the filamentary structures have distinct velocity gradients perpendicular to their major axis, with average values in the range of 4–10 km s−1 pc−1. These findings are in support of the theoretical models of filament formation by 2D inflow in the shock layer created by colliding turbulent cells. We also find evidence of velocity gradients along the length of two filamentary structures; the gradients suggest that these filaments are inflowing toward the cloud core.

Hierarchical Fragmentation in the Perseus Molecular Cloud: From the Cloud Scale to Protostellar Objects

Abstract We present a study of hierarchical structure in the Perseus molecular cloud, from the scale of the entire cloud ( pc) to smaller clumps (∼1 pc), cores (∼0.05–0.1 pc), envelopes (∼300–3000 au), and protostellar objects (∼15 au). We use new observations from the Submillimeter Array (SMA) large project “Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES)” to probe the envelopes, and recent single-dish and interferometric observations from the literature for the remaining scales. This is the first study to analyze hierarchical structure over five scales in the same cloud complex. We compare the number of fragments with the number of Jeans masses in each scale to calculate the Jeans efficiency, or the ratio of observed to expected number of fragments. The velocity dispersion is assumed to arise either from purely thermal motions or from combined thermal and non-thermal motions inferred from observed spectral line widths. For each scale, thermal Jeans fragmentation predicts more fragments than observed, corresponding to inefficient thermal Jeans fragmentation. For the smallest scale, thermal plus non-thermal Jeans fragmentation also predicts too many protostellar objects. However, at each of the larger scales thermal plus non-thermal Jeans fragmentation predicts fewer than one fragment, corresponding to no fragmentation into envelopes, cores, and clumps. Over all scales, the results are inconsistent with complete Jeans fragmentation based on either thermal or thermal plus non-thermal motions. They are more nearly consistent with inefficient thermal Jeans fragmentation, where the thermal Jeans efficiency increases from the largest to the smallest scale.

The VLA Nascent Disk And Multiplicity Survey of Perseus Protostars (VANDAM). III. Extended Radio Emission from Protostars in Perseus

Abstract Centimeter continuum emission from protostars offers insight into the innermost part of the outflows, as shock-ionized gas produces free–free emission. We observed a complete population of Class 0 and I protostars in the Perseus molecular cloud at 4.1 and 6.4 cm with resolution and sensitivity superior to previous surveys. From a total of 71 detections, eight sources exhibit resolved emission at 4.1 cm and/or 6.4 cm. In this paper, we focus on this subsample, analyzing their spectral indices along the jet and their alignment with respect to the large-scale molecular outflow. Spectral indices for fluxes integrated toward the position of the protostar are consistent with free–free thermal emission. The value of the spectral index along a radio jet decreases with distance from the protostar. For six sources, emission is well aligned with the outflow central axis, showing that we observe the ionized base of the jet. This is not the case for two sources, where we note misalignment of the emission with respect to the large-scale outflow. This might indicate that the emission does not originate in the radio jet, but rather in an ionized outflow cavity wall or disk surface. For five of the sources, the spectral indices along the jet decrease well below the thermal free–free limit of −0.1 with significance. This is indicative of synchrotron emission, meaning that high-energy electrons are being produced in the outflows close to the disk. This result can have far-reaching implications for the chemical composition of the embedded disks.

Alignment between Protostellar Outflows and Filamentary Structure

Abstract We present new Submillimeter Array (SMA) observations of CO(2–1) outflows toward young, embedded protostars in the Perseus molecular cloud as part of the Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES) survey. For 57 Perseus protostars, we characterize the orientation of the outflow angles and compare them with the orientation of the local filaments as derived from Herschel observations. We find that the relative angles between outflows and filaments are inconsistent with purely parallel or purely perpendicular distributions. Instead, the observed distribution of outflow-filament angles are more consistent with either randomly aligned angles or a mix of projected parallel and perpendicular angles. A mix of parallel and perpendicular angles requires perpendicular alignment to be more common by a factor of ∼3. Our results show that the observed distributions probably hold regardless of the protostar’s multiplicity, age, or the host core’s opacity. These observations indicate that the angular momentum axis of a protostar may be independent of the large-scale structure. We discuss the significance of independent protostellar rotation axes in the general picture of filament-based star formation.

IN-SYNC VI. Identification and Radial Velocity Extraction for 100+ Double-Lined Spectroscopic Binaries in the APOGEE/IN-SYNC Fields

We present radial velocity measurements for 70 high confidence, and 34 potential binary systems in fields containing the Perseus Molecular Cloud, Pleiades, NGC 2264, and the Orion A star-forming region. Eighteen of these systems have been previously identified as binaries in the literature. Candidate double-lined spectroscopic binaries (SB2s) are identified by analyzing the cross-correlation functions (CCFs) computed during the reduction of each APOGEE spectrum. We identify sources whose CCFs are well fit as the sum of two Lorentzians as likely binaries, and provide an initial characterization of the system based on the radial velocities indicated by that dual fit. For systems observed over several epochs, we present mass ratios and systemic velocities; for two systems with observations on eight or more epochs, and which meet our criteria for robust orbital coverage, we derive initial orbital parameters. The distribution of mass ratios for multi-epoch sources in our sample peaks at q = 1, but with a significant tail toward lower q values. Tables reporting radial velocities, systemic velocities, and mass ratios are provided online. We discuss future improvements to the radial velocity extraction method we employ, as well as limitations imposed by the number of epochs currently available in the APOGEE database. The Appendix contains brief notes from the literature on each system in the sample, and more extensive notes for select sources of interest.

The H i-to-H2 Transition in a Turbulent Medium

Abstract We study the effect of density fluctuations induced by turbulence on the H i/H2 structure in photodissociation regions (PDRs) both analytically and numerically. We perform magnetohydrodynamic numerical simulations for both subsonic and supersonic turbulent gas and chemical H i/H2 balance calculations. We derive atomic-to-molecular density profiles and the H i column density probability density function (PDF) assuming chemical equilibrium. We find that, while the H i/H2 density profiles are strongly perturbed in turbulent gas, the mean H i column density is well approximated by the uniform-density analytic formula of Sternberg et al. The PDF width depends on (a) the radiation intensity–to–mean density ratio, (b) the sonic Mach number, and (c) the turbulence decorrelation scale, or driving scale. We derive an analytic model for the H i PDF and demonstrate how our model, combined with 21 cm observations, can be used to constrain the Mach number and driving scale of turbulent gas. As an example, we apply our model to observations of H i in the Perseus molecular cloud. We show that a narrow observed H i PDF may imply small-scale decorrelation, pointing to the potential importance of subcloud-scale turbulence driving.

Embedded binaries and their dense cores

We explore the relationship between young, embedded binaries and their parent cores, using observations within the Perseus Molecular Cloud. We combine recently published VLA observations of young stars with core properties obtained from SCUBA-2 observations at 850 um. Most embedded binary systems are found toward the centres of their parent cores, although several systems have components closer to the core edge. Wide binaries, defined as those systems with physical separations greater than 500 au, show a tendency to be aligned with the long axes of their parent cores, whereas tight binaries show no preferred orientation. We test a number of simple, evolutionary models to account for the observed populations of Class 0 and I sources, both single and binary. In the model that best explains the observations, all stars form initially as wide binaries. These binaries either break up into separate stars or else shrink into tighter orbits. Under the assumption that both stars remain embedded following binary breakup, we find a total star formation rate of 168 Myr^-1. Alternatively, one star may be ejected from the dense core due to binary breakup. This latter assumption results in a star formation rate of 247 Myr^-1. Both production rates are in satisfactory agreement with current estimates from other studies of Perseus. Future observations should be able to distinguish between these two possibilities. If our model continues to provide a good fit to other star-forming regions, then the mass fraction of dense cores that becomes stars is double what is currently believed.

AN EXPLORATION OF THE STATISTICAL SIGNATURES OF STELLAR FEEDBACK

ABSTRACT All molecular clouds are observed to be turbulent, but the origin, means of sustenance, and evolution of the turbulence remain debated. One possibility is that stellar feedback injects enough energy into the cloud to drive observed motions on parsec scales. Recent numerical studies of molecular clouds have found that feedback from stars, such as protostellar outflows and winds, injects energy and impacts turbulence. We expand upon these studies by analyzing magnetohydrodynamic simulations of molecular clouds, including stellar winds, with a range of stellar mass-loss rates and magnetic field strengths. We generate synthetic 12CO(1–0) maps assuming that the simulations are at the distance of the nearby Perseus molecular cloud. By comparing the outputs from different initial conditions and evolutionary times, we identify differences in the synthetic observations and characterize these using common astrostatistics. We quantify the different statistical responses using a variety of metrics proposed in the literature. We find that multiple astrostatistics, including the principal component analysis, the spectral correlation function, and the velocity coordinate spectrum (VCS), are sensitive to changes in stellar mass-loss rates and/or time evolution. A few statistics, including the Cramer statistic and VCS, are sensitive to the magnetic field strength. These findings demonstrate that stellar feedback influences molecular cloud turbulence and can be identified and quantified observationally using such statistics.