Perseus Cloud Research Articles

Cloud structure and young star distribution in the Dragonfish complex

Star formation is a complex process involving several physical mechanisms that interact with each other at different spatial scales. One way to shed some light on this process is to analyse the relation between the spatial distributions of gas and newly formed stars. In order to obtain robust results, it is necessary for this comparison to be made using quantitative and consistent descriptors that are applied to the same star-forming region. We used fractal analysis to characterise and compare in a self-consistent way the structure of the cloud and the distribution of young stellar objects (YSO) in the Dragonfish star-forming complex. Different emission maps of the Dragonfish nebula were retrieved from the NASA/IPAC Infrared Science and the Planck Legacy archives. Moreover, we used photometric information from the AllWISE catalogue to select a total of 1082 YSOs in the region. We derived the physical properties for some of these from their spectral energy distributions (SEDs). For the cloud images and YSOs, the three-dimensional fractal dimension ($D_f$) was calculated using previously developed and calibrated algorithms. The fractal dimension of the Dragonfish nebula ($D_f = 2.6-2.7$) agrees very well with values previously obtained for the Orion, Ophiuchus, and Perseus clouds. On the other hand, YSOs exhibit a significantly lower value on average ($D_f = 1.9-2.0$), which indicates that their structure is far more clumpy than the material from which they formed. Younger Class I and Class II sources have lower values ($D_f = 1.7 0.1$) than more evolved transition disk objects ($D_f = 2.2 0.1$), which shows a certain evolutionary effect according to which an initially clumpy structure tends to gradually disappear over time. The structure of the Dragonfish complex is similar to that of other molecular clouds in the Galaxy. However, we found clear and direct evidence that the clustering degree of the newly born stars is significantly higher than that of the parent cloud from which they formed. The physical mechanism behind this behaviour is still not clear.

Tracing dense gas in six resolved GMCs of the Andromeda Galaxy

ABSTRACT We present dense-gas-tracing molecular observations of six resolved Giant Molecular Clouds (GMCs) in the Andromeda Galaxy (M31). Using the NOEMA interferometer, we observed the transitions of HCN(1–0), HCO+(1–0), and HNC(1–0), as well as 13CO(1–0) and 100 GHz continuum emission. This complements our earlier work with the Submillimetre Array, including resolved dust continuum detections of these clouds at 230 GHz. In this work, we first compare different continuum measurements to conclude that the average free–free contamination of the observed flux is 71 per cent at 3 mm but only 13 per cent at 1 mm, confirming that emission at 3 mm is less reliable than that at 1 mm for calculating dust masses of star-forming clouds. While the 13CO emission is more extended than both HCN and HCO+ emission, which in turn is more extended than HNC emission, we find that both HCN and HCO+ are spatially coincident with, and similarly extended as, the 230 GHz dust emission. This suggests that both the 230 GHz dust continuum and most importantly the HCN emission traces the dense gas component of these GMCs. From comparison of the molecular emission with dust masses derived from the 230 GHz continuum emission, we obtain the first direct measurements of the dust-mass-to-light ratios ($\alpha ^\prime _{\rm HCN}$ and $\alpha ^\prime _{\rm HCO^+}$) in GMCs of an external galaxy. For HCN, the result is broadly similar to a measurement in the local Perseus cloud suggesting that these are indeed dense gas conversion factors. A larger cloud sample will be required to assess whether HCN is tracing comparable cloud-scale density regimes across the environments of M31.

Properties of dust in the North - East part of Perseus Cloud within the open cluster IC 348 using data from IRIS and AKARI

In this work, we have studied the dust properties of the North-East part of Perseus cloud having a size of 0.5o × 0.5o located at RA (ICRS): 56.14o DEC (ICRS): +32.15o, within the Open Cluster IC 348, using IRIS and AKARI data. An isolated region of size 0.39o×0.23o in IRIS and 0.34o×0.16o in AKARI data is detected within it. The infrared fluxes extracted using Aladin v11.0 are used to study the dust temperature and dust mass. The distance of the selected dust structure is calculated using Gaia EDR3, which is 309.98 pc. The infrared flux density is found to be increased for long-wavelength data. The average dust color temperature calculated from short-wavelength IRIS data is more than that calculated from long-wavelength AKARI data, which are 26.34 K±0.11 K for IRIS and 17.63 K±0.02 K for AKARI data. The mass of dust within the entire dust structure is 0.06 Mʘ for IRIS data and 37.44 Mʘ for AKARI data. Jeans mass for isolated region gives contradictory results in two surveys, for IRIS survey total mass is smaller than Jeans mass but for AKARI survey the total mass is larger than the Jeans mass. A good correlation between infrared fluxes is noticed for linear regression. The study background sources observed from the SIMBAD database explore the large number of stars, X-ray sources, YSOs, etc., embedded within the dust structure; some of them are responsible for dust heating and some for the contribution of dust mass. The contour map shows the identical distribution between infrared fluxes, dust color temperature and Planck’s function and dissimilar distribution between dust mass and visual extinction in IRIS and AKARI data. The high temperature at the central region suggests that the core of dust structure is thermally active, radiating the large thermal radiation in comparison to the outer region.

3D magnetic-field morphology of the Perseus molecular cloud

Context.Despite recent observational and theoretical advances in mapping the magnetic fields associated with molecular clouds, their three-dimensional (3D) morphology remains unresolved. Multi-wavelength and multi-scale observations will allow us to paint a comprehensive picture of the magnetic fields of these star-forming regions.Aims.We reconstructed the 3D magnetic field morphology associated with the Perseus molecular cloud and compared it with predictions of cloud-formation models. These cloud-formation models predict a bending of magnetic fields associated with filamentary molecular clouds. We compared the orientation and direction of this field bending with our 3D magnetic-field view of the Perseus cloud.Methods.We used previous line-of-sight and plane-of-sky magnetic field observations as well as Galactic magnetic field models to reconstruct the complete 3D magnetic field vectors and morphology associated with the Perseus cloud.Results.We approximated the 3D magnetic field morphology of the cloud as a concave arc that points in the decreasing longitude direction in the plane of the sky (from our point of view). This field morphology preserves a memory of the Galactic magnetic field. In order to compare this morphology to cloud-formation model predictions, we assume that the cloud retains a memory of its most recent interaction. After incorporating velocity observations, we find that the line-of-sight magnetic field observations are consistent with predictions of shock-cloud-interaction models.Conclusions.To our knowledge, this is the first time that the 3D magnetic fields of a molecular cloud have been reconstructed. We find the 3D magnetic field morphology of the Perseus cloud to be consistent with the predictions of the shock-cloud-interaction model that describes the formation mechanism of filamentary molecular clouds.

ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): A Hot Corino Survey toward Protostellar Cores in the Orion Cloud

The presence of complex organic molecules (COMs) in the interstellar medium is of great interest since it may link to the origin and prevalence of life in the universe. Aiming to investigate the occurrence of COMs and their possible origins, we conducted a chemical census toward a sample of protostellar cores as part of the Atacama Large Millimeter/submillimeter Array Survey of Orion Planck Galactic Cold Clumps project. We report the detection of 11 hot corino sources, which exhibit compact emissions from warm and abundant COMs, among 56 Class 0/I protostellar cores. All of the hot corino sources discovered are likely Class 0, and their sizes of the warm region (>100 K) are comparable to 100 au. The luminosity of the hot corino sources exhibits positive correlations with the total number of methanol and the extent of its emissions. Such correlations are consistent with the thermal desorption picture for the presence of hot corinos and suggest that the lower-luminosity (Class 0) sources likely have a smaller region with COM emissions. With the same sample selection method and detection criteria being applied, the detection rates of the warm methanol in the Orion cloud (15/37) and the Perseus cloud (28/50) are statistically similar when the cloud distances and the limited sample size are considered. Observing the same set of COM transitions will bring a more informative comparison between the cloud properties.

The Per-Tau Shell: A Giant Star-forming Spherical Shell Revealed by 3D Dust Observations

Abstract A major question in the field of star formation is how molecular clouds form out of the diffuse interstellar medium (ISM). Recent advances in 3D dust mapping are revolutionizing our view of the structure of the ISM. Using the highest-resolution 3D dust map to date, we explore the structure of a nearby star-forming region, which includes the well-known Perseus and Taurus molecular clouds. We reveal an extended near-spherical shell, 156 pc in diameter (hereafter called the “Per-Tau Shell”), in which the Perseus and Taurus clouds are embedded. We also find a large ring structure at the location of Taurus (hereafter called the “Tau Ring”). We discuss a formation scenario for the Per-Tau Shell, in which previous stellar and supernova feedback events formed a large expanding shell, where the swept-up ISM has condensed to form both the shell and the Perseus and Taurus molecular clouds within it. We present auxiliary observations of H i, Hα, 26Al, and X-rays that further support this scenario, and estimate the Per-Tau Shell’s age to be ≈6–22 Myrs. The Per-Tau shell offers the first 3D observational view of a phenomenon long-hypothesized theoretically, molecular cloud formation and star formation triggered by previous stellar and supernova feedback.

Dark cloud-type chemistry in photodissociation regions with moderate ultraviolet field

ABSTRACT We present a study of emission lines of small hydrocarbons C2H and c-C3H2, and COMs precursors H2CO and CH3OH in order to better understand the possible chemical link between the molecular abundances and UV radiation field in photodissociation regions (PDRs). We study two PDRs around extended and compact H ii regions with G ≤ 50 Habings in the S235 star-forming complex. We find the highest abundances of both hydrocarbons on the edges of molecular clumps, while c-C3H2 is also abundant in the low-density expanding PDR around compact H ii region S235 A. We see the highest methanol column density towards the positions with the UV field G ≈ 20−30 Habings and explain them by reactive desorption from the dust grains. The $N_{\rm C_2H}/N_{\rm CH_3OH}$ ratio is lower by a factor of few or the order of magnitude in comparison with the Horsehead and Orion Bar PDRs. The ratio is similar to the value observed in hot corinos in the Perseus cloud. We conclude that ion-molecular and grain surface chemical routes rule the molecular abundances in the PDRs, and the PDRs inherit molecular abundances from the previous dark stage of molecular cloud evolution in spite of massive stars already emitting in optics.

Characterizing the line emission from molecular clouds

Context. The traditional approach to characterize the structure of molecular clouds is to map their line emission. Aims. We aim to test and apply a stratified random sampling technique that can characterize the line emission from molecular clouds more efficiently than mapping. Methods. We sampled the molecular emission from the Perseus cloud using the H2 column density as a proxy. We divided the cloud into ten logarithmically spaced column density bins, and we randomly selected ten positions from each bin. The resulting 100 cloud positions were observed with the IRAM 30 m telescope, covering the 3 mm-wavelength band and parts of the 2 and 1 mm bands. Results. We focus our analysis on the 11 molecular species (plus isotopologs) detected toward most column density bins. In all cases, the line intensity is tightly correlated with the H2 column density. For the CO isotopologs, the trend is relatively flat, while for high-dipole moment species such as HCN, CS, HCO+, and HNC, the trend is approximately linear. To reproduce this behavior, we developed a cloud model in which the gas density increases with column density, and where most species have abundance profiles characterized by an outer photodissociation edge and an inner freeze-out drop. With this model, we determine that the intensity behavior of the high-dipole moment species arises from a combination of excitation effects and molecular freeze out, with some modulation from optical depth. This quasi-linear dependence with the H2 column density makes the gas at low column densities dominate the cloud-integrated emission. It also makes the emission from most high-dipole moment species proportional to the cloud mass inside the photodissociation edge. Conclusions. Stratified random sampling is an efficient technique for characterizing the emission from whole molecular clouds. When applied to Perseus, it shows that despite the complex appearance of the cloud, the molecular emission follows a relatively simple pattern. A comparison with available studies of whole clouds suggests that this emission pattern may be common.

Physical properties of the ambient medium and of dense cores in the Perseus star-forming region derived from Herschel Gould Belt Survey observations

The complex of star-forming regions in Perseus is one of the most studied due to its proximity (about 300 pc). In addition, its regions show variation in star-formation activity and age, with formation of low-mass and intermediate-mass stars. In this paper, we present analyses of images taken with the Herschel ESA satellite from 70 μm to 500 μm. From these images, we first constructed column density and dust temperature maps. We then identified compact cores in the maps at each wavelength, and characterised the cores using modified blackbody fits to their spectral energy distributions (SEDs): we identified 684 starless cores, of which 199 are bound and potential prestellar cores, and 132 protostars. We also matched the Herschel-identified young stars with Gaia sources to model distance variations across the Perseus cloud. We measure a linear gradient function with right ascension and declination for the entire cloud. This function is the first quantitative attempt to derive the gradient in distance across Perseus, from east to west, in an analytical form. We derived mass and temperature of cores from the SED fits. The core mass function can be modelled with a log-normal distribution that peaks at 0.82 M⊙ suggesting a star formation efficiency of 0.30 for a peak in the system initial mass function of stars at 0.25 M⊙. The high-mass tail can be modelled with a power law of slope ~−2.32, which is close to the Salpeter’s value. We also identify the filamentary structure of Perseus and discuss the relation between filaments and star formation, confirming that stars form preferentially in filaments. We find that the majority of filaments with ongoing star formation are transcritical against their own internal gravity because their linear masses are below the critical limit of 16 M⊙ pc−1 above which we expect filaments to collapse. We find a possible explanation for this result, showing that a filament with a linear mass as low as 8 M⊙ pc−1 can already be unstable. We confirm a linear relationship between star formation efficiency and the slope of dust probability density function, and we find a similar relationship with the core formation efficiency. We derive a lifetime for the prestellar core phase of 1.69 ± 0.52 Myr for the whole Perseus complex but different regions have a wide range in prestellar core fractions, suggesting that star formation began only recently in some clumps. We also derive a free-fall time for prestellar cores of 0.16 Myr.

Seeds of Life in Space (SOLIS)

Context. Low-mass protostars drive powerful molecular outflows that can be observed with millimetre and submillimetre telescopes. Various sulfuretted species are known to be bright in shocks and could be used to infer the physical and chemical conditions throughout the observed outflows. Aims. The evolution of sulfur chemistry is studied along the outflows driven by the NGC 1333-IRAS4A protobinary system located in the Perseus cloud to constrain the physical and chemical processes at work in shocks. Methods. We observed various transitions from OCS, CS, SO, and SO2 towards NGC 1333-IRAS4A in the 1.3, 2, and 3 mm bands using the IRAM NOrthern Extended Millimeter Array and we interpreted the observations through the use of the Paris-Durham shock model. Results. The targeted species clearly show different spatial emission along the two outflows driven by IRAS4A. OCS is brighter on small and large scales along the south outflow driven by IRAS4A1, whereas SO2 is detected rather along the outflow driven by IRAS4A2 that is extended along the north east–south west direction. SO is detected at extremely high radial velocity up to + 25 km s−1 relative to the source velocity, clearly allowing us to distinguish the two outflows on small scales. Column density ratio maps estimated from a rotational diagram analysis allowed us to confirm a clear gradient of the OCS/SO2 column density ratio between the IRAS4A1 and IRAS4A2 outflows. Analysis assuming non Local Thermodynamic Equilibrium of four SO2 transitions towards several SiO emission peaks suggests that the observed gas should be associated with densities higher than 105 cm−3 and relatively warm (T > 100 K) temperatures in most cases. Conclusions. The observed chemical differentiation between the two outflows of the IRAS4A system could be explained by a different chemical history. The outflow driven by IRAS4A1 is likely younger and more enriched in species initially formed in interstellar ices, such as OCS, and recently sputtered into the shock gas. In contrast, the longer and likely older outflow triggered by IRAS4A2 is more enriched in species that have a gas phase origin, such as SO2.

The Specific Angular Momentum Radial Profile in Dense Cores: Improved Initial Conditions for Disk Formation

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 $j(r)$ towards 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: $j_{fit}(r)=10^{-3.60\pm0.15}\left(r/\textrm{1,000au}\right)^{1.80\pm0.04}$ km s$^{-1}$ pc. This power-law relation is in between solid body rotation ($\propto r^2$) and pure turbulence ($\propto r^{1.5}$). This strongly suggests that even at 1,000\,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 $\approx3\times$ higher than previously estimated, while at 1,000\,au it is lower by $2\times$. 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) use a larger simulation box to include some level of driven turbulence or connection to the parental cloud, or b) incorporate the observed $j(r)$ to setup the dense core kinematics initial conditions.

The parsec–scale relationship between ICO and AV in local molecular clouds

We measure the parsec-scale relationship between integrated CO intensity (I_CO) and visual extinction (A_V) in 24 local molecular clouds using maps of CO emission and dust optical depth from Planck. This relationship informs our understanding of CO emission across environments, but clean Milky Way measurements remain scarce. We find uniform I_CO for a given A_V, with the results bracketed by previous studies of the Pipe and Perseus clouds. Our measured I_CO-A_V relation broadly agrees with the standard Galactic CO-to-H2 conversion factor, the relation found for the Magellanic clouds at coarser resolution, and numerical simulations by Glover & Clark (2016). This supports the idea that CO emission primarily depends on shielding, which protects molecules from dissociating radiation. Evidence for CO saturation at high A_V and a threshold for CO emission at low A_V varies remains uncertain due to insufficient resolution and ambiguities in background subtraction. Resolution of order 0.1 pc may be required to measure these features. We use this I_CO-AV relation to predict how the CO-to-H2 conversion factor (X_CO) would change if the Solar Neighborhood clouds had different dust-to-gas ratio (metallicity). The calculations highlight the need for improved observations of the CO emission threshold and HI shielding layer depth. They are also sensitive to the shape of the column density distribution. Because local clouds collectively show a self-similar distribution, we predict a shallow metallicity dependence for X_CO down to a few tenths of solar metallicity. However, our calculations also imply dramatic variations in cloud-to-cloud X_CO at subsolar metallicity.

HP2 survey

We present new high resolution and dynamic range dust column density and temperature maps of the California Molecular Cloud derived from a combination of Planck and Herschel dust-emission maps, and 2MASS NIR dust-extinction maps. We used these data to determine the ratio of the 2.2 micron extinction coefficient to the 850 micron opacity and found the value to be close to that found in similar studies of the Orion B and Perseus clouds but higher than that characterizing the Orion A cloud, indicating that variations in the fundamental optical properties of dust may exist between local clouds. We show that over a wide range of extinction, the column density probability distribution function (PDF$_N$) of the cloud can be well described by a simple power law with an index that represents a steeper decline with column density than found in similar studies of the Orion and Perseus clouds. Using only the protostellar population of the cloud and our extinction maps we investigate the Schmidt relation within the cloud. We show that the protostellar surface density, $\Sigma_*$, is directly proportional to the ratio of the protostellar and cloud pdfs. We use the cumulative distribution of protostars to infer the functional forms for both $\Sigma_*$ and PDF$_*$. We find that $\Sigma_*$ is best described by two power-law functions with steeper indicies than found in other local GMCs. We find that the protostellar pdf is a declining function of extinction also best described by two power-laws whose behavior mirrors that of $\Sigma_*$. Our observations suggest that variations both in the slope of the Schmidt relation and in the sizes of the protostellar populations between GMCs are largely driven by variations in the slope of the cloud pdf. This confirms earlier studies suggesting that cloud structure plays a major role in setting the global star formation rates in GMCs.

Deuterated methanol on a solar system scale around the HH212 protostar

Context: Methanol is thought to be mainly formed during the prestellar phase and its deuterated form keeps memory of the conditions at that epoch. Thanks to the unique combination of high angular resolution and sensitivity provided by ALMA, we wish to measure methanol deuteration in the planet formation region around a Class 0 protostar and to understand its origin. Aims: We mapped both the $^{13}$CH$_3$OH and CH$_2$DOH distribution in the inner regions ($\sim$100 au) of the HH212 system in Orion B. To this end, we used ALMA Cycle 1 and Cycle 4 observations in Band 7 with angular resolution down to $\sim$0.15$"$. Results: We detected 6 lines of $^{13}$CH$_3$OH and 13 lines of CH$_2$DOH with upper level energies up to 438 K in temperature units. We derived a rotational temperature of (171 $\pm$ 52) K and column densities of 7$\times$10$^{16}$ cm$^{-2}$ ($^{13}$CH$_3$OH) and 1$\times$10$^{17}$ cm$^{-2}$ (CH$_2$DOH), respectively. Consequently, the D/H ratio is (2.4 $\pm$ 0.4)$\times$10$^{-2}$, a value lower by an order of magnitude with respect to what was previously measured using single dish telescopes toward protostars located in Perseus. Our findings are consistent with the higher dust temperatures in Orion B with respect to that derived for the Perseus cloud. The emission is tracing a rotating structure extending up to 45 au from the jet axis and elongated by 90 au along the jet axis. So far, the origin of the observed emission appears to be related with the accretion disk. Only higher spatial resolution measurements however, will be able to disentangle between different possible scenarios: disk wind, disk atmosphere, or accretion shocks.

H i, CO, and Dust in the Perseus Cloud

Abstract Comparison analyses between the gas emission data ( line and line) and the Planck/IRAS dust emission data (optical depth at and dust temperature ) allow us to estimate the amount and distribution of the hydrogen gas more accurately, and our previous studies revealed the existence of a large amount of optically thick gas in the solar neighborhood. Referring to this, we discuss the neutral hydrogen gas around the Perseus cloud in the present paper. By using the J-band extinction data, we found that increases as a function of the 1.3th power of column number density of the total hydrogen ( ), and this implies dust evolution in high density regions. This calibrated relationship shows that the amount of the gas can be underestimated to be if the optically thin method is used. Based on this relationship, we calculated the optical depth of the line ( ) and found that around the molecular cloud. The effect of is still significant, even if we take into account the dust evolution. We also estimated a spatial distribution of the -to- conversion factor ( ), and we found its average value is . Although these results are inconsistent with some previous studies, these discrepancies can be well explained by the difference of the data and analyses methods.

ANISOTROPIC FORMATION OF MAGNETIZED CORES IN TURBULENT CLOUDS

In giant molecular clouds (GMCs), shocks driven by converging turbulent flows create high-density, strongly-magnetized regions that are locally sheetlike. In previous work, we showed that within these layers, dense filaments and embedded self-gravitating cores form by gathering material along the magnetic field lines. Here, we extend the parameter space of our three-dimensional, turbulent MHD core formation simulations. We confirm the anisotropic core formation model we previously proposed, and quantify the dependence of median core properties on the pre-shock inflow velocity and upstream magnetic field strength. Our results suggest that bound core properties are set by the total dynamic pressure (dominated by large-scale turbulence) and thermal sound speed c_s in GMCs, independent of magnetic field strength. For models with Mach number between 5 and 20, the median core masses and radii are comparable to the critical Bonnor-Ebert mass and radius defined using the dynamic pressure for P_ext. Our results correspond to M_core = 1.2 c_s^4/sqrt(G^3 rho_0 v_0^2) and R_core = 0.34 c_s^2/sqrt(G rho_0 v_0^2) for rho_0 and v_0 the large-scale mean density and velocity. For our parameter range, the median M_core ~ 0.1-1 M_sun, but a very high pressure cloud could have lower characteristic core mass. We find cores and filaments form simultaneously, and filament column densities are a factor ~2 greater than the surrounding cloud when cores first collapse. We also show that cores identified in our simulations have physical properties comparable to those observed in the Perseus cloud. Superthermal cores in our models are generally also magnetically supercritical, suggesting that the same may be true in observed clouds.

Evolutionary stages and disk properties of young stellar objects in the Perseus cloud

We investigated the evolutionary stages and disk properties of 211 young stellar objects (YSOs) across the Perseus cloud by modeling their broadband optical to mid-infrared (IR) spectral energy distribution (SED). Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC). About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage III phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M⊙ respectively. By exploring the relationships among the turnoff wave bands λturnoff (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index αexcess as determined for λ > λturnoff, and the disk inner radius Rin (determined from SED modeling) for YSOs at different evolutionary stages, we found that the median and standard deviation of αexcess for YSOs with optically thick disks tend to increase with λturnoff, especially at λturnoff ≥5.8 μm, whereas the median fractional dust luminosities Ldust/L★ tend to decrease with increasing λturnoff. This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between αexcess and Rin was found at αexcess ≳ 0 and Rin ≳ 10 × the dust sublimation radius Rsub, irrespective of λturnoff, Ldust/L★ and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at λ ≲ 24 μm. About 23% of our YSO disks are classified as transitional disks, which have λturnoff ≥ 5.8 μm and Ldust/L★ > 10−3. The transitional disks and full disks occupy distinctly different regions on the Ldust/L★ vs. αexcess diagram. Taking Ldust/L★ as an approximate discriminator of disks with (>0.1) and without (<0.1) considerable accretion activity, we found that 65% and 35% of the transitional disks may be consistent with being dominantly cleared by photoevaporation and dynamical interaction with giant planets respectively. None of our transitional disks have αexcess (<0.0) or Ldust/L★ (>0.1) values that would otherwise be suggestive of disk clearing dominanted by grain growth.

THE KINEMATIC AND CHEMICAL PROPERTIES OF A POTENTIAL CORE-FORMING CLUMP: PERSEUS B1-E

We present 13CO and C18O (1-0), (2-1), and (3-2) maps towards the core-forming Perseus B1-E clump using observations from the James Clerk Maxwell Telescope (JCMT), Submillimeter Telescope (SMT) of the Arizona Radio Observatory, and IRAM 30 m telescope. We find that the 13CO and C18O line emission both have very complex velocity structures, indicative of multiple velocity components within the ambient gas. The (1-0) transitions reveal a radial velocity gradient across B1-E of 1 km/s/pc that increases from north-west to south-east, whereas the majority of the Perseus cloud has a radial velocity gradient increasing from south-west to north-east. In contrast, we see no evidence of a velocity gradient associated with the denser Herschel-identified substructures in B1-E. Additionally, the denser substructures have much lower systemic motions than the ambient clump material, which indicates that they are likely decoupled from the large-scale gas. Nevertheless, these substructures themselves have broad line widths (0.4 km/s) similar to that of the C18O gas in the clump, which suggests they inherited their kinematic properties from the larger-scale, moderately dense gas. Finally, we find evidence of C18O depletion only toward one substructure, B1-E2, which is also the only object with narrow (transonic) line widths. We suggest that as prestellar cores form, their chemical and kinematic properties are linked in evolution, such that these objects must first dissipate their turbulence before they deplete in CO.

CHARACTERIZING THE YOUNGESTHERSCHEL-DETECTED PROTOSTARS. I. ENVELOPE STRUCTURE REVEALED BY CARMA DUST CONTINUUM OBSERVATIONS

We present CARMA 2.9 mm dust continuum emission observations of a sample of 14 Herschel-detected Class 0 protostars in the Orion A and B molecular clouds, drawn from the PACS Bright Red Sources (PBRS) sample (Stutz et al.). These objects are characterized by very red 24 \micron\ to 70 \micron\ colors and prominent submillimeter emission, suggesting that they are very young Class 0 protostars embedded in dense envelopes. We detect all of the PBRS in 2.9 mm continuum emission and emission from 4 protostars and 1 starless core in the fields toward the PBRS; we also report 1 new PBRS source. The ratio of 2.9 mm luminosity to bolometric luminosity is higher by a factor of $\sim$5 on average, compared to other well-studied protostars in the Perseus and Ophiuchus clouds. The 2.9 mm visibility amplitudes for 6 of the 14 PBRS are very flat as a function of uv-distance, with more than 50\% of the source emission arising from radii $<$ 1500 AU. These flat visibility amplitudes are most consistent with spherically symmetric envelope density profiles with $\rho$~$\propto$~R$^{-2.5}$. Alternatively, there could be a massive unresolved structure like a disk or a high-density inner envelope departing from a smooth power-law. The large amount of mass on scales $<$ 1500 AU (implying high average central densities) leads us to suggest that that the PBRS with flat visibility amplitude profiles are the youngest PBRS and may be undergoing a brief phase of high mass infall/accretion and are possibly among the youngest Class 0 protostars. The PBRS with more rapidly declining visibility amplitudes still have large envelope masses, but could be slightly more evolved.

Herschelobservations of B1-bS and B1-bN: two first hydrostatic core candidates in the Perseus star-forming cloud

We report far-IR Herschel observations obtained between 70 $\mu$m and 500 $\mu$m of two star-forming dusty condensations, B1-bS and B1-bN, in the B1 region of the Perseus star-forming cloud. In the Western part of the Perseus cloud, B1-bS is the only source detected in all of the 6 PACS and SPIRE photometric bands without being visible in the Spitzer map at 24 $\mu$m. B1-bN is clearly detected between 100 $\mu$m and 250 $\mu$m. We have fitted the spectral energy distributions of these sources to derive their physical properties, and find that a simple greybody model fails to reproduce the observed SEDs. At least a two-component model, consisting of a central source surrounded by a dusty envelope is required. The properties derived from the fit, however, suggest that the central source is not a Class 0 object. We then conclude that while B1-bS and B1-bN appear to be more evolved than a pre-stellar core, the best-fit models suggest that their central objects are younger than a Class 0 source. Hence, they may be good candidates to be examples of the first hydrostatic core phase. The projected distance between B1-bS and B1-bN is a few Jeans lengths. If their physical separation is close to this value, this pair would allow the mutual interactions between two forming stars at a very early stage of their evolution to be studied.