Warm Extended Dense Gas Lurking At The Heart Of A Cold Collapsing Dense Core

In order to investigate when and how the birth of a protostellar core occurs, we made survey observations of four well-studied dense cores in the Taurus molecular cloud using CO transitions in submillimeter bands. We report here the detection of unexpectedly warm (~ 30 - 70 K), extended (radius of ~ 2400 AU), dense (a few times 10^{5} cm^{-3}) gas at the heart of one of the dense cores, L1521F (MC27), within the cold dynamically collapsing components. We argue that the detected warm, extended, dense gas may originate from shock regions caused by collisions between the dynamically collapsing components and outflowing/rotating components within the dense core. We propose a new stage of star formation, "warm-in-cold core stage (WICCS)", i.e., the cold collapsing envelope encases the warm extended dense gas at the center due to the formation of a protostellar core. WICCS would constitutes a missing link in evolution between a cold quiescent starless core and a young protostar in class 0 stage that has a large-scale bipolar outflow.Comment: Accepted for publication in The Astrophysical Journal Letter

Infall, outflow, and rotation in the G19.61-0.23 hot molecular core

Aims: The main goal of this study is to perform a sub-arcsecond resolution analysis of the high-mass star formation region G19.61-0.23, both in the continuum and molecular line emission. While the centimeter continuum images will be discussed in detail in a forthcoming paper, here we focus on the (sub)mm emission, devoting special attention to the hot molecular core. Results: Our observations resolve the HMC into three cores whose masses are on the order of 10^1-10^3 Msun. No submm core presents detectable free-free emission in the centimeter regime, but they appear to be associated with masers and thermal line emission from complex organic molecules. Towards the most massive core, SMA1, the CH3CN (18_K-17_K) lines reveal hints of rotation about the axis of a jet/outflow traced by H2O maser and H13CO+ (1--0) line emission. Inverse P-Cygni profiles of the 13CO (3--2) and C18O (3--2) lines seen towards SMA1 indicate that the central high-mass (proto)star(s) is (are) still gaining mass with an accretion rate $ge 3 ~10^{-3}$ Msun/yr. Due to the linear scales and the large values of the accretion rate, we hypothesize that we are observing an accretion flow towards a cluster in the making, rather than towards a single massive star.Comment: A&A accepted; 18 pages; Preprint with full-resolution figures is available at http://subarutelescope.org/staff/rsf/publication.htm

A 1000 AU Scale Molecular Outflow Driven by a Protostar with an age of <4000 Years

To shed light on the early phase of a low-mass protostar formation process, we conducted interferometric observations towards a protostar GF9-2 using the CARMA and SMA. The observations have been carried out in the CO J=3-2 line and in the continuum emission at the wavelengths of 3 mm, 1 mm and 850 micron. All the continuum images detected a single point-like source with a radius of 250+/-80 AU at the center of the previously known ~3 Msun molecular cloud core. A compact emission is detected towards the object at the Spitzer MIPS and IRAC bands as well as the four bands at the WISE. Our spectroscopic imaging of the CO line revealed that the continuum source is driving a 1000 AU scale molecular outflow, including a pair of lobes where a collimated "higher" velocity red lobe exists inside a poorly collimated "lower" velocity red lobe. These lobes are rather young and the least powerful ones so far detected. A protostellar mass of M~<0.06 Msun was estimated using an upper limit of the protostellar age of (4+/-1)x10^3 yrs and an inferred non-spherical steady mass accretion rate of ~10^{-5} Msun/yr. Together with results from an SED analysis, we discuss that the outflow system is driven by a protostar whose surface temperature of~3,000K, and that the natal cloud core is being dispersed by the outflow.Comment: 27 pages, 14 figures, accepted for publication in Astrophysical Journa

The Initial Conditions for Gravitational Collapse of a Core: An Extremely Young Low-Mass Class 0 Protostar GF9-2

We present a study of the natal core harboring the class 0 protostar GF9-2 in the filamentary dark cloud GF 9 (d = 200 pc). GF9-2 stands unique in the sense that it shows H2O maser emission, a clear signpost of protostar formation, whereas it does not have a high-velocity large-scale molecular outflow evidenced by our deep search for CO wing emission. These facts indicate that GF9-2 core is early enough after star formation so that it still retains some information of initial conditions for collapse. Our 350 um dust continuum emission image revealed the presence of a protostellar envelope in the center of a molecular core. The mass of the envelope is ~0.6 Msun from the 350 um flux density, while LTE mass of the core is ~3 Msun from moleuclar line observations. Combining visibility data from the OVRO mm-array and the 45m telescope, we found that the core has a radial density profile of $\rho(r)\propto r^{-2}$ for 0.003 < r/pc < 0.08 region. Molecular line data analysis revealed that the velocity width of the core gas increases inward,while the outermost region maintains a velocity dispersion of a few times of the ambient sound speed. The broadened velocity width can be interpreted as infall. Thus, the collapse in GF9-2 is likely to be described by an extension of the Larson-Penston solution for the period after formation of a central star. We derived the current mass accretion rate of ~3E-05 Msun/year from infall velocity of ~ 0.3 km/s at r~ 7000 AU. All results suggest that GF9-2 core has been undergoing gravitational collapse for ~ 5000 years since the formation of central protostar(s), and that the unstable state initiated the collapse ~2E+05 years (the free-fall time) ago.Comment: ApJ Accepted. The preprint including figures with the original quality is available at http://subarutelescope.org/staff/rsf/publication.htm

Proper Motion of H2O Masers in IRAS 20050+2720 MMS1: An AU Scale Jet Associated with An Intermediate-Mass Class 0 Source

We conducted a 4 epoch 3 month VLBA proper motion study of H$_2$O masers toward an intermediate-mass class 0 source IRAS 20050+2720 MMS1 (d=700 pc). From milli-arcsecond (mas) resolution VLBA images, we found two groups of H2O maser spots at the center of the submillimeter core of MMS1. One group consists of more than $\sim 50$ intense maser spots; the other group consisting of several weaker maser spots is located at 18 AU south-west of the intense group. Distribution of the maser spots in the intense group shows an arc-shaped structure which includes the maser spots that showed a clear velocity gradient. The spatial and velocity structures of the maser spots in the arc-shape did not significantly change through the 4 epochs. Furthermore, we found a relative proper motion between the two groups. Their projected separation increased by 1.13+/-0.11 mas over the 4 epochs along a line connecting them. The spatial and velocity structures of the intense group and the relative proper motions strongly suggest that the maser emission is associated with a protostellar jet. Comparing the observed LSR velocities with calculated radial velocities from a simple biconical jet model, we conclude that the most of the maser emission are likely to be associated with an accelerating biconical jet which has large opening angle. The large opening angle of the jet traced by the masers would support the hypothesis that poor jet collimation is an inherent property of luminous (proto)stars.Comment: 14 pages, 10 figures, Fig.3 was downsized significantly. accepted for publication in A&

First results from a VLBA proper motion survey of H2O masers in low-mass YSOs: the Serpens core and RNO15-FIR

This article reports first results of a long-term observational program aimed to study the earliest evolution of jet/disk systems in low-mass YSOs by means of VLBI observations of the 22.2 GHz water masers. We report here data for the cluster of low-mass YSOs in the Serpens molecular core and for the single object RNO~15-FIR. Towards Serpens SMM1, the most luminous sub-mm source of the Serpens cluster, the water maser emission comes from two small (< 5 AU in size) clusters of features separated by ~25 AU, having line of sight velocities strongly red-shifted (by more than 10 km/s) with respect to the LSR velocity of the molecular cloud. The two maser clusters are oriented on the sky along a direction that is approximately perpendicular to the axis of the radio continuum jet observed with the VLA towards SMM1. The spatial and velocity distribution of the maser features lead us to favor the interpretation that the maser emission is excited by interaction of the receding lobe of the jet with dense gas in the accretion disk surrounding the YSO in SMM1. Towards RNO~15-FIR, the few detected maser features have both positions and (absolute) velocities aligned along a direction that is parallel to the axis of the molecular outflow observed on much larger angular scales. In this case the maser emission likely emerges from dense, shocked molecular clumps displaced along the axis of the jet emerging from the YSO. The protostar in Serpens SMM1 is more massive than the one in RNO~15-FIR. We discuss the case where a high mass ejection rate can generate jets sufficiently powerful to sweep away from their course the densest portions of circumstellar gas. In this case, the excitation conditions for water masers might preferably occur at the interface between the jet and the accretion disk, rather than along the jet axis.Comment: 18 pages (postscript format); 9 figures; to be published into Astronomy & Astrophysics, Main Journa

Entanglement versus mixedness for coupled qubits under a phase damping channel

Quantification of entanglement against mixing is given for a system of coupled qubits under a phase damping channel. A family of pure initial joint states is defined, ranging from pure separable states to maximally entangled state. An ordering of entanglement measures is given for well defined initial state amount of entanglement.Comment: 9 pages, 2 figures. Replaced with final published versio

Low-Mass Star Forming Cores in the GF9 Filament

We carried out an unbiased mapping survey of dense molecular cloud cores traced by the NH3 (1,1) and (2,2) inversion lines in the GF9 filament which contains an extremely young low-mass protostar GF9-2 (Furuya et al. 2006, ApJ, 653, 1369). The survey was conducted using the Nobeyama 45m telescope over a region of ~1.5 deg with an angular resolution of 73". The large-scale map revealed that the filament contains at least 7 dense cores, as well as 3 possible ones, located at regular intervals of ~0.9 pc. Our analysis shows that these cores have kinetic temperatures of $\lesssim$ 10 K and LTE-masses of 1.8 -- 8.2 Msun, making them typical sites of low-mass star formation. All the identified cores are likely to be gravitationally unstable because their LTE-masses are larger than their virial masses. Since the LTE-masses and separations of the cores are consistent with the Jeans masses and lengths, respectively, for the low-density ambient gas, we argue that the identified cores have formed via the gravitational fragmentation of the natal filamentary cloud.Comment: accepted by pas