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Register a new userPlanck cold clumps in the $lambda$ Orionis complex: I. Discovery of an extremely young Class 0 protostellar object and a proto-brown dwarf candidate in a bright rimmed clump PGCC G192.32-11.88
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We are performing a series of observations with ground-based telescopes toward Planck Galactic cold clumps (PGCCs) in the $lambda$ Orionis complex in order to systematically investigate the effects of stellar feedback. In the particular case of PGCC G192.32-11.88, we discovered an extremely young Class 0 protostellar object (G192N) and a proto-brown dwarf candidate (G192S). G192N and G192S are located in a gravitationally bound bright-rimmed clump. The velocity and temperature gradients seen in line emission of CO isotopologues indicate that PGCC G192.32-11.88 is externally heated and compressed. G192N probably has the lowest bolometric luminosity ($sim0.8$ L$_{sun}$) and accretion rate (6.3$times10^{-7}$ M$_{sun}$~yr$^{-1}$) when compared with other young Class 0 sources (e.g. PACS Bright Red sources (PBRs)) in the Orion complex. It has slightly larger internal luminosity ($0.21pm0.01$ L$_{sun}$) and outflow velocity ($sim$14 km~s$^{-1}$) than the predictions of first hydrostatic cores (FHSCs). G192N might be among the youngest Class 0 sources, which are slightly more evolved than a FHSC. Considering its low internal luminosity ($0.08pm0.01$ L$_{odot}$) and accretion rate (2.8$times10^{-8}$ M$_{sun}$~yr$^{-1}$), G192S is an ideal proto-brown dwarf candidate. The star formation efficiency ($sim$0.3%-0.4%) and core formation efficiency ($sim$1%) in PGCC G192.32-11.88 are significantly smaller than in other giant molecular clouds or filaments, indicating that the star formation therein is greatly suppressed due to stellar feedback.
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Massive stars have a strong impact on their local environments. However, how stellar feedback regulates star formation is still under debate. In this context, we studied the chemical properties of 80 dense cores in the Orion molecular cloud complex composed of the Orion A (39 cores), B (26 cores), and lambda Orionis (15 cores) clouds using multiple molecular line data taken with the Korean Very Long Baseline Interferometry Network (KVN) 21-m telescopes. The lambda Orionis cloud has an H ii bubble surrounding the O-type star lambda Ori, and hence it is exposed to the ultraviolet (UV) radiation field of the massive star. The abundances of C2H and HCN, which are sensitive to UV radiation, appear to be higher in the cores in the lambda Orionis cloud than those in the Orion A and B clouds, while the HDCO to H2CO abundance ratios show an opposite trend, indicating a warmer condition in the lambda Orionis cloud. The detection rates of dense gas tracers such as the N2H+, HCO+, and H13CO+ lines are also lower in the lambda Orionis cloud. These chemical properties imply that the cores in the lambda Orionis cloud are heated by UV photons from lambda Ori. Furthermore, the cores in the lambda Orionis cloud do not show any statistically significant excess in the infall signature of HCO+ (1 - 0), unlike the Orion A and B clouds. Our results support the idea that feedback from massive stars impacts star formation in a negative way by heating and evaporating dense materials, as in the lambda Orionis cloud.
Based on the 850 $mu$m dust continuum data from SCUBA-2 at James Clerk Maxwell Telescope (JCMT), we compare overall properties of Planck Galactic Cold Clumps (PGCCs) in the $lambda$ Orionis cloud to those of PGCCs in the Orion A and B clouds. The Orion A and B clouds are well known active star-forming regions, while the $lambda$ Orionis cloud has a different environment as a consequence of the interaction with a prominent OB association and a giant Hii region. PGCCs in the $lambda$ Orionis cloud have higher dust temperatures ($Td=16.13pm0.15$ K) and lower values of dust emissivity spectral index ($ beta=1.65pm0.02$) than PGCCs in the Orion A (Td=13.79$pm 0.21$K, $beta=2.07pm0.03$) and Orion B ($Td=13.82pm0.19$K, $beta=1.96pm0.02$) clouds. We find 119 sub-structures within the 40 detected PGCCs and identify them as cores. Of total 119 cores, 15 cores are discovered in the $lambda$ Orionis cloud, while 74 and 30 cores are found in the Orion A and B clouds, respectively. The cores in the $lambda$ Orionis cloud show much lower mean values of size R=0.08 pc, column density N(H2)=$(9.5pm1.2) times 10^{22}$ cm$^{-2}$, number density n(H2)=$(2.9 pm 0.4)times10^{5}$ cm$^{-3}$, and mass $M_{core}$=$1.0pm0.3$ M$_{odot}$ compared to the cores in the Orion A (R=0.11pc, $N(H2)=(2.3pm0.3) times 10^{23}$ cm$^{-2}$, n(H2)=$(3.8pm0.5) times 10^{5}$cm$^{-3}$, and $M_{core}$=$2.4 pm 0.3$ M$_{odot}$) and Orion B (R=0.16pc, N(H2)=$(3.8 pm 0.4) times 10^{23}$cm$^{-2}$, n(H2)=$(15.6pm1.8)times10^{5}$ cm$^{-3}$, and $M_{core}$= $2.7pm0.3$ M$_{odot}$) clouds. These core properties in the $lambda$ Orionis cloud can be attributed to the photodissociation and external heating by the nearby Hii region, which may prevent the PGCCs from forming gravitationally bound structures and eventually disperse them. These results support the idea of negative stellar feedback on core formation.
The low dust temperatures (<14 K) of Planck Galactic Cold Clumps (PGCCs) make them ideal targets to probe the initial conditions and very early phase of star formation. TOP-SCOPE is a joint survey program targeting ~2000 PGCCs in J=1-0 transitions of CO isotopologues and ~1000 PGCCs in 850 micron continuum emisison. The objective of the TOP-SCOPE survey and the joint surveys (SMT 10-m, KVN 21-m and NRO 45-m) is to statistically study the initial conditions occurring during star formation and the evolution of molecular clouds, across a wide range of environments. The observations, data analysis and example science cases for these surveys are introduced with an exemplar source, PGCC G26.53+0.17 (G26), which is a filamentary infrared dark cloud (IRDC). The total mass, the length and the mean line-mass (M/L) of the G26 filament are ~6200 Msun, ~12 pc and ~500 Msun/pc, respectively. Ten massive clumps including eight starless ones are found along the filament. The most massive Clump as a whole may be still in global collapse while its denser part seems to be undergoing expansion due to outflow feedback. The fragmentation in G26 filament from cloud scale to clump scale is in agreement with gravitational fragmentation of an isothermal, non-magnetized, and turbulent supported cylinder. A bimodal behavior in dust emissivity spectral index ($beta$) distribution is found in G26, suggesting grain growth along the filament. The G26 filament may be formed due to large-scale compression flows evidenced by the temperature and velocity gradients across its natal cloud.
Magnetospheric processes seen in gas-giants such as aurorae and circularly-polarized cyclotron maser radio emission have been detected from some brown dwarfs. However, previous radio observations targeted known brown dwarfs discovered via their infrared emission. Here we report the discovery of BDR J1750+3809, a circularly polarized radio source detected around 144 MHz with the LOFAR telescope. Follow-up near-infrared photometry and spectroscopy show that BDR J1750+3809 is a cold methane dwarf of spectral type T$6.5pm 1$ at a distance of $65^{+9}_{-8},{rm pc}$. The quasi-quiescent radio spectral luminosity of BDR J1750+3809 is $approx 5times 10^{15},{rm erg},{rm s}^{-1},{rm Hz}^{-1}$ which is over two orders of magnitude larger than that of the known population of comparable spectral type. This could be due to a preferential geometric alignment or an electrodynamic interaction with a close companion. In addition, as the emission is expected to occur close to the electron gyro-frequency, the magnetic field strength at the emitter site in BDR J1750+3809 is $Bgtrsim 25,{rm G}$, which is comparable to planetary-scale magnetic fields. Our discovery suggests that low-frequency radio surveys can be employed to discover sub-stellar objects that are too cold to be detected in infrared surveys.
We present the results from a series of ground-based radio observations toward a Planck Galactic Cold Clump (PGCC), PGCC G108.84-00.81, which is located in one curved filamentary cloud in the vicinity of an extended HII region Sh2-152 and SNR G109.1-1.0. PGCC G108.84-00.81 is mainly composed of two clumps, G108-N and G108-S. In the 850 micron dust continuum emission map, G108-N is shown as one component while G108-S is fragmented into four components. There is no infrared source associated with G108-N while there are two infrared sources (IRS 1 and IRS 2) associated with G108-S. The total mass of G108-N is larger than the jeans mass, suggesting that G108-N is gravitationally unstable and a potential place for a future star formation. The clump properties of G108-N and G108-S such as the gas temperature and the column density, are not distinctly different. However, G108-S is slightly more evolved than G108-N, in the consideration of the CO depletion factor, molecular abundances, and association with infrared sources. G108-S seems to be affected by the compression from Sh2-152, while G108-N is relatively protected from the external effect
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