Kazuyoshi Sunada

13CO, C18O, and CS Observations toward Massive Dense Cores

We present results of 13CO J = 1–0, C18O J = 1–0, and CS J = 2–1 map observations toward 10 massive star-forming regions selected from the previous CO line survey of cold IRAS sources along the Galactic plane. CS line emission was detected from 9 out of 10 sources, and 13CO line emission was detected in all sources. C18O J = 1–0 line emission was detected in only three sources. Physical parameters are derived for the detected sources. The 13CO and C18O data support the idea that gradual dissipation of the internal turbulence leads to formation of denser cores and subsequent star formation. There is no apparent relationship between the CS abundance and the CO temperature. The ratios of LIR to MLTE vary by no more than a factor of 3 for the CS cores and by nearly 1 order of magnitude for the 13CO cores. This indicates that star formation is determined by the gas with high volume density and does not depend on the mass of the cloud. We find that the star formation rate per unit mass is nearly constant in the dense cores. Divided into two subgroups, low and high, by their FIR color indexes, the low sources are in an earlier stage than the high sources, based on the high sources association with H2O masers.

Millimeter-wave survey of molecular clouds around the W5-East triggered star-forming region

Aims. We examined the physical properties of molecular clouds (morphology, column density, number density, mass) to investigate the mechanism of triggered star formation by UV radiation from a massive star. Methods. We made extensive, high-resolution maps of molecular clouds associated and interacting with the W5-East H ii region using the 45-m telescope at the Nobeyama Radio Observatory (HPBW = 15. �� 6) in 13 CO (J = 1−0) and C 18 O( J = 1−0) to reveal details in the high-density regions of the molecular clouds. In addition, to investigate the spatial distributions of young stellar objects (YSOs) in the W5-East H ii region, we mapped the spatial distributions of Class I and II candidates. Results. We identified eight 13 CO molecular clouds (three of them are known bright-rimmed clouds) and nine C 18 Oc lumps. The

NGC 7538: multiwavelength study of stellar cluster regions associated with IRS 1–3 and IRS 9 sources

We present deep and high-resolution (FWHM ∼ 0.4 arcsec) near-infrared (NIR) imaging observations of the NGC 7538 IRS 1–3 region n (in JHK bands), and IRS 9 region (in HK bands) using the 8.2u2009m Subaru telescope. The NIR analysis is complemented with Giant Metrewave Radio Telescope (GMRT) low-frequency n observations at 325, 610, and 1280 MHz, molecular line observations of H 13 CO + (J=1–0), and archival Chandra X-ray observations. Using the ‘J − H/H − K’ diagram, 144 Class II and 24 Class I young stellar object (YSO) candidates are identified in the IRS 1–3 region. Further n analysis using ‘K/H − K’ diagram yields 145 and 96 red sources in the IRS 1–3 and IRS 9 regions, respectively. A total of 27 sources are found to n have X-ray counterparts. The YSO mass function (MF), constructed using a theoretical mass–luminosity relation, shows peaks n at substellar (∼0.08–0.18u2009M ⊙ ) and intermediate (∼1–1.78u2009M ⊙ ) mass ranges for the IRS 1–3 region. The MF can be fitted by a power law in the low-mass regime with a slope of Γ ∼ 0.54–0.75, n which is much shallower than the Salpeter value of 1.35. An upper limit of 10.2 is obtained for the star to brown dwarf ratio n in the IRS 1–3 region. GMRT maps show a compact H ii region associated with the IRS 1–3 sources, whose spectral index of 0.87 ± 0.11 suggests optical thickness. This compact n region is resolved into three separate peaks in higher resolution 1280 MHz map, and the ‘east’ subpeak coincides with the n IRS 2 source. H 13 CO + (J=1–0) emission reveals peaks in both IRS 1–3 and IRS 9 regions, none of which are coincident with visible nebular emission, n suggesting the presence of dense cloud nearby. The virial masses are approximately of the order of 1000 and 500u2009M ⊙ for the clumps in IRS 1–3 and IRS 9 regions, respectively.

LUMINOSITY AND MASS FUNCTIONS AT THE VERY LOW MASS SIDE IN NGC 1333

We present the results of a deep near-infrared (NIR) imaging survey searching for very low mass young stellar objects (YSOs) in the embedded cluster associated with the Perseus molecular cloud. Our observations cover an area of ~5× 5 in the NGC 1333-S region at J-, H-, and Ks-bands. The 10σ limiting magnitudes exceed 18 mag in all three bands. Based on NIR color-color diagrams, embedded YSO candidates were identified using NIR excesses. The derived frequency of these YSO candidates with NIR excess emission among all the detected sources is 58+10 –13%. The higher frequency of YSOs with NIR excesses implies that NGC 1333 is an active and young star-forming region. Approximately half of the YSO candidates exhibit extremely low luminosity, indicating very low mass. Combining the reddening-corrected luminosity with theoretical evolutionary models, the low-luminosity YSO candidates are considered to be young substellar-mass objects. Furthermore, some sources could have planetary masses. In addition, we carried out CO molecular-line observations of the same cloud region. The results suggested that the YSO candidates are likely formed on the side of the parent molecular cloud and star-formation activity could be high. The K-band luminosity function of all the detected sources revealed a significant population of extremely low-luminosity sources in NGC 1333. The reddening-corrected J-band luminosity function of the YSO candidates does not clearly decline to the completeness limit and seems to be bimodal. We also argue that the fraction of substellar objects is larger than those in other young clusters and the mass function of the YSO candidates appears to be increasing toward the substellar-mass regime, similar to that of dust clumps. It implies that substellar-mass distributions may depend on the initial conditions of the molecular cloud.