Star formation in a clustered environment around the UCH ${\mathsf{II}}$ region in IRAS 20293+3952

Abstract

Aims. We aim at studying the cluster environment surrounding the UCH ii region in IRAS 20293+3952, a region in the first stages of formation of a cluster around a high-mass star. Methods. BIMA and VLA were used to observe the 3 mm continuum, N 2 H + (1-0), NH 3 (1, 1), NH 3 (2, 2), and CH 3 OH (2-1) emission of the surroundings of the UCH ii region. We studied the kinematics of the region and computed the rotational temperature and column density maps by fitting the hyperfine structure of N 2 H + and NH 3 . Results. The dense gas traced by N 2 H + and NH 3 shows two different clouds, a main cloud to the east of the UCH ii region, of ∼0.5 pc and ∼250 M , and a western cloud, of ∼0.15 pc and ∼30 M . The dust emission reveals two strong components in the northern side of the main cloud, BIMA 1 and BIMA 2, associated with Young Stellar Objects (YSOs) driving molecular outflows, and two fainter components in the southern side, BIMA 3 and BIMA 4, with no signs of star forming activity. Regarding the CH 3 OH, we found strong emission in a fork-like structure associated with outflow B, as well as emission associated with outflow A. The YSOs associated with the dense gas seem to have a diversity of age and properties. The rotational temperature is higher in the northern side of the main cloud, around 22 K, where there are most of the YSOs, than in the southern side, around 16 K. There is strong chemical differentiation in the region, since we determined low values of the NH 3 /N 2 H + ratio, ∼50, associated with YSOs in the north of the main cloud, and high values, up to 300, associated with cores with no detected YSOs, in the south of the main cloud. Such a chemical differentiation is likely due to abundance/depletion effects. Finally, interaction between the different sources in the region is important. First, the UCH ii region is interacting with the main cloud, heating it and enhancing the CN (1-0) emission. Second, outflow A seems to be excavating a cavity and heating its walls. Third, outflow B is interacting with the BIMA 4 core, likely producing the deflection of the outflow and illuminating a clump located ∼0.2 pc to the northeast of the shock. Conclusions. The star formation process in IRAS 20293+3952 is not obviously associated with interactions, but seems to take place where density is highest.

Prestellar and protostellar cores in Orion B9

“…Hotzel et al (2004) found a similar tendency in B217 and L1262: the NH 3 /N 2 H + abundance ratios are at least twice as large in the dense starless parts of the cores than in the regions closer to the YSO (see Caselli et al 2002b, for other low-mass star-forming regions). The same trend is also found in the high-mass starforming region IRAS 20293+3952 (Palau et al 2007). This is in accordance with chemistry models (Aikawa et al 2005) and previous observations (Tafalla et al 2004), which suggest that NH 3 develops slightly later than N 2 H + , and can resist depletion up to higher densities.…”

Three intermediate-mass young stellar objects with different properties emerging from the same natal cloud in IRAS 00117+6412

“…assuming that the filling factor is ∼1 and following Caselli et al (2002b). We note that the excitation temperature of ∼3 K, and the N 2 H + column densities are similar to the values found in low-mass star-forming regions (e.g., Caselli et al 2002a;Chen et al 2007;Kirk et al 2009), and slightly smaller than the values found in massive star-forming regions observed with interferometers (e.g., Palau et al 2007a;Beuther & Henning 2009). The small excitation temperature obtained is suggestive of either low density and/or cold gas.…”

“…The small excitation temperature obtained is suggestive of either low density and/or cold gas. Note however that our values could be affected by the missing flux problem caused by the lack of short uv-spacings in the interferometric data (for the PdB, the largest angular scale detectable is ∼11 , see Appendix, while in Palau et al (2007a) and Beuther & Henning (2009), the largest angular scale was 20-30 , which means that our PdB data are more affected by the missing flux problem).…”

Ammonia observations in the LBV nebula G79.29+0.46

“…Heavily destroyed in UV fields (e.g. Fuente et al 1990, and references therein), it is present in cold dark clouds (Jijina et al 1999;Sepúlveda et al 2011) and also in regions affected by shocks (Tafalla & Bachiller 1995;Zhang et al 2002;Palau et al 2007). Since the very beginnings of molecular spectroscopy, it has been widely recognized as an excellent thermometer of the ISM (Ho & Townes 1983;Guesten et al 1985;Maret et al 2009).…”