Context. The outflow force of molecular bipolar outflows is a key parameter in theories of young stellar feedback on their surroundings. The focus of many outflow studies is the correlation between... Show moreContext. The outflow force of molecular bipolar outflows is a key parameter in theories of young stellar feedback on their surroundings. The focus of many outflow studies is the correlation between the outflow force, bolometric luminosity, and envelope mass. However, it is difficult to combine the results of different studies in large evolutionary plots over many orders of magnitude due to the range of data quality, analysis methods, and corrections for observational effects, such as opacity and inclination. Aims: We aim to determine the outflow force for a sample of low-luminosity embedded sources. We quantify the influence of the analysis method and the assumptions entering the calculation of the outflow force. Methods: We used the James Clerk Maxwell Telescope to map $^{12}$CO J = 3-2 over 2'{ imes} 2' regions around 16 Class I sources of a well-defined sample in Ophiuchus at 15{Prime} resolution. The outflow force was then calculated using seven different methods differing, e.g., in the use of intensity-weighted emission and correction factors for inclination. Two well studied outflows (HH 46 and NGC1 333 IRAS4A) are added to the sample and included in the comparison. Results: The results from the analysis methods differ from each other by up to a factor of 6, whereas observational properties and choices in the analysis procedure affect the outflow force by up to a factor of 4. Subtraction of cloud emission and integrating over the remaining profile increases the outflow force at most by a factor of 4 compared to line wing integration. For the sample of Class I objects, bipolar outflows are detected around 13 sources including 5 new detections, where the three nondetections are confused by nearby outflows from other sources. New outflow structures without a clear powering source are discovered at the corners of some of the maps. Conclusions: When combining outflow forces from different studies, a scatter by up to a factor of 5 can be expected. Although the true outflow force remains unknown, the separation method (separate calculation of dynamical time and momentum) is least affected by the uncertain observational parameters. The correlations between outflow force, bolometric luminosity, and envelope mass are further confirmed down to low-luminosity sources. Appendices are available in electronic form at http://www.aanda.org Show less
Evaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapor abundances of ~{}10$^{-4}$ relative to H$... Show moreEvaporation of water ice above 100 K in the inner few 100 AU of low-mass embedded protostars (the so-called hot core) should produce quiescent water vapor abundances of ~{}10$^{-4}$ relative to H$_{2}$. Observational evidence so far points at abundances of only a few 10$^{-6}$. However, these values are based on spherical models, which are known from interferometric studies to be inaccurate on the relevant spatial scales. Are hot cores really that much drier than expected, or are the low abundances an artifact of the inaccurate physical models? We present deep velocity-resolved Herschel-HIFI spectra of the 3$_{12}$-3$_{03}$ lines of H_2^{}${$16$}$O and H_2^{}${$18$}$O (1097 GHz, E $_u$/k = 249 K) in the low-mass Class 0 protostar NGC 1333 IRAS2A. A spherical radiative transfer model with a power-law density profile is unable to reproduce both the HIFI data and existing interferometric data on the H_2^{}${$18$}$O 3$_{13}$-2$_{20}$ line (203 GHz, E $_u$/k = 204 K). Instead, the HIFI spectra likely show optically thick emission from a hot core with a radius of about 100 AU. The mass of the hot core is estimated from the C$^{18}$O J = 9-8 and 10-9 lines. We derive a lower limit to the hot water abundance of 2 { imes} 10$^{-5}$, consistent with the theoretical predictions of ~{}10$^{-4}$. The revised HDO/H$_{2}$O abundance ratio is 1 { imes} 10$^{-3}$, an order of magnitude lower than previously estimated. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. Show less
