High mass star formation in the infrared dark cloud G11.11-0.12

We report detection of moderate to high-mass star formation in an infrared dark cloud (G11.11-0.12) where we discovered class II methanol and water maser emissions at 6.7 GHz and 22.2 GHz, respectively. We also observed the object in ammonia inversion transitions. Strong emission from the (3,3) line indicates a hot (~60 K) compact component associated with the maser emission. The line width of the hot component (4 km/s), as well as the methanol maser detection, are indicative of high mass star formation. To further constrain the physical parameters of the source, we derived the spectral energy distribution (SED) of the dust continuum by analysing data from the 2MASS survey, HIRAS, MSX, the Spitzer Space Telescope, and interferometric 3mm observations. The SED was modelled in a radiative transfer program: a) the stellar luminosity equals 1200 L_sun corresponding to a ZAMS star of 8 M_sun; b) the bulk of the envelope has a temperature of 19 K; c) the mass of the remnant protostellar cloud in an area 8x10^17 cm or 15 arcsec across amounts to 500M_sun, if assuming standard dust of the diffuse medium, and to about 60 M_sun, should the grains be fluffy and have ice mantles; d) the corresponding visual extinction towards the star is a few hundred magnitudes. The near IR data can be explained by scattering from tenuous material above a hypothetical disk. The class II methanol maser lines are spread out in velocity over 11 km/s. To explain the kinematics of the masing spots, we propose that they are located in a Kepler disk at a distance of about 250 AU. The dust temperatures there are around 150 K, high enough to evaporate methanol--containing ice mantles.Comment: 10 pages, 6 figures, Accepted for publication in Astronomy & Astrophysics Journa

Dust emission from young outflows: the case of L1157

We present new high-sensitivity 1.3 mm bolometer observations of the young outflow L1157. These data show that the continuum emission arises from four distinct components: a circumstellar disk, a protostellar envelope, an extended flattened envelope --the dense remnant of the molecular cloud in which the protostar was formed--, and the outflow itself, which represents ~20% of the total flux. The outflow emission exhibits two peaks that are coincident with the two strong shocks in the southern lobe of L1157. We show that the mm continuum is dominated by thermal dust emission arising in the high velocity material. The spectral index derived from the new 1.3 mm data and 850 mu observations from Shirley et al. (2000), is ~5 in the outflow, significantly higher than in the protostellar envelope (~3.5). This can be explained by an important line contamination of the 850 mu map, and/or by different dust characteristics in the two regions, possibly smaller grains in the post-shocks regions of the outflow. Our observations show that bipolar outflows can present compact emission peaks which must not be misinterpreted as protostellar condensations when mapping star forming regions

Accuracy of core mass estimates in simulated observations of dust emission

We study the reliability of mass estimates obtained for molecular cloud cores using sub-millimetre and infrared dust emission. We use magnetohydrodynamic simulations and radiative transfer to produce synthetic observations with spatial resolution and noise levels typical of Herschel surveys. We estimate dust colour temperatures using different pairs of intensities, calculate column densities and compare the estimated masses with the true values. We compare these results to the case when all five Herschel wavelengths are available. We investigate the effects of spatial variations of dust properties and the influence of embedded heating sources. Wrong assumptions of dust opacity and its spectral index beta can cause significant systematic errors in mass estimates. These are mainly multiplicative and leave the slope of the mass spectrum intact, unless cores with very high optical depth are included. Temperature variations bias colour temperature estimates and, in quiescent cores with optical depths higher than for normal stable cores, masses can be underestimated by up to one order of magnitude. When heated by internal radiation sources the observations recover the true mass spectra. The shape, although not the position, of the mass spectrum is reliable against observational errors and biases introduced in the analysis. This changes only if the cores have optical depths much higher than expected for basic hydrostatic equilibrium conditions. Observations underestimate the value of beta whenever there are temperature variations along the line of sight. A bias can also be observed when the true beta varies with wavelength. Internal heating sources produce an inverse correlation between colour temperature and beta that may be difficult to separate from any intrinsic beta(T) relation of the dust grains. This suggests caution when interpreting the observed mass spectra and the spectral indices.Comment: Revised version, 17 pages, 17 figures, submitted to A&

Probing the formation of intermediate- to high-mass stars in protoclusters: A detailed millimeter study of the NGC 2264 clumps

We present the results of dust continuum and molecular line observations of two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, including extensive mapping performed with the MAMBO bolometer array and the HERA heterodyne array on the IRAM 30m telescope. Both NGC 2264 clumps are located in the Mon OB1 giant molecular cloud complex, adjacent to one another. Twelve and fifteen compact millimeter continuum sources (i.e. MMSs) are identified in clumps C and D, respectively. Evidence for widespread infall motions is found in, e.g., HCO+(3-2) or CS(3-2) in both NGC 2264-C and NGC 2264-D. A sharp velocity discontinuity ~ 2 km/s in amplitude is observed in N_2H+(1-0) and H^{13}CO+(1-0) in the central, innermost part of NGC 2264-C, which we interpret as the signature of a strong dynamical interaction between two MMSs and their possible merging with the central MMS C-MM3. Radiative transfer modelling supports the idea that NGC 2264-C is a highly unstable prolate clump in the process of collapsing along its long axis on a near free-fall dynamical timescale ~ 1.7x10^5 yr. Our model fit of this large-scale collapse suggests a maximum mass inflow rate ~ 3x10^{-3} Msun/yr toward the central protostellar object C-MM3. Such infall rates are sufficiently high to overcome radiation pressure and allow the formation of ~ 20 Msun stars by accretion in ~ 1.7x10^5 yr, i.e., a time similar to the global dynamical timescale of the central part of NGC 2264-C. We conclude that we are likely witnessing the formation of a high-mass (> 10 Msun) protostar in the central part of NGC 2264-C. Our results suggest a picture of massive star formation intermediate between the scenario of stellar mergers of Bonnell et al. (1998) and the massive turbulent core model of McKee & Tan (2003).Comment: 22 pages, 16 figures, accepted for publication in A&A. Most of the Figures have been de-resolved in order to reduce file size

MAMBO Mapping of Spitzer c2d Small Clouds and Cores

AIMS: To study the structure of nearby (< 500 pc) dense starless and star-forming cores with the particular goal to identify and understand evolutionary trends in core properties, and to explore the nature of Very Low Luminosity Objects (< 0.1 L_sun; VeLLOs). METHODS: Using the MAMBO bolometer array, we create maps unusually sensitive to faint (few mJy per beam) extended (approx. 5 arcmin) thermal dust continuum emission at 1.2 mm wavelength. Complementary information on embedded stars is obtained from Spitzer, IRAS, and 2MASS. RESULTS: Our maps are very rich in structure, and we characterize extended emission features (``subcores'') and compact intensity peaks in our data separately to pay attention to this complexity. We derive, e.g., sizes, masses, and aspect ratios for the subcores, as well as column densities and related properties for the peaks. Combination with archival infrared data then enables the derivation of bolometric luminosities and temperatures, as well as envelope masses, for the young embedded stars. CONCLUSIONS: (abridged) Starless and star-forming cores occupy the same parameter space in many core properties; a picture of dense core evolution in which any dense core begins to actively form stars once it exceeds some fixed limit in, e.g., mass, density, or both, is inconsistent with our data. Comparison of various evolutionary indicators for young stellar objects in our sample (e.g., bolometric temperatures) reveals inconsistencies between some of them, possibly suggesting a revision of some of these indicators.Comment: Accepted to A&A. In total 46 pages, with 20 pages of tables, figures, and appendices. High-resolution version of this article at https://www.xythosondemand.com/home/harvard_iic/Users/jkauffma/Public/mambo_spitzer.pd

Molecular Gas and Star Formation in Lynds 870

We present molecular line and submillimeter dust continuum observations of the Lynds 870 cloud in the vicinity of IRAS 20231+3440. Two submillimeter cores, SMM1 and SMM2, are identified mapping the 870 micron dust continuum and ammonia emission. The total molecular mass is ~70-110 solar mass. The northern core is warmer and denser than the southern one. Molecular outflows are discovered in both cores. In the northern one a significant amount of low velocity (1.3-2.8 km/s) outflowing gas is found, that is hidden in the relatively broad CO lines but that is revealed by the narrower HCO+ spectra. While IRAS 20231+3440 is most likely the exciting star of the northern outflow, the driving source of the southern outflow is not detected by infrared surveys and must be deeply embedded in the cloud core. Large scale (~0.2 pc) infall motion is indicated by blue asymmetric profiles observed in the HCO+ J = 3-2 spectra. Red K_s band YSO candidates revealed by the 2MASS survey indicate ongoing star formation throughout the cloud. The calculated masses and the measured degree of turbulence are also reminiscent of clouds forming groups of stars. The excitation of the molecular lines, molecular abundances, and outflow properties are discussed. It is concluded that IRAS 20231+3440 is a ClassI object, while the southern core most likely contains a Class0 source.Comment: 14 pages, 13 figures, accepted for publication in A&

Effects of phone versus mail survey methods on the measurement of health-related quality of life and emotional and behavioural problems in adolescents

<p>Abstract</p> <p>Background</p> <p>Telephone interviews have become established as an alternative to traditional mail surveys for collecting epidemiological data in public health research. However, the use of telephone and mail surveys raises the question of to what extent the results of different data collection methods deviate from one another. We therefore set out to study possible differences in using telephone and mail survey methods to measure health-related quality of life and emotional and behavioural problems in children and adolescents.</p> <p>Methods</p> <p>A total of 1700 German children aged 8-18 years and their parents were interviewed randomly either by telephone or by mail. Health-related Quality of Life (HRQoL) and mental health problems (MHP) were assessed using the KINDL-R Quality of Life instrument and the Strengths and Difficulties Questionnaire (SDQ) children's self-report and parent proxy report versions. Mean Differences ("d" effect size) and differences in Cronbach alpha were examined across modes of administration. Pearson correlation between children's and parents' scores was calculated within a multi-trait-multi-method (MTMM) analysis and compared across survey modes using Fisher-Z transformation.</p> <p>Results</p> <p>Telephone and mail survey methods resulted in similar completion rates and similar socio-demographic and socio-economic makeups of the samples. Telephone methods resulted in more positive self- and parent proxy reports of children's HRQoL (SMD ≤ 0.27) and MHP (SMD ≤ 0.32) on many scales. For the phone administered KINDL, lower Cronbach alpha values (self/proxy Total: 0.79/0.84) were observed (mail survey self/proxy Total: 0.84/0.87). KINDL MTMM results were weaker for the phone surveys: mono-trait-multi-method mean r = 0.31 (mail: r = 0.45); multi-trait-mono-method mean (self/parents) r = 0.29/0.36 (mail: r = 0.34/0.40); multi-trait-multi-method mean r = 0.14 (mail: r = 0.21). Weaker MTMM results were also observed for the phone administered SDQ: mono-trait-multi-method mean r = 0.32 (mail: r = 0.40); multi-trait-mono-method mean (self/parents) r = 0.24/0.30 (mail: r = 0.20/0.32); multi-trait-multi-method mean r = 0.14 (mail = 0.14). The SDQ classification into borderline and abnormal for some scales was affected by the method (OR = 0.36-1.55).</p> <p>Conclusions</p> <p>The observed differences between phone and mail surveys are small but should be regarded as relevant in certain settings. Therefore, while both methods are valid, some changes are necessary. The weaker reliability and MTMM validity associated with phone methods necessitates improved phone adaptations of paper and pencil questionnaires. The effects of phone versus mail survey modes are partly different across constructs/measures.</p

Estimation of mislocated fixations from eye-movement data

Source code in MATLAB (The MathWorks) for the estimation of mislocated fixations from eye-movement recordings during sentence readin