All Figures

$\begin{figure} \par\resizebox{15.8cm}{!}{\includegraphics{5311fig1.eps}} \end{figure}$ Figure 1: Integrated intensity maps from our molecular survey of L1498. The two top left panels show the 1.2 mm continuum and N₂H⁺(1-0) data presented in Paper I. In contrast with these centrally concentrated distributions, the other molecular-line maps are ring-like or centrally-depressed, and have relative minima at the 1.2 mm/N₂H⁺ peak. This is an indication of a central drop in the abundance of most species (see text). Both IRAM 30 m and FCRAO maps have been convolved with a Gaussian beam of 20-30 arcsec to filter out high-frequency noise, and for all lines, the contours are at 15, 30, ... percent of the peak intensity (peak intensity in K km s^-1 is indicated on the top right corner of each panel). To better compare the survey line maps with the N₂H⁺(1-0) emission, the contour at 75% of the peak is superimposed in red. The dots indicate the original map sampling. Central coordinates are $\alpha_{1950}=4^{\rm h}7^{\rm m}50\hbox{$.\!\!^{\rm s}$ }0$ , $\delta_{1950}=25\degr02'13\hbox{$.\!\!^{\prime\prime}$ }0$ .
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{15.9cm}{!}{\includegraphics{5311fig2.eps}} \end{figure}$ Figure 2: Same as Fig. 1 but for the L1517B core. Central coordinates are $\alpha_{1950}=4^{\rm h}52^{\rm m}7\hbox{$.\!\!^{\rm s}$ }2$ , $\delta_{1950}=30\degr33'18\hbox{$.\!\!^{\prime\prime}$ }0$ .
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{14.5cm}{!}{\includegraphics{5311fig3.eps}} \end{figure}$ Figure 3: Radial profiles of integrated intensity and central spectra for all line data observed toward L1498. The squares in the radial profiles and the histograms in the spectra are observed data while the lines represent Monte Carlo model results. The blue dashed lines are models that assume a constant abundance chosen to fit the data at a relatively large fiducial radius (see text), and the red solid lines are the prediction from the best fit model. Note how the constant abundance models over predict the central intensity typically by a factor of 2 or more. The integrated intensities in the radial profiles ( left panels) have a typical 1- $\sigma$ uncertainty of 0.01-0.02 K km s^-1 for the IRAM data (with the exception of the high frequency lines HCN(3-2) and HCO⁺(3-2), which have 1- $\sigma$ uncertainties of 0.06 and 0.09 K km s^-1), 0.02-0.065 K km s^-1 for the FCRAO data, and 0.09 K km s^-1 for the 100 m data. These values are smaller than the internal point-to-point scatter. The spectra in the right panels have been generated from the average of typically 5 spectra within a 20'' radius from the core center (50'' for FCRAO data), in order to produce a relatively high S/N observation. To model this observation, we have generated synthetic spectra for each of the (typically 5) observed radial locations, and we have averaged them as we have done with the data.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{15cm}{!}{\includegraphics{5311fig4.eps}} \end{figure}$ Figure 4: Same as Fig. 3 but for the L1517B core.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{% \includegraphics{5311fig5.eps}} \end{figure}$ Figure 5: Abundance comparison between L1498 and L1517B. Top: ratio between the abundances outside the central hole (X₀) in the two cores (for HC₃N and C₃H₂, X₀ is the abundance between the hole and the outer cutoff). For most species, this ratio is close to 1 (within a factor of 2), indicating a similar pre-freeze out composition. Bottom: ratio between central depletion holes ( $r_{\rm h}$ ). L1498 presents systematically larger hole ratios by a factor of about 1.5, which is consistent with the visual impression from the integrated maps.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{5311fig6.eps}} \end{figure}$ Figure 6: Normalized radius of the abundance hole $r_{\rm h}$ for all molecules in the survey. The red squares represent L1498 data and the blue triangles are L1517B data (normalizing radius is $1.04 \times 10^{17}$ cm for L1498 and $0.66 \times 10^{17}$ for L1517B). Species like CO, SO, and C₂S present larger $r_{\rm h}$ values, while HC₃N, DCO⁺, and HCN have smaller $r_{\rm h}$ values and therefore must remain in the gas phase to higher densities.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{5311fig7.eps}} \end{figure}$ Figure 7: Correction factors needed to make the abundances predicted by the Aikawa et al. (2005) $\alpha =1.1$ model reproduce the observed intensities in the L1498/L1517B molecular survey. The blue triangles (L1517B data) and the red squares (L1498 data) indicate that order of magnitude corrections are needed in a number of species. The comparison between model and observations has been done at the fiducial outer radius defined in Sect. 4.2. The dashed and dotted lines indicate factor of 2 and 10 corrections, respectively.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{5311fig8.eps}} \end{figure}$ Figure 8: Comparison between the concentration ratios predicted by the Aikawa et al. (2005) model and the observations of L1498 (red squares) and L1517B (blue triangles). A value equal to 1 indicates that the model predicts emission with the same central concentration as observed, a value larger than 1 indicates that the model is more concentrated than the data (small central hole), and a value less than 1 indicates a model prediction flatter than the data (too large a hole). There is an overall (factor of 2) agreement between model and data, although the L1517B data seems systematically lower than 1. The model therefore overestimates the central hole seen in L1517B.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{5311fig9.eps}} \end{figure}$ Figure 9: Effect of depletion on the different lines and transitions observed in the survey. The y-axis represents the ratio between the central intensities of a constant abundance model and the best fit model for each of the lines observed in L1498 (red squares) and L1517B (blue triangles). Large values indicate a strong effect of the central depletion in the emission from the core center.
Open with DEXTER

In the text

$\begin{figure} \par\resizebox{15cm}{!}{\includegraphics{5311fig0.eps}} \end{figure}$ Figure 10: Normalized contribution functions of representative species in L1517B (the observer is at large radius, i.e., to the far right of each panel). The red solid and dotted lines are the contribution functions, while the black dashed lines indicate the normalized density profile shown for reference (the normalized square of the density profile is also shown for CH₃OH). In the best fit models ( right column), the solid line corresponds to our simple abundance step function, while the dotted lines are the contribution functions expected for the abundance profiles predicted by the Aikawa et al. (2005) models (scaled appropriately to fit the L1517B data). In each panel, the vertical dashed lines indicates the radius at which half of the total emission is reached. Note how in the moderately thick C¹⁸O(2-1) and extremely thick HCO⁺(1-0) lines most of the emission arises from the front outer layer of the core.
Open with DEXTER

In the text

$\begin{figure}\par\resizebox{8.8cm}{!}{\includegraphics{5311figa.eps}} \end{figure}$ Figure B.1: Spectra towards L1498 illustrating the presence of a red gas component. The bottom (H¹³CN) line shows that the LSR velocity of the cloud is about 7.8 km s^-1(vertical line). The HCN line (next up) shows a deep red self-absorption and a low level red wing, while the CO isotopologue lines show an increasing contribution of the red component with abundance. The coincidence of the red component with the absorption in HCN (also HCO⁺ and CS) suggests that the component lies in front of the L1498 core.

In the text

$\begin{figure}\par\resizebox{8.8cm}{!}{\includegraphics{5311figb.eps}} \end{figure}$ Figure C.1: Comparison of L1498 data taken from the literature (solid squares) with the predictions of the best fit model of Sect. 4.2 (red lines). The top three panels show that the model fits well the C₂S radial profiles generated from the data of Wolkovitch et al. (1997). The bottom two panels show that the model fits well the H₂CO(3₁₂-2₁₁) line of Young et al. (2004), but fails to fit the H₂CO(1₁₁-1₁₀) line (from the same authors), which appears in absorption against the cosmic background. To illustrate the sensitivity of the 1₁₁-1₁₀ absorption to the core low density gas, a model with a backside envelope is shown in blue dashed lines (see text).

In the text

$\begin{figure} \par\resizebox{15.9cm}{!}{\includegraphics{5311fig2.eps}} \end{figure}$	Figure 2: Same as Fig. 1 but for the L1517B core. Central coordinates are $\alpha_{1950}=4^{\rm h}52^{\rm m}7\hbox{$.\!\!^{\rm s}$ }2$ , $\delta_{1950}=30\degr33'18\hbox{$.\!\!^{\prime\prime}$ }0$ .
Open with DEXTER

$\begin{figure} \par\resizebox{15cm}{!}{\includegraphics{5311fig4.eps}} \end{figure}$	Figure 4: Same as Fig. 3 but for the L1517B core.
Open with DEXTER

$\begin{figure} \par\resizebox{8.8cm}{!}{\includegraphics{5311fig9.eps}} \end{figure}$	Figure 9: Effect of depletion on the different lines and transitions observed in the survey. The y-axis represents the ratio between the central intensities of a constant abundance model and the best fit model for each of the lines observed in L1498 (red squares) and L1517B (blue triangles). Large values indicate a strong effect of the central depletion in the emission from the core center.
Open with DEXTER