Molecular Ions in L1544. I. Kinematics

By P. Caselli, C. Walmsley, A. Zucconi, M. Tafalla, L. Dore, P. Myers. 2001

163 citations recorded by the source corpus.

We have mapped the dense dark core L1544 in H13CO+ (1-0), DCO+ (2-1), DCO+ (3-2), N2H+ (1-0), N2H+ (3-2), N2D+ (2-1), N2D+ (3-2), C18O (1-0), and C17O (1-0) using the IRAM 30 m telescope. We have obtained supplementary observations of HC18O+ (1-0), HC17O+ (1-0), and D13CO+ (2-1). Many of the observed maps show a general correlation with the distribution of dust continuum emission, in contrast to C18O (1-0) and C17O (1-0), which give clear evidence for depletion of CO at positions close to the continuum peak. In particular, N2D+ (2-1) and (3-2) and to a lesser extent N2H+ (1-0) appear to be excellent tracers of the dust continuum. Our DCO+ maps have the same general morphology as the continuum while H13CO+ (1-0) is more extended. We find also that many apparently optically thin spectral lines such as HC18O+ and D13CO+ have double or highly asymmetric profiles toward the dust continuum peak. We have studied the velocity field in the high-density nucleus of L1544, putting particular stress on tracers such as N2H+ and N2D+, which trace the dust emission and which we therefore believe trace the gas with density of order 105 cm-3. We find that the tracers of high-density gas (in particular, N2D+) show a velocity gradient along the minor axis of the L1544 core and that there is evidence for larger line widths close to the dust emission peak. We interpret this using the model of the L1544 proposed by Ciolek and Basu and by comparing the observed velocities with those expected on the basis of their model. The results show reasonable agreement between observations and model in that the velocity gradient along the minor axis and the line broadening toward the center of L1544 are predicted by the model. This is evidence in favor of the idea that ambipolar diffusion across field lines is one of the basic processes leading to gravitational collapse. However, the double-peaked nature of the profiles is reproduced only at the core center and if a "hole" in the molecular emission, due to depletion, is present. Moreover, line widths are significantly narrower than observed and are better reproduced by the Myers & Zweibel model, which considers the quasi-static vertical contraction of a layer due to dissipation of its Alfvénic turbulence, indicating the importance of this process for cores on the verge of forming a star.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/9857a2a19903b87481c9bcc9597f3c789f194b84

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In Astronomy and Astrophysics

1. P. Caselli
2. E. Bergin
3. M. Tafalla
4. N. Evans II
5. E. Herbst
6. Cecilia Ceccarelli
7. P. Myers
8. Ralf Klessen

In Instrumentation

1. N. Evans II
2. P. Myers
3. P. Caselli
4. M. Tafalla
5. E. Herbst
6. E. Bergin
7. Cecilia Ceccarelli
8. A. Crapsi

Citations in the corpus

• Water in Star-forming Regions with the Herschel Space Observatory (WISH). I. Overview of Key Program and First Results (2010, background): “Several of these so-called prestellar cores are thought to be on the verge of collapse and thus represent the earliest stage in the starformation process (e.g., Tafalla et al. 1998; Caselli et al. 2002; Crapsi et al. 2005).”
• Molecular Evolution in Collapsing Prestellar Cores. III. Contraction of a Bonnor-Ebert Sphere (2004, methodology): “Caselli et al. (2002a) obtained column density ratios for N(DCO+)/N(HCO+) and N(N2D +)/N(N2H +) towards the dust peak of L1544 of 0.04 and 0.2, respectively.”
• The degree of CO depletion in pre-stellar cores ? (2002, background): “CO depletion in dense cores has already been discussed by Kramer et al. (1999), Willacy et al. (1998), and Caselli et al. (1999, 2002a, 2002b) who focussed on L1544, a core similar to the ones we discuss in this work.”
• On The Internal Structure Of Starless Cores. Physical and Chemical Properties of L1498 and L1517B (2004, unknown): “We have presented detailed models of the internal structure of two close-to-round starless cores in the nearby Taurus-Auriga star formation complex, L1498 and L1517B.”
• THE ORIGIN OF COMPLEX ORGANIC MOLECULES IN PRESTELLAR CORES (2014, background): “In conclusion, L1544 is a core on the verge of collapsing (Caselli et al. 2002; Keto et al. 2014).”
• Interstellar Turbulence I: Observations and Processes (2004, background): “The rotational properties of molecular clouds and cores have been investigated by several groups (e.g., Goldsmith & Arquilla 1985, Goodman et al. 1993, Caselli et al. 2002).”
• Systematic Molecular Differentiation in Starless Cores (2001, methodology): “The cores were selected from previous work (Caselli et al. 2002a) for having nearly circular contour maps.”
• Dense Cores in Dark Clouds. XIV. N2H+ (1-0) Maps of Dense Cloud Cores (2002, methodology): “The agreement between dust and N2H + profiles suggests that the molecular gas traced by the N2H + line is not significantly depleted in relation to the dust, unlike CO and CS (Caselli et al. 1999, 2002a, 2002b; Bergin et al. 2001; Tafalla et al. 2002).”
• The Spitzer c2d Survey of Nearby Dense Cores. II. Discovery of a Low-Luminosity Object in the “Evolved Starless Core” L1521F (2006, background): “As noted in §1, prior to Spitzer L1521F was one of the two best examples of an evolved starless core, the other being the well studied core L1544 (Tafalla et al. 1998; Caselli et al. 2002; Crapsi et al. 2005a).”
• Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “The effects of freeze-out can alter both the pre-factor and the exponent of the density dependence (Bergin & Langer 1997; Caselli et al. 2002c; Walmsley et al. 2004), but see also Ciolek & Mouschovias (1998).”
• Probing the Evolutionary Status of Starless Cores through N2H+ and N2D+ Observations (2004, methodology): “Another possibility is that depletion of N2 (and hence of N2H + andN2D +) may occur in regions with density higher than 5 ;105 cm 3 (see also Caselli et al. 1999, 2002c; Bergin et al. 2001; Crapsi et al. 2004; Belloche & André 2004).”
• Observing the gas temperature drop in the high-density nucleus of L 1544 (2007, methodology): “The central velocity information was used to compute the velocity gradient across the core, in analogous fashion to Caselli et al. (2002a) using N2H+ and N2D+.”
• On the internal structure of starless cores II. A molecular survey of L1498 and L1517B (2006, background): “In the larger and better resolved L1498 core, the maps of C3H2, H2CO, CH3OH, SO, HCO+ (plus isotopes), HCN (plus isotope), HC3N, and C2S all present distributions that differ from the centrally concentrated dust or N2H+.”
• Molecular Cloud Formation behind Shock Waves (2004, unknown): “Observations of isolated pre-stellar molecular cores, such as L1544 in the Taurus Molecular Cloud, have provided fertile ground for comparison to these theories (Caselli et al 2002; Ciolek & Basu 2000; Williams et al 1999; Tafalla et al 1998).”
• Complete depletion in prestellar cores (2004, background): “Estimates of the ionization degree in L 1544 (Caselli et al. 2002a) are of order 2 10−9.”