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J/ApJ/833/97     Infall/expansion velocities in 3 dense cores     (Keown+, 2016)

Infall/expansion velocities in the low-mass dense cores L492, L694-2, and L1521F: dependence on position and molecular tracer. Keown J., Schnee S., Bourke T.L., Di Francesco J., Friesen R., Caselli P., Myers P., Williger G., Tafalla M. <Astrophys. J., 833, 97-97 (2016)> =2016ApJ...833...97K (SIMBAD/NED BibCode)
ADC_Keywords: Molecular clouds ; Millimetric/submm sources Keywords: stars: formation; stars: protostars Abstract: Although surveys of infall motions in dense cores have been carried out for years, few surveys have focused on mapping infall across cores using multiple spectral-line observations. To fill this gap, we present IRAM 30m telescope maps of N2H+(1-0), DCO+(2-1), DCO+(3-2), and HCO+(3-2) emission toward two prestellar cores (L492 and L694-2) and one protostellar core (L1521F). We find that the measured infall velocity varies with position across each core and choice of molecular line, likely as a result of radial variations in core chemistry and dynamics. Line-of-sight infall speeds estimated from DCO+(2-1) line profiles can decrease by 40-50m/s when observing at a radial offset ≥0.04pc from the core's dust continuum emission peak. Median infall speeds calculated from all observed positions across a core can also vary by as much as 65m/s, depending on the transition. These results show that while single-pointing, single-transition surveys of core infall velocities may be good indicators of whether a core is either contracting or expanding, the magnitude of the velocities they measure are significantly impacted by the choice of molecular line, proximity to the core center, and core evolutionary state. Description: Our data were obtained at the IRAM 30m single-dish telescope in Pico de Veleta, Spain from 2002 July-December. Each core was observed in frequency-switching mode. Frequency windows were centered on N2H+(1-0) at 93.174GHz, DCO+(2-1) at 144.077GHz, DCO+(3-2) at 216.113GHz, and HCO+(3-2) at 267.558GHz. Beam widths were 27.0", 17.5", 11.6", and 9.4" FWHM for each transition, respectively. See section 2 for further details. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 49 3 Summary of dense core properties from the literature table3.dat 83 42 L492 infall/expansion measurements table4.dat 83 72 L694-2 infall/expansion measurements table5.dat 83 42 L1521F infall/expansion measurements
See also: J/A+A/584/A91 : Dense cores in Aquila from Herschel (Konyves+, 2015) J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008) J/ApJS/175/277 : Submillimeter-Continuum SCUBA detections (Di Francesco+, 2008) J/ApJ/664/928 : Starless cores in HCN(J=1-0) (Sohn+ 2007) J/A+A/432/369 : Leiden Atomic and Molecular Database (LAMDA) (Schoeier+, 2005) J/ApJS/153/523 : Starless cores in CS(3-2) and DCO+(2-1) lines (Lee+, 2004) J/ApJ/578/914 : Low-mass stars in Taurus (Hartmann, 2002) J/ApJ/526/788 : Survey of infall motions toward starless cores (Lee+, 1999) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 6 A6 --- Name Core identifier 8- 10 I3 pc Dist [140/250] Distance from Crapsi+ 2005ApJ...619..379C 12- 16 F5.1 arcsec Rad Radius in arcsec 17 A1 --- r_Rad Reference for rad (1) 19- 23 F5.3 pc Radpc [0.05/0.2] Radius in parsec 25- 27 F3.1 Msun Mass Mass 28 A1 --- r_Mass Reference for Mass (1) 30- 33 F4.2 --- D/H [0.05/0.3] deuterium fractionation N(N2D+)/N(N2H+) from Crapsi+ 2005ApJ...619..379C 35- 38 F4.2 --- e_D/H [0.01/0.05] D/H uncertainty 40- 43 F4.2 km/s HCO+ [0.1/0.5]? HCO+ (3-2) infall velocity from Schnee+ 2013ApJ...777..121S 45- 48 F4.2 km/s e_HCO+ ? HCO+ uncertainty 49 A1 --- f_HCO+ [d] Flag on L492 infall asymmetry in HCO+ (3-2) (2)
Note (1): Reference as follows: c = Kauffmann et al. 2008, J/A+A/487/993 e = Di Francesco et al. 2008, J/ApJS/175/277 Note (2): d = Although Schnee+ (2013ApJ...777..121S) labeled L492 as a "static core" due to the subtlety of its infall asymmetry in HCO+(3-2), this core has been classified as a "contracting core" by Sohn+ (2007, J/ApJ/664/928) due to infall asymmetries in all three hyperfine components of HCN(1-0). Lee & Myers (2011ApJ...734...60L) also classify L492 as a "contracting core" based on infall asymmetries determined from CS, HCN, and N2H+ spectra.
Byte-by-byte Description of file: table[345].dat
Bytes Format Units Label Explanations
1- 2 I2 --- Seq Spectrum observation number 4- 6 I3 arcsec dRA Offset from central pointing, in RA, arcsec (1) 8- 10 I3 arcsec dDE Offset from central pointing, in DE, arcsec (1) 12- 17 F6.3 km/s dVin1 [-0.2/0.2] N2H (1-0) infall/expansion velocity (G1) 19- 23 F5.3 km/s e_dVin1 [0/2.5] Uncertainty in dVin1 25- 29 F5.1 --- SNR1 [2/130] N2H (1-0) spectrum signal to noise ratio 31- 36 F6.3 km/s dVin2 [-0.3/0.5]? DCO+ (2-1) infall/expansion velocity (G1) 38- 42 F5.3 km/s e_dVin2 [0/7]? Uncertainty in dVin2 44- 47 F4.1 --- SNR2 [2/68]? DCO+ (2-1) spectrum signal to noise ratio 49- 54 F6.3 km/s dVin3 [-0.3/0.6]? DCO+ (3-2) infall/expansion velocity (G1) 56- 60 F5.3 km/s e_dVin3 [0/9]? Uncertainty in dVin3 62- 65 F4.1 --- SNR3 [2/47]? DCO+ (3-2) spectrum signal to noise ratio 67- 72 F6.3 km/s dVin4 [-0.2/0.3]? HCO+ (3-2) infall/expansion velocity (G1) 74- 78 F5.3 km/s e_dVin4 [0/6]? Uncertainty in dVin4 80- 83 F4.1 --- SNR4 [2/25]? HCO+ (3-2) spectrum signal to noise ratio
Note (1): For L492 (table 3), offset from map's central pointing: 18:15:46.08, -03:46:12.8 (J2000) For L694-2 (table 4), offset from map's central pointing: 19:41:04.5, +10:57:02 (J2000) For L1521F (table 5), offset from map's central pointing: 04:28:39.8, +26:51:15 (J2000)
Global note: Note (G1): Measured infall (positive) or expansion (negative) velocity. Blank entries indicate the position was not observed using the given column's tracer. An uncertainty value = 0.000 indicates a low SNR spectrum for which MPFIT was unable to calculate an uncertainty (these sources were omitted from all analyses presented in this paper).
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Apr-2017
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