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 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:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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1- 6 A6 --- Name Core identifier
8- 10 I3 pc Dist [140/250] Distance
from Crapsi+ 2005ApJ...619..379C 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 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 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)
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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 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 2011ApJ...734...60L) also classify L492 as a
"contracting core" based on infall asymmetries determined from CS, HCN,
and N2H+ spectra.
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Byte-by-byte Description of file: table[345].dat
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Bytes Format Units Label Explanations
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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
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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)
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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).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 19-Apr-2017