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J/ApJ/526/788 Survey of infall motions toward starless cores (Lee+, 1999)
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A survey of infall motions toward starless cores. I. CS (2-1) and
N_2_H^+^ (1-0) observations
Lee C.W., Myers P.C., Tafalla M.
<Astrophys. J. 526, 788 (1999)>
=1999ApJ...526..788L
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ADC_Keywords: Interstellar medium ; Radio sources ; Molecular clouds
Keywords: ISM: globules - ISM: kinematics and dynamics - ISM: molecules -
stars: formation
Abstract:
We present the first results of a survey of 220 starless cores
selected primarily by their optical obscuration and observed in
CS (2-1), N_2_H^+^ (1-0), and C^18^O (1-0) using the Northeast Radio
Observatory Corporation (NEROC) Haystack 37 m telescope. We have
detected 163 out of 196 sources observed in CS, 72 out of 142 in
N_2_H^+^, and 30 out of 30 in C18O. In total, 69 sources were detected
in both CS and N_2_H^+^. The isolated component of the N_2_H^+^ (1-0)
spectrum (F_1_F = 0,1-1,2) usually shows a weak symmetric profile that
is optically thin. In contrast, a significant fraction of the CS
spectra show non-Gaussian shapes, which we interpret as arising from a
combination of self-absorption due to lower excitation gas in the core
front and kinematics in the core. The distribution of the normalized
velocity difference ({delta}V_CS_) between the CS and N_2_H^+^ peaks
appears significantly skewed to the blue (V_CS_ < 0), as was found in
a similar study of dense cores with embedded young stellar objects
(YSOs). The incidence of sources with blue asymmetry tends to increase
as the total optical depth or the integrated intensity of the N_2_H^+^
line increases.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 78 151 Starless Cores Observed in CS, N_2_H^+^,
and C^18^O
table2.dat 116 69 Parameters of starless cores observed in both
CS and N_2_H^+^
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See also:
J/A+A/288/601 : Dense molecular cores (Zinchenko+ 1994)
J/A+AS/111/95 : Studies of dense molecular cores (Zinchenko+, 1995)
J/A+AS/118/191 : Multitransition CS-study towards H2O masers (Juvela, 1996)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name
12 A1 --- f_RAh [cd] Indicates source position obtained
elsewhere (1)
15- 16 I2 h RAh Right Ascension (B1950) from
Lee+ (1999ApJS..123..233L)
18- 19 I2 min RAm Right Ascension (B1950) from Lee+ (1999)
21- 24 F4.1 s RAs Right Ascension (B1950) from Lee+ (1999)
27 A1 --- DE- Declination (B1950) from Lee+ (1999)
28- 29 I2 deg DEd Declination (B1950) from Lee+ (1999)
31- 32 I2 arcmin DEm Declination (B1950) from Lee+ (1999)
34- 35 I2 arcsec DEs Declination (B1950) from Lee+ (1999)
37- 41 F5.2 km/s VCS ? Velocity of CS
43- 44 A2 --- f_VCS [ND] Indicates object was not detected in CS
46- 49 F4.2 km/s e_VCS ? Error in VCS
51- 55 F5.2 km/s VN2H ? Velocity of N_2_H
57- 58 A2 --- f_VN2H [ND] Indicates object was not detected
in N_2_H^+^
60- 64 F5.3 km/s e_VN2H ? Error in VN2H
65- 69 F5.2 km/s VC18O ? Velocity of C^18^O
75- 78 F4.2 km/s e_VC18O ? Error in VC18O
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Note (1):
c = Source position from Benson & Myers (1989ApJS...71...89B)
d = Source position from the FCRAO map (C. W. Lee, P. C. Myers, & M.
Tafalla, in preparation)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Source name
12 A1 --- f_RAh [fg] Indicates source position obtained
elsewhere (1)
14- 15 I2 h RAh Right Ascension (B1950) from
Lee+ (1999ApJS..123..233L)
17- 18 I2 min RAm Right Ascension (B1950) from Lee+ (1999)
20- 23 F4.1 s RAs Right Ascension (B1950) from Lee+ (1999)
25 A1 --- DE- Declination (B1950) from Lee+ (1999)
26- 27 I2 deg DEd Declination (B1950) from Lee+ (1999)
29- 30 I2 arcmin DEm Declination (B1950) from Lee+ (1999)
32- 33 I2 arcsec DEs Declination (B1950) from Lee+ (1999)
36- 40 F5.2 km/s VCS ? Velocity of CS
43- 46 F4.2 km/s e_VCS ? 1{sigma} error in VCS
49- 53 F5.2 km/s VN2H ? Velocity of N_2_H
56- 59 F4.2 km/s e_VN2H ? 1{sigma} error in VN2H
62- 66 F5.2 km/s VC18O ? Velocity of C^18^O
69- 72 F4.2 km/s e_VC18O ? 1{sigma} error in VC18O
75- 79 F5.2 km/s FWHM ? FWHM of N_2_H
82- 85 F4.2 km/s e_FWHM ? 1{sigma} error in FWHM
89- 92 F4.1 km/s Tau ? Optical depth of N_2_H
96- 99 F4.1 km/s e_Tau ? 1{sigma} error in Tau
101 A1 --- f_Tau [e] Indicates values are difficult to
ensure because S/N < 5
103-107 F5.2 km/s DCS ? Normalized velocity difference of CS (2)
110-113 F4.2 km/s e_DCS ? 1{sigma} error in DCS
115 A1 --- n_DCS [h] Note on DCS (3)
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Note (1):
f = Source position from Benson & Myers (1989ApJS...71...89B)
g = Source position from the FCRAO map (C. W. Lee, P. C. Myers, & M.
Tafalla, in preparation)
Note (2): The normalized velocity difference, VCS, is defined as
V_CS_ = (V_CS_ - V_N_2_H^+^_)/FWHM_N_2_H^+^_
Note (3): These two sources (L1544 and L429-1) have an intensity ratio of the
blue to the red peak in CS spectra close to 1.0 within error.
The CS peak velocities for these two were obtained by the
Gaussian fit after masking a fainter peak between two components,
although the difference between two is less than 1{sigma}. We do
not use these CS optical depth values in our statistics.
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History:
From ApJ electronic edition
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(End) Greg Schwarz [AAS] 16-Mar-2000