J/AJ/132/1851 Arecibo obs. of formaldehyde in L1551 (Araya+, 2006)
Arecibo observations of formaldehyde in L1551.
Araya E., Hofner P., Olmi L., Kurtz S., Linz H.
<Astron. J., 132, 1851-1858 (2006)>
=2006AJ....132.1851A 2006AJ....132.1851A
ADC_Keywords: Molecular clouds ; Spectroscopy ; Models
Keywords: ISM: individual (L1551) - ISM: molecules - radio lines: ISM -
stars: formation
Abstract:
We report observations of the formaldehyde (H2CO) 6cm (4.8GHz) line
toward L1551. The observations were conducted with the Arecibo
Telescope (beam FWHP∼1') to verify the tentative detection of H2CO
thermal emission reported by Duncan and collaborators in
1987MNRAS.224..721D 1987MNRAS.224..721D. The H2CO emission lines were expected to be
present with a signal-to-noise ratio of ≳10 in our spectra. However,
we did not detect H2CO emission; i.e., our data rule out their
tentative detection. The absence of H2CO emission is also confirmed
by the fact that the H2CO line profiles at the two positions of
expected emission are well fitted by a single absorption component
(accounting for the hyperfine structure of the line) in one of the
positions and by a single absorption line plus a red-wing absorption
component in the second position. The Orion BN/KL region remains the
only H2CO 6cm thermal emitter known. Our observations also
demonstrate that the H2CO 6cm absorption line traces not only the
quiescent molecular cloud but also the kinematics associated with the
star formation process in L1551-IRS5.
Description:
The observations were conducted from 2004 December 13 to 19 with the
305m Arecibo Radio Telescope.
Objects:
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RA (2000) DE Designation(s)
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04 31 30.0 +18 12 20 L1551 = LDN 1551
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 60 64 Model Results
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See also:
J/A+A/318/879 : IR photometry of L1551/IRS5 (Men'shchikov+ 1997)
J/A+A/420/945 : L1551 ISOCAM observations (Galfalk+, 2004)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 arcmin oRA Offset along Right Ascension (1)
4- 5 I2 arcmin oDE Offset along Declination (1)
7- 10 F4.2 K Tex0 Excitation temperature lower limit
12- 15 F4.2 K Tex1 Excitation temperature upper limit
17- 20 F4.2 --- tau0 Optical depth lower limit
22- 25 F4.2 --- tau1 Optical depth upper limit
27- 30 F4.2 km/s DelV0 Line width lower limit
32- 35 F4.2 km/s DelV1 Line width upper limit
37- 40 F4.2 km/s VLSR0 The F=2-2 hyperfine component
LSR velocity, lower limit
42- 45 F4.2 km/s VLSR1 The F=2-2 hyperfine component
LSR velocity, upper limit
47- 52 F6.2 --- chi2 χ2 value (2)
54- 58 F5.2 --- Dchi2 ? Different χ2 value for
DelV and VLSR ranges (3)
60 A1 --- Wing [c] Presence of wings (4)
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Note (1): Reference position is 04:31:21.8+18:05:54 (J2000).
Note (2): When χ2 values of less than 23.5 were obtained, we explored
the convergence of the parameters at fixed χ2 levels, i.e.,
χ2=4.72, 7.78, 9.70, 13.3, 16.3, and 23.5 levels, which
correspond to confidence levels of 68.3%, 90.0%, 95.4%, 99.0%, 99.73%,
and 99.99% for a four-degrees-of-freedom χ2 fitting (Press et
al., 1999, Numerical Recipes in C (2nd ed.; Cambridge: Cambridge Univ.
Press) ). When convergence better than the χ2=23.5 value was not
achieved, then arbitrary χ2 levels were used.
Note (3): In some cases the DelV and VLSR parameters converge within given
χ2 value, whereas the tau and Tex parameters show multiple
solutions for the same χ2 contour level. For those cases we
report DelV and VLSR ranges for a different χ2 contour level
than the one used to obtain the tau and Tex ranges.
Note (4): Presence of wings precluded a reliable fit of the complete line
profile. See lower panels of Figure 6 as example.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 23-Jul-2008