Far from the NANTEN Telescope (a.k.a. What regions have been observed
now in CO in the Southern Hemisphere, and what can be said about
CfA Star Formation
Journal Club, November 3, 1999, Alyssa
- C18O (J=1-0) is at 109.78 GHz
- 13CO (J=1-0) is at 110.20 GHz
- A 4-m telescope at 110 GHz has 1.2l/D of 2.7
- Joint venture of Nagoya University and Carnegie
Institution, located on Las Campanas in Chile
- Receiver uses 4 K cryogenically cooled Nb
S-I-S mixer which gives Tsys~140 K near
zenith at 3 mm
- Spectrometer is AOS with 2048 channels and
usual BW=40 MHz
- Typical frequency resolution is 40 kHz, giving
0.1 km s-1 at 3 mm
- What are effects of depletion and/or optical
depth on ability of C18O (J=1-0) to trace dense gasdoes
this line really trace"cores"?
- Is resolution an issue w.r.t. the above question?
(See L1251 example).
The papers summarized in the table below
are all to appear in an upcoming special issue of the Publications
of the Astronomical Society of Japan, and were presented by Y.
Fukui, A. Mizuno et al. at the October 1999 ALMA meeting at the
Carnegie Institution of Washington. Papers& abstracts already
published are listed in the ADS printout handout.
|Hara et al.
||A Study of Dense Cloud Cores
and Star Formation in Lupus: C18O and 13CO
J=1-0 Observations with NANTEN
- Distances ~150 pc
- C18O is done as follow-up to 13CO,
in regions where 13CO column density is high.(see
- YSO density (including TTS) correlated with C18O
"core" distribution (e.g. Fig.
- Typical C18O Core properties: 9.7 Msun;
0.17 pc; 4.1 ¥ 1021
cm-2; 0.90 km s-1 (see Fig.
- Mass spectrum dN/dM~M-1.7± 0.6 for M>3Msun
- Claim is that Taurus is unusual in having
very small Mvir/Mcore; Lupus more like
Oph North or L1333 (see Figs
- t(C18O) is determined
from 12CO excitation temperature (true for most of
the NANTEN papers)
- Is depletion of C18O (as found by Kramer
et al. 1999 above 10 mag AV) a problem?
- General comment--for discussion: Is a C18O
clump really a "core"? (See L1251 example in handouts
from Toth & Walmsley 1996; Goodman
et al. 1998)
Mizuno et al.
(see also Mizuno et al. 1998, ApJL, 507, L83.)
|Dense Cores and Star
Formation Activities in the Chamaeleon Dark-Cloud Complex
- Distances ~150 pc
- Star formation activity highest in Cha I and lowest in Cha
III (evolutionary sequence suggested where Cha I is most "gravitationally
relaxed"). Cha I comparable with Taurus.
- Typical C18O Core properties: 22 Msun;
0.22 pc; 9.7 ¥ 1021
cm-2; 0.82 km s-1
- "Threshold Effect" proposed as explanation for
better correlation of CTTS (actually YSOs identified with DENIS)
with areas with N>1022 cm-2 (see Figs. 8-12) Effect strongest for sources
with FIR excess.
|Mizuno et al. 1998
suggested cloud dissipation by ouflows to explain lack of (13CO-traced)
molecular gas around many (X-ray identified) YSOs in the area.
(see their Fig 1 & 3) Does
IR identification (rather than X-ray, etc.) choose a different
set of YSOs? Does C18O trace
different gas than 13CO? IR
vs. X-ray identification alone can explain apparent discrepancies
between Mizuno et al 98 & 99, but line choice may matter
|Hayakawa et al.
||A New Derivation of the Extinction-to-CO
Column Density Ratio in the Chamaeleon I Dark Cloud
- Table 1a presents summary of
all previous AV-N(13CO) relations and the
- Figure 5 shows significant region-to-region
variations in correlation slope, even just within Chamaeleon.
Slope is steeper (¥ 2) near cluster
|Neither 13CO nor
C18O observations in this paper probe range above
10 mag AV, so no comments on Kramer et al. 1999 depletion
results. The jury's still out on whether the dust in
these regions is the best tracer of the matter, or whether spectral
lines are reliable.
|Yonekura et al.
||NANTEN Observations of Dense
Cores in Corona Australis Molecular Cloud
- 2.2 sq. deg area observed, nearly 2000 spectra
- Identified 8 "C18O cores"
- Typical C18O Core properties: 18 Msun;
0.13 pc; 1.1 ¥ 1022
cm-2; 0.66 km s-1 ; 1.4 ¥
- For most "active" star-forming core(s?), line width,
column density, size, mass and density are all higher than average,
and M is also higher w.r.t. virial mass (see Fig.
|What was YSO sourcelist source?
(e.g. are any embedded sources missing?) Results are
intriguing, but sample is very small.
|Saito et al.
||A study of the molecular cloud
toward HII regions S35 and S37 with NANTEN
12CO, C18O, 13CO
- 10 sq. deg. observed
- GMC found with ~1.3 ¥ 105
- Extends ~100 pc off plane
- Four strong outflows discovered, in addition to one previously
known, all associated with C18O clumps
- CO is located at the edge of an H I hole that has 55 pc radius
- Supershell proposed as origin of GMC
|HH80/81 is in this region Supershell
ass'n. very interesting
|Yamaguchi et al.
||Molecular Clouds and Star Formation
in the Southern HII Regions
- 23 H II regions observed
- Significant increase of SF activity on side of molecular
clouds facing H II region
- Suggestion is that about 30% of stars in the M.W. form through
such compression by H II regions
|Someone should review this very
long paper, on its own, for J.C.