Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/whats_on/workshops/mm_science2002/talks/twong.pdf Äàòà èçìåíåíèÿ: Tue Nov 26 05:49:42 2002 Äàòà èíäåêñèðîâàíèÿ: Wed Dec 26 08:12:18 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: annular solar eclipse

Dense Gas in the LMC and the Circumstellar Shell of R Scl
Tony Wong, ATNF
Millimetre Workshop 21 Nov 2002 With: John Whiteoak, Maria Hunt, Michael Lindqvist, Hans Olofsson


1. Dense Gas in the LMC
· At a distance of ~50 kpc (1" = 0.25 pc), the LMC is the nearest actively star-forming galaxy. · Low metallicity (~0.25 Z!) less dust very different interstellar environment! · Due to strong FUV field, most molecular gas will be in photon-dominated regions (PDRs). · Initial target: N113 cloud, observed with SEST by Chin et al. (1997). · The Future: Take advantage of CO survey at 160" resolution conducted with 4m NANTEN telescope (N. Mizuno et al.) · Follow up with SEST, Mopra, and ATCA.
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HCO+/HCN in N113

Chin et al. 1997

· SEST 58" beam · Tmb(HCO+) 0.6 K · Flux 15 Jy
Fukui et al. 2001
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Massive Star Formation in N113

NANTEN CO contours over H image from Kennicutt

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First ATCA Observations
HCO
+

· 9 Jul 2001, single baseline · Additional observations on 10 Jul and with 3-element system on 4 and 8 Oct. · No Tsys or flux calibration ­ assumed fluxes for calibrators.
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HCN


Emission is Heavily Resolved
75m

120m

45m

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2002 Observations
90m

135m

45m

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Integrated Spectrum

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Conclusions for N113 core
· Deconvolved FWHM 1.5 pc R ~ 1 pc. · Line width v ~ 5 km s-1. · For a virialized cloud, ignoring optical depth effects, M 200(Rpc)(vkm/s)2 5000 M". · For constant density, nH ~ 5 x 104 cm-3. · Peak flux ~ 2 Jy, only ~13% of SEST flux. · Most of the HCO+ is probably in relatively diffuse gas associated with the PDR. · HCO+ enhanced due to high C+ abundance (Graedel et al. 1982).
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2. Circumstellar Envelopes
· In late AGB evolution, a slow wind produces a circumstellar envelope (CSE) of gas & dust. · Strong variations in mass-loss rate (He shell flashes?) can lead to a detached shell of molecular gas (Olofsson et al. 1990). U Cam (CO) Lindqvist et al. (1999)

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Circumstellar Shell Around R Scl
· R Sculptoris has been inferred from SEST CO (3-2) observations to have a detached shell (Olofsson et al. 1996). · However, the data had insufficient resolution (16") to determine the mass loss rate or shell thickness.
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ATCA Observations
61m 92m 31m EW214 02JUN21

171m

111m

61m H168 02OCT13

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ATCA Observations
138m 413m 275m 750A 02OCT15

138m

413m

275m 750A 02OCT18

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No shell emission (3 = 75 mJy)

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Peak flux ~1.3 Jy

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Central source is resolved
source FWHM 1" (400 AU)

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Not decorrelation!

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Not decorrelation!

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Conclusions for R Scl
· HCN (1-0) emission has been resolved with a deconvolved FWHM 1" (400 AU). · Peak flux ~ 1.3 Jy, virtually all of SEST flux (0.05 K x 25 Jy/K). S/N ratio of ~40. · No evidence for emission from the R 10" shell inferred from CO data, or R 20" shell seen in scattered light (Gonzalez Delgado et al. 2001). · HCN is probably emitted from present mass-loss envelope. Dissociation of HCN CN probably leads to low HCN abundance in the CO shell. · Would be interesting to image the CN line at 113.3 GHz, as well as CO and/or 13CO.
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An Overview of the 3mm System in 2003
Tony Wong, ATNF
Millimetre Workshop 21 Nov 2002


Current System (2001 Sep)
· 3 antennas (CA02, CA03, CA04) with dual polarisation receivers. · 2 observing bands: 84.9-87.3 and 88.5-91.3 GHz. Module swap at antenna required to change bands. · Up to 128 MHz bandwidth in each of 2 frequencies. · Minimum baseline 30m. · Both N-S and E-W configurations possible (since 2002 Aug).
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3mm Receiver System
84.9-87.3 GHz

80.5 GHz

· At present, the tuning range is limited since we are using a fixed frequency LO at 80.5055 GHz. · The sky frequency range is 84.9-87.3 GHz using the Cband filter module or 88.5-91.3 GHz using the X-band module.
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3mm Receiver System
88.5-91.3 GHz

80.5 GHz

· At present, the tuning range is limited since we are using a fixed frequency LO at 80.5055 GHz. · The sky frequency range is 84.9-87.3 GHz using the Cband filter module or 88.5-91.3 GHz using the X-band module.
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Improvements in 2003
· Currently, C and X modules must be swapped manually to switch from one band to the other. · May: 3 antennas with prototype systems (CA02, CA03, CA04) get new down-conversion systems, eliminating need to swap modules. · Allows one to quickly switch to 86 GHz SiO masers for pointing, even when observing at 89-91 GHz. · Will NOT permit simultaneous observations at 86 and 90 GHz. · September: 4th antenna (CA01) may be equipped with "production" 3mm receiver, but frequency range not compatible with CA02/3/4.
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Priorities for Testing
· Pointing errors: there appears to be a systematic offset in antenna pointing between 9, 20, and 86 GHz (M. Kesteven). · Working on freq-dependent pointing model. · Phase errors: phase jumps when changing sources, seems to be mostly (or to mimic) a baseline error. · May need a freq-dependent baseline model ­ but errors appear to also vary in time! · Still more to be done...
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Baseline errors 2002
in mm, CA03 as reference

X2 EW214 750B H75 EW367 H168 750A
1.14 0.81 -1.83 -0.39 2.01 0.96

Y2
0.03 0.18 -3.96 1.11 0.60 0.36

Z2
-1.68 0.93 2.73 0.63 -1.11 0.03

X4
-0.75 -1.8

Y4
2.01 2.67

Z4
-2.37 0.78 6.33 -11.13 0.06 1.14
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-8.58 -10.38 12.06 -2.82 -0.99 2.46 1.83 -0.60


Planned configurations
· 2002 May term: EW214, EW367, 750C, 1.5C · Proposal deadline: 15 February!

EW214123 + EW367123 7.1" x 3.6" at = ­45°

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Suggested Projects
· Quasar absorption lines: can calibrate out most phase errors, u-v coverage unimportant. · Compact emission sources unresolved with SEST: can expect good S/N. · Ratios of 2 lines that can be observed simultaneously: less reliant on matched uv coverage. · Low dec (<­45°) sources: less shadowing in compact arrays · Anything that looked good today!
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Questions to Consider
1. Does the Australian user community accept the new timeline for the 3mm upgrade? 2. Does it have a choice? 3. Are there mechanisms in place to ensure that goals and deadlines are meaningful? 4. Does ATNF have its priorities straight? 5. Are we sufficiently involving the engineers in the scientific program? 6. Should the ATNF Steering Committee be asked to take action?
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