Arizona
Radio
Observatory
– HCO+ very abundant in molecular clouds
– It’s detection in circumstellar envelopes has been
elusive
– Models of oxygen-rich circumstellar envelopes
predicting the presence of HCO+ are sparse
– Only recently detected around one oxygen-rich
star, VY CMa
Continuing the search for HCO+
around o-rich evolved stars
Evolved stars
Oxygen-rich chemistry
C/O ratio is less than 1
PLANETARY NEBULA
Stellar envelope completely
detached
3.40 —
6.00 —
Log
(L)
Log (L)
To
White
3.25
5.50—— Dwarf
• Most stars investigated
are in the early AGB
phase
• O-rich evolved stars
haven’t yet undergone
third dredge- up
40 MΘ
5.00——
3.10
AGB
He & H Shell
Burning Envelope
Triple -Process
H Shell
Burning
25 MΘ
4.50 —
2.95 —
4.00 —
2.80 —
4.30
PROTO-PLANETARY
NEBULA (PPN)
Nucleosynthesis stops
CRL2688
He Core
Burning
H Shell
Narrows
RED
GIANT
BRANCH
MAIN SEQUENCE
15 MΘ Burning
Hydrogen Core
First Dredge-up:
Sun
Surface Abundances Change
4.5
4.00
3.50
4.15
4.00
3.85
3.60
Log Log
(Te) (T )
e
• Modeling of o-rich circumstellar
envelopes of AGB stars by Mamon et
al. in 1987
• HCO+ abundance decreases as mass
loss rate increases
Mamon et al., ApJ, 323, 1987
• Recent observations show HCO+ in
this star (Ziurys et al., Nature, 1094,
2007)
– Oxygen-rich supergiant
– ~25 solar masses
– 2x10-4 Mʘ yr-1
– Calculated abundance of HCO+ :
2x10-8
Sun Kwok, Nature, 447, 2007
Figure Courtesy of Stefanie Milam
•The 12-m telescope on Kitt Peak
- Frequency range: 65-116 and 125-180 GHz
•The Sub-millimeter telescope on Mt. Graham
- Frequency range: 210-279, 320-375, and 600-720 GHz
Source
Star Type Mass Mass Loss Rate
(Mʘ)
(Mʘ yr-1)
NML Cyg1 Supergiant
Distance
(pc)
VLSR
(km s-1)
Coordinates
(B1950.0)
50
(1-2)x10-5
1800
-5.0
03:50:43.6 11:15:32.2
IK Tau2
AGB
1
(2-5)x10-6
250
34.5
20:44:33.8 39:55:57.0
TX Cam3
AGB
1
3x10-6
450
9.2
04:56:40.6 56:06:28.0
W Hya4
AGB
1
3.5x10-7
115
41.0
13:46:12.2 -25:40:12.0
Transition
J+1J
1  0
2  1
3  2
4  3
1Boboltz
Frequency
(MHz)
89188.523
178375.010
267557.526
356734.134
et al., ApJ, 545, 2000
et al., ApJ, 625, 2005
3Olofsson et al., A&A, 245, 1991
4Justtanont, et al., A&A, 417, 2005
2Boboltz
Wavelength
(mm)
3.4
1.7
1.1
0.8
Beam Size
(arcsecs)
70
35
28
21
Telescope
ARO 12m
ARO 12m
ARO SMT
ARO SMT
Current Observational Results:
•
IK Tau
•IK
Tau
• Detected the J=1-0 and J=3-2
•Detected
• J=3-2 blended the
with SOJ=1-0 and
•
W Hya
J=3-2
• W
• Hya
DetectedJ=1-0 and J=3-2
with SO2
•• •J=3-2
Narrow
lineblended
profiles
Detected
J=1-0 and
0.012
0.006
0.006
0.009
0.004
2
•
TX Cam
TX
• Cam
Narrow line profiles
• Proving more difficult
•• J=3-2
is more
not blended
Proving
difficult
The J=1-0 emerging from the noise
SO2 emerging from
•• with
The
J=1-0
The J=3-2
needs more integration
time
the noise
•• Contaminated
SO2 more
The J=3-2 with
needs
integration time
• NML
Cyg
• Contaminated
with SO2
• All four transitions
observed
• Both J=3-2 and J=4-3
blended with SO2
*
TTTRR**
R
42 hrs
36hrs
hrs
69
0.006
0.002
0.002
0.003
0.000
0.000
0.000
-0.002
-0.002
-0.003
0.003
0.006
0.006
0.002
0.004
*
•
J=3-2
is not blended with SO2
J=3-2
*
TTTA
AA
•
0.004
TXTau
Cam
IK
W
Hya
JJJ===111 000
J JJ===333 222
SO2
SO
2
SO
2
6430
hrs
hrs
100
hrs
0.004
0.001
0.002
0.002
0.000
0.000
0.000
-0.001
-0.002
-0.002
-0.002
-150
-100 -50 -50 0
-150
-150 -100
-100
-50
0
0 50
50
50100 100
150
100
150
-1
-1-1
/
km
/
km
s


LSR
LSR
/ km ss

LSR
150
200
200
0.005
66 hrs
0.006
*
*
TR / K
0.008
0.007
NML Cyg
J=1 0
TA / K
0.010
0.004
J=3
SO2
2
43 hrs
0.003
0.002
0.001
0.000
-0.001
-0.002
0.010
J=2
1
SO2
41 hrs
TA / K
*
0.004
J=4
3
62 hrs
0.006
0.008
*
TR / K
0.012
0.002
0.000
-0.002
-0.004
-0.008
-200
-150 -100
-50
0
50
-1
LSR / km s
100
150
200
-0.006
-200
-150 -100
-50
0
50
-1
 LSR / km s
100
150
200
• Preliminary analysis: constructed rotational diagram and determined
column densities
• Tentative agreement; need to calculate fractional abundances
Source
Column Density
(cm-2)
Tex
(K)
IK Tau
NML Cyg
TX Cam
W Hya
1.4 x1011
1.8 x1011
1.3 x1011
5.7 x1010
8
8
8*
10
Mass
(Mʘ)
Mass Loss Rate
(Mʘ yr-1)
NML Cyg1
IK Tau2
TX Cam3
50
1
1
(1-2)x10-5
(2-5)x10-6
3x10-6
W Hya4
VY CMa
1
25
3.5x10-7
2x10-4
Source
1Boboltz
Source
Mass
(Mʘ)
Mass Loss Rate
(Mʘ yr-1)
NML Cyg1
IK Tau2
TX Cam3
50
1
1
(1-2)x10-5
(2-5)x10-6
3x10-6
W Hya4
1
3.5x10-8
et al., ApJ, 545, 2000; 2Boboltz et al., ApJ, 625, 2005; 3Olofsson et al., A&A, 245, 1991;
4Justtanont, et al., A&A, 417, 2005
Mamon et al., 1987
• Four new detections of HCO+ in evolved oxygenrich stars
• HCO+ common constituent in these stars
• Finish observations this up coming Fall:
J=2 1 in IK Tau, TX Cam, and W Hya
J=3 2 in TX Cam
J=4 3 in IK Tau, TX Cam, and W Hya
• Tentative agreement with model by Mamon et al.
• Model line profiles, determine abundances of
HCO+ to help further understand ion-molecule
chemistry in circumstellar envelopes
Acknowledgements
•
•
•
•
•
•
•
•
•
Prof. Lucy Ziurys
Dr. DeWayne Halfen
Emmy Tenenbaum
Ming Sun
Lindsay Zack
Jessica Dodd
Gilles Adande
ARO telescope operators and staff
NSF and NASA for funding