– 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

• Most stars investigated are in the early AGB phase

• O-rich evolved stars haven’t yet undergone third dredge- up

2.80 —

3.40 —

2.95 —

3.10 —

3.25 —

3.603.854.004.154.30

PLANETARY NEBULAStellar envelope completely detached

To White Dwarf

PROTO-PLANETARY NEBULA (PPN)

Nucleosynthesis stopsCRL2688AGB

He & H Shell Burning Envelope

Triple -Process

RED GIANT BRANCH

H Shell Narrows

H Shell Burning

First Dredge-up: Surface Abundances Change

MAIN SEQUENCEHydrogen Core BurningSun

Log

(L

)

Log (Te)

He Core Burning

Evolved starsOxygen-rich chemistryC/O ratio is less than 1

4.00 —

6.00 —

4.50 —

5.00 —

5.50 —

3.504.004.5

Log

(L

)

Log (Te)

25 MΘ

15 MΘ

40 MΘ

• 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

Figure Courtesy of Stefanie MilamSun Kwok, Nature, 447, 2007

•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

1Boboltz et al., ApJ, 545, 20002Boboltz et al., ApJ, 625, 20053Olofsson et al., A&A, 245, 19914Justtanont, et al., A&A, 417, 2005

Source Star Type Mass(Mʘ)

Mass Loss Rate(Mʘ yr-1)

Distance(pc)

VLSR

(km s-1)Coordinates

(B1950.0)

NML Cyg1 Supergiant 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

TransitionJ+1J

Frequency(MHz)

Wavelength(mm)

Beam Size(arcsecs)

Telescope

1 0 89188.523 3.4 70 ARO 12m 2 1 178375.010 1.7 35 ARO 12m 3 2 267557.526 1.1 28 ARO SMT4 3 356734.134 0.8 21 ARO SMT

Current Observational Results:• IK Tau

• Detected the J=1-0 and J=3-2• J=3-2 blended with SO2

• TX Cam• Proving more difficult• The J=1-0 emerging from

the noise• The J=3-2 needs more

integration time• Contaminated with SO2

• W Hya • Detected J=1-0 and

J=3-2• Narrow line profiles • J=3-2 is not blended

with SO2

• NML Cyg • All four transitions

observed• Both J=3-2 and J=4-3

blended with SO2

•IK Tau•Detected the J=1-0 and J=3-2•J=3-2 blended with SO2

• W Hya • DetectedJ=1-0 and J=3-2• Narrow line profiles

• J=3-2 is not blended with SO2

• TX Cam• Proving more difficult• The J=1-0 emerging from the noise• The J=3-2 needs more integration time • Contaminated with SO2

TR

*

-0.003

0.000

0.003

0.006

0.009

0.012

J = 1 0IK Tau

LSR / km s-1-150 -100 -50 0 50 100 150 200

TA

*

-0.002

0.000

0.002

0.004

0.006 J = 3 2 SO2

LSR / km s-1

TR

*

-0.002

0.000

0.002

0.004

0.006

-150 -100 -50 0 50 100 150 200

TA

*

-0.002

0.000

0.002

0.004

0.006

W HyaJ = 1 0

J = 3 2SO2

TR

*

-0.002

0.000

0.002

0.004

0.006

LSR / km s-1

-150 -100 -50 0 50 100 150

TA

*

-0.002

-0.001

0.000

0.001

0.002

0.003

SO2

TX Cam

J = 3 2

J = 1 036 hrs

30 hrs

69 hrs

64 hrs

42 hrs

100 hrs

LSR / km s-1-200 -150 -100 -50 0 50 100 150 200

TR

* / K

-0.008

-0.004

0.000

0.004

0.008

0.012 J = 2 1

TR

* / K

-0.002

0.000

0.002

0.004

0.006

0.008

0.010

J = 1 0NML Cyg

LSR / km s-1

TA

* / K

-0.001

0.001

0.003

0.005

0.007

-200 -150 -100 -50 0 50 100 150 200-0.006

-0.002

0.002

0.006

0.010

TA

* / K

J = 3 2

J = 4 3SO2

SO2

66 hrs

62 hrs

43 hrs

41 hrs

Source Mass(Mʘ)

Mass Loss Rate(Mʘ yr-1)

NML Cyg1 50 (1-2)x10-5

IK Tau2 1 (2-5)x10-6

TX Cam3 1 3x10-6

W Hya4 1 3.5x10-7

VY CMa 25 2x10-4

Source Column Density(cm-2)

Tex

(K)IK Tau 1.4 x1011 8

NML Cyg 1.8 x1011 8TX Cam 1.3 x1011 8*

W Hya 5.7 x1010 10

• Preliminary analysis: constructed rotational diagram and determined column densities

• Tentative agreement; need to calculate fractional abundances

Source Mass(Mʘ)

Mass Loss Rate(Mʘ yr-1)

NML Cyg1 50 (1-2)x10-5

IK Tau2 1 (2-5)x10-6

TX Cam3 1 3x10-6

W Hya4 1 3.5x10-8

Mamon et al., 19871Boboltz 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

• Four new detections of HCO+ in evolved oxygen-rich stars

• HCO+ common constituent in these stars• Finish observations this up coming Fall:

J=2 1 in IK Tau, TX Cam, and W HyaJ=3 2 in TX CamJ=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