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Phosphorus Chemistry in Circumstellar Envelopes: PN in IRC+10216, VY CMa, and CRL 2688 Aldo J. Apponi, Stefanie N. Milam, DeWayne T. Halfen, Emily D. Tenenbaum,

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Presentation on theme: "Phosphorus Chemistry in Circumstellar Envelopes: PN in IRC+10216, VY CMa, and CRL 2688 Aldo J. Apponi, Stefanie N. Milam, DeWayne T. Halfen, Emily D. Tenenbaum,"— Presentation transcript:

1 Phosphorus Chemistry in Circumstellar Envelopes: PN in IRC+10216, VY CMa, and CRL 2688 Aldo J. Apponi, Stefanie N. Milam, DeWayne T. Halfen, Emily D. Tenenbaum, and Lucy M. Ziurys University of Arizona, Steward Observatory, Arizona Radio Observatory

2 Gas Phase –C-rich: Carbon Chains (HC n N, HC n ) –O-rich: Sulfur (SO, SO 2 and CS) Compounds of refractory elements –Silicon (SiO, SiS and SiC 2 ) –Sodium, Aluminum and Magnesium Where is the Phosphorus? –Until very recently, only CP and tentatively PN in IRC –Depleted in dense gas (Orion-KL) Models indicate that Phosphorus is depleted by a factor of 100 Phosphorus forms refractory compounds like Schreibersite (NiP) –Higher sensitivity telescope receivers C-rich Envelope IRC Cernicharo et al O-rich Envelope VY CMa Circumstellar Chemistry Pasek (2007)

3 ALMA Band 6 (211 – 275 GHz) ALMA Memo August 2006 First Astronomical Observations with an ALMA Band 6 ( GHz) Sideband-Separating SIS Mixer-Preamp E. F. Lauria 1, A. R. Kerr 2, G. Reiland 1, R. F. Freund 1, A.W. Lichtenberger 3, L. M. Ziurys 1, M. Metcalf 1 and D. Forbes 1 1 University of Arizona, Arizona Radio Observatory (ARO), Tucson, AZ 2 National Radio Astronomy Observatory (NRAO), Charlottesville, VA 3 University of Virginia Microfabrication Laboratory (UVML), Charlottesville, VA Abstract - A GHz SIS receiver using an ALMA Band 6 sideband-separating mixer-preamp has been installed on the Submillimeter Telescope (SMT) on Mt. Graham, Arizona, a facility of the University of Arizona. Initial observations have yielded single-sideband system noise temperatures as low as 107 K referred to outside the atmosphere. The image rejection, measured on the sky, was > 12 dB (15 dB typical) for the upper sideband, and > 20 dB for the lower sideband. Excellent baseline stability was also observed: a 4° position offset in galactic latitude yielded a peak-to-peak baseline of only 10 mK. The receiver has separate 4-8 GHz IF outputs for the upper and lower sidebands, although in the present observations the bandwidth was limited by the available spectrometers to 2 GHz in each sideband.

4 Mixer Block (from NRAO) Initially on SMT as a test system (Spring 2006) Incorporated as Facility Receiver (Fall 2007) - added second channel (x2 integration time) - upgrade electronics to accommodate new receiver Incorporation into“Insert” “Insert” put into Dewar

5 On the Sky… First time ALMA Receiver on a telescope (SMT)  First test of ALMA technology  Improved Sensitivity (factor of 10 in time)  T sys ~ 107 K, SSB (20 dB rejection)  Excellent baseline stability  Wide IF Bandwidth High sensitivity: 4 mK rms in 3.7 hours SMT IRC and happy Fred Lo

6 Impact of New ALMA Band 6 Receiver Enhanced sensitivity makes O-rich sources viable –O-rich circumstellar chemistry not well studied –Lack of observations and close objects Survey of VY CMa revealed a rich chemistry –Highlights of the results published in Nature (Ziurys et al., 28 June 2007 issue) –Talk WI03 – Lucy Ziurys will discuss this source in detail –One interesting result was the detection of PN Led us to look for PN in other circumstellar sources –Re-confirmed PN in IRC –Found it in CRL 2688

7 Introduction to Phosphorus Chemistry What was looked for, what was found and when –No detection: PH 3 or HCP (Hollis et al. 1980, 1981) –PN: Orion-KL (Ziurys 1987; Turner & Bally 1987) –CP: IRC (Guelin et al. 1990) No detection of PN or HCP in that work –No detection of PS (Ohishi et al. 1990) VY CMa IRC OH231 –PN in IRC Blended line at 140 GHz (Cernicharo et al. 2000) Confirming line at 94 GHz (Guelin et al. 2000) Re-confirmed (Milam et al. in prep.) –HCP detected in IRC (Agundez et al. 2007) –Tenenbaum and Ziurys independently detect HCP less than a month later

8 141 GHz 95 GHz 235 GHz 282 GHz Cernicharo, Guelin and Kahane 2000 M. Guelin, S. Muller, J. Cernicharo, A. J. Apponi, M.C. McCarthy, C.A. Gottlieb, and P. Thaddeus 2000 Observations of PN


10 Rotational Diagram N tot = 2 x cm -2 ; 57 K Ntot = 3 x cm -2 ; 14 K Ntot = 1 x cm -2 ; 34 K

11 Millar et al –Depletion factor of about 100 or more –“…searches should be carried out (for PN) in O-rich circumstellar envelopes.” MacKay & Charnley 2001 –HCP (C-rich) and PS (O-rich) dominate the chemistry –No PN observable in either case –CP abundance reproduced as a daughter product of HCP (C-rich) –PS remains undetected (O-rich) C-rich O-rich HCP CP PS P Models on PN Chemistry

12 Observations vs. the Models Agundez et al Only HCP predicted by LTE Models of C- rich envelopes Only P 4 O 6 predicted by LTE Models of O- rich envelopes

13 Agundez et al Two reactions added to produce the observed PN N + CP → PN + C P + CN → PN + C Spatial extent crucial for validation of the model

14 Estimating the Source Size Compare lines –30m horned profile –12m flat top Compare intensities –T R = 9 mK vs. 18 mK –Compute the ratio of filling factors –30 arcsec source size 40” beam 16” beam T R = 18 mK T R = 9 mK Agundez et al arcsec Phosphorus model in IRC+10216

15 HCP –20 mK vs. 9 mK –~20 arcsec source CP –25 mK vs. ~10 mK –~20 to 30 arcsec source HCP Agundez et al GHz Guelin (1990) Agundez et al arcsec Phosphorus model in IRC+10216

16 Summary PN observed in circumstellar envelopes –C-rich envelopes of IRC and CRL 2688 –O-rich envelope VY CMa Models of IRC –Reproduce PN in the outer envelope Required the addition of two new reactions N + CP → PN + C and P + CN → PN + C –Reproduces HCP and CP CP a daughter product of HCP Both HCP and CP depleted in the outer envelope onto grains

17 Summary Models of O-rich envelopes less successful –No available observations to guide the models –Current O-rich models vary PS dominant (MacKay and Charnley 2001) P 2 O 4 dominant (Agundez et al. 2007) –Absence of PS detection Dipole moment estimated to be 2.0 D No calculation or measurement available Could be much smaller (NO: 0.16 D) –PN not predicted to be abundant in the current available models Millar et al suggested looking for it in O-rich envelopes PN is an inner envelope component in VY CMa Could be an LTE product PO PN PS PH High “freeze-out” temps High abundance of PO, PN, PS and PH

18 Acknowledgements Funding from NASA Astrobiology Institute and NSF Astronomy Research Associates: Lucy Ziurys and Neville Woolf The Ziurys research group –Stefanie Milam –DeWayne Halfen –Emily Tenenbaum

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