Understanding the chemistry of AGB circumstellar envelopes through the study of IRC

Transcription

1 Understanding the chemistry of AGB circumstellar envelopes through the study of IRC Marcelino Agúndez LUTH, Observatoire de Paris 28 janvier m 2MASS

2 PART I. INTRODUCTION: - Interest of studying this particular object

3 PART I. INTRODUCTION: - Interest of studying this particular object PART II. METHODS: - Astronomical observations - Radiative transfer and chemical modelling

4 PART I. INTRODUCTION: - Interest of studying this particular object PART II. METHODS: - Astronomical observations - Radiative transfer and chemical modelling PART III. RESULTS: - the molecular envelope of IRC molecules with phosphorus - molecular anions

5 PART I. INTRODUCTION Interest of studying this particular object

6 PART I. INTRODUCTION the asymptotic giant branch (AGB) phase log(l/l ) HR DIAGRAM luminosity toward hacia planetary nebulosa planetaria nebula "Asymptotic Giant Branch" (AGB) asymptotic giant branch (AGB) flash helium de flash helio "Red red Giant giant Branch" branch (RGB) main secuencia sequence principal effective temperature log(t ) ef

7 PART I. INTRODUCTION the asymptotic giant branch (AGB) phase RED GIANT: - R * increases by a factor ~ L * increases by a factor ~10,000 - T * decreases from ~6000 K down to ~ K Jupiter Sun Earth Mars

8 PART I. INTRODUCTION the asymptotic giant branch (AGB) phase: dredge up processes C

9 PART I. INTRODUCTION oxygen-rich star [C]/[O] < 1 carbon-rich star [C]/[O] > 1 abundance relative to total H n = cm -3 n = cm -3 abundance relative to total H temperature (K) temperature (K) oxygen-bearing molecules: H 2 O, SiO, OH, carbon-bearing molecules: C 2 H 2, HCN, CS,

10 PART I. INTRODUCTION AGB stars loss mass through isotropic winds extended circumstelar envelope of molecular gas and dust Leao et al

11 PART I. INTRODUCTION AGB stars loss mass through isotropic winds # main recycling mechanism of ISM extended circumstelar envelope of molecular gas and dust AGB star interstellar medium

12 PART I. INTRODUCTION AGB stars loss mass through isotropic winds # main recycling mechanism of ISM # stellar light strongly extincted extended circumstelar envelope of molecular gas and dust F(Jy) blackbody 2330 K ISO spectrum of IRC ( m)

13 PART I. INTRODUCTION AGB stars loss mass through isotropic winds # main recycling mechanism of ISM # stellar light strongly extincted extended circumstelar envelope of molecular gas and dust inner envelope # large wealth of molecules external envelope RED GIANT chemical equilibrium shock waves dust formation zone photochemistry

14 IRC : - carbon-rich AGB star closest to the Earth (~120 pc) - brigthest astronomical object (outside the Solar System) in the sky at ~5-10 m

15 IRC : - carbon-rich AGB star closest to the Earth (~120 pc) - brigthest astronomical object (outside the Solar System) in the sky at ~5-10 m 10 m; ESO/La Silla B. Stecklum & H.-U. Kaüfl So why studying IRC ? - prototype of AGB star - one of richest molecular sources in the sky

16 PART II. METHODS

17 Astronomical observations

18 PART II. METHODS: astronomical observations IRAM 30-m radiotelescope Pico Veleta (Granada)

19 PART II. METHODS: astronomical observations Frequency (GHz) Frequency (GHz) Frequency (GHz)

20 PART II. METHODS: astronomical observations Frequency (GHz) Cernicharo et al Frequency (GHz) Cernicharo et al. in preparation Frequency (GHz)

21 PART II. METHODS: astronomical observations Zoom in the 83 GHz spectral region: Rest frequency (GHz)

22 PART II. METHODS ISM/CSM cloud Astronomical observations Observed molecular abundances

23 PART II. METHODS ISM/CSM cloud Astronomical observations Excitation and radiative transfer calculations Observed molecular abundances

24 Excitation and radiative transfer calculations

25 PART II. METHODS: excitation and radiative transfer calculations T A * (K) J=34-33 Rotational temperature diagram 3kW log 2 8 S N log Z 3 HC 5 N in IRC J=43-42 J=53-52 rot log e E kt log (3kW/8 3 S 2 ) rot up Frequency (GHz) Line integrated intensities E up (K) Rotational temperature (T rot ) Column density (N)

26 PART II. METHODS: excitation and radiative transfer calculations T A * (K) J=34-33 Rotational temperature diagram 3kW log 2 8 S N log Z 3 HC 5 N in IRC J=43-42 J=53-52 rot log e E kt log (3kW/8 3 S 2 ) rot up Frequency (GHz) Line integrated intensities E up (K) Rotational temperature (T rot ) Column density (N) Approximate method based on various hypotheses: 1) rotational levels in thermodynamic equilibrium 2) homogeneous emitting medium 3) optically thin emission 4) emission in the Rayleigh-Jeans regime (h << kt rot ) 5) T rot >> T CMB

27 PART II. METHODS: excitation and radiative transfer calculations T A * (K) J=34-33 Rotational temperature diagram 3kW log 2 8 S N log Z 3 HC 5 N in IRC J=43-42 J=53-52 rot log e E kt log (3kW/8 3 S 2 ) rot up Frequency (GHz) Line integrated intensities E up (K) Rotational temperature (T rot ) Column density (N) Approximate method based on various hypotheses: 1) rotational levels in thermodynamic equilibrium 2) homogeneous emitting medium 3) optically thin emission 4) emission in the Rayleigh-Jeans regime (h << kt rot ) 5) T rot >> T CMB

28 PART II. METHODS: excitation and radiative transfer calculations u Statistical equilibrium n j ( 4 JB ji jin) n j Aji ni (4 JBij ijn) ni j i j i j i j i A ul 4 JB lu 4 JB ul ul n lu n n i J dn dt i A ij radiative collisional l J ( 1 ) S I LVG approximation bg n i populations

29 PART II. METHODS: excitation and radiative transfer calculations u Statistical equilibrium n j ( 4 JB ji jin) n j Aji ni (4 JBij ijn) ni j i j i j i j i A ul 4 JB lu 4 JB ul ul n lu n n i J dn dt i A ij radiative collisional l J ( 1 ) S I LVG approximation bg n i populations ray tracing intensity n i n i n i n i frequency

30 PART II. METHODS ISM/CSM cloud Astronomical observations Excitation and radiative transfer calculations Observed molecular abundances

31 PART II. METHODS ISM/CSM cloud Astronomical observations Excitation and radiative transfer calculations Observed molecular abundances Chemical modelling Calculated molecular abundances

32 PART II. METHODS ISM/CSM cloud Astronomical observations Excitation and radiative transfer calculations Observed molecular abundances agreement? Chemical modelling Calculated molecular abundances

33 Chemical modelling

34 PART II. METHODS: chemical modelling circumstellar envelope INNER ENVELOPE red giant chemical equilibrium OUTER ENVELOPE chemical kinetics

35 PART II. METHODS: chemical modelling chemical equilibrium T P i K p,n kt i p i ( p ) ( p ) N h i n c i j n 1 K p, n n ( p k ) o n... non linear system of algebraic equations Newton-Raphson x n

36 PART II. METHODS: chemical modelling chemical equilibrium T P i K p,n kt i p i ( p ) ( p ) N h i n c i j n 1 K p, n n ( p k ) o n... non linear system of algebraic equations Newton-Raphson x n chemical kinetics T(t) n(t) x i 0 k j dn dt i N f N j reac k n k n j j, l m i j 1 l 1 m 1 s 1 formation of i N d N m reac n destruction of i m, s non-linear system of ordinary differential equations Runge-Kutta x i (t)

37 PART III. RESULTS

38 the molecular envelope of IRC

39 PART III. RESULTS: the molecular envelope of IRC INNER ENVELOPE OUTER ENVELOPE red giant

40 PARTE III. RESULTADOS: La envoltura molecular de IRC INNER ENVELOPE OUTER ENVELOPE IRAM PdBI Guélin et al. 1997

41 10-3 CO C 2 H 2 HCN 10-6 CH 4 C 2 H C 4 H C 2 C 3 NH 3 CN HC 3 N C 3 N CS SiC 2 SiS H 2 O OH H 2 CO C 3 O HCO + C 5 l-c 3 H C 6 H C 5 H c-c 3 H 2 CH 3 C 2 H c-c 3 H C 2 H 4 H 2 C 4 C 8 H C 7 H H 2 C 6 C 6 H - C 8 H - H 2 C 3 C 4 H - HC 5 N HNC CH 3 CN HC 7 N HC 9 N CH 2 CN HC 2 N C 5 N HCCNC C 2 H 3 CN C 5 N - HC 4 N C 3 N - HNCCC C 2 S C 3 S H 2 CS H 2 S C 5 S SiH 4 SiO SiC SiN c-sic 3 SiC 4 SiCN SiNC HCP CP PH 3 PN C 2 P AlCl NaCN MgNC AlF NaCl AlNC MgCN KCl

42 C 2 H C 4 H C 2 C 3 CN HC 3 N C 3 N SiC OH C 5 l-c 3 H C 6 H C 5 H c-c 3 H 2 CH 3 C 2 H c-c 3 H HC 5 N HNC CH 3 CN HC 7 N C 2 S SiC H 2 CO C 3 O HCO + H 2 C 4 C 8 H C 7 H H 2 C 6 C 6 H - C 8 H - H 2 C 3 C 4 H - HC 9 N CH 2 CN HC 2 N C 5 N HCCNC C 2 H 3 CN C 5 N - HC 4 N C 3 N - HNCCC C 3 S H 2 CS C 5 S SiN c-sic 3 SiC 4 SiCN SiNC CP PN C 2 P MgNC AlNC MgCN

43 PART III. RESULTS: the molecular envelope of IRC Rotational temperature diagrams are a reasonably good first approximation for the molecules formed in the outer envelope medium approximately homogeneous cm -3, 50 K 10 4 cm -3, 20 K

44 PART III. RESULTS: the molecular envelope of IRC C 2 H l-c 3 H c-c 3 H C 4 H Molecule N(cm -2 ) T rot (K) C 2 H 4.1(3)x (2) l-c 3 H 7.1(5)x (5) c-c 3 H 2.7(3)x (1) C 4 H 3.5(2)x (3) C 5 H 4.3(5)x (10) C 6 H 4.7(5)x (16) C 7 H 5.0(30)x (21) C 8 H 1.2x CN 2.5x C 3 N 3.8(2)x (5) C 5 N 5.9(23)x (12) HNC 1.6x HC 3 N 6.1(4)x (6) HC 5 N 2.9(3)x (6) up to 50 molecules

45 10-3 CO 1(-3) H 2 O 1(-7) OH 4(-8) H 2 CO 1.3(-8) C 3 O 2(-9) HCO + 7(-10) C 2 H 2 CH 4 C 2 H C 4 H C 2 C 3 C 5 l-c 3 H C 6 H C 5 H c-c 3 H 2 CH 3 C 2 H c-c 3 H C 2 H 4 H 2 C 4 C 8 H C 7 H H 2 C 6 C 6 H - C 8 H - H 2 C 3 C 4 H - 8(-5) 3.5(-6) 3(-6) 2.5(-6) 1(-6) 1(-6) 1(-7) 5(-8) 4(-8) 3(-8) 3(-8) 3(-8) 2(-8) 2(-8) 1.4(-8) 8(-9) 3(-9) 3(-9) 3(-9) 1.5(-9) 1.5(-9) 3(-10) HCN NH 3 CN HC 3 N C 3 N HC 5 N HNC CH 3 CN HC 7 N HC 9 N CH 2 CN HC 2 N C 5 N HCCNC C 2 H 3 CN C 5 N - HC 4 N C 3 N - HNCCC 2(-5) 2(-6) 1.7(-6) 1.4(-6) 4(-7) 2(-7) 1(-7) 3(-8) 2(-8) 8(-9) 7(-9) 6(-9) 4(-9) 4(-9) 4(-9) 2.3(-9) 2(-9) 1.1(-9) 5(-10) CS 5(-7) C 2 S 3(-8) C 3 S 1.2(-8) H 2 CS 7(-9) H 2 S 4(-9) C 5 S 1.2(-9) SiC 2 SiS SiH 4 SiO SiC SiN c-sic 3 SiC 4 SiCN SiNC 1.2(-6) 1(-6) 2.2(-7) 1.2(-7) 4(-8) 8(-9) 4(-9) 3(-9) 2(-9) 1.1(-9) HCP CP PH 3 PN C 2 P 2.5(-8) 1(-8) 8(-9) 1(-9) 1(-9) AlCl NaCN MgNC AlF 3.5(-8) 8(-9) 7.5(-9) NaCl 1(-9) AlNC 1(-9) MgCN 5(-10) KCl 2.5(-10)

46 PART III. RESULTS: the molecular envelope of IRC abundance relative to H 2 radius (cm) C 3 H C 5 H C 7 H C n H (n odd) C C 2 H 2 C 2 H C C 2 H C 4 H 2 C 6 H 2 C h h C 2 H C 4 H C 6 H C n H (n even)

47 PART III. RESULTS: the molecular envelope of IRC Molecules with C, H Molecules with C, H, N Molecules with Si, S, O, P

48 PART III. RESULTS: the molecular envelope of IRC Molecules with C, H Molecules with C, H, N Molecules with Si, S, O, P

49 molecules with phosphorus

50 PART III. RESULTS: molecules with phosphorus why we talk about molecules with phosphorus? first astronomical detection of HCP y PH 3! Agúndez et al. 2007, ApJ, 662, L91 Agúndez et al. 2008, A&A, 485, L33

51 PART III. RESULTS: molecules with phosphorus some basic facts about the chemistry of phosphorus -P is in the same group of N in Mendeleiev s table

52 PART III. RESULTS: molecules with phosphorus some basic facts about the chemistry of phosphorus -P is in the same group of N in Mendeleiev s table -P is a main biogenic element, altogether with C, H, O, N, S

53 PART III. RESULTS: molecules with phosphorus some basic facts about the chemistry of phosphorus -P is in the same group of N in Mendeleiev s table -P is a main biogenic element, altogether with C, H, O, N, S -P has a moderately low cosmic abundance P/N = 1/300 P/H = 2.3 x 10 7 elemental abundance

54 PART III. RESULTS: molecules with phosphorus

55 PART III. RESULTS: molecules with phosphorus HCP in IRC

56 PART III. RESULTS: molecules with phosphorus HCP in IRC

57 PART III. RESULTS: molecules with phosphorus HCP in IRC

58 PART III. RESULTS: molecules with phosphorus HCP in IRC

59 PART III. RESULTS: molecules with phosphorus HCP in IRC in IRC PH3

60 PART III. RESULTS: molecules with phosphorus abundance relative to H 2 radius (cm) radius (R*) radius ( ) - HCP detection is in agreement with thermochemical calculations (HCP is the most abundant P-bearing species in C-rich CSEs) [HCP] obs = 1 [HCP] calc 20 - The observed abundance of PH 3 is much higher than predicted (PH 3 is probably formed in grain surfaces)

61 PART III. RESULTS: molecules with phosphorus abundance relative to H 2 radius (cm) radius (R*) radius ( ) - HCP detection is in agreement with thermochemical calculations (HCP is the most abundant P-bearing species in C-rich CSEs) [HCP] obs = 1 [HCP] calc 20 - The observed abundance of PH 3 is much higher than predicted (PH 3 is probably formed in grain surfaces) - The photodissociation of HCP and PH 3 allow the formation of other P-bearing species in the outer envelope, e.g. CP, C 2 P, PN,

62 molecular anions

63 PART III. RESULTS: molecular anions why we talk about molecular anions? first astronomical detection of molecular anions! C 6 H -, C 4 H -, C 8 H -, C 3 N -, C 5 N -

64 PART III. RESULTS: molecular anions Some basic facts on molecular anions Thermodynamics anion formation is favored A - A energy electron affinity Kinetics anion formation is badly favored A + e - A - + h except for species A with a high electron affinity and size e.g. C 4 H, C 6 H, C 8 H, C 3 N, C 5 N,

65 PART III. RESULTS: molecular anions except for species A with a high electron affinity and size e.g. C 4 H, C 6 H, C 8 H, C 3 N, C 5 N,

66 PART III. RESULTS: molecular anions History of molecular anions in space: 2006 C 6 H - in IRC and TMC-1 (McCarthy et al)

67 PART III. RESULTS: molecular anions History of molecular anions in space: 2006 C 6 H - in IRC and TMC-1 (McCarthy et al) 2007 C 4 H - in IRC (Cernicharo et al) 2007 C 8 H - in IRC and TMC-1 (Remijan et al; Brünken et al) 2008 C 3 N - in IRC (Thaddeus et al) 2008 C 5 N - in IRC (Cernicharo et al)

68 PART III. RESULTS: molecular anions History of molecular anions in space: 2006 C 6 H - in IRC and TMC-1 (McCarthy et al) 2007 C 4 H - in IRC (Cernicharo et al) 2007 C 8 H - in IRC and TMC-1 (Remijan et al; Brünken et al) 2008 C 3 N - in IRC (Thaddeus et al) 2008 C 5 N - in IRC (Cernicharo et al) Additional detections: C 6 H - in L1527 (Sakai et al 2007) C 4 H - in L1527 (Agúndez et al 2008) C 6 H - in L1544 and L1521F (Gupta et al 2009)

69 PART III. RESULTS: molecular anions History of molecular anions in space: 2006 C 6 H - in IRC and TMC-1 (McCarthy et al) 2007 C 4 H - in IRC (Cernicharo et al) 2007 C 8 H - in IRC and TMC-1 (Remijan et al; Brünken et al) 2008 C 3 N - in IRC (Thaddeus et al) 2008 C 5 N - in IRC (Cernicharo et al) Additional detections: C 6 H - in L1527 (Sakai et al 2007) C 4 H - in L1527 (Agúndez et al 2008) C 6 H - in L1544 and L1521F (Gupta et al 2009) IRC only astronomicalsource where the 5 molecular anions C 4 H -, C 6 H -, C 8 H -, C 3 N -, y C 5 N - have been observed

70 PART III. RESULTS: molecular anions C 4 H - C 3 N - C 5 N -

71 PART III. RESULTS: molecular anions anion-to-neutral abundance ratios in IRC [C 4 H - ]/[C 4 H] [C 6 H - ]/[C 6 H] [C 8 H - ]/[C 8 H] [C 3 N - ]/[C 3 N] [C 5 N - ]/[C 5 N] % % % % %

72 PART III. RESULTS: molecular anions Formation of A - : k ra A + e - A - + h electron attachment Destruction of A - : k H A - + H AH + e - reaction with H atoms k + A - + C + A + C neutralization with cations C + A A - + h A + e - photodetachment steady state [ A ] [ A] k H k [ H ] k ra [ e [ C ] ] A / n

73 PART III. RESULTS: molecular anions Formation of A - : k ra A + e - A - + h electron attachment Destruction of A - : k H A - + H AH + e - reaction with H atoms k + A - + C + A + C neutralization with cations C + A A - + h A + e - photodetachment steady state [ A ] [ A] k H k [ H ] k ra [ e [ C ] ] A / n [ A ] [ A] k ra

74 PART III. RESULTS: molecular anions reaction k ra (300 K) IRC k ra (300 K) theoretical (a) C 4 H + e - C 4 H - + h 2-7x x10-8 C 6 H + e - C 6 H - + h 3.0x x10-8 C 8 H + e - C 8 H - + h 1.5x x10-8 C 3 N + e - C 3 N - + h 2-5x x10-10 C 5 N + e - C 5 N - + h 5.0x k ra with units cm 3 s -1 (a) Herbst & Osamura 2008; Petrie & Herbst 1997.

75 PART III. RESULTS: molecular anions reaction k ra (300 K) IRC k ra (300 K) theoretical (a) C 4 H + e - C 4 H - + h 2-7x x10-8 C 6 H + e - C 6 H - + h 3.0x x10-8 C 8 H + e - C 8 H - + h 1.5x x10-8 C 3 N + e - C 3 N - + h 2-5x x10-10 C 5 N + e - C 5 N - + h 5.0x k ra with units cm 3 s -1 (a) Herbst & Osamura 2008; Petrie & Herbst 1997.

76 PART III. RESULTS: molecular anions anion-to-neutral abundance ratios in various astronomical sources anion-to-neutral ratio % C-CSEs dense molecular clouds PDRs diffuse clouds - in a given source, [A - ]/[A] increases with the size of A - for a given anion, [A - ]/[A] is proportional to the ratio [e - ]/[H] of each source

77 PERSPECTIVES

78 - IRAM-30m LINE SURVEY IN THE 0.9 mm NEW BAND ( GHz), on the way Kahane et al.

79 - OBSERVATIONS WITH THE HERSCHEL SPACE OBSERVATORY (HIFI, SPIRE, PACS) on the way Decin et al.

80 M e r c i d e v o t r e a t t e n t i o n!