j. cernicharo. “the interpreation h 2 o observations” water vapour in astrophysics models and...

J. Cernicharo. “The interpreation H2O Observations”

Water Vapour in AstrophysicsModels and Observations

FROM ISO, SWAS and ODIN TO HERSCHEL

José CernicharoCSIC. IEM

Dpt. of Molecular and Infrared Astrophysics (DAMIR)

Madrid. Spain


The problem of the observation of water vapor :

Our atmosphere is full of water vapor.

Water vapor was detected in the ISM and CSM in 1969 from observations at a 22 GHz (Cheung et al.).

Our atmosphere is transparent at this frequency as the transition involves two levels at 700 K and the line strength is rather low.

Water detected only in small regions of the ISM and CSM

To observe H2O we have to go to space !!!

But this is not completely true !!!!!!


GROUND : Large amount of data at 22 GHz.Data on some millimeter and submillimeter masering lines. Large amount of data at 183.3 GHz with the 30-m IRAM telescope.

KAO : Search for H218O

Search for H2O from high redshift galaxies (Encrenaz and collab.)

ISO : OBSERVATION OF A LARGE NUMBER OF PURE ROTATIONAL AND RO-VIBRATIONAL LINES

SWAS & ODIN : LARGE SCALE MAPS WITH HIGH SPECTRAL RESOLUTION OF INSTERSTELLAR CLOUDS AT 556 GHz.

WHAT IS KNOWN ON WATER VAPOUR IN THE ISM AND CSM ? WHY WE BUILD NEW INSTRUMENTS TO OBSERVEH2O


GROUND OBSERVATIONS

OF

WATER VAPOUR


In 1994 we had an exceptional weather. The water vapor amount about the telescope was 0.3-0.5 mm. Several sources were observed (Orion, W49, HH7-11) and more than 40 evolved stars were detected


1989

1994

Orion IRc2


H2O at 325 GHz

HPBW = 22”

Cernicharo et al. 1999, ApJ Letters

The ground based observationsof water vapour at 183 and 325 GHzindicated a high abundance forthis species, x(H2O)=10-4, in theshocked gas around IRc2, an abun-dance 10-5 in the gas surrounding this source ( 50”) and >10-6 over spatial scales 2 arcminutes.

There is not way to pump thisweak masers if x(H2O) is below10-6


Cernicharo et al., 1996, A&A, 305, L5


WATER OBSERVATIONS

FROM

SPACE


ISO : OBSERVATION OF A LARGE NUMBER OF PURE ROTATIONAL AND RO-VIBRA-TIONAL LINES

SWAS : LARGE SCALE MAPS WITH HIGH SPECTRAL RESOLUTION OF INSTERSTE-LLAR CLOUDS.

WHAT IS KNOWN ON WATER VAPOURIN THE ISM AND CSM ?


The pumping ofH2O is stronglyaffected by the dustgrains absorption/emission.

Radiative transfermodels have to in-clude these effectsas they becomecrucial as soon as the dust opacity is 1.

González-Alfonso et.al. 1998, ApJ Letters,502,L169

J. Cernicharo. “The interpreation H2O Observations”González-Alfonso et al., 1999


The interpretation of the data requires extra information about the spatial distribution of the different physical conditions in the region

The SWAS data on the 110-101 line indicate a larger region ofemission at 556 GHz with linewidths of a few km s-1

The IRAM 30-m and CSO data indicate a large region of emission at 183.3 and 325 GHz (weak masers). These data show that severalregions with very different physical conditions have to be conside-red in any realistic model. Large H2O abundances are required.

Photons emitted in the dense internal regions of the Orion ridge are absorbed and reemitted again in the low density surrounding gas.

H2O at 556 GHz is much more sensitive to these effects than the180m line because its upper energy level will be unpopulated in the low density regions

J. Cernicharo. “The interpreation H2O Observations”3/22/2004 5:56:49 AM J. Cernicharo. “H2O with HIFI”

SWAS datain the directionof SgrB2

Neufeld et al., 2000, ApJ, 539, L111


Modelling water in SgrB2:

Absolute need for 183.3 GHzdata

Three different codes :

J. Cernicharo (non local)A. Asensio (non local)C. Ceccarelli (LVG)

Velocity resolution limits theInterpretation : HERSCHEL

Cernicharo et al. in preparation


N(H2O)=1.8 1016 cm-2


N(H2O)=1.8 1017 cm-2


IRAM30-m radiotelescopeobservations

Herschel willhave a similar beam


The ISO data on Orion and SgrB2 indicate that the interpretation of the observations is not obvious at all.

Dust emission and absorption produces importanteffects in the excitation of the ro-vibrational levelsof H2O. Detailed modelling is required.

High spectral resolution is needed to resolve thecomplex H2O line profiles.

High spatial angular resolution is needed to resol-ve the different components of the observed absorp-tion/emission ==> HERSCHEL


LOW MASS STAR FORMING REGIONS :

EXCITATION THROUGH COLLISIONS

LESS IMPORTANT EFFECTS OF THE DUST

VERY IMPORTANT EFFECTS IF THE UNCERTAINTIES ON THE COLLISIONAL RATES ARE LARGE

ISO HAS PROVIDE A LOT OF DATA ON THIS FIELD(Ceccarelli, Saraceno, Nissini, ....)


Young low massstars :

Shocks propagatinginto the cold surroun-ding gas.

How we trace theshocked gas ?

In the submillimeter and far-infrared do-main through high-J lines of CO, H2O and other molecular species.

Cep E

Moro et al., 2000, ApJ, submitted

J. Cernicharo. “The interpreation H2O Observations”Moro et al., 2000, ApJ, submitted


Water in evolved stars

O-rich stars : H2O a key molecule

C-rich ProtoPlanetary Nebula : H2O as a product of photodissociation and shocks

C-rich AGB stars : H2O from vaporizationof cometary bodies ! ?


W Hya

Barlow et al., 1996; Neufeld et al., 1996

J. Cernicharo. “The interpreation H2O Observations”Asensio, Cernicharo, González-Alfonsoin preparation

VY CMa

All features are real

All pure rotational lines of wapour with >43 um detected

Some lines from the v2=1bending level also detected

Modelling requires collisionalrates for Tk=20-2000 K includingro-vibrational collisions


In O-rich stars water vapour is an excellent tracer of the physical conditions of the circustellar envelope. The systematic observation of as many lines as possible of water could permit to determine the temperature and density profile if (and only if)

1) Collisional rates are well known

2) Good spectral resolution is achieved at all wavelengths (HIFI)

3) CO and other key species are observed and interpreted with the same models than water vapour

4) Good and fast radiative transfer codes are available

Systematic surveys of a few selected lines of O-rich stars could per-mit to derive reasonably accurate mass loss rates even for very low dM/dt


DARK CLOUDS


The Galactic Center region offers the possibility to study dark clouds through the absorption of its pure rotational and ro-vibrational lines (background continuum emission is high enough at 6.2 micron and in the far infrared).

The different opacity of the pure rotational lines and of the rovibra-tional lines can permit to derive reasonable estimates of the water vapour abundance in dark clouds in front of bright background sources.

The pure rotational lines are optically thick even for low water vapourabundances (110-101; 556 GHz) = 2 108 x(H2O) / v(km s-1) (212-101; 180 m) = 2 108 x(H2O) / v(km s-1)

Much larger abundances are needed to get similar opacities in themid-infrared (bending mode of water vapour)

J. Cernicharo. “The interpreation H2O Observations”ISO/SWS data on Sgr A* (Moneti, Cernicharo & Pardo ApJ Letters,2001)


Gas Phase (Moneti et al. 2001)

x(13CO)/x(H2O) 5.8 andx(CO)/ x(H2O) 350assuming x(CO)=10-4 thenx(H2O) 3 10-7

(212-101; 180 m) 100

SWAS in TMC1 provides x(H2O) < 8 10-8 Ices (Chiar et al. 2000 -SgrA*-)

N(CO) = 1.4 1017 cm-2

N(H2O) = 1.2 1018 cm-2

Nice+gas(CO)/Nice+gas(H2O) 5


HERSCHEL will provide a unique opportunity to study the role ofwater vapour in the chemistry and energy balance of Interstellarand Circumstellar clouds.

The high spectral resolution provided by HIFI will permit to getinformation on the kinematics of the innermost zones of starforming regions and of evolved stars.

The full wavelength coverage of HIFI + PACS + SPIRE will permitto determine the physical conditions of regions similar to Orion butmuch more distant. Objects like Arp220 but at larger refshift couldbe easily detected.

Water vapour is an excellent tracer of shocked regions. The highangular resolution of HERSCHEL and the high spectral resolution ofHIFI will permit to study in detail the physical conditions of thegas surrounding low mass star forming regions.

J. Cernicharo. “The interpreation H2O Observations”González et al., 2004


183.3 GHz water line in low redshift AGNs : a new H2O megamaserCernicharo et al., 2004, in preparation


Important efforts have been made to model H2O emission/absorption

Calculation of collisional cross sections in progress !!!

Interpreting very optically thick lines !

Herschel :: multi-line observations of H2O More realistic physics in the modeling of water vapour

Ground based observations : 183.3 GHz high angular resolution with ALMA the possibility to trace H2O in protostellar disks !!

j. cernicharo. “the interpreation h 2 o observations” water vapour in astrophysics models and...

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