Issue |
A&A
Volume 521, October 2010
Herschel/HIFI: first science highlights
|
|
---|---|---|
Article Number | L7 | |
Number of page(s) | 5 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361/201015108 | |
Published online | 01 October 2010 |
Herschel/HIFI: first science highlights
LETTER TO THE EDITOR
Herschel/HIFI deepens
the circumstellar NH
enigma
,![[*]](/icons/foot_motif.png)
K. M. Menten1 - F. Wyrowski1 - J. Alcolea2 - E. De Beck3 - L. Decin3,4 - A. P. Marston5 - V. Bujarrabal6 - J. Cernicharo7 - C. Dominik5,8 - K. Justtanont9 - A. de Koter5,10 - G. Melnick11 - D. A. Neufeld12 - H. Olofsson9,13 - P. Planesas6,15 - M. Schmidt14 - F. L. Schöier9 - R. Szczerba14 - D. Teyssier5 - L. B. F. M. Waters4,3 - K. Edwards16,17 - M. Olberg9,17 - T. G. Phillips18 - P. Morris19 - M. Salez20,21 - E. Caux22,23
1 - Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121
Bonn, Germany
2 - Observatorio Astronómico Nacional (IGN), Alfonso XII No 3,
28014 Madrid, Spain
3 - Instituut voor Sterrenkunde, Katholieke Universiteit Leuven,
Celestijnenlaan 200D, 3001 Leuven, Belgium
4 - Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam,
Science Park 904, 1098 Amsterdam, The Netherlands
5 - European Space Astronomy Centre, ESA, PO Box 78, 28691
Villanueva de la Cañada, Madrid, Spain
6 - Observatorio Astronómico Nacional (IGN), Ap 112, 28803 Alcalá de
Henares, Spain
7 - CAB, INTA-CSIC, Ctra de Torrejón a Ajalvir, km 4, 28850
Torrejón de Ardoz, Madrid, Spain
8 - Department of Astrophysics/IMAPP, Radboud University, Nijmegen, The
Netherlands
9 - Onsala Space Observatory, Dept. of Radio and Space Science,
Chalmers University of Technology, 43992 Onsala, Sweden
10 - Astronomical Institute, Utrecht University, Princetonplein 5, 3584
CC Utrecht, The Netherlands
11 - Harvard-Smithsonian Center for Astrophysics, 60 Garden Street,
Cambridge, MA 02138, USA
12 - The Johns Hopkins University, 3400 North Charles St,
Baltimore, MD 21218, USA
13 - Department of Astronomy, AlbaNova University Center, Stockholm
University, 10691 Stockholm, Sweden
14 - N. Copernicus Astronomical Center, Rabianska 8, 87-100 Torun,
Poland
15 - Joint ALMA Observatory, El Golf 40, Las Condes, Santiago, Chile
16 - Department of Physics and Astronomy, University of Waterloo,
Waterloo, ON Canada N2L 3G1, Canada
17 - SRON Netherlands Institute for Space Research, Landleven 12, 9747
AD Groningen, The Netherlands
18 - California Institute of Technology, Cahill Center for Astronomy
and Astrophysics 301-17, Pasadena, CA 91125, USA
19 - Infrared Processing and Analysis Center, California Institute of
Technology, MS 100-22, Pasadena, CA 91125, USA
20 - Laboratoire d'Études du Rayonnement et de la Matière en
Astrophysique, UMR 8112 CNRS/INSU, OP, ENS, UPMC, UCP, Paris, France
21 - LERMA, Observatoire de Paris, 61 avenue de l'Observatoire, 75014
Paris, France
22 - Institute Centre d'Étude Spatiale des Rayonnements, Université de
Toulouse [UPS], 31062 Toulouse Cedex 9, France
23 - CNRS/INSU, UMR 5187, 9 avenue du Colonel Roche, 31028 Toulouse
Cedex 4, France
Received 31 May 2010 / Accepted 29 June 2010
Abstract
Context. Circumstellar envelopes (CSEs) of a variety
of evolved stars have been found to contain ammonia (NH3)
in amounts that exceed predictions from conventional chemical models by
many orders of magnitude.
Aims. The observations reported here were performed
in order to better constrain the NH3 abundance
in the CSEs of four, quite diverse, oxygen-rich stars using the NH3
ortho JK
= 10 - 00 ground-state
line.
Methods. We used the Heterodyne Instrument for the
Far Infrared aboard Herschel to observe the NH3
JK = 10-00
transition near 572.5 GHz, simultaneously with the ortho-H2O
JKa,Kc
= 11,0 - 10,1 transition,
toward VY CMa, OH 26.5+0.6, IRC+10420, and IK Tau. We conducted non-LTE
radiative transfer modeling with the goal to derive the NH3
abundance in these objects' CSEs. For the last two stars, Very Large
Array imaging of NH3 radio-wavelength inversion
lines were used to provide further constraints, particularly on the
spatial extent of the NH3-emitting regions.
Results. We find remarkably strong NH3
emission in all of our objects with the NH3 line
intensities rivaling those of the ground state H2O
line. The NH3 abundances relative to H2
are very high and range from
to
for the objects we have studied.
Conclusions. Our observations confirm and even
deepen the circumstellar NH3 enigma. While our
radiative transfer modeling does not yield satisfactory fits to the
observed line profiles, it does lead to abundance estimates that
confirm the very high values found in earlier studies. New ways to
tackle this mystery will include further Herschel
observations of more NH3 lines and imaging with
the Expanded Very Large Array.
Key words: stars: AGB and post-AGB - supergiants - circumstellar matter
1 Introduction
Ammonia (NH3) was the first polyatomic molecule detected in an astronomical object (Cheung et al. 1968). It is ubiquitous in dark, dense interstellar cloud cores and an eminently useful thermometer of these regions (Walmsley & Ungerechts 1983; Danby et al. 1988). This, aided by the easy observability of its inversion lines - many of the astronomically most important ones crowd around 1.3 cm wavelength (24 GHz frequency) - make NH3 one of the most frequently observed interstellar molecules (Ho & Townes 1983).
NH3 has also been detected toward a
still limited, but diverse number of CSEs around evolved stars, first
using infrared (IR) heterodyne absorption spectroscopy toward the high
mass-loss asymptotic giant branch (AGB), extreme carbon star CW Leo (=
IRC+10216; Betz et al. 1979).
In addition, absorption was found toward a number of oxygen-rich
objects that included the long-period variable (LPV) o
Ceti (Betz & Goldhaber 1985)
and the super- or even hyper-luminous objects VY CMa and IRC+10420 (Monnier
et al. 2000; McLaren & Betz 1980). The
last study finds that around VY CMa the NH3 is
forming at 40 stellar
radii away from the star, where dust formation has well started.
Contemporaneously, several radio inversion lines were detected
also toward IRC+10216 (Kwok
et al. 1981; Bell
et al. 1982; Nguyen-Q-Rieu
et al. 1984). Later on, high-velocity cm-wavelength
NH3 emission plus absorption was found toward
the bipolar protoplanetary nebulae (PPNe) CRL 2688 and CRL 618 (Truong-Bach et al. 1988;
Martin-Pintado &
Bachiller 1992; Truong-Bach
et al. 1996). Toward CRL 618, P Cygni
profiles are observed with a full width at zero power (FWZP) of 100 km s-1.
Menten & Alcolea
(1995) detected high-velocity NH3
radio emission toward IRC+10420, the high mass-loss rate LPV IK Tau,
and the PPN OH 231.8+4.2. In the last case, they find high-velocity
emission over
70 km s-1
FWZP. Recently, Hasegawa
et al. (2006) report and discuss observations of the
NH3 line central to the present study, the
ortho-NH3 10-00
transition, toward IRC+10216 made with the Odin satellite.
One common, surprising result of all the
above studies is the exceedingly high NH3
abundances they report. Most of them cite values of several times 10-7
or even 10-6 relative to molecular hydrogen.
These numbers are in stark contrast to the results of thermodynamical
equilibrium calculations for the atmospheres of cool stars, which
predict the production of only negligible amounts of NH3,
of order 10-12 (Tsuji
1964). The pioneering study of Tsuji has been confirmed by
more recent work (see, e.g., Lafont
et al. 1982; Cherchneff
& Barker 1992, both for C-rich CSEs). Somewhat ad hoc
approaches to bringing observations and theory closer together involved
injecting a significant amount of NH3 in the
inner envelope (Nejad &
Millar 1988;
Nercessian et al. 1989).
Willacy &
Cherchneff (1998) include shock chemistry in their model of
IRC+10216, but still only produce an abundance of ,
at least three orders of magnitude below the value implied by
observations. As to bona fide shocked regions like PPN outflows, Morris et al. (1987)
suggested that, for OH 231.8+4.2, N2, which
binds most of the nitrogen, might be dissociated in the high-velocity
gas and that the high NH3 abundance might be the
result of a series of hydrogenation reactions. Whether this can be
confirmed by detailed chemical models remains to be explored.
For the present study, as described in Sect. 2, we observed the NH3 JK = 10-00 ortho ground-state transition in O-rich stars of widely different natures and mass loss rates: the high mass-loss LPV IK Tau, the peculiar red supergiant VY CMa, the archetypical OH/IR star OH 26.5+0.6, and the hypergiant IRC+10420. We chose a receiver setting that allowed simultaneous observations of the JKa,Kc = 11,0-10,1 transition of ortho-H2O. All of these objects have dense CSEs, and NH3 has been previously detected toward all of them but OH 26.5+0.6. In particular, for IK Tau and IRC+10420, single-dish observations of the (J,K) = (1,1) and (2,2) inversion lines have been reported by Menten & Alcolea (1995). Moreover, the emission in these lines has subsequently been imaged with the NRAO Very Large Array (VLA) with a resolution of a few arcseconds (Menten et al., in prep.; see Sect. 2.3).
The critical density of the cm-wavelength inversion lines is
on the order of 104 cm-3,
while that of the sub-mm 10-00
transition has a value 4 orders
of magnitude higher. Thus, both types of lines should provide
complementary information on different regions of the envelope. In
Sect. 3.1,
we give a general description of the sub-mm spectra we obtained with
HIFI aboard Herschel (Pilbratt
et al. 2010). Thereafter, in Sect. 3.2, we present
radiative transfer calculations conducted to model the observed line
profiles, taking advantage of the constraints from the VLA imaging.
These lead to NH3 abundance determinations.
2 Observations
2.1 Herschel/HIFI submillimeter observations
The observations were made with
the two orthogonal HIFI receivers available for each band, which in all
cases work in double side-band (DSB) mode (see de Graauw et al. 2010).
This effectively doubles the instantaneous intermediate frequency (IF)
coverage. We observed the four stars described above with a tuning
that, in the upper sideband, covers the frequency of the JK
= 10-00 ground state
transition of ortho-NH3 at
572.4981 GHz. The tuning was chosen to also cover the
frequency of the JKa,Kc
= 11,0-10,1 ground state
line of ortho-H2O at 556.9360 GHz in HIFI's
lower sideband. The observations were obtained using the
dual-beam-switching (DBS)
mode. In this mode, the HIFI internal steering mirror chops between the
source position and a position believed to be free of emission, which
was certainly the case for our observations. The
telescope then alternately locates the source in either of the
chopped beams, providing a double-difference calibration scheme, which
allows a more efficient cancellation of the residual standing waves in
the spectra. Additional details on this observing mode can be found in
de Graauw et al.
(2010). The double sideband system temperature was 100 K,
and the calibration uncertainty is estimated to be 10%. Spectral
baselines were excellent. Herschel's beam had a
size of 37'' FWHM at the observing frequency, which
is much larger than the NH3-emitting regions of
all our sources.
The HIFI data shown here were obtained using the wide band
spectrometer (WBS), which is an acousto-optical spectrometer,
providing a simultaneous coverage of the full instantaneous IF band in
the two available orthogonal receivers, with a (oversampled) channel
spacing of 0.5 MHz (0.27 km s-1),
about half the effective resolution. Spectra in the figures have been
resampled and smoothed to a channel spacing of 1.1 km s-1.
The data were processed with the standard HIFI pipeline using
HIPE, and nonstitched Level-2 data were exported using the HiClass tool
available in HIPE. Further processing, i.e. blanking spurious signals,
first order polynomial baseline removal, stitching of the spectrometer
subbands and averaging, was performed in CLASS. Since the quality of
the spectra measured in both horizontal and vertical polarization was
good, these were averaged to lower the final noise in the spectrum.
This approach is justified since polarization is not a concern for the
presented molecular-line analysis. All HIFI data were originally
calibrated in units of antenna temperature (
)
and were converted to the main-beam temperature (
)
scale according to
,
with the main-beam efficiency
.
In all cases we have assumed a side-band gain ratio of one.
2.2 Ammonia spectroscopy and astrophysics
The main focus of this letter is on the JK
= 10-00 line of ortho-NH3.
Ammonia microwave spectroscopy has a long history (see, e.g., Townes
& Schawlow 1955; Kukolich 1967).
Very briefly, because of the possible orientations of the hydrogen
spins, two different species of NH3 exist that
do not interconvert, ortho-NH3 and para-NH3.
Ortho-NH3 assumes states, JK,
with K = 0 or 3n, where n
is an integer (all H spins parallel) , whereas
for para-NH3 (not all H spins parallel). The
principal quantum numbers J and K
correspond to the total angular momentum and its projection on the
symmetry axis of the pyramidal molecule.
The temperature corresponding to the energy of the lowest para level (JK = 11) is 22 K above that of the lowest ortho level (JK = 00). Therefore, for formation in the interstellar gas phase, which involves reactions with high exothermicities, the ortho- to para-NH3 ratio is expected to attain its equilibrium value of unity (Umemoto et al. 1999). This situation is also expected to hold for CSEs, given that the IR studies cited above place the NH3 they observe in the hot medium close to the star.
A high-resolution study of the NH3 10-00
transition has very recently been presented by Cazzoli et al.
(2009). (Only) its upper state is split into several
hyperfine structure (hfs) components with the 1-2 MHz splitting resulting from the
coupling of the quadrupole moment of the N nucleus with the electric
field of the electrons. Two of these components are further split by
magnetic interactions. The mean frequency is 572498.1 MHz and
the centroid frequencies of the three main hfs groups are all within 2
MHz, corresponding to
1 km s-1,
much less than the line widths observed for the targets of this study
(see Fig. 1).
![]() |
Figure 1: HIFI spectra compared to radiative transfer model results: The thick black lines show spectra of the JK = 10-00 transition of ortho-NH3 for ( top to bottom) IK Tau, VY CMa, OH 26.5+0.6, and IRC+10420. The blue lines represent the ortho-H2O JKa,Kc = 11,0-10,1 spectra for the same stars in the same order. The dashed red lines represent the predictions for the NH3 line resulting from our radiative transfer modeling. The left- and right hand ordinates give the main-beam brightness temperature scales for the NH3 and the H2O lines, respectively. Except for IRC+10420, they have different ranges. |
Open with DEXTER |
2.3 VLA observations of inversion lines
In Sect. 3.2
we use data of the (J,K)
= (1,1) and (2,2) inversion lines to constrain our models for IK Tau
and IRC+10420. For these stars, single-dish observations of those lines
made with the Effelsberg 100 m telescope were reported by Menten & Alcolea (1995).
In addition, to place constraints on the spatial distribution of the NH3
molecules, we have used data obtained with the VLA that will be
published separately (Menten et al. in prep.). The hfs
splitting in the inversion lines in velocity units is much wider than
for the rotation line. However, because both the (1, 1) and
(2, 2) lines are very optically thin, as indicated by the
spectra and supported by our modeling (see Sect. 3.2), any
contribution of the hfs components will be factors of several weaker
than the main hfs component and neglected in the modeling. The
intensities of the spectra produced from the VLA images, which were
restored with a circular beam of
FWHM, used in that section, are consistent with the
published 100 m telescope values.
3 Results and analysis
3.1 NH
versus H
O
emission
In Figs. 1,
A.1 and
Table 1
we present the results of our HIFI observations of both the NH3
and the H2O ortho ground state lines, together
with the results of our NH3 modeling. All our
observed positions agree to within 2'' with the stars' 2MASS positions,
which themselves have an absolute accuracy of better than
(Cutri et al. 2003).
The determination of the LSR ranges is somewhat subjective and the
upper and lower velocities are uncertain by
a few km s-1 for weaker lines.
For all entries, the formal error in
is smaller than 0.1 K km s-1.
For VY CMa we used the higher of the literature mass-loss rate
values scaled to the recently measured trigonometric parallax distance,
1100 pc (Choi et al.
2008). For both IK Tau and IRC+10420 the lower and the higher
values of
are implied by the cm lines and the submm line, respectively.
Inspecting Fig. 1
and the table, it is striking to see that the luminosity (integrated
intensity) in the NH3 and H2O
ground-state lines is of comparable magnitude for all of our objects.
The NH3/H2O line ratios
are
0.50, 0.30, 0.28, and
0.42 for IK Tau, VY CMa, OH 26.5+0.6, and IRC+10420,
respectively. One has to keep in mind that H2O
is a major molecular constituent of our CSEs, while even the presence
of observable NH3 emission is completely
unexplained!
Another remarkable result is that the velocity ranges covered by the two lines are almost identical, which suggests that the bulk of the material producing the emission for both is similar. Moreover, for all our targets, both lines' FWZP values are lower, but comparable to twice the terminal velocity, implying that both molecules are present in the outer layers of the envelope, where the material has almost been fully accelerated. Furthermore, we point out the clear self absorption in the blue wing of the H2O lines toward IK Tau and VY CMa, which proves that the line emitting region covers the whole envelope. Whether this is also true for the NH3 line is a priori not clear.
3.2 Radiative transfer modeling and constraints on abundances
Table 1: Results of HIFI NH3 and H2O observations and NH3 modeling.
The NH3 emission of the sources has
been modeled with the Monte
Carlo radiative transfer code RATRAN developed and described by Hogerheijde & van der Tak
(2000). For NH3, RATRAN uses collision
rates calculated by Danby
et al. (1988). Power
laws for the density and temperature were used to describe the
physical structure of the envelope, using as input published values for
the mass loss rate and expansion velocity (see Table 1). For
IRC+10420, envelope parameters from Dinh-V.-Trung
et al. (2009) were used and
for IK Tau, VY CMa, and OH26.5+0.6 we refer to the modeling of Decin et al. (2010),
Decin et al. (2006),
and Justtanont et al.
(2006), respectively.
The VLA data yield an extent of 4'' for the NH3
emitting region around IRC+10420 and
for that around IK Tau, numbers we use for our modeling.
To fit the submm NH3 lines observed with HIFI, the NH3 abundance was varied in a first iteration. For the two sources with additional data from the cm inversion lines, those (para) lines were modeled as well, using an ortho-to-para ratio of 1, appropriate for formation of NH3 under high temperatures (see Sect. 2.2). Interestingly, this does not lead to a satisfying fit for both the cm NH3 inversion lines and the submm ground state line. With a fit adjusted to reproduce the cm lines, the submm line is underestimated by a factor of 10 for IK Tau.
Since high densities are needed to excite the submm line, its
emission must arise from the inner part of the envelope, further inward
than the cm-line emitting region. Our modeling suggests densities above
a few times 106 cm-3
and temperatures in the 10-100 K range.
This discrepancy between the physical conditions required to produce
the observed cm emission, on the one hand, and the submm emission, on
the other, is even greater for the very extended but relatively
low-density shell
of IRC+10420. To reach densities high enough to excite the NH3
sub-mm line, the mass-loss rate had to be increased to
yr-1,
i.e., a factor
3 higher than the value derived by Dinh-V.-Trung
et al. (2009) and the inner radius reduced to
cm,
which is twice the value of the hot inner shell proposed by these
authors. Then agreement between the
abundances obtained from the cm and submm lines can be reached within
a factor of 2. Interestingly, De Beck et al. (2010,
accepted for publication), derive a value of
yr-1
for IRC+10420's mass loss rate based on multi-transition modeling of
CO.
To reproduce the strong submm NH3 line
from VY CMa, the highest mass-loss rate and largest radius from the
various shells discussed by
Decin et al. (2006)
had to be used, scaled to D = 1100 pc (see
Sect. 3.1).
The outer radius that led to a best fit
for OH26.5+0.6 is cm.
For this source, the same
temperature profile as for IK Tau was used.
The line profiles produced by our NH3
model calculations are shown in Figs. 1 and A.1 overlaid on the
measured spectra.
The resulting NH3 abundances for the four
observed stars range from
to
(see Table 1).
While they are in line with circumstellar NH3
abundances derived from the inversion lines alone and from IR
spectroscopy, we note, as a caveat, that our model calculations did not
consider the possibility of IR pumping of the 10-00
transition. IR pumping of the H2O 11,0-10.1
line in IRC+10216's CSE via various vibrational bands has been
investigated by Agúndez
& Cernicharo (2006), who found it to be the dominant
source of excitation of this high critical density line
over much of the star's outer envelope. Consequently, their modeling
suggests an order of magnitude lower H2O
abundance than invoked earlier from SWAS and Odin observations (Melnick et al. 2001;
Hasegawa et al. 2006).
4 Summary and outlook
The high critical density of the JK = 10-00 ortho-NH3 line allows investigations of NH3 in a new density regime of circumstellar envelopes. However, the remarkably high abundances we determine for all our objects confirm and significantly strengthen the finding that this molecule exists in a variety of CSEs at levels not explained by current chemical models. Better constraints on the emitting regions will come from HIFI observations of a number of NH3 lines, which are actually evident in the (heavily spectrally diluted) PACS spectrum of VY CMa (Royer et al. 2010). Given their intensities, such observations appear eminently feasible. They would place tight constraints on future radiative transfer modeling that includes infrared excitation. Additionally, with its extremely wideband new generation digital correlator, the Expanded Very Large Array (EVLA) will allow simultaneous imaging of many NH3 inversion lines. Nevertheless, given the weakness of these lines toward ordinary AGB stars, PPNe being an exception, EVLA observations will be challenging.
AcknowledgementsHIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France, and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri- INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiología (CSIC-INTA); Sweden: Chalmers University of Technology - MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University - Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. HCSS / HSpot / HIPE is a joint development by the Herschel Science Ground Segment Consortium, consisting of ESA, the NASA Herschel Science Center, and the HIFI, PACS and SPIRE consortia. This work has been partially supported by the Spanish MICINN, within the program CONSOLIDER INGENIO 2010, under grant ``Molecular Astrophysics: The Herschel and ALMA Era - ASTROMOL'' (ref.: CSD2009-00038). R. Sz. and M. Sch. acknowledge support from grant N 203 393334 from the Polish MNiSW. K. J. acknowledges the funding from SNSB. J. C. thanks funding from MICINN, grant AYA2009-07304.
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Appendix A: NH3 rotational and inversion line spectra and fits for IK Tau and IRC+10420
Figure A.1 shows, for IK Tau and IRC+10420, the HIFI spectra of the JK = 10-00 ortho-NH3 line and the spectra of the (J,K) = (1,1) and (2,2) para-NH3 lines produced from our VLA data together with our best fit model predictions.
![]() |
Figure A.1: Spectra of NH3 transitions for IK Tau ( left column) and IRC+10420 ( right column). Top row: HIFI spectra of the JK = 10-00 ortho-NH3 line. Middle row: VLA spectra of the (J,K) = (1,1) para-NH3 line. Bottom row: VLA spectra of the (J,K) = (2,2) para-NH3 line. The intensity scales apply for both sources. The lefthand ordinate gives main-beam brightness temperature in a 40'' FWHM beam, while the righthand ordinate gives flux density in Jy units. In all panels the red dashed line represents our best-fit model prediction. The blue bars give the spacings and theoretical relative intensities of the main groups of hfs components determined by Cazzoli et al. (2009) for the 10-00 transition and by Kukolich (1967) for the (1, 1) and (2, 2) inversion lines, respectively. |
Open with DEXTER |
Footnotes
- ... enigma
- Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
- ...
- Appendix A (page 5) is only available in electronic form at http://www.aanda.org
All Tables
Table 1: Results of HIFI NH3 and H2O observations and NH3 modeling.
All Figures
![]() |
Figure 1: HIFI spectra compared to radiative transfer model results: The thick black lines show spectra of the JK = 10-00 transition of ortho-NH3 for ( top to bottom) IK Tau, VY CMa, OH 26.5+0.6, and IRC+10420. The blue lines represent the ortho-H2O JKa,Kc = 11,0-10,1 spectra for the same stars in the same order. The dashed red lines represent the predictions for the NH3 line resulting from our radiative transfer modeling. The left- and right hand ordinates give the main-beam brightness temperature scales for the NH3 and the H2O lines, respectively. Except for IRC+10420, they have different ranges. |
Open with DEXTER | |
In the text |
![]() |
Figure A.1: Spectra of NH3 transitions for IK Tau ( left column) and IRC+10420 ( right column). Top row: HIFI spectra of the JK = 10-00 ortho-NH3 line. Middle row: VLA spectra of the (J,K) = (1,1) para-NH3 line. Bottom row: VLA spectra of the (J,K) = (2,2) para-NH3 line. The intensity scales apply for both sources. The lefthand ordinate gives main-beam brightness temperature in a 40'' FWHM beam, while the righthand ordinate gives flux density in Jy units. In all panels the red dashed line represents our best-fit model prediction. The blue bars give the spacings and theoretical relative intensities of the main groups of hfs components determined by Cazzoli et al. (2009) for the 10-00 transition and by Kukolich (1967) for the (1, 1) and (2, 2) inversion lines, respectively. |
Open with DEXTER | |
In the text |
Copyright ESO 2010
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