We report the identification of SH $\Delta v=1$ ro-vibrational lines in the
published high-resolution infrared spectrum of the S-type star, R And. This is
the first astronomical detection of this molecule. The lines show inverse
P-Cygni profiles, indicating infall motion of the molecular layer due to
stellar pulsation. A simple spherical shell model with a constant infall
velocity is adopted to determine the condition of the layer. It is found that a
single excitation temperature of 2200 K reproduces the observed line
intensities satisfactory. SH is located in a layer from 1.0 to ~1.1 stellar
radii, which is moving inward with a velocity of 9 km s-1. These results are
consistent with the previous measurements of CO $\Delta v=3$ transitions. The
estimated molecular abundance SH/H is 1x10^-7, consistent with a thermal
equilibrium calculation.Comment: 10 pages, 2 figures. Accepted for publication in ApJ Letter

Beck H. K. B.

de Graauw Th.

Duari D.

Duley W. W.

Heiles C. E.

I. Yamamura

K. Kawaguchi

Kessler M. F.

Omont A.

S. T. Ridgway

Tsuji T.

Woitke P.

Yamamura I.

English

arXiv

山村, 一誠

Kawaguchi, K.

Ridgway, S. T.

Yamamura, Issei

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Identification of SH Δv=1 Ro-vibrational Lines in R Andromedae

Yamamura, I.

Ridgway, S.T.

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Identification of SH Delta_v=1 Ro-vibrational Lines in R Andromedae
Yamamura, I.; Kawaguchi, K.; Ridgway, S.T.
Published in:
Astrophysical Journal
DOI:
10.1086/312420
Link to publication
Citation for published version (APA):
Yamamura, I., Kawaguchi, K., & Ridgway, S. T. (2000). Identification of SH Delta_v=1 Ro-vibrational Lines in R
Andromedae. Astrophysical Journal, 528, L33-L36. https://doi.org/10.1086/312420
General rights
It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s),
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Download date: 05 Feb 2021
L33
The Astrophysical Journal, 528:L33–L36, 2000 January 1
q 2000. The American Astronomical Society. All rights reserved. Printed in U.S.A.
IDENTIFICATION OF SH RO-VIBRATIONAL LINES IN R ANDROMEDAEDv = 1
I. Yamamura
Astronomical Institute “Anton Pannekoek,” University of Amsterdam, Kruislaan 403,
1098 SJ, Amsterdam, The Netherlands; yamamura@astro.uva.nl
K. Kawaguchi
Faculty of Science, Okayama University, 3-1-1, Tsushima-naka,
Okayama 700-8530, Japan; okakent@cc.okayama-u.ac.jp
and
S. T. Ridgway
National Optical Astronomy Observatories,1 P.O. Box 26732, Tucson, AZ 85726; ridgway@noao.edu
Received 1999 September 2; accepted 1999 November 2; published 1999 December 1
ABSTRACT
We report the identification of SH ro-vibrational lines in the published high-resolution infrared spectrumDv = 1
of the S-type star R Andromedae. This is the first astronomical detection of this molecule. The lines show inverse
P Cygni profiles, indicating infall motion of the molecular layer due to stellar pulsation. A simple spherical shell
model with a constant infall velocity is adopted to determine the condition of the layer. It is found that a single
excitation temperature of 2200 K reproduces the observed line intensities satisfactorily. SH is located in a layer
from 1.0 to ∼1.1 stellar radii, which is moving inward with a velocity of 9 km s21. These results are consistent
with the previous measurements of CO transitions. The estimated molecular abundance SH/H isDv = 3
, consistent with a thermal equilibrium calculation.271 # 10
Subject headings: infrared: stars — line: identification — stars: AGB and post-AGB — stars: atmospheres —
stars: individual (R Andromedae)
1. INTRODUCTION
The chemistry of sulfur-containing species in space is es-
pecially interesting because of their chemical activity and rel-
atively high abundance (Duley, Millar, & Williams 1980). It is
known that abundances of sulfur-bearing molecules are strongly
influenced by the presence of shocks (Hartquist, Oppenheimer,
& Dalgarno 1980). So far, 14 sulfur-bearing species have been
identified in space; CS, SO, NS, SiS, SO1, SH2, OCS, CCS,
C3S, H2CS, HNCS, SO2, HCS
1, and CH3SH. However, the
simplest sulfur compound, SH, has not been detected in spite
of radio astronomical searches using the L-type doubling tran-
sitions (Meeks, Gordon, & Litvak 1969; Heiles & Turner 1971).
While sulfur chemistry in the circumstellar envelope of red
giant stars has been studied extensively (e.g., Omont et al.
1993), that in the atmosphere has been regarded as in the ther-
mal equilibrium state (Tsuji 1964, 1973). In the atmosphere of
oxygen-rich giants, SH is the molecule first formed from the
sulfur atom, at a temperature of about 2000 K. The SH abun-
dance decreases when the temperature is below ∼1500 K, and
H2S and SiS become the dominant species. On the other hand,
Yamamura et al. (1999a) report the detection of the n3 infrared
band of SO2 in the spectra of oxygen-rich Mira variables ob-
tained by the Short-Wavelength Spectrometer (SWS: de
Graauw et al. 1996) on board the Infrared Space Observatory
(ISO: Kessler et al. 1996). Their model analysis indicates that
the molecules are located in the extended atmosphere at about
5 R?. The abundance of SO2 is 5–10 orders of magnitude larger
than the values in thermal equilibrium (Tsuji 1973; Woitke et
al. 1999). The result strongly suggests the presence of non-
equilibrium processes in the extended atmosphere, probably
related to shocks due to stellar pulsation (Beck et al. 1992;
Duari, Cherchneff, & Willacy 1999).
1 Operated by the Association of Universities for Research in Astronomy
under cooperative agreement with the National Science Foundation.
In this Letter, we report the detection of SH ro-vibrational
transition lines in the published high-resolution infrared spec-
trum of the S-type star R And. We discuss the physical and
chemical conditions of the SH layer in the star.
2. IDENTIFICATION OF SH LINES
The data used in this study were obtained with the Fourier-
transform spectrometer at the Kitt Peak National Observatory
4 m telescope and were published in Ridgway et al. (1984).
R And is a Mira variable with a period of 409 days and a
visual amplitude of 9.1 mag (Kholopov et al. 1988). The spec-
tral type is in the range S3,5e–S8,8e. The observation of
R And was performed at the optical variable phase of f =
. Unfortunately, the reduced data were lost after several0.82
updates of archive formats at the observatory. Therefore, we
redigitized the data from the printed spectrum. The results may
be as accurate as the original within ∼0.02 cm21 in wavenumber
and a few percent in intensity. The spectrum was shifted by
5.2 km s21 to longer wavelengths to adjust the absorption min-
imum of HCl lines at their rest frequencies (Ridgway et al.
1984). No correction for terrestrial motion was applied. In their
original paper, Ridgway et al. (1984) give identifications of
OH, NH, CH, SiO, CS, HCl, and atomic lines. The spectrum
of R And, especially in the wavelengths shorter than the SiO
first-overtone bandheads, is dominated by HCl lines. OH and
NH lines are detected, but much less prominently than in the
oxygen-rich stars like a Ori and a Tau. There are many strong
lines left unidentified. Figure 1 shows the spectrum of R And
between 2700 and 2750 cm21. The positions of SH and HCl
ro-vibrational transitions are indicated. The frequencies are cal-
culated from the molecular constants given by Ram et al. (1995)
for SH and are taken from the HITRAN database 1996 edition
(Rothman et al. 1992) for HCl. It is obvious that many un-
identified strong lines are attributed to SH transitions. We as-
L34 IDENTIFICATION OF SH IN R AND Vol. 528
Fig. 1.—Part of the spectrum of R And obtained by Ridgway et al. (1984). The positions of transitions of SH and 34SH (upper) and HCl (lower) areDv = 1
indicated by tick marks. The notation of the transitions is the electronic angular momentum, the upper vibrational level, and the rotational line index for SH, and
the rotational line index, the isotope index (5: H35Cl, 7: H37Cl), and the upper vibrational level for HCl, respectively.
Fig. 2.—Synthesized model spectrum (upper) compared with the observation in six wavelength regions. The regions are chosen so that contamination of other
spectral lines is minimized and that a wide range of energy levels is covered. The model assumes a spherical shell falling toward the stellar surface with a velocity
of 9 km s21. The molecules are distributed from 1.0 R? with a scale height of 0.08 R?. The model assumes constant excitation temperature of 2200 K, column
density of cm22, and Doppler broadening velocity of 6 km s21. The model spectrum is shifted by 214 km s21. Lines indicated by tick marks are listed204.0 # 10
in Table 1.
signed 39, 41, and 11 transitions in the , 2–1, and 3–2v = 1–0
bands, respectively, between 2500 and 2778 cm21. The lower
state energies of these transitions are up to 7000 cm21, indi-
cating that the molecules are highly excited. The isotope 34SH
may also be detected. The frequencies of 34SH lines are esti-
mated from the molecular constants of SH using the relation
of reduced mass (Herzberg 1950).
3. MODELING
We analyze the observed SH line profiles with a simple
model. The SH (and also HCl) lines in R And show inverse
P Cyg profiles, indicating that the molecular layer is moving
inward toward the star due to stellar pulsation. We therefore
apply a spherical shell model with a constant infall velocity.
No. 1, 2000 YAMAMURA, KAWAGUCHI, & RIDGWAY L35
TABLE 1
SH Lines Indicated in Figure 2
Numbera
Frequency
(cm21) Qb Transitionc
El
d
(cm21)
1 . . . . . . . 2532.1257 3/2 1–0 P 3.5ff 110.7175
2532.1486 3/2 1–0 P 3.5ee 110.6810
2 . . . . . . . 2534.7858 1/2 3–2 R 7.5ee 6038.9539
2534.8657 1/2 3–2 R 7.5ff 6040.7705
3 . . . . . . . 2546.2628 1/2 2–1 R 1.5ee 2994.8376
4 . . . . . . . 2546.4908 1/2 2–1 R 1.5ff 2995.3755
5 . . . . . . . 2546.9511 1/2 3–2 R 8.5ee 6192.1858
2547.0067 1/2 3–2 R 8.5ff 6194.1577
6 . . . . . . . 2549.2843 1/2 1–0 P 2.5ff 446.0913
7 . . . . . . . 2549.5750 1/2 1–0 P 2.5ee 445.2626
8 . . . . . . . 2641.3159 3/2 3–2 R 24.5ee 10354.2802
2641.3458 3/2 3–2 R 24.5ff 10358.7197
9 . . . . . . . 2642.8296 3/2 1–0 R 1.5ee 0.0000
2642.8395 3/2 1–0 R 1.5ff 0.0037
10 . . . . . . 2644.6568 1/2 1–0 R 1.5ee 396.9951
2644.7048 3/2 2–1 R 8.5ee 3286.0606
2644.7949 3/2 2–1 R 8.5ff 3286.4309
2644.8958 1/2 1–0 R 1.5ff 397.5540
11 . . . . . . 2659.3953 3/2 1–0 R 2.5ee 46.1293
2659.4143 3/2 1–0 R 2.5ff 46.1440
12 . . . . . . 2661.5489 1/2 2–1 R 9.5ee 3889.9056
2661.5866 1/2 2–1 R 9.5ff 3892.0848
13 . . . . . . 2661.9331 1/2 1–0 R 2.5ee 445.2626
2662.1518 1/2 1–0 R 2.5ff 446.0913
14 . . . . . . 2709.9111 1/2 1–0 R 5.5ee 705.7060
2710.0575 1/2 1–0 R 5.5ff 707.2638
15 . . . . . . 2710.9529 1/2 2–1 R 14.5ff 5042.3624
2711.0189 1/2 2–1 R 14.5ee 5039.8647
16 . . . . . . 2770.9408 3/2 1–0 R 10.5ee 1074.9261
2771.0636 3/2 1–0 R 10.5ff 1075.6188
a Numbers in Figure 2.
b Electronic angular momentum index.
c Vibrational and rotational transition indices.
d Lower state energy relative to , , .v = 0 J = 1.5 Q = 3/2
The molecules in front of the star cause absorption, while those
extended in the blank sky contribute as emission. Considering
that the shell may be in the atmosphere, we adopt an expo-
nential density law , where r0 is the scalen(r) ∝ exp (2r/r )0
height. The star is assumed to be a 3000 K blackbody. For
simplification, a constant excitation temperature is adopted, and
the energy population of the molecule is calculated by assuming
local thermodynamic equilibrium. This may be justified if the
molecular shell is thin and in the high-density region near the
photosphere. The line intensity of SH is calculated based on
Benidar et al. (1991), which takes account of the Herman-Wallis
effect. The spectrum is normalized by the stellar continuum.
No smoothing is applied.
The excitation temperature can be determined from the rel-
ative intensities of the lines at different energy levels; higher
temperatures excite the molecules to higher energy levels and
increase the line strength from these levels. We find that 2200
K is most reasonable for the present case. A turbulent velocity
of 6 km s21 and infall velocity of 9 km s21 reproduce the line
profiles. The model spectrum is shifted by 214 km s21. Con-
sidering the terrestrial velocity of 22.7 km s21 at transit of the
observation and the shift applied by Ridgway et al. (1984),
15.2 km s21, a radial velocity of 216.5 km s21 is obtained.
The inner radius and the scale height of the SH shell is 1.0
and 0.08 times the stellar radius, respectively. The SH column
density in the shell is cm22. The uncertainties of204.0 # 10
the parameters, which changes the model spectrum by about
10%, are 5100 K for excitation temperature, a factor of 2 for
column density, 50.01 R? for scale height, and 51 km s
21
for the velocities. The radial velocity has an error of 52
km s21 due to the redigitization process. The model spectrum
is compared with the observation in Figure 2. The wavelength
regions are selected so that the contamination of other spectral
lines is minimal and that a wide range of energy levels is
covered. Strong lines in Figure 2 are listed in Table 1. The fit
is satisfactory in most of the lines. Fitting of 34SH lines results
in an isotopic abundance ratio of 5%–10%. We note that the
same parameters also give reasonable fits for the HCl lines with
a column density of cm22.193.0 # 10
4. DISCUSSION
Why are SH lines so prominent in R And, an S-type star?
S-type stars are characterized by their chemical anomaly of
similar carbon and oxygen abundances. This leaves few C and
O atoms for further chemical processes after formation of CO
molecules at 4000–5000 K. SH should be quite abundant in
the atmosphere of oxygen-rich stars but a minor product in a
carbon-rich environment (Tsuji 1973). Since we do see SiO
lines, but no CS line, in the spectrum of R And, the star is
slightly oxygen rich. Nevertheless, it is not expected that SH
is much more abundant in S-type stars than O-rich stars. This
also holds for HCl, which is the most abundant Cl-bearing
molecule in an oxygen-rich environment, although the absolute
abundance is by 1 order of magnitude lower than SH. Ridgway
et al. (1984) suggested that the atmosphere of S-type stars is
more transparent than O-rich stars, so that the lines of minor
species could be stronger due to larger path length. We espe-
cially emphasize the contribution of the H2O molecules. In the
same paper, Ridgway et al. reported that an enormous number
of lines heavily blanket the 2400–2800 cm21 region of the
Ceti spectrum. They suspected that these are highly excitedo
water lines. This is supported by the ISO/SWS observation of
Ceti (Yamamura, de Jong, & Cami 1999b). Despite the rel-o
atively poor resolution of the SWS spectrum, they demonstrate
that the star shows highly excited H2O lines in the 3.5–4.0 mm
region, arising from a hot (2000 K) and optically thick mo-
lecular layer. Probably, in O-rich stars, SH (and HCl) lines are
weaker because of the shorter path length and also heavily
contaminated by the hot water lines. On the other hand, H2O
molecules are not favored in the atmosphere of S-type stars.
The thermal equilibrium abundance of H2O in S-type stars is
3–4 orders of magnitude lower than in O-rich stars (Tsuji 1964).
The derived infall velocity and the excitation temperature of
the SH layer are consistent with the measurement of CO
lines by Hinkle, Scharlach, & Hall (1984) at ,Dv = 3 f = 0.80
indicating that the SH molecules are in the same region as hot
CO near the photosphere. Comparison with the CO column
density cm22 given by Hinkle et al. (1984) leads242.6 # 10
to . In thermal equilibrium at the temperature27SH/H = 1 # 10
of 2200 K and gas pressure of , the SH abundancelog (P ) = 1.0g
is (Tsuji 1973; T. Tsuji 1999, private communication).272 # 10
This value is insensitive to the C/O ratio as long as .C/O ! 1
The present estimate of SH abundance in R And, although it
is rather crude, is consistent with this calculated value. The
sulfur chemistry in the SH layer still follows thermal equilib-
rium because of its high density and high temperature.
We see no clear evidence of distinct velocity and/or different
temperature components of SH lines in the spectrum. This im-
plies that the SH molecules are distributed only in a thin layer
in the atmosphere. In thermal equilibrium, SH is most abundant
around 1800 K and then is rather quickly transformed to H2S
or SiS below ∼1500 K (Tsuji 1973). Otherwise, nonequilibrium
chemical reactions may lead to completely different compo-
L36 IDENTIFICATION OF SH IN R AND Vol. 528
sitions in the extended atmosphere, e.g., the enhancement of
SO2 in oxygen-rich stars (Yamamura et al. 1999a; Beck et al.
1992). We could not find any clear indications of H2S or SO2
in the spectrum of R And. The upper limit of the H2S column
density is at least a factor of 10 larger than the observed amount
of SH. A dioxide molecule SO2 may not be abundant in the
atmospheres of S-type stars. Other possible candidates—SO
and SiS—have no transition in the present wavelength cov-
erage.
The authors are grateful to Professor T. Tsuji for his sug-
gestion on thermal equilibrium chemistry and calculations of
SH abundance. I. Y. acknowledges financial support from a
NWO PIONIER grant.
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Identification of SH Delta_v=1 Ro-vibrational Lines in R Andromedae

International Migration, Integration and Social Cohesion online publications

UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl)UvA-DARE (Digital Academic Repository)Identification of SH Delta_v=1 Ro-vibrational Lines in R AndromedaeYamamura, I.; Kawaguchi, K.; Ridgway, S.T.DOI10.1086/312420Publication date2000Published inAstrophysical JournalLink to publicationCitation for published version (APA):Yamamura, I., Kawaguchi, K., & Ridgway, S. T. (2000). Identification of SH Delta_v=1 Ro-vibrational Lines in R Andromedae. Astrophysical Journal, 528, L33-L36.https://doi.org/10.1086/312420General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s)and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an opencontent license (like Creative Commons).Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, pleaselet the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the materialinaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letterto: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. Youwill be contacted as soon as possible.Download date:14 Apr 2023L33The Astrophysical Journal, 528:L33–L36, 2000 January 1q 2000. The American Astronomical Society. All rights reserved. Printed in U.S.A.IDENTIFICATION OF SH RO-VIBRATIONAL LINES IN R ANDROMEDAEDv = 1I. YamamuraAstronomical Institute “Anton Pannekoek,” University of Amsterdam, Kruislaan 403,1098 SJ, Amsterdam, The Netherlands; yamamura@astro.uva.nlK. KawaguchiFaculty of Science, Okayama University, 3-1-1, Tsushima-naka,Okayama 700-8530, Japan; okakent@cc.okayama-u.ac.jpandS. T. RidgwayNational Optical Astronomy Observatories,1 P.O. Box 26732, Tucson, AZ 85726; ridgway@noao.eduReceived 1999 September 2; accepted 1999 November 2; published 1999 December 1ABSTRACTWe report the identification of SH ro-vibrational lines in the published high-resolution infrared spectrumDv = 1of the S-type star R Andromedae. This is the first astronomical detection of this molecule. The lines show inverseP Cygni profiles, indicating infall motion of the molecular layer due to stellar pulsation. A simple spherical shellmodel with a constant infall velocity is adopted to determine the condition of the layer. It is found that a singleexcitation temperature of 2200 K reproduces the observed line intensities satisfactorily. SH is located in a layerfrom 1.0 to ∼1.1 stellar radii, which is moving inward with a velocity of 9 km s21. These results are consistentwith the previous measurements of CO transitions. The estimated molecular abundance SH/H isDv = 3, consistent with a thermal equilibrium calculation.271 # 10Subject headings: infrared: stars — line: identification — stars: AGB and post-AGB — stars: atmospheres —stars: individual (R Andromedae)1. INTRODUCTIONThe chemistry of sulfur-containing species in space is es-pecially interesting because of their chemical activity and rel-atively high abundance (Duley, Millar, & Williams 1980). It isknown that abundances of sulfur-bearing molecules are stronglyinfluenced by the presence of shocks (Hartquist, Oppenheimer,& Dalgarno 1980). So far, 14 sulfur-bearing species have beenidentified in space; CS, SO, NS, SiS, SO1, SH2, OCS, CCS,C3S, H2CS, HNCS, SO2, HCS1, and CH3SH. However, thesimplest sulfur compound, SH, has not been detected in spiteof radio astronomical searches using the L-type doubling tran-sitions (Meeks, Gordon, & Litvak 1969; Heiles & Turner 1971).While sulfur chemistry in the circumstellar envelope of redgiant stars has been studied extensively (e.g., Omont et al.1993), that in the atmosphere has been regarded as in the ther-mal equilibrium state (Tsuji 1964, 1973). In the atmosphere ofoxygen-rich giants, SH is the molecule first formed from thesulfur atom, at a temperature of about 2000 K. The SH abun-dance decreases when the temperature is below ∼1500 K, andH2S and SiS become the dominant species. On the other hand,Yamamura et al. (1999a) report the detection of the n3 infraredband of SO2 in the spectra of oxygen-rich Mira variables ob-tained by the Short-Wavelength Spectrometer (SWS: deGraauw et al. 1996) on board the Infrared Space Observatory(ISO: Kessler et al. 1996). Their model analysis indicates thatthe molecules are located in the extended atmosphere at about5 R?. The abundance of SO2 is 5–10 orders of magnitude largerthan the values in thermal equilibrium (Tsuji 1973; Woitke etal. 1999). The result strongly suggests the presence of non-equilibrium processes in the extended atmosphere, probablyrelated to shocks due to stellar pulsation (Beck et al. 1992;Duari, Cherchneff, & Willacy 1999).1 Operated by the Association of Universities for Research in Astronomyunder cooperative agreement with the National Science Foundation.In this Letter, we report the detection of SH ro-vibrationaltransition lines in the published high-resolution infrared spec-trum of the S-type star R And. We discuss the physical andchemical conditions of the SH layer in the star.2. IDENTIFICATION OF SH LINESThe data used in this study were obtained with the Fourier-transform spectrometer at the Kitt Peak National Observatory4 m telescope and were published in Ridgway et al. (1984).R And is a Mira variable with a period of 409 days and avisual amplitude of 9.1 mag (Kholopov et al. 1988). The spec-tral type is in the range S3,5e–S8,8e. The observation ofR And was performed at the optical variable phase of f =. Unfortunately, the reduced data were lost after several0.82updates of archive formats at the observatory. Therefore, weredigitized the data from the printed spectrum. The results maybe as accurate as the original within ∼0.02 cm21 in wavenumberand a few percent in intensity. The spectrum was shifted by5.2 km s21 to longer wavelengths to adjust the absorption min-imum of HCl lines at their rest frequencies (Ridgway et al.1984). No correction for terrestrial motion was applied. In theiroriginal paper, Ridgway et al. (1984) give identifications ofOH, NH, CH, SiO, CS, HCl, and atomic lines. The spectrumof R And, especially in the wavelengths shorter than the SiOfirst-overtone bandheads, is dominated by HCl lines. OH andNH lines are detected, but much less prominently than in theoxygen-rich stars like a Ori and a Tau. There are many stronglines left unidentified. Figure 1 shows the spectrum of R Andbetween 2700 and 2750 cm21. The positions of SH and HClro-vibrational transitions are indicated. The frequencies are cal-culated from the molecular constants given by Ram et al. (1995)for SH and are taken from the HITRAN database 1996 edition(Rothman et al. 1992) for HCl. It is obvious that many un-identified strong lines are attributed to SH transitions. We as-L34 IDENTIFICATION OF SH IN R AND Vol. 528Fig. 1.—Part of the spectrum of R And obtained by Ridgway et al. (1984). The positions of transitions of SH and 34SH (upper) and HCl (lower) areDv = 1indicated by tick marks. The notation of the transitions is the electronic angular momentum, the upper vibrational level, and the rotational line index for SH, andthe rotational line index, the isotope index (5: H35Cl, 7: H37Cl), and the upper vibrational level for HCl, respectively.Fig. 2.—Synthesized model spectrum (upper) compared with the observation in six wavelength regions. The regions are chosen so that contamination of otherspectral lines is minimized and that a wide range of energy levels is covered. The model assumes a spherical shell falling toward the stellar surface with a velocityof 9 km s21. The molecules are distributed from 1.0 R? with a scale height of 0.08 R?. The model assumes constant excitation temperature of 2200 K, columndensity of cm22, and Doppler broadening velocity of 6 km s21. The model spectrum is shifted by 214 km s21. Lines indicated by tick marks are listed204.0 # 10in Table 1.signed 39, 41, and 11 transitions in the , 2–1, and 3–2v = 1–0bands, respectively, between 2500 and 2778 cm21. The lowerstate energies of these transitions are up to 7000 cm21, indi-cating that the molecules are highly excited. The isotope 34SHmay also be detected. The frequencies of 34SH lines are esti-mated from the molecular constants of SH using the relationof reduced mass (Herzberg 1950).3. MODELINGWe analyze the observed SH line profiles with a simplemodel. The SH (and also HCl) lines in R And show inverseP Cyg profiles, indicating that the molecular layer is movinginward toward the star due to stellar pulsation. We thereforeapply a spherical shell model with a constant infall velocity.No. 1, 2000 YAMAMURA, KAWAGUCHI, & RIDGWAY L35TABLE 1SH Lines Indicated in Figure 2NumberaFrequency(cm21) Qb TransitioncEld(cm21)1 . . . . . . . 2532.1257 3/2 1–0 P 3.5ff 110.71752532.1486 3/2 1–0 P 3.5ee 110.68102 . . . . . . . 2534.7858 1/2 3–2 R 7.5ee 6038.95392534.8657 1/2 3–2 R 7.5ff 6040.77053 . . . . . . . 2546.2628 1/2 2–1 R 1.5ee 2994.83764 . . . . . . . 2546.4908 1/2 2–1 R 1.5ff 2995.37555 . . . . . . . 2546.9511 1/2 3–2 R 8.5ee 6192.18582547.0067 1/2 3–2 R 8.5ff 6194.15776 . . . . . . . 2549.2843 1/2 1–0 P 2.5ff 446.09137 . . . . . . . 2549.5750 1/2 1–0 P 2.5ee 445.26268 . . . . . . . 2641.3159 3/2 3–2 R 24.5ee 10354.28022641.3458 3/2 3–2 R 24.5ff 10358.71979 . . . . . . . 2642.8296 3/2 1–0 R 1.5ee 0.00002642.8395 3/2 1–0 R 1.5ff 0.003710 . . . . . . 2644.6568 1/2 1–0 R 1.5ee 396.99512644.7048 3/2 2–1 R 8.5ee 3286.06062644.7949 3/2 2–1 R 8.5ff 3286.43092644.8958 1/2 1–0 R 1.5ff 397.554011 . . . . . . 2659.3953 3/2 1–0 R 2.5ee 46.12932659.4143 3/2 1–0 R 2.5ff 46.144012 . . . . . . 2661.5489 1/2 2–1 R 9.5ee 3889.90562661.5866 1/2 2–1 R 9.5ff 3892.084813 . . . . . . 2661.9331 1/2 1–0 R 2.5ee 445.26262662.1518 1/2 1–0 R 2.5ff 446.091314 . . . . . . 2709.9111 1/2 1–0 R 5.5ee 705.70602710.0575 1/2 1–0 R 5.5ff 707.263815 . . . . . . 2710.9529 1/2 2–1 R 14.5ff 5042.36242711.0189 1/2 2–1 R 14.5ee 5039.864716 . . . . . . 2770.9408 3/2 1–0 R 10.5ee 1074.92612771.0636 3/2 1–0 R 10.5ff 1075.6188a Numbers in Figure 2.b Electronic angular momentum index.c Vibrational and rotational transition indices.d Lower state energy relative to , , .v = 0 J = 1.5 Q = 3/2The molecules in front of the star cause absorption, while thoseextended in the blank sky contribute as emission. Consideringthat the shell may be in the atmosphere, we adopt an expo-nential density law , where r0 is the scalen(r) ∝ exp (2r/r )0height. The star is assumed to be a 3000 K blackbody. Forsimplification, a constant excitation temperature is adopted, andthe energy population of the molecule is calculated by assuminglocal thermodynamic equilibrium. This may be justified if themolecular shell is thin and in the high-density region near thephotosphere. The line intensity of SH is calculated based onBenidar et al. (1991), which takes account of the Herman-Walliseffect. The spectrum is normalized by the stellar continuum.No smoothing is applied.The excitation temperature can be determined from the rel-ative intensities of the lines at different energy levels; highertemperatures excite the molecules to higher energy levels andincrease the line strength from these levels. We find that 2200K is most reasonable for the present case. A turbulent velocityof 6 km s21 and infall velocity of 9 km s21 reproduce the lineprofiles. The model spectrum is shifted by 214 km s21. Con-sidering the terrestrial velocity of 22.7 km s21 at transit of theobservation and the shift applied by Ridgway et al. (1984),15.2 km s21, a radial velocity of 216.5 km s21 is obtained.The inner radius and the scale height of the SH shell is 1.0and 0.08 times the stellar radius, respectively. The SH columndensity in the shell is cm22. The uncertainties of204.0 # 10the parameters, which changes the model spectrum by about10%, are 5100 K for excitation temperature, a factor of 2 forcolumn density, 50.01 R? for scale height, and 51 km s21for the velocities. The radial velocity has an error of 52km s21 due to the redigitization process. The model spectrumis compared with the observation in Figure 2. The wavelengthregions are selected so that the contamination of other spectrallines is minimal and that a wide range of energy levels iscovered. Strong lines in Figure 2 are listed in Table 1. The fitis satisfactory in most of the lines. Fitting of 34SH lines resultsin an isotopic abundance ratio of 5%–10%. We note that thesame parameters also give reasonable fits for the HCl lines witha column density of cm22.193.0 # 104. DISCUSSIONWhy are SH lines so prominent in R And, an S-type star?S-type stars are characterized by their chemical anomaly ofsimilar carbon and oxygen abundances. This leaves few C andO atoms for further chemical processes after formation of COmolecules at 4000–5000 K. SH should be quite abundant inthe atmosphere of oxygen-rich stars but a minor product in acarbon-rich environment (Tsuji 1973). Since we do see SiOlines, but no CS line, in the spectrum of R And, the star isslightly oxygen rich. Nevertheless, it is not expected that SHis much more abundant in S-type stars than O-rich stars. Thisalso holds for HCl, which is the most abundant Cl-bearingmolecule in an oxygen-rich environment, although the absoluteabundance is by 1 order of magnitude lower than SH. Ridgwayet al. (1984) suggested that the atmosphere of S-type stars ismore transparent than O-rich stars, so that the lines of minorspecies could be stronger due to larger path length. We espe-cially emphasize the contribution of the H2O molecules. In thesame paper, Ridgway et al. reported that an enormous numberof lines heavily blanket the 2400–2800 cm21 region of theCeti spectrum. They suspected that these are highly excitedowater lines. This is supported by the ISO/SWS observation ofCeti (Yamamura, de Jong, & Cami 1999b). Despite the rel-oatively poor resolution of the SWS spectrum, they demonstratethat the star shows highly excited H2O lines in the 3.5–4.0 mmregion, arising from a hot (2000 K) and optically thick mo-lecular layer. Probably, in O-rich stars, SH (and HCl) lines areweaker because of the shorter path length and also heavilycontaminated by the hot water lines. On the other hand, H2Omolecules are not favored in the atmosphere of S-type stars.The thermal equilibrium abundance of H2O in S-type stars is3–4 orders of magnitude lower than in O-rich stars (Tsuji 1964).The derived infall velocity and the excitation temperature ofthe SH layer are consistent with the measurement of COlines by Hinkle, Scharlach, & Hall (1984) at ,Dv = 3 f = 0.80indicating that the SH molecules are in the same region as hotCO near the photosphere. Comparison with the CO columndensity cm22 given by Hinkle et al. (1984) leads242.6 # 10to . In thermal equilibrium at the temperature27SH/H = 1 # 10of 2200 K and gas pressure of , the SH abundancelog (P ) = 1.0gis (Tsuji 1973; T. Tsuji 1999, private communication).272 # 10This value is insensitive to the C/O ratio as long as .C/O ! 1The present estimate of SH abundance in R And, although itis rather crude, is consistent with this calculated value. Thesulfur chemistry in the SH layer still follows thermal equilib-rium because of its high density and high temperature.We see no clear evidence of distinct velocity and/or differenttemperature components of SH lines in the spectrum. This im-plies that the SH molecules are distributed only in a thin layerin the atmosphere. In thermal equilibrium, SH is most abundantaround 1800 K and then is rather quickly transformed to H2Sor SiS below ∼1500 K (Tsuji 1973). Otherwise, nonequilibriumchemical reactions may lead to completely different compo-L36 IDENTIFICATION OF SH IN R AND Vol. 528sitions in the extended atmosphere, e.g., the enhancement ofSO2 in oxygen-rich stars (Yamamura et al. 1999a; Beck et al.1992). We could not find any clear indications of H2S or SO2in the spectrum of R And. The upper limit of the H2S columndensity is at least a factor of 10 larger than the observed amountof SH. A dioxide molecule SO2 may not be abundant in theatmospheres of S-type stars. Other possible candidates—SOand SiS—have no transition in the present wavelength cov-erage.The authors are grateful to Professor T. Tsuji for his sug-gestion on thermal equilibrium chemistry and calculations ofSH abundance. I. Y. acknowledges financial support from aNWO PIONIER grant.REFERENCESBeck, H. K. B., Gail, H.-P., Henkel, R., & Sedlmayr, E. 1992, A&A, 265,626Benidar, A., Farrenq, R., Guelachvili, G., & Chackerian, C., Jr. 1991, J. Mol.Spectrosc., 147, 383de Graauw, Th., et al. 1996, A&A, 315, L49Duari, D., Cherchneff, I., & Willacy, K. 1999, A&A, 341, L47Duley, W. W., Millar, T. J., & Williams, D. A. 1980, MNRAS, 192, 945Hartquist, T. W., Oppenheimer, M., & Dalgarno, A. 1980, ApJ, 236, 182Heiles, C. E., & Turner, B. E. 1971, Astrophys. Lett., 8, 89Herzberg, G. F. R. S. 1950, Molecular Spectra and Molecular Structure I:Spectra of Diatomic Molecules (New York: van Nostrand)Hinkle, K. H., Scharlach, W. W. G., & Hall, D. N. B. 1984, ApJS, 56, 1Kessler, M. F., et al. 1996, A&A, 315, L27Kholopov, P. N., et al. 1988, General Catalogue of Variable Stars (4th ed;Moscow: Nauka)Meeks, M. L., Gordon, M. A., & Litvak, M. M. 1969, Science, 163, 173Omont, A., Lucas, R., Morris, M., & Guilloteau, S. 1993, A&A, 267, 490Ram, R. S., Bernath, P. F., Engleman, R., Jr., & Brault, J. W. 1995, J. Mol.Spectrosc., 172, 34Ridgway, S. T., Carbon, D. F., Hall, D. N. B., & Jewell, J. 1984, ApJS, 54,177Rothman, L. S., et al. 1992, J. Quant. Spectrosc. Radiat. Transfer, 48, 469Tsuji, T. 1964, Ann. Tokyo Astron. Obs., 2d Series, 9, 1———. 1973, A&A, 23, 411Woitke, P., Helling, Ch., Winters, J. M., & Jeong, K. S. 1999, A&A, 348, L17Yamamura, I., de Jong, T., Onaka, T., Cami, J., & Waters, L. B. F. M. 1999a,A&A, 341, L9Yamamura, I., de Jong, T., & Cami, J. 1999b, A&A, 348, L55

UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl)UvA-DARE (Digital Academic Repository)Identification of SH Delta_v=1 Ro-vibrational Lines in R AndromedaeYamamura, I.; Kawaguchi, K.; Ridgway, S.T.DOI10.1086/312420Publication date2000Published inAstrophysical JournalLink to publicationCitation for published version (APA):Yamamura, I., Kawaguchi, K., & Ridgway, S. T. (2000). Identification of SH Delta_v=1 Ro-vibrational Lines in R Andromedae. Astrophysical Journal, 528, L33-L36.https://doi.org/10.1086/312420General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s)and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an opencontent license (like Creative Commons).Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, pleaselet the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the materialinaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letterto: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. Youwill be contacted as soon as possible.Download date:15 Apr 2023L33The Astrophysical Journal, 528:L33–L36, 2000 January 1q 2000. The American Astronomical Society. All rights reserved. Printed in U.S.A.IDENTIFICATION OF SH RO-VIBRATIONAL LINES IN R ANDROMEDAEDv = 1I. YamamuraAstronomical Institute “Anton Pannekoek,” University of Amsterdam, Kruislaan 403,1098 SJ, Amsterdam, The Netherlands; yamamura@astro.uva.nlK. KawaguchiFaculty of Science, Okayama University, 3-1-1, Tsushima-naka,Okayama 700-8530, Japan; okakent@cc.okayama-u.ac.jpandS. T. RidgwayNational Optical Astronomy Observatories,1 P.O. Box 26732, Tucson, AZ 85726; ridgway@noao.eduReceived 1999 September 2; accepted 1999 November 2; published 1999 December 1ABSTRACTWe report the identification of SH ro-vibrational lines in the published high-resolution infrared spectrumDv = 1of the S-type star R Andromedae. This is the first astronomical detection of this molecule. The lines show inverseP Cygni profiles, indicating infall motion of the molecular layer due to stellar pulsation. A simple spherical shellmodel with a constant infall velocity is adopted to determine the condition of the layer. It is found that a singleexcitation temperature of 2200 K reproduces the observed line intensities satisfactorily. SH is located in a layerfrom 1.0 to ∼1.1 stellar radii, which is moving inward with a velocity of 9 km s21. These results are consistentwith the previous measurements of CO transitions. The estimated molecular abundance SH/H isDv = 3, consistent with a thermal equilibrium calculation.271 # 10Subject headings: infrared: stars — line: identification — stars: AGB and post-AGB — stars: atmospheres —stars: individual (R Andromedae)1. INTRODUCTIONThe chemistry of sulfur-containing species in space is es-pecially interesting because of their chemical activity and rel-atively high abundance (Duley, Millar, & Williams 1980). It isknown that abundances of sulfur-bearing molecules are stronglyinfluenced by the presence of shocks (Hartquist, Oppenheimer,& Dalgarno 1980). So far, 14 sulfur-bearing species have beenidentified in space; CS, SO, NS, SiS, SO1, SH2, OCS, CCS,C3S, H2CS, HNCS, SO2, HCS1, and CH3SH. However, thesimplest sulfur compound, SH, has not been detected in spiteof radio astronomical searches using the L-type doubling tran-sitions (Meeks, Gordon, & Litvak 1969; Heiles & Turner 1971).While sulfur chemistry in the circumstellar envelope of redgiant stars has been studied extensively (e.g., Omont et al.1993), that in the atmosphere has been regarded as in the ther-mal equilibrium state (Tsuji 1964, 1973). In the atmosphere ofoxygen-rich giants, SH is the molecule first formed from thesulfur atom, at a temperature of about 2000 K. The SH abun-dance decreases when the temperature is below ∼1500 K, andH2S and SiS become the dominant species. On the other hand,Yamamura et al. (1999a) report the detection of the n3 infraredband of SO2 in the spectra of oxygen-rich Mira variables ob-tained by the Short-Wavelength Spectrometer (SWS: deGraauw et al. 1996) on board the Infrared Space Observatory(ISO: Kessler et al. 1996). Their model analysis indicates thatthe molecules are located in the extended atmosphere at about5 R?. The abundance of SO2 is 5–10 orders of magnitude largerthan the values in thermal equilibrium (Tsuji 1973; Woitke etal. 1999). The result strongly suggests the presence of non-equilibrium processes in the extended atmosphere, probablyrelated to shocks due to stellar pulsation (Beck et al. 1992;Duari, Cherchneff, & Willacy 1999).1 Operated by the Association of Universities for Research in Astronomyunder cooperative agreement with the National Science Foundation.In this Letter, we report the detection of SH ro-vibrationaltransition lines in the published high-resolution infrared spec-trum of the S-type star R And. We discuss the physical andchemical conditions of the SH layer in the star.2. IDENTIFICATION OF SH LINESThe data used in this study were obtained with the Fourier-transform spectrometer at the Kitt Peak National Observatory4 m telescope and were published in Ridgway et al. (1984).R And is a Mira variable with a period of 409 days and avisual amplitude of 9.1 mag (Kholopov et al. 1988). The spec-tral type is in the range S3,5e–S8,8e. The observation ofR And was performed at the optical variable phase of f =. Unfortunately, the reduced data were lost after several0.82updates of archive formats at the observatory. Therefore, weredigitized the data from the printed spectrum. The results maybe as accurate as the original within ∼0.02 cm21 in wavenumberand a few percent in intensity. The spectrum was shifted by5.2 km s21 to longer wavelengths to adjust the absorption min-imum of HCl lines at their rest frequencies (Ridgway et al.1984). No correction for terrestrial motion was applied. In theiroriginal paper, Ridgway et al. (1984) give identifications ofOH, NH, CH, SiO, CS, HCl, and atomic lines. The spectrumof R And, especially in the wavelengths shorter than the SiOfirst-overtone bandheads, is dominated by HCl lines. OH andNH lines are detected, but much less prominently than in theoxygen-rich stars like a Ori and a Tau. There are many stronglines left unidentified. Figure 1 shows the spectrum of R Andbetween 2700 and 2750 cm21. The positions of SH and HClro-vibrational transitions are indicated. The frequencies are cal-culated from the molecular constants given by Ram et al. (1995)for SH and are taken from the HITRAN database 1996 edition(Rothman et al. 1992) for HCl. It is obvious that many un-identified strong lines are attributed to SH transitions. We as-L34 IDENTIFICATION OF SH IN R AND Vol. 528Fig. 1.—Part of the spectrum of R And obtained by Ridgway et al. (1984). The positions of transitions of SH and 34SH (upper) and HCl (lower) areDv = 1indicated by tick marks. The notation of the transitions is the electronic angular momentum, the upper vibrational level, and the rotational line index for SH, andthe rotational line index, the isotope index (5: H35Cl, 7: H37Cl), and the upper vibrational level for HCl, respectively.Fig. 2.—Synthesized model spectrum (upper) compared with the observation in six wavelength regions. The regions are chosen so that contamination of otherspectral lines is minimized and that a wide range of energy levels is covered. The model assumes a spherical shell falling toward the stellar surface with a velocityof 9 km s21. The molecules are distributed from 1.0 R? with a scale height of 0.08 R?. The model assumes constant excitation temperature of 2200 K, columndensity of cm22, and Doppler broadening velocity of 6 km s21. The model spectrum is shifted by 214 km s21. Lines indicated by tick marks are listed204.0 # 10in Table 1.signed 39, 41, and 11 transitions in the , 2–1, and 3–2v = 1–0bands, respectively, between 2500 and 2778 cm21. The lowerstate energies of these transitions are up to 7000 cm21, indi-cating that the molecules are highly excited. The isotope 34SHmay also be detected. The frequencies of 34SH lines are esti-mated from the molecular constants of SH using the relationof reduced mass (Herzberg 1950).3. MODELINGWe analyze the observed SH line profiles with a simplemodel. The SH (and also HCl) lines in R And show inverseP Cyg profiles, indicating that the molecular layer is movinginward toward the star due to stellar pulsation. We thereforeapply a spherical shell model with a constant infall velocity.No. 1, 2000 YAMAMURA, KAWAGUCHI, & RIDGWAY L35TABLE 1SH Lines Indicated in Figure 2NumberaFrequency(cm21) Qb TransitioncEld(cm21)1 . . . . . . . 2532.1257 3/2 1–0 P 3.5ff 110.71752532.1486 3/2 1–0 P 3.5ee 110.68102 . . . . . . . 2534.7858 1/2 3–2 R 7.5ee 6038.95392534.8657 1/2 3–2 R 7.5ff 6040.77053 . . . . . . . 2546.2628 1/2 2–1 R 1.5ee 2994.83764 . . . . . . . 2546.4908 1/2 2–1 R 1.5ff 2995.37555 . . . . . . . 2546.9511 1/2 3–2 R 8.5ee 6192.18582547.0067 1/2 3–2 R 8.5ff 6194.15776 . . . . . . . 2549.2843 1/2 1–0 P 2.5ff 446.09137 . . . . . . . 2549.5750 1/2 1–0 P 2.5ee 445.26268 . . . . . . . 2641.3159 3/2 3–2 R 24.5ee 10354.28022641.3458 3/2 3–2 R 24.5ff 10358.71979 . . . . . . . 2642.8296 3/2 1–0 R 1.5ee 0.00002642.8395 3/2 1–0 R 1.5ff 0.003710 . . . . . . 2644.6568 1/2 1–0 R 1.5ee 396.99512644.7048 3/2 2–1 R 8.5ee 3286.06062644.7949 3/2 2–1 R 8.5ff 3286.43092644.8958 1/2 1–0 R 1.5ff 397.554011 . . . . . . 2659.3953 3/2 1–0 R 2.5ee 46.12932659.4143 3/2 1–0 R 2.5ff 46.144012 . . . . . . 2661.5489 1/2 2–1 R 9.5ee 3889.90562661.5866 1/2 2–1 R 9.5ff 3892.084813 . . . . . . 2661.9331 1/2 1–0 R 2.5ee 445.26262662.1518 1/2 1–0 R 2.5ff 446.091314 . . . . . . 2709.9111 1/2 1–0 R 5.5ee 705.70602710.0575 1/2 1–0 R 5.5ff 707.263815 . . . . . . 2710.9529 1/2 2–1 R 14.5ff 5042.36242711.0189 1/2 2–1 R 14.5ee 5039.864716 . . . . . . 2770.9408 3/2 1–0 R 10.5ee 1074.92612771.0636 3/2 1–0 R 10.5ff 1075.6188a Numbers in Figure 2.b Electronic angular momentum index.c Vibrational and rotational transition indices.d Lower state energy relative to , , .v = 0 J = 1.5 Q = 3/2The molecules in front of the star cause absorption, while thoseextended in the blank sky contribute as emission. Consideringthat the shell may be in the atmosphere, we adopt an expo-nential density law , where r0 is the scalen(r) ∝ exp (2r/r )0height. The star is assumed to be a 3000 K blackbody. Forsimplification, a constant excitation temperature is adopted, andthe energy population of the molecule is calculated by assuminglocal thermodynamic equilibrium. This may be justified if themolecular shell is thin and in the high-density region near thephotosphere. The line intensity of SH is calculated based onBenidar et al. (1991), which takes account of the Herman-Walliseffect. The spectrum is normalized by the stellar continuum.No smoothing is applied.The excitation temperature can be determined from the rel-ative intensities of the lines at different energy levels; highertemperatures excite the molecules to higher energy levels andincrease the line strength from these levels. We find that 2200K is most reasonable for the present case. A turbulent velocityof 6 km s21 and infall velocity of 9 km s21 reproduce the lineprofiles. The model spectrum is shifted by 214 km s21. Con-sidering the terrestrial velocity of 22.7 km s21 at transit of theobservation and the shift applied by Ridgway et al. (1984),15.2 km s21, a radial velocity of 216.5 km s21 is obtained.The inner radius and the scale height of the SH shell is 1.0and 0.08 times the stellar radius, respectively. The SH columndensity in the shell is cm22. The uncertainties of204.0 # 10the parameters, which changes the model spectrum by about10%, are 5100 K for excitation temperature, a factor of 2 forcolumn density, 50.01 R? for scale height, and 51 km s21for the velocities. The radial velocity has an error of 52km s21 due to the redigitization process. The model spectrumis compared with the observation in Figure 2. The wavelengthregions are selected so that the contamination of other spectrallines is minimal and that a wide range of energy levels iscovered. Strong lines in Figure 2 are listed in Table 1. The fitis satisfactory in most of the lines. Fitting of 34SH lines resultsin an isotopic abundance ratio of 5%–10%. We note that thesame parameters also give reasonable fits for the HCl lines witha column density of cm22.193.0 # 104. DISCUSSIONWhy are SH lines so prominent in R And, an S-type star?S-type stars are characterized by their chemical anomaly ofsimilar carbon and oxygen abundances. This leaves few C andO atoms for further chemical processes after formation of COmolecules at 4000–5000 K. SH should be quite abundant inthe atmosphere of oxygen-rich stars but a minor product in acarbon-rich environment (Tsuji 1973). Since we do see SiOlines, but no CS line, in the spectrum of R And, the star isslightly oxygen rich. Nevertheless, it is not expected that SHis much more abundant in S-type stars than O-rich stars. Thisalso holds for HCl, which is the most abundant Cl-bearingmolecule in an oxygen-rich environment, although the absoluteabundance is by 1 order of magnitude lower than SH. Ridgwayet al. (1984) suggested that the atmosphere of S-type stars ismore transparent than O-rich stars, so that the lines of minorspecies could be stronger due to larger path length. We espe-cially emphasize the contribution of the H2O molecules. In thesame paper, Ridgway et al. reported that an enormous numberof lines heavily blanket the 2400–2800 cm21 region of theCeti spectrum. They suspected that these are highly excitedowater lines. This is supported by the ISO/SWS observation ofCeti (Yamamura, de Jong, & Cami 1999b). Despite the rel-oatively poor resolution of the SWS spectrum, they demonstratethat the star shows highly excited H2O lines in the 3.5–4.0 mmregion, arising from a hot (2000 K) and optically thick mo-lecular layer. Probably, in O-rich stars, SH (and HCl) lines areweaker because of the shorter path length and also heavilycontaminated by the hot water lines. On the other hand, H2Omolecules are not favored in the atmosphere of S-type stars.The thermal equilibrium abundance of H2O in S-type stars is3–4 orders of magnitude lower than in O-rich stars (Tsuji 1964).The derived infall velocity and the excitation temperature ofthe SH layer are consistent with the measurement of COlines by Hinkle, Scharlach, & Hall (1984) at ,Dv = 3 f = 0.80indicating that the SH molecules are in the same region as hotCO near the photosphere. Comparison with the CO columndensity cm22 given by Hinkle et al. (1984) leads242.6 # 10to . In thermal equilibrium at the temperature27SH/H = 1 # 10of 2200 K and gas pressure of , the SH abundancelog (P ) = 1.0gis (Tsuji 1973; T. Tsuji 1999, private communication).272 # 10This value is insensitive to the C/O ratio as long as .C/O ! 1The present estimate of SH abundance in R And, although itis rather crude, is consistent with this calculated value. Thesulfur chemistry in the SH layer still follows thermal equilib-rium because of its high density and high temperature.We see no clear evidence of distinct velocity and/or differenttemperature components of SH lines in the spectrum. This im-plies that the SH molecules are distributed only in a thin layerin the atmosphere. In thermal equilibrium, SH is most abundantaround 1800 K and then is rather quickly transformed to H2Sor SiS below ∼1500 K (Tsuji 1973). Otherwise, nonequilibriumchemical reactions may lead to completely different compo-L36 IDENTIFICATION OF SH IN R AND Vol. 528sitions in the extended atmosphere, e.g., the enhancement ofSO2 in oxygen-rich stars (Yamamura et al. 1999a; Beck et al.1992). We could not find any clear indications of H2S or SO2in the spectrum of R And. The upper limit of the H2S columndensity is at least a factor of 10 larger than the observed amountof SH. A dioxide molecule SO2 may not be abundant in theatmospheres of S-type stars. Other possible candidates—SOand SiS—have no transition in the present wavelength cov-erage.The authors are grateful to Professor T. Tsuji for his sug-gestion on thermal equilibrium chemistry and calculations ofSH abundance. I. Y. acknowledges financial support from aNWO PIONIER grant.REFERENCESBeck, H. K. B., Gail, H.-P., Henkel, R., & Sedlmayr, E. 1992, A&A, 265,626Benidar, A., Farrenq, R., Guelachvili, G., & Chackerian, C., Jr. 1991, J. Mol.Spectrosc., 147, 383de Graauw, Th., et al. 1996, A&A, 315, L49Duari, D., Cherchneff, I., & Willacy, K. 1999, A&A, 341, L47Duley, W. W., Millar, T. J., & Williams, D. A. 1980, MNRAS, 192, 945Hartquist, T. W., Oppenheimer, M., & Dalgarno, A. 1980, ApJ, 236, 182Heiles, C. E., & Turner, B. E. 1971, Astrophys. Lett., 8, 89Herzberg, G. F. R. S. 1950, Molecular Spectra and Molecular Structure I:Spectra of Diatomic Molecules (New York: van Nostrand)Hinkle, K. H., Scharlach, W. W. G., & Hall, D. N. B. 1984, ApJS, 56, 1Kessler, M. F., et al. 1996, A&A, 315, L27Kholopov, P. N., et al. 1988, General Catalogue of Variable Stars (4th ed;Moscow: Nauka)Meeks, M. L., Gordon, M. A., & Litvak, M. M. 1969, Science, 163, 173Omont, A., Lucas, R., Morris, M., & Guilloteau, S. 1993, A&A, 267, 490Ram, R. S., Bernath, P. F., Engleman, R., Jr., & Brault, J. W. 1995, J. Mol.Spectrosc., 172, 34Ridgway, S. T., Carbon, D. F., Hall, D. N. B., & Jewell, J. 1984, ApJS, 54,177Rothman, L. S., et al. 1992, J. Quant. Spectrosc. Radiat. Transfer, 48, 469Tsuji, T. 1964, Ann. Tokyo Astron. Obs., 2d Series, 9, 1———. 1973, A&A, 23, 411Woitke, P., Helling, Ch., Winters, J. M., & Jeong, K. S. 1999, A&A, 348, L17Yamamura, I., de Jong, T., Onaka, T., Cami, J., & Waters, L. B. F. M. 1999a,A&A, 341, L9Yamamura, I., de Jong, T., & Cami, J. 1999b, A&A, 348, L55

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Identification of SH [FORMULA][F]Δv=1[/F][/FORMULA] Ro-vibrational Lines in R Andromedae

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Identification of SH $\Delta v=1$ ro-vibrational lines in R And

Identification of SH $\Delta v=1$ ro-vibrational lines in R And

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Identification of SH Δv=1\Delta v=1Δv=1 ro-vibrational lines in R And

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International Migration, Integration and Social Cohesion online publications

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Identification of SH $\Delta v=1$ ro-vibrational lines in R And