CH stars at high Galactic latitudes

Abstract

Carbon-rich stars of Population II, such as CH stars, can provide direct information on the role of low- to intermediate-mass stars of the halo in early Galactic evolution. Thus accurate knowledge of the CH stellar population is a critical requirement for building up scenarios for early Galactic chemical evolution. In the present work, we report on several CH stars identified in a sample of faint high-latitude carbon stars from the Hamburg survey and discuss their medium-resolution spectra covering the wavelength range 4000–6800 Å. Estimation of the depths of the (1,0)12C12C λ4737 and (1,0)12C13C λ4744 bands in these stars indicates an isotopic ratio 12C/13C ∼ 3, apart from a few exceptions; these ratios are consistent with existing theories of CH stellar evolution. The stars of the Hamburg survey, a total of 403 objects, were reported to be carbon star candidates with strong C2 and CN molecular bands. In the first phase of observation, we acquired spectra of 91 objects. Inspection of the spectra of those objects shows 51 objects with C2 molecular bands in their spectra, of which 13 stars have low flux below about 4300 Å. There are 25 objects that show weak or moderate CH and CN bands, 12 objects that show weak but detectable CH bands, and three objects that do not show any molecular bands due to C2, CN or CH in their spectra. Objects with C2 molecular bands and with good signals bluewards of 4300 Å that show prominent CH bands in their spectra are potential candidate CH stars. There were 35 such candidates found in the present sample of 91 objects observed so far. The set of CH stars identified could be the targets of subsequent observation at high resolution for a detailed and comprehensive analysis to understand their role in early Galactic chemical evolution.

Full text

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arXiv:astro-ph/0507202v1 8 Jul 2005
Mon. Not. R. Astron. Soc. 000, 1–?? (2005) Printed 5 February 2008(MN LATEX style file v1.4)
CH stars at High Galactic Latitudes
Aruna Goswami⋆
Indian Institute of Astrophysics, Koramangala, Bangalore 560034, India
Accepted 2005 Feb 9: Received 2005 Feb 3; in original form 2004 Nov 24
ABSTRACT
Carbon-rich stars of population II, such as CH stars, can provide direct information on
the role of low to intermediate-mass stars of the halo on the early Galactic evolution.
Thus an accurate knowledge of CH stellar population is a critical requirement for
building up scenarios for early Galactic chemical evolution. In the present work we
report on several CH stars identified in a sample of Faint High Latitude Carbon
stars from Hamburg survey and discuss their medium resolution spectra covering a
wavelength range 4000 - 6800˚ A. Estimation of the depths of bands (1,0)12C12C
λ4737 and (1,0)12C13C λ4744 in these stars indicate isotopic ratio12C/13C ∼ 3,
except for a few exceptions; these ratios are consistent with existing theories of CH
stars evolution. The stars of Hamburg survey, a total of 403 objects were reported
to be carbon star candidates with strong C2 and CN molecular bands. In the first
phase of observation, we have acquired spectra of ninety one objects. Inspection of
the objects spectra show fifty one objects with C2molecular bands in their spectra of
which thirteen stars have low flux below about 4300˚ A. Twenty five objects show weak
or moderate CH and CN bands , twelve objects show weak but detectable CH bands
in their spectra and there are three objects which do not show any molecular bands
due to C2, CN or CH in their spectra. Objects with C2 molecular bands and with
good signals bluewards of 4300˚ A which show prominent CH bands in their spectra
are potential candidate CH stars. Thirty five such candidates are found in the present
sample of ninty one objects observed so far. The set of CH stars identified could be the
targets of subsequent observation at high resolution for a detail and comprehensive
analysis for understanding their role in early Galactic chemical evolution.
Key words:
stars: AGB - stars: population II
stars: CH stars -variable: carbon - stars: spectral characteristics -
1 INTRODUCTION
Knowledge of stellar population offers a fossil record of for-
mation and evolution of galaxies and thus provide strong
constraints on the scenarios of the Galaxy formation and
evolution. Carbon stars, for instance, were thought to be gi-
ants without exceptions and sought as tracers of the outer
halo. Recent surveys on stellar populations have led to the
discovery of different types of stars, numerous metal-poor
stars, carbon and carbon-related objects etc. (Beers et al.
1992, Totten and Irwin 1998, Beers 1999). One of the re-
sults of these efforts is the great discovery that the frac-
tion of carbon-rich stars increases with decreasing metallic-
ity (Rossi, Beers and Sneden 1999). Extensive analysis of
many carbon-enhanced metal-poor stars at high resolution
(Norris et al. 1997a, 1997b, 2002, Bonifacio et al. 1998, Hill
et al. 2000, Aoki et al. 2002b) have revealed many more in-
⋆E-mail: aruna@iiap.res.in
triguing results; however, the specific trend of increase in
carbon-enhanced stars with decreasing metallicity still re-
mains unexplained. Also, the production mechanisms of car-
bon in these stars still remain unknown. There are different
types of carbon-enhanced stars; (i) stars showing carbon en-
hancement with s-process element enhancement, (ii) carbon
enhancement with r-process element enhancement and (iii)
carbon enhancement with normal n-capture element abun-
dances. There is yet another type of very metal-poor stars
with strong s-process enhancement but only slightly carbon-
enhanced ([C/Fe] = +0.2; Hill et al. 2002). Certainly a single
well defined production mechanism is unlikely to lead to such
a diversity in abundances. To shed light on the production
mechanisms of carbon-excess resulting in different types of
carbon-enhanced stars and to understand the nucleosynthe-
sis of s-process, and r-process elements at low metallicity it
is desirable to conduct analysis of as many different types of
C-enhanced stars as possible.
Christlieb et al. (2001) reported a sample of 403 Faint
c ? 2005 RAS

Page 2

High Latitude Carbon (FHLC) stars identified by means
of line indices - i.e. ratios of the mean photographic den-
sities in the carbon molecular absorption features and the
continuum band passes, which were the basis for the Ham-
burg catalog of high Galactic latitude carbon stars. The
identification was primarily based on the presence of strong
C2 and CN molecular bands shortward of 5200˚ A; it did
not consider CH bands. At high galactic latitudes, although
the surface density of FHLC stars is low, different kinds of
carbon stars are known to populate the region (Green et
al. 1994). One kind is the normal asymptotic giant-branch
(AGB) stars, carbon-enriched by dredge-up during post-
main-sequence phase which are found among the N-type
carbon stars. Another kind is the FHLC stars showing sig-
nificant proper motions and having luminosities of main- se-
quence dwarf called dwarf carbon stars (dCs). A third kind
of FHLC stars is the so-called CH-giant stars, similar to
the metal-poor carbon stars found in Globular clusters and
some in dwarf spheroidal (d Sph) galaxies (Harding 1962).
Among these, at high galactic latitudes warm carbon stars
possibly some C-R stars are also likely to be present. The
sample of stars offerred by Christlieb et al. (2001) being
high latitude objects, with smaller initial mass and possible
lower metallicity is likely to contain a mixture of these ob-
jects. Different kinds of objects have different astrophysical
implications and hence it is important to distinguish them
from one another, although in certain cases it is not easy
to do so. For example, dCs are difficult to distinguish from
C-giants as they exhibit remarkable similarity in their spec-
tra with those of C-giants. They are however distinguishable
through their relatively high proper motion and apparently
anomalous JHK infrared colours (Green et al. 1992).
Interpretationof
of the intermediate-mass stars formed from the interstellar
matter is not straight forward as the interstellar matter is
already affected by the ejecta of many generations of more
massive stars. In comparison, the halo red giant stars of-
fer more direct information on the role of intermediate-mass
stars of the halo. Thus, existance of CH stellar component
has important astrophysical implications for Galactic chem-
ical evolution. The processes responsible for carbon excess
in these stars to a large extent are responsible for the origin
and evolution of carbon, nitrogen and heavy elements in the
early Galaxy. Furthermore, isotopic ratios of12C/13C in C
and C-related stars provide useful probes of nucleosynthe-
sis processes and their location leading to carbon excess in
these stars. To determine these ratios useful candidates are
those with strong isotopic carbon bands in their spectra; CH
stars provide an useful set of candidates.
Determination of the chemical compositions as well as
carbon isotopic ratios12C/13C would require high resolution
spectroscopy. But before this, a target list of CH stars needs
to be generated and this can be done from spectral analysis
of stars using even low resolution spectroscopy. Prompted
by this we have undertaken to identify the CH as well as
other types of stellar objects in the sample of FHLC stars
of Christlieb et al. using low resolution spectroscopy. These
identifications and the low resolution spectroscopic analysis
of the candidate CH stars is the main theme of this paper.
Observations and data reductions are described in sec-
tion 2. In section 3 we briefly discuss different types of C
stars and their spectral characteristics. JHK photometry of
chemical compositions
the stars is briefly described in section 4. Description of the
program stars spectra and results are drawn in section 5.
Section 6 contains a brief discussion on the atmospheres of
candidate CH stars. Concluding remarks are presented in
section 7.
2 OBSERVATION AND DATA REDUCTION
The stars listed in Table 1 (51 stars) and Table 2 (40
stars) have been observed with 2-m Himalayan Chandra
Telescope (HCT) at the Indian Astronomical Observatory
(IAO), Mt. Saraswati, Digpa-ratsa Ri, Hanle during June
2003 - May 2004. Spectra of a number of carbon stars such
as HD 182040, HD 26, HD 5223, HD 209621, Z PSc, V460
Cyg and RV Sct are also taken for comparison. A spec-
trum of C-R star HD 156074 taken from Barnbaum et al.’s
(1996) atlas is also used for comparison. The spectrograph
used is the Himalayan Faint Object Spectrograph Cam-
era (HFOSC). HFOSC is an optical imager cum a spec-
trograph for conducting low and medium resolution grism
spectroscopy (http://www.iiap.ernet.in/iao/iao.html). The
grism and the camera combination used for observation pro-
vided a spectral resolution of ∼ 1330( λ/δλ ); the observed
bandpass ran from about 3800 to 6800˚ A .
Observations of Th-Ar hollow cathod lamp taken im-
mediately before and after the stellar exposures provided
the wavelength calibration. The CCD data were reduced us-
ing the IRAF software spectroscopic reduction packages. For
each object two spectra were taken each of 15 minutes expo-
sures, the two spectra were combined to increase the signal-
to-noise ratio. 2MASS JHK measurements for the stars in
Table 1 are also listed. These measurements are available
on-line at http://irsa.ipac.caltech.edu/ . In Table 2, the ob-
jects observed on 2nd and 3rd March, 2004 are acquired
using OMR spectrograph at the cassegrain focus of the 2.3
m Vainu Bappu Telescope (VBT) at Kavalur. With a 600
lmm−1grating, we get a dispersion of 2.6˚ A per pixel. The
spectra of these objects cover a wavelength range 4000 - 6100
˚ A, at a resolution of ∼ 1000.
3 TYPES OF C STARS AND THEIR
SPECTRAL CHARACTERISTICS
Carbon stars are classified into different spectral types based
on their characteristic spectral properties. We briefly discuss
here the main characteristics essential for our purpose. More
detail discussion on this can be found in literature including
Wallerstein (1998) and references therein. Among the carbon
stars, the C-N stars have lower temperatures and stronger
molecular bands than those of C-R stars. C-N stars exhibit
very strong depression of light in the violet part of the spec-
trum. They are used as tracers of an intermediate age popu-
lation in extragalactic objects. The C-R stars as well as CH
stars have warmer temperatures and blue/violet light is ac-
cessible to observation and atmospheric analysis. C-N stars
are easily detected in infrared surveys from their character-
istic infrared colours. The majority of C-N stars show ratios
of12C/13C more than 30, ranging nearly to 100 while in C-R
stars this ratio ranges from 4 to 9. The strength/weakness

Page 3

of CH band in C-rich stars provides a measure of the degree
of hydrogen deficiency in carbon stars.
The characteristic behaviour of s-process elements in
C-stars can also be used as an useful indicator of spectral
type. The s-process element abundances are nearly solar in
C-R stars (Dominy 1984); whereas most of the carbon and
carbon related stars show significantly enhanced abundances
of the s-process elements relative to iron (Lambert et al.
1986, Green and Margon 1994).
CH stars are characterised by strong G-band of CH in
their spectra. These stars are not a homogeneous group of
stars. They consist of two populations, the most metal-poor
ones have a spherical distribution and the ones slightly richer
in metals are characterised by a flattened ellipsoidal distri-
bution (Zinn 1985). These stars form a group of warm stars
of equivalent spectral types G and K giants, but show weak
metallic lines. The ratio of the local density of CH stars is
as high as 30% of metal-poor giants (Hartwick & Cowley
1985); and being the most populous type of halo carbon
stars known, are important objects for our understanding of
galactic chemical evolution, the evolution of low mass stars
and nucleosynthesis in metal poor stars.
Most of the CH stars are known to be high velocity ob-
jects. ‘CH-like’ stars, where CH are less dominant have low
space velocities Yamashita (1975). At low resolution to make
a distinction between CH and C-R stars is difficult as many
C-R stars also show quite strong CH band. In such cases
secondary P-branch head near 4342˚ A is used as a more
useful indicator. Another important feature is the strength
of Ca I at 4226˚ A which in case of CH stars is weakened by
the overlying faint bands of the CH band systems. In C-R
star this feature is quite strong. These spectral characteris-
tics allow for an identification of CH and C-R stars even at
low resolution. Enhanced lines of s-process elements, weaker
Fe group elements as well as various strengths of C2 bands
are some other distingushing spectral features of CH stars.
However, at low dispersion the narrow lines are difficult to
estimate and essentially do not provide with a strong clue to
distinguish C-R stars from CH stars. Although CH and C-
R stars have similar range of temperatures the distribution
of CH stars place most of them in the Galactic halo, their
large radial velocities , typically ∼ 200km s−1are indicative
of their being halo objects (McClure 1983, 1984).
The objects observed from Hanle are classified consider-
ing these spectral characteristics. In the following we discuss
the medium resolution spectra of the objects listed in Table
1 with their photometric data.
4 JHK PHOTOMETRY
Infrared colours made from JHK photometry provide a
supplementary diagnostics for stellar classification. Figure
1 is a two colour JHK diagram where J-H versus H-K
colours of HE stars listed in Table 1 are plotted. The HE
stars 2MASS JHK measurements are available on-line at
http://iras.ipac.caltech.edu/.
The two boxes superimposed in the figure representing
the location of CH stars (thick line solid box) and the C-N
stars (thin line solid box) illustrate the loci of the separate
carbon-star types and are taken from Totten et al. (2000). In
this figure, the CH stars classified by us (following our dis-
cussions in the subsequent sections), plotted with open cir-
cles fall well within the CH box, except the three outliers HE
1429-0551, HE 2218+0127 and HE 0457-1805. These three
stars are represented by solid circles. The spectral charac-
teristics of these stars led us to classify them as CH stars.
Their spectra do not show any peculiarities from which their
location in the J-H, H-K plane seems obvious. A difference
between the spectra of the first two stars lies in molecular
C2 bands in the spectral region 5700 - 6800˚ A . In this re-
gion HE 1429-0551 does not show molecular C2 bands (or
could be marginally detected) whereas HE 2218+0127 shows
molecular C2 bands as strongly (or marginally stronger) as
they are seen in CH star HD 5223. Ba II feature at 6496˚ A
is weak in HE 1429-0551. In HE 2218+0127, this feature ap-
pears to be of equal depth to its counterpart in HD 5223. HE
2218+0127 seems to be the warmest among the candidate
CH stars (Table 3). HE 0457-1805, another CH star outside
the CH box resembling HD 26, a known CH star, shows
stronger CN molecular band around 4215˚ A and slightly
stronger features due to Ba II at 6496˚ A and Na I D. Hαfea-
ture is marginally weaker but G-band of CH appears almost
of equal strength. There are ten stars in the present sample
which show spectral characteristics of C-N stars, they are
represented by solid triangles. Four of them fall well within
the C-N box, three of them just outside the C-N box and
the rest two fall within the CH box. Stars HE 2319-1534 and
HE 1008-0636 at the redder edge of the C-N box show Hα
and Hβ in emission whereas HE 2331-1329, HE 0915-0327
and HE 1254-1130 with lower H-K values do not show Hα
and Hβ features in their spectra. HE 1501-1500, HE 1228-
0402 and HE 1107-2005 (inside the CH box) do not have
flux below 4500˚ A. CN molecular bands are weaker in HE
1228-0402 than their counterparts in other C-N stars. This
is not the case with HE 1501-1500. Hα and Hβ features are
not detectable in these two stars. At present it remains to
be understood why these two stars occupy a location among
the CH stars in the J-H, H-K plane.
5 RESULTS
5.1 Spectral characteristics of the program stars
The spectra are examined in terms of the following spectral
characteristics.
1. The strength (band depth) of CH band around 4300˚ A.
2. Prominance of Secondary P-branch head near 4342˚ A.
3. Strength/weakness of Ca I feature at 4226˚ A.
4. Isotopic band depths of C2 and CN, in particular the
Swan bands of12C13C and13C13C near 4700˚ A.
5. Strength of other C2 bands in the 6000 -6200˚ A region.
6.13CN band near 6360˚ A and other CN bands across the
wavelength range.
7. Strength of s-process element such as Ba II features at
4554˚ A and 6496˚ A.
To establish the membership of a star in a particular
group we have conducted a differential analysis of the pro-
gram stars spectra with the spectra of carbon stars available
in the low resolution spectral atlas of carbon stars of Barn-
baum et al. (1996). We have also acquired spectra for some
of the objects from this Atlas and used them for comparison
of spectra at the same resolution.

Page 4

Figure 1. A two colour J-H versus H-K diagram of the stars listed in Table 1. The candidate CH stars are represented by open circles
except the three outliers represented by solid circles. C-N stars are represented by solid triangles and C-R stars by open hexagon. The two
boxes superimposed in the figure illustrate the loci of separate carbon-star types and are taken from Totten et al. (2000). The location
of the comparison stars are labeled and maked with solid squares.
5.2 Candidate CH stars: Description of the
spectra
At low resolution the spectra of C-R and CH stars look very
similar and this makes distinction between them a difficult
task. The differences are made apparent by making a com-
parison between spectra of known C-R and CH stars. Appli-
cation of this comparison to the program stars helped in an
easy identification of their spectral class. In figures 2 and 3
we show a comparison of the spectra of a pair of C-R stars
HD 156074 and HD 76846 and a pair of CH stars HD209621
and HD 5223. Although we have considered here four stars,
the comparison is generally true for any C-R and CH stars.
A comparison of known C-R and CH stars spectra
(i) Wavelength region 4000 - 5400˚ A (Figure 2):
G-band of CH is strong in all the spectra, almost of equal
strength. However, the secondary P-branch head around
4343˚ A is distinctly seen in the CH stars spectra. In C-R
stars spectra this feature is merged with contributions from
molecular bands.
In C-R stars the Ca I at 4226˚ A line depth is almost
equal to the CN band depth at 4215˚ A whereas in CH stars
spectra this line is marginally noticed. CN band around 4215
˚ A is much deeper in C-R stars than in the CH stars.
Narrow atomic lines are blended with contributions
from molecular bands and hence their real strength could
not be estimated at this resolution. In the above wavelength
range Hβ and Ba II at 4554˚ A are the two features clearly
noticeable in the CH stars. In C-R star this region is a com-
plex combination of atomic and molecular lines. There is no
obvious distinction in the isotopic bands around 4700˚ A in
C-R and CH stars. C2 molecular bands around 5165˚ A and
5635˚ A are two prominent features in this region.
(ii) Wavelength region 5400 -6800˚ A (Figure 3)
C2 molecular bands around 5635˚ A is the most prominent
feature in this region. This region too is a complex mixture
of atomic and molecular lines. A blended feature of Na I D1

Page 5

Table 1: HE stars with prominent C2 molecular bands
Star No. RA(2000)a
DEC(2000)a
lb
Ba
J
Va
B-Va
U-Ba
JHK Dt of Obs
HE 0002+0053
HE 0017+0055
HE 0038-0024
HE 0043-2433
HE 0110-0406
HE 0111-1346
HE 0151-0341
HE 0207-0211
HE 0308-1612
HE 0310+0059
HE 0314-0143
HE 0319-0215
HE 0322-1504
HE 0429+0232
HE 0457-1805
HE 0507-1653
HE 0518-2322
HE 0915-0327
HE 0932-0341
HE 1008-0636
HE 1027-2501
HE 1056-1855
HE 1104-0957
HE 1107-2105
HE 1125-1357
HE 1145-0002
HE 1204-0600
HE 1211-0435
HE 1228-0402
HE 1254-1130
HE 1259-2601
HE 1304-2046
HE 1305+0132
HE 1418+0150
HE 1425-2052
HE 1429-0551
HE 1446-0112
HE 1501-1500
HE 1523-1155
HE 1524-0210
HE 1528-0409
HE 2144-1832
HE 2145-1715
HE 2207-0930
HE 2207-1746
HE 2218+0127
HE 2221-0453
HE 2239-0610
HE 2319-1534
HE 2331-1329
HE 2339-0837
00 05 25.0
00 20 21.6
00 40 48.2
00 45 43.9
01 12 37.1
01 13 46.5
01 53 43.3
02 10 12.0
03 10 27.1
03 12 56.9
03 17 22.2
03 21 46.3
03 24 40.1
04 31 53.7
04 59 43.6
05 09 16.5
05 20 35.5
09 18 08.2
09 35 10.2
10 10 37.0
10 29 29.5
10 59 12.2
11 07 19.4
11 09 59.6
11 27 43.0
11 47 59.8
12 07 11.6
12 14 12.0
12 30 50.6
12 56 57.0
13 01 52.4
13 06 50.1
13 08 17.8
14 21 01.2
14 28 39.5
14 32 31.3
14 49 02.2
15 04 26.3
15 26 41.0
15 26 56.9
15 30 54.3
21 46 54.7
21 48 44.5
22 09 57.5
22 10 37.5
22 21 26.1
22 24 25.7
22 41 53.1
23 22 11.1
23 33 44.5
23 41 59.9
+01 10 04
+01 12 07
-00 08 05
-24 16 48
-03 50 30
-13 30 49
-03 27 14
-01 57 39
-16 00 41
+01 11 10
-01 32 37
-02 04 34
-14 54 24
+02 39 01
-18 01 11
-16 50 05
-23 19 14
-03 39 57
-03 54 33
-06 51 13
-25 17 16
-19 11 08
-10 13 16
-21 22 01
-14 13 32
-00 19 19
-06 17 06
-04 52 26
-04 18 59
-11 46 19
-26 17 16
-21 02 10
+01 16 49
+01 37 18
-21 06 05
-06 05 00
-01 25 24
-15 12 00
-12 05 43
-02 20 45
-04 19 40
-18 18 15
-17 01 03
-09 16 06
-17 31 38
+01 42 20
-04 38 02
-05 54 22
-15 18 16
-13 12 34
-08 21 19
99.71
106.90
117.09
98.33
136.11
145.01
157.78
163.12
201.12
178.95
182.98
184.58
201.90
192.72
217.85
217.54
225.62
235.26
238.38
248.12
266.68
269.48
265.35
273.53
274.20
271.30
283.56
285.83
293.16
305.08
305.84
307.75
312.52
346.80
331.40
343.02
352.42
344.28
351.87
0.98
359.87
34.65
36.63
50.27
38.87
65.46
59.04
61.61
58.09
66.55
78.51
-59.61
-60.70
-62.89
-86.88
-66.17
-75.42
-62.04
-58.55
-55.96
-45.73
-46.69
-46.17
-52.39
-29.17
-32.51
-29.96
-29.74
+30.09
+33.41
+38.35
+27.42
+36.29
+44.92
+35.65
+43.93
+58.60
+54.91
+56.76
+58.16
+51.08
+36.52
+41.69
+63.84
+56.66
+36.64
+48.76
+49.80
+36.78
+35.63
+42.35
+40.30
-46.78
-46.73
-47.96
-51.77
-43.80
-48.38
-52.61
-66.14
-67.12
-65.05
14.5
12.6
15.4
13.8
13.4
13.3
14.6
15.5
12.5
12.6
12.7
14.6
15.0
14.2
12.1
15.6
13.7
14.5
14.8
14.5
13.9
13.6
14.7
14.3
15.2
13.5
14.9
15.0
16.3
16.1
13.9
15.2
13.8
14.2
13.6
13.5
14.5
16.5
14.2
14.4
15.8
12.6
14.2
14.4
11.8
14.6
14.7
14.1
15.3
16.2
14.9
13.31.721.25 11.018
9.309
12.433
11.064
10.523
10.684
11.847
11.505
10.027
9.871
8.993
11.785
12.105
11.088
8.937
10.883
11.151
9.968
12.295
9.952
10.386
8.693
11.768
10.493
9.988
10.155
11.364
10.605
9.475
9.296
8.222
11.218
11.533
10.520
8.421
10.430
10.672
8.989
11.807
9.073
10.118
8.498
11.573
10.365
9.866
10.039
11.248
10.010
9.331
9.196
8.000
11.063
11.340
10.325
8.186
10.315
10.568
8.609
11.708
8.527
06.11.04
15.11.03
06.11.04
07.11.04
17.9.03
07.11.04
07.11.04
07.11.04
17.9.03
17.9.03
17.9.03
16.9.03
06.11.04
07.11.04
07.11.04
06.11.04
15.11.03
10.4.04
06.11.04
29.3.04
30.3.04
20.12.04
20.12.04
30.3.04
12.4.04
11.4.04
11.4.04
12.4.04
11.4.04
30.3.04
03.3.04
30.3.04
28.3.04
10.4.04
28.3.04
05.9.03
06.9.03
10.4.04
29.3.04
06.9.03
29.3.04
16.9.03
17.9.03
16.9.03
06.9.03
16.9.03
17.9.03
07.11.04
17.9.03
06.11.04
06.11.04
14.4
13.1
1.86
1.04
1.67
1.00
13.4
14.0
1.27
2.16
0.87
2.13
13.6
13.8
13.3
11.2
12.4
1.43
1.63
1.35
1.25
1.06
1.01
1.24
1.08
1.20
0.68
12.9
13.9
12.9
12.7
2.29
1.23
2.28
1.73
2.12
1.02
2.11
1.51
10.784
8.262
8.279
11.730
10.911
11.517
12.492
12.805
10.731
10.249
7.561
7.229
11.057
10.240
10.898
11.962
12.070
9.821
10.090
7.317
6.696
10.842
10.006
10.703
11.916
11.847
9.406
12.1
14.1
13.6
14.0
14.2
15.1
14.5
12.8
14.3
12.8
3.11
1.41
1.48
1.36
1.08
1.68
2.13
1.77
1.32
1.35
2.44
1.40
1.49
1.45
0.90
1.92
2.37
1.56
1.36
1.25
11.978
10.621
9.988
10.043
10.734
10.983
12.725
11.372
11.740
12.945
8.768
11.032
10.527
9.115
11.826
11.524
13.830
10.866
11.841
12.632
11.386
9.994
9.356
9.446
10.272
10.379
12.030
10.846
11.079
12.455
8.180
10.356
9.812
8.579
11.509
10.997
13.296
9.937
10.990
12.107
11.219
9.814
9.127
9.273
10.066
10.162
11.830
10.748
10.896
12.358
7.958
10.255
9.607
8.450
11.433
10.815
13.164
9.367
10.652
12.026
12.7 1.271.29
13.5
15.3
13.4
13.3
15.0
1.38
1.65
1.14
1.53
1.10
1.39
1.61
0.70
1.25
0.78
13.2
13.1
1.39
1.82
1.18
1.40
14.0
13.7
13.1
13.8
14.5
14.0
0.80
1.36
1.34
2.09
2.29
1.32
0.31
1.11
1.59
2.16
2.19
0.62
aFrom Christlieb et al. (2001)
and Na I D2 in C-R stars is sharper with two distinct dips.
In CH stars this feature is shallower and the individual con-
tribututions of Na I D1 and Na I D2 are not distinguishable.
Hα feature appears as a distinct feature in CH stars; in C-R
stars this feature seems to be contaminated by molecular
contributions. Ba II feature at 6496˚ A is also blended with
contributions from CN bands around 6500˚ A; in CH stars
this blending is not so severe. CN molecular bands, although
present are in general weaker in CH stars than in C-R stars.
The main features of the above comparison are used to
identify the spectral type ( CH or C-R ) of the program stars.
A small number of C-N stars were easily identified from their
distinct spectral properties. In figure 4 we present the spec-
tra of the comparison stars in the wavelength region 4000
-6800˚ A. In figure 5 we show one example of HE stars cor-

Page 6

Table 2: HE stars without prominent C2 bands
Star No.RA(2000)a
DEC(2000)a
lb
Ba
Va
B-Va
U-Ba
Bands
noticed
Dt of Obs
HE 0201-0327
HE 0333-1819
HE 0359-0141
HE 0408-1733
HE 0417-0513
HE 0419+0124
HE 0443-1847
HE 0458-1754
HE 0508-1604
HE 0518-1751
HE 0519-2053
HE 0536-4257
HE 0541-5327
HE 0549-4354
HE 0900-0038
HE 0916-0037
HE 0918+0136
HE 0919+0200
HE 0930-0018
HE 0935-0145
HE 0939-0725
HE 1042-2659
HE 1117-2304
HE 1119-3229
HE 1227-3103
HE 1304-3020
HE 1356-2752
HE 1455-1413
HE 1500-1101
HE 1514-0207
HE 1521-0522
HE 1527-0412
HE 2115-0522
HE 2121-0313
HE 2124-0408
HE 2138-1616
HE 2141-1441
HE 2145-0141
HE 2224-0330
HE 2352-1906
02 03 49.0
03 35 18.8
04 02 21.2
04 11 06.0
04 19 46.8
04 21 40.4
04 46 10.9
05 00 34.5
05 10 47.0
05 20 28.4
05 21 54.4
05 37 40.4
05 42 14.3
05 50 34.3
09 02 50.5
09 18 47.6
09 21 26.1
09 22 13.0
09 33 24.7
09 37 59.0
09 42 11.9
10 44 24.2
11 19 42.8
11 22 21.9
12 30 34.5
13 07 24.2
13 59 25.0
14 57 51.6
15 03 40.9
15 16 38.9
15 24 12.2
15 29 42.3
21 18 11.8
21 23 46.2
21 27 06.8
21 41 16.6
21 44 25.7
21 47 48.3
22 26 47.9
23 54 49.0
-03 13 05
-18 09 54
-01 33 05
-17 25 40
-05 06 17
+01 31 46
-18 41 40
-17 50 21
-16 00 40
-17 48 43
-20 50 36
-42 55 39
-53 26 31
-43 53 24
-00 50 20
-00 50 35
+01 23 28
+01 47 56
-00 31 46
-01 58 36
-07 39 06
-27 15 30
-23 21 07
-32 46 19
-31 19 54
-30 36 36
-28 06 59
-14 25 10
-11 13 09
-02 18 33
-05 32 52
-04 22 22
-05 10 07
-03 00 51
-03 55 22
-16 02 40
-14 27 33
-01 27 50
-03 14 58
-18 49 31
161.94
208.37
192.03
211.87
198.66
192.17
217.23
217.73
216.82
219.71
223.06
248.71
261.05
250.28
230.15
232.63
230.81
230.52
234.74
236.99
243.19
271.05
277.08
282.08
297.72
306.99
320.71
343.27
347.25
358.67
357.20
369.56
46.39
49.51
49.09
36.95
39.43
55.23
61.23
62.50
-60.49
-51.32
-37.64
-43.11
-35.82
-31.92
-35.75
-32.26
-29.31
-27.84
-28.62
-31.11
-31.59
-28.98
+28.43
+31.79
+33.55
+33.93
+35.01
+35.12
+32.50
+27.64
+34.87
+26.47
+31.33
+32.14
+32.40
+38.36
+40.01
+44.29
+40.70
+40.49
-34.80
-34.90
-36.09
-44.70
-44.77
-39.10
-48.01
-74.57
14.1
12.6
14.5
13.1
14.6
15.7
13.1
13.5
12.8
13.5
13.6
13.8
13.6
13.7
14.2
13.7
14.0
13.5
14.2
13.8
14.0
14.7
13.3
14.0
14.3
13.5
13.3
13.1
13.8
13.6
14.7
13.8
17.4
14.9
14.8
14.7
14.3
13.4
14.3
12.9
13.41.02 0.95 CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN,
CH, CN
CH, CN
07.11.04
16.9.03
15.11.03
17.9.03
15.11.03
07.11.04
16.9.03
02.3.04
20.12.04
07.11.04
15.11.03
03.3.04
03.3.04
03.3.04
29.3.04
03.3.04
03.3.04
03.3.04
02.3.04
02.3.04
20.12.04
03.3.04
11.4.04
03.3.04
02.3.04
02.3.04
03.3.04
03.3.04
29.3.04
05.9.03
11.4.04
05.9.03
07.11.04
05.9.03
17.9.03
16.9.03
16.9.03
16.9.03
16.9.03
16.9.03
13.4
12.2
13.7
13.0
12.9
12.7
12.1
12.8
13.7
12.7
1.26
1.28
1.31
1.44
1.27
1.18
1.04
1.05
1.18
1.44
1.08
1.26
1.21
1.37
1.21
1.09
1.15
1.22
1.14
1.41
12.8
13.3
12.8
13.1
12.6
14.7
12.9
13.1
12.6
1.31
1.27
1.24
1.30
1.31
1.43
1.16
1.20
1.18
1.19
1.02
1.21
1.20
1.45
1.07
1.13
CH
CH, CN
CH
CH
CH
CH
CH
CH, CN,
CH
CH, CN
CH 13.1
13.3
12.7
1.18
1.39
1.17
1.25
1.54
1.06 CH
CH
CH
CH12.9 1.281.24
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
CH, CN
13.8
12.9
14.3
13.9
13.9
13.9
13.5
12.6
13.5
1.24
1.21
1.22
1.35
1.26
1.01
1.13
1.10
1.08
1.11
1.19
1.15
1.47
1.15
0.91
1.03
1.02
0.94
aFrom Christlieb et al. (2001)
responding to each comparison star’s spectrum in figure 4,
in the sequence top to bottom. In the following we present
the spectral description of the individual star.
HE 2145-1715, HE 0518-2322, HE 0457-1805,
HE 0043-2433, HE 1056-1855
The spectra of these objects closely resemble the spectrum
of HD 26, a known CH star. CH bands around λ4300 are
of almost equal strength in the spectra of these stars. Ca I
4226˚ A line is very weak, 4271 Fe I line is barely detectable.
Strength of G-band of CH, prominent secondary P-branch
head around 4342˚ A and a weak Ca I feature at 4226˚ A
show that these stars could be CH stars.
C2 molecular bands around 4730˚ A, 5165˚ A and 5635˚ A
are much deeper in HE 2145-1715 than their counterparts in
HD 26. Hβ features are of equal strength. Ba II line around
4545˚ A is marginally weaker in the spectrum of HE 2145-
1715 whereas Ba II feature at 6496˚ A and Hα are of equal
strength. The effective temperature of HD 26 is ∼ 4880 K,
and [Fe/H]=-0.5 (Aoki & Tsuji 1997). A marginally weaker
NaI D feature than in HD 26 spectrum and the deeper C2
bands in HE 2145-1715 perhaps is an indication of slightly
lower metallicity and lower temperature for HE 2145-1715
than HD 26. This statement however can be asscertained
only from high resolution spectral analysis.
In HE 0518-2322, CN molecular band depth matches well
with that of HD 26. Na I D appears weakly in emission,
Ba II at 6496˚ A and Hα features are marginally stronger.
Hα feature has an weak emission at the absorption core. HE
0043-2433 has a stronger CN band around 4215˚ A but Hα,
Hβand Ba II at 6496˚ A appear with almost similar strength
to those in HD 26. Na I D feature appears weakly in absorp-
tion in this star. In HE 0457-1805, Na I D is stronger than
in HD 26 but Hα, Hβ and Ba II at 6496˚ A appear with
almost similar strength. In HE 1056-1855, Hα and Hβ are
marginally weaker but Ba II at 6496˚ A appear with almost
equal strength as in HD 26.

Page 7

HE 0310+0059, HE2239-0610, HE 0932-0341,
HE 0429+0232
These four stars spectra resemble the spectrum of HD 26
to a large extent. G-band of CH around 4300˚ A is of sim-
ilar strength to that in HD 26 but the secondary P-branch
head around 4342˚ A is not seen prominently as it is seen in
CH stars. Further, in contrast to HD 26, these stars spec-
tra exhibit strong Ca I feature at 4226˚ A in their spec-
tra. These stars do not seem to be potential candidate CH
stars. In HE 0310+0059, lines appear much sharper than
in HD 26 and especially Na I D feature is seen as a much
stronger feature in absorption. In HE 0429+0232, this fea-
ture is marginally weaker than in HD 26. In HE 2239-0610
and HE 0932-0341 Na I D features appear in weak emission.
CN bands are stronger in HE 0310+0059 but C2 bands are
of similar strength. Hα, Hβ, and Ba II feature at 6496˚ A
appear in these stars almost with equal strength as in HD
26.
HE 0110-0406, HE 0308-1612, HE 0314-0143,
HE 1125-1357, HE 1211-0435, HE 1225-2052, HE
1446-0112, HE 1524-0210, HE 1528-0409, HE 2144-
1832, HE 2207-1746
The spectra of these stars closely resemble the spectrum
of HD 209621 except for some marginal differences in the
molecular band depths. The star HD 209621 is a known CH
giant with effective temperature ∼ 4700 K and metallicity
-0.9 (Wallerstein 1969, Aoki & Tsuji 1997).
Except for HE 1446-0112 and HE 1524-0210 the CN
band depth around λ4215 are weaker in the program stars
spectra than in the spectrum of HD 209621. Ca I at 4226˚ A
is not detectable in the spectra of HE 1446-0112, HE 1127-
1357, and HE 1211-0435, but appears weakly in the rest of
the stars spectra. In the first three stars although Ca I fea-
ture at 4226˚ A is seen with its depth almost half the depth
of CN band around 4215˚ A it should be noted that in these
three stars CN band itself is much weaker than its coun-
terpart in HD 209621 and in C-R stars. CH band at λ4300
in the spectra of the program stars are equal or stronger
than in the spectrum of HD 209621 except for HE 2207-
1746, HE 0308-1612 and HE 0110-0406 where this features
are slightly weaker. In these stars CN band around 4215˚ A
is also weak, much weaker than in C-R stars. Secondary P-
branch head around 4342˚ A is seen prominently in all the
cases. We assign the membership of these stars to the CH
group. Molecular band heads of C2 around λ4700 is of equal
strength in HE 1446-0112, HE 1524-0210 and HE 1127-1357;
in the rest of the stars spectra this band is slightly weaker
than in HD 209621. C2 band depth around λ5165 and λ5635
are almost of equal strength except for stars HE 2207-1746,
HE 1211-0435, HE 0308-1612, and HE 0110-0406. Ba II fea-
ture at 4554˚ A is detectable and of similar strength; however
Hβ feature is weaker in HE 1524-0210 and HE 1528-0409.
Except in HE 1446-0112 and HE 1528-0409 where NaI D fea-
ture appears slightly weaker, in the rest of the stars spectra
this feature is of similar strength with that of NaI D feature
in HD 209621. Ba II feature at 6496˚ A which is distinctly
seen in HD 209621 appears blended with CN molecular band
in HE 1446-0112. In HE 1125-1357, HE 1528-0409 and HE
1211-0435 this feature appears slightly weaker than in HD
209621 and in the rest they seem to be of equal strength.
Hα profile is of equal strength in all the stars except in HE
0314-0143 where this feature is slightly weaker. In figure 6,
we show as an example a comparison of spectra of three
objects in the wavelength region 4125 - 5400˚ A with the
spectrum of HD 209621.
HE 1429-0551, HE 1523-1155, HE 2218+0127,
HE 2221-0453, HE 1204-0600, HE 1418+0150, HE
2207-0930, HE 1145-0002, HE 0111-1346, HE 0151-
0341, HE 0507-1653, HE 0038-0024, HE 0322-1504,
HE 2339-0837
With marginal differences in the molecular band depths
these stars spectra closely resemble the spectrum of HD
5223, a well known CH giant with effective temperature ∼
4500 K, and metallicity -1.3 (Aoki & Tsuji 1997).
The CN band depth around λ4215 in the HE stars spec-
tra are very similar to the CN band depth in the spectrum
of HD 5223 except in HE 1145-0002 where this feature is
weaker and does not show a sharp clear band head. G-band
of CH around λ4300 in the spectra of the program stars re-
semble greatly to their counterparts in HD 5223. Ca I at
4226˚ A is seen in the spectra of HE 2218+0127, HE 1204-
0600 and HE 2207-0930 but not as prominently as they are
seen in C-R stars. Moreover, the line depth of this feature
is quite shallow compared to the CN molecular band depth
around 4215˚ A. We note, in C-R stars these two features ap-
pear almost with equal depth and CN band depth is deeper
in C-R stars than in CH stars.
The Ca I feature is seen marginally also in the rest of
the stars spectra. Fe I at 4271.6˚ A although weak could
be marginally detected in all the spectra. Prominance of
secondary P-branch head near 4342˚ A, strong G-band of CH
and weak or marginally detectable Ca I feature at 4226˚ A
allow these stars to be placed in CH group. The dominance
of CH is shown not only by the marked band depths, but
also by the weakness of Ca I at 4226˚ A and distortion of
metallic lines between 4200 and 4300˚ A. In figure 7, we show
a comparison of three spectra in the wavelength region 4000
- 5400˚ A with the spectrum of HD 5223.
Isotopic bands of Swan system around λ4700 appear to
be of equal strength in HE 1204-0600 and HE 2218+0127
with their counterpart in HD 5223. These bands are slighly
deeper in HE 2207-0930, HE 1145-0002 and HE 2221-0453
and marginally swallower in HE 1429-0551 and HE 1523-
1155. C2 bands around λ5165 and λ5635 greatly resemble
those in the spectrum of HD 5223, except for stars HE
2207-0930 and HE 1145-0002 where these bands are slightly
deeper. As in the case of HD 5223, Ba II feature at 4554˚ A
is distinctly seen in the program stars spectra. However in
HE 1429-0551, HE 1523-1155 and HE 2218+0127 this fea-
ture is marginally weaker, and in the rest the feature is of
similar strength. Hβ feature appears in all the spectra with
similar strength as in HD 5223. Except in HE 1429-0551,
HE 1523-1155, and HE 2121-0453, NaI D feature appears
slightly stronger as compared to this feature in HD 5223.
Ba II feature at 6496˚ A appears weaker in HE 1429-0551,
HE 1523-1155 and HE 2218-0127 than in HD 5223, this fea-
ture appears blended with contributions from CN molecular
bands in HE 1204-0600, HE 2207-0930 and HE 1145-0002.
Hα profile is of equal strength in HE 1429-0551, HE 1523-
1155, HE 2218-0127, and HE 2221-0453; this feature ap-
pears slightly weaker in HE 1204-0600, HE 2207-0930 and
HE 1145-0002 and blended with contributions from molecu-

Page 8

lar bands. The spectra of HE 1204-0600, HE 2207-0930 and
HE 1145-0002 resemble closely the spectrum of HD 5223 in
the wavelength region 4000 - 5800˚ A; they show marginally
stronger CN bands in the wavelength region 5700 - 6800˚ A.
The spectra of HE 0111-1346 and HE 0322-1502 show a
very good match with the spectrum of HD 5223, with similar
depths in molecular bands and also line depths of Hα, Hβ
and Ba II at 6496˚ A appear with similar strength. In HE
0322-1502 Na I D appears weakly in emission.
In HE 0151-0341, G-band of CH around 4300˚ A and CN
band around 4215˚ A have similar strength but C2 bands
are marginally weaker than in HD 5223. Hα and Hβ are
of equal strength but Na I D and Ba II at 6496 ˚ A are
much weaker than in HD 5223. HE 0507-1653 has marginally
weaker bands and also Na I D feature is slightly weaker than
in HD 5223; Hα, Hβand Ba II at 6496˚ A appear with similar
strength. The spectra of HE 0038-0024 and HE 2339-0837
show marginally stronger CN band around 4215˚ A and G-
band of CH around 4300˚ A but exhibit slightly weaker C2
molecular bands. Na I D feature appears in weak emission,
Hα, is of similar strength but Ba II at 6496˚ A appear in
equal strength in HE 0038-0024 which is marginally weaker
in HE 2339-0837.
HE 1305+0132, HE 1027-2501, HE 1304-2046,
HE 0017+055, HE 0319-0215
The spectra of these stars also show spectral characteristics
of CH stars. The spectra exhibit strong G-band of CH. Sec-
ondary P-branch head of CH near 4342˚ A is distinctly seen
as usually seen in CH stars spectra. Ca I feature at 4226˚ A is
weak or undetectable in their spectra. We place these stars
in CH group. Ba II at 4554˚ A, Sr II around 4606˚ A and Hβ
are seen in their spectra. Strong molecular bands include C2
Swan bands around 4700˚ A and C2 bands around 5165˚ A
and 5635˚ A. Ba II feature around 6496˚ A is blended with
contributions from CN bands. CN bands around 5730˚ A and
6300˚ A are detected. Na I D features appear very similar as
seen in most of the CH stars except in HE 0319-0215, where
this feature appears in weak emission.
5.3 Candidate C-N stars: Description of the
spectra
HE 2319-1534, HE 1008-0636, HE 2331-1329,
HE 0207-0211, HE 1107-2105
The spectra of these stars show a close resemblance with
the spectrum of C-N star Z Psc with similar strengths of
CN and C2 bands in them seen across the wavelength re-
gions. In figure 8, we show as an example, a comparison
of spectra for three objects in the wavelength region 5500 -
6800˚ A with the spectrum of Z Psc. The spectra of HE 2319-
1534, HE 1008-0636 and HE 1107-2105 have low flux below
about 4500˚ A. In HE 1008-0636 the SiC2 bands around 4800
- 5000˚ A are seen. These red-degraded features are not seen
in the other four and Z Psc. Na I D feature is much deeper
in HE 1008-0636 than in HE 2319-1534. In the spectrum of
HE 2331-1329, Ca I feature at 4226˚ A is much weaker than
in Z PSc. G-band of CH around 4300˚ A and C2 molecu-
lar bands are of similar strength but CN bands are much
weaker in HE 2331-1329 than their counterparts in Z PSc.
Na I D, Hα and Hβ are marginally detectable in this star.
In HE 0207-0211 CN bands are much weaker than in Z PSc
but C2 bands are in good match; Na I D feature is weak and
barely detectable. In HE 0207-0211 and HE 1107-2105 Hα
and Hβ appear in emissionr; these two features are also seen
strongly in emission in the spectra of HE 2319-1534 and HE
1008-0636 are indicative of a possible strong chromospheric
activity or shock-waves of the type associated with Mira
variables.
HE 1228-0402, HE 0915-0327, HE 1254-1130,
HE 1501-1500, HE 1259-2601
The specta of these stars show very low flux below about
4500˚ A. Their spectra mostly resemble the spectra of C-N
star with prominent CN and C2 bands seen across the wave-
length regions. The spectrum of C-N star V460 Cyg com-
pares closest to the spectra of these stars. Na I D feature is
weaker in their spectra as compared to their counterparts in
V460 Cyg. We place these stars in C-N group. In V460 Cyg
the molecular bands of C2 as well as CN are much deeper
than in Z Psc.
HE 0002+0053, HE 1104-0957
The spectra of these two objects greatly resemble the spec-
trum of C-R star RV Sct. C2 bands in the spectrum of HE
0002+0053 match closely with those in RV Sct but CN bands
are much weaker. In HE 1104-0957 molecular bands due to
both CN and C2 are much weaker than those in RV Sct. In
both the stars, Hα and Hβ are weakly seen in absorption.
Na I D is marginally detectable but weaker than in RV Sct.
but G-band of CH around 4300˚ A is marginally stronger
in these stars. Ca I feature around 4226˚ A which appears
weakly in the spectrum of RV Sct is missing in the spec-
tra of these two stars.
absent in these two stars. CN band around 5200 and 5700
˚ A distinctly seen in RV Sct is marginally detected in HE
0002-0053 but not seen in HE 1104-0957.
13C isotopic band around 4700˚ A is
6 ATMOSPHERES OF CH STARS
6.1 Effective temperature
Preliminary estimates of the effective temperatures of the
candidate CH stars are determined by using temperature
calibrations derived by Alonso et al. (1996). These calibra-
tions were derived by using a large number of lower main
sequence stars and subgiants, whose temperatures were mea-
sured by infrared flux method, and holds within a tempera-
ture and metallicity range 4000 ≤ Teff ≤ 7000 K and -2.5
≤ [Fe/H] ≤ 0 . This calibration relates Teff with Stromgren
indices as well as [Fe/H] and colours (V-B), (V-K), (J-H) and
(J-K). By considering the uncertainties arising from different
sources such as uncertainties in the Stromgren photometry,
reddening and the calibration of the absolute flux in the in-
frared, Alonso et al. (1996) estimated an uncertainty of ∼
90 K in Teff determination. The broad band B-V colour
is often used for the determination of Teff, however B-V
colour of a giant star depends not only on Teff but also on
metallicity of the star and the molecular carbon absorption
features, due to the effect of CH molecular absorption in
the B band. For this reason, we have not used the empirical
Teff scale for the B-V colour indices. Since there is a neg-
ligible difference between the 2MASS infrared photometric

Page 9

Table 3: Estimated effective temperatures (Teff) of the candidate CH stars
Star NamesTeff−
(J-K)
Teff−
(J-H)
Teff−
(V-K)
12C/13C
HE 0017+0055
HE 0038-0024
HE 0043-2433
HE 0110-0406
HE 0111-1346
HE 0151-0341
HE 0308-1612
HE 0314-0143
HE 0319-0215
HE 0322-1504
HE 0457-1805
HE 0507-1653
HE 0518-2322
HE 1027-2501
HE 1056-1855
HE 1145-0002
HE 1125-1357
HE 1204-0600
HE 1211-0435
HE 1304-2046
HE 1305+0132
HE 1425-2052
HE 1418+0150
HE 1429-0551
HE 1446-0112
HE 1523-1155
HE 1524-0210
HE 1528-0409
HE 2144-1832
HE 2145-1715
HE 2207-0930
HE 2207-1746
HE 2218+0127
HE 2221-0453
HE 2339-0837
3919.1
3783.8
4263.8
4405.6
4449.5
4619.2
4274.8
3454.4
4188.9
4054.8
4097.6
4740.2
4680.9
-
4280.5
3665.5
3708.6
3910.0
4710.3
4073.0
3931.4
4038.5
3781.1
4367.4
3891.9
4524.2
3826.9
4666.7
3922.2
4019.1
3628.5
4378.8
5544.6
4231.7
4592.6
4124.4
3929.2
4271.3
4444.0
4481.0
4696.5
4369.2
3561.6
4314.8
4293.7
4513.4
4846.3
4689.1
-
4427.3
3905.5
3897.9
4102.6
4476.0
4200.9
4061.2
4179.1
4042.8
4800.0
4160.2
4491.1
3942.1
4662.4
4226.4
3862.1
3751.7
4448.4
5631.3
4487.1
4499.1
- 1.3
1.9
-
2.1
2.5
1.7
2.8
76.8
4.7
2.2
-
6.7
-
1.8
-
1.4
3.7
1.7
3.7
1.7
1.4
1.7
1.5
1.9
1.8
2.5
2.3
2.4
2.1
2.2
1.4
3.2
4.2
12.6
2.3
4306.2
4379.3
-
-
4912.7
-
-
4480.4
4614.6
4165.5
4983.1
-
-
–
3691.2
3910.2
3881.6
4732.4
4061.1
4131.2
3824.0
-
-
3854.9
4380.8
4611.2
4388.4
-
4214.1
3736.5
-
-
4163.8
5104.5
HD 26
HD 209621
HD 5223
5.9
8.8
6.1
system and the photometry data measured on TCS system
used by Alonso et al. (1998) in deriving the Teff scales; we
have used the empirical Teff scales with 2MASS photomet-
ric data. We have further assumed that the effects of redden-
ing on the measured colours are negligible. In estimating the
Teff from Teff - (J-H) and Teff - (V-K) relations we had
to adopt a value for metallicity of the star as the metallicity
of these stars are not known. We assumed the metallicity of
the stars to be same as their closest comparison star. This
assumption has definitely affected the accuracy of the Teff
measurements. Estimated effective temperatures are listed
in Table 3.
For a reliable determination of metallicity, effective tem-
peratures and chemical compositions of these stars, observa-
tion at high resolution is necessary. High resolution spectra
will also enable us for an accurate measurement of12C/13C
ratios.
6.2Isotopic ratio12C/13C from molecular band
depths
Carbon isotopic ratio12C/13C provides an important probe
of stellar evolution but low resoltuion of the spectra does
not allow a meaningful estimation of this ratio.
We have estimated the ratio of the molecular band
depths using the bands of (1,0)
12C13C λ4744. For a majority of the sample stars, we find
from the depths of molecular bands the ratio12C/13C ∼ 3,
with an exception of three stars for which this ratio is 7,
13 and 77 respectively. The ratios are presented in Table
3. This ratio measured on the spectra of the welknown CH
stars HD 26, HD 5223 and HD 209621 are respectively 5.9 ,
6.1 and 8.8 . Tsuji et al. (1991) had suggested two kinds of
CH stars; one with very high
with the values less than about 10. Our estimated ratios of
12C/13C are consistent with this.
Several explanations on the significance of the range of
values of12C/13C ratios are put forward in terms of the stars
evolutionary scenarios. One explanation for a lower value of
12C12C λ4737 and (1,0)
12C/13C ratio and the other

Page 10

12C/13C ratio is that, generally, the12C/13C ratio and to-
tal carbon abundances decrease due to the convection which
dredges up the products of internal CNO cycle to stellar at-
mosphere as ascending RGB. If it reaches AGB stage, fresh
12C may be supplied from the internal He burning layer to
stellar surface leading to an increase of12C/13C ratio again.
Since the abundance anomalies observed in CH giants are
believed to have originated by the transfer of mass from
a now extinct AGB companion, the CH giant’s atmosphere
should be enhanced in triple α products from the AGB star’s
interior- primarily12C. This explanation is in favour of stars
which give high12C/13C ratios. The low carbon isotope ra-
tios imply that the material transferred from the now unseen
companion has been mixed into the CN burning region of
the CH star or constitutes a minor fraction of the envelope
mass of the CH star, thus giving isotope ratios typical of
stars on their first ascent of the giant branch.
7 CONCLUDING REMARKS
Large samples of high latitude carbon stars such as one re-
ported by Christlieb et al. allows a search for different kinds
of carbon stars; the present work is a step in this direction.
The sample of carbon star candidates offered by Christlieb
et al. being high latutude objects, smaller initial masses and
possible lower metallicity, it is likely that a reasonable frac-
tion of it could be CH stars. Indentification of several CH
stars and description of their spectra are the main results
of this paper. Another effort is known to be underway to
make a medium-resolution spectroscopic study of the com-
plete sample of stars from Christlieb et al. 2001 (Marsteller
et al. 2003, Beers et al. 2003). From the sample list we have
acquired spectra for ninety one stars in the first phase of
observation. Out of these, fifty one objects were found to
exhibit strong C2 molecular bands in their spectrs of which
thirteen stars have low flux below about 4300˚ A. Twenty five
objects show weak or moderate CH and CN bands, twelve
objects show weak but detectable CH bands in their spectra
and there are three objects which do not show any molecular
bands due to C2, CN or CH in their spectra. As an example,
in figure 9 we show three spectra: a spectrum of HE 0443-
1847 which exhibits very weak molecular bands due to CN
around 4215˚ A and a weak G-band of CH around 4300˚ A
(but no C2 molecular bands); a spectrum of HE 0930-0018
which show a weak signature of G-band of CH around 4300
˚ A and a spectrum of HE 1227-3103 which do not show any
molecular bands due to C2, CN or CH in its spectrum.
Although spectroscopically, appearance of strong C2
molecular bands is an obvious indication of a star being
a carbon star, the conventional defination of a carbon star
is a star with C/O ≥ 1 (Wallerstein et al. 1997). Hence
if one adopts this conventional definition non appearance of
any C2 molecular bands will not necessarily disqualify a star
from being a carbon star as this does not exclude the condi-
tion C/O ≥ 1; which at our resolution of the spectra is not
derivable.
Westerlund et al. (1995) defined dwarf carbon stars as
having J-H ≤ 0.75, H-K ≥ 0.25 mag. None of the stars oc-
cupies a region defined by these limits in J-H, H-K plane.
With respect to J-H, H-K colours there is a clear separation
between the C-N type stars and dwarf carbon-star popula-
tions; there are CH stars with J-H ≤ 0.75 but their H-K
values are less than the lower limit of 0.25 mag set for dwarf
carbon stars. We find that the sample of stars under investi-
gation is comprised mostly of CH stars and a small number
of C-N and C-R stars.
We have derived the effective temperatures of the can-
didate CH stars from correlations of Alonso et al. (1996)
making use of (J-K), (J-H) and (V-K) colour indices. They
vary over a wide range of temperature with an average of
± 240 K. These temperature estimates provide a prelimi-
nary temperature check for the program stars and can be
used as starting values in deriving atmospheric parameters
from high resolution spectra using model atmospheres. For
majority of the sample stars, we find carbon isotopic ratio
12C/13C ∼ 3 with an exception of three stars HE 0507-1653,
HE 2221-0453 and HE 0314-0143 for which this ratio is 7, 13
and 77 respectively. It was suggested by Tsuji et al. (1991)
that there could be two kinds of CH stars, one with very
high
12C/13C estimates are consistent with this. This range of
ratios is the same as found for the population II giants and
globular cluster giant stars (Vanture 1992). Different evo-
lutionary scenarios are held responsible for the two groups
of CH stars, one with high and the other with low12C/13C
ratios.
From radial velocity survey CH stars are known to be
binaries. For the moderately metal-poor classical CH stars
([Fe/H] ∼ -1.5), a scenario for abundance anomalies and
the origin of carbon was proposed in which the carbon-
enhanced star is a member of a wide binary system that
accreted material from a former primary, during the asymp-
totic giant branch (AGB) phase of the latter, as described by
McClure & Woodsworth (1990). In such a scenario CH stars
with large12C/13C ratios indicates that their atmosphere is
enhanced in triple α products. The process of convection
dredges up the products of internal CNO cycle to the stellar
atmospheres as ascending RGB and this leads to a decrease
of or a small value of12C/13C ratio and a small total car-
bon abundance; on reaching the AGB stage
increases again due to the receipt of fresh12C supplied from
the internal helium burning layer to the stellar surface. Ac-
cording to the models of McClure (1983, 1984) and McClure
& Woodsworth (1990) the CH binaries have orbital charac-
teristics consistent with the presence of a white dwarf com-
panion, these stars have conserved the products of carbon
rich primary and survived untill the present in the Galactic
halo.
However, in case of a few carbon-enhanced, metal-poor
stars (subgiants) monitoring of radial velocity over a pe-
riod of eight years did not reveal radial velocity variations
greater than 0.4 km s−1which is against the mass transfer
scenario for these stars (Norris et al. 1997a, Aoki et al. 2000,
Preston and Sneden 2001). Furthermore, it is expected that
the star we observe today should display an enrichment of
s-process elements, produced by the former primary in its
AGB phase, while the carbon-enhanced metal-poor star CS
22957-027 (Norris et al. 1997b, Bonifacio et al. 1998), as
well as the stars reported by Aoki et al. 2000 do not exhibit
this behaviour. The carbon-enhanced metal-poor stars that
do show s-process enrichment provide strong observational
constraints for theoretical models of the structure, evolution
and nucleosynthesis of early-epoch AGB stars and permit
12C/13C ratio and the other with values ∼ 10. Our
12C/13C ratio

Page 11

studies of the s-process operating at very low metallicities.
It was shown by Goriely & Siess (2001) that even at the
absence of iron seeds efficient production of s-process ele-
ments can take place at zero metallicity provided protons
are mixed into carbon-rich layers producing13C, which acts
as a strong neutron source via
discovery of carbon-enhanced metal-poor stars with strong
overabundances of Pb support these predictions ( Aoki et al.
2000, Van Eck et al. 2001). Thus CH stars being the most
prominent of the few types of heavy element stars that exist
in both the field of the Galaxy and globular clusters are an
important class of objects which can provide some of the
very few direct observational tests to stellar evolution the-
ory.
13C(α ,n)16O. The recent
While in the present work, the spectra of the stars listed
in table 1, are discussed the analysis and description of the
spectra of the stars listed in table 2 will be discussed in a
subsequent work.
Acknowledgement
We thank the staff at IAO and at the remote control station
at CREST, Hosakote for assistance during the observations.
This work made use of the SIMBAD astronomical database,
operated at CDS, Strasbourg, Franch, and the NASA ADS,
USA. I am grateful to the referee Prof Timothy Beers for his
many constructive suggestions which has improved consid-
erably the readability of the paper. The author would also
like to thank Professor N. K. Rao for his guidance in the
observational program, and helpful suggestions.
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Page 12

Figure 2. A comparison of the spectra of a pair of C-R stars HD 156074 and HD 76846 and a pair of CH stars HD 5223 and HD 209621
in the wavelength region 4100-5400˚ A. The most prominent features noticeable are marked on the figure.

Page 13

Figure 3. Same as figure 2 but for the wavelength region 5400-6800˚ A. The prominent features of Na I D, Ba II at 6496˚ A Hα and C2
molecular bands around 5635˚ A are indicated.

Page 14

Figure 4. The spectra of the comparison stars in the wavelength region 4000-6800˚ A.

Page 15

Figure 5. The figure shows one example from the HE stars corresponding to the comparison stars presented in figure 4, in the top to
bottom sequence, in the wavelength region 4000-6800˚ A. The locations of some prominent features seen in the spectra are marked on the
figure. HE 1254-1130 has low flux below about 4400˚ A. Ba II at 6496˚ A and Hα seen in the top three stars spectra are not detectable in
the lower three stars spectra. Except for the Na I D feature which is barely detectable in the spectra of HE 2331-1329 and HE 1254-1130,
these two stars spectra resemble closely to their comparison stars spectra of Z Psc and V460 Cyg respectively.