EDP Sciences
Free Access
Issue
A&A
Volume 606, October 2017
Article Number A74
Number of page(s) 10
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361/201730791
Published online 13 October 2017

© ESO, 2017

1. Introduction

IRC +10216 (CW Leo) is a well-known carbon-rich Asymptotic Giant Branch (AGB) star with a high mass-loss rate of about 1−4 × 10-5M yr-1 (e.g., Crosas & Menten 1997; De Beck et al. 2012; Cernicharo et al. 2015a) at a distance of 123 ± 14 pc (Groenewegen et al. 2012). The effective stellar temperature is between 2500 and 2800 K (Men’shchikov et al. 2001). The radial velocity (LSR) and terminal expansion velocity of IRC +10216 have been estimated at −26.5 ± 0.3 km s-1 and 14.5 ± 0.2 km s-1, respectively (Cernicharo et al. 2000). IRC +10216 is surrounded by an extended circumstellar envelope (CSE) owing to its extensive mass loss. The CSE is a physically and chemically rich environment forming molecules and condense dust grains (e.g., Fonfría et al. 2008; Agúndez et al. 2012; Fonfría et al. 2014).

Observations at centimeter (cm) and millimeter (mm) wavelengths probe the cool, outer part of AGB winds and bring valuable evidence of molecular species, from simple radicals such as OH to more complex species like cyanopolyynes. In previous works, linear carbon-chain molecules like CnH, HC2n+1N, and CnS were observed to be abundant in the circumstellar envelopes of carbon-rich AGB stars (Winnewisser & Walmsley 1978; Cernicharo & Guélin 1996; Guélin et al. 1997; Agúndez et al. 2014; Gong et al. 2015; Agúndez et al. 2017). These molecules are proposed to be related to the formation and destruction of polyaromatic hydrocarbons (PAH) (Henning & Salama 1998; Tielens 2008). The full characterization of carbon-chain molecules is regarded to be an important issue in astrochemistry (Sakai et al. 2010).

Molecular line survey is a powerful tool for analyzing both physical and chemical parameters of astronomical objects. Several systematical spectral line surveys of IRC +10216 have been reported in the literature. From Table 1, we find that existing surveys cover the frequency range from 4 to 636.5 GHz for IRC +10216. Over 80 species (Agúndez et al. 2014) have been discovered toward IRC +10216, including unusual carbon-chain and silicon-carbon molecules such as SiC2, MgCCH, NCCP, and SiCSi (Thaddeus et al. 1984; Cernicharo et al. 2010; Agúndez et al. 2014; Cernicharo et al. 2015b), metal cyanides/isocyanide such as MgNC, MgCN, AlNC, KCN, FeCN, NaCN, HMgNC, and SiH3CN (Ziurys et al. 1995, 2002; Pulliam et al. 2010; Zack et al. 2011; Agúndez et al. 2012, 2014; Cabezas et al. 2013), and even metal halides such as NaCl, KCl, AlCl, and AlF (Cernicharo & Guélin 1987; Quintana-Lacaci et al. 2016).

Complex molecules have small rotational constants meaning that their lowest-energy transitions arise at cm wavelengths. From Table 1, we find that there are several systematic and high-sensitivity surveys at cm wavelengths toward IRC +10216. However, no systematic survey has been reported in the frequency range between 6 and 17.8 GHz.

In this paper, the results of a spectral line survey of IRC +10216 between 13.3 and 18.5 GHz are presented. The observations are introduced in Sect. 2. The observational results derived from the analysis of the molecular emission are shown in Sect. 3. Section 4 contains the analysis of the lines and the comparison of the results with those of previous works. Finally, the conclusions are presented in Sect. 5.

Table 1

Existing line surveys of IRC +10216.

2. Observations and data reduction

The Tian Ma Radio Telescope (TMRT) is a 65 m diameter fully steerable radio telescope located in the western suburbs of Shanghai, China (Li et al. 2016; Yan et al. 2015). The Digital Backend System (DIBAS) of TMRT is a Field Programmable Gate Array (FPGA) based spectrometer based upon the design of Versatile GBT Astronomical Spectrometer (VEGAS).

The observations were performed in a position-switching mode at Ku band (11.5–18.5 GHz) towards IRC +10216 in 2016 March and April with the TMRT. On-source and off-source integration times were two minutes per scan. In this work, the DIBAS sub-band mode 2 with a single spectral window was adopted for Ku band observation. The window has 16 384 channels and a bandwidth of 1500 MHz, supplying a velocity resolution of about 2.08 km s-1 (13.3 GHz) to 1.491 km s-1 (18.5 GHz). The intensity was calibrated by injecting periodic noise, and the accuracy of the calibration was estimated from frequency ranges where the spectrum was apparently free of lines. The system temperature was about 55–64 K at Ku band. Across the whole frequency range, the FWHM beam size was 52′′–84′′. The adopted coordinates for our searches were: RA (2000) = 09:47:57.45, Dec (2000) = 13:16:43.8. The pointing accuracy was better than 12′′. The resulting antenna temperatures were scaled to main-beam temperatures (TMB) by using a main-beam efficiency of 0.6 for a moving position of sub-reflector at Ku band (Li et al. 2016).

The data were reduced using GILDAS software package1 including CLASS and GREG. Linear baseline subtractions were used for all the spectra. Because of the contamination due to time-variable radio frequency interference (RFI), the channels from 11.5 to 13.3 GHz were discarded from further analysis. Since some unknown defects occurred at the edges of the spectra, the channels with a bandwidth of 150 MHz at each edge were excluded. All the spectra including two polarizations were averaged to reduce rms noise levels resulting in a total integration time of about 2 h.

thumbnail Fig. 1

Overview of the spectral line survey of IRC +10216 between 13.3 and 18.5 GHz with strong lines marked.

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thumbnail Fig. 2

Zoom in of all detected and tentatively detected lines for HC3H, H13CCCN, HC13CCN, HCC13CN, HC5H, and HC7H. The corresponding rest frequency in MHz is shown in the upper right of each panel. Weak lines have been smoothed to have a channel width of 3.0–3.6 km s-1, and are marked with “smoothed” in the upper left of the corresponding panels. Otherwise, the channel width is 1.5–2.1 km s-1. The blue dashed lines of the blended transitions trace the systematic LSR velocity (26.5 km s-1) of IRC +10216.

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thumbnail Fig. 3

Same as Fig. 2 but for HC9H.

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thumbnail Fig. 4

Same as Fig. 2 but for c-C3H2, l-C5H, C6H, and C6H.

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thumbnail Fig. 5

Same as Fig. 2 but for C8H and Si bearing species.

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3. Results

Based on the molecular database “Splatalogue”2, which is a compilation of the Jet Propulsion Laboratory (JPL, Pickett et al. 1998), Cologne Database for Molecular Spectroscopy catalogs (CDMS, Müller et al. 2005), and Lovas/NIST catalogs (Lovas 2004), the line identifications are performed. The local standard of rest (LSR) radial velocity of −26.5 km s-1 is adopted to derive the rest frequency of the observed lines. A line is considered real if it has a signal-to-noise ratio (S/N) of at least five (Gong et al. 2015), although, a line is already significant if it is characterized by a S/N above three (Fonfría et al. 2014). Lines with a S/N of at least three are discussed in this paper. Figure 1 presents an overview of the spectral line survey of IRC +10216 between 13.3 and 18.5 GHz with strong lines marked.

All detected transitions are shown in Figs. 25 and Table A.1. There are 41 transitions assigned to 12 different molecules and radicals found in this survey. Except for SiS, all other molecules are C-bearing molecules. The detected transitions include one transition of HC3N, three transitions of the 13C-bearing isotopologs of HC3N, two transitions of HC5N, five transitions of HC7N, and nine transitions of HC9N, which are shown in Figs. 2 and 3. In Fig. 2, HC13CCN (v = 0,J = 2−1) is blended with HCC13CN (v = 0,J = 2−1). Additionally, eight transitions of C6H are detected. In Fig. 4, C6H () is blended with C6H (), and C6H () is blended with C6H (). There is a transition of c-C3H2, five transitions of l-C5H from the ladder and one transition of C6H in Figure 4. Spectra line profiles of three transitions of C8H from the ladder, SiS (v = 0,J = 1−0), SiC2 (v = 0,J = 7(2,5)−7(2,6)) and SiC4 (v = 0,J = 5−4) are shown in Fig. 5. There are five transitions of SiC2 and two transitions of SiC4 in this band. Other transitions of SiC2 and SiC4 are too weak to be detected. The peak intensities of the smoothed lines of HC13CCN, HCC13CN, l-C5H, C8H , and C6H are smaller than 20 mK. These smoothed lines are weak and tentatively detected. The rest frequencies and the upper energy levels of these lines are obtained from the molecular database “Splatalogue”.

The SHELL fitting routine in Continuum and Line Analysis Single-dish Software (CLASS) is used to derive line parameters including peak intensity, integrated intensity, and expansion velocity which is defined as the half-width at zero power. Except for the blended lines, the observed lines are either double peaked or flat topped. The fitting profiles are shown in Figs. 25 when possible. For the line of HC3N with hyperfine structure, only the main component is fitted to obtain the expansion velocity. For the lines that are blended and weak, the parameters are estimated directly by integrating the line profiles. Firstly, we estimate the maximum velocities υ1 and υ2 of blueshift and redshift. Then, we return the integrated area (K km s-1) of the current spectrum between velocities υ1 and υ2 by using the function TDV(υ1,υ2) in CLASS. The observed properties of the lines are displayed in Table A.1.

The spectrum is dominated by the strong transitions from five species: SiS, HC3N, HC5N, HC7N, and c-C3H2. The peak intensities of SiS, HC3N, and HC5N lines are larger than 120 mK. The peak intensities of HC7N and c-C3H2 lines are larger than 50 mK. The peak intensities of other lines are about 20 mK. Weak lines with the peak intensities smaller than 20 mK have been smoothed to have a channel width of 3.0–3.6 km s-1 to improve signal to noise ratios. The smoothed lines are marked with red “smoothed” in the upper left of the corresponding panels in Figs. 25 and marked with “S” in Table A.1. The rms noise of peak intensity, which is estimated by fitting the baseline to a line or polynomial from frequency ranges around each particular transition where the spectrum is apparently free of lines, is about 3–7 mK in 1.5–3.6 km s-1 wide channel. The lines in this work reveal an average LSR velocity of about −26.7 ± 2.0 km s-1 and an average terminal expansion velocity of about 13.9 ± 2.0 km s-1, which are consistent with previous studies (e.g., −26.5 ± 0.3 km s-1 and 14.5 ± 0.2 km s-1, respectively, Cernicharo et al. 2000; −26.404 ± 0.004 km s-1 and 13.61 ± 0.05 km s-1, respectively He et al. 2008). The terminal expansion velocity of IRC +10216 has been estimated at ~14.5 km s-1 in previous studies. The error of integrated intensity given in this work, which is the product of the rms noise of peak intensity and the width of the line for about 29 km s-1, is about 100–200 mK km s-1.

4. Discussion

It was suggested that single-peaked lines arise from optically thick transitions, while flat-topped and double-peaked lines arise from optically thin spatially unresolved and resolved transitions, respectively (Olofsson et al. 1982; Kahane et al. 1988). There are 11 double-peaked lines and 19 flat-topped lines among the 30 unblended lines detected in this work. Therefore, we can assume the lines detected in this work to be optically thin. By assuming LTE, rotational temperatures and column densities can be estimated from the rotational diagrams. The equation (Cummins et al. 1986): (1)gives the relation between the column density and the line intensity, where k is the Boltzmann constant, W (TR dυ, K km s-1) is the observed line integrated intensity, ν (Hz) is the frequency of the transition, Sμ2 is the product of the total torsion-rotational line strength and the square of the electric dipole moment. Trot and Tbg (2.73 K) are the rotational temperature and background brightness temperature, respectively. Eu is the upper level energy, and Q(Trot) is the partition function. Values of EU/k and Sμ2 are taken from the “Splatalogue” spectral line catalogs.

From Eq. (1), the formula for rotational diagrams is: (2)where . To determine rotational temperatures with this method, there must be at least two transitions of the same molecule with significant rotational temperature differences.

SiS (1−0) is a maser in IRC +10216 (Henkel et al. 1983) and its populations must deviate from LTE, therefore this transition is excluded from the fitting. The lines of HC13CCN (v = 0,J = 2−1) and HCC13CN (v = 0,J = 2−1) are blended owing to large uncertainties of intensities, so are also excluded. Since only one line is detected in this work for each of HC3N, H13CCCN, c-C3H2, SiC2, SiC4, and C6H, these lines cannot be used to determine rotational temperatures directly. For molecules of HC5N, HC7N, HC9N, C6H, C8H, and l-C5H, although at least two lines are detected, they do not have a wide dynamic range in upper level energies. The 17.8 GHz to 26.3 GHz data from Gong et al. (2015), the 28 GHz to 50 GHz data from Kawaguchi et al. (1995), the C8H data from Remijan et al. (2007) and the H13CCCN data from He et al. (2008) are adapted as the complementary to data in the current survey to derive rotational temperatures more precisely.

The integrated intensity (, mK km s-1) of Gong et al. (2015) is obtained from the integrated flux density (, mJy km s-1), which is taken from Table 3 in Gong et al. (2015). The conversion factor from the flux density (Sν, Jy) to the main beam brightness temperature (Tmb, K) is Tmb/Sν ~ 1.5 K/Jy at 22 GHz. In Gong et al. (2015), across the whole frequency range, the beam size is 35″−50″ (~40″ at 23 GHz). The rms noise of intensity is estimated in the same way as in this work using online data of the observed spectrum. In Kawaguchi et al. (1995), the main beam efficiency (η) was measured to be 0.78 ± 0.06 at 30 GHz, 0.79 ± 0.05 at 43 GHz, and 0.71 ± 0.07 at 49 GHz. The main beam efficiency at the other frequencies was assumed to be 0.78 in the region between 28 and 35 GHz, and was interpolated from the measured values in the region between 35 and 50 GHz. The measured beam size, that is, the full width at half maximum (FWHM), was 34.9″ ± 1.1″ at 49 GHz and 41.5″ ± 1.1″ at 43 GHz. The brightness temperature (TR) of the molecular transition in the source is related to the antenna temperature () as . The integrated intensity () and the rms noise of antenna temperature are taken from Table 1 in Kawaguchi et al. (1995). In Remijan et al. (2007), the beam size (FWHM) is approximated by θbeam = 740″ /ν(GHz). The main beam efficiency (η), the integrated intensity () and the error to the integrated intensity are taken from Table 1 in Remijan et al. (2007). In He et al. (2008), the FWHM beam size of the KP12M is 43′′ at 145 GHz. The integrated intensity () and the rms noise of main beam temperature are taken from Table 10 in He et al. (2008). The errors to the integrated intensities here are computed in the same way as in Gong et al. (2015), He et al. (2008) and Kawaguchi et al. (1995).

The intensities of the detected lines should be divided by for beam dilution to derive the physical parameters, where θs is the source size, and θbeam is the beam size (Bell 1993). Therefore, the brightness temperature (TR) of the molecular transition in the source is related to the main beam temperature (TMB) as (3)The source sizes are taken based on previous high-resolution mapping of different molecules toward IRC +10216 by interferometer. For species without high-resolution mapping, their sizes are taken to be the same as chemically related species. Therefore, source sizes of HC3N and HC5N are 30″ as determined by new JVLA observations. Source size of H13CCCN is taken to be the same as that of HC3N. Source sizes of HC7N and HC9N are taken to be the same as that of HC5N. The sizes of l-C5H, c-C3H2, C6H, C6H, and C8H are taken to be the same as that of C4H (Guélin et al. 1993), which is 30″. The size of SiC2 is 27″, and the source size of SiC4 is assumed to be the same as in (Lucas et al. 1995). The size of SiS is 18″ by IRAM Plateau de Bure interferometer (Lucas et al. 1995). We carried out linear least-square fits to the rotational diagrams of 12 species. The results are shown in Fig. 6 and Table 2. The results of Gong et al. (2015) and Kawaguchi et al. (1995) in Table 2 are obtained from the methods of rotational diagrams as well.

thumbnail Fig. 6

Rotational diagrams for the observed molecules in IRC +10216. The variable L denotes the left-hand side of Eq. (2). Black dashed lines represent linear least-squares fit to the rotational diagram. The blue circles are from our TMRT-65 m observations. The green triangles are obtained from Gong et al. (2015). The red diamonds are obtained from Kawaguchi et al. (1995). The magenta crosses are obtained from Remijan et al. (2007). The cyan asterisks are obtained from He et al. (2008). Their values have been corrected for beam dilution. The molecules and their corresponding rotational temperatures are given in each panel.

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thumbnail Fig. 7

Comparison of column densities.

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This work assumes the same source sizes as Gong et al. (2015), and the H2 average column density (NH2) of 2.1 × 1021 cm-2 within a typical radius of 15″ taken from Gong et al. (2015) is used to calculate molecular fractional abundances relative to H2. The derived rotational temperatures (Trot), column densities (N), and molecular fractional abundances relative to H2 (X(N/NH2)) together with results from the literature, are listed in Table 2. The column densities of the molecules range from 1012 to 1015 cm-2, and the fractional abundances relative to H2 of the species detected in Ku band range from 2.91 × 10-9 to 9.24 × 10-7 in IRC +10216.

The blue-shifted component of the SiS (v = 0,J = 1−0) line shown in Fig. 5 is stronger than the red-shifted one due to maser amplification (18 154.9 MHz; Henkel et al. 1983). The peak intensity ratio of the blue-shifted component to the red-shifted component is estimated to be 1.97 ± 0.02 in Gong et al. (2015). In this work, the peak intensity ratio is about 1.20 ± 0.02, which is smaller than the ratio observed in Gong et al. (2015). The reason for the difference of the peak intensity ratio of SiS may be that the velocity resolution at 18154.888 MHz of 1.5 km s-1 in the work is bigger than that of 1.008 km s-1 in Gong et al. (2015). Lines of HC7N (v = 0,J = 16−15), HC3N (v = 0,J = 2−1) and c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)) have also been detected in Gong et al. (2015). The observed properties of these lines are displayed in Table 3, together with those from Gong et al. (2015) for comparison.

The integrated intensities (), obtained from Eq. (3), are shown in Table 4. The integrated intensities of HC7N (v = 0,J = 16−15), SiS (v = 0,J = 1−0) and HC3N (v = 0,J = 2−1) in this work are consistent with the results derived from Gong et al. (2015). But the integrated intensity of c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)) in this work is much smaller than that in Gong et al. (2015). Since the c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)) line is at the edge of the frequency range covered by the receiver, the flux calibration is less reliable there.

Light variability may also affect the accuracy of the integrated intensities. Intensity comparisons are more difficult for weaker lines. Also, for abundant species and their isotopologues toward the archetypical circumstellar envelope of IRC+10216, based on the existed observations (Cernicharo et al. 2000, 2014), some line intensities of the high rotational lines may follow the infrared flux variations, and some line intensities of the low-J transitions may not. Although there is no direct evidence indicating line intensities of the emission lines detected in this work, Gong et al. (2015), and Kawaguchi et al. (1995) correlate with the continuum intensity. Since most of the detected lines in this work are weak, the data for the strong transitions in this work are not sufficient to study the effect of the variability on the integrated intensity. Therefore, it is assumed that the periodic variations of the stellar IR flux do not modulate molecular line emission here.

The source sizes of HC2n+1N assumed in Kawaguchi et al. (1995) are the same as those in this paper and Gong et al. (2015). The column densities of HC2n+1N among this paper, Gong et al. (2015), and Kawaguchi et al. (1995) in Table 2 can be compared directly, shown in Fig. 7. The column densities of HC3N, HC5N, HC7N, and HC9N in this work are greater than the densities derived by Gong et al. (2015) and Kawaguchi et al. (1995). The abundance ratios for HC3N: HC5N: HC7N: HC9N are shown in Table 5. The ratio in this work is consistent with the ratio derived by Gong et al. (2015), but is greater than the ratio in Kawaguchi et al. (1995). The abundance ratio for C6H : C8H is calculated to be (1.1 ± 0.3):1, which is much smaller than the ratio observed in Gong et al. (2015), (11.9 ± 2.3):1. The obvious difference in abundances may suffer from low data quality in lines of C6H and C8H.

The transitions of HC3N and its 13C substitutions are optically thin. Thus, the isotopic ratio can be directly obtained from their integrated intensity ratio. The derived 12C/13C ratios are 32 ± 16 from [HCCCN]/[H13CCCN] (v = 0,J = 2−1). This is much smaller than 71 obtained from [12CO]/[13CO] by Ramstedt & Olofsson (2014) and is also smaller than 49 ± 9 derived from HC5N and its 13C isotopologs by Gong et al. (2015). This value agrees with 34.7 ± 4.3 derived from [SiCC]/[Si13CC] by He et al. (2008). Since, there is only one transition used for calculating the isotopic ratio in this work, more transitions need to be adapted as the complementary to derive the isotopic ratio more precisely.

Table 2

Column densities and rotational temperatures of the molecules in IRC +10216.

Table 3

Line Parameters of HC7N (v = 0,J = 16−15), SiS (v = 0,J = 1−0), HC3N (v = 0,J = 2−1), and c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)) detected in this work and Gong et al. (2015).

Table 4

Integrated intensity ratios (this work: Gong et al. 2015) of HC7N (v = 0,J = 16−15), SiS (v = 0,J = 1−0), HC3N (v = 0,J = 2−1) and c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)).

thumbnail Fig. 8

Comparison of rotational diagrams for HC5N, HC7N, and HC9N, computed separately for this and other works. The blue circles are from our TMRT-65 m observations. The green triangles are obtained from Gong et al. (2015). The red diamonds are obtained from Kawaguchi et al. (1995). The dashed lines of different colors represent linear least-squares fit to the rotational diagram accounting for data obtained from corresponding surveys.

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Bell et al. (1992) have reported that the HC5N molecule in the circumstellar envelope of IRC +10216 traces two molecular regions: a warm one (Tex ~ 25 K) traced by high-J transitions, that is, those with upper-state energies EU/k greater than 20 K, and a cold region with Tex ~ 13 K traced by low-J transitions with EU/k< 10 K. In Fig. 8, we compare rotational temperatures obtained separately from the different surveys. For HC5N, these are estimated to be This work: Gong: Kawaguchi = 1: 2.1: 5.9. The fitted rotational temperature of HC5N for high-J transitions is greater. And the rotational temperatures (Trot) of HC7N and HC9N are estimated to be This work: Gong: Kawaguchi = 1: 2.8: 7.2 and 1: 1.9: 3.3. Similar to the HC5N case, the rotational temperatures of HC7N and HC9N for high-J transitions are also greater. Therefore, the high-J transitions of the HC5N, HC7N, and HC9N molecules in the circumstellar envelope of IRC +10216 trace the warmer molecular regions. The abundance ratios of HC5N, HC7N, and HC9N derived from surveys of different frequency ranges are estimated to be This work: Gong: Kawaguchi = 100: 43: 55, 100: 24: 28 and 100: 30: 44, respectively. Obvious differences exist in the abundance ratios derived from different transitions, and this result may suffer from opacity effects. This also suggests that the assumption of thermal equilibrium is not accurate when estimating rotational temperatures and column densities.

5. Summary

A spectral line survey of IRC +10216 between 13.3 and 18.5 GHz was carried out using the TMRT. Forty-one spectral lines of 12 different molecules and radicals were detected in total. Several carbon-chain molecules are detected, including HC3N, HC5N, HC7N, HC9N, C6H, C8H, C6H, l-C5H, SiC2, SiC4, and c-C3H2.

The rotational temperatures and column densities of the detected molecules are derived by assuming LTE. Their rotational temperatures range from 4.7 to 40.1 K, and molecular column densities range from 1012 to 1015 cm2. Molecular abundances relative to H2 range between 2.91 × 10-9 and 9.24 × 10-7. From the comparison with previous works, it is clear that the higher-J transitions of the HC5N, HC7N, and HC9N molecules in the circumstellar envelope of IRC +10216 trace the warmer molecular regions. Furthermore, there are obvious differences in the abundance ratios derived from different transitions.

Table 5

Abundance ratios (HC3N: HC5N: HC7N: HC9N) of this work, Gong et al. (2015), and Kawaguchi et al. (1995).


Acknowledgments

This work is supported by the Natural Science Foundation of China (Nos. 11421303, 11590782).

References

Appendix A: Additional table

Table A.1

Line Parameters of transitions detected in IRC +10216.

All Tables

Table 1

Existing line surveys of IRC +10216.

Table 2

Column densities and rotational temperatures of the molecules in IRC +10216.

Table 3

Line Parameters of HC7N (v = 0,J = 16−15), SiS (v = 0,J = 1−0), HC3N (v = 0,J = 2−1), and c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)) detected in this work and Gong et al. (2015).

Table 4

Integrated intensity ratios (this work: Gong et al. 2015) of HC7N (v = 0,J = 16−15), SiS (v = 0,J = 1−0), HC3N (v = 0,J = 2−1) and c-C3H2 (v = 0,J = 1(1, 0)−1(0, 1)).

Table 5

Abundance ratios (HC3N: HC5N: HC7N: HC9N) of this work, Gong et al. (2015), and Kawaguchi et al. (1995).

Table A.1

Line Parameters of transitions detected in IRC +10216.

All Figures

thumbnail Fig. 1

Overview of the spectral line survey of IRC +10216 between 13.3 and 18.5 GHz with strong lines marked.

Open with DEXTER
In the text
thumbnail Fig. 2

Zoom in of all detected and tentatively detected lines for HC3H, H13CCCN, HC13CCN, HCC13CN, HC5H, and HC7H. The corresponding rest frequency in MHz is shown in the upper right of each panel. Weak lines have been smoothed to have a channel width of 3.0–3.6 km s-1, and are marked with “smoothed” in the upper left of the corresponding panels. Otherwise, the channel width is 1.5–2.1 km s-1. The blue dashed lines of the blended transitions trace the systematic LSR velocity (26.5 km s-1) of IRC +10216.

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In the text
thumbnail Fig. 3

Same as Fig. 2 but for HC9H.

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In the text
thumbnail Fig. 4

Same as Fig. 2 but for c-C3H2, l-C5H, C6H, and C6H.

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In the text
thumbnail Fig. 5

Same as Fig. 2 but for C8H and Si bearing species.

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In the text
thumbnail Fig. 6

Rotational diagrams for the observed molecules in IRC +10216. The variable L denotes the left-hand side of Eq. (2). Black dashed lines represent linear least-squares fit to the rotational diagram. The blue circles are from our TMRT-65 m observations. The green triangles are obtained from Gong et al. (2015). The red diamonds are obtained from Kawaguchi et al. (1995). The magenta crosses are obtained from Remijan et al. (2007). The cyan asterisks are obtained from He et al. (2008). Their values have been corrected for beam dilution. The molecules and their corresponding rotational temperatures are given in each panel.

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In the text
thumbnail Fig. 7

Comparison of column densities.

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In the text
thumbnail Fig. 8

Comparison of rotational diagrams for HC5N, HC7N, and HC9N, computed separately for this and other works. The blue circles are from our TMRT-65 m observations. The green triangles are obtained from Gong et al. (2015). The red diamonds are obtained from Kawaguchi et al. (1995). The dashed lines of different colors represent linear least-squares fit to the rotational diagram accounting for data obtained from corresponding surveys.

Open with DEXTER
In the text

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