Table 3
Overview of envelope terminal velocities, mass-loss rates, and 29Si/30Si ratios toward the selected evolved stars.
| Source | d | V e | Ṁ | 29Si/30Sia | Spectral type | Stellar type | Note |
| (pc) | (km s-1) | (M⊙ yr-1) | |||||
|
|
|||||||
| VY CMa | 1170 | 46.5 | 2.0 × 10-4 | 1.55 ± 0.08 | M2/4II | RSG | APEX-1+HIFId |
| NML Cyg | 1610 | 33.0 | 8.7 × 10-5 | 1.50 ± 0.20 | M6I | RSG | Tsuji et al. (1994) |
| IRC+10216 | 120 | 14.5 | 1.2 × 10-5 | 1.46 ± 0.18 | C9,5e | MIRA | Tsuji et al. (1994) |
| IK Tau | 260 | 18.5 | 4.6 × 10-6 | 1.60 ± 0.30b | M8/10IIe | MIRA | Decin et al. (2010); Kim et al. (2010) |
| TX Cam | 380 | 21.2 | 6.5 × 10-6 | 1.06 ± 0.54 | M8.5 | MIRA | Cho & Ukita (1998) |
| CIT 6 | 440 | 20.8 | 3.2 × 10-6 | 0.95 ± 0.35 | Ce | SRa | Zhang et al. (2009) |
| G Her | 310 | 13.0 | 7.0 × 10-7 | 1.35 ± 0.31 | M6III | SRb | Tsuji et al. (1994) |
| R Cas | 106 | 13.5 | 4.0 × 10-7 | 1.09 ± 0.41 | M7IIIe | MIRA | HIFId |
| SW Vir | 170 | 7.5 | 4.0 × 10-7 | 1.33 ± 0.32 | M7III | SRb | Tsuji et al. (1994) |
| RX Boo | 155 | 9.0 | 3.6 × 10-7 | 1.31 ± 0.28 | M7.5e | SRb | Tsuji et al. (1994) |
| o Ceti | 107 | 8.1 | 2.5 × 10-7 | 1.04 ± 0.06 | M7e | MIRA | APEX-1/2+HIFId |
| χ Cyg | 149 | 8.5 | 2.4 × 10-7 | 1.06 ± 0.22c | S6 | MIRA | HIFId |
| R Dor | 45 | 6.0 | 2.0 × 10-7 | 1.14 ± 0.16 | M8IIIe | SRb | HIFId |
| R Leo | 130 | 5.0 | 1.8 × 10-7 | 1.32 ± 0.04 | M8IIIe | MIRA | APEX-2d |
| W Hya | 77 | 8.5 | 7.8 × 10-8 | 0.99 ± 0.05 | M7e | SRa | APEX-1+HIFI d |
Notes. The data of distance d, terminal velocity of CO envelope Ve, and mean mass-loss rate Ṁ of the selected sources were compiled from Woods et al. (2003), De Beck et al. (2010), Justtanont et al. (2012), and Schöier et al. (2013). We note that Schöier et al. (2013) adopted smaller distances for χ Cyg (110 pc) and RX Boo (120 pc), and the distance to VY CMa was averaged from two measurements (Choi et al. 2008; Zhang et al. 2012). The mean 29Si/30Si ratios for VY CMa, o Ceti, and W Hya were derived from the thermal 29SiO/30SiO emission ratios obtained by the APEX and Herschel telescopes. The 29Si/30Si ratios for R Cas, χ Cyg, and R Dor were derived from the Herschel/HIFI data. The 29Si/30Si ratios of G Her, SW Vir, and RX Boo were taken from Tsuji et al. (1994), TX Cam from Cho & Ukita (1998), and CIT 6 from Zhang et al. (2009). Spectral types were taken from the SIMBAD database, De Beck et al. (2010), and the references therein. when more than one transition was detected.
The Herschel/HIFI data only show a 2-σ detection of 29SiO and 30SiO J = 26−25 lines with a ratio of 1.6 ± 0.8. However, judging from the APEX J = 8−7 and 7−6 data of Kim et al. (2010), the integrated ratios are also close to 1.6. We note that the baselines in the 30SiO spectra of Kim et al. (2010) may be too low. Therefore, the actual 29SiO/30SiO ratio should be ≲ 1.6 (see also the discussion of Decin et al. 2010, who adopted an abundance ratio of 3 ± 2 from their modeling results).
The ratio reported by Ukita & Kaifu (1988) and Tsuji et al. (1994) is about 2.4 with a large uncertainty (same as V1111 Oph) estimated from J = 2−1, which may be affected by masing effects. Therefore, we estimated the 29SiO/30SiO ratio only from the new HIFI measurements.
The SiO intensity measurements are listed in Table 2.
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