An unbiased spectral line survey observation toward the low-mass star-forming region L1527

Abstract

An unbiased spectral line survey toward a solar-type Class 0/I protostar, IRAS04368+2557, in L1527 has been carried out in the 3 mm band with the Nobeyama 45 m telescope. L1527 is known as a warm carbon-chain chemistry (WCCC) source, which harbors abundant unsaturated organic species such as C n H (n = 3, 4, 5, . . .) in a warm and dense region near the protostar. The observation covers the frequency range from 80 to 116 GHz. A supplementary observation has also been conducted in the 70 GHz band to observe fundamental transitions of deuterated species. In total, 69 molecular species are identified, among which 27 species are carbon-chain species and their isomers, including their minor isotopologues. This spectral line survey provides us with a good template of the chemical composition of the WCCC source.comparison with other sources such as starless cores showing cold carbon-chain chemistry (e.g., TMC-1 (CP); Kaifu et al. 2004) will give us valuable information on formation of these molecules in space.As an independent study, a similar spectral line survey observation toward this source was also carried out with the IRAM 30 m telescope, as part of the ASAI (Astrochemical Surveys At Iram) program. Its summary result has recently been reported (Lefloch et al. 2018), although detailed data exploitation has not been presented. The ASAI survey almost covers the frequency range of our survey in the 3 mm band with a larger beam size by a factor of 1.5.Nevertheless, independent spectral line surveys with different telescopes are always important for the fundamental sources such as L1527, because they give opportunities to confirm the consistency of the results, and also provide additional information such as the source sizes by taking advantage of the different beam sizes. Here, we report the results of our spectral line survey with NRO 45 m. 2 Observation The spectral line survey observations of L1527 were carried out with NRO 45 m during the seasons from 2006 to 2012. The frequency range was from 79.8 GHz to 116.8 GHz. The observed position was (α 2000 , δ 2000 ) = (4 h 39 m 53. s 89, 26 • 03 11. 0), which is the position of the protostar (Sakai et al. 2008b). In this observation, we used the SIS mixer receivers, S80 and S100, simultaneously from 2006 to 2008, while we employed the dual-polarization sidebandseparating SIS receiver T100H/V (Nakajima et al. 2008) from 2009 to 2012. The system temperatures varied from 250 to 350 K in the former and from 150 to 250 K in the latter.The intensity scale was calibrated by using the chopper-wheel method, and the calibration uncertainty is estimated to be better than 20%. The telescope pointing was checked once every 1 to 1.5 hour by observing the nearby SiO maser sources (NML-Tau and Ori-KL). The pointing accuracy was ensured to be better than 6 . The main-beam efficiency (η mb ) at 86 GHz was 0.43 from 2006 to 2008, 0.49 in 2009, and 0.42 from 2010 to 2012, as reported on the NRO website. The antenna temperature (T * A ) is converted to the main-beam brightness temperature (T...

A sensitive λ 3 mm line survey of L483

“…Curiously, the other 13 C isotopolog of c -C 3 H 2 substituted in the carbon bonded to hydrogen ( c -HCC 13 CH) does not suffer such a severe dilution in 13 C, as its 12 C/ 13 C ratio is 106 ± 32, that is, only slightly above the local ISM value. A similar result was recently found in L1527, where the 12 C/ 13 C ratios for c -HC 13 CCH and c -HCC 13 CH were found to be 310 ± 80 and 122 ± 22, respectively (Yoshida et al 2015), or 200 ± 30 and 82 ± 16, respectively, according to Yoshida et al (2019). It seems clear that 13 C fractionation works differently for these two 13 C isotopologs of c -C 3 H 2 and that 13 C dilution is much more favorable for c -HC 13 CCH.…”

“…Moreover, C 2 H is likely to be affected by 13 C dilution, as the C 2 H/C 13 CH and C 2 H/ 13 CCH ratios are found to be >71 and >165, respectively. A similar result was found in TMC-1 and L1527, where the C 13 CH/ 13 CCH ratio is ~1.6 and the 12 C/ 13 C ratios are significantly above the local ISM value (Sakai et al 2010; Yoshida et al 2019).…”

“…The λ 3 mm line survey covered the 2 1,2 -1 1,1 line of doubly deuterated formaldehyde, which was detected, leading to a D 2 CO/H 2 CO ratio of 3.2 %, which is comparable to that found in L1544, B1-b, and IRAS 16293–2422. This ratio has been reported to be as high as 44 % in L1527 (Parise et al 2006), although more recently Yoshida et al (2019) derived a much lower value of 1.4 %, which is more in line with the D 2 CO/H 2 CO ratios found in the other sources. The singly deuterated form of formaldehyde, HDCO, does not have favorable lines in the 80-116 GHz range and therefore could not be observed.…”

“…It is also interesting to note that while in the case of L1527, the presence of carbon chains and COMs seems to be mutually exclusive (Sakai et al. 2008a; Yoshida et al 2019), this is not the case for L483, where both types of molecules coexist in the ambient cloud.…”

“…For L1544 and B1-b, most data are based on IRAM 30m observations, some of which were taken in the context of ASAI (e.g., Fuente et al 2016; Vastel et al 2018b). In the case of L1527, column densities are mostly taken from the λ 3 mm line survey carried out with the Nobeyama 45m telescope recently published by Yoshida et al (2019). All the literature sources used are given in the caption of Fig.…”