SiO AND H ₂ O MASER SURVEY TOWARD POST-ASYMPTOTIC GIANT BRANCH AND ASYMPTOTIC GIANT BRANCH STARS

Abstract

We performed simultaneous observations of SiO v = 1, 2, 29 SiO v = 0, J = 1-0 and H 2 O 6 16 -5 23 maser lines toward 143 AGB and 164 post-asymptotic giant branch (AGB) stars in order to investigate how evolutionary characteristics from AGB to post-AGB stars appear in both SiO and H 2 O maser emissions. The observations were carried out from 2011 February to 2012 March using the Korean VLBI Network single-dish telescopes. We have detected SiO and/or H 2 O maser emission from 21 sources out of 164 post-AGB stars including 12 new detections. Of 143 AGB stars, we detected SiO and/or H 2 O maser emission from 44 stars including 24 new detections. SiO v = 2, J = 1-0 maser emission without a SiO v = 1 maser was detected from 7 sources among 14 SiO-detected post-AGB stars, and the intensity of the SiO v = 2, J = 1-0 maser tends to be much stronger than that of SiO v = 1, which is different from those of AGB stars. This may be related to the development of hot dust shells according to the evolutionary processes of post-AGB stars. We also found that both SiO and H 2 O masers were detected in the blue group (LI, or Left of IRAS), while only the H 2 O maser was detected in the red group (RI, or Right of IRAS) for post-AGB stars. These different detection rates between SiO and H 2 O masers may originate from the different abundances of masing molecules in the circumstellar envelope according to the different mass and expansion velocity between LI and RI regions together with their evolutionary stages.

A search for water maser emission toward obscured post-AGB star and planetary nebula candidates

“…), located ∼11 away, which spilled into the sidelobes of the single-dish telescope. We believe that the detection reported by Yoon et al (2014) toward IRAS 19071+0857 is likewise contaminated by W49A.…”

“…We have also included some optically visible post-AGB stars from Suárez et al (2006) that were not included in our previous water maser observations of Suárez et al (2007 or for which those observations had poor sensitivity. There are previous water maser observations of some sources in our sample, which are also cited in Table 1 (including those by Yoon et al 2014, who also selected 76 sources from Ramos-Larios et al 2009 as part of their sample of 164 post-AGB candidates), although our data have significantly higher sensitivity (over one order of magnitude more in most cases). A total of 133 sources were observed.…”

“…Previous observations of water maser emission toward this source resulted in non-detections (Gómez et al 1990;Deacon et al 2007;Yoon et al 2014). However, we detected water maser emission with a single component of 1 Jy at V LSR = −107.6 km s −1 , above the detection threshold of Deacon et al (2007) and Yoon et al (2014).…”

“…No OH maser emission has been detected toward this source (te Lintel Hekkert et al 1991). Yoon et al (2014) report the presence of H 2 O maser emission, with only one velocity component at V LSR = −16.3 km s −1 having been clearly detected. Our Robledo spectrum resolves two spectral components around that velocity.…”

The physics of water masers observable with ALMA and SOFIA: model predictions for evolved stars

“…Infra-Red Astronomy Satellite (IRAS) colour-colour diagrams in Kim et al (2014) indicate that H2O masers form at an earlier evolutionary stage than SiO masers, but the H2O masers may also persist into the PPN (proto-planetary nebula) stage, probably in a new form dominated by asymmetric outflow. Development of water (and SiO) maser emission in the transition from AGB (Asymptotic Giant Branch) to post-AGB stars is surveyed in more detail in Yoon et al (2014).…”