Maser and Infrared Studies of Oxygen-Rich Late/Post-Asymptotic Giant Branch Stars and Water Fountains: Development of a New Identification Method

Abstract

We explored an efficient method to identify evolved stars with oxygen-rich envelopes in the late AGB or post-AGB phase of stellar evolution, which include a rare class of objects -the "water fountains". Our method considers the OH and H 2 O maser spectra, the near infrared Q-parameters (these are colour indices accounting for the effect of extinction), and far-infrared AKARI colours. Here we first present the results of a new survey on OH and H 2 O masers. There were 108 colour-selected objects: 53 of them were observed in the three OH maser lines (1612, 1665, and 1667 MHz), with 24 detections (16 new for 1612 MHz); and 106 of them were observed in the H 2 O maser line (22 GHz) with 24 detections (12 new). We identify a new potential water fountain source, IRAS 19356+0754, with large velocity coverages of both OH and H 2 O maser emission. In addition, several objects with high velocity OH maser emission are reported for the first time. The Q-parameters as well as the infrared [09]−[18] and [18]−[65]AKARI colours of the surveyed objects are then calculated. We suggest that these infrared properties are effective in isolating aspherical from spherical objects, but the morphology may not necessarily be related to the evolutionary status. Nonetheless, by considering altogether the maser and infrared properties, the efficiency of identifying oxygen-rich late/post-AGB stars could be improved.

Extreme infrared variables from UKIDSS – II. An end-of-survey catalogue of eruptive YSOs and unusual stars

“…sources not satisfying our YSO selection) that extends to the left and down from the group of known AGB stars (black circles) and candidate AGB stars (green squares) clearly separated from the majority of YSOs. (The five candidate AGB stars were identified by Lewis & Grinspoon 1990, Chengalur et al 1993, Kwok et al 1997and Yung et al 2014. Sources in this region of the plot, as far to the left as W1-W2=1.5, are in every case amongst the brightest mid-infrared sources in the catalogue, as shown in the middle and lower panels of figure 8.…”

Interferometric confirmation of ‘water fountain’ candidates

“…We also note that IRAS 18596+0315 harbours OH maser emission, whereas IRAS 17291-2147 does not. All WFs have been observed in OH, and only in the case of IRAS 16552-3050, IRAS 18113-2503, and IRAS 19134+2131 (in addition to IRAS 17291-2147) this emission has not been detected (Lewis, Eder, & Terzian 1987;Hu et al 1994;Yung, Nakashima, & Henkel 2014). The remaining WFs tend to show double-peaked OH spectra similar to other AGB and post-AGB stars, probably tracing the expansion of the remnant circumstellar envelope.…”

“…The solid line represents the locii of the colours for black-body brightness distributions. The ellipse is the area marked by Yung et al (2014) as encompassing most of the post-AGB stars in the Meixner et al (1999) sample.…”

“…7 by including all confirmed water fountains listed in Table 6. As a comparison group, we have plotted in that figure the obscured post-AGB stars from Ramos-Larios et al (2009, 2012, instead of the post-AGB stars used in Yung et al (2014), which were a sample compiled by Meixner et al (1999), most of which are optically visible objects. Since WFs tend to be optically obscured, a comparison with more similar objects will help to isolate other differential characteristics.…”

Star Formation Conditions in a Planck Galactic Cold Clump, G108.84–00.81

“…One large filament structure is shown in the integrated intensity map of CO 1-0 ( Figure 1). This filament structure is largely divided into three parts: the northeast region associated with a star (Yung et al 2014), IRAS 22576+5843, the southern region directly linked to Sh2-152, and the central part defined as G108, containing IRAS 22565+5839. As shown in the 13 CO 1-0 map in Figure 2, G108 is composed of two components.…”