SiO Maser Survey of Cold IRAS Sources

Abstract

We present the results of observations of cold IRAS sources in the Galactic disk area, −10 • < l < 100 • and |b| < 5 • , in the SiO J = 1-0, v = 1 and 2 maser lines. SiO masers were detected in 51 out of 143 observed sources; 45 were new detections in SiO masers. The selected IRAS sources were objects with dust temperatures of between 160 and 280 K. According to a confirmation using 2MASS near-infrared images, a majority of the sample are AGB or post-AGB stars, although dense cores in the starforming regions (or dusty Hii regions) are involved in part of the sample. Among new detections, two were candidates for post-AGB stars: IRAS 18450−0148 (W 43A), and 19312+1950. We found that the intensity ratios of the SiO J = 1-0, v = 2 to the v = 1 line of the objects clearly correlate with those IRAS colors. The detection rates of SiO masers tend to increase toward the Galactic center as well as the cases of previous SiO maser surveys of typical AGB stars. No strong associations of the objects to the spiral arms were found. The radial-velocity dispersion of the present sample is comparable with the dispersion of the SiO maser sample of typical AGB stars. These facts suggest that the present sample of cold IRAS sources with SiO masers has a kinematic property very similar with that of typical AGB stars.

SiO maser observations of a wide dust-temperature range sample

“…The line intensities used to calculate the intensity ratios are velocity-integrated intensities. In panel A of Figure 1 we can clearly confirm the positive correlation between the log(F 25 /F 12 ) color and the intensity ratio of the SiO J = 1−0 v = 2 to v = 1 lines as reported by Nakashima & Deguchi (2003b). Interestingly, the intensity ratios of the J = 1−0 v = 3 to v = 2 lines and of the J = 1−0 v = 3 to v = 1 lines seem to also correlate with the log(F 25 /F 12 ) color (see, panels B and C) even though the correlation coefficients are slightly smaller than that of panel A.…”

“…However, in the early 1990s the number of cold SiO maser sources (like OH/IR stars) was quite limited, and it was difficult to statistically investigate the relation between infrared colors and the intensity ratios of SiO maser lines. Nakashima & Deguchi (2003b) recently extended the Nyman et al (1993) study by surveying SiO maser emissions in cold, dusty IRAS sources exhibiting dust temperature …”

MONITORING OBSERVATIONS OF H2O AND SiO MASERS TOWARD POST-AGB STARS

“…(Jewell et al 1985). On 2001 March, the SiO v=1, J=1-0 maser emission was not detected, whereas the SiO v=2, J=1-0 maser emission was detected with a peak flux density of 0.78 Jy at V LSR = −62.7 km s −1 by Nakashima & Deguchi (2003) using the Nobeyama 45-m radio telescope. Engels & Jiménez-Esteban (2007) detected the 1612 MHz OH maser emission with a doublepeaked profile structure at two velocities (V LSR = −85.3 and −47.3 km s −1 ) using the Effelsberg radio telescope.…”

“…After that, Nakashima & Deguchi (2003) detected both SiO v=1 and 2, J=1-0 maser lines at V LSR = −21.9 and −21.8 km s −1 with the Nobeyama 45-m radio telescope. We also detected both maser emissions at average V LSR = −21.4 and −21.2 km s −1 in the range of the doublepeaked H 2 O maser lines.…”

KVN Monitoring Observations Toward the Recent Outburst Symbiotic Star V407 Cygni

“…This indicates that the Mira variable of the V407 Cyg system stands at a very late evolutionary stage compared to common Mira variables. It may be related to the development of thick and hot dust shell (Nakashima & Deguchi 2003;Ramstedt et al 2012) according to late stellar evolutionary phases, which can provide direct SiO v = 2 pumping by absorbing the four micron of dust (Langer & Watson 1984).…”