The trigonometric parallax of IRAS 23385+6053 and physical properties of molecular clouds based on the VLBI astrometry

Abstract

We performed very long baseline interferometry (VLBI) observations to measure the trigonometric parallax of H$_2$O maser sources in the outer massive star-forming region IRAS 23385+6053 using the VLBI Exploration of Radio Astrometry (VERA) in Japan. The annual parallax is $π=0.460 \pm 0.086$~mas, which corresponds to a distance of $2.17^{+0.50}_{-0.34}$ kpc, roughly half the kinematic distance of 4.9 kpc reported in previous studies. The proper motion of IRAS 23385+6053 is obtained to be ($μ_α\cosδ$,$μ_δ$)=($-3.73\pm0.53$, $-2.0{7}\pm0.73$) mas yr$^{-1}$. Based on VLBI astrometry result, we derived the physical properties of molecular clouds in which H$_2$O masers have been detected, including IRAS 23385+6053 in the Cepheus and Cassiopeia region. We discuss the line-of-sight structures of the giant molecular clouds using the trigonometric distances obtained from the H$_{2}$O maser sources. Our results suggest that molecular clouds in the Perseus arm extend over approximately $2$ kpc at the Cepheus and Cassiopeia region.

Figures (10)

• Figure 1: A three-color composite infrared image of IRAS 23385+6053 obtained by the WISE satellite. Blue, green, and red indicate $3.4\ \mu$m, $12\ \mu$m, and $22\ \mu$m, respectively. The red cross mask shows the position of the H$_2$O maser source associated with IRAS 23385+6053. Alt text: The WISE three-color composite image of IRAS 23385+6053.
• Figure 2: Parallax and proper motion results for the maser feature 4 (see Table \ref{['table:data_type']}). (Left) Position offsets in the east (filled circles) and north (open circles) directions relative to the phase reference J2339+6010 are shown as a function of time. For clarity, the northerly data is plotted offset from the easterly data. The solid and dashed curves represent the results of model fitting to the easterly and northerly data, respectively. (Right) Same as left, but with the proper motion components subtracted. Only the parallax result is shown.
• Figure 3: Distribution and internal motion of H$_{2}$O maser features in IRAS 23385+6053. The map origin is $(\alpha_{\rm J2000},\delta_{\rm J2000}) = (\timeform{23h40m54.s5224}, \timeform{61D10'28"080})$. The color of each circle shows LSR velocity. The arrows represent the internal motion vectors. The scales of 50 AU and 20 km s$^{-1}$ at a distance of 2.17 kpc are shown in the bottom right of the map, respectively. The size of each circle is proportional to the peak flux density, with the minimum and maximum flux densities being 0.8 Jy and 8.0 Jy, respectively.
• Figure 4: (a) The $^{12}$CO $J$ = 1--0 integrated intensity map obtained by the outer Galactic plane CO survey 1998ApJS..115..241H. The integrated velocity range is from $-90$ km s$^{-1}$ to $0$ km s$^{-1}$. (b) The $^{12}$CO $J$ = 1--0 longitude-velocity diagram for the integrated latitude range from $\timeform{-3.0D}$ to $\timeform{+4.0D}$. The cross marks show the H$_2$O maser sources whose distances have been measured by VERA and VLBA 2019ApJ...885..131R2020PASJ...72...50V. The lowest contour level and interval are 0.3 K degree and 0.8 K degree, respectively. The source names corresponding to the numbers (IDs) are shown in Figure \ref{['fig:h20']} and Table \ref{['table:phys']}. Alt text: The 12-CO integrated intensity map and longitude-velocity diagram.
• Figure 5: CO spectra containing each H$_2$O maser source. Red lines show the fitted results of the Gaussian function fitting. The vertical blue line indicates the peak velocity of each H$_2$O maser source. Alt text: CO spectrum associated with each H$_2$O maser source.